MILLENNIAL LEADERS’ DISPLAY OF GENERATIONAL COHORT STEREOTYPES: A QUALITATIVE RESEARCH APPROACH

This paper investigates how Millennial leaders perceive themselves in their leadership role and whether generational cohort stereotypes prevail with ascending hierarchy levels. There is a lack of research, which applies generational cohort stereotypes to Millennials in a leadership context. This limits our understanding of this generational cohort and how its members can benefit organizations in their role as leaders. Millennials in leadership positions are a new and underresearched phenomenon. Therefore, an explorative, qualitative research approach was followed, including interviews at 15 organizations from different industry segments in Germany. The data was analyzed through a qualitative content analysis. The study shows that Millennial leaders displayed generational stereotypes, but also adapt their behavior to corporate structures. This is problematic since it can limit Generation Ys’ value creating potential for organizations (e.g. driving innovation). This study contributes novel insights on Millennial leadership and organizational challenges in integrating this generational cohort within corporate structures. Organizations are advised to support the development of structures and processes that allow Millennials to unfold their potential. Directions for future research are outlined to further investigate this new phenomenon.

Introduction
The term 'Millennials' refers to the generation of so-called Generation Y, born between 1980 and 1995 (Würzburger, 2016). They are one of the youngest generations currently in the workforce and will follow in the footsteps of the soon-to-retire Generation X and Baby Boomers, increasingly comprising a significant number of employees within organizations across the globe (Baker Rosa & Hastings, 2018;Weldy, 2020).
The literature mentions a number of generational stereotypes related to Generation Y, such as a high degree of selfconfidence, low need for security (Anderts, 2011), high demand for feedback (Weldy, 2020), and a strong relationship to technology (Özcelik, 2015). These characteristics entail both, difficulties for organizations in dealing with Millennials, but also great opportunities for future value creation when Millennials are given the opportunity to accelerate their performance (Stewart et al., 2017;Graen & Schiemann, 2013).
Millennials are described as the key generation to drive change towards a better future in a world confronted with diverse economic, political, and environmental challenges (Hershatter & Epstein, 2010;Keszei, 2018). Consequently, organizations are eager to utilize the unique characteristics of Generation Y and increase the efficiency and effectiveness of Millennial employees to improve company performance and maintain organizational competitiveness in a quickly changing, highly dynamic world (Stewart et al., 2017;Weldy, 2020).
In recent years, the first members of this generational cohort have replaced earlier generations in their leadership positions. Nevertheless, how Millennials act and perceive themselves as leaders is not discussed in the literature (Chou, 2012;Keszei, 2018;Porter et al., 2019). Although there is extensive research on Millennials personal aspirations, expectations towards superiors, and how managers can lead this generational cohort (Mayangdarastri & Khusna, 2020;Özcelik, 2015;Pînzaru et al., 2016;Putriastuti & Stasi, 2019;Valenti, 2019), the literature is missing empirically validated contributions that uncover how Millennials behave as leaders themselves. This gap limits an understanding of how academics and practitioners can approach this generational cohort from a leadership perspective and how organizations can benefit from Millennial leaders.
The objective of this paper is to contribute to the academic literature by supplying empirically derived insights into whether generational stereotypes, that most of the existing literature relies on, are evident on higher hierarchical levels. Do these stereotypes prevail or will the theoretical perspective on this generational cohort have to be revised when Millennials take over roles on higher hierarchical levels?

Literature Review
In the literature, the concept of generation is approached from different perspectives, spanning life phases or birth cohorts (Baker Rosa & Hastings, 2018). In social sciences, the concept of generational cohorts is commonly used (Özcelik, 2015;Pînzaru et al., 2016;Sauser & Sims, 2012).
Researchers have questioned whether generational membership is a valid theoretical concept or only represents vague stereotypes with limited relevance to the academic discourse (e.g. Costanza & Finkelstein, 2015;Kelan, 2014;Rudolph et al., 2017). While going deeper into this debate is beyond the scope of this paper, this study follows the premises that there is evidence of differences between generations and that generational membership is crucial to an individual's identity due to the unique social and historic influences experienced by a generation (Baker Rosa & Hastings, 2018;Lyons et al. 2015;Porter et al., 2019).

Millennials and communication
One of the most noticeable differences between Millennials and earlier generations is their strong relationship to technology. Millennials are often referred to as digital natives, implying their generation's incorporation of technology to be an intuitive part of their lives (Hershatter & Epstein, 2010). Their digital immersion represents a significant value of Millennials to organizations in driving the shift to digital channels (Alsop, 2008). Members of Generation Y spend a significant proportion of their time communicating via mobile phones and the Internet, using social platforms, instant messengers, etc. (Venter, 2017). Unlike Baby Boomers, who prefer faceto-face communication, Millennials prefer to call, use instant messaging, or send e-mails (Hershatter & Epstein, 2010;Stewart et al., 2017).
Due to their economic advantage, Millennials are argued to have more time and propensity to generate and distribute content (Hershatter & Epstein, 2010). According to a survey conducted in 2009 that investigated the amount of content created online, members of Generation Y showed a greater desire to publicly express their opinion than previous generations (Jones & Fox, 2009). The need to communicate one's opinion on a broad basis matches with the synonym of Generation Me that is commonly applied to the self-centered Generation Y, who have, however, proven to be more motivated and affirmative than their predecessors (Twenge et al., 2010). In a professional context, direct and prompt feedback is a natural part of dayto-day work for Millennials (Weldy, 2020). They are eager to learn from their mistakes, expect to receive feedback and do not shy away from giving it to others (Moskaliuk, 2016). Moreover, Millennials are used to praise and direct feedback, which their parents used as reinforcements and corrective mechanisms (Kilber et al., 2014).

Proposition 2:
Millennials are willing to voice their opinions, give and receive direct feedback.

Millennials and Decision-making
The characteristics and expectations of Millennials can influence the development of labor relations with colleagues, especially when it comes to Millennials' preferences to make decisions and information processing (Alsop, 2008;Gursoy et al., 2008;Hershatter & Epstein, 2010;Myers & Sadaghiani, 2010). Due to Generation Y's extensive use of digital, non-linear communication platforms, rapid and parallel processing of vast amounts of information, it is argued that Millennials tend to follow neural patterns, rather than operating in a sequential way, as their predecessors do. For instance, Tapscott (2008) showed through his observations that Generation Y's are looking for the higher stimulus of interactive communication and information processing, instead of receiving information in a strictly scheduled, one-way, broadcast-fashion. This is related to their preferred way of learning, based on an interactive and comparatively unstructured, learning-by-doing approach. Their preferred personal development process starts with discovery and only secondly moves on to learning about techniques and applying a more rigid structural approach to learning and searching for information (Kim, 2018).
Proposition 3: Millennials prefer to operate following neural patterns, rather than operating in a sequential way.
The struggle with 'gray areas', decision-making, and problem-solving under less structured and vague conditions is argued to be especially challenging for Generation Y (Hershatter & Epstein, 2010). Most Millennials have not been exposed to taking high risks, compared to what their parents or grandparents experienced (Alsop, 2008). Moreover, Generation Ys' parents often took on the task of making important decisions for their children (Hershatter & Epstein, 2010). Hence, they often did not learn to evaluate situations by themselves (Alsop, 2008). Due to their aversion to risktaking and uncertainty Millennials seek continuous feedback and direction in the workplace, while preferring to make decisions in a team rather than on their own (Graen & Schiemann, 2013;Alsop, 2008).
Proposition 4: Millennials are risk-averse in their decision-making.
Due to the exact specifications given to Generation Y by others at an early stage, hoping that they would thereby meet the requirements for a successful future, a generation emerged that functions exclusively according to those specifications (Hershatter & Epstein, 2010). They are used to having the route to success clearly mapped out for them. The literature argues that any ambiguous element or any project and test that Millennials must face without clear instructions, templates, and examples raises great concern (Gallicano et al., 2012). Therefore, it is assumed that Millennials are unaccustomed to not receiving clear instructions that contain the criteria for success and specific deadlines set by others (Alsop, 2008).

5:
Millennials expect requirements to be clearly formulated.

Millennials and relationships
Parents of Generation Y took on an active role in the lives of their children and continuously push them towards personal and material success (Myers & Sadaghiani, 2010). As a result of the strong parental socialization and institutional support, Millennials emphasize and expect personal success, and feel pressured to achieve it (Hershatter & Epstein, 2010;Myers & Sadaghiani, 2010). From a very young age, Millennials are expected to seize every opportunity given to them, receiving grades, trophies and credentials, and pursuing leadership positions for which they have been prepared for by the most prestigious universities (Hershatter & Epstein, 2010). It is, therefore, unsurprising that members of this very progressive group of Millennials are represented among the young professionals hired by thriving business organizations (Moritz, 2018;Myers & Sadaghiani, 2010). Although this elite is not entirely representative of their generation, they have a significant influence on organizations and their expectations in terms of recruitment, demands, commitment and motivation. Therefore, this Generation Y character trait is important to consider for this study.
Proposition 6: Millennials are focused on increasing efficiency to stand out in a highly competitive society.
The network of relationships is their generation's presumed key to improve their personal competitive profile and efficiency to reach their goals. Following this, Millennials strive to build close relationships with their superiors, who, according to popular literature, are regarded as parents in the workplace (Alsop, 2008). Generation Ys have been led and cared for by authority figures, such as their parents and teachers, and emphasis has been placed on imparting a high level of self-esteem and entitlement to Millennials (Hershatter & Epstein, 2010). As such, Generation Y's are drawn to authority figures and seek their support for their own personal and professional development (Twenge et al., 2010). Moreover, this generational cohort expects a continuous exchange of information, regular performance evaluations, a supportive environment, and organizational transparency (Myers & Sadaghiani, 2010). Additionally, Millennials expect to have easy access to top management and they have no problem skipping hierarchies if it serves their goals (Hershatter & Epstein, 2010). They look up to leaders who level out the playing field and do not reinforce hierarchies (Weldy, 2020).

Proposition 7:
Millennials consider close ties to authority figures and flat hierarchies to be crucial for their professional development and satisfaction.
The value of these relationships only increases over time and their establishment is, therefore, time-consuming (Graen & Uhl-Bien, 1995). Millennials, who are known to seek quick external rewards through, for instance, job changes, may find building a quality relationship with their manager not worthwhile (Anderson et al., 2017;D'Amato & Herzfeldt, 2008;McGinnis Johnson & Ng, 2016). Therefore, and considering that Millennial employees are described as rather self-involved and even selfish, they are argued to believe that they can achieve goals more easily if they work on them independently, which often results in their tendency to disregard the potential of team efforts (Anderson et al., 2017), unless it eases their decision-making process (Alsop, 2008). Similarly, Harris-Boundy and Flatt (2010) concluded from their study on Millennials working in teams, that this generational cohort demonstrate higher levels of individualism than collectivism when striving for success.
Proposition 8: Millennials prefer to reach goals independently.

Millennials and motivation
While older generations value job security, rank and prestige, the Millennial generation also strives for accomplishing purposeful work and self-realization (Moon, 2014). Millennials value companies that positively impact society and reflect their own core values, often related to innovative work or sustainability (Hershatter & Epstein, 2010). For instance, according to an empirical study by Cone Inc. (2006), more than 50% of Millennials refuse to work for companies that lack social and environmental responsibility. Millennials are highly motivated to improve issues they care about and are willing to invest their time when day-to-day tasks are connected to bigger issues impacting their lives (Weldy, 2020). From a company internal perspective, they value a working culture that fosters equitable treatment at the workplace, as they are argued to have a strong sense of fairness (Valenti, 2019).
Proposition 9: Millennials place great value on purposeful work that reflects their values.
The Millennial generation has grown up with strong, highly innovative brands and have been accustomed, from an early age, to companies continuously releasing new products and regular updates (Klein & Sharma, 2018). To remain competitive in today's market, companies must be visionary in their approach, relentlessly forwardthinking and, above all, they need to be innovative (Moon, 2014). Millennials are very attracted to innovative products (Klein & Sharma, 2018) and are argued to see innovation work as purposeful and fun (Chou,212). This generational cohort does not only focus on driving innovation processes efficiently but is also most capable to create and innovate (Lancaster and Stillman, 2010;Hou, 2017). Millennials are explorers with an entrepreneurial mindset, continuously pushing frontiers with a relentless transformational drive (Tapscott, 2008). To Generation Ys innovation is part of everyday life (Hershatter & Epstein, 2010).
Millennials place high demands on employers, increasingly wishing to only fulfill tasks of their choice and only under the conditions that they prefer, which may be a result of institutions being very considerate of their needs from an early age (Hershatter & Epstein, 2010). For instance, flexible working hours are highly important for Generation Y's, while they expect their work to be evaluated according to the fulfilment of set goals and not based on their daily working hours (Putriastuti & Stasi, 2019). Bund et al. (2015) remark that as long as Millennials' demands are met, they will be loyal, but if the employer fails to meet their requirements, they have no problem leaving a company. While some scholars found that organizations attempt to fully assimilate Millennials into the workforce (Kilbert et al., 2014), others showed the enormous potential that Millennials can unfold when allowing them to operate freely (Stewart et al,. 2017). Proposition 11: Millennials expect a lot of freedom to operate in their way of choosing.
Millennial employees are argued to display lower levels of loyalty than previous generations (Mayangdarastri & Khusna, 2020). Therefore, institutional loyalty has become very important for companies in retaining and dealing with this generational cohort. From an organization's perspective, Generation Y loyalty finds expression in eager, passionate, and intelligent work (Hershatter & Epstein, 2010). Whereas, from Millennial employees' perspective, loyalty involves companies ensuring that there are sufficient opportunities for self-realization in their daily work. Millennials are said to be highly energetic, skillful, and always looking for new challenges (Valenti, 2019). Hence, they become bored easily with routine tasks (Kilber et al., 2014 In contrast to Generation Y's desire for self-realization and to do purposeful work, it is argued that they are increasingly motivated by extrinsic factors (e.g. monetary rewards) (Chen & Choi, 2008;Twenge et al., 2010). This discrepancy and Millennials' struggle between intrinsic and extrinsic motivation is a key issue in the literature on Generation Y. From early childhood on, Millennials learned that professional development and surpassing monetary gains are a key goal in life. Moreover, they personally experience these goals to be realistic due to the high level of education that many of them have enjoyed and based on the efficient working relationships that they established in the course of their professional development (Hansen & Leuty, 2012;Twenge & Kasser, 2013).
Proposition 13: Millennials are motivated by extrinsic factors.
The above outlined propositions and the summary in Table 1 represent a comprehensive overview of common stereotypes of this generational cohort in the literature.

P2
Millennials are willing to voice their opinions, give and receive direct feedback.

P3
Millennials prefer to operate following neural patterns, rather than operating in a sequential way.

P4
Millennials are risk-averse in their decision-making.

P5
Millennials expect requirements to be clearly formulated.

P6
Millennials are focused on increasing efficiency to stand out in a highly competitive society.

P7
Millennials consider close ties to authority figures and flat hierarchies to be crucial for their professional development and satisfaction.

P8
Millennials prefer to reach goals independently.

P9
Millennials place great value on purposeful work that reflects their values. P10 Millennials are innovation driven. P11 Millennials expect a lot of freedom to operate in their way of choosing. P12 Millennials value self-realization and expect advanced training offered by employers. P13 Millennials are motivated by extrinsic factors.

Method, Data, and Analysis
A qualitative research approach was chosen for this study, which is especially useful if the purpose is not to explain by means of numbers, but explore through dialogue and observation (Flick, 2016;Maruster & Gijsenberg, 2013). Of course, Millennials and their character traits have been discussed at length in the literature. Nevertheless, the research objective of this study, Millennials' self-perception, and behavior when they become leaders themselves, has not been sufficiently investigated. As such, this study investigates a well-researched phenomenon that, however, may need to be rediscovered in a new context. The preexisting of an extensive body of knowledge and the transformation of this knowledge into a new context calls for a mix of an inductive and deductive research design. Consequently, existing literature played a key role prior to the field study, as the aggregation of literature supplied the necessary background to confirm the research objective/gap, supported the relevance of the derived propositions and coding categories, and assured a better comprehension of the collected data.
This deductive process of qualitative research was argued for by Eisenhardt (1989) who outlined the benefits of an a priori specification of constructs (deductive) to shape the research design while allowing the discovery of the unexpected (inductive). As such, introducing even a high degree of deduction to data generation in qualitative research is not counterintuitive to discovery per se, although it may arguably reduce the extent to which exploration is possible (Ali & Birley, 1999). Nevertheless, as a first exploratory contribution, a balanced approach including inductive and deductive elements was chosen.

Data acquisition
Qualitative social research is characterized by a relatively small sample and a dialogue-approach, as its aim is explorative rather than explanatory (Baur & Blasius, 2019). In this study, interviews with Millennials in leadership positions at 15 organizations in Germany were conducted and analyzed based on the theoretically derived propositions 1-13. Germany represented a relevant research context for this study. Although economic stagnation during the past decade impacted Millennials in many European countries, the negative effects on spending power and career opportunities were comparatively minimal on Millennials in Germany (Klein & Sharma, 2018).
For this study, Millennial leaders were defined as experts on the phenomenon of interest: the display of generational stereotypes among Millennial leaders. Gläser and Laudel (2010) define an expert as a source of special, factual, and experiencebased knowledge about the social issues being researched. In this respect, in-depth expert interviews were chosen as a useful way to acquire data on special knowledge domains and subjective interpretations (Baur & Blasius, 2019).
In the process of developing an appropriate sample for interview-based qualitative research, the approach discussed by Robinson (2013) was used, which includes four aspects: defining the sample universe, deciding on a sample size, selecting a sampling strategy and sourcing cases.
The sample universe or boundary of the sample plays a significant theoretical role when analyzing and interpreting the data by determining what the sample is a sample of and, therefore, specifying who or what the study is about (Robinson, 2013). To define and to draw boundaries around the sample universe inclusion and exclusion criteria for the interviewees' attributes were specified. Individuals had to belong to the appropriate age-group as members of Generation Y, they had to be in a leadership position and have at least six months of leadership experience.
Regarding the sample size, as the aim of this study was to exploratory rather than to supply generalizable explanations, the comparatively small sample size is argued to be sufficient to gather first empirical insights (Robinson, 2013). To achieve a broad perspective of Millennial leaders, the sample included leaders from various business sectors. These sectors were chosen based on their relevance for the German GDP in 2015.
Regarding the sample strategy, purposive sampling was used. This approach is a nonrandom way of guaranteeing that specific categories of cases within a sample universe are represented in the final sample of the study (Robinson, 2013). The selection was based on existing theory and the idea that certain people may have a unique and relevant perspective on the research phenomenon, and that their presence should, therefore, be guaranteed in the sample (ibid.).
In the process of sourcing relevant cases, the participants for this study's interviews were recruited by first contacting relevant companies without any prior knowledge. This resulted in a sample of 15 experts. All interviews were conducted faceto-face between April and August 2015 (see Table 2). Prior to the interviews an interview guide based on the research objective, previously reviewed literature and the derived propositions was developed to curate the interviews (see Table 3).
In the first step, questions alongside the propositions mentioned earlier were collected. The questions were carefully formulated to not lead answers. In a second step, the questions were clustered into the four master categories: communication, decision making, relationship and motivation. For inductive reasons, further questions were asked in case that new aspects emerged spontaneously during the conversations (semi-structured interviews).

Decision-making
How do you make decisions (process)? Alone or involving others? Do you follow a set pattern or decide ad hoc? What do you base your decisions on (extensiveness of information)? Relationships How important is personal success to you? How important are relationships to reach it within and between hierarchical levels? How do you prefer to reach your goals (alone or in a team)? Motivation What is your motivation to work in this organization and leadership role (intrinsic / extrinsic)? How important is it for you (a) to be able to innovate and (b) that the firm is considerate of your needs (freedom to operate, personal development etc.)?
At the beginning of each interview, participants were informed that their personal perceptions and attitudes towards work and leadership would be investigated, but no reference to possible differences with other colleagues would be made. This ensured that participants would respond as openly and unbiased as possible and encouraged spontaneous answers.
Whenever the time available to the respondents allowed, the conversation lasted until a saturation point regarding the topics of discussion had been reached, which also served to validate the collected data. All interviews were transcribed in their original language (German) for the analysis process.

Data analysis
To analyze the derived data a qualitative content analysis was conducted. The goal of content analysis is the systematic processing records of communication, which is converted into text elements in the course of the analysis, through a reduction process of paraphrasing, generalizing, and summarizing (Flick, 2016;Mayring, 2015). Using a category system, a content analysis primarily aims at the reduction and interpretation of text (Flick, 2016). The transcripts of the expert interviews were examined by one team member according to the theoretically derived propositions 1-13, which also represented the categories for analysis. In the process of coding, text passages were assigned to a certain category when they supported the confirmation or rejection of a proposition (deductive). Moreover, the analysis process allowed for new insights to emerge and text being coded and organized according to unexpectedly revealing categories (inductive), especially when the data did not seem to support the propositions.
In this process, the categories were continuously re-examined in multiple steps of data triangulation, moving back and forth between theory and empirics. This iterative process assured the study's sufficient theoretical foundation and supported the validity of the obtained data in regards to its accordance with the research objective, while maintaining the strength of qualitative research that lies within discovering the previously unknown (Maruster & Gijsenberg, 2013;Mayring, 2015).

Result and Discussion
The analysis resulted in a differentiated picture of Generation Y leaders. It was shown that despite ascending hierarchy levels, Millennial leaders show certain generationtypical character traits as discussed in the literature and summarized within proposition 1-13. However, this study has also derived new insights, deviating from the literature and formulated within the following propositions A-E.
The most profound discrepancy between the empirics and theory was found within proposition 1. Opposed to the common representation in the literature (e.g. Venter, 2017;Hershatter & Epstein, 2010;Stewart et al., 2017), Millennial leaders in this study resided in traditional ways of communicating (especially face-to-face), due to their perceived importance of maintaining a personal connection to subordinates in fulfilling their leadership role (P1). This resulted in a modified proposition.
Proposition A: Millennials in leadership positions value personal and face-to-face communication.
The data indicates that Millennials in leadership positions prefer to consult with others before deciding (e.g. employees, superiors, or a private contact) (P4). In line with the literature (Hershatter & Epstein, 2010;Graen & Schiemann, 2013;Alsop, 2008), they take a cautious approach on a secure base, rather than taking risks by making spontaneous or trial-and-error decisions. According to the participants, this is based on the responsibility that comes with their role as leaders, with a focus on strategic decisionmaking, a long-term perspective, and little room for errors.
Nevertheless, the data gives room for interpretation, whether Millennial leaders' hesitation stems from their dependence on strictly formulated rules, guidelines, and instructions (P5) or if it is based on the increased responsibility, which also makes it more important to gather differentiated input from multiple sources. However, in contradiction to the literature, the data indicates that Millennial leaders are more likely to follow a structured, sequential path in the decision-making and information gathering process (P3). Hence, a new proposition emerged from the analysis.

Proposition B: With increasing responsibility
Millennial leaders prefer to make decisions in a structured way and based on comprehensive information.
Contradicting the reviewed literature (e.g. Anderson et al., 2017;Harris-Boundy and Flatt, 2010), most Millennial leaders in this study were agreed that goals can be reached more efficiently through collaboration within teams, as multiple opinions, experience, and knowledge were perceived to lead to more successful results and improve efficiency, especially when it concerns innovations (P8). However, the data also reveals an exception from this preference. In case that teamwork was not delivering the wanted results, Millennial leaders have no problem to take matters into their own hands and attempt to reach goals independently to attain a competitive advantage over others.
Proposition C: Millennial leaders prefer to reach goals in collaboration with others unless teamwork shows to be inefficient.
As the literature suggests (Hershatter & Epstein, 2010;Myers & Sadaghiani, 2010), efficiency was an important topic for the interviewed Millennial leaders (P6), which they described as essential for their own and their teams' competitive profile. This became especially apparent in relation to efficiencyoriented communication, which they proclaimed to be key to their leadership style. The data shows that being approachable by subordinates, encouraging an open exchange and 'living' a flat hierarchy culture is a top leadership priority for Millennial leaders, even when it may not be an explicit part of their organization's culture (P7). Participants also stated that they see themselves as mentors and coaches to guide their subordinates and set an example. In this process, the interviewed experts were willing to give honest and direct feedback to their employees. Moreover, they reported to regularly give open feedback not only to subordinates, but also to superiors (P2). Consequently, and in line with the literature (Alsop, 2008;Moskaliuk, 2016;Twenge et al., 2010;Weldy, 2020), it was shown that Millennial leaders value flat hierarchies as structures in which open exchange is nurtured and close links between hierarchical levels assured (P2/P7). Extrinsic factors were mentioned by the experts in this study to have a motivational impact, such as the increased power and authority through their leadership position, monetary rewards, praise, and appreciation (P13). Yet, key to Millennial leaders' motivation were intrinsic aspects, such as their drive for selfrealization within their leadership role, their wish for professional development, and their desire to contribute to something of value and with a larger impact (P12). As such, the dominance of extrinsic factors on motivation could not be confirmed (e.g. Hansen & Leuty, 2012;Twenge & Kasser, 2013) leading to an altered proposition.
Proposition D: Millennial leaders show a tendency to be more intrinsically than extrinsically motivated.
Study participants placed high importance on the issue of an organization's innovation potential for identifying with the company, as to them and confirming the literature (Chou, 2012;Lancaster and Stillman, 2010;Hou, 2017;Tapscott, 2008), contributing to innovation represented purposeful work (P10/P9). Respondents outlined organizational structures as key facilitators or hindrance to innovative processes and as such, acknowledged their own role as leaders within changing these processes.
Overall, participants expressed a sense of confinement within the company structures, which would often not allow them to operate in their desired way (e.g. use of digital communication tools, innovative drive). Although Millennial leaders value aspects of these structures (e.g. direct, faceto-face communication, gathering advice from different sources) when they support them in fulfilling their role, they also try to change these structures, within the context of their position, to fulfil their own perception of what defines a good leader (e.g. open feedback culture and flat hierarchies).
Contradicting the literature (Hershatter & Epstein, 2010;Bund et al., 2015), the data suggests that Millennial leaders are willing to put their personal preferences of operating aside and adapt to organizational structures (P11). Yet, they offer this freedom of carrying out tasks according to individual preferences to their subordinates. This shows that Millennial leaders are willing to make a trade-off between their own, their subordinates' preferences, and the structural circumstances that they are confronted with, while pushing the boundaries of what is possible.
Proposition E: Millennial leaders are willing to adapt their way of operating but use their position to drive strategic, operative, and structural change to accommodate their preferences.

Conclusion and Suggestion
This study is one of the first to empirically investigate Generation Y in a leadership context. A key issue that this study's insights puts focus on is the integration of Millennial leaders within corporate structures and processes, which can collide with the values and preferences of Generation Y, as they were designed by members of earlier generations (Generation X, Baby Boomers) who had different preferences and values (Pînzaru et al., 2016).
The literature agrees that organizations need to win and keep Millennial leaders to guide their business into the future, create value, and competitive advantage (Keszei, 2018). However, this study indicates that Millennial leaders can feel confined in fulfilling their role as desired (e.g. driving innovation). Ironically, this concerns Millennial characteristics that are most valuable to organizations (Stewart et al., 2017). Consequently, on a broader perspective this study indicates that there is a disadvantage in forcing Millennials' assimilation into an organization and its more traditional structures and processes, as it can decrease this Generations' value creating potential.
For organizations to benefit from this highly motivated and capable generation, organizations are well-advised to account for this Millennials' needs, allow them to prosper, innovate, contribute to and change organizational developments, as scholars have previously argued (e.g. Stewart et al., 2017). Instead of attempting their complete assimilation into predefined structures and standards, the results of this study support that organizations can greatly benefit from giving them the freedom to design these according to their needs.
This organizational struggle of finding the right balance between expecting Millennials to adapt and adapting the organization to accommodating their needs and preferences has long been discussed in the literature (Hershatter & Epstein, 2010;Kilbert et al., 2014;Stewart et al., 2017;Weldy, 2020). Now that Millennials have climbed up the hierarchy ladder, they have gained more power and control over what influences their work (working culture, structures, routines etc.) and, as is outlined in this study, they are pushing change through their behavior as leaders.
This study also shows how stereotypical characteristics may change due to an individual's environment and different responsibilities that come with a leadership role. This enriches the literature with arguments for more qualitative research on generational members within their environment and the interdependencies that may be evident there.
This is an explorative, qualitative study and the small data set is a clear limitation. More research is needed to scrutinize its conclusions.
This study suggests that relevant future research should investigate how Millennials integrate into an organization's context, whether and how it changes their perceptions and behavior over time.
Researchers may also engage more deeply with the change processes that are initiated by Millennial leaders and the resistance they may experience, the struggle that it creates, and how it is resolved.
These novel research endeavors could not only enrich our understanding of Millennial leadership, but also contribute to the literature on inter-generational work, change management, and innovation processes.


extfieldsofstudy:
Physics
Computer Science

text:
Analysis of Interference and Signal Quality in Cellular Wireless Networks

An analytical model to compute the effect of co-channel interference from the base stations at the Multi-cell CDMA systems is proposed. The objective is to study the effect of multiple-access interference generated by the neighbor cells on multi-cell CDMA and W-CDMA systems capacity. The potential of adaptive antennas in interference reduction and signal quality improvement in CDMA mobile communications systems is analyzed. The study shows that improvement in base-station sensitivity can boost system performance.

Introduction
The limited radio spectrum allocated for a cellular system results in crowded communication channels making the cellular network capacity increasing to be an important issue for cellular service providers to face the extraordinary demand for cellular communication services [1] . Multiple access and channel assignment are mostly used techniques to maximize the efficient use of the available radio frequency spectrum [2]. Frequency reuse technique is usually used in wireless networks to improve capacity. It implies that the radio frequency used to serve a cell can be reused in a different cell for completely different transmission. This introduces interference in cells that use the same channel thereby decreasing the system capacity and its service quality [3].
In multi-cell Code Division Multiple Access (CDMA) networks, and Wideband Code Division Multiple Access (WCDMA) that use a spread spectrum technique for capacity extension, base stations transmit power to all users within their coverage area introducing (intra-cell interference) in addition to interference from neighboring cells causing other cell interference(inter-cell interference). Since the interference produced by users in other cells cannot be fully power controlled by their serving base stations, the CDMA, and WCDMA networks are interference limited [4][5][6].
In [7], a model to estimate the number of interferers in adjacent cells of CDMA networks is proposed. The effect of user density and the cell radius in CDMA systems was presented through two different propagation models in [8]. In [9], a mathematical analysis is presented to investigate the propagation model parameter effects on cellular network performance considering the effect of multiple tiers of co-channel cells at different frequencies. The effect of user location on other cell interference and CDMA network capacity is investigated in [10]. The WCDMA network capacity and coverage area are evaluated in terms of the number of co-channel interferers, and the antenna gain. The interference probability model has been established based on a random distribution of mobiles in time and space with the utilization of Monte Carlo Simulation (MCS) in [11]. This paper aimed to characterize the average inter-cell interference and the average number of users that can be managed by the cellular CDMA -WCDMA systems. In the following, a model to evaluate the number of the users moving at surrounding interfering cells will be presented in section II. The propagation channel and the other cell interference will be characterized and analyzed in Sections III. The simulation results are presented and discussed in section IV.

Derivation of the Cell Size and Number of Users
Assume that the typical cellular network illustrated in Figure 1, having cells of hexagonal shape that approximated by circular cells each with a radius of R c . All cells are assumed to be fully covered by their serving base stations. The average number of mobile stations ( m ) located within any cell in the system including cell edges have the potential to contribute to other cell interference and traffic can be evaluated from the cell coverage area and the average mobile station density ) ( m  that denotes the number of mobiles per unit area. Therefore, the average number of mobiles can be obtained by integrating the elementary surface (r dr dφ) of radius r : The acuall carried traffic per interfering cell is given by the product of the traffic produced by each mobile station for the active user (A u ) and the total number of mobile stations located within the interfering cell.
The offered traffic intensity by each user is equal to the call request rate (λ) by the user multiplied by the call time (H) [1][2].
The actual carried traffic intensity carried by a channel related to the volume of the offered traffic intensity by the relation: where P B is the system blockage probability, and P o is the outage probability of the system. Equation (4) implies that the actual load (traffic carried by a cell) depends upon system blockage probability, outage probability and the offered traffic that is a function of the users' number within the cell. The outage probability depends upon the location probability that the received signal does not satisfy the required level in the cell with a certain radius R c . Equations (2), and (4), allow us to write It can be noticed that the cell size (radius) is a function of the actual traffic managed. The acceptable blockage and outage probability for the network must be known to decide the cell size(radius). Higher mobile unit density requires lower the cell radius to become [2,12].
In the downlink, base stations radiate power shared between traffic and control channels, introducing interference at mobile stations from other cells, as well as from the users at the home cell. The multi-cell CDMA network capacity depends on the SNR required for each user, which can be expressed as a function of bit energy (E b ) and total interference N t . The total interference (N t ) can be given as P ( −1)(1+ ) where f is the other-cell interference factor. If the imperfect power control factor( ) is added, the actual number of users (M) that can be supported by the system is given as [13][14]: Where P is the signal power, N o is the thermal noise, E b /N t represent the required SNR required for the reliable link, W is the bandwidth, ν f is the voice activity factor, G p is the processing gain(G p =W/R) where R is the data rate of the user, and f is the interference factor, that denotes the other cells interference to same cell interference ratio. The reliable link between the mobile and base station requires sufficient E b /N t to cover all the active users at any cell. Any mobile should exceed the base station sensitivity value P to tolerate interference from other mobiles[15].

Propagation and Interference Modeling
Assuming uniform mobile station density in target and interferer cells over the whole system, the actual coverage area will be located at the region between (A 1 ) and (A 2 ) that represents the far-field zone of the serving base station antennas located at the cell center. This area can be given as: Any active user can be at a location of distance r from its home base station, then the probability of the distance r is (R c -R o ), which means it can be at the shadowed area whose circumference is 2π (R c -R o ) as shown in Figure 1. The probability distribution function (PDF) of any mobile location relative to its serving base station or its distance and direction relative to its home base station can be given in polar coordinates as The power received from the reference cell base station (P ri ) at mobile station i is directly proportional to the average transmitted power from the reference base station P t , and inversely proportional to the separation distance between the mobile and its serving station r i raised to the propagation path loss exponent(γ). Therefore, the power received by a mobile station at distance r i can thus be expressed as: Where K is the proportionality constant that will be the same for all base stations as all base stations are assumed to produce the same transmitted power. The power received by the mobile P ri will be also received by other mobiles in the same cell causing the same cell interference (intra-cell interference). In order to determine the inter-cell interference generated by all of the operating base stations in the  system, we will assume omnidirectional base stations that are uniformly distributed over the whole network coverage area. Let us assume the elementary surface (r dr dθ) at a distance r from the user i. With a circular shape coverage area whose radius is R ca , the number of network base stations is equal to the number of base stations located within a ring of width dr and the base station density evaluated in base station per unit area. Then, the elementary surface contains (   d dr r BS ) base stations as shown in Figure 2.

Figure 2. Cellular Network Configuration
The closet base station is located at a distance ( i c r R  2 ) from the user i, and the farthest base station will be at ( i ca r R  ), where R ca is the radius of the whole area covered by the cellular system. Therefore, the interference may be caused by the total number of the base station can be given as: The ratio of the other-cell interference power received from other base stations to the same cell interference power received from the serving base station that is the interference factor f can be used to determine the reuse efficiency, then the network capacity (the number of users can be supported).
From equation (11), it can be noticed that the interference factor depends on user location within its own cell.

Simulation and Results
Interference signals coming from the surrounding cells depends on the interference factor. As the W-CDMA system capacity is interference limited, any interference will result in a linear increase in the system capacity. The link performance for each user increases as the number of users decreases. Figure 3 shows the base station sensitivity and the capacity (number of users) dependence for different values of the interfering factor. It can be noticed that the reduction in interference factor results in more users supported by the system. Furthermore, increasing the required E b /N t will decrease the number of mobiles as illustrated in Figure 4.   Due to the potential of the adaptive antenna in increasing the directivity by focusing the pattern in the desired direction other than jamming sources, it will provide a good reduction in base station number required in the system. Figure 5, shows that increasing the gain by 6.0 dB, will result in decreasing the base station density by 50%. The base stations number reduction can be translated into cell size extension, and interference reduction. In a 50% loaded system, increasing the gain by 4.0 dB gain in the receiver's sensitivity could lead to a power reduction of about 6 dB as shown in Figure 6. The reduction in base station transmitted power is translated into the mobile battery life extension. In our proposed model, it can be noticed that as the mobile unit approaches the cell edge, it will experience more interference as shown in Figure 7. It is clear that the interference factor is increased as the mobile station approaches the cell boundary.

Conclusion
The results presented have focused on the multi-cell CDMA systems. It has been shown that any improvement in base station sensitivity can increase the network capacity or the number of mobiles held by the system. The adaptive antenna technique can provide more diversity gain in rich multipath urban areas. It should be noticed that the utilization of adaptive antenna has a good potential in power consumption enhancement and can decrease the base station density contributing to interference reduction.


Typology of Additional Facilities at The Dock of Tambak Lorok Fisherman Settlement in Semarang, Indonesia

This study aims to explore the typology of additional facilities at Tambak Lorok dock in Semarang, Indonesia. The revitalized dock is in an appropriate condition with permanent materials and additional facilities that naturally added by user. These facilities are intended as spaces to support fishing activities. This study employed a qualitative rationalistic paradigm by collecting primary data in the form of interviews with related actors and physical data in the field. The results of this study revealed two categories of additional space properties, namely static and dynamic. The static additional space has a laying pattern at the edge of the dock bordering the settlement or the sea, whereas the dynamic additional space has a laying pattern at the center of the dock.

Introduction
Tambak Lorok Semarang is a fishing settlement that has existed since 1950 and survived from generation to generation to the present. Its inhabitants include fishermen and a variety of other livelihoods, such as labourers, employees and micro, small medium enterprises. The condition of the Tambak Lorok fishermen settlement is considered slum. Regarding the condition of the houses and public facilities, many parts are below road level so tides and floods often occur. Fishermen facilities, including docks and fish auction centre appear inadequate to facilitate fishing activities. The central government of the Republic of Indonesia has attempted to improve the condition by carrying out the construction of Tambak Lorok as Kampung Bahari. This project began in 2018 with the construction of important facilities for fishing settlement, such as markets, docks, and environmental road management. The current condition of Tambak Lorok fishing settlement can be seen in Figure 1.1. Firmandhani Several phenomena occur as backdrops to the government's efforts to revitalize this area. In 2007 a new fish auction place was inaugurated. Initially it was used to auction off the fishing catches of fishermen on Tambak Rejo street with public facilities, such as (lighting and environmental roads). However, the fish auction place was not used by residents after three months of being inaugurated, and now the building has collapsed (Firmandhani & Alfia Riza, 2018). The existing docks are also made of semi-permanent materials, such as bamboo without any arrangement, thus creating a slum condition and not maintaining the safety of the users. Supporting rooms for fishing activities are also often built around the dock area, such as places for drying fish and repairing boats.
The current condition of the Tambak Lorok dock has been built with permanent materials, designed to be the border between Tambak Lorok and the bay, which is usually used for fishing boats to dock. An interesting phenomenon occurs, namely the occurrence of additional spaces on the new dock. This space is formed by the existence of physical elements of space and people with activities that contained in it (Pandelaki et al., 2018). The emerging spaces support fishing activities, such as storage, rest rooms, boat repair rooms, boat ramps and fish drying area. From this phenomenon, it is necessary to conduct a study to explore the additional spaces at Tambak Lorok dock. This research explores a new phenomenon that occurs in Tambak Lorok. Several previous studies investigated Tambak Lorok in terms of the typology of interaction space that conducted by inhabitant. There are 3 typologies of interaction space such as primary, secondary and tertiary (Ramandhika, 2019) and the Conceptual Spatial Model for fishermen's settlements that formulated an ideal spatial arrangement in facing the problem and potential (Setioko et al., 2011). Indicators of cultural community in the fishermen settlement have been formulated. One of them is residential environment such as fishermen supporting facilities (Rahmadaniyati et al., 2017). The dock as one of the supporting facility in Tambak Lorok is also quite adaptive, it can be adjusted by using dynamic material -materials which have the ability to change their physical appearance and characteristics (Lelieveld et al., 2007). Based on the previous studies, there are no case that studied the typology of additional space/adapted space, therefore this paper explores it with the case study of Tambak Lorok's dock. It need to be explored to give the understanding of the arrangement and the nature of additional space that naturally adapted by the user.

Methods
This research was conducted with a qualitative rationalistic paradigm by examining information from primary sources, namely interviews with the actors involved at the dock, who were in dialogue with existing physical data. Several stages carried out in this research include: 2.1.

Grand tour
The grand tour aimed to observe the overall condition of Tambak Lorok as background knowledge and find more detailed issues in the spot investigated in this study, namely the dock area.

2.2.
Mini tour The mini tour became an observation that focused on the investigated spot by collecting physical data. At this stage, initial observations on the phenomena were carried out at the dock, namely the addition of spaces and physical data, such as dock dimensions.

2.3.
Interviews Interviews were conducted with actors who were directly or indirectly involved in adding space on the dock. The directly involved actors were the fishermen who anchored their boats. Meanwhile, the indirectly involved actors included fish auction place officers and residents. The interviews aimed to find out the motivations for adding space, the function of space and the expectations of these actors. The results of the interviews became primary data, then were analysed and dialogued with the physical data obtained.

Analysis
The analysis stage aimed to find out pattern of additional space on the dock so that in the future it can be used as a basis for structuring a dock in a fisherman's settlement. The analysis was based on the results of interviews and dialogues with physical data.

Result and Discussion
Before discussing the results of the analysis, it is necessary to review physical data of the Tambak Lorok dock to illustrate the existing conditions. Then, there is an illustration of the physical condition and primary data as a representation, proceeded with the analysis and results.

Condition of The Dock
Tambak Lorok fishing settlement is located in North Semarang District, Semarang City, Indonesia. This settlement is inhabited by a heterogeneous community, not only fishermen, but also employees, traders and labourers. Relevant data to understand in this study include: 3.1.1. Dock physical data The physical data of the dock are in the form of dimensions, functions and distribution of fishermen facilities around the Tambak Lorok dock. The physical data of the dock can be seen in Figure 3.1.
The physical data shows that the dock is the border of the fishing settlement with an offset dimension of 6.5 meters jutting into the bay. The material used is cast concrete with the distribution of fishing facilities in and around it, including:nInside the dock: fish drying room, net maintenance and storage room, fisherman rest room, boat repair room. Around the dock: TPI (Fish Auction Center), SPBN (Fishermen Fuel Station). The location of the TPI is at the center of the dock with inadequate building conditions, only in the form of a small compartment measuring 3x2 meters used for auction organizers. The auction activities are carried out in a pedestrian corridor with shade in the form of a 3x4 meter tent. The SPBN (Fishermen Fuel Station) location is in the north approaching the end of the land and sea border. However, the SPBN condition is no longer functional.
Tambak Lorok Dock as the research locus was built in 2018 with permanent material using reinforced concrete construction. The dock spaces that are used for the fishing boats dock have additional functions so that adaptations and additional facilities were built independently by users. The additional facilities are in the form of resting place for fishermen, a place to store fishing nets and equipment, a place to dry fish and a place to repair boats. The condition of the dock can be seen in Figure 3.2.

Interview result
In the interview process, points of questions were asked and answered openly. These questions include: (1) How do you think the condition of Tambak Lorok dock? (2) Is the dock sufficient for fishing activities? (3) What are your hopes for the future? The three  questions were asked to the dock users where most of them were fishermen or salted fish makers. Of the three questions, the answers obtained were almost unanimous, namely grateful for the dock renovation, which is now feasible with permanent material and a width of 6.5 meters. It is quite wide compared to the condition before renovation with wood and bamboo materials with a width of 1-2 meters, making it difficult for fishermen to walk with fish catches. For the utilization of the dock, now it has shortcomings, namely the supporting facilities that are unavailable at the dock, such as boat docks, resting places, tool storage places, fish drying places, so that fishermen take the initiatives to build these facilities independently based on the area where the boat is anchored. This was carried out because fishermen perceived that the dock area was a public area, so everyone could utilize the space. They hoped that the Tambak Lorok dock in the future can be equipped with facilities that support their activities properly as well as other infrastructure, such as a suitable Fish Auction Center. Interviews were conducted with fishermen who docked their boats at Tambak Lorok dock. Several principles from the interview results were obtained, including: a. Fishermen thought that the dock area was a public space where everyone could utilize it. b. Based on the activities carried out in the dock, fishermen needed other facilities, such as storage and maintenance of nets, rest areas on land, a place to repair boats and a circulation route from the dock to the settlement. c. Many salted fish craftsmen dried the fish in the dock area, thus obstructing the circulation of the dock.

Additional Space to Support Fishermen Activities
Based on the results of interviews and physical data, several points could be attributed to causes and effects:

Settlement
The appearing spaces were an adaptation of dock users to be able to accommodate core activities other than anchoring the boat. The emergence of these spaces was due to the encouragement of perceptions from within the fishermen and the existence of an attractive factor from the environment in the form of dock space, which could accommodate these activities.

Addition of Net and Equipment Storage Area
Storage and maintenance of nets are two of the special activities for fishermen that must be accommodated. Before the dock was built, this activity was carried out on the Tambak Lorok road sections to the terrace of the house. The addition of the storage area for nets and equipment was made with a semi-permanent building made of wood and a tin roof, built on the west side of the dock, bordering the dock and settlement wall. Nets and equipment were also stored under the circulation ramp. Frequently the net storage area was also used for resting fishermen.
The addition of space with more rhythm in the northern part of the dock was also because more fishermen docked in the northern area. In contrast, in the southern area, there were more fish drying.

Additional Boat Ramps and Boat Repair
The dock as the fishermen's berth area is the closest inland space to the boat, so that in terms of reach it is the easiest area for boats. The need for boat maintenance must also be accommodated by providing land space for the boat to be repaired. Before the renovation, the boat reparation was carried out at the dock at the end of the alley directly adjacent to the bay. With this dock, fishing boats were also repaired here with various adaptations of facilities by the fishermen, including the circulation space for the boat crane in the form of a wooden ramp to pull the boat up to the dock. Apart from that, the space for the boat reparation is necessary. In the current condition, if there is a boat reparation at the dock, the boat body will cover the dock area so that it will disrupt the circulation of the dock. The boat reparation is carried out in the area closest to the boat ramp, which is located at 3 spots to the south (1 spot) and north (2 spots).

Additional Fish Drying Areas
The fish drying area is an area used for salted fish craftsmen to dry fish. This drying activity is often found in empty spaces in Tambak Lorok, including at the dock. It is usually carried out in the southern area adjacent to the fish auction center. In addition, several points in the dock corridor adjacent to the craftsmen's homes become the areas for the drying activity, including on the west side by the wall or in the middle of the dock.
3.2.4. Addition of the dock circulation area to the settlement Tambak Lorok Dock is 6.5 meters protruding into the bay bordered by a brick wall as high as 1.2 meters along the dock corridor. A permanent access from the settlement to the dock is in the form of a ramp. The width of the ramp is 1.8 meters with hollow iron railings. The location of the ramp is considered inadequate for circulation due to only three points of the ramp, namely in the south adjacent to the fish auction center, in the middle and at the northern end. Three ramps along the dock corridor with a length of 400m were considered insufficient so that users have renovated the area with the addition of semi-permanent ladder facilities made of wood for circulation from the dock to the settlement.

Additional Space Pattern
The analysis process obviously shows various additional spaces at the Tambak Lorok dock. The additional space can be categorized as a space to support fishermen's activities, forming a pattern following the design of the dock that extends across the bay. Based on the distribution of the adaptation of the facilities, it shows the pattern of placing the additional facilities by overlaying all the existing distributions. Regarding the pattern of additional facilities, it appears that circulation access facilities and additional space (non-portable) are placed on the west side of the dock adjacent to the wall, whereas portable and temporary facilities that require a large space are placed in the middle of the dock, such as a fish drying area and boat repair. Additional facilities for the boat ramp are located to the east to access the dock from the sea. The distribution has a character where the drying area for fish is in the south approaching the fish auction centre, while the boat repair area is in the north followed by a boat ramp. The resting space for fishermen and tool storage are spread across almost all areas of the dock, but they are quite concentrated in the northern part of the dock because more boats are docked in the northern area. The additional space in Tambak Lorok Dock reflects the adaptive nature of the dock where additional space is based on physical ambience from post occupancy evaluation (Demers et al., 2013). From this funding, it can be seen that there are 2 characteristics of additional space on the Tambak Lorok dock namely static and dynamic. The both characters support the fishermen activity on Tambak Lorok and divided based on the location and the nature of the space whether movable or not. The additional space such as ladder/access to settlement, boat ramp, fishermen rest room and storage are categorized as a static additional space. Boat repair area and fish drying area are categorized as dynamic additional space.
Mapping of additional facilities can be seen in Figure 3.4 and the location pattern of additional space can be seen in Figure 3.5.

Conclusion
The additional supporting spaces at Tambak Lorok dock have two characteristic categories, namely static and dynamic supporting spaces. The additions of static supporting spaces with semi-permanent materials are in the forms of storage space, fishermen rest room, dock access to settlements and boat ramps. Meanwhile, the dynamic supporting spaces are in the forms of a fish drying area and a boat repair area. The pattern of laying out the static supporting spaces is at the border between the dock and the settlement as well as the dock to the sea, while the pattern of laying the dynamic supporting space is in the center area of the dock.


Optimisation of electro-spark coating method

Application of wear resistant coatings on cutting tools in a technological process requires taking into account multiple factors. Optimisation of the hardening process presents one of the main steps that needs to be addressed. This paper describes a method of optimisation of the electro-spark coating (ESC) process. The performance of the process was chosen as the target function. A parametric function was defined based on the previously developed mathematical model of the process whereby the condition of the strong connection of coating material with the foundation was used. Another parametric function is a prerequisite for a suitable coating thickness. Additional limitations are the characteristics of the equipment for the reinforcement

Introduction
Given the economically unstable situation in the world, the efficient use of available resources becomes a first priority. Minimising the cost of manufacturing new products leads to a significant increase in profits. [1] One of the tools to achieve profit growth is the introduction of lean manufacturing methods (Lean Production). The basic idea of lean production is to increase the efficiency of the producers within existing resources through the modernisation of all processes. [2] The first lean production practices have been applied by Toyota. The basic idea of this principle was the elimination of some losses in the existing technological process: loss of time and budget due to standby, overproduction, extra processing steps, unnecessary transportation, redundant inventory, and defective goods. [3] Implementation of lean ideas in large-scale and mass production instantly brings significant profit to companies; however, it is a complicated task since one has to operate in the already running process.
One of means of increasing the wear resistance of the cutting tool is a method of electro-spark coating (ESC). The organisation of this method in the production environment for hardening of tools not only requires special equipment, but also optimisation of the process. This will reduce the operational time spent on resurfacing and the costs associated with it.
The process of ESC in the real environment is defined by the following parameters [4,5,6]: 1) the power of a pulse generator, W; 2) the speed of an electrode, υ; 3) the thickness of a coating, h.

Mathematical model of the process
To obtain a coating with a durable connection of the anode material (tool) with the cathode material (product), it is necessary to comply with a condition stating that the surface temperature of the cathode equals the melting temperature [7,8]. Thus, this condition can be written as In this equation, the unknown variables are the intensity of the heat source,q0,and the velocity of the source, which is the argument of functionF(k).
In [7], it was determined that the heating of the cathode is supplied from two sources, the total power of which is determined by the power pulse generator whereη is the efficiency of the pulse generator;η ≈ 0,8;W is the discharge power determined by the type of a generator used in a particular case.
Equation (1) is the lower technical limit that is a function of equal temperatures which should provide a set of parameters: generator power W and the velocity of the source υ, which is taken into account by function F(k).
The speed of the source determines the performance of the coating process and in the calculation of the optimal mode should be selected as large as practical. This expression(υ max) will be the objective function for the system optimisation.
To determine the third process parameter, the coating thickness, we assume that in a steady process of electro-spark alloying all the energy supplied to the anode (electrode) is spent on its partial melting and is transferred to the cathode. This assumption is fair since in a steady process electrode (anode) gives the heat to the cathode through the material as well as to the environment. The heat exchange with the environment is via air which is a poor conductor of the heat. According to authors of [4,5], for most materials in normal conditions, in the most effective modes from the perspective of quality indicators and process performance values of the gain are high, that is, the thickness of the formed layer on the cathode is limited. The limited thickness of the formed layers on the cathode (product) in many cases hinders the practical use of ESC [9,10,11]. Therefore, the analysis of the factors determining such nature of the process and opportunities for targeted management become highly important.

Process optimization
Numerous experimental studies of electrode erosion (the anode) and the metal transfer to the product (cathode) allows to manifest that in the process of ESC the erosion and the release material of the anode do not stop with time, rather settling of the anode on the cathode slows down due to evaporation to the environment [12,13,14]. The limitation of the layer thickness can only be explained by considering the entire set of physical, chemical and mechanical effects on the surface of working electrodes. As ESC is associated with multiple-pulse thermal and mechanical effects on the material of the electrodes of phase and structural transformations in the generated layers [15,16,17], we can assume that these processes should determine the nature of the growth and limitation of the thickness of the applied layer. Phase and structural transformations, heating and cooling of the surface layers of the electrode's material under the influence of electric pulses lead to the formation of residual stresses of types I and II [15,18,19], characterising their ultimate irreversible stress state. Consequently, in real conditions of coating the whole complex of the processes occurring between the anode and cathode is determined by the law of energy conservation. Given the above-mentioned statements, it can be said with a small extent of error associated with the evaporation of materials into the environment (according to estimates of different authors [15,20,21], evaporation takes 3-5%) that the intensity of the heat flux of transferred energy is equal to This expression determines the melting rate (deposition) of the electrode material. The mass transferred per unit time of the electrode is determined by the product of the density and the volume: Therefore, expression (4) can be represented as follows: This expression links the power generator of impulses in specific process conditions with the coating thickness and the speed of the anode.
The thickness of the coating is selected from experience, applied for various materials and operating conditions, it may be different, but one should keep in mind that the greater thickness of the coating, the more fragile the coating becomes. Therefore, most often the coating thickness of the cutting tool is taken from the the range of 8-12 µm. The test tool in the production environment confirmed the validity of this statement. Coating thickness of 20 µm and more typically wears off due to chipping.
Given the equations above, the process of electro-spark alloying is described by the following system of equations: Let us consider the example of applying a carbide coating(ρ = 5.37 g/sm 3 , λ = 0.21 W/(sm·ºC), LfE = 1.45·107 W/(g·sec)) on the tool steel (melting temperature TM= 1550 ºC) under the following conditions: a = 1, d = 2 mm. For these conditions,F(k)is satisfactorily approximated by the exponential function Let us assume that the capacity of the plant is equal to W=150-400 Watts. Therefore, the solution of equations (8)- (11) can be represented by the plot in Figure 1.   (8) shows the values of the generator powerW = F(υ)at which the temperature on a surface of the hardened product equals the melting temperature, that is, this function represents the lower limit in the optimisation system.
The function based on equation (9) shows that the maximum output powerW = F(υ)that provides the required coating thickness, that is, this function represents an upper limit in the optimisation system.
Functions represented by equations (10) and (11) Fig. 1, functions (8)-(11) selected area searched possible solutions, the optimal solution corresponds to a point in the delineated area with υmax. This point lies on a curve of equal temperature with a value ofυopt ≈ 0.39 sm/sec. Therefore, for these conditions the coating technological process should be conducted on the optimal mode for the following parameters: υopt ≈ 0.39 sm/sec; W = 400 W; h = 12 µm. Fig. 2 shows a photo of microsection of the sample after hardening at optimal conditions. The coating was applied using Elitron-22A. The figure shows that the coating has a relatively uniform structure without any breaks.

Conclusions
The paper presents the system of equations for the optimisation of the process where the objective function is the productivity. The lower limit is a function of equal temperatures (θ(x,y,τ)=TM, the melting point of the electrode). The upper limit is the required thickness of the coating. Additional limitations are the capabilities of the equipment.
The optimisation system was pilot-tested and it showed the uniformity and reliability of the applied layer.
The introduction of electro-spark coating on a cutting tool increases its wear resistance, is embedded in the concept of the lean production and leads to a decrease in tool wear.