Turret punch presses are generally used as a press tool for making blanks of a plurality of certain shapes with a single machine. A turret punch press comprises a pair of upper and lower turrets which have upper dies (i.e., punches) and lower dies (i.e., dies) respectively and punches a workpiece, setting the upper and lower dies in positions under a hammer by indexing. A turret punch press can deal with a comparatively small number of lots, say, 100 to 5000 lots so that they are used in the field as a machine tool suited for use in small quantity production of multiple kinds of items.
In recent years, there have arisen strong demands in the market to sales of multiple items in a small number of lots with short delivery times and under such a situation, conventional turret punch presses, in which the maximum number of dies which can be attached is only about 70, can no longer adjust themselves to the market demand.
To overcome this problem, one turret punch press provided with an automatic die replacement system has been proposed and put to practical use. According to this press tool, a die storage (i.e., die repository) for storing a number of dies is incorporated in or installed separately from the turret punch press and the automatic die replacement system supplies dies to the pressing head from the die storage.
In such a turret punch press provided with an automatic die replacement system, dies to be used for pressing operation are required to be supplied quickly and reliably from the die storage to the pressing head and therefore it is necessary to assure the effective management of, for example, the address of each die in the die storage and data on the number of times each die has been used. One die management method is disclosed in Japanese Patent Publication No. 4-50088 (1992), in which a die number is assigned to each die and the shape and size of each die is registered in a master file with its corresponding die number and in which data on the number of times each die has been used is updated to register in the master file. In this method, the die management is usually performed with a die number assigned to either upper or lower die.
In the case of a turret punch press, an upper die and lower die are used in a pair and the use of upper and lower dies in different combinations enables it to produce a variety of articles different in thickness and material. In cases where upper and lower dies are used in different combinations, if the above conventional die management method is adapted, that is, the management of upper and lower dies is performed for example by the use of information on lower dies only, the durability, die clearance and other information of individual dies cannot be administered. This obviously makes it difficult to ensure the effective management of information necessary for die arrangement for punching operation and the automation of punching operation.
In addition, a die is accessed indirectly with its address in the die storage in the conventional die management method, so that in the event of a failure in the storage arrangement of dies, proper pressing operation cannot be performed resulting in defective products.
The invention has been made to overcome the above problems and therefore one of the objects of the invention is to provide a die management method for a punch press, which not only enables the effective management of information necessary for die arrangement for punching operation and the perfect automation of die replacement but also reduces the possibility of production of defective articles.