The vibration welding process has five main variables: frequency, amplitude, pressure, time, and depth. Frequency refers to how many times per second a vibration cycle is completed. Most machinery runs at 120 Hz, although machinery is available that runs from 100–240 Hz. Frequency is dependent on the mass of the vibrating assembly, and as such can only be changed by switching out components of the assembly. Amplitude refers to the distance traveled during each vibratory cycle. Higher amplitudes tend to be used with lower frequencies, and vice versa. Higher amplitudes increase heat input at the cost of cleanliness and dimensional tolerances, making them more useful for larger parts. Lower amplitudes range from 0.7-1.8mm, while higher amplitudes describe cycles that cover 2-4mm. Pressure is the primary controller of melt layer thickness, and must be kept within an optimal range in order to produce quality joints. Although pressure can vary between 0.5-20MPa across different materials and geometries, the tolerances for a given application are quite tight. Too little pressure will prevent sufficient heat generation, while too much pressure can cause all of the molten material to squeeze out of the joint. Both scenarios will result in a weak weld. Pressure is controlled by the lifting table. The length of time that vibration is applied to the workpiece is another key factor. Time is directly proportional to heat generation and material loss to flash. Processes can be either time or depth controlled, with most modern processes being depth controlled. A depth controlled process will have a variable time, and vice versa. Depth refers to the distance traveled by the workpieces after vibration is started. Sometimes referred to as displacement, it is directly related to the amount of material loss to flash. In general depth should be kept close to or above the thickness of the melt layer at the beginning of the steady state stage. After this value, more depth only results in loss of material without an accompanying rise in joint strength. Weld design for vibration welding must include a relatively large flat surface, although some out of plane curvature can be accommodated for. The most common type of joint is a butt joint, where two flat pieces with the same cross section are welded together. Variations on this joint can include u-flanges, tongue and groove joints, and even double tongue and groove joints. When appearances are important, flash traps can be used. Flash traps refer to  hollow areas in the cross section next to the weld area that collect the flash and hide it from view.