1. Adjustment of surface roughness:
The surface roughness is determined by pulse width, peak current, electrode material and workpiece material.The edM surface is different from the machined surface, which is composed of numerous pits and hard edges without directivity. The edM surface roughness is usually expressed by the average arithmetic deviation Ra of the flatness of the micro profile.
The surface roughness is affected by the diameter of graphite particles. The larger the particles are, the coarser the surface roughness is.Usually choose fine particle graphite to improve the surface finish;
The larger the pulse width, the longer the discharge time per unit time, the deeper the discharge marks, and the thicker the machining surface.The graphite electrode completes the discharge process with a smaller pulse width, thus forming a shallower etching, which is beneficial to polishing.In order to reduce the loss, copper electrode uses longer pulse width to complete the discharge, which results in deep etching and high surface hardness, which leads to the difficulty of polishing.
The larger the peak current is, the roughness of the machined surface has a greater influence than the pulse width. Therefore, the principle of "large current, small pulse width" of graphite electrode also reduces the roughness of the machined surface.
Spindle shaking machining is also an effective method to reduce surface roughness and obtain uniform grain surface.
2. Adjustment of electrode loss:
In discharge machining, the amount of electrode removal per unit time is called loss rate.In practical production, the relative loss is usually used to measure the loss resistance of tool electrode.
There are four kinds of losses in EDM: integral loss, angular loss, end loss and side loss.Because the Angle loss determines the final machining accuracy, so its loss rate is the most important, especially when the electrode finishing should pay attention to the Angle loss.
When the graphite electrode is discharged, the larger the current, the smaller the electrode loss.
Under normal circumstances, the larger the pulse width, the smaller the electrode loss.However, excessive pulse width will lead to burr negative damage of graphite electrode in discharge machining, so the maximum pulse width of graphite electrode is generally not more than 420μs, and the pulse width decreases with the smaller discharge area.
When IP=10A ~ 120A and ON=100μs ~ 300μs, there is no loss condition in graphite electrode discharge machining.