The strategies for graphite electrode roughing and finishing are different. Generally, roughing should leave less allowance for finishing, so when using small diameter tools, high feed (cutting feed and feed) should be used. Under the premise of minimizing tool wear, high unit cutting volume and single blade effective cutting amount are obtained, and the residual cutting amount must meet the requirements of finishing.
The goal of finishing is to obtain the highest processing quality with the shortest processing time, and the ratio of the best surface quality to the minimum tool wear should be optimized. During processing, the processing speed should be increased and the processing time should be shortened to minimize the instability of the processing process caused by the change in cutting amount and maximize the tool life.
Roughing Strategy
Graphite electrode cutting is carried out on block material, and the processing allowance is easy to describe. Its processing goal is to remove the maximum amount of material in the shortest time. Roughing can be done by copy milling or contour milling.
Copy milling uses ball nose end mills, and the cutting depth and cutting width are both changing. The cutting depth is small, the tool wears quickly, and the processing time is long.
Contour milling uses a flat end mill, which has short processing time, small tool wear, fixed cutting width, no too much reciprocating motion, and can have a large feed rate.
he quality of the roughing process depends on the NC programming based on the tool surface profile curve function, which allows fast and easy milling along the envelope contour.
Finishing Strategy
The goal of finishing is to make the processing stable, with small shape errors and good surface quality, reduce tool wear, and reduce processing costs. In finishing, the critical conditions of tool quality and the stability and reliability of the processing process should be considered. For corner processing, the influence of milling direction on processing accuracy and surface quality, as well as tool load and machine vibration should be considered.
The best strategy for milling along a plane contour should be a combination of reverse milling and plane contour milling. When milling along a curved surface, pull milling (upward feed) or drilling milling (downward feed) will occur, and the deformation of the tool will cause the workpiece contour deviation. The contour deviation of drilling milling is smaller than that of pull milling, and the contour deviation of reverse milling is also better than that of down milling.
Prismatic Surface Processing Strategy
The main problem of prismatic surface processing is the fracture of local corners of the mold, and the direction of the cutting force is mainly considered.
Processing the bottom plate edge: the surface roughness does not change much during down milling, and the quality of the bottom corner is good. However, the surface roughness value increases during reverse milling, and the quality of the bottom corner decreases. In order to obtain high-quality corners, the edge should be processed by down milling first.
Processing the vertical plate: the force direction of the two sides is different during down milling. That is, one side is pressed in and the other side is pressed out. Therefore, the actual feed direction must be changed when cutting each corner.
Processing the top corner of the vertical plate: the entry point position during reverse milling should be changed to avoid the breakage of the workpiece corner. Tool angles such as the main deflection angle have a great influence on this kind of edge collapse, which is generally controlled at about 30°.
