Key points for selecting end mills in graphite processing

The key points for selecting end mills in graphite processing mainly include tool diameter, number of edges, material and coating, geometric parameters, length design, and chip removal performance, etc. The following is a specific analysis:

Tool diameter: Select based on the milling width and depth. Generally speaking, the greater the milling depth and width, the larger the diameter of the milling cutter should be. When performing rough milling, the diameter of the milling cutter on the milling machine can be smaller. When performing finish milling, the diameter of the milling cutter should be larger to cover the entire processing width of the workpiece as much as possible, so as to reduce the tool connection marks between adjacent feed rates.

Blade number selection:

The number of edges mainly includes types such as 2 edges, 3 edges, 4 edges, and 6 edges. The difference in the number of edges directly affects the size of the chip trap. Two-edge, three-edge and four-edge end mills for milling machines are the most commonly used.

The more edges there are, the higher the rigidity will be, and the processing accuracy will improve, but the cutting discharge effect will be worse. Poor chip discharge can affect the accuracy of the machined surface, and even cause chip blockage, resulting in damage to the cutting edge or the overall breakage of the end mill cutter on the milling machine.

When a large radial depth of cut (width of cut) is intended or grooving is performed, end mills with fewer cutting edges are generally used. End mills with a larger number of cutting edges are more suitable for finish machining.

Material and coating:

In terms of materials, for high-speed milling of graphite materials, hard alloy milling cutters with AITiN coating or diamond coating are mainly used. The coatings have high hardness and are wear-resistant. Ultrafine-grained cemented carbide has good toughness, high strength, and impact resistance, and the cutting edge is less likely to be damaged.

In terms of coating, diamond coating can further enhance the durability and cutting performance of the tool, especially suitable for high-precision processing scenarios. This combination not only extends the tool life but also ensures that each cut is precise and error-free.

Geometric parameters:

Rake Angle: Graphite is a multi-layer brittle material. To prevent the blocky fragmentation of graphite on the machined surface, a positive rake Angle should be adopted to reduce compressive stress, minimize the damage to the machined surface, and improve the quality of the machined surface. Due to its high hardness and the fact that a large rake Angle is not suitable, the rake Angle for rough milling is generally 5° to 6°, and for finish milling it is 10°.

Relief Angle: Due to the hardness and brittleness of graphite, when cutting thin-walled workpieces, significant elastic deformation occurs, and the elastic recovery produced by the cutting teeth is relatively large. To reduce subsequent wear, a larger relief Angle is selected. The rough milling relief Angle is 9° to 10°, and the finish milling relief Angle is 5° to 6°.

Helix Angle: The rigidity of thin-walled graphite electrodes is very low. During milling, the feed force should be reduced to prevent the part from vibrating. Therefore, a smaller helix Angle should be selected, usually 15°. However, if the helix Angle is too small, the impact generated by the cutting teeth on the workpiece during milling will be relatively large, increasing the vibration during cutting. For graphite workpieces with good rigidity, milling cutters with larger helix angles should be used to gradually insert the cutting teeth into the workpiece, reducing the impact on the workpiece and minimizing the vibration during cutting. The helix Angle should be between 30° and 45°.

Length design: For tasks that require deep hole processing or cutting of complex shapes, an extended designed end mill is the best choice. Meanwhile, choosing the shortest tool length can greatly enhance the stability of the tool.

Chip removal performance: Appropriate chip removal is very important because re-cutting the chips will significantly reduce the tool life. A smaller number of grooves (2 to 3 groove tools) will provide more groove space for long chip materials (such as aluminum); More chip removal grooves reduce the space of chip removal grooves, but they can increase the productivity of shorter chip materials (such as medium carbon to high carbon steel and iron).