CNC Milling Chip Thickness Problems

Milling chip thickness problems

The chip thickness generated by machining center milling greatly affects cutting forces, cutting temperatures, tool life and chip formation, and chip evacuation. If the chip is too thick, the excessive load will be generated, resulting in microchipping or fracture of the cutting edge. If the cut is too thin, the cutting process only takes place on a smaller portion of the cutting edge, and the increased friction generates heat, which then accelerates wear.

Then, the chip thickness can be measured by being perpendicular to the effective cutting edge. As mentioned above, the chip formed during milling varies in thickness as the cutting edge cuts through the workpiece. For programming purposes, tool manufacturers use the concept of "average chip thickness". The average thickness is the average of the thickest and thinnest chip sizes.

The tool manufacturer provides an average chip thickness for a specific tool flute pattern, which, if properly applied and maintained, will produce optimum tool life and productivity, saving the business operating costs.

In addition, the machine operator uses this average chip thickness value to determine the tool feed rate to maintain the recommended average chip thickness. Tool radial engagement, tool diameter, tool position, and cutting edge main deflection angle are factors in determining the proper feed rate. Radial engagement is the ratio of the radial depth of cut (ae) to the milling cutter diameter (Dc). The greater the radial engagement of the tool, the lower the feed rate required to produce the required chip thickness. Similarly, the lower the tool engagement, the higher the feed rate required to obtain the same chip thickness. The main deflection angle of the cutting edge also affects the feed requirement. The chip thickness is greatest when the main deflection angle is 90 degrees, so to achieve the same chip thickness, reducing the main deflection angle requires higher feed rates.

A sharp cutting edge produces less cutting force than ground or chamfered edge, but it is also more likely to chip. In order to prevent microchipping and fracture, the mechanical load on the cutting edge must be limited, so a smaller average chip thickness is recommended when applying a sharp cutting edge. In this case, the cutting edge flute type used determines how the correct average chip thickness is selected and vice versa.

Machine operators can use these principles and methods in basic milling applications to control intermittent stresses on milling tools. However, as part requirements have become increasingly complex, manufacturers of CAM software and CNC equipment have developed machining strategies such as cycloid milling and chip skinning as well as software programming modules such as Dynamic Milling, Volumill, and Adaptive Clearing with a constant radial depth of cut modules. These advances in software and machine control technology represent high-tech developments in the basic concepts of tool entry and exit and chip thickness management, facilitating control of the effectiveness of intermittent tool milling processes.