Metal cutting produces temperatures as high as 800 to 900 °C in the cutting zone. In this cutting zone, the cutting edge will cause the workpiece material to deform and remove it. In the interrupted cutting conditions, which are mainly in milling, the meshing radian, feed, cutting speed, and cutting edge geometry of the carbide inserts have an impact on the heat generation, absorption and control. The different thermal conductivity of the workpiece material and other processing factors will have a significant impact on the heat distribution. When processing a workpiece with poor thermal conductivity, the heat transferred to the tool will increase. Machining materials with higher hardness will generate more heat than machining materials with lower hardness. Under normal circumstances, higher cutting speeds will increase heat generation, and higher feed rates will increase the area of the cutting edge affected by high temperatures.
Due to the intermittent nature of the milling process, the cutting teeth only generate heat during part of the machining time. The cutting time percentage of the cutting tooth is determined by the meshing arc of the milling cutter, and the meshing arc is affected by the radial depth of cut and the tool diameter.
The meshing arcs of different milling processes are also different. In slot milling, the workpiece material encloses half of the tool, and the meshing arc is 100% of the tool diameter. Half of the machining time of the cutting edge is spent on cutting, so heat builds up quickly. In side milling, the relatively small part of the tool engages with the workpiece, and the cutting edge has more opportunities to dissipate heat into the air.
In order to keep the chip thickness and temperature in the cutting area equal to the value of the tool during full cutting, the tool supplier has formulated a compensation coefficient to increase the cutting speed when the percentage of tool engagement decreases.
From a thermal load point of view, the meshing arc is small and the cutting time may not be enough to produce the minimum temperature required for maximum tool life. Increasing the cutting speed usually produces more heat, and combining a small engagement arc with a higher cutting speed can help raise the cutting temperature to the desired level. Higher cutting speeds shorten the time that the cutting edge contacts the chips, thereby reducing the heat transferred to the tool. In general, higher cutting speeds will reduce machining time and increase productivity.
On the other hand, a lower cutting speed will lower the processing temperature. Excessive heat is generated during processing, and reducing the cutting speed can reduce the temperature to an acceptable level.
Contact: Gerry Zeng
Add: No.52 Hongqi North Road,Shifeng District,Zhuzhou,Hunan,China