In numerical control programming, the programmer must determine the cutting amount of each process, in the form of instructions written into the program. Cutting parameters include spindle speed, back knife, feed speed, etc. For different processing methods, different cutting parameters need to be selected. The selection principle of cutting dosage is: to ensure the machining accuracy and surface roughness of parts, give full play to the cutting performance of the tool, ensure the reasonable tool durability and give full play to the performance of the machine tool, maximize the productivity, reduce the cost.
(1)Determination of spindle speed should be based on the allowable cutting speed and workpiece (or tool) diameter to choose. The calculation formula is:n= 1000V /(πD)
The calculation of the spindle speed n finally according to the machine tool manual selects the machine tool some or close to the speed.
(2) The determination of the feed speed F is an important parameter in the CNC machine tool cutting parameters, mainly according to the machining accuracy and surface roughness requirements of parts and tool, workpiece material properties selection. The maximum feed speed is limited by the stiffness of the machine and the performance of the feed system. In contour machining, the feed rate should be reduced appropriately near the corner to overcome the phenomenon of “over range” or “under range” at the corner of the contour due to inertia or process system deformation.
The principle for determining the rate of feed:
1)When the quality of the workpiece can be guaranteed, in order to improve production efficiency, a higher feed speed can be selected. Generally, it is selected in the range of 100 to 200mm/min.
2) When cutting, machining deep holes, or machining with high-speed steel tools, it is advisable to choose a lower feed speed, generally in the range of 20~50mm/min.
3) When the processing accuracy and surface roughness are high, the feed speed should be smaller, generally within the range of 20~50mm/min.
4) The maximum feed speed given by the CNC system of the machine tool can be selected when the tool is traveling in the air, especially when the distance is “back to zero”.
(3) Back to determine back to eat the amount of knife (AP) according to the stiffness of the machine tool, the workpiece and the tool to determine, in the stiffness allowed conditions, should be as far as possible to make back to eat the amount of knife is equal to the workpiece processing allowance, so that can reduce the number of cutting, improve production efficiency. In order to ensure the quality of the processed surface, a margin of 0.2~0.5mm can be left for finishing.