The selection of the amount of back-grabbing should be determined according to the rigidity of the machine tool, fixture, moon tool and workpiece, and the power of the machine tool. If the process system permits, choose a larger amount of back-grabbing as much as possible. Except for the allowance left for later processes, the remaining rough machining allowance should be cut at one time as much as possible to minimize the number of passes.
Roughing is usually done on a medium-power machine tool, and the amount of back-grabbing for roughing is 8-10 mm (single side). The semi-finish machining of the CNC lathe factory is 0.5-5 mm; the precision machining is 0 2-1.5 mm.
The amount of back-grabbing during CNC turning is determined by the rigidity of the machine tool, workpiece and tool. When the stiffness allows, the amount of back-grabbing should be equal to the machining allowance of the workpiece as much as possible, which can reduce the number of passes and increase production. effectiveness. In order to ensure the quality of the processed surface, a small amount of finishing allowance can be left, generally 0.2～0.5mm.
Whether the above cutting parameters (ap, f, v) are selected reasonably, play an important role in achieving high quality, high yield, low cost and safe operation. The selection principle of turning amount is:
1) When roughing, first consider choosing a back-cutting amount ap as large as possible, and then choosing a larger feed amount f, and finally determining a suitable cutting progress v. Increasing the back-cutting amount ap can reduce the number of passes, and increasing the feed amount f is beneficial to chip breaking. Therefore, selecting the rough turning amount according to the above principles is beneficial to improve production efficiency, reduce tool consumption, and reduce processing costs.
2) When finishing turning, the machining accuracy and surface roughness are required to be high, and the machining allowance is not large and uniform, so choose a small (but not too small) back-cutting amount ap and feed amount f, and select cutting performance High tool materials and reasonable geometric parameters to increase the cutting speed v as much as possible.
3) When arranging rough and fine turning quantities, pay attention to the allowable cutting quantity range given in the machine tool manual. For CNC lathes whose spindle adopts AC frequency conversion speed regulation, since the torque of the spindle decreases at low speeds, special attention should be paid to the selection of cutting parameters at this time. Table 3-1 shows the recommended table of CNC turning parameters for reference during programming.
In short, the specific value of cutting parameters should be determined by simulation method based on the performance of the machine tool, related manuals and combined with actual experience. At the same time, the spindle speed, the amount of back cutting and the feed speed can be adapted to each other to form the best cutting amount.