1、Selection principle of machining allowance between processes
The principle of minimum machining allowance is adopted in order to shorten the processing time and reduce the processing cost of parts. There should be sufficient machining allowance, especially for the final process.
2. When selecting machining allowance, you should also consider the following conditions:
Due to the different sizes of parts, the deformation caused by cutting force and internal stress will also be different. If the workpiece is large, the deformation will increase, and the machining allowance should be correspondingly larger. If deformation is caused during heat treatment of parts, machining allowance shall be appropriately increased.
The rigidity of processing method, clamping method and process equipment may cause part deformation, and excessive machining allowance will cause part deformation due to the increase of cutting force.
3. Method of determining machining allowance
(1) Look up table method: this method is based on the production practice of each factory and the accumulated data of experimental research, first make various tables, and then collect them into manuals. When determining the machining allowance, refer to these manuals and make appropriate modifications in combination with the actual situation of the factory. At present, the look-up table method is widely used in factories in China.
(2) Experience estimation method: this method is to determine the machining allowance according to the actual experience of the process preparers. In general, in order to prevent scrap due to too small margin, the value of empirical estimation method is always too large. Empirical estimation method is often used in single piece small batch production.
(3) Analysis and calculation method: this method is based on certain test data and machining allowance calculation formula, analyzes various factors affecting machining allowance, and calculates and determines machining allowance. This method is reasonable, but there must be comprehensive and reliable test data. At present, it is only used in factories where materials are very valuable and a few are mass-produced.
