CNC machining The thickness of the metal layer removed in each process can be called the machining allowance between processes. For the torsion of the outer circle and the hole, the machining allowance generally needs to be considered from the diameter, so it is called the symmetric allowance (that is, the bilateral allowance). In reality, the thickness of the layer of the metal removed is generally the diameter. Half of the processing allowance on the market. The machining allowance of the plane is the one-sided allowance, which is the thickness of the metal layer cut off in reality.
The goal of leaving the machining allowance on the workpiece is generally to remove the machining deviation and external defects left by the previous process, such as the cold hard layer, pores, sand inclusion layer on the outside of the casting, the scale, decarburization layer and the outside of the forging Cracks on the outside, internal stress layer after cutting and roughness on the outside. Thereby improving the accuracy and roughness of the workpiece. The size of the processing allowance will have a greater impact on processing quality and production efficiency.
The machining allowance is too large, which will increase the labor of mechanical processing, which will reduce the productivity, and increase the data, objects and power consumption. CNC machining has increased the processing cost. If the processing allowance is too small, it is not only impossible to eliminate the various shortcomings and deviations of the previous process, but also to compensate for the clamping deviation during the processing of the process, then it will be easy to form waste products. The selection criterion is to make the margin as small as possible under the premise of quality assurance CNC machining. Generally speaking, the more finishing, the smaller the process margin.
When determining the CNC machining sequence, it is necessary to clarify whether the parts should be pre-processed before machining. Pre-machining is often done by ordinary machine tools. If the blank precision is high, the positioning is more reliable, or the machining allowance is sufficient and uniform, then it can be processed directly on the CNC machine without pre-processing. At this time, the division of CNC machine tool processes should be considered according to the accuracy of the rough rough reference, which can be completed in one process or divided into several processes.