In order to produce qualified parts, the thickness of the metal layer that must be cut off from the blank is called machining allowance. CNC Machining allowance can also be divided into working allowance and total allowance. The thickness of the metal that needs to be removed in a process is called the machining allowance. The total allowance that needs to be removed from the blank to the finished product is called the total allowance, which is equal to the sum of the allowances of each process on the corresponding surface.
The purpose of reserving machining allowance on workpiece is to remove the machining errors and surface defects left during the previous process, such as the surface hardening layer, blowhole, sand layer, oxide skin, decarburization layer, surface crack, internal stress layer and surface roughness after cutting. Thereby improving the accuracy and surface roughness of the workpiece.
The machining allowance has a great influence on the machining quality and production efficiency. The excessive processing allowance not only increases the workload of mechanical processing and reduces productivity, but also increases the consumption of materials, tools and power, and increases the processing cost. If the processing allowance is too small, it can neither eliminate the defects and errors of the previous process nor compensate the clamping errors of the process, resulting in waste products. The principle of selection is to make the allowance as small as possible under the premise of guaranteeing quality. Generally speaking, the more machining is, the smaller the working allowance.