In order to process a qualified part, the thickness of the layer of metal that must be cut from the blank is called the machining allowance. The machining allowance can be further divided into process margin and total margin. The thickness of the layer of metal that needs to be removed in a certain process is called the processing allowance of the process. The total amount that needs to be cut off from the blank to the finished product is called the total remaining amount, which is equal to the sum of the residuals of the respective surfaces of the corresponding surface.
The purpose of leaving the machining allowance on the workpiece is to remove the machining error and surface defects left by the previous process, such as the chill layer on the surface of the casting, the pores, the sand layer, the scale on the surface of the forging, the decarburization layer, and the surface. Crack, internal stress layer after cutting, surface roughness, etc. Thereby improving the accuracy and surface roughness of the workpiece.
The size of the machining allowance has a great influence on the processing quality and production efficiency. Excessive machining allowance not only increases the labor of machining, reduces productivity, but also increases material, tool and power consumption, and increases processing costs. If the machining allowance is too small, it will not eliminate the various defects and errors of the previous process, and it will not compensate for the clamping error during the processing of this process, resulting in waste. The principle of selection is to make the margin as small as possible under the premise of ensuring quality. In general, the more finished, the smaller the process margin.
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