Why should CNC machining manufacturers leave machining allowance on workpieces for CNC machining?

For the twisted outer edges of inner holes and holes, the processing capacity is measured by the diameter, so it is called symmetrical capacity (i.e. multilateral capacity), that is, the thickness of the alloy layer actually cut is half of the processing capacity on the diameter. The processing capacity of the plan is the capacity of one side, which is the thickness of the alloy layer actually cut.

The overall objective of leaving processing capacity on the product workpiece is to better remove the processing errors and external defects left by the previous process flow, such as the cold hardening layer, air outlet, intercalated weathering layer on the outside of the casting, the oxide skin, carburizing layer and external cracks on the outside of the casting, the thermal stress layer and external surface roughness after drilling. And then develop the precision and outer surface roughness of the product workpiece. The size of processing capacity is very harmful to the processing quality and productivity.

Excessive processing surplus not only increases the workload of mechanical equipment processing and reduces the production efficiency, but also increases the consumption of materials, targets and power engineering. CNC processing has developed the processing cost. If the processing capacity is too small, it can not be better to eliminate all kinds of defects and errors in the previous process, nor can it be better to compensate for the clamping errors during the processing of this process flow, resulting in waste. The clamping rule is to make the capacity as small as possible under the premise of ensuring product quality and CNC processing. Generally speaking, the more precise the processing, the smaller the process capacity.

When defining the CNC processing sequence, it is also necessary to determine whether the parts are to be pre processed before processing. Pre machining is usually carried out by a general CNC lathe. If the precision of the rough embryo is high, the accurate positioning is reliable, or the processing capacity is sufficient and symmetrical, it can be processed on the CNC lathe at the same time without pre-processing. At this time, it is necessary to consider the division of the NC lathe process flow according to the precision of the rough standard, which can be one process flow or divided into several process flows.