What is Machining Allowance?


To ensure to machining qualified components,the thickness of metal that need to cut from the workpiece is called machining allowance.The machining allowance include process allowance and total allowance.The metal which need to cut in one process is called the allowance of this process.The allowance which need to cut from the workblank to finished products is called total allowance.It’s the sum of each process allowance.


The aim to leave allowance on workpiece is cutting the machining error and surface defect which leaved by previous process.Like the chilling layer,air hole,sand layer of casting parts,the oxide skin,decarburized layer,surface crack of forge pieces,the internal stress layer and surface roughness after machining,etc.After machining the allowance,then improve the precision and surface roughness of workpiece.


The machining allowance can affect the quality of components and production efficiency.If the machining allowance is too big,It will not only increase the work of machining,reduce the efficiency,but also increase material,consumption of tooling and power,and then improve the costs.If the machining allowance is too small,it can’t ensure to cut the machining error and surface defect of each process.The principle to leave machining allowance is on the premise of quality assurance,leave the machining allowance as small as possible.Generally speaking,the high precise of components,the smaller the machining allowance leaving.


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