What is the machining allowance? What are the factors that affect the machining allowance?

The Machining allowance is the thickness of the metal layer cut on the surface of the workpiece during machining. Machining allowance generally refers to the nominal margin, the nominal margin, that is, the difference between the nominal size. Also known as rough margin, refers to the rough size and part of the design difference between the size.

The factors that affect the machining allowance:

1. The surface quality (surface defect depth and surface roughness) of the front (or blank) before machining.

(1) The chill of castings, porosity and slag layer, forgings and heat treatment parts of the oxide layer, decarburized layer, surface cracks and other surface defects, as well as the residual stress after cutting machining.

(2) The surface roughness after the previous process.

2. Dimensional tolerances of the preceding process

(1) The size error and shape error after machining previous process, the sum does not exceed the size tolerance of the previous process.

⑵ When machining a number of parts, if not consider other errors, the machining margin of this process should not be less than the size tolerance of the previous process.

3. The shape and position tolerance of the previous process (such as straightness, coaxial, vertical tolerance, etc.)

⑴ The formed shape and position error after machining previous process, the sum of the two is generally less than the shape and position tolerance of the previous process.

⑵ When not considering the existence of other errors, the machining margin of this process should not be less than the shape and position tolerance of the previous process.

⑶ When there are two or more shapes and position errors, the total error is the sum of each vector errors

4. The installation error of machining this process. The installation error is equal to the sum of the vector error of the positioning error and clamping error.