Machining accuracy of parts machined surface quality of parts

The machining accuracy and machined surface quality of parts are two important aspects of the machining quality of parts. Part quality is one of the contents that need to be inspected after production and processing. The quality of parts has a great influence on the production of products. Therefore, the quality inspection of parts is an essential and important process in production.
1、 Machining accuracy of parts
Machining accuracy is the actual geometric parameters of parts after machining, such as shape, size and the mutual position of surfaces. The consistency of these parameters with the ideal geometric parameters. The higher the degree of conformity, the higher the machining accuracy. The machining accuracy of parts mainly includes dimensional accuracy, shape accuracy and position accuracy.
1. Dimensional accuracy
The degree to which the actual values of the diameter, length, surface distance and other dimensions of the part are close to the values is the dimensional accuracy, which is mainly controlled by dimensional tolerance.

2. Shape accuracy
Shape accuracy is the degree of conformity between the actual shape and the ideal shape of the line and surface on the part. The evaluation items of shape accuracy include straightness, flatness, roundness, cylindricity, West Bank profile and surface profile.
3. Position accuracy
Position accuracy refers to the actual position of points, lines and surfaces on the part after machining and the degree of compliance with the ideal position. During the inspection, the parallelism, verticality, inclination, coaxiality, symmetry, position, circular runout and total runout shall be inspected according to the provisions of gb/t1182-1996.

2、 Machined surface quality of parts
Machining surface quality mainly includes the geometric characteristics of the machined surface and the changes of the material of the machined surface layer. In fact, the surface of machined parts is not an ideal smooth surface. There are different degrees of surface roughness, cold hardness and cracks on its surface. These will affect the accuracy, wear resistance, fitting accuracy, corrosion resistance and fatigue strength of mechanical parts, and even endanger the service performance and life of products.
1. Influence of surface quality on wear resistance of parts
The surface roughness is too large, the actual pressure on the contact surface increases, and the rough peaks bite, crack and cut each other, so the wear is intensified. If the surface roughness is too small, it will also lead to increased wear. Because the surface is too smooth, the lubricating oil cannot be stored, and the oil film cannot be formed on the contact surface, molecular bonding is easy to occur, which intensifies the wear.

2. Influence of surface quality on fatigue strength of parts
The greater the surface roughness, the worse the ability to resist fatigue damage. It has a great influence on the fatigue strength of parts under alternating load. Under the action of alternating load, the concave part of surface roughness is easy to cause stress concentration and fatigue cracks. The smaller the surface roughness value is, the less defects are avoided, and the better the fatigue resistance of the workpiece is; On the contrary, the rougher the machined surface, the deeper the striation marks on the surface, and the smaller the radius of the bottom of the striation, the worse its ability to resist fatigue damage.
3. Influence of surface quality on working accuracy of parts
The greater the surface roughness, the lower the fitting accuracy. The surface layer has large residual stress, which will affect the stability of their accuracy.
4. Influence of surface quality on corrosion resistance of parts
The rougher the part surface is, the more corrosive substances are likely to accumulate, and the deeper the valley is, the stronger the effect of penetration and corrosion will be. Therefore, in order to improve the corrosion resistance of parts, the common method in production is to reduce the surface roughness of parts.