Machined surface quality
Destruction of mechanical parts, almost always started from the surface layer. Product performance, in particular its reliability and durability depends largely on the quality of parts of the surface layer. Objective To study the quality of the machined surface is to master the machining process of various factors on the surface quality affect the law in order to apply these laws to control the process, and ultimately to improve the surface quality, the purpose of improving product performance.
First, use the machined surface quality performance impact machine
Effect of (a) the quality of the surface wear resistance
Surface roughness on wear resistance
Between a newly processed friction of the two contact surfaces, only the initial stage of the rough surface contacting peaks, the actual contact area is far less than the theoretical contact area, contact each other at the peak portion of the unit has a very large stress, the the actual contact area generated at the shear failure plastic deformation and elastic deformation between the peaks, causing severe wear.
Wear parts can generally be divided into three stages, the early stages of wear and tear, normal wear and severe wear stage stage.
Great influence on the surface roughness of the part surface wear. Generally, the smaller the surface roughness value, the better the wear resistance. But the surface roughness is too small, the lubricating oil is not easy to store, prone to molecular bonding between the contacting surfaces, but increased wear. Therefore, the roughness of the contact surface there is an optimum value, the value of the part of the work related to increased work load, the initial wear amount increases, the surface roughness of the greater value of the optimum.
Effect of cold hardening on the surface abrasion resistance
Work hardening process so that the surface friction of the surface layer of the metal hardness increase, it will generally improve the wear resistance. But not the higher the degree of work hardening, the higher abrasion resistance, it is because of too much work hardening will cause excessive tissue loose metal, and even cracks and flaking surface of the metal, so that the wear resistance decreased.
Effect (ii) the surface quality of the fatigue strength
Fatigue damage produced after the metal by alternating loads tend to occur in parts of the surface and below the surface of chill layer, the surface quality of the parts and therefore a great influence on the fatigue strength.
Surface roughness on fatigue strength
In alternating loads, the surface roughness of the valley portions easily cause stress concentration, fatigue cracks. The greater the surface roughness value, surface pattern marks deeper, smaller grain bottom radius, the more fatigue failure capability bottom poor.
Residual stress, work hardening on fatigue strength
I stress a great influence on the fatigue strength of the part. The surface layer of residual tensile stress fatigue cracks will expand and accelerate fatigue failure; but the surface layer of residual stress can prevent fatigue crack extension, delay fatigue damage generated
Chilled surface usually associated with the generation of residual stress, can prevent cracks and crack propagation have been prevented, enabling to improve the fatigue strength.
Effect (iii) the surface quality of corrosion resistance
Parts corrosion resistance depends largely on the surface roughness. The larger the surface roughness, the concave valley on the more corrosive substances accumulate. The more poor corrosion resistance.
Tensile residual stress of the surface layer will produce stress corrosion cracking, reducing parts wear and the residual compressive stress is to prevent stress corrosion cracking.
Effect (iv) to match the quality of the surface quality
The size of the surface roughness values will affect the quality of the mating surfaces of the mating. For the gap with the roughness of the General Assembly to increase the wear, the gap increases, with the destruction of the nature of the request. For an interference fit assembly process pushed part of the surface convex peak level, the actual amount of interference is reduced, reducing the strength of the connection between the mating parts.
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