Criteria for evaluating surface quality in machining

Criteria for evaluating surface quality in machining
Through the quality of the mechanically machined surface, it will help you accurately assess the mechanical processing service provider.
Are you looking for a reputable, professional, good quality mechanical processing unit but don’t know where to look? You also do not know how to evaluate a work order is qualified. Then please refer to the article of Cosmo Vietnam right away .
Because in order to evaluate the quality of mechanical processing services, besides the accuracy factor when machining, the quality of the machined surface is also an extremely important factor.
And in this article, we will help you understand the concept of “what is a mechanically machined surface” and what factors help you evaluate the quality of this surface.
All will be answered through the article below.
What is the concept of machined surface quality?
Machined surface quality, also known as surface integrity, is the surface state of a part after it has been machined.
This surface quality is evaluated from two main factors:
Geometrical characteristics of the surface layer
For the geometrical characteristics of the surface layer, it is divided into 4 aspects including:
*Roughness of machined surface
– This is probably a rather difficult concept for everyone because they are assessed based on knowledge of geometry. So, if you are not in the industry, it will be difficult to visualize specifically. However, we will also use the simplest words to understand to explain to you.
– Machined surface roughness is evaluated based on micro-geometric features including: small distances, vertices and pins on the machined surface.
– In addition, you also need to base on its evaluation parameters which mainly include: arithmetic deviation of contour (denoted Ra) or average height of micro roughness of the contour (denoted Rz).
*Surface Wavelength
– You can simply understand that the surface roughness is a periodic error between the macroscopic shape and the microscopic surface roughness. This phenomenon is mainly caused by the machining method and the law of cutting motion.
*Machined surface texture
The machined surface texture will refer to the shape and orientation of the cut grain in surface cutting. The shape quality will depend on the machining method used and the law of the cutting motion.
*Surface defect
Poor quality machined surface will appear surface defects such as: trachoma, pores, cracks, scratches, and not according to any rules.
Mechanical properties of the surface layer
The mechanical and mechanical properties of the surface layer will be evaluated, focusing mainly on the following three aspects:
– Ability to harden the surface layer
– Changes the microstructure of the surface layer
– Residual stress in the surface layer.
How does the quality of the machined surface affect the quality of the machining?
Through the following 5 aspects will help you understand the impact that the quality of the machined surface has on the machining quality:
* About the corrosion resistance of work pieces
– For mechanically machined parts, wear resistance is one of the most important performance indicators. The wear resistance is demonstrated when the friction material, lubrication conditions and machining accuracy are determined.
– More stress is generated when the surface roughness is larger, which leads to wear of the contact surface of the part.
* Fatigue stress on part
– The quality of the machined surface is also considered to have a great impact on the fatigue strength of the machined parts.
– Properly treated hardener can limit and prevent existing cracks, not create new ones. Therefore, it is necessary to improve the fatigue strength of the parts.
And vice versa, if the hardening process is too much, it will make the surface structure of the parts brittle and easy to crack. Leads to a decrease in fatigue strength.
*About corrosion resistance
– The larger the surface roughness of the parts, the easier it is to create a corrosive environment at the sunken points. Thereby causing chemical corrosion and electrochemical corrosion on the work pieces.
*Relevance of details
– Conformity of two fitting parts is assessed by the degree of tightness or clearance. The degree of clearance is considered suitable if the roughness of the mounting surface is large, the clearance will increase rapidly due to wear, leading to a decrease in the quality of the joint.
*About other properties of work pieces
In addition, the quality of the machined surface will have a direct influence on other aspects of part performance. For example, reducing the surface roughness (Ra) will reduce leakage and improve the sealing performance of sealed hydraulic cylinders and slide valves.

– As for other sliding parts, the lower the surface roughness (Ra), the lower the coefficient of friction, the more flexible the movement, and the less heat and energy loss.

So it can be said that improving the quality of the machined surface is very important because they will determine the performance and life of the machined parts.