Stainless steel parts are usually ground to achieve surface quality and machining accuracy. Due to the high toughness, low thermal conductivity and low modulus of elasticity of stainless steel, the following problems often exist in the grinding process.
1) easy adhesion and blockage of the grinding wheel; 2) easy burns on the processed surface
3) serious hardening; 4) easy deformation of the workpiece.
It is easy to see that the choice of grinding wheel and grinding fluid directly affects the grinding efficiency and machining accuracy. This paper conducts an experimental study on the factors affecting adhesion blockage and surface roughness.
2 Experimental conditions and methods
The test piece material is 1Gr18Ni9Ti, with mechanical properties: σb=530MPa, σ=40%, hardness HB=187. The test piece size is φ50mm in diameter, 300mm in length, φ50 external surface finish turning, and both end faces are punched with a central hole. The experiments were carried out on an MGB1420 cylindrical grinding machine with a grinding wheel of P400×40×203 and the grinding method was cylindrical longitudinal grinding. In order to improve the reliability of the test results, repeated tests were carried out to observe the average effect and eliminate the influence of random factors, while keeping the grinding conditions basically unchanged as far as possible. The effect on the grinding effect was examined by changing the grinding wheel grit, hardness, abrasive, grinding fluid and grinding quantity.
3 Analysis of experimental results
3.1 Effect of grinding wheel grit size on adhesion rate
Four grinding wheels of white corundum, hardness K and grit size 36, 46, 60 and 80 were selected for longitudinal grinding of the outer circle of the test piece with a grinding length of 600 mm, and the adhesion rate was tested.
3.2 Influence of grinding wheel hardness on adhesion rate
Abrasive wheels of white corundum with a grit size of 46 and hardnesses of H, J, K and L were used to grind the specimens with a grinding stroke of 600 mm, and the adhesion rate was tested. The higher the wheel hardness, the more severe the adhesion. This is due to the fact that with a lower hardness grinding wheel, the abrasive grains are easily dislodged from the surface of the wheel under the action of the grinding force, forming a new chip space that is less likely to be blocked.
3.3 The influence of abrasives on the adhesion rate
Commonly used grinding wheel abrasives are white corundum and green silicon carbide, experiments show that the impact of the two abrasives on the adhesion rate is not very different, green silicon carbide can slightly reduce the adhesion phenomenon, the reason is that the sex is brittle and sharp.
3.4 Effect of grinding fluids on surface roughness
Three kinds of emulsions, inorganic salt grinding fluids and oil-based grinding fluids were used respectively, and extreme pressure additives such as sulphur and chlorine were added to observe the surface roughness of the workpiece after processing, and the flow rate of the grinding fluid was 20L/min and the grinding stroke was 600mm, and the experimental results are shown in Table 3.
It can be seen that the surface tension is low and the surface quality obtained by grinding is good with the inclusion of extreme pressure additives. The reasonable use of grinding fluid can improve the heat dissipation conditions, and the grinding fluid can flush out the grinding chips and dislodged abrasive particles, while forming an oil film on the metal surface to play a lubricating role and reduce the surface roughness of the workpiece.
3.5 Influence of grinding quantity on adhesion rate
The workpiece speed, feed and grinding depth have little effect on the machining, as can also be seen from Tables 1 and 2, and the change in grinding depth has little effect on the adhesion rate.
1) When grinding stainless steel, reducing the adhesion blockage of the grinding wheel is an important factor in improving the grinding efficiency, and the grinding wheel should be trimmed frequently during processing to keep the cutting edge sharp.
2) Grinding wheels for grinding stainless steel with a good self-sharpening grinding wheel is the main goal, generally choose a grinding wheel with low hardness to achieve good results, but also can not choose too low hardness, otherwise the abrasive grain will fall off before grinding blunt. It is recommended to use J grade.
3) In order to reduce the adhesion blockage of the grinding wheel during grinding, a coarse-grained grinding wheel should be used. For coarse grinding, use 36 or 46 grit, and for fine grinding, use 60 grit.
4) When grinding stainless steel, the use of GC grinding wheels can improve the grinding efficiency.
5) The choice of grinding fluid must take into account the two roles of lubrication and cleaning, and supply sufficient, so that an emulsion with low surface tension and containing extreme pressure additives can be used to obtain a high surface quality.
6) The choice of grinding dosage can be determined according to the machining allowance.
7) During the experiment, it was found that the organization of the grinding wheel and the bonding agent have a certain influence on the grinding process of stainless steel, which is currently limited by the experimental means and needs further research.