Effect of lapping pressure on surface quality of polycrystalline diamond

Abstract

ObjectivesPolycrystalline diamond (PCD), as a superhard material with high hardness, high wear resistance, and good impact toughness, has a wide range of applications in fields such as cutting tools for superhard materials. However, due to its high hardness, the precision surface processing of PCD has always been a technical challenge. This paper aims to study the influence of lapping pressure on the surface quality of PCD, particularly focusing on the material removal rate, surface roughness, and changes in surface morphology under high-speed grinding conditions.MethodsThe experiment adopts a single-factor test method, keeping the abrasive particle size W5 of the diamond flat grinding disc and the lapping speed of 43.3 m/s constant, while varying the lapping pressure (from 0.10 MPa to 0.18 MPa) to study its impact on the material removal rate, the surface roughness, and the surface morphology of polycrystalline diamond material. The experimental material is a ϕ13 mm × 2 mm polycrystalline diamond composite sheet with a diamond layer thickness of approximately 1 mm. The experimental apparatus is a high-speed grinding testing machine, which uses an electric spindle to drive the diamond flat grinding disc, with a lapping time of 20 minutes. The lapping process is conducted without the use of coolant to avoid its influence on the experimental results.ResultsThe experimental results indicate that the lapping pressure has a significant impact on the material removal rate of PCD. As the lapping pressure increases from 0.10 MPa to 0.18 MPa, the lapping removal rate increases from 0.005 mg/min to 0.030 mg/min, indicating that an increase in lapping pressure significantly improves material removal efficiency. The influence of lapping pressure on the surface roughness of PCD is also significant. With an increase in lapping pressure, the surface roughness gradually decreases, reducing from a higher value at 0.10 MPa to a lower value at 0.18 MPa, with a roughness Ra reduction of approximately 0.020 μm. The impact of lapping pressure on the surface morphology of PCD is manifested by a reduction in surface defects and an expansion of smooth areas. At lower lapping pressures, the surface exhibits numerous pits, interstitial cracks, and mechanical scratches. As the lapping pressure increases, the number of these defects gradually decrease, and smooth areas gradually expand. Scanning electron microscope observations reveal that an increase in grinding pressure helps reduce defects such as intergranular fractures, minute pits, and mechanical scratches, resulting in a smoother surface.ConclusionsThis paper experimentally studies the influence of lapping pressure on the material removal rate, surface roughness, and surface morphology of PCD, and draws the following conclusions. The lapping removal rate of PCD material significantly increases with an increase in lapping pressure, primarily attributed to the high-frequency collisions and frictional heat between diamond abrasive particles and PCD during the lapping process. An increase in lapping pressure significantly reduces the surface roughness of PCD, primarily benefiting from the decreased cutting depth of abrasive particles and increased actual contact area caused by the increased lapping pressure, and the promotion of surface thermochemical reactions and mechanical thermal removal effects by frictional heat. An increase in lapping pressure leads to a reduction in surface defects, an expansion of smooth areas, smaller mechanical scratches, and a significant improvement in the surface quality of PCD.

Keywords

• polycrystalline diamond
• high speed lapping
• lapping pressure
• material removal rate
• surface quality