Study Of Micro-abrasive Suspension Jet Machining Mechanism

Micro-abrasive suspension jet polishing is a new type of special precision processing technology developed on the basis of abrasive water jet machining technology. Abrasive Water Jet Technology is more superior because of its easy to control, low cutting force, automatically clear the debris, non-thermal damage, non-hard injury, non-pollution, high abrasive re-use rate, high flexibility, applicable to the free-form surfaces and high steepness parts processing, which has a unique advantage especially in small parts of complex surface and a longer length to diameter ratio of the cavity surface processing. This paper first introduces the research status of the micro-abrasive suspension jet polishing techniques, and then developed a series of experiments. The micro-abrasive suspension jet characteristics, the micro abrasive suspension jet machining morphology and micro-abrasive suspension jet polishing process and mechanism were studied. At last, explored the micro-abrasive suspension jet modification process under the guidance of the research conclusions, and proposed the modify thought and theory. The main conclusions of this paper are as follows:The micro-abrasive suspension jet acceleration is divided into acceleration in the pipeline, the nozzle and the air. At different incident angles, the erosion central area distribution and water film shape formed after the jet collision are different. Normal erosion force increases parabolic as the jet incident angle gradually grow, the maximum force appear at an incident angel of25°. Jet tangential erosion force increases with the incident angle gradually increased, when reaches the maximum value and then gradually decreases, the maximum tangential erosion force appear at25°incident angle. The maximum jet horizontal impact force appears near the area of5mm from the jet erosion center. There exist jet undulation phenomena.At90°incident angle, the erosion area is comparison a rule annular and the erosion region sectional view like a two attached flat double "W" shape. When the incident angle is60°, the jet first contact to the region showing a "crescent" shape, polishing region as a whole is similar to typical "horseshoe-shaped" and cross-section curve is a "W" shape. When the incident angle is30°, the erosion area is similar to a "tuning fork" shape, the overall erosion holes like an oval "blade-shaped", and cross-sectional curve is a "V" shape. When the Nozzle moving tangentially, the polishing removal are more uniform, and the depth is deeper, while the nozzle moving laterally, the removing area is unevenness but the effective removal area is larger. The surface has more obvious scratches and pits before polishing, after polishing the polished work-piece surface is smooth and almost has no macroeconomic scratches. Before polishing the work-piece surface roughness Ra=0.3068μm, Rz=2.6646μm, after polishing half an hour, the polished surface Ra=0.1628μm, Rz=1.3612μm, the work-piece surface quality has been improved significantly.The injection pressure and feed speed have most significant effect on the material removal depth during polishing. The abrasive types and feed speed have most significant effect on the work-piece surface roughness (Ra). Most of the abrasive particles contact angles are favorable on the material remove when the incident angle is about25°. When particles impact the work-piece with smaller contact angle, most of them play shearing action. Particles outer surface sharp corners and "blade" played an important role in the material removal, and only when they are blunt, the particles will be smaller or lose the ability to continue removing material, while the particles update the surface sharp corners and blade by breakage or rupture constantly, which greatly enhance the reusability of the particles. Compared to glass and mold steel work-piece erosion surface topography, we initial determined that the plastic removal is the predominant part in the plastic material removal, and in brittle material removal, all are brittle removal.The orthogonal experiment shows that abrasive type, injection pressure have most significant effect on the erosion hole material removal volume. Straight-line morphologies processed by different path pattern have its own characteristics. The incident angle is not90°, the processing line’s width is wider and depth is shallower, the processing area is asymmetric when the nozzle moves laterally, while the processing line’s width will be narrower and depth is deeper, the processing area is symmetrical when the nozzle moves longitudinally. When the repair area is relatively small, so that let the nozzle facing the repair area to accomplish erosion repair. If the defect is a straight line or geometric rule curve, whether on flat or curved surface, allows the nozzle moves along the needs to be repaired curve at a curtain feed rate, thus completing the erosion repair. When the scratch is deep or irregular, consider to repair the area around the curve. The large area surface repair problem can be solved by divided the large area into several sub-regional ones, the middle part can be polished by normal method, and can take the transition processing strategy to repair transition region. Due to the presence of the mask, the jet flow is blocked and direction changed, so as the erosion hole area changed, too. The hard metal material masks are easy to scratch the surface of the work-piece. In the area with mask, the material has not been removed, so we can add a mask to obtain the required repair shape. At90°incident angle, there almost non-existent blind processing area at the work-piece and the mask junction transition area. At30°incident angle, the region back to the jet are unprocessed, there are blind processing area.