The influence of hardness and surface condition of polishing process

Polishing machine operation is the key to try to get the maximum polishing rate, in order to remove polishing when the damage layer as soon as possible. At the same time also want to make polishing damaged layer does not affect the final observation to the organization, namely not cause false organization. The former requires the use of relatively coarse grinding, polishing rate to the larger in order to make sure there are damage layer to remove the grinding, polishing damaged layer is deeper; The latter requires the use of the finest materials, polishing damaged layer is shallow, but the polishing rate is low. The best way to solve this contradiction is the polishing is divided into two stages. Coarse behind the purpose is to remove the grinding damage layer, this phase should have maximum rate of polishing, the surface layer of rough cast formation damage is a secondary consideration, but also should be as small as possible; The second is the essence behind ( Or eventually throw) , its purpose is to remove the coarse surface damage, make the polishing damage to a minimum. Polishing machine polishing, grinding surface and sample pads should be absolutely parallel and evenly gently press on the pads, pay attention to prevent fly out of sample and the new grinding crack due to pressure is too great. At the same time should also make sample rotation and moving back and forth along the wheel radius direction, in order to avoid local wear too fast in the process of polishing polishing cloth to keep adding powder slurry, keep polishing cloth certain humidity. Too much humidity can abate polishing grinding crack effect, make the hard phase in the sample presents projection and non-metallic inclusions in steel and cast iron graphite phase in the 'smear' phenomenon; Humidity too hours, due to the friction heat production can make the sample temperature, lubrication, grinding surface loses luster, appear even dark spots, light alloy will wound surface. In order to achieve the purpose of rough cast, low rotary speed, had better not more than 600 r/min. Polishing time should be longer than the time needed for removing scratches, because also remove deformation layer. Lackluster coarse cast after grinding surface is smooth, but, under the microscope has a uniform meticulous grinding crack, fine buffing to be eliminated. Due to mechanical polishing is still mainly rely on artificial to complete, so polishing technology is the main reason affecting the quality of polishing. In addition, also with the mold material, the surface condition, heat treatment before polishing process and so on. High quality steel is a prerequisite for good polishing quality, if there are differences between the steel on the uneven surface hardness or features, tend to produce polishing difficult. All kinds of inclusions in steel and pores are not conducive to polishing. Higher hardness increased the difficulty of grinding, but after polishing roughness decreases. Due to the higher hardness, to achieve lower roughness of the polishing time increases correspondingly. Hardness increased at the same time, the possibility of polishing excessive decrease accordingly. Steel in the process of the broken of cutting machining, the surface will be damaged by heat, internal stress, or other factors, improper cutting parameters affect the polishing effect. After the edm surface is much more difficult than ordinary mechanical processing or the surface of the heat treatment after grinding, so fine gauge should be used before the end of edm edm dressing, otherwise will form the surface hardening thin layer. If improper selection edm refinement gauge the depth of the heat affected layers up to 0. 4mm。 Hardening of the thin layer of hardness is higher than matrix hardness, must be removed. So it's best to increase a coarse grinding, thoroughly remove damaged surface layer, average constitute a rough metal surface, polishing processing to provide a good foundation. In the plastic mold processing of polishing and other industries in the required surface polishing is very different, strictly speaking, the mould polishing should be referred to as the mirror processing. It not only have high request for polishing itself and the surface roughness, smoothness and geometric accuracy also has a high standard. Surface polishing typically demand the polished surface. Mirror processing standard is divided into four levels: AO = Ra0. 008μm A1 = Ra0。 016μm，A3=Ra0. 032μm，A4=Ra0. 063 microns, such as electrolytic polishing, fluid polishing methods are difficult to control parts of geometry accuracy, precision and chemical polishing, ultrasonic polishing, magnetic abrasive polishing methods, such as surface quality can not meet the requirements, so the precision mould mirror processing is given priority to with mechanical polishing.