Polishing refers to the use of mechanical, chemical, or electrochemical action to reduce the surface roughness of the workpiece to obtain a bright and smooth surface. The modification of the surface of a workpiece using polishing tools and abrasive particles or other polishing media.
Development and Status of Mirror Polishing Process:
In recent years, with the continuous development of technology in the field of domestic machinery and equipment manufacturing, in the process of equipment development in various industries, some workpieces that are difficult to be processed by traditional processes have appeared. These workpieces have high requirements for surface quality, and their design appearance is mirror or super-mirror.
In the traditional mechanical polishing process, when the grinding wheel is in initial contact with the surface of the machine, the amount of wear is large, and the surface accuracy of the machine cannot be guaranteed. Under the strong extrusion action of the abrasive tool, the cusp metal begins to produce plastic flow and is forced into the microscopic pit, which hides the real appearance of its surface. In the later use process, the surface quality becomes poor due to the continuous shedding caused by fatigue wear. The parts processed by this process have a bright appearance but no obvious mirror effect and the surface roughness can only reach Ra 0. It is about 1 μm, and it is not easy to guarantee the size of the workpiece.
The machining mode is suitable for polishing a single type of product, and different types and shapes of products need to change the fixture or table structure. However, the advantages of automatic polishing are undeniable, high production efficiency and relatively fixed products can be mass-produced. Secondly, mechanical polishing can save a lot of labor, reduce labor costs, improve the production environment, and reduce dust hazards. Polishing automation is also the trend in the current polishing machine industry
The Principle of Polishing:
Surface finishing of workpieces using flexible polishing tools and abrasive particles or other polishing media. Polishing does not improve the dimensional accuracy or geometric accuracy of the workpiece but aims to obtain a smooth surface or mirror gloss, and sometimes it is also used to eliminate gloss. Usually, a polishing wheel is used as a polishing tool. The polishing wheel is generally made of multi-layer canvas, felt, or leather, and the two sides are clamped by metal discs. During polishing, the high-speed rotating polishing wheel (circumferential speed above 20 m/s) presses against the workpiece, causing the abrasive to roll and micro-cut the surface of the workpiece. The polishing removal unit is very small, so the processing efficiency is low, and because it is easy to use a Deformed polishing machine, so it is a process that is prone to shape collapse. Therefore, in the construction, use as little removal as possible to obtain a bright machined surface, and the surface roughness can generally reach Ra0.63 ~ 0.01 microns; when a non-greasy matting polishing agent is used, the bright surface can be matt to improve.
Factors of Polishing Efficiency:
- Polishing amount R=k.p.v.t where p is the polishing pressure, v is the polishing speed, t is the processing time, and k is the proportionality constant.
- Polishing efficiency is proportional to additional pressure (p) and polishing distance (v.t).
- To maintain a certain processing efficiency, in addition to the processing conditions such as polishing pressure and speed, strict management of the concentration of the slurry, temperature, and the state of the polishing machine are important factors to stabilize polishing.
The Function of Mirror Polishing Processing Technology:
- Improves surface roughness and eliminates defects such as scratches, dirt inclusions, and micro-cracks.
- Reduce surface friction coefficient and improve wear resistance.
- Improve the physical and mechanical properties of the surface of the part, and improve the stress distribution state of the surface of the part.
- Improve the accuracy of parts and ensure assembly manufacturability.
- Improve the gloss and brightness of the surface of the parts, and meet the requirements of cleaner production.
- Improve the service life of parts and the whole machine.
- Improve the bonding force between the coating layer and the substrate, and meet the requirements of appearance and decoration.
Advantages and Disadvantages of Mirror Polishing Process:
Polishing processing technology can be divided into three categories: mechanical method, chemical and electrochemical method, and thermal energy method according to the active form of energy during processing. According to the state of abrasives or abrasives during processing, mechanical methods can be divided into two forms: free abrasive polishing and non-free abrasive polishing.
What are the Types of Polishing Processes?
Grinding Process Metamorphic Layer:
- Dry grinding wheel polishing method:
In the polishing process of roller shaft parts, non-free abrasive mechanical polishing technology is generally used. The most widely used is the dry grinding wheel polishing method, which has the characteristics of high production efficiency, low input cost, and is suitable for batch production and processing. During dry polishing, the surface of the grinding wheel is coated with polishing wax, which rotates at high speed along the tangential direction and is in contact with the surface of the machine. Due to the strong extrusion of the cutting force, high temperature is generated on the surface of the machine, plastic deformation occurs on the surface of the metal matrix, and the sharp point metal begins to generate plastic flow and is forced into the microscopic pit, and the concave part is filled. Under the action of high temperature, a very thin oxide film or other compound film is rapidly formed on the metal surface. After repeated polishing of the film, the surface morphology is improved, and finally, a smooth and mirror-like decorative surface is formed.
- Haokeneng metal mirror processing technology:
The working principle is that the ultrasonic vibration energy generated by the ultrasonic high-frequency vibration system with appropriate output power (50-1000W) is attached to the polishing tool, and acts on the surface of the metal workpiece to be processed, causing plastic deformation of the surface metal of the workpiece. In the process of plastic deformation, the surface polishing processing method for mirror polishing of the workpiece is achieved, and cold work hardening occurs during the polishing process, which achieves the purpose of improving the surface quality. The improvement of this surface quality is comprehensive, which not only increases the hardness, but also reduces the surface roughness, and bridges some microscopic cracks, improving the fatigue strength, wear resistance, and corrosion resistance of the workpiece.
- Wet abrasive belt polishing method:
During wet abrasive belt polishing, the abrasive belt contacts the surface of the workpiece through the contact wheel. The material of the contact wheel is generally rubber or plastic, and the base material of the abrasive belt is cloth, paper, or polyester film, all of which have a certain elasticity. During grinding, due to the extrusion of abrasive particles, the machined surface will also produce plastic deformation. However, due to the large area of the elastic deformation zone, the load on the abrasive particles is small and the force is more uniform. From the analysis of the processing principle, wet abrasive belt polishing adopts various combinations of refined abrasive grains, carrier abrasive belts, and processing fluid, and has the functions of grinding and polishing. It is a composite processing technology. Ultra-precision vibration grinding is performed on the surface of the machine to achieve a super-mirror decorative effect.
- Electrochemical polishing:
Generally, the electrolytic polishing solution based on phosphoric acid is used, and the parts are anodes. During the electrolysis process, the parts with microscopic roughness are processed, the metal workpiece is anodic dissolved, the surface roughness is reduced, and the finishing effect of mirror brightness and leveling can be obtained, which can be used for the pretreatment of decorative electroplating. Electrochemical polishing has good brightness and leveling properties, the long service life of the solution, fast polishing speed, and high polishing efficiency. The burr removal effect on the surface of the part and the punching edge of the plate is good, the surface roughness can be reduced, the light reflectivity is high, the decorative effect is good, and the geometric shape of the part is not required high. The stainless-steel products and various metal components after bright treatment have no hydrogen embrittlement, no deformation of the workpiece, etc., the polishing equipment and fixtures are simple, and the investment is small.
The processing metamorphic layer causes the structure, organization, and composition of the workpiece material to be damaged or close to a damaged state. Deformation and stress exist in the metamorphic layer, as well as its physical and chemical effects. Mechanical properties such as hardness and changes in surface strength and chemical properties such as corrosion resistance also differ from the base material.
The ground surface of hard and brittle materials and the ground single crystal silicon surface are chemically etched with fluorine and nitric acid series solutions, and the surface layer is removed in turn. When the crystal is observed by the electron diffraction method, the order from the surface layer to the inside is amorphous Layers or polycrystalline layers, damascene layers, distorted layers, and fully crystalline structures. In addition, from the viewpoint of Elastoplast city using X-ray diffraction, the surface layer is composed of an extremely small plastic flow layer, a crack layer with foreign matter mixed under it, a crack layer, an elastic deformation layer, and a layer under it. main material.
When grinding metal materials, although no fragmentation occurs, when the abrasive particles are rotated and scraped, due to the plastic deformation of the material, a processing deterioration layer like the above-mentioned silicon wafer is usually formed. On the contrary, for example, in a polycrystalline metal material, the closer to the surface layer to be processed, the finer the crystal grains, the more dislocations are accumulated in the outermost layer, and the amorphous state becomes. In this part, the metal becomes active in combination with the reactive oxygen species in the atmosphere. In some cases, abrasive grains and the like are easily embedded in the metal due to plastic deformation.