Polishing Machine

The Polishing Machine is used to polish the surface of the workpiece. It grinds and polishes the surface of the workpiece through rotation or friction, using Abrasives or polishing agents to improve its finish, flatness and appearance, so as to achieve the purpose of fine processing and improve product quality.

Comparison and application of surface roughness value levels

In general, the surface quality requirements of important or critical parts are higher than those of ordinary parts. This is because parts with good surface quality will greatly improve their wear resistance, corrosion resistance and fatigue damage resistance. Mirror is the ideal state of metal cutting processing, is the most effective means to improve the service life of mechanical parts. Mirror is the traditional synonym for very good roughness after mechanical machining, which can clearly reflect the image of the metal surface.

The mechanical processing methods to obtain the mirror are: removing the material method, no cutting method (rolling processing).
Material removal processing methods: grinding, grinding, polishing, electric spark.
Non-cutting processing methods are: rolling (using mirror tools), extrusion.

Ra/ μm	Surface Shape Feature		Examples of Processing Methods
	A surface obtained or maintained in its original state of supply with no removal of material		Forgings, castings, hot rolled profiles and other non-machined surfaces
50	Rough surface	Knife marks are evident	Sawing, rough turning, rough milling, rough planing, drilling and processing with coarse file and rough grinding wheel
25		Visible knife mark
12.5		Slight knife marks
6.3	Semi-polished surface	Visible work mark	Cold drawing, fine turning, fine twisting, rough twisting, rough grinding, scraping, rough broach processing, etc
3.2		Slight machining marks
1.6		No processing marks visible
0.8	Smooth surface	The direction of the work marks is discernible	Grinding, diamond turning tool finishing, finishing, cold drawing, broach processing, polishing, etc
0.4		Microidentification of the direction of the machining marks
0.2		The direction of the work marks is not discernible
0.1	Brightest surface	Dull surface	Fine grinding, grinding, polishing, super fine grinding, mirror grinding, etc
0.05		Glossy finish
0.025		Mirror-like gloss
0.012		Fog mirror
0.008		Mirror surface

Function

Grinding and removal of surface defects: around the polishing machine can remove the defects on the surface of the workpiece, oxide film, oxide and other bad surface layer, improve the surface quality of the workpiece.
Smooth and trim the surface: through the rotating movement around the polishing machine and the movement of the abrasive, the surface of the workpiece can be more flat, remove the convex and concave uneven and surface roughness.
Improve the surface finish: Around the polishing machine can use the role of polishing agent, fine grinding on the surface of the workpiece, so that its finish is improved to achieve higher brightness and luster.
Improve the surface appearance: By processing around the polishing machine, the surface texture and appearance of the workpiece can be improved, so that it has a better visual effect.
Increase the coating adhesion: Improve the surface finish of the workpiece treated around the polishing machine, which can make the coating better attached to the surface of the workpiece, improve the adhesion and durability of the coating.

Grinding and Polishing Before Electroplating

Most parts that need to be plated often have rough surfaces. We call this rough part to be plated a blank. For a wide variety of metal parts in the manufacturing industry, the surface of the final product needs to be electroplated, electroplated or coated in order to improve the decoration, functionality and service life of the product. For this reason, the surface of the part must be pre-processed before electroplating and coating to make it smooth, so that the appearance is brighter after plating and the quality of the coating is improved. Grinding and polishing is the most commonly used method in electroplating and finishing process, especially when the surface of the plating is required to have a shiny luster, and the coating has a higher quality, the polishing work is particularly important and key.

Practice shows that many plating quality problems are not caused by the plating process itself, but by improper treatment before plating. For example, the key process of copper/nickel/chromium plating is the grinding of the blank of the plating. A motorcycle factory in the process of electroplating muffler, due to the lack of understanding of grinding and polishing, grinding and polishing parts of the grain is obviously palpable, and the grain is inconsistent, the plating time is extended from 0.5h to longer, resulting in higher costs and low pass rate. Later, the grinding and polishing is strengthened, the plating time is shortened, and the product pass rate is also greatly improved. This is precisely because surface polishing has a great effect on the quality of electroplating or finishing. Metal products can meet the requirements of the surface state before electroplating is the premise of obtaining high-quality coating. On rough metal surfaces and greasy metal surfaces, smooth and bright coatings cannot be obtained.

Steel parts are generally only ground before electroplating, as long as the grinding is fine, it is usually no longer polished, because the hardness of steel parts is high, and it is difficult to effectively polish with cloth polishing wheels.

The experiment shows that the surface roughness of the workpiece before plating has an important influence on the quality of the coating. Under the same requirement of the thickness of the chromium plating layer (0.07~0.09 mm), the worse the surface roughness before plating, the worse the surface roughness of the chromium plating layer after plating, the higher the porosity, the more obvious the incomplete coating, the poor adhesion between the coating and the workpiece surface, the easier to rust and affect the service life. In order to ensure the complete chrome plating layer and extend the service life of the chrome plating workpiece, the surface roughness must be controlled below Ra0.2μm or even Ra0.1μm before electroplating to improve the integrity of the chrome plating layer.

Copper, brass or aluminum parts often need to be polished after grinding, this is because the surface hardness of copper, aluminum parts is low, can be thrown very bright.

Some stainless steel products and brass products, such as stainless steel pen sleeves and signboard copper characters, after mechanical grinding and polishing, the stainless steel material should be electrolytic polishing; The signature copper lettering is passivated and then covered with organic paint to prevent its discoloration. This process, which does not require electroplating, can also obtain bright characteristics and achieve the purpose of protective decoration, and the length of the surface color retention time depends on the quality of the paint.

Surface Roughness Requirements Before Plating

Type of coating layer	The surface roughness before plating is Ra (no more than)/μm	Rounding value/mm
Engineering iliac plating (porosity check required)	0.8	≥0.5
Engineering chrome plating (no porosity check required)	1.6	……
Loose hole chrome plating	0.2	……
Decorative chrome plating	The visual brightness requirement is determined	≥0.5
Porcelain anodizing	0.2	……
Palladium plated, rhodium plated	0.2	≥0.5
Hard anodizing, insulation anodizing	0.8	≥0.5
Anti-carburizing, anti-nitriding, anti-oxidation and copper or tin plating	3.2	……
Note 1: This table is based on plating without polishing, grinding and other finishing. Note 2: In excess of this table. To be agreed between the buyer and the plating party.

Steel Polishing

The Stainless Steel Pipe is roughed with #80-#, 180-#, 320-#, 400-#, 500-#, 600 sand belt in turn, so that the surface has no obvious sand hole and porosity defects. Then the Polishing Wheel and rough polishing wheel are used to polish with polishing white paste to deal with the residual grinding marks and improve the surface smoothness and gloss. It is then polished with a medium polishing wheel to further improve the surface smoothness and gloss. Finally, the light is collected with a fine casting wheel to form a good mirror effect.

Copper Polishing

First, the Copper Tube is roughed with #80 Abrasive Belt to remove the rough surface and potholes on the surface, and then the surface is finely ground and the outline is trimmed with #180, #320 abrasive belt in turn. Then the third grinding with #400, #500 sand belt is carried out successively, so that the surface tends to be more ideal appearance and the line is clear and the structure is symmetrical. Followed by finishing with #600 sand belt, the surface reaches the ideal appearance profile, and the surface has no obvious sand hole and porosity defects. Finally, polishing the pipe with polishing cloth wheel and polishing slurry (yellow) can achieve a good mirror effect.

6 common polishing processes

Polishing refers to the use of mechanical, chemical or electrochemical action to reduce the surface roughness of the workpiece in order to obtain a bright, flat surface processing method.

Mechanical Polishing

Mechanical polishing, generally using automatic, semi-automatic or manual methods, the workpiece is pressed to the surface of the rotating elastic wheel coated with polishing agent. The surface effect of making a metal surface smooth or shiny by cutting, deforming, and wearing.

Chemical Polishing

Chemical polishing is to dissolve the microscopic protruding part of the surface of the material in the chemical medium preferentially than the concave part, so as to obtain a smooth surface. The main advantage of this method is that it does not require complex equipment, can polish the workpiece with complex shape, and can polish many workpieces at the same time, with high efficiency. The core problem of chemical polishing is the preparation of polishing liquid.

Electrolytic Polishing

The basic principle of electrolytic polishing is the same as that of chemical polishing, that is, the surface is smooth by selectively dissolving small protruding parts on the surface of the material. Compared with chemical polishing, the effect of cathode reaction can be eliminated and the effect is better.

Ultrasonic Polishing

The workpiece is put into the abrasive suspension and placed together in the ultrasonic field, and the abrasive is ground and polished on the workpiece surface by relying on the oscillation of the ultrasonic wave. Ultrasonic processing macroscopic force is small, will not cause workpiece deformation, but tooling production and installation is more difficult.

Ultrasonic Polishing

Fluid polishing relies on high-speed flowing liquid and the abrasive particles it carries to wash the surface of the workpiece to achieve the purpose of polishing.

Magnetic Grinding and Polishing

Magnetic grinding and polishing is the use of magnetic abrasive under the action of magnetic field to form an abrasive brush, grinding the workpiece. This method has the advantages of high processing efficiency, good quality, easy control of processing conditions and good working conditions.