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In the whole process of rapid prototyping, after selecting the appropriate processing method (CNC machining or 3D printing), most rapid prototyping products need surface treatment. The purpose of surface treatment is to meet the requirements of corrosion resistance, wear resistance, decoration or other special functions of the product. There are dozens of surface treatment processes for rapid prototyping. As a large-scale rapid prototyping factory, Yea-Lin can provide most of the surface treatment process requirements for rapid prototyping and has standardized production processes. Next, let's introduce what are the common surface treatment processes for rapid prototyping:
Grinding is one of the most common surface treatment techniques. Generally, rough objects (such as sandpaper containing higher hardness particles) are used to change the physical properties of the material surface by friction, removing burrs, machining lines, and adhesion marks on the surface of the workpiece. And other defects, thereby improving the flatness of the workpiece, reducing the roughness, and making the surface of the workpiece smooth and fine.
Polishing uses a flexible polishing tool and abrasive particles or other polishing media to modify the surface of the workpiece on the basis of grinding. Polishing cannot improve the dimensional accuracy or geometric accuracy of the workpiece, but is used for the purpose of obtaining a smooth surface or specular gloss, and sometimes to eliminate gloss (matting). The surface roughness of the workpiece after polishing process can generally reach Ra 0.63 ~ 0.01 microns.
Electroplating is the use of electrodes to pass current to the metal to adhere to the surface of the object, the purpose is to change the characteristics or size of the surface of the object. Electroplating is generally divided into two types: wet plating and dry plating. The wet method is usually referred to as water plating; the dry method is usually referred to as vacuum plating.
Water plating is the process of electrodeposition of the plated metal through the electrode method, which produces ion replacement and adheres to the surface of the plated part; while vacuum plating uses high voltage and large current to make the plated metal instantaneously vaporize into ions under the vacuum environment and then vaporize to the surface of the plated part. Water plating has good adhesion and does not require other treatment in the later stage; vacuum plating has poor adhesion, and generally requires PU or UV on the surface. PC cannot be electroplated, duplicate parts cannot be water-plated, only vacuum-plated. The color of water plating is relatively monotonous. Common water plating includes chrome, nickel, gold, etc., and vacuum plating can solve the problem of seven colors. The surface effect of the workpiece before water plating must be sanded to 1500-2000 sandpaper, and then polished for water plating, so water-plated workpieces are generally very expensive; the effect of vacuum plating and sanding can be slightly worse than 800-1000 sandpaper. So vacuum plating is also relatively cheap.
Oxidation treatment of metal is to form a protective oxide film on the surface of the metal with oxygen or oxidant to prevent metal corrosion. Oxidation is divided into chemical oxidation and electrochemical oxidation (that is, anodization).
(1) The oxide film produced by chemical oxidation is relatively thin, about 0.3-4um thick, porous, has good adsorption capacity, is soft and not abrasion resistant, and has good electrical conductivity. It is suitable for occasions with shielding requirements. A variety of colors, with good adsorption capacity, can be painted in a variety of colors, and then painted on the surface, can effectively improve the corrosion resistance and decorative properties of aluminum products.
(2) The oxide film produced by anodization is relatively thick, with a thickness of 5-20um in general, and a hard anodized film thickness of 60-2500um, high hardness, good wear resistance, good chemical stability, and good corrosion resistance. Good adsorption capacity, good insulation performance, strong heat insulation and heat resistance, can be painted in various colors.
After chemical oxidation treatment of aluminum and aluminum alloy, especially after anodizing, the oxide film formed on the surface has good protective decoration characteristics, so it is widely used in aviation, electrical, electronics, machinery manufacturing and light industry. aspect.
Under certain conditions, when the potential of a metal moves to the positive direction due to an applied anode current or a local anode current, the surface state of the original active and dissolved metal will suddenly change. The rate of dissolution of metals decreases rapidly. This sudden change in surface state is called passivation.
Passivation can improve the passivation performance of metal materials, promote the passivation of metal materials in the use environment, and improve the mechanical strength of metals. It is one of the most effective ways to control corrosion and enhance the adhesion between metal and coatings.
The surface is blackened, and it is also called blue. Blackening treatment is now commonly used in traditional alkaline heating blackening and darkening at room temperature.
The blackened protective film is black, which improves the corrosion resistance and mechanical strength of the metal surface, and can also be used as a good primer for coatings. (Stainless steel cannot be blackened, iron has the best blackening effect)
Phosphating is the process of treating the metal surface with an orthophosphate solution of metals such as manganese, zinc, and iron to form a layer of insoluble phosphate protective film. The protective film generated after the phosphating treatment can improve the metal's insulation and corrosion resistance, improve the protection and decoration performance of the workpiece, and can also be used as a good primer for coatings. Metal surface phosphating methods are divided into cold phosphating (normal temperature phosphating), hot phosphating, spray less phosphating, and electrochemical phosphating. Phosphating is the main method for pre-coating of painted parts such as automobile covers, driver's cabs, and cabin boards in the automobile industry. It requires that the phosphating film be fine, smooth, uniform, moderate in thickness, and have certain heat resistance.
It uses compressed air as the power to form a high-speed jet beam to spray the blasting material (copper ore, quartz sand, corundum, iron sand, sea sand) at a high speed on the surface of the workpiece to be treated. Due to the impact of the abrasive on the workpiece surface and the cutting effect, Make the surface of the workpiece a certain degree of cleanliness and different roughness, and improve the mechanical properties of the surface of the workpiece, thus improving the fatigue resistance of the workpiece, increasing the adhesion between the workpiece and the spray coating, and extending the paint film. Durability is also good for paint leveling and decoration.
Surface painting is one of the most widely used surface processes. Spraying has the following advantages:
(1) Can cover the surface defects of the workpiece after molding;
(2) The surface of the workpiece can be sprayed to obtain a variety of colors, different gloss, different visual effects and a variety of different feels;
(3) Enhance the hardness and scratch resistance of the surface of the workpiece;
The effects of spraying are: matte, semi-matte, bright (high light), various colors, various textures, etched lines, brushed effects (metallic colors can be brushed), leather effects, elastic feel effects (Rubber paint) and so on.
The wire drawing process is a surface treatment method for forming decorative lines on the surface of the workpiece by grinding the product. The wire drawing can well reflect the texture of the metal material, and the metal surface can obtain a non-mirror-like metallic luster. According to different surface effects, it can be divided into straight silk (hairline pattern) and random silk (snow pattern).
The difference between the types of silk patterns is very subjective. Each user has different requirements for the surface line texture and different preferences for the line texture effect. Therefore, there must be a drawing template to process the effect that the user likes. The arc (the intersection of the arc surface and the straight surface is very ugly, and the drawing is uneven), and the painted surface (the surface of the metal color can be finely drawn) should not be drawn.
Electrostatic spraying uses the corona discharge phenomenon to make the powder coating adhere to the workpiece. The process is as follows: The powder coating is sent to the spray gun by the powder supply system by compressed air gas. The high voltage generated by the high-voltage electrostatic generator is added to the front end of the spray gun. Due to the corona discharge, a dense charge is generated near the powder. When sprayed, charged paint particles are formed. It is attracted to the opposite polarity of the workpiece by the electrostatic force. As the powder sprayed increases, the charge builds up more. When it reaches a certain thickness, it will generate static electricity. The repulsive effect does not continue to adsorb, so that the entire workpiece obtains a powder coating of a certain thickness, and then the powder is melted, leveled, and solidified by heat, that is, a hard coating film is formed on the surface of the workpiece.
Advantages and disadvantages of electrostatic dusting: no thin materials, no toxicity, no pollution to the environment, good coating quality, very high adhesion and mechanical strength, corrosion resistance, short curing time, no primer, low technical requirements for workers, powder recycling The rate is high; the coating is very thick, the surface effect is wavy, not smooth, and can only process two appearance effects: semi-matte and bright.
(1) Silk screen: Part of the mesh of the screen printing plate can pass through the ink and leak to the substrate; the mesh of the remaining portion of the printing plate is blocked and cannot penetrate the ink to form a blank on the substrate. The mesh on the printing plate is not closed, and the ink penetrates during printing, forming ink marks on the substrate. When printing, the ink is poured into one end of the screen printing plate, and the ink will not act by itself without external force. Leakage on the substrate through the mesh. When the ink is scraped by the squeegee at a certain inclination angle and pressure, the ink is transferred to the substrate under the screen through the screen, thereby achieving image reproduction. (The printed pattern is raised)
Advantages of silk screen:
A. Low cost and quick results.
B. Adapt to printing on the surface of irregular substrates.
C. Strong adhesion and good inking.
D. Thick ink layer and strong three-dimensional effect.
E. Strong resistance to rotation and rotation, good color formation.
F. Wide range of materials to be printed, large printing area.
(2) Pad printing (curved surface printing): refers to the use of a piece of flexible rubber to print the characters and patterns to be printed on the surface of plastic molded products containing curved surfaces or slightly uneven surfaces. Pad printing is to put the ink in the gravure engraved with characters or patterns, then copy the characters or patterns onto rubber, then use rubber to transfer the characters or patterns to the surface of the plastic molded product, and finally use heat treatment or ultraviolet light irradiation Allow the ink to cure.
Laser engraving, also called laser engraving, is a process of surface treatment using optical principles. For example, to make a keyboard, the words on it are blue, green, red, and gray, and the key body is white. When laser engraving, first spray oil, blue, green, red, and gray, and spray the corresponding colors. It seems that there are blue keys, green keys and so on, and then spray a layer of white as a whole, so that is a whole white keyboard, each blue and green is wrapped below. Then use the laser technology and the film made by the industrial designer to make the film, carving off the white oil on it, and the blue and green buttons are displayed.
Limitations of Laser Carving:
(1) Laser carving depth: 0.1mm for aluminum, plastic paint coating: 0.2-0.3mm, other metals such as iron up to 0.08mm;
(2) The limit surface area of laser engraving is: 100X100mm, laser engraving needs to be spliced beyond 100X100mm, the connection position is not beautiful, and the connection marks are obvious.
(3) White and near-white colors cannot be engraved, and characters carved out of radium on surfaces are prone to deformation.
