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The surface finishing of metal parts
Surface finishing is to form a layer with one or more special properties on the surface of the material through physical or chemical methods. Surface treatment can improve prototype appearance, texture, function and other aspects of performance.
Anodizing
Mainly is the anodizing of aluminum, which use electrochemical principles to form a layer of Al2O3 (aluminum oxide) film on the surface of aluminum and aluminum alloys. This layer of oxide film has special characteristics, such as protection, decoration, insulation, and abrasion resistance.
Process flow
Solid color, gradients: Polishing / Sand blasting / Brushing -> degreasing -> Anodizing->Neutralizing > Tinting ->Hole sealing->Drying.
①Polishing/Sand blasting/Brushing-> degreasing-> Masking-> Anodizing 1-> Anodizing 2-> Hole sealing->Drying.
②Polishing/Sand blasting/Brushing-> degreasing-> Masking-> Anodizing 1-> Laser engraving-> Anodizing 2-> Hole sealing->Drying.
Technical feature
1. Improve intensity.
2. Achieve any color except white.
3. Achieve nickel-free sealing and meet nickel-free requirements from Europe countries and United States.
Technical difficulties and improvement
The defective rate level of anodizing is related to the cost of the final prototype, the key to improving the defective rate of anodizing is the appropriate amount of oxidant, appropriate temperature and current density, which requires manufacturers keeping continuous exploration and seeks a breakthrough in the process of production.
Electrophoresis
Used in stainless steel, aluminum alloy, etc, it can make the prototype show various colors, and keep metallic luster, at the same time can enhance the surface property, also have better anticorrosion property.
Process flow: Pretreatment-> Electrophoresis-> Drying
Advantage:
1.Rich color selection
2.No metal texture, can be used with sand blasting, polishing, brushing, etc.
3.Processing in a fluid environment, and can achieve surface treatment of complex structures.
4.Mature technology and apply to mass manufacturing.
Electrophoresis Aluminum
Shortcoming: Ability to conceal defects is mediocre, and electrophoresis for die castings requires higher pre-treatment.
Micro-arc oxidation
Applying a high voltage in electrolyte solution (usually a weak alkaline solution) to generate a ceramic surface film, this process is the result of synergistic effect of physical discharge and electrochemical oxidation.
Process flow: Pretreatment-> hot washing -> Micro-arc oxidation-> Drying
Advantage:
1.Ceramic texture.
2.Widely base material: Al, Ti, Zn, Zr, Mg, Nb, and other alloys.
3.Simple pretreatment, the prototype has excellent corrosion resistance, weather resistance, and good heat dissipation property.
Micro-arc oxidation Aluminum
Shortcoming: Colors are limited currently, only black and grey are more common, bright colors are difficult to achieve currently. The cost is mainly affected by high electricity consumption, which is one of the most expensive surface finishing.
Micro-arc oxidation aluminum prototypes
PVD Vacuum Plating
Under vacuum conditions, use low-voltage, high-current arc discharge technology, take advantage of gas discharge to vaporize the target material and ionize both the vaporized substance and gas, take advantage of acceleration of the electric to deposit the evaporated substance and its reaction prototypes on the workpiece.
Process flow: Cleaning before PVD-> Vacuum in the furnace-> Target cleaning and ion cleaning-> Coating-> Finish coating and cooling-> Post processing (Polishing, AFP)
Technical feature：PVD （Physical Vapor Deposition）can be coated with high-hardness, high-wear resistance of cermet decorative coating on the metal surface.
PVD Vacuum Plating Parts
Electroplating
Take advantage of electrolysis to attach a metal film on the metal surface, can prevent corrosion, improve wear resistance, electrical conductivity, light reflectivity, and enhance aesthetics.
Process flow: Pretreatment-> non-cyanide alkaline copper plating-> Cyanide-free white copper tin-> Electroplating
Advantage:
1. The coating has high gloss and high-quality metal appearance;
2. Base material is SUS, Al, Zn, Mg, etc.; the cost is relatively low compared to PVD.
Shortcoming: Poor environmental protection, and great risk of environmental pollution.
Electroplating Part
Powder Coating
It uses powder spraying equipment (electrostatic spraying machine) to spray powder on the surface of the workpiece. The powder will be uniformly absorbed on the workpiece to form a powdery coating under the electrostatic interaction. The powder coating is cured by high temperature baking and becomes the final coating with different effects (different types of powder with different coating effects).
Process flow: Clamping the workpiece-> Electrostatic precipitator-> Spray coating-> Low temperature leveling-> Baking
Advantage:
1. Rich color selection, high gloss, matte optional.
2. Low cost, suitable for building furniture prototypes and heat sink shells, etc.
3. High utilization rate, 100% utilization, environmental protection
4. Strong ability to hide defects.
5. Imitate wood grain effect.
Powder Coating
Shortcoming: At present, it is less used in electronic prototypes.
Metal Brushed
It is a surface treatment method that forms lines on the surface of the workpiece by grinding prototypes to achieve a decorative effect. According to the different lines after brushed, it can be divided into: straight line brushing, random line brushing, corrugation, and swirling.
Technical feature：The Metal Brushed processing can make the metal surface obtain a nonspecular surface metallic luster, and the wire drawing processing can eliminate the fine defects on the metal surface.
Aluminum Brushed
Sand blasting
It is a process that uses compressed air as the power to form a high-speed jet beam to spray the spray material on the surface of the workpiece, so that the appearance or shape of the outer surface of the workpiece is changed, and obtained a certain degree of cleanliness and different roughness.
Technical feature：
1.Achieve different reflective or matt.
2.It can clean up the tiny burrs on the surface of the workpiece, and make the surface of the workpiece smoother, eliminating the hazard of the burr, and improving the grade of the workpiece.
3.Clear the residue left over from the pre-treatment, improve the finish of the workpiece, and make the workpiece show a uniform and consistent metal color, making the appearance of the workpiece more beautiful and attractive.
Sand blasting
Polishing
Use flexible polishing tools and abrasive particles or other polishing medium to modify the surface of the workpiece. For different polishing processes: rough polishing (basic polishing process), medium polishing (finishing process) and fine polishing (coating process), choosing a suitable polishing wheel can achieve the best polishing effect and improve polishing efficiency.
Technical feature：Improve the dimensional accuracy or geometric accuracy of the workpiece, to obtain a smooth surface or mirror gloss, and it can eliminate the gloss also.
Polishing PMMA
Etching
Generally referred to as etching is also called photochemical etching, which refers to the removal of the protective film of the area to be etched after exposure to plate making and development, and contact with chemical solutions during etching to achieve the effect of dissolving and corroding, forming effect of unevenness or hollowing out.
Process flow: It can be divided into two method, exposure method and screen printing method.
Exposure method: Prepare the material according to the drawing-> clean the material-> drying->film or coating-> drying-> exposure-> development-> drying-> etching-> demould-> finish
Screen printing method: Prepare material-> clean the material (Stainless steel or other metallic material)-> screen printing-> etching-> demould-> finish
Advantage:
1.Can do fine machining of the metal surface.
2.Give a special effect of metal surface.
Etching aluminum parts
Disadvantages: Most of the corrosive liquids (acids, alkalis, etc.) used in etching are harmful to the environment.
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