Detailed explanation of the surface treatment process of commonly used materials in machine parts

Surface treatment is a process of artificially forming a surface layer on the surface of the base material that is different from the mechanical, physical and chemical properties of the base.
The purpose of surface treatment is to meet the product's corrosion resistance, wear resistance, decoration or other special functional requirements. Our more commonly used surface treatment methods are mechanical polishing, chemical treatment, surface heat treatment, and spraying the surface. Surface treatment is to clean, sweep, deburr, degrease, and deoxidize the surface of the workpiece.

Common surface treatment processes are:
Vacuum electroplating, electroplating process, anodic oxidation, electrolytic polishing, pad printing process, galvanizing process, powder spraying, water transfer printing, screen printing, electrophoresis, etc.

01. 
—— Vacuum Metalizing ——
Vacuum plating is a physical deposition phenomenon. That is, argon is injected in a vacuum state, the argon hits the target material, and the separated molecules of the target material are adsorbed by the conductive goods to form a uniform and smooth metal-like surface layer.
Applicable materials:
1. Many materials can be vacuum electroplated, including metals, soft and hard plastics, composite materials, ceramics and glass. Among them, the most common surface treatment for electroplating is aluminum, followed by silver and copper.
2. Natural materials are not suitable for vacuum plating, because the moisture of natural materials will affect the vacuum environment.
Process cost: In the vacuum plating process, the workpiece needs to be sprayed, loaded, unloaded and re-sprayed, so the labor cost is quite high, but it also depends on the complexity and quantity of the workpiece.
Environmental impact: Vacuum plating has very little environmental pollution, similar to the environmental impact of spraying.



02. Electrolytic polishing
—— Electropolishing ——
Electrolytic polishing is an electrochemical process in which the atoms of the workpiece immersed in the electrolyte are converted into ions and removed from the surface due to the passage of current, so as to achieve the effect of removing fine burrs and increasing brightness on the surface of the workpiece.
Applicable materials:
1. Most metals can be electrolytically polished, of which the most commonly used for surface polishing of stainless steel (especially suitable for austenitic nuclear grade stainless steel).
2. Different materials cannot be electropolished at the same time, or even put in the same electrolytic solvent.
Process cost: The whole process of electrolytic polishing is basically completed by automation, so the labor cost is very low.
Environmental impact: Electrolytic polishing uses less harmful chemicals. The whole process requires a small amount of water and is easy to operate. In addition, it can extend the properties of stainless steel and play a role in delaying corrosion of stainless steel.



03. Pad printing process
—— Pad Printing ——
The ability to print text, graphics and images on the surface of irregular and heterogeneous objects is now becoming an important special printing.
Applicable materials:
Almost all materials can be used for pad printing, except for materials that are softer than silicone pads, such as PTFE.
Process cost: low mold cost and low labor cost.
Environmental impact: Since this process is limited to soluble inks (which contain harmful chemicals), it has a great impact on the environment.


04. Galvanizing process
—— Galvanizing ——
The surface treatment technology of plating a layer of zinc on the surface of steel alloy materials for aesthetics and rust prevention. The zinc layer on the surface is an electrochemical protective layer to prevent metal corrosion. The main methods used are hot-dip galvanizing and Electro-galvanized.
Applicable materials:
As the galvanizing process relies on metallurgical bonding technology, it is only suitable for surface treatment of steel and iron.
Process cost: No mold cost, short cycle/medium labor cost, because the surface quality of the workpiece largely depends on the manual surface treatment before galvanizing.
Environmental impact: As the galvanizing process increases the service life of steel parts by 40-100 years, it can prevent the rust and corrosion of the workpiece, so it has a positive effect on the protection of the bad environment. In addition, the galvanized workpiece can be returned to the galvanizing tank after its service life expires, and the repeated use of liquid zinc will not produce chemical or physical waste.




05. Electroplating process
—— Electroplating ——
The process of using electrolysis to attach a layer of metal film to the surface of the part, thereby preventing metal oxidation, improving wear resistance, conductivity, light reflection, corrosion resistance and enhancing aesthetics. The outer layer of many coins is also electroplated .
Applicable materials:
1. Most metals can be electroplated
But different metals have different levels of purity and plating efficiency. The most common of these are: tin, chromium, nickel, silver, gold and rhodium.
2. The most commonly used plastic for electroplating is ABS.
3. Nickel metal cannot be used for electroplating products that touch the skin, because nickel is irritating and toxic to the skin.
Process cost: No mold costs, but fixtures are required to fix the parts/time cost depends on temperature and metal type/labor cost (medium-high), depending on the type of specific electroplated parts, for example, the electroplating of silverware and jewelry requires extreme The operation is performed by highly skilled workers because of the high requirements for appearance and durability. To
Environmental impact: A large number of toxic substances will be used in the electroplating process, so professional diversion and extraction are required to ensure the smallest environmental impact.


06. Water transfer
—— Hydro Transfer Printing ——
It is a way to use water pressure to print the color patterns on the transfer paper on the surface of the three-dimensional product. As people's requirements for product packaging and surface decoration increase, the use of water transfer printing has become more and more extensive.
Applicable materials:
All hard materials are suitable for water transfer printing, and the materials suitable for spraying must also be suitable for water transfer printing. The most common are injection molded parts and metal parts.
Process cost: There is no mold cost, but it is necessary to use a fixture to transfer multiple products at the same time. The time cost generally does not exceed 10 minutes per cycle.
Environmental impact: Compared with product spraying, water transfer printing more fully applies printing coatings, reducing the possibility of waste leakage and material waste.


07. Screen printing
—— Screen Printing ——
Through the squeeze of the squeegee, the ink is transferred to the substrate through the mesh of the image and text part to form the same image and text as the original. The screen printing equipment is simple, convenient to operate, simple in printing and plate making, low in cost, and strong in adaptability.
Common printed materials include: color oil paintings, posters, business cards, bound covers, commodity signs, and printed and dyed textiles.
Applicable materials:
Almost all materials can be screen printed, including paper, plastic, metal, pottery and glass.
Process cost: The mold cost is low, but it still depends on the number of colors, because each color has to be made separately. The labor cost is high, especially when it comes to colorful printing.
Environmental impact: Light-colored screen printing inks have little impact on the environment, but inks containing PVC and formaldehyde have harmful chemical substances and need to be recycled and processed in time to prevent water pollution.



08. Anodizing
—— Anodic Oxidation ——
Mainly the anodization of aluminum, which uses electrochemical principles to generate a layer of Al2O3 (aluminum oxide) film on the surface of aluminum and aluminum alloys. This oxide film has special characteristics such as protection, decoration, insulation, and abrasion resistance.
Applicable materials:
Aluminum products such as aluminum and aluminum alloys.
Process cost: In the production process, the consumption of water and electricity is quite large, especially in the oxidation process. The heat consumption of the machine itself needs to be continuously cooled with circulating water, and the electricity consumption per ton is often about 1000 degrees.
Environmental impact: Anodizing is not excellent in terms of energy efficiency. At the same time, in the production of aluminum electrolysis, the anode effect can also produce gases that cause destructive side effects on the atmospheric ozone layer.



09. Metal wire drawing
—— Metal Wired ——
It is a surface treatment method that forms lines on the surface of the workpiece by grinding products to achieve a decorative effect. According to the different lines after drawing, it can be divided into: straight drawing, chaotic drawing, corrugation, and swirling.
Applicable materials: Almost all metal materials can use metal wire drawing process.
Process cost: The process method is simple, the equipment is simple, the material consumption is low, the cost is relatively low, and the economic benefit is high.
Environmental impact: pure metal products, no paint and any chemical substances on the surface, 600 degrees high temperature does not burn, no toxic gas, and meets the requirements of fire protection and environmental protection.




10. In-mold decoration
—— In-Mold Decoration-IMD ——
It is a molding method in which the film with the printed pattern is put into a metal mold, and the resin for forming is injected into the metal mold to join the film, so that the printed film and the resin are integrated and cured into a finished product.
Applicable material: plastic surface.
Process cost: Only need to open a set of molds, which can reduce costs and man-hours for highly automated production. The process is simplified. There is a one-time injection molding method to achieve both molding and decoration at the same time.
Environmental impact: The technology is green and environmentally friendly, avoiding the pollution caused by traditional spray paint and electroplating.