The difference between electroplating, electroforming, electrophoresis, sputtering and anodizing of adjustable power supply

Electroplating

Electroplating is the process of plating a thin layer of other metals or alloys on certain metal surfaces using the principle of electrolysis. The principle of electroplating is consistent with the principle of electrolytic refining of copper. During electroplating, an electrolyte containing plating metal ions is generally used to prepare a plating solution; the metal product to be plated is immersed in the plating solution and connected to the negative electrode of the DC power supply as the cathode; the plating metal is used as the anode and connected to the positive electrode of the DC power supply. When low-voltage direct current is passed, the anode metal dissolves in the solution to become cations and moves to the cathode. These ions obtain electrons at the cathode and are reduced to metals, which are covered on the metal products to be electroplated.

Characteristics of electroplating:

A technology that uses the principle of electrolytic cell to deposit a metal coating with good adhesion but different performance from the base material on a mechanical product. Electroplating can enhance the corrosion resistance of metals (the plating metal is mostly corrosion-resistant metals), increase hardness, prevent wear, and improve conductivity, smoothness, heat resistance and surface beauty. Through electroplating, decorative protective and various functional surface layers can be obtained on mechanical products, and workpieces with wear and processing errors can also be repaired.

?Electroplating has different functions according to needs:

?1. Copper plating: used for base coating, improving the adhesion and corrosion resistance of the electroplated layer. (Copper is easy to oxidize. After oxidation, the patina is no longer conductive, so copper-plated products must be protected by copper)

?2. Nickel plating: used for base coating or appearance, improving corrosion resistance and wear resistance (chemical nickel has a wear resistance that exceeds chrome plating in modern technology). (Note that many electronic products, such as DIN heads and N heads, no longer use nickel base coating, mainly because nickel is magnetic and will affect the passive intermodulation in electrical properties)

?3. Gold plating: improve conductive contact impedance and enhance signal transmission. (Gold is the most stable and the most expensive.)

?4. Palladium nickel plating: improve conductive contact impedance, enhance signal transmission, and have higher wear resistance than gold.

?5. Tin-lead plating: improve welding ability and is about to be replaced by other substitutes (most of them are now replaced by bright tin and matte tin because they contain lead).

?6. Silver plating: Improves conductive contact impedance and enhances signal transmission. (Silver has the best performance, is easy to oxidize, and is also conductive after oxidation).

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Electroforming

Electroforming can be roughly divided into three categories, namely decorative electroplating (represented by nickel-chromium, gold, and silver plating), protective electroforming (represented by zinc plating) and functional electroplating (represented by hard chromium plating. Electroforming is one of the functional electroplating methods used to manufacture products.

It is said that electroforming began in 1838 and was mainly used for arts and crafts. At that time, Jacoli in Russia coated paraffin on the plaster master mold, made its surface conductive through graphite, and then plated the surface with copper, demolded after plating, and made a copper replica. In the early years of the Showa era in Japan, the Kyoto City Industrial Research Institute and the Osaka Mint Department and other units had actively carried out research on casting copper on plaster masters and electroplating on insulators, and produced many exquisite metal crafts.

However, when electroforming with plaster or wax as the master mold, not only does it require high manufacturing skills and troublesome operation, but the master mold is easily damaged, making it difficult to make exquisite replicas, so the application range of electroforming is very limited.

After a century of development, electroforming technology has been widely used in many fields such as light industry and electronics industry, especially in the manufacture of thin-walled, precise or complex-shaped parts that are difficult to machine (such as metal foil, nozzles, waveguides, surface roughness measuring instruments, etc.) and molds (such as record stampers, plastic molds, rubber stampers, etc.). It has been highly valued as a cutting-edge processing technology.

Later, due to the advent of plastic master materials and the improvement of electroplating level, electroforming technology has also been greatly developed and widely used to manufacture urgently needed products that cannot be manufactured by other methods or are difficult to process.

In recent years, especially because electroforming is used to manufacture certain parts for aerospace or atomic energy, it has attracted people's attention as a cutting-edge processing technology. (In addition, the so-called "electric bonding technology" that combines metal with metal through electroplating has also been studied. This kind of electrically bonded metal will not change the mechanical properties and physical properties of the metal material due to heat.

Electroforming is the process of manufacturing or replicating metal products by electrolyzing metal to deposit on a mold. The precision of electroforming can reach 0.001mm~~0.01mm.

?Features of electroforming:

1. Accurately and precisely replicate the mold surface and fine lines;

2. Replicas with high dimensional accuracy and surface roughness less than 0.1um can be obtained. The electroforming products produced by the same original mold have good consistency;

3. With the help of some special materials, the inner surface of complex parts can be replicated as the outer surface, and the outer surface can be replicated as the inner surface. The replicated products are consistent with the original mold.

?Electroforming is mainly used for:

1. Replicating fine surface contour patterns (such as record molds, arts and crafts molds, banknotes, securities, and stamp printing plates);

2. Replicating injection molds and electrode tools for EDM;

3. Manufacturing complex, high-precision hollow parts and thin parts (such as waveguides, etc.)

4. Manufacturing surface roughness templates, reflectors, dials, special-shaped nozzles and other special parts.

At present, electroforming technology has attracted worldwide attention. Whenever difficulties arise in mechanical processing, electroforming technology can be applied to transform the inner surface of parts that are more difficult to process into the outer surface of the core mold, and to transform metal materials that are difficult to form into core mold materials that are easy to form (such as wax, resin, plastic, etc.). This makes electroforming a cutting-edge processing technology that is widely used in the mechanical industry. Electroforming is widely used in mechanical processing bodies, precision optical instruments, rocket engines, chemicals, radar and laser waveguides, and can electroform metal lines below 0.5um on large workpieces.

The metals that can be electroformed now include copper, nickel, nickel-cobalt alloy, iron, nickel-manganese alloy, etc. The products processed by electroforming mainly include waveguides, wind speed tubes, venturi tubes, supersonic gas cutting nozzles, metal foils, screens, printing and dyeing rollers, record stamping molds, plastic or rubber parts die-casting cavities, bellows, wind tunnel nozzle inner walls, rocket engine regenerative cooling thrust chamber outer walls, etc.

The electroformed copper layer has good electrical and thermal conductivity and is mainly used in occasions requiring good electrical and thermal conductivity, such as waveguides, supersonic gas cutting tubes, and the outer layer of the main body of plastic or rubber molding molds.

Electroformed nickel has high strength and hardness, good corrosion resistance and is often used as a structural part. Such as venturi tubes, wind tunnel test models, molding mold cavities of plastic or zinc die castings, surface roughness standard blocks, etc. To increase hardness, nickel-cobalt alloys can be cast, and nickel-manganese alloys can be cast to improve welding performance.

Electrophoretic coating

It is a coating method that uses an external electric field to make the particles such as pigments and resins suspended in the electrophoretic liquid migrate in a directional manner and deposit on the substrate surface of one of the electrodes. The principle of electrophoretic coating was invented in the late 1930s, but the development of this technology and its industrial application was after 1963. Electrophoretic coating is a special coating film formation method developed in the past 30 years and is the most practical construction process for water-based coatings. It has the characteristics of water solubility, non-toxicity, and easy automation control, and has been widely used in the automotive, building materials, hardware, home appliances and other industries.

Electrophoretic coating is a coating method that puts the workpiece and the corresponding electrode into a water-soluble paint, connects to the power supply, and relies on the physical and chemical action generated by the electric field to make the resin and pigment in the paint evenly precipitate and deposit on the surface of the coated object as the electrode to form a water-insoluble paint film. Electrophoretic coating is an extremely complex electrochemical reaction process, which includes at least four processes: electrophoresis, electrodeposition, electroosmosis, and electrolysis.

Electrophoretic coating can be divided into anodic electrophoresis (the workpiece is the anode and the paint is anionic) and cathodic electrophoresis (the workpiece is the cathode and the paint is cationic) according to the deposition performance; it can be divided into direct current electrophoresis and alternating current electrophoresis according to the power supply; and there are constant voltage and constant current methods according to the process method. At present, the anodic electrophoresis with a constant voltage method of a direct current power supply is widely used in industry.

The difference between electroplating and electrophoresis:

is that the intermediate objects are different, one is a metal ion and the other is a colloid. The results after treatment are also different. Electroplating is to coat a layer of metal, which has the functions of protection, rust prevention, and beauty; electrophoresis is generally used for spray painting, that is, a layer of paint is applied on the surface, which is often used in the automotive industry.

?Electroplating has a metallic texture. Electrophoresis is just a high imitation of electroplating, and there is still a certain gap in performance and color. It is difficult for electrophoresis to produce the metallic texture of electroplating.

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Sputtering

The principle mainly uses glow discharge to ionize argon (Ar) and impact the target surface. The atoms of the target material are ejected and accumulated on the surface of the substrate to form a thin film. The properties and uniformity of the sputtered film are better than those of the evaporated film, but the coating speed is much slower than that of the evaporated film. Almost all new sputtering equipment uses a strong magnet to make the electrons move in a spiral shape to accelerate the ionization of the argon gas around the target material, resulting in an increase in the probability of collision between the target and the argon ions, thereby increasing the sputtering rate.

Generally, metal coating is usually done by direct current sputtering, while non-conductive ceramic materials are sputtered by RF alternating current sputtering. The basic principle is to use glow discharge (glowdis-charge) in a vacuum to impact argon (Ar) ions on the target surface. The positive ions in the plasma will accelerate to the negative electrode surface of the sputtered material. This impact will cause the target material to fly out and deposit on the substrate to form a thin film.

?Several characteristics of sputtering process for thin film coating:

?(1) Metals, alloys or insulators can be made into thin film materials.

?(2) Under appropriate setting conditions, multiple complex target materials can be made into thin films of the same composition.

?(3) By adding oxygen or other active gases to the discharge atmosphere, a mixture or compound of the target material and gas molecules can be made.

?(4) The target input current and sputtering time can be controlled, and it is easy to obtain high-precision film thickness.

?(5) Compared with other processes, it is more conducive to the production of large-area uniform thin films.

?(6) The sputtered particles are almost unaffected by gravity, and the positions of the target and substrate can be freely arranged.

(7) The adhesion strength between the substrate and the film is more than 10 times that of the general evaporation film. Since the sputtered particles carry high energy, they will continue to diffuse on the film-forming surface to obtain a hard and dense film. At the same time, this high energy allows the substrate to obtain a crystalline film at a relatively low temperature.

(8) The nucleation density is high at the initial stage of film formation, and an extremely thin continuous film below 10nm can be produced.

(9) The target material has a long life and can be automatically produced continuously for a long time.

(10) The target material can be made into various shapes, and can be better controlled and produced most efficiently with the special design of the machine.

?Differences between evaporation and sputtering:

?Sputtering is the abbreviation of vacuum sputtering coating, which is a physical coating method.

?Vacuum coating mainly refers to a type of coating that needs to be carried out under a high vacuum degree. There are many types, including vacuum ion evaporation, magnetron sputtering, MBE molecular beam epitaxy, PLD laser sputtering deposition, etc. The main idea is to divide it into two types: evaporation and sputtering.

?The substrate to be coated is called the substrate, and the material to be coated is called the target. The substrate and the target are in the same vacuum chamber.

?Evaporation coating generally involves heating the target so that the surface components are evaporated in the form of atomic groups or ions, and are deposited on the surface of the substrate, and a thin film is formed through the film-forming process (scattered points-island structure-vagal structure-layered growth).

?For sputtering coating, it can be simply understood as bombarding the target with electrons or high-energy lasers, and sputtering the surface components in the form of atomic groups or ions, and finally depositing on the surface of the substrate, undergoing a film-forming process, and finally forming a thin film.

Anodic oxidation

?An electrolytic process, in which the metal sheet providing the plating metal acts as an anode, the electrolyte is usually an ion solution with metal plating, and the plated object acts as a cathode. After the voltage is input between the anode and the cathode, the metal ions in the electrolyte are attracted to swim to the cathode, and are plated on it after reduction. At the same time, the metal at the anode is dissolved again, providing the electrolyte with more metal ions. In some cases, an insoluble anode is used, and new electrolyte needs to be added during electroplating to supplement the plated metal ions.

Generally, aluminum alloys are easily oxidized. Although the oxide layer has a certain passivation effect, it will still peel off and lose its protective effect as a result of long-term exposure. Therefore, the purpose of anodizing is to use its easy oxidation characteristics to control the formation of the oxide layer by electrochemical methods to prevent further oxidation of the aluminum material and increase the mechanical properties of the surface.