Analysis of Various Surface Treatment Processes

Analysis of Various Surface Treatment Processes

There are so many surface treatment processes! The boring definitions are hard to understand? This blog organizes the definitions and process diagrams for you, making it easy for you to understand the various surface treatment processes in minutes!

1. PVD (Physical Vapor Deposition)

PVD is an industrial manufacturing process, belonging to a type of coating technology, primarily using physical means to heat or excite materials to deposit thin films. This technique, also known as vacuum coating or vapor deposition, is commonly employed in surface treatments of cutting tools, various molds, and in the manufacturing processes of semiconductor devices.

AD: Compared to chemical vapor deposition, physical vapor deposition has a wider range of applications. Almost all materials can be used to prepare thin films through physical vapor deposition.

DIS: The uniformity of film thickness is indeed a concern in physical vapor deposition.

2. Mechanical Polishing

Mechanical polishing relies on the grinding and rolling action of very fine polishing particles, as well as cutting and plastic deformation of the material surface, to remove protrusions from the polished surface of the metal sample, thus obtaining a smooth surface.

AD: The equipment structure is relatively simple, and the price is generally lower compared to other methods.

DIS:

• Mechanical polishing is challenging for polishing workpieces with complex shapes or surfaces featuring special patterns or textures.
• It tends to generate metal dust, which can affect the health of polishing workers.
• It requires a high level of skill from workers, making it difficult to control the consistency and stability of workpiece quality.
• Mechanical processing inevitably leaves microscopic cracks and residual stress on the workpiece surface, which may affect the quality and lifespan of the workpiece and pose safety hazards for production.

  

3. Chemical Polishing

Chemical polishing is a method that relies on the selective dissolution of surface irregularities on samples through the chemical etching action of chemical reagents, eliminating scratches and leveling surfaces.

AD: Chemical polishing does not require special fixtures or DC power supply equipment. It is simple to operate, energy-efficient, and not limited by the size or shape of the workpiece. Additionally, the direct cost of polishing is relatively low.

DIS: The pollution issue is particularly severe, as handling the waste liquid generated during the polishing process can increase costs.

4. Electropolishing

Electropolishing, also known as electrochemical polishing or electrolytic polishing, utilizes the phenomenon of electrochemical dissolution generated by the anode in an electrolytic cell to selectively dissolve micro-protrusions on the anode surface, resulting in a smoother surface. In this process, the workpiece to be polished serves as the anode, while an inert metal acts as the cathode. Both poles are immersed in an electrolyte solution, and a direct current is passed through to achieve selective anodic dissolution, thereby increasing the brightness of the workpiece surface.

AD:

1. Consistent internal and external color, long-lasting luster, and the ability to smooth out concave areas that mechanical polishing cannot reach.
2. High production efficiency and low cost, suitable for large-scale sample preparation.
3. Enhanced corrosion resistance of the workpiece surface, applicable to all stainless steel materials.

DIS:

1. The quality of electrolytic polishing is influenced by the specifications of the electrolyte, as well as the current and voltage settings, making it difficult to determine the correct parameters.
2. Achieving satisfactory results for samples with cast iron or impurities is more challenging.
3. The electrolyte composition is complex, requiring careful attention to safety during use.

   

   

5. Spray Painting

spray painting is a coating method where the liquid is dispersed into uniform and fine droplets using a spray gun or disk atomizer, typically with the aid of pressure or centrifugal force, and applied to the surface of the object to be coated.

AD: Fast construction, good surface smoothness, no texture differences.

DIS: Spray painting machines are relatively expensive, and there is a significant amount of paint wastage.

6. Powder Coating

Powder coating is a process where powder coating material is sprayed onto the surface of a workpiece using powder coating equipment (electrostatic spray gun). Under the influence of static electricity, the powder evenly adheres to the surface of the workpiece, forming a powdery coating layer.

AD:

• Powder coatings do not contain VOCs (volatile organic compounds), eliminating issues such as fire hazards, toxicity, and environmental pollution.
• Minimal material loss and high utilization.
• Easy control of coating thickness, high construction efficiency, low construction difficulty, and energy and labor-saving.
• Scratch-resistant, impact-resistant, durable, and excellent chemical resistance.

DIS:

• The investment required for manufacturing powder coatings and replacing coating equipment is significant.
• Color matching for powder coatings can be challenging, and changing colors or types during coating is more cumbersome and costly.
• Cannot be used on substrates with poor heat resistance such as plastic, wood, or paper.
• Powder coatings are susceptible to clumping during storage due to pressure, temperature, and humidity fluctuations.

  

7. Sandblasting

Sandblasting, using compressed air as the driving force, involves high-speed jet streams of abrasive materials (such as copper ore sand, quartz sand, emery, iron sand, and sea sand) being sprayed onto the surface of workpieces, causing changes in the appearance or shape of the workpiece surface. Due to the impact and cutting action of the abrasives on the workpiece surface, the surface cleanliness and roughness of the workpiece are altered. This process improves the mechanical properties of the workpiece surface, enhancing fatigue resistance, increasing adhesion between the workpiece and coatings, prolonging the durability of the coatings, and facilitating coating leveling and decoration.

AD:

• Sandblasting can quickly clean the surface of objects, and the surface quality after sandblasting is good, effectively prolonging the lifespan of objects.
• Sandblasting can be adapted to various types of objects, whether they are made of steel, ceramic, or plastic.
• Simple operation.

DIS:

• Sandblasting generates a large amount of dust and waste, causing environmental pollution.
• Sandblasting operations require certain knowledge and skills; incorrect operation may damage the surface of objects.
• Sandblasting requires regular maintenance and cleaning to ensure its proper functioning.

  

8. Shot Peening

Shot peening is a widely used surface strengthening process in factories. It involves bombarding the surface of workpieces with shot particles to implant residual compressive stress, thereby enhancing the fatigue strength of the workpiece through cold working. This technique is extensively used to improve the mechanical strength, wear resistance, fatigue resistance, and corrosion resistance of components. Types of shot particles include steel shot, cast iron shot, glass beads, ceramic beads, etc.

AD:

• Simple equipment, low cost
• Not restricted by the shape and position of the workpiece
• Convenient operation

DIS:

• Poor working environment
• Low unit output
• Lower efficiency compared to shot blasting

  

9. Electroplating

Electroplating is a process that involves using electrolysis to deposit a metal film onto the surface of metal or other material components. This process helps prevent metal oxidation (such as rusting), enhances wear resistance, conductivity, reflectivity, corrosion resistance, and improves aesthetics.

AD: Attractive surface appearance, excellent corrosion resistance, strong mechanical properties.

DIS: Improper handling of generated wastewater and exhaust may lead to environmental pollution, high energy consumption, and potential health hazards to humans.

10. Anodizing (Anodic Oxidation)

Anodizing refers to the process where aluminum and its alloys, under specific electrolyte and process conditions, form an oxide film on the surface of aluminum products (the anode) due to the action of an external electric current.

AD:

• Anodizing can form a dense oxide film on the surface of metal, effectively preventing oxidation and corrosion.
• It increases the hardness of the metal surface, making it more resistant to wear and scratches, thus extending its lifespan.
• Different colors of oxide films formed on the metal surface enhance its aesthetic appearance and decorative properties.
• The roughness of the metal surface increases after anodizing, which promotes adhesion between coatings and substrates, making the coating more durable.
• An insulating oxide film formed on the metal surface improves its insulation properties.

DIS:

• Particularly when dealing with large areas or thicknesses of metal products, significant energy consumption increases production costs.
• Strict control of processing conditions and operating standards is required, leading to longer processing times that may affect production efficiency.
• The oxide film formed during anodizing may affect the dimensions and shapes of the metal, posing a certain risk to the normal operation of high-precision or high-demand components.
• The anodizing process is mainly suitable for certain metals such as aluminum, magnesium, and titanium. For other metals like steel, copper, and silver, the anodizing process may not be applicable or effective.
• Although the oxide film formed by anodizing has high hardness and corrosion resistance, it may be damaged under certain conditions such as mechanical wear or chemical corrosion, requiring regular maintenance and repair.

11. EPD (Electrophoretic deposition)

Electrophoretic deposition is a process where, under the influence of an applied voltage between positive and negative poles, charged paint particles in an electrophoretic coating migrate toward the cathode. They react with alkaline substances generated on the cathode surface, forming insoluble deposits on the surface of the workpiece.

AD:

• Safety in production: Electrophoretic coating uses water as a solvent, making it non-toxic and non-flammable.
• High-quality coating: Electrophoretic paint has strong adhesion, uniform thickness, and excellent corrosion resistance.
• High utilization rate: Electrophoretic paint is efficiently used.

DIS:

• Limited applicability to small and medium-sized parts due to equipment constraints.
• Restricted to conductive substrates and single-layer coating: Once a part is coated with electrophoretic paint, it becomes an insulator, preventing further electrophoretic coating.
• Limited color options: Electrophoretic paint colors are predominantly dark.

  

12. Micro-arc Oxidation

Micro-arc oxidation, also known as micro-plasma oxidation, is a process where, through a combination of electrolyte and specific electrical parameters, an instant high-temperature and high-pressure effect is generated on the surface of aluminum, magnesium, titanium, and their alloys via arc discharge. This process results in the growth of a ceramic coating layer primarily composed of metal oxide on the substrate.

AD:

• The metal oxide layer formed by micro-arc oxidation is metallurgically fused with the substrate, resulting in high bond strength. The ceramic layer has a dense structure, good toughness, and exhibits characteristics such as wear resistance, corrosion resistance, high-temperature shock resistance, and electrical insulation. It can also meet requirements for thermal insulation, catalysis, antibacterial properties, etc.
• The process has a wide range of applications and is environmentally friendly during processing.

DIS: The surface may be rough and uneven.

13. Metal Brushing

Metal brushing is a manufacturing process involving repeatedly scraping aluminum plates with sandpaper to create lines. The main process consists of three parts: degreasing, sanding, and washing. During the brushing process, a special film technique applied after anodizing treatment enables the metal surface to form a film layer containing metal components. This process makes each fine scratch clearly visible, allowing the metal to exhibit a subtle sheen amidst its matte finish.

AD:

• Wear-resistant, high-temperature-resistant, and corrosion-resistant.
• Easy maintenance and cleaning in daily use.
• Fine texture.
• Long lifespan.

DIS: Relatively expensive price.

14. Etching

Etching is a technique that removes part of the material through chemical reactions or physical impacts. Etching typically refers to photolithographic etching, where after exposure and development, the protective film on the area to be etched is removed. When exposed to a chemical solution during etching, it dissolves and corrodes the material, creating a concave or hollow effect.

AD:

• Metal etching processes can create extremely precise shapes and patterns, and the consistency of the metal etching process ensures that each product in mass production has the same quality and characteristics.
• Etching processes can be applied to various metals, including copper, nickel, gold, silver, iron, and some non-metallic materials.
• Metal etching processes generate relatively little waste, and in many cases, waste can be recycled and treated.
• High efficiency.

DIS:

• Etching processes require precise control of factors such as chemical solution concentration, temperature, and etching time, leading to high complexity.
• High equipment and manufacturing costs: Etching processes require specialized equipment and materials such as etching tanks, power supplies, heat exchangers, etc. Additionally, precise control of the production process is needed to ensure product quality and consistency.
• Workers may be exposed to hazards such as chemical substances, high temperatures, and noise.

  

15. IMD (In-Mold Decoration technology)

IMD, also known as non-painting technology, is an internationally popular surface decoration technique. It involves applying a surface-hardened transparent film, printing the pattern layer in the middle, and injecting the back molding layer. The ink is sandwiched between layers, making the product resistant to friction, preventing surface scratches, and maintaining color brightness for an extended period without fading.

AD:

• Strong scratch resistance and corrosion resistance.
• Long service life.
• Excellent three-dimensional effect.
• Strong resistance to dust, moisture, and deformation.
• Color can be changed as desired.
• Patterns can be easily modified.

DIS:

• Long lead time.
• Prone to issues such as film detachment and distortion.
• High defect rate in products.

  

  

16. OMD (Out Mold Decoration)

OMD is an extension of IMD (In-Mold Decoration) technology that integrates visual, tactile, and functional elements. It combines printing, texture structure, and metallization characteristics to achieve 3D surface decoration.

AD:

• Substrate material is not limited, can be metal or plastic.
• Can achieve 3D shapes.
• Can encapsulate internal structures (back-molding).
• Allows for simultaneous processing of multiple small products.

DIS:

• High equipment investment.
• Unable to achieve complex 3D shapes.

  

17. Laser Engraving

Laser engraving, also known as laser etching or laser marking, is a surface treatment process based on optical principles. It involves using a laser beam to engrave permanent marks on the surface of a material or within transparent materials.

AD:

• Fast marking speed, low cost
• Attractive patterns, high resolution, and high precision
• Wear-resistant

DIS: Limited color options

18. EDM (Electrical Discharge Machining)

EDM is a specialized machining method that utilizes the erosive effect produced by pulsed discharges between two electrodes immersed in a working fluid to remove conductive materials. It is also known as spark machining or spark erosion machining. The tool electrode is typically made of materials with good conductivity, high melting points, and easy machinability, such as copper, graphite, copper-tungsten alloy, and molybdenum. During the machining process, there is wear on the tool electrode, but it is usually less than the material removal from the workpiece metal, and in some cases, it can be negligible.

AD:

• Capable of machining materials and complex-shaped workpieces that are difficult to cut using conventional cutting methods, such as sharp corners.
• Does not produce burrs and tool marks.
• Tool electrode material does not need to be harder than the workpiece material.
• Enables automation due to the direct use of electrical energy.

DIS: Low efficiency.

19. Laser Etching

Laser etching involves the treatment of steel surfaces with high-energy density lasers to create patterns such as snake skin, etchings, pearlescent finishes, or other forms of textures.

AD: High welding accuracy and small heat-affected zone, suitable for repairing precision molds.

DIS:

• Welding wire is relatively expensive, leading to lower efficiency.
• Bulky equipment makes mobility difficult, and unsuitable for on-site operations. Welding repairs need to be performed on a workbench, making it impractical for large molds or workpieces.
• Repairing irregular-shaped defects can be challenging compared to straight-line repairs.
• Large heat-affected zones during welding repairs increase the likelihood of workpiece sagging, deformation, and undercutting.
• Lower welding accuracy, unable to meet the requirements of high-precision molds.
• Many mold repairs require preheating, insulation, and other processes, making them cumbersome and time-consuming.

  

20. Pad Printing

Pad printing, also known as tampon printing, is a specialized printing method that involves using a steel (or copper, thermoplastic) plate with an engraved design. A curved surface pad made of silicone rubber material is used to pick up ink from the plate's surface. The ink is then transferred onto the desired object's surface by pressing the pad against it, resulting in the printing of text, patterns, or other images.

AD:

• Wide application range: Pad printing is commonly used on products with recesses or on the back of objects where screen printing is not feasible. It can achieve clean printing results even on uneven surfaces.
• Convenient operation: Equipment can be operated semi-automatically or fully automatically, with low labor costs and high production efficiency.

DIS:

• Ordinary results.
• Pad printing cannot create patterns with large areas.
• Due to the clear edges of the recesses processed by steel plates, gradient colors cannot be produced.

  

21. Screen Printing

Screen printing refers to a printing method that uses a screen as the printing plate, which is made into a screen printing plate with images or text through photosensitive plate-making methods. Screen printing consists of five main elements: the screen printing plate, squeegee, ink, printing table, and substrate. The basic principle of screen printing is that the ink can pass through the mesh holes of the image/text part of the screen printing plate, while the non-image/text part of the mesh holes cannot pass through the ink. During printing, ink is poured into one end of the screen printing plate, and a certain pressure is applied to the inked area on the screen printing plate using a squeegee. At the same time, the squeegee moves steadily towards the other end of the screen printing plate, and the ink is squeezed from the mesh holes of the image/text part onto the substrate.

AD:

• Screen printing can use various types of inks: oil-based, water-based, synthetic resin emulsion-based, powder, etc.
• Screen printing plates are flexible and have a certain elasticity, suitable for printing on soft materials such as paper and fabric, as well as on hard objects such as glass and ceramics.
• Screen printing requires low printing pressure, making it suitable for printing on fragile objects.
• Thick ink layer with strong coverage.
• Not limited by the surface shape or size of the substrate. Screen printing can be applied on flat surfaces, as well as on curved or spherical surfaces. It is suitable for printing on both small and large objects.

DIS:

• Only one color can be printed at a time.
• Plate-making and film output costs are relatively high, making it unsuitable for small-batch production.
• Poor performance when used on uneven surfaces.
• Ink quantity cannot be easily controlled.

  

22. Direct Thermal Printing

Direct thermal printing refers to a method where a thermal-sensitive agent is coated on paper to create thermal recording paper. When subjected to heat, the thermal recording paper causes a physical or chemical change in the substance (coloring agent) to produce an image.

AD:

• Fast printing speed and low noise level.
• Clear printing and easy to use.

DIS: Direct thermal printers cannot print duplicates directly, and the printed documents cannot be permanently archived.

23. Thermal Transfer Printing

Thermal transfer printing works by first digitally printing the desired image onto transfer paper using specialized transfer ink in an inkjet printer. Then, a dedicated heat transfer machine applies high temperature and pressure to accurately transfer the image onto the surface of the product, completing the printing process.

AD:

• Simple printing process with accurate positioning.
• Does not cause damage to the material.
• Suitable for printing images with color gradients and on multiple materials.

DIS:

• Poor breathability.
• Fine cracks may appear in the printed pattern on clothing when stretched.
• Poor durability.

  

24. Planographic Printing

Planographic printing is a printing method that uses flat printing plates. It is the most widely used printing process globally and is also employed in the manufacturing of semiconductor and MEMS devices. Planographic printing, also referred to as "offset printing" or "indirect printing," is a common commercial printing technology. It involves transferring images or text from flat printing plates onto rubber blankets, which are then used to print onto paper or other materials.

AD:

• Fast printing speed, relatively low printing cost, and high print quality.
• Suitable for large-scale and repeat printing jobs.

DIS:

• Requires preparation of preliminary work such as plate making and setup.
• Not suitable for short-run printing and customization.

  

  

25. Curved Surface Printing

Curved surface printing involves placing ink into engraved plates with text or patterns, and then transferring them onto curved surfaces. The text or patterns are then transferred onto the surface of the molded product using the curved surface. Finally, methods such as heat treatment or ultraviolet light exposure are used to cure the ink.

AD:

• Wide applicability: It can be used for printing on various curved surfaces, such as cylinders, spheres, and irregular shapes.
• High customization: It can print complex patterns, text, and images on curved surfaces, achieving personalized customization.
• High production efficiency, and stable quality.

DIS:

• Higher cost due to the need for more equipment and technical support.
• Subject to limitations of printing machinery and technology, some specific shapes of curved surfaces may not be fully covered.
• Design complexity may increase as designers need to consider the variations and distortions of curved surfaces.
• Ink curing in surface printing may be uneven or incomplete due to the influence of the surface shape.

  

26. Hot Stamping

Hot stamping refers to a process where hot stamping materials or hot stamping patterns are transferred onto objects such as paper, cardboard, fabric, or coated materials using heat and pressure. Hot stamping is commonly used in the binding process, especially on covers.

AD:

• Precision and meticulous craftsmanship, with minimal equipment errors, resulting in finer patterns on hot-stamped items.
• Capable of performing three-dimensional hot stamping.
• Energy-efficient, reducing environmental pollution, and offering fast hot stamping speeds.

DIS:

• The high precision requirement of the hot stamping process for equipment leads to increased costs.
• The process involves relatively complex and intricate procedures.

  

27. Water Transfer Printing

Water transfer printing is a technique that transfers printed images or graphics from a flat surface onto the surface of different materials using water. It is divided into two types: water immersion transfer and water overlay transfer (curved surface overlay). Water immersion transfer is mainly used for transferring text and photographic images, while water overlay transfer is primarily used for complete transfer over the entire surface of an object.

AD:

• Aesthetic appeal: It can transfer any natural patterns, photos, and graphics onto products.
• Innovation: Water transfer printing technology can overcome the limitations of traditional printing methods such as heat transfer, offset printing, screen printing, and surface coating, allowing for the creation of complex shapes and angles.
• Versatility: Applicable to surface printing on hardware, plastics, leather, glass, ceramics, wood, etc. (not suitable for fabric and paper).
• Personalized design.
• Efficiency: No need for plate-making; direct printing and immediate transfer.

DIS:

• Transferred images or graphics are prone to deformation.
• Fully manual operation leads to high labor costs and low production efficiency.

  

28. Flat Screen Printing

Flat screen printing involves fixing printing molds onto square frames, which are usually made of polyester or nylon mesh (screen) with hollow patterns. The patterned areas of the screen allow ink to pass through, while the non-patterned areas are sealed with a polymer film layer to block the mesh openings. During printing, the screen is pressed tightly against the fabric, ink is poured onto the screen, and a squeegee is used to repeatedly scrape and press the ink through the patterns onto the fabric surface.

AD:

• Convenient plate-making process, with large repeat lengths, multiple color matching options, ability to print fine patterns without color bleeding, high ink volume, and the capability to achieve a three-dimensional effect. Suitable for printing on silk, cotton, synthetic fabrics, and knitted fabrics, especially for high-end fabrics with small batches and multiple variety requirements.
• Hand scraping of the ink on the hot table allows for unlimited printing repeats.

DIS:

• Due to the long distance between color frames, it is difficult to achieve overlapping colors.
• Manual fabric placement, manual lifting of the frame, and hand scraping of the ink result in high labor intensity and uneven ink scraping.
• The heat source for the hot table is typically steam heating, though some use electric heating, which consumes a lot of electricity and is prone to accidents.

  

29. Calendering

Calendering, also known as pressing, is the final process of finishing leather. It involves using the plasticity of fibers under heated conditions to flatten or create parallel fine diagonal lines on the surface of the fabric, enhancing the gloss of the fabric. This process is typically carried out using a swing calender machine or a bottom leather rolling machine. Usually, it involves two passes: the first pass compresses the leather body, done after even wetting, followed by stacking to balance moisture content. The second pass is for calendering, which results in a smooth and glossy leather surface with a compacted leather body, thus achieving the finished leather.

Conclusion

With such an array of surface finishing processes available, navigating through their definitions and intricacies can be daunting. However, this blog streamlines the information by organizing definitions and process diagrams, making it effortless to grasp the various surface treatment techniques in just a few minutes. Each method's advantages and disadvantages are neatly presented, enabling a quick understanding of their applications, efficiencies, and limitations.

 

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