Regardless of how good a finished component is, high-quality metal surface processing makes it even better. Surface processing is an essential process in the production of metal components. Proper surface finishing ensures that a metal part looks better and lasts longer.
However, there are several types of metallic finishes for metals. Therefore, it is important to understand the details of the different finishes available. Not knowing the correct surface engineering for a project can result in wasted materials, longer cycle times and higher manufacturing costs.
In this guide, you will learn all about the different metal finishing techniques available. This way you avoid unwanted manufacturing results and improve the quality of your products. Let's start!
Surface finishing basics: What is surface finishing?
Surface finishing is a collective term for various processes of altering metal surfaces through removal, addition or remodeling. It is a chemical, mechanical or electrical protection process that helps improve the aesthetics, resistance and other properties of metal components.
The individual result of a finishing process depends on the method chosen. Depending on your needs, you can select one or more metallic finishes to achieve optimal product quality.
Why is surface finish important for metals?
Surface finishing can be beneficial to both the end user and the manufacturer. In general, high-quality surface finishing ensures that the final product looks better and lasts longer. Therefore, the end user enjoys using the product more.
Some surface finishing processes also facilitate the manufacturing process. For example, brushing the surface of a metal before painting it increases the adhesion of the metal to the paint. This makes it easier for the manufacturer to achieve high-quality surface finishing.
The numerous advantages of surface finishing processes include:
- Greater durability
- Greater corrosion resistance
- Elimination of surface defects
- Helps with the adhesion of paints and other coatings
- Improved aesthetic appearance
- Greater chemical resistance
- Improved electrical conductivity
- High strength and wear resistance
Types of metal surfaces
There are different types of surface finishes, each with its own advantages. The type of project and your choice of materials will determine the type of machining you will use. Below are some of the common finishes available for metal:
Plating or Conversion Coatings
Metal plating involves altering the surfaces of substrates by coating them with thin layers of other metals, such as zinc, nickel, chromium or cadmium. Metallic coating improves the durability, surface friction, corrosion resistance and aesthetic appearance of a component. However, coating machines may not be suitable for removing surface defects.
There are two main types of coating:
- Electroplating . In this process, the component is immersed in a bath with metal ions for coating. A direct current is then applied to the metal so that the ions deposit on the metal part and leave a new layer on the surface.
- Chemical coating. This method does not use electrical current as it is an autocatalytic coating without an external power source. Instead, the metal part is placed in solutions filled with copper or nickel to trigger a reaction that breaks down the metal ions.
These processes give the metal a durable finish and can also be used to repair and maintain worn components. They add hardness to metal parts and increase their resistance to corrosion, making them useful for a variety of applications.
Electroplating is often a large-scale, chemical-intensive process. Therefore, it is carried out by qualified and experienced technicians.
Anodizing
This electrochemical process helps create a durable, decorative and corrosion-resistant anodic oxide surface. Manufacturers achieve this finish by immersing the metal in an acidic electrolyte bath before passing an electrical current through the medium. Aluminum acts as the anode while a cathode is mounted in the anodizing vessel.
Consequently, the oxygen ions released from the electrolyte combine with the aluminum atoms and form an anodic oxide on the surface of the part. Therefore, anodization is a strictly controlled oxidation of the metal substrate. It is primarily useful for finishing aluminum parts, but can also be used on non-ferrous metals such as magnesium and titanium.
metal grinding
Manufacturers use grinders to smooth metal surfaces with adhesives. This is one of the final stages of machining and helps to reduce the surface roughness left on the metal by machining. There are different sanders that achieve different levels of smoothness.
Surface grinders are the most commonly available machines. However, there are also many other specialized grinders, such as Blanchard grinders and centerless grinders. A precision Blanchard grinder is often used for large parts. Straight grinders, on the other hand, help with detailed work using specially shaped grinding wheels.
polishing
In these processes, abrasives help to reduce the surface roughness of metals after processing. These abrasive powders are combined with felt or leather wheels to polish and smooth metal surfaces as needed.
Manufacturers can polish metal manually or automatically (using robotic polishing). In addition to reducing the surface roughness of the material, polishing also increases the metal's shine. Therefore, the main purpose of polishing and polishing is to improve the aesthetics of a metal part.
Electropolishing
Electropolishing is the exact opposite of the electroplating process. Instead of depositing metal ions on the surfaces of metal components, electropolishing removes metal ions from the surface. During the process, the substrate is immersed in an electrolytic bath before applying electrical current.
The substrate becomes the anode from which ions flow to remove defects, rust, dirt, etc. The result is a polished and smooth surface, without protrusions or dents. Electropolishing removes peaks and valleys from metal surfaces down to the microscopic level. This is one of the best surface finish options for metals that require a clean, flawless appearance.
Coating
Coating is a broad term that includes several subcategories of surface treatments. The most common and economical option is to apply commercially available paints. Some colors can add color to the product to make it more aesthetically pleasing. Others can help actively protect the component from corrosion.
There is also powder coating, a modern variant of painting. Dust particles are attracted to metal parts by electrostatic charge. The powder particles evenly cover the surface of the material before being hardened by heat treatment or the use of ultraviolet rays. This method can be used to quickly and efficiently refine metal parts such as bicycle frames, body panels and various other metal components.
Rays
Sandblasting is typically used for products that require a uniform, matte texture. It is an economical process that combines cleaning and surface finishing in a single operation. Sandblasting involves spraying the metal surface with a high-pressure jet to change its texture, remove dirt and create a smooth surface.
It can also serve as a surface preparation coating and coating to increase the durability of metal parts. The typical blasting system consists of:
- An air compressor to adjust pressure and volume
- Water-assisted system to suppress dust development
- Moisture separator to reduce humidity
- Air supply line
- detonation system
- hose and nozzle
- Abrasives including sand, metal pellets, glass beads, steel shot, steel shot, silicon carbide, etc.
The common blasting methods are sand blasting and shot blasting. Another unique sandblasting process is sandblasting. This process applies compressive stress to metal surfaces to improve fatigue and corrosion resistance. Blasting often saves time and costs and allows product managers to get products to market faster.
to brush
Brushing creates a uniform surface structure and smoothes the outside of metal products. Unlike plating, this metallic finishing technique is ideal for removing imperfections on metal surfaces. Wire brushes or sanding belts are typically used for this purpose.
Depending on how the manufacturer uses the process, results may vary. For example, moving the brush or tape in one direction can create slightly rounded edges on the surface. Wire brushing aims to remove slag produced during welding. It also removes sand and scale from the surface of metals before cleaning, galvanizing or coating.
painting
Painting and powder coating are very similar. It involves exchanging a metal part for substances such as paint, pigment or ink. This surface finishing technique gives metal surfaces a colored protective layer.
The process begins with atomizing the ink to convert it into tiny droplets using high pressure and other external forces. The machinist then applies the paint to the metal part using the most suitable method. The different methods available include spray painting, powder coating, screen printing, etc.
The method used depends on the desired surface depending on the size, shape and quality of the material. The objective of painting is to create a protective layer on the surface of the piece and give it an improved appearance, achieving a high level of shine.
Choosing a Metal Surface Finishing Process: Factors to Consider
Surface processing is an essential aspect of metal processing. A good understanding of the requirements will help you achieve the desired finish. The right combination of consumables and knowledge of materials is the key to achieving a high-quality finish in a short time and at affordable prices. Here are some factors you need to consider before choosing a finish for your metal parts:
material
Not all surface finishing techniques are suitable for all metals. For example, anodizing is ideal for aluminum and other non-ferrous metals. Therefore, you must first consider the metal material used in manufacturing the component before selecting the surface finish of that metal.
Some metals are soft, so you should not use sharp abrasives to avoid damaging their surface. On the other hand, using techniques that are too gentle on hard or strong materials may not produce the desired results.
speed
Different finishes have different completion periods; some are fast, others slow. Therefore, you need to consider the time it will take to complete a project. Analyze machining options and consider your processing times. If you need to complete a project quickly, you need to choose a finish with a very fast processing time.
Forms
The application of your product and the environment to which it will be exposed should also influence your choice. For parts with high-intensity applications, you should choose a protective surface coating. These protective coatings add durability to components and prevent premature damage. On the other hand, for pieces that are not exposed to intense environments, you can opt for an aesthetic coating.
budget
You may have found the perfect finishing technique for your metal products, but is it within your budget? Your budget will determine the type of finish you choose. You should choose one that is within your scope and at the same time provides high-quality results. Expensive finishes can increase product costs and impact your company's bottom line.
Concluding
High-quality surface treatment is crucial in the production of metal parts. It is not only beneficial for the end users but also offers several advantages for the manufacturer. However, not knowing how to properly address it can negatively impact both manufacturers and end users in the long run. Therefore, you need to understand your needs and look for the most suitable surface for your project.
