Surface finishing is a broad range of industrial processes that alter the surface of a manufactured item to achieve a certain property. [1] Finishing processes may be employed to: improve appearance, adhesion or wettability, solderability, corrosion resistance, tarnish resistance, chemical resistance, wear resistance, hardness, modify electrical conductivity, remove burrs and other surface flaws, and control the surface friction. [1] [2] In limited cases some of these techniques can be used to restore original dimensions to salvage or repair an item. An unfinished surface is often called mill finish .
Surface finishing processes can be categorized by how they affect the workpiece:
Mechanical processes may also be categorized together because of similarities in the final surface finish.
Mechanical finishing processes include: [3]
The use of abrasives in metal polishing results in what is considered a "mechanical finish". [3]
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Annealed and descaled after hot rolling, this finish is suitable for industrial applications requiring heat resistance and corrosion resistance, where smoothness of finish is unimportant, such as chemical tanks, aircraft heaters, steam turbine shrouds and piping. [4]
Also known as grinding, roughing or rough grinding. These finishes are coarse in nature and usually are a preliminary finish applied before manufacturing. An example would be grinding gates off of castings, deburring or removing excess weld material. It is coarse in appearance and applied by using 36–100 grit abrasive. [5]
When the finish is specified as #3, the material is polished to a uniform 60–80 grit.
Also known as brushed, directional or satin finish. A #4 architectural finish is characterized by fine polishing grit lines that are uniform and directional in appearance. It is produced by polishing the metal with a 120–180 grit belt or wheel finish and then softened with an 80–120 grit greaseless compound or a medium non woven abrasive belt or pad.
This finish is commonly used for the medical and food industry and almost exclusively used on stainless steel. This finish is much finer than a #4 architectural finish. This finish enhances the physical appearance of the metal as well as increases the sanitary benefits. [6] One takes great care to remove any surface defects in the metal, like pits, that could allow bacteria to grow. A #4 dairy or sanitary finish is produced by polishing with a 180–240 grit belt or wheel finish softened with 120–240 grit greaseless compound or a fine non woven abrasive belt or pad.
Also known as a fine satin finish. This finish is produced by polishing with a 220–280 grit belt or wheel softened with a 220–230 grit greaseless compound or very fine non woven abrasive belt or pad. Polishing lines will be soft and less reflective than a #4 architectural finish.
A #7 finish is produced by polishing with a 280–320 grit belt or wheel and sisal buffing with a cut and color compound. This is a semi-bright finish that will still have some polishing lines but they will be very dull. Carbon steel and iron are commonly polished to a #7 finish before chrome plating. A #7 finish can be made bright by color buffing with coloring compound and a cotton buff. This is commonly applied to keep polishing costs down when a part needs to be shiny but not flawless.
Also known as a mirror finish. This finish is produced by polishing with at least a 320 grit belt or wheel finish. Care will be taken in making sure all surface defects are removed. The part is sisal buffed and then color buffed to achieve a mirror finish. The quality of this finish is dependent on the quality of the metal being polished. Some alloys of steel and aluminum cannot be brought to a mirror finish. Castings that have slag or pits will also be difficult, if not impossible, to polish to a #8. A polished PVD finish can achieve a similar appearance due to the smooth, reflective nature of the coating process. [7]
Metalworking is the process of shaping and reshaping metals in order to create useful objects, parts, assemblies, and large scale structures. As a term, it covers a wide and diverse range of processes, skills, and tools for producing objects on every scale: from huge ships, buildings, and bridges, down to precise engine parts and delicate jewelry.
An abrasive is a material, often a mineral, that is used to shape or finish a workpiece through rubbing which leads to part of the workpiece being worn away by friction. While finishing a material often means polishing it to gain a smooth, reflective surface, the process can also involve roughening as in satin, matte or beaded finishes. In short, the ceramics which are used to cut, grind and polish other softer materials are known as abrasives.
Sandpaper, also known as glasspaper or as coated abrasive, is a type of material that consists of sheets of paper or cloth with an abrasive substance glued to one face. In the modern manufacture of these products, sand and glass have been replaced by other abrasives such as aluminium oxide or silicon carbide. It is common to use the name of the abrasive when describing the paper, e.g. "aluminium oxide paper", or "silicon carbide paper".
Tumble finishing, also known as tumbling or rumbling, is a technique for smoothing and polishing a rough surface on relatively small parts. In the field of metalworking, a similar process called barreling, or barrel finishing, works upon the same principles.
Chrome plating is a technique of electroplating a thin layer of chromium onto a metal object. A chrome plated part is called chrome, or is said to have been chromed. The chromium layer can be decorative, provide corrosion resistance, facilitate cleaning, and increase surface hardness. Sometimes, a less expensive substitute for chrome, such as nickel may be used for aesthetic purposes.
Brushed stainless steel or dull polished metal is metal with a unidirectional satin finish. It is produced by polishing the metal with a 120–180 grit belt or wheel then softening with an 80–120 grit greaseless compound or a medium non-woven abrasive belt or pad.
Shot peening is a cold working process used to produce a compressive residual stress layer and modify the mechanical properties of metals and composites. It entails striking a surface with shot with force sufficient to create plastic deformation.
Knife making is the process of manufacturing a knife by any one or a combination of processes: stock removal, forging to shape, welded lamination or investment cast. Typical metals used come from the carbon steel, tool, or stainless steel families. Primitive knives have been made from bronze, copper, brass, iron, obsidian, and flint.
Optical manufacturing and testing is the process of manufacturing and testing optical components. It spans a wide range of manufacturing procedures and optical test configurations.
Buffing are finishing processes for smoothing a workpiece's surface using an abrasive and a work wheel or a leather strop. Technically, polishing refers to processes that uses an abrasive that is glued to the work wheel, while buffing uses a loose abrasive applied to the work wheel. Polishing is a more aggressive process, while buffing is less harsh, which leads to a smoother, brighter finish. A common misconception is that a polished surface has a mirror-bright finish, however, most mirror-bright finishes are actually buffed.
Physical vapor deposition (PVD), sometimes called physical vapor transport (PVT), describes a variety of vacuum deposition methods which can be used to produce thin films and coatings on substrates including metals, ceramics, glass, and polymers. PVD is characterized by a process in which the material transitions from a condensed phase to a vapor phase and then back to a thin film condensed phase. The most common PVD processes are sputtering and evaporation. PVD is used in the manufacturing of items which require thin films for optical, mechanical, electrical, acoustic or chemical functions. Examples include semiconductor devices such as thin-film solar cells, microelectromechanical devices such as thin film bulk acoustic resonator, aluminized PET film for food packaging and balloons, and titanium nitride coated cutting tools for metalworking. Besides PVD tools for fabrication, special smaller tools used mainly for scientific purposes have been developed.
Belt grinding is an abrasive machining process used on metals and other materials. It is typically used as a finishing process in industry. A belt, coated in abrasive material, is run over the surface to be processed in order to remove material or produce the desired finish.
A diamond tool is a cutting tool with diamond grains fixed on the functional parts of the tool via a bonding material or another method. As diamond is a superhard material, diamond tools have many advantages as compared with tools made with common abrasives such as corundum and silicon carbide.
Floor sanding is the process of removing the top surfaces of a wooden floor by sanding with abrasive materials.
Low plasticity burnishing (LPB) cold compresses metal to provide deep, stable surface residual stresses to improve damage tolerance and extend metal fatigue life; mitigating surface damage, including fretting, corrosion pitting, stress corrosion cracking (SCC), and foreign object damage (FOD). Improved fretting fatigue and stress corrosion performance has been documented, even at elevated temperatures where the compression from other metal improvement processes: low stress grinding (LSG) etc. relax. The resulting deep layer of compressive residual stress has also been shown to improve high cycle fatigue (HCF), low cycle fatigue (LCF), and stress corrosion cracking (SCC) performance.
Mass finishing is a group of manufacturing processes that allow large quantities of parts to be simultaneously finished. The goal of this type of finishing is to burnish, deburr, clean, radius, de-flash, descale, remove rust, polish, brighten, surface harden, prepare parts for further finishing, or break off die cast runners. The two main types of mass finishing are tumble finishing, also known as barrel finishing, and vibratory finishing. Both involve the use of a cyclical action to create grinding contact between surfaces. Sometimes the workpieces are finished against each other; however, usually a finishing medium is used. Mass finishing can be performed dry or wet; wet processes have liquid lubricants, cleaners, or abrasives, while dry processes do not. Cycle times can be as short as 10 minutes for nonferrous workpieces or as long as 2 hours for hardened steel.
Surface integrity is the surface condition of a workpiece after being modified by a manufacturing process. The term was coined by Michael Field and John F. Kahles in 1964.
Steel abrasives are steel particles that are used as abrasive or peening media. They are usually available in two different shapes that address different industrial applications.
A diamond grinding cup wheel is a metal-bonded diamond tool with diamond segments welded or cold-pressed on a steel wheel body, which usually looks like a cup. Diamond grinding cup wheels are usually mounted on concrete grinders to grind abrasive building materials like concrete, granite and marble.