Surface finishing is a process used in manufacturing to alter physical or chemical properties of a surface. Surface roughness can be smoothed out through grinding, sanding, buffing, and polishing. Surface properties can be measured using contact or non-contact profilometers and interferometers. Surface finishing is used in various industries to enhance product characteristics and value. It can involve coating, electroplating, embossing, engraving, and other techniques to modify the surface of the finished object.
Surface finish in manufacturing applies to any final procedure or series of procedures that result in a change in a desired property of a face of the manufactured item. Physical or chemical properties can be altered. The metallurgical, textile and polymer industries often use surface finishing to enhance the characteristics and value of their products.
Surface roughness is a common physical feature that needs to be smoothed out in a product. Grinding, sanding, buffing and polishing are steps used in sequence to increase smoothness. A smooth surface may be desirable for material handling, close mating of machined parts, or for aesthetic reasons. Reducing the friction between the object and another material is a frequent reason for smoothing surfaces.
Surface roughness, expressed as Ra, is a measure of the arithmetic mean of the peaks and valleys of a surface. It can be measured directly by a contact profilometer, a device in which a diamond needle on a stylus slides up and down the profile, following a programmed grid while recording the results. These devices measure Ra from 0.1 to 0.4 microinches (3 to 10 nanometers). Non-contact profilometers and interferometers measure Ra using a wide variety of optical measurements, comparing the angles at which light is reflected and interference patterns. These machines can measure roughness in the range of 0.012 to 0.02 microinches (3 to 5 angstroms).
The surface properties of the mirrors used in telescopes largely determine the quality of the images obtained. Measuring the smoothness of these mirrors becomes as challenging as the surface finishing techniques themselves. The surface area of the Hubble telescope’s primary mirror has a total variance of less than 0.04 microinches (10 angstroms).
Sheet metal or metal objects are often coated with polymer or paint to protect the material from corrosion and pitting. These finishes can be applied by spraying or sputtering, or by vapor or powder deposition. With these methods a mirror finish can be achieved. The final step may involve a cure, annealing or firing to set the finish and ensure adhesion to the underlying material. Embossing or engraving can also be employed to modify the surface of the finished object.
Electroplating is the practice of bonding a surface coating of one material to another by electrochemical methods. Typically, these are metals or metal alloys bonded to other metal substrates. A tough, corrosion-resistant, and attractive surface finish is a requirement for many automotive, aircraft, and marine components. Similarly, medical components use electroplating to obtain a surface that can be sanitized or sterilized.
In the textile industry, fabrics may go through surface finishing steps that add sheen to the material, starch for ease of handling, or an embossed pattern. The texture of the material can be enhanced with a brushing or scraping technique. Items made with polymers are often subjected to surface finishing to alter their texture, gas or liquid permeability, or stiffness.
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