7 Methods For Finishing A Metal Surface

All metal prototyping and CNC machined components will leave behind a pattern of characteristic scratches on the workpiece. These are caused by the type of cutting tool, how sharp it is and the material it`s made from. In some cases these scratches can be ignored but usually to make a truly [finished" part one or more secondary processes need to be applied. Below are brief descriptions of the 7 main finishing processes to remove these scratches to make your final piece look perfect. 1. Sanding Sanding is simply a method for rubbing abrasive particles against the surface of a workpiece to create a random, non-linear surface texture. Different abrasive media are used, glued onto a backing paper or plate. The size of the cutting grains is refered to as [grit": the higher the grit number, the smaller and finer the particles are and hence the finer the surface finish they are able to achieve. Very coarse grits can remove a lot of material quickly, while finer grits are able to achieve a mirror polish. Water or some other lubricant is often used to flush material away and expose a fresh cutting surface. Sanding is especially useful for contoured or curved surfaces, but it`s not ideal for getting into very tight corners or pockets. When making a tool for plastic injection molding or pressure die casting, it`s often necessary to give the inner cavity a fine polish to make a beautiful finished part. But tool steels are heat-treated and very hard, so polishing them is difficult. It`s also not easy to reach into holes, pockets, and other complex shapes. Ultrasonic polishing is used in these cases. A soft, fine-tipped tool is mounted onto an ultrasonic spindle that vibrates at 30KHz. In combination with an abrasive slurry medium, the tool tip does not actually touch the work surface but it induces a pressure wave that safely works away at the surface to create a fine polish. This technique works even on hardened steels and there`s little chance of damaging the workpiece. This is the process of treating the surface of a part by blasting it with an abrasive media under high pressure. The type of media used again will determine the quality of the resulting finish. Sandblasting, or blasting with a combination of air and water, can cover a large surface area quickly. It can also improve some of the mechanical properties of metal, by increasing fatigue strength and improving corrosion resistance through shot-peening.