Surface treatment specifications of precision metal parts and their impact on parts processing costs

When designing a custom precision machined part, the engineer must define all the characteristics of the part and communicate them effectively to the machinist or manufacturer. This is usually done by creating and transferring drawings that contain numerical dimensions that define the size and location of each feature of the part. It also conveys other important precision metalworking component properties, including material type, hardness, allowable dimensional deviations, coatings, fabrication methods, and other industrial manufacturing processes.

A more important requirement that the drawings also define is the surface finish or 'permissible roughness' of the many surfaces of the precision metal-machined part. Surface finish can have a significant impact on a part's ability to perform its intended function. Surfaces that need to be sealed or contain gases or liquids must be defined in a way that allows them to seal to a specified level. Surfaces with relative motion between them may require low or high friction to function as intended. Even if the surface finish has no effect on the function of the part, it may be purely necessary to improve it in the precision metalworking manufacturing process.

The average roughness of precision metal parts is the most common parameter that engineers use to define the surface finish of a part. The precision metalworking solution preferably provides the arithmetic mean of surface irregularities measured from the mean line between the highest and lowest points.

Machined part surface comparison can be used in many different manufacturing processes to produce textured surfaces on precision metal machined parts. They are handy tools that allow engineers to get a 'feel' of surface roughness at the most commonly specified Ra levels. This is a comparator for many common metalworking processes in use today.

If a precision metal fabrication shop uses a lot of finishing cuts, surface grinding, polishing and grinding to meet a specified surface finish, it can double or triple the cost of producing a part. Point faces, grooves, bumps, and raised bosses can be added to product designs to minimize the size of surface areas that require extensive surface preparation and inspection.

Producing very smooth and highly polished surfaces over large areas can be an extremely expensive manual process. This is usually done with a fine abrasive compound, paper or tape, where the material removal rate is very slow compared to major machining processes that use cutting tools to remove large amounts of material. If manual grinding and polishing is required, one way to reduce the cost of parts containing highly polished sealing surfaces is to dimensionally limit and minimize the surface area that requires additional manual work. When specifying surface finishes, engineers must analyze and understand the downstream time and cost implications of roughness averages recalled on the drawing.

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