Functional Surfaces of the Workpiece
The surfaces which must be developed on the workpiece in the process of manufacturing are known as the functional surfaces. Consider a workpiece to be machined. Practically, the machined surfaces must mate with other machined surfaces. The areas which must be machined are identified from the part prints in three major ways.
1. Surface finish
2. Basic geometry
3. Tolerances
The standards for surface finish and their symbols shown on the product drawings are extremely useful to the process engineer in determining which surfaces must be machined. To some extent, they also limit the choice of how these surfaces must be accomplished.
The need for machining is identified by the basic shape of the part. A particular degree of roundness, squareness, flatness, parallelism or other specific descriptions of shape aid in recognizing machined surfaces. The process employed in originating the workpiece will often dictate how well these basic characteristics can be maintained. For example, shell mould casting may require little or no machining compared to the same part produced as a sand casting.
The preliminary part print analysis gives the general idea of dimensional limitations. As far as the functional requirements of the workpiece are concerned, tolerances indicate the margin of error that can be tolerated in manufacturing and still considered as the acceptable part. The basic configuration of the workpiece and the general notes and dimensions indicate to what degree these characteristics are needed.