(BQ) Part 2 book "Precision manufacturing" has contents: Process planning for precision manufacturing, process planning for precision manufacturing, precision manufacturing applications and challenges, future of precision manufacturing. | IX PROCESS PLANNING FOR PRECISION MANUFACTURING Manufacturing system characteristics At a very basic level, there are key elements of a process that determine what its capabilities are, for example number of degrees of freedom of the work created (where a milling process has more degrees of freedom than a drilling process.) This can be represented as in Figure which shows achievable dimensions (for both surface finish and tolerance) for a range of manufacturing processes from normal to ultraprecision manufacturing. By contrast, Figure , one of the famous “Ashby Charts” from Ashby204 is a chart used for selecting processes to meet the combined specifications of tolerance and surface roughness over a range of materials. The tolerance indicated is the permitted allowance in the dimension of the part. The surface roughness R is the root mean square (RMS) amplitude of the surface irregularities. The basic requirement is that the tolerance must be greater than twice the roughness. For a specific surface with a measured RMS roughness, it is known that the maximum peaks of the irregularities are about 5 x RMS roughness. The chart also shows relative processing costs increasing as tolerance and roughness requirements become more stringent. Although this is typically true, one can find ample examples to the contrary in high production manufacture of products. In fact, you are probably aware of many examples where, due to efficient manufacturing, very high precision products are available at relatively low cost — think about the disk drive in your laptop for starters! 426 PRECISION MANUFACTURING Figure . Achievable dimensions (for both surface finish and tolerance) for a range of manufacturing processes from normal to ultraprecision manufacturing. In a paper written in 1971, the author, Jim Bryan, discusses the “myth” that tighter tolerances necessarily mean higher costs205. First defining close tolerances as ”one that is smaller than that currently in .
