Tham khảo tài liệu 'process selection - from design to manufacture episode 2 part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 284 Costing designs These are material to process compatibility geometry to process suitability including complexity size and thickness tolerance requirements and surface finish. The equation used for the calculation of the relative cost coefficient Rc is as follows Rc CmpCcCsCft where Cmp relative cost associated with material-process compatibility when compared with an ideal material process combination Cc relative cost associated with producing different geometries from the ideal for the process under consideration Cs relative cost associated with achieving a section reduction thickness or size outside the envelope of the ideal design and Cft Ct or Cf whichever is greater where Ct relative cost associated with obtaining a specified tolerance and Cf relative cost associated with obtaining a specified surface finish. The combination of Ct and Cf into Cft is based on the assumption that when a fine surface finish is being produced fine tolerances can be produced for the same amount of cost and vice versa. This method of comparison and accumulation of costs based on the product of the above variables is analogous to the methodologies used by experts in the field of cost engineering and cost estimating. Note that when engineering the above elements going to make up Rc Cmp Cc Cs Ct and Cf they need to take account of all the secondary processing required to achieve the specified reductions tolerances and finish etc. for the component design. For a simple or ideal design of component each of the relative cost coefficients is unity but as a component design moves away from that state the coefficients tend to increase in magnitude thus increasing the processing cost. If Rc data is not obtained any estimate produced will be a lower bound only the quality of the estimate will improve as more information is represented regarding the effect of the designdependent factors. Addition of Rc data for a new manufacturing process The steps proposed are as follows 1 Following on
