Tham khảo tài liệu 'process selection - from design to manufacture part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 134 Selecting candidate processes Machining operations should be reduced to a minimum for simplicity and lower cycle time . Fillet corners and chamfer edges where possible to increase tool life. Holes should be drilled with a standard drill point at the bottom for economy. Required number of full threads should always be specified. Leading threads on both male and female work should be chamfered to assure efficient assembly. Auxiliary operations made possible by special attachments for example drilling and milling perpendicular to the length of the work. Some special machines allow larger pieces but then operations restricted. Sizes ranging mm-02m for manual and CNC machining. Automatic machines usually have a capacity of less than 060 mm. Quality issues Machinability of the material to be processed is an important issue with regard to surface roughness surface integrity tool life cutting forces and power requirements. Machinability is expressed in terms of a machinability index for the material. Multiple setups can be a source of variability. Selection of appropriate cutting tool coolant lubricant feed rate depth of cut and cutting speed with respect to material to be machined is important. Coolant also helps flush swarf from cutting area. Regular inspection of cutting tool condition and material specification is important for minimum variability. Surface detail is good to excellent. Surface roughness values ranging mm Ra are obtainable. Process capability charts showing the achievable dimensional tolerances for turning boring using conventional and diamond tipped cutting tools are provided see . Note the tolerances on these charts are greatly influenced by the machinability index for the material used and the part geometry. Machinability index for a material is expressed as a percentage based on the relative ease of machining a material with respect to free cutting mild steel which is 100 per cent and taken as the standard. Automatic and manual
