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Process Selection - From Design to Manufacture Episode 1 Part 9

Tham khảo tài liệu 'process selection - from design to manufacture episode 1 part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 144 Selecting candidate processes Accurate re-grinding of the drill point geometry is required to maintain correct hole size and balance cutting forces to avoid drill breakage. Rigidity of drilling machine workpiece and drill holder and concentricity of drill spindle are important in preventing oversize holes chatter and poor surface finish. Selection of appropriate drill geometry including relief and rake angles coolant lubricant size of cut hole feed rate and cutting speed with respect to material to be machined is important. Drills may require chip breakers for ductile materials to efficiently remove swarf from cutting area. Coolant also helps flush swarf from cutting area in long through holes and blind holes. Surface detail is fair. Surface roughness values ranging 0.4-12.5 mm Ra are obtainable. A process capability chart showing the achievable dimensional tolerances is provided see 4.4CC . Note the tolerances on this chart are greatly influenced by the machinability index for the material used. 4.4CC Drilling process capability chart. Broaching 145 4.5 Broaching Process description The removal of material by chip processes using a multiple-point cutting tool which is pushed or pulled across the workpiece surface. With successively deeper cuts the desired profile is gradually generated in a single pass see 4.5F . 4.5F Broaching process. Materials All metals mostly free machining . Process variations Horizontal vertical or rotary broaching machines with push and or pull capability. Broaching tools can be single or combination types internal or external performing either roughing or finishing operations. Some indexable insert broaches are available for surface broaching and titanium nitride coatings are also used to increase tool life. Economic considerations Production rates up to 400 h. To improve production rates many parts can be machined at once called stacking. Stacking is best suited to internal features. Automation possible to improve production rates. .