Machining: Family of Material Removal Processes  Material is removed from a starting work part to create a desired geometry

Module 62 Principle of the process Structure/Configuration Process modeling Defects Design For Manufacturing (DFM) Process variation

handout 9 machining process3 Machining Process - Concept Material In Removal of chips Material Out - Not any type of materials could be cut: ceramic not - There is a family of machining processes: abrasive, etc

handout 9 machining process4 Various types of machining processes Turning Drilling Peripheral milling Face milling

handout 9 machining process5 What function and quality level can machining processes achieve? - Dimension accuracy: mm - Surface quality:0.4 µm - Any shape

handout 9 machining process6 What are generic features with any machining operations to make cutting processes work? - Two motions: tool motion and work motion - Primary speed and secondary speed (or feed (rate) - Relative motion between the two motions generates mechanics to form chips and remove them

handout 9 machining process7 Cutting Tools Cutting Mechanisms

handout 9 machining process8 Cutting Tools Major cutting parameters Material Removal Rate MRR = (v)(f)(d)

Module 69 Principle of the process Structure/Configuration Process modeling Defects Design For Manufacturing (DFM) Process variation

handout 9 machining process10 Engineering Analysis - Machine equipment to do material removal process: Chip formation, energy, and power - Tool life: tool failure causes quality problem - Productivity - Quality assurance

handout 9 machining process11 Theory of chip formation Ls tctc to - Chip thickness ratio, r = to/tc (tc > to) )( - MRR = (v)(to)(w) Orthogonal Cutting Model –converts 3d to 2d

handout 9 machining process12 Theory of chip formation E- Efficiency that accounts for loss of the machine tool

handout 9 machining process13 Tool life -Fracture failure: force becomes excessive, causing sudden brittle fracture - Temperature failure: temperature is too high, causing the material at the tool point to soften - Gradual wear: (1) crater wear (2) flank wear

handout 9 machining process14 - The objective of selecting tools should ensure that only the gradual wear mode will occur - Tool design: materials and geometry - Except for tool design parameters (system parameters), tool life is a function of operating parameters (d) (f) (v) Cooling methods ( fluids)

handout 9 machining process15 Productivity is also called removal rate which is computed by the following equation: (d) (f) (v) Example: - Rough cutting (f: mm/rev; d=2.5-20mm) - Finish cutting (f: mm/rev; d= mm) Productivity Quality System parameters Operating parameters

handout 9 machining process16 Summary System parameters Operating parameters Tool Material (d) (f) (v) -> Power Cooling methods Goal: Select operating parameters to ensure no failure with the whole system and satisfactory quality

Module 617 Principle of the process Structure/Configuration Process modeling Defects Design For Manufacturing (DFM) Process variation

Design Considerations in Machining  Design parts that require little, and if possible, no machining Use net shape or near net shape processes  Specify tolerances Use tighter tolerances only where required  Specify surface finish Use better surface finishes where required  Avoid machining sharp features (i.e. internal corners) where possible Require sharp cutting tools that can break more easily  Avoid deep holes that must be bored Difficult to maintain tool stiffness  Provide seats for drilling  Design part so standard cutting tools can access easily

Design Considerations in Machining  Design with materials that have good machinability  Design part features that used standard cutting tools Avoid unusual hole sizes, threads, angles, and shapes requiring special form tools or special contouring  Design part with simpler geometries Minimize or avoid angles and contours where possible  Design parts to have as few setups, one if possible I.E. changing position of part and changing cutting tool

Design Considerations in Machining  Design machined part sizes that are close to standard available stock sizes Less material to cut  Design machined parts to be rigid enough to withstand cutting forces and clamping Avoid thin and narrow parts  Avoid undercuts as they require additional setups and special tooling

Summary: 1.Machining is a material removal process by cutting tools on work material (stock). 2.For machining, one need to select tools and operation parameters (v, f, d). 3.The selection criteria: tool life, quality. 4.The productivity is the multiplication of v, f, d. 5.Operating principle: chip formation with two important angles (rake angle, and frank angle). 6.DFM rules