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

Principle of the process Structure/Configuration Process modeling Defects Design For Manufacturing (DFM) Process variation Module 6

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 process

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

handout 9 machining process What function and quality level can machining processes achieve? - Dimension accuracy: 0.025 mm - Surface quality: 0.4 µm - Any shape handout 9 machining process

handout 9 machining process 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 process

handout 9 machining process Cutting Tools Cutting Mechanisms handout 9 machining process

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

Principle of the process Structure/Configuration Process modeling Defects Design For Manufacturing (DFM) Process variation Module 6

handout 9 machining process 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 process

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

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

handout 9 machining process 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 process

handout 9 machining process - 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 process

handout 9 machining process Productivity Productivity is also called removal rate which is computed by the following equation: (d) (f) (v) Quality System parameters Operating parameters Example: - Rough cutting (f: 0.4-1.25mm/rev; d=2.5-20mm) - Finish cutting (f: 0.125-0.4mm/rev; d=0.75-2.0mm) handout 9 machining process

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

Principle of the process Structure/Configuration Process modeling Defects Design For Manufacturing (DFM) Process variation Module 6

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