ME 330 Manufacturing Processes CUTTING PROCESSES Overview of processes Cutting processes Principle of the process Structure and configuration Process modeling Defects Design For Manufacturing (DFM) Process variation Module 4a 3 Major cutting processes Mechanical processes Bulk 1. Machining and grinding (will be covered in later classes) 2. Shearing, blanking, and punching (sheet metalworking operations) 3. Ultrasonic machining (USM) 4. Water jet cutting (WJC or hydrojet) 5. Abrasive water jet cutting (AWJC or abrasive hydrojet) For sheet and plate Definition of sheets and plates Sheets: thickness is 1/64” (0.04 mm) to 1/4” (6 mm). Plates: thickness is greater than: 1/4” (6mm) Principle of the process Structure and configuration Process modeling Defects Design For Manufacturing (DFM) Process variation Module 4a 6 Principle of cutting for sheets and plates: There is a shear stress induced on the surface of the cross section area of plates or sheets. The shearing stress causes the fracture of two parts. Module 4a 7 Principle of the process Structure/Configuration of the operation Process modeling Defects Design For Manufacturing (DFM) Process variation Module 4a 8 Shearing, Blanking, and Punching Three principal configurations in press working that cut sheet metal: Shearing Blanking Punching Different configurations of the manufacturing system or machine to generate shear stress, and they share the same principle of cutting. Shearing Operation (a) Side view of the operation; (b) front view of the operation, equipped with inclined upper cutting blade Blanking and Punching Blanking (a) - sheet metal cutting to separate piece (called a blank) from surrounding stock Punching (b) - similar to blanking except cut piece is scrap, called a slug Shearing, Blanking, and Punching Generic configurations: punch, die, work piece Shearing Generic configurations: punch, die, work piece Punch and Die in blanking and punching Components of a punch and die for a punch operation Punch Die Components of a punch and die for a blanking operation Cost of tooling is concern The cost for tooling is even higher than the press machine in itself. Punch and die may need frequently change due to wear, which is a part of the reasons for the high cost of tooling. Non-traditional Cutting Processes Cutting force is not generated by solid state force such as solid punch and solid die. Non-traditional Processes: why Newly developed metals and non-metals with special properties that make them difficult or impossible to cut or machine by the solid force approach. Complex part geometries that cannot readily be accomplished by conventional cutting and machining. Avoid surface damage that often accompanies with the conventional machining and cutting. Principle of the process Structure and configuration Process modeling Defects Design For Manufacturing (DFM) Process variation Module 4a 18 Major cutting processes Mechanical processes 1. Machining and grinding (will be covered in later classes) 2. Shearing, blanking, and punching (sheet metalworking operations) 3. Ultrasonic machining (USM) 4. Water jet cutting (WJC or hydrojet) 5. Abrasive water jet cutting (AWJC or abrasive hydrojet) Water Jet Cutting (WJC) or Hydro-jet Cutting Uses high pressure, high velocity stream of water directed at work surface for cutting The punch is a water stream WJC & Applications Usually automated by CNC or industrial robots to manipulate nozzle along desired trajectory. Water also acts as a cooling agent. Can cut complex shaped parts. Used to cut narrow slits in flat stock such as plastic, textiles, composites, floor tile, carpet, leather, and cardboard. Not suitable for brittle materials (e.g., glass). Intensity of water-jet is not enough, as opposed to the solid force, to make a clear-cut. The material tends to spreading around. Abrasive Water Jet Cutting (AWJC) Abrasive particles are added to jet stream for quicker cutting, which increases the intensity of water jet so that the high force can be created. Suitable to cut metals. Slower than laser cutting, but produces a cleaner finish. Note that the water jet cut is tapered. Major cutting processes Thermal Energy Processes 1. 2. 3. 4. 5. Ram electric discharge machining (Ram EDM) Wire electric discharge machining (Wire EDM) Electron beam machining (EBM) Laser beam machining (LBM) Plasma arc cutting (PAC) or plasma arc machining (PAM) 6. Air carbon arc cutting 7. Oxyfuel Cutting (OFC) or flame cutting Principle of the process Structure and configuration Process modeling Defects Design For Manufacturing (DFM) Process variation Module 4a 24 Electric Discharge Machining (EDM) EDM Operation One of the most widely used non-traditional processes Shape of a finished work surface produced by a shape of electrode tool Can be used only on electrically conducting work materials Requires dielectric fluid, which creates a path for each discharge as fluid becomes ionized in the gap. Metal is melted/vaporized by the series of electrical discharges Can be very precise and produces a very good surface finish Work Materials in EDM Work materials must be electrically conducting Hardness and strength of work material are not factors in EDM Material removal rate depends on melting point of work material Principle of the process Structure and configuration Process modeling Defects Design For Manufacturing (DFM) Process variation Module 4a 28 Wire EDM Special form of EDM uses small diameter wire as electrode to cut a narrow kerf in work Operation of Wire EDM Work is fed slowly past wire along desired cutting path. CNC used for motion control. While cutting, wire is continuously advanced between supply spool and take-up spool to maintain a constant diameter. Dielectric fluid is required. Applied using nozzles directed at tool-work interface or submerging work part Wire EDM Applications Ideal for stamping die components Since kerf is so narrow, it is often possible to fabricate punch and die in a single cut Other tools and parts with intricate outline shapes, such as lathe form tools, extrusion dies, and flat templates Dental part cut from nitinol material by wire EDM Laser Beam Machining (LBM) Uses the light energy from a laser to remove material by vaporization and ablation The punch is a light beam LBM Applications Drilling, slitting, slotting, scribing, and marking operations Drilling small diameter holes - down to 0.025 mm (0.001 in) Generally used on thin stock Work materials: metals with high hardness and strength, soft metals, ceramics, glass and glass epoxy, plastics, rubber, cloth, and wood Plasma Arc Cutting (PAC) Uses plasma stream operating at very high temperatures to cut metal by melting The punch is a plasma arc Operation of PAC Plasma = a superheated, electrically ionized gas PAC temperatures: 10,000C to 14,000C (18,000F to 25,000F) Plasma arc generated between electrode in torch and anode work piece The plasma flows through water-cooled nozzle that constricts and directs stream to desired location Applications of PAC Most applications of PAC involve cutting of flat metal sheets and plates. Hole piercing and cutting along a defined path. Comparable to laser cutting, but cuts are usually is more coarse. Can cut any electrically conductive metal. Most frequently cut metals: carbon steel, stainless steel, aluminum. Important: Water Jet, Laser, Plasma Need to start the cut away from the wanted cut to prevent a rough surface irregularity where the cut starts Starting cut Wanted cut Summary of Cutting Processes for Sheets and Plates in terms of Quality & Cost Wire EDM Machining Quality (In terms of tolerances & surface finish Water Jet Laser Punching/ Blanking Plasma Cost Comparison: sheet and plate cutting 1. Plasma 2. Laser 3. Waterjet Comparison: sheet and plate cutting Main criteria for comparison: 1. Materials 2. Cost 3. Quality 4. Productivity Comparison: sheet and plate cutting Processes Material Plasma All electrically Gauge to 2 in conductive materials Laser A variety of materials Waterjet A variety of materials, usually soft material Cost: decided by the speed. Thickness ¼ in and thinner Quality Cost Note Poor Low Need high power Middle Middle Problem with reflective materials Highest High Major cutting processes Electrochemical process: 1. Electrochemical Machining (ECM) Principle of the process Structure and configuration Process modeling Defects Design For Manufacturing (DFM) Process variation Module 4a 44 Electrochemical Machining (ECM) Material removal by anodic dissolution, using electrode (tool) in close proximity to work but separated by a rapidly flowing electrolyte (-) (+) Electrochemical Machining (ECM) Material removal by anodic dissolution, using electrode (tool) in close proximity to work but separated by a rapidly flowing electrolyte . Electrochemical Machining (ECM) Processes Electrical energy used in combination with chemical reactions to remove material Reverse of electroplating Work material must be a conductor Processes: 1. Electrochemical machining (ECM) 2. Electrochemical deburring (ECD) 3. Electrochemical grinding (ECG) ECM Operation Material is depleted from anode workpiece (positive pole) and transported to a cathode tool (negative pole) in an electrolyte bath Electrolyte flows rapidly between two poles to carry off depleted material, so it does not plate onto tool Electrode materials: Cu, brass, or stainless steel Tool has inverse shape of part – Tool size and shape must allow for the gap General benefits to manufacture parts by cutting from sheets and plates: Fast to manufacture Parts are low in cost Helps drive costs for assembled products down From low to high quantities Simple to complex parts Parts can later be formed (bent) to make more complex shapes Summary Sheet and plate cutting. Sheet and plate can be further processed by bending, forming, and drawing. Principle of cutting. 1. 2. 3. Shear stress principle (solid force, water-jet) Electric or light or plasma energy to thermal energy Electric-chemical effect Structure and configuration of each principle. Mechanical process (blanking/shearing/punching, waterjet), Thermal process (EDM, Laser, Plasma), Chemical (ECM). Constraints, pros and cons of each cutting process.