Kalp Chap 27 Advanced Machining Processes.ppt
- 1. Manufacturing Processes Chap. 27 - Advanced Machining Processes
- 2. Advanced Machining Processes • When processing a component, typical material removal methods may not always work. • Possible reasons are: – Material hardness, strength is too high. – Workpiece too flexible, delicate, or thin. – Shape/features too complex. – Highly rigorous surface finish, dimensional tolerances. – Undesirable temperature rise/residual stresses remaining after processing.
- 3. Advanced Machining Processes • More advanced methods were developed for such conditions. • Typically referred to as Non-Traditional or Unconventional Machining. • Have major technical/economical advantages and also limitations.
- 4. Some Non-Traditional Machining Processes • Electrical Discharge Machining (EDM) • Wire Electrical Discharge Machining (WEDM) • Chemical Machining (CM) – Chemical Milling – Chemical Blanking – Photochemical Blanking • Electrochemical Machining (ECM) • Laser Beam Machining (LBM) • Waterjet Machining – Abrasive Water Jet Machining
- 5. Electrical Discharge Machining (EDM) • Also known as spark erosion machining. • Based on the erosion of metals by spark discharges. • When an arc is produced between two metals, part of the metal is eroded. • This erosion process, when controlled, can create a desired shape. • Only works with materials that are electrical conductors.
- 6. Basic EDM Operation • Tool and the workpiece are connected to a DC power supply. • An electrode with the desired shape is cut and secured to the machine ram. • Work is secured to a table an immersed in a tank containing a dielectric fluid typically mineral oils or deionized water). • If potential between tool (electrode) and work is high enough, a spark is discharged across the fluid.
- 7. Basic EDM Operation • Spark removes a small amount of metal from workpiece. • Discharges are repeated many times. • Gap: space between tool and workpiece - very critical. • Downfeed (Z motion) is NC controlled to maintain constant gap. • No mechanical energy required: hardness, strength, toughness don’t affect material removal rate (MRR).
- 8. EDM Parameters • Current – Surface Finish is a function of current and frequency. • If current is increased: – more powerful sparks are generated. – more material is removed per unit time. – larger craters are generated. – a rougher finish is produced. – If current is decreased, the opposite occurs. – However, it is more time consuming.
- 9. EDM Parameters • Frequency – Increasing/decreasing frequency has little effect on the MRR (while keeping current constant). – MRR is directly proportional to current. • Increasing frequency: – means less power for each spark. – less material is removed by each. – a smoother surface can be achieved. – however, it is more time consuming.
- 10. EDM Tooling • Electrodes are made of graphite or other alloys. • Can make electrodes by machining, forming, casting. • Can make very small and deep holes (dia. 0.005") ratio as large as 400:1. • Tool wears as it erodes; graphite electrodes have greatest wear resistance. • Must make multiple electrodes to cut the same cavity to compensate for wear.
- 11. EDM Capabilities • Great for irregular shaped cavities. • Can make sharp corners. • MRR can be 2 - 400 mm3/min, depending on material and parameters. • Used for: – Die and mold cavities. – Small deep holes. – Multiple Intricate Shapes – Internal Cavities
- 12. EDM Machines
- 13. Wire EDM (WEDM) • Process is similar to cutting with a band saw. • Moving wire travels along specified path. • Wire cuts workpiece by discharging sparks. • Dielectric floods the spark region, carrying away debris. • Can cut plates 12" thick. • When doing inside cuts, must have previous pilot hole to thread wire.
- 14. WEDM Tooling • Wire – Made of brass, copper or tungsten. – Can be as thin as 0.005". – Must be strong and tough. – Used only once, but cheap. – Kerf: gap left by wire on material after cutting. – Typical wire velocity: 0.15-9 m/min. – Cutting Speed: 6 mm/min for steel.
- 15. WEDM Machine
- 16. Wire EDM Example
- 17. Chemical Machining (CM) • Chemicals can attach and etch metals. • Etching removes small amounts of material from surface. • Reagents/etchants are typically acid/alkaline solutions. • Used in the past for engraving.
- 18. Chemical Machining (CM) • Can produce shallow cavities on sheets, plates up to 0.5". • Main purpose: weight reduction. • Can selectively attack regions of the material via: • masking • partial immersion
- 19. Chemical Machining Procedure (I) • Stress-relieve the part to prevent post-CM warping. • Thoroughly clean/degrease part ( to ensure good mask adherence & material removal.) • Apply masking material to entire part. • Remove masking material from regions to be etched.
- 20. Chemical Machining Procedure (II) • Expose material to etchants (i.e. NaOH, HNO3) while controlling temperature, stirring and time. • Wash part thoroughly. • Remove masking material, clean part, inspect.
- 21. Chemical Blanking (CB) • Blanking consists in producing shapes that fully penetrate the thickness of the material. • Chemical blanking is done via chemical dissolution rather than shearing. • No burrs are left. • Can blank complex, small or decorative shapes on thin metal.
- 22. Photo Chemical Blanking (PCB) • A variation of chemical milling. • Material is removed via photographic techniques. • Can create shapes on metal as thin as 0.0001".
- 23. PCB Procedure (I) • Prepare a design to be blanked, magnified up to 100X. • Make a negative and reduce to part scale (the artwork). • Coat sheet blank with photoresist (dip, spray, coat and oven dry). – Coat is called emulsion.
- 24. PCB Procedure (II) • Place negative over coated blank and expose to UV light, hardening exposed areas. • Develop blank to dissolve unexposed areas. • Immerse blank in reagent to etch away exposed areas. • Remove masking and wash thoroughly.
- 25. PCB Considerations • Etchant attacks material in horizontal and vertical direction. • Undercuts develop and must be taken into account. • Must control environment to control size changes. • Avoid designs with sharp corners, deep narrow cavities, seams tapers.
- 26. Electrochemical Machining (ECM) • Process similar to EDM. • Reverse process of electroplating. • Shaped tool is made of brass, copper, bronze or SS. • Electrolyte is an inorganic salt, circulating at high rate. • Creates complex cavities in hard materials.
- 27. Electrochemical Machining (ECM) • Leaves burr-free surface, no thermal damage to part. • No tool wear. • Not suited for sharp corners or flat bottomed features. • Difficulty controlling the electrolyte solution can produce irregular shapes/accuracies.
- 28. Laser Beam Machining (LBM) • Source of energy is laser: highly focused, high density energy beam. • Most common Laser types: – CO2 – Nd:YAG • Can be pulsed or continuous wave.
- 29. Laser Beam Machining (LBM) • Important Physical parameters of workpiece: (the lower the better) • Reflectivity • Thermal conductivity • Specific Heat • Latent heats of melting/evaporation
- 30. Laser Beam Machining (LBM)
- 31. Laser Beam Machining (LBM) • Process Capabilities – Drilling (as small as 0.0002") – Cutting of Metals, non-metals, ceramics, composites (as thick as 1.25") – Very flexible: can compete with sheet metal cutting with traditional punching processes.
- 32. Laser Beam Machining (LBM)
- 33. Laser Beam Machining (LBM) • Other Uses: Welding Localized Heat Treating Marking,engraving of parts. • Design Considerations Use on dull, unpolished surfaces. Avoid sharp corners. Deep cuts produce tapers.
- 34. Waterjet Machining (WJM) • Force of water is used to cut. • Recall continuity equation for incompressible fluids: A1V1 = A2V2 – Let A2 << A1; • A jet of water concentrated on a small area can have very high velocity. • Water acts like saw cutting narrow grove in material.
- 37. Waterjet Machining (WJM) • Typical pressures 60-200 kips/square inch. • Nozzle diameters (0.0002" - 0.040"). • Can cut variety of materials, 1" thick and more. • Excellent for foam, vinyl parts using multi- axis machines. • Also used in food industry for food cutting.
- 38. Waterjet Machining (WJM) • Advantages: - No need for pilot holes. - No heat generated. - Suitable for flexible parts. - Little wetting of work area. - Very little burrs. - Environmentally safe process.
- 39. Abrasive Waterjet Machining (AWJM) • Water is mixed with abrasive particles (silicon carbide, aluminum oxide). • Better Material Removal Rate than regular WJM. • Cutting Speeds: 25 ft/min for plastics, lower for harder materials. • Min hole diam. 0.12”; max. depth: 1”