Chapter 19

1. Chapter 19 Processes Used to Separate Metallic Materials

2. Objectives • Shearing process. • Chip making machine. • Cutting tools. • Drilling. • Grinding.

3. Introduction • The processes that use a cutting tool turn the unwanted material into chips. • The chips become scrap that may be recycled but none the less are wasted material. • Conversion efficiency (reducing the amount of waste generated) is an important factor in selecting a separating process.

4. Shearing • Shearing is a mechanical separating process that is used to cut sheet metal or plate. • Three types: straight shearing (similar to scissors), punch and die shearing (similar to paper hole punch), and rotary shearing (to cut small radii and irregular shapes).

5. Turning • Most common machine is a lathe (turning center). • Drilling and boring: A drill bit carves a hole in the work piece. • Facing: As work piece is rotated, a cutting tool reduces it to desired length. • Knurling: Tool forms diamond shape indentations on work piece to provide gripping surface on part. • Parting: Cutting tool cuts off portion of material. • Threading: To form internal or external threads. • Turning: Cutting tool makes rotating stock form part with various diameters or tapered profile.

6. Turning tools • Cemented carbide: most common engineered material used in tool inserts. • Cermet: carbide material. Fragile - used in shock free or low shock applications. • Productivity factors: Minimizing the amount of material that must be removed saves time and minimizes waste.

7. Planing • Planing: is an operation used to remove large amounts of material from horizontal, vertical, or angular flat surfaces. • Slotting: A slotter is a vertical shaper that is sometimes used to cut both internal and external slots and key ways. • Broaching: It is used for internal machining of keyways, splines, and irregular shaped openings.

8. Milling and Drilling • Milling: is used to produce slots, grooves, pockets, and contoured surfaces. • Because of their versatility production milling machines are now also called machining centers. • Drilling: Drilling operations can be accomplished with equipment ranging from a battery powered hand drill to a machining center.

9. Reaming and Tapping • Reaming: is a final finishing process that improves the dimensional accuracy and surface finish of a drilled hole. Reaming produces a smoother finish required for the insertion of bushings and bearings. • Tapping: is a process to cut threads inside a hole (internal threads). Tapping can be done by hand or with a machine such as a drill press, automatic screw machine, or lathe.

10. Grinding • Grinding is a cutting process that uses abrasive particles to perform the cutting action. • Grinding wheels: are used on both rough and precision grinders. Coarse wheels are used for rapid material removal. • Surface grinding: is a form of precision grinding that is done on flat work pieces. • Cylindrical grinding: is used on work pieces with curved surfaces (cylindrical shapes).

11. Abrasive Jet Machining • Abrasive jet machining: is a grinding process that suspends tiny particles of abrasive material in a low pressure stream of gas (dry air, carbon dioxide, or nitrogen) sprayed through a sapphire nozzle. • This process is used to etch, scribe, groove, and cut holes or slots in hard metals and non metallic material such as ceramics or glass.

12. Water Jet Machining • Water Jet Machining: is a process that uses a high velocity stream of water to cut materials ranging from paper to stone or metals. • The pressurized water stream can cut and slit porous material such as wood, paper, leather, brick, and foam. • When abrasives are introduced to the stream of water, the process is effective for cutting hard metals.

13. Laser Cutting • Laser Cutting: Metal cutting is the single largest application of the laser in manufacturing, and is normally done using a carbon dioxide gas laser. • Laser is a good tool for cutting small holes, narrow slots, and closely spaced patterns. • With laser cutting there are no cutting tools to break or wear. • The most common power range for commercial carbon dioxide lasers is 400 to 1500 watts.

14. Chemical Milling • Chemical blanking involves forming a part by etching metal away completely through the work piece. • Contour machining selectively etches a desired area to some specific depth. • Chemical milling can be used on virtually all metals and alloys. • Chemical machining is basically a photographic process. • Contouring is a method used to remove metal from surfaces of irregularly shaped parts. The part is selectively etched to the desired depth. • Chemically machined parts are stronger and more consistent. Changes in design can be made quickly without long lead times required for tooling revisions. • The aviation industry is the largest user of chemically milled parts.

15. Ultrasonic Machining • Ultrasonic machining is a process that removes material by eroding it using high frequency sound waves. • Ultrasonic machining can be used to drill and shape very hard, small, and high tolerance parts. • The tool must vibrate at a specific frequency – resonance frequency.

16. Electrochemical Machining • An important advantage of ECM is that there is no tool wear. • A limitation is that the work piece must conduct electricity. • Cast iron does not work well with ECM. • The aircraft industry is a major user of ECM.

17. Electron Beam Machining • Useful for drilling small holes and perforating or slotting material that is difficult to machine such as super alloys, ceramic oxides, carbides, and diamonds. • Material is instantly removed by the melting and vaporizing action caused by concentrating the high velocity electron beam on the work piece (fig 19-50, page 294).

18. Electro discharging Machine • Electro discharging machine (EDM) is a process that uses electrical energy to remove stock from metal work pieces. • Electro discharge machining bombards the work piece with 20,000 to 30,000 electrical sparks per second. • EDM is used to cut hard metals and can form deep internal shapes or irregularly shaped holes. • However EDM is a slow process. Thus it is not cost effective for conventional machining applications.

19. Travelling Wire EDM • In travelling wire EDM cutting takes place using a round wire that travels through the work piece. • This is sometimes compared to band saw cutting because it can be used to cut intricate shapes from a metal work piece. • The sparks arcing to the work piece from the electrode act like small teeth each removing a small amount of metal.

20. CNC • A computer numerical controlled machine (CNC) uses programs of ten developed along with a CAD drawing in a CAD/CAM (computer aided machining) software. • The ability of CAD/CAM software to generate code for CNC machines has simplified and expanded the use of CNC machines.

21. Summary • Abrasive jet machining process is used to etch, scribe, groove, and cut holes or slots in hard metals and non metallic material such as ceramics or glass. • Water Jet Machining is a process that uses a high velocity stream of water to cut materials ranging from paper to stone or metals. • The advantage of laser cutting is that with laser cutting there are no cutting tools to break or wear. • EDM is used to cut hard metals and can form deep internal shapes or irregularly shaped holes. However EDM is a slow process. Thus it is not cost effective for conventional machining applications.

22. Home Work • 1. Where is abrasive jet machining used? • 2. What is water jet machining? • 3. What is an advantage of laser cutting? • 4. What are the advantages and disadvantages of EDM?