Chapter 19 Processes Used to Separate Metallic Materials

Objectives

• • • • • Shearing process.

Chip making machine.

Cutting tools.

Drilling.

Grinding.

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.

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).

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.

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.

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.

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.

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.

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).

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.

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.

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.

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.

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.

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.

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).

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.

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.

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.

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.

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?