Material Removal ProcessesA family of shaping operations through which undesired excess materialis removed from a starting workpart so the remaining part become closerto the desired shape

Cutting ProcessRemoves Material from the surface of a workpiece by producing chips.

Turning Operation

Straight Turning

Cutting Off

Slab Milling

End Milling

Chip Formation• Chips are produced by the shearing process, and that shearing takes

place along a shear zone.

Types Of Chips Produced

• Continuous Chips– Usually formed with ductile materials with a high cutting

speed.– It develops a secondary shear zone at the tool-chip interface.– It may also take place along with a primary shear zone with

curved boundaries.

• Built-up Edge (BUE)– Consisting of layers of material from the workpiece that are

gradually deposited on the tool.– BUE chips may form at the top of the tool during cutting.– BUE material is carried away by the tool side of the chip and

the rest is deposited randomly on the workpiece surface.

• Serrated Chips– Also called segmented or nonhomogeneous chips are semi

continuous chips with zones of low and high shear zone strain.– The chips have a semi toothlike appearance

• Discontinuous Chips– Consist of segments that may be firmly or loosely attached to

each other.– Usually form under the following conditions:

• Brittle workpiece material.• Materials contain hard inclusions and impurities.• Very low or very high cutting speeds.• Large depths of cut.• Lack of an effective cutting fluids.• Low stiffness of the machine tool.

Oblique Cutting• In oblique cutting, the cutting edge is at an angle called the

inclination angle.

Cutting Tools and Cutting Fluids• Cutting tool must possess the following characteristics:

– Hardness• Particularly at elevated temperature (hot hardness), so

that the hardness, strength, and wear resistance of thetool are maintained at the temperatures encountered incutting operations.

– Toughness• So that the impact forces on the tool in interrupted

cutting operations or due to vibration and chatter duringmachining do not chip or fracture the tool.

– Wear resistance• So that an acceptable tool life is obtained before the

tool is indexed or replaced.– Chemical stability and inertness

• With respect to the workpiece material, so that anyadverse reactions contributing to tool wear are avoided.

Cutting Tools

1. Carbon and Medium-alloy steels– Carbon steels are the oldest of tool material and have been

used widely for drills, tap, broaches, and reamers since1880’s. Low alloy and medium alloy steels were developed laterfor similar applications but with longer tool life.

2. High-speed steels– They were developed to cut at higher speeds.– They can be hardened to various depths, have good wear

resistance, and are relatively inexpensive.

– There are two types of high-speed steels: Molybdenum (Mseries) and Tungsten (T series).

– High-speed steels account for the largest tonnage of materialsused today.

– They can be coated for improved performance.3. Cast-cobalt alloys

– Because of their high hardness, they have good wear resistanceand can maintain their hardness at elevated temperatures.

– They are not as tough as high-speeds and are sensitive toimpact forces.

– Commonly known as stellite tools.4. Carbides

– Also known as cemented or sintered carbides, with a high hardnessover a wide range of temperatures.

– Carbides are among the most important, versatile, and cost-effective tool and die materials for a wide range ofapplications.

– The two basic groups of carbides used for machining operationare tungsten carbide and titanium carbide.

– Inserts are usually clamped on the tool shank with variouslocking mechanism, inserts may also be brazed to the tool.

Carbide Inserts

5. Coated Tools– Because of their unique properties, such as lower friction and

higher resistance to cracks and wear, coated tools can be usedat high cutting speeds, reducing both the time required fomachining operations and costs.

– Coatings for cutting tools, as well as for die, should havethe following general characteristics:

– High Hardness at elevated temperature– Chemical stability and inertness– Low thermal conductivity– Good bonding– Little or no porosity

6. Alumina-based Ceramics– Have a very high abrasion resistance and hot hardness.– They are more stable than high-speed steels and carbides.– Ceramic inserts are available in shapes similar to the shapes

of carbide inserts.

CERAMIC INSERTS

7. Cubic Boron Nitride– Next to diamond, cubic boron nitride is the hardest material

presently available.– The cubic boron nitride layer provides very high wear

resistance and cutting edge strength.8. Silicon-Nitride based Ceramics

– These tools have toughness, hot hardness, and good thermal-shock resistance.

– It is recommended for machining cast irons and nickel-basedalloys at intermediate cutting speeds.

– It is not suitable for machining steels.9. Diamond

– The hardest material for cutting tools.– It has low friction, high wear resistance, and the ability to

maintain sharp cutting edge.– Diamond is used when good surface finish and dimensional

accuracy is required.– Diamond tools can be used satisfactorily at almost any speed.

– It is also used as an abrasive in grinding and polishingoperations.

10. Whisker-Reinforced and Nano crystalline tool materials– Recent developments include the use of whiskers as reinforcing

fibers in composite cutting-tool materials.– It includes silicon-nitride base tools reinforced with

silicon-carbide whiskers.– Progress in nanomaterial has lead to the development of

cutting tools made of very-fine-grained carbides.– These tool materials are stronger, harder, and more wear

resistant, improving productivity.Cutting Fluids

• Also called lubricants and coolants, cutting fluids are used extensively inmachining as well as abrasive machining processes to achieve thefollowing result:

– Reduce friction and wear, thus improving tool life and surfacefinish

– Reduce forces and energy consumption– Cool the cutting zone, thus reducing workpiece temperature and

thermal distortion– Wash away the chips– Protect the machined surfaces from environmental corrosion.

Types of Cutting fluids• Oils• Emulsion• Semisynthetics• Synthetics.

Planing Process• Planing is a manufacturing process of material removal in which the

workpiece reciprocates against a stationary cutting tool producinga plane or sculpted surface.

• The mechanism used for this process is known as a planer. The sizeof the planer is determined by the largest workpiece that can bemachined on it. The cutting tools are usually carbide tipped ormade of high speed steel and resemble those used in facingand turning.