ME 341 – Manufacturing Processes

University of Nevada Las Vegas	MEG426/626 Manufacturing Processes
Department of Mechanical Engineering	Fall Semester 2000

Cutting Tool Geometry

What is Machining:

Machining is manufacturing process in which a cutting tool is used to remove excess material from a workpart so that the remaining material is the desired part shape.

Machining is important:

It can be applied to a wide variety of work materials.

It can be used to generate any regular geometry, such as flat or curved planes, round or special formed holes, and cylinders.

It can produce dimensions to very close tolerances of less than 0.001 in. (0.025 mm). It is more accurate than most other processes.

Machining is capable of creating very smooth surface finishes of better than 16 μin. (0.4 μm). Some abrasive processes can achieve even better finishes.

Types of machining operation:

Traditional (Conventional)

Turning,	Milling,	Drilling,	Grinding
Shaping,	Planing,	Broaching,	Sawing
Boring,	Reaming,	etc.

Nontraditional (Nonconventional)

	EDM,	WEDM,	ECM,	AFM,
	USM,	Water Jet Machining,	etc.

In turning, a cutting tool with a single cutting edge is used to remove material from a rotating workpiece to form a cylindrical shape and/or an end face. It can also be used to make screw bar.

Motion: speed motion (work rotates), feed motion (tool in two directions), and depth of cut (tool penetration beneath original work surface). The tool and the workpiece both move in a machining operation.

Horizontal/Vertical turning.

Drilling is used to create a round hole. It is usually accomplished with a rotating tool that has two cutting edges.

Motion: speed motion (tool rotates), feed motion (tool in direction parallel to tool axis). Workpiece is held stationary in a cutting operation.

In milling, a rotating tool with multiple cutting edges is moved slowly relative to the material to generate a straight surface.

Motion: speed motion (tool rotates), feed motion (work in two directions), depth of cut is tool penetration beneath original surface.

Peripheral/Face Milling.

The differences between traditional machining and nontraditional machining.

Cutting Tool Geometry

A cutting tool has one or more sharp cutting edges. The cutting edges serves to separate a chip from the parent work material.

A cutting tool must posses a shape that is suited to the machining operation.

Rake face, which directs the flow of the newly formed chip, is oriented at a certain angle called the rake angle .

Range: mostly +5⁰ to -5⁰; some +10⁰ to -10⁰; a few +20⁰ to -20⁰.

Flank face, which provides a clearance between the tool and the newly generated work surface. Is oriented at an angle call the clearance angle.

Range: +(2⁰-10⁰), must be positive.

Inclination angle, Cutting edge, Nose radius, Main cutting edge.

Function of the angles:

Chip Breakers are frequently used with single-point tools to force the chips to curl more tightly than they would naturally be inclined to do, thus causing them to fracture.

Groove-type chipbreaker

Obstruction-type chip breaker

A single-point tool has a main cutting edge and a tool point from which the name of this cutting tool is derived.

For turning.

A Multiple-cutting-edge tool has more than one cutting edge and usually achieve their motion relative to the workpart by rotating.

For drilling and milling.

(not covered)
Effect of Tool Material on Tool Geometry

What are the common tool Materials?

	High-Speed Steels (HSS),	Cemented Carbides,
	Coated Carbides,	Ceramics,
	CBN,	PCD,
	Diamonds.

HSS cutting tools are almost always ground with positive rake angles, typically ranging from +5⁰ to + 20⁰.

Good strength and toughness.

Cemented carbides are used with rake angles typically in the range from -5⁰ to - 15⁰. Clearance angles are made very small (+5⁰) to provide as much as support for the cutting edge as possible.

Cutting Conditions:

In most cases, it means cutting speed, feed, and depth of cut. It also distinguished by purpose and cutting conditions: roughing cuts, semi-roughing cuts, semi-finishing cuts, and finishing cuts.

Roughing cuts are used to remove large amounts of material from the starting workpart as rapidly(and economically) as possible in order to produce a shape close to the desired form, but leaving some material on the piece for a subsequent finishing operation.

high speed and depth, with feeds of 0.015 to 0.050 in./rev (0.4 to 1.24 mm), and depths of 0.030 to 0.075 in. (0.75 to 2.0 mm) are typical.

Finishing cuts are used to complete the part and achieve the final dimensions, tolerances, and surface finish.

Cutting speed, feed rate and depth of cut are lower. Feeds of 0.005 in./rev (0.125 mm) or above, and depths of 0.030 in. (0.75 mm) or lower.

Cutting conditions also include cutting fluid. It is used to cool and/or lubricate the cutting tool.

For cooling purpose: use water-based fluid,

For lubricating purpose: use oil-based fluid,

Or use combined fluid for both purposes.

Cutting speed v,

Feed f,

Depth of cut d

Material Removal Rate (MRR):

	MRR = v f d
		Unit for MRR: in.³/min (mm³/s),
		Unit for v: ft/min (m/s),
		Unit for f: in.(mm),
		Unit for d: in.(mm).

Machine Tools:

A machine tool is used to hold the workpart (stiffly), position the tool (accurately) relative to the work, and provide power for the machining process at the speed, feed, and depth that have been set. By controlling the tool, work, and cutting conditions, machine tools permit parts to be made with great accuracy and repeatability to the given tolerances.

The term machine tool applies to any power-driven machine that performs a machining operation.

Created by Dr. Wang