Manufacturing Chapter 20

Conventional machining

Material removal using a sharp cutting tool to mechanically cut the material to achieve geometry

Predominant cutting action in machining involves:

shear deformation of the work material to form a chip

According to the Merchant equation, an increase in rake angle has which two of the following effects, all other factors being the same? Select all that apply.

1. Increase in shear plane angle 2. Decrease in power requirements

Disadvantages of machining

1. Wasteful of material 2. Time-consuming

Which one of the following metals would usually have the lowest specific energy in a machining operation?

Aluminum

Finishing

Grinding, polishing, and cutting operations sometimes required for glass products

Size effect

In machining and grinding, the increase in specific energy and unit power that results from decreasing the feed and chip size

The most frequently used sensor technology for measuring temperatures in machining is which one of the following?

Thermocouple

Specific energy in metal machining is a measure of the amount of energy required to remove a unit volume of material.

True

A lathe is used to perform which one of the following manufacturing operations?

Turning

As a chip is removed by the cutting edge of the tool:

a new surface is exposed

The material removal processes are a family of shaping operations in which excess material is removed from a starting work part so that what remains is the desired final geometry.

True

Finishing operations are performed at

low feeds and depths. Feeds of .125-.4 mm/rev and depths of .75-2mm

Cutting speeds are

lower in roughing than finishing

Feed motion is achieved by

the cutting tool moving in a direction slowly in a direction parallel to the axis of rotation to the workpiece

The speed motion in turning is provided by

the rotating work part

Which two of the following cutting conditions are factors in the Cook equation for calculating cutting temperature? Select all that apply.

1. Chip thickness before the cut 2. Cutting speed

The tool in orthogonal cutting has only two elements of geometry

1. Rake angle 2. Clearance angle

Four common types of machining processes

1. Turning 2. Drilling 3. Peripheral milling 4. Face milling

Machining is important commercially and technologically for several reasons

1. Variety of work materials 2. Variety of part shapes and geometric features 3. Dimensional accuracy 4. Good surface finishes

Which three of the following are features of the orthogonal cutting model? Select all that apply.

1. When two elements of tool geometry are rake angle and relief angle 2. When the cutting edge is perpendicular to the direction of cutting speed 3. When only two dimensions play an active role in the analysis

Of the total energy consumed in a machining operation, what proportion of the energy is converted to heat?

98%

Material removal processes

A family of shaping operations in which excess is removed from a starting work part so that what remains is the desired geometry

Turning

A machining operation in which a single-point cutting tool removes metal from a rotating, usually cylindrical, workpiece to reduce its diameter

Computer numerical control

A numerical control system in which the MCU is a computer

Machine tool

A tool refers to to any power-driven machine that performs a machining operation, including grinding

Single-point tool

A tool that has one cutting edge and is used for operations such as turning

Specific energy U

Also known as unit power

Cutting fluid

Any liquid or gas that is applied directly to the machining operation to improve cutting performance

Good surface finishes

Capable of very smooth surface finishes. Roughless value of less than .4 microns can be achieved in conventional machining operations. Some abrasive processes can achieve even better finishes

The chip thickness ratio in orthogonal cutting is which one of the following?

Chip thickness before the cut divided by chip thickness after the cut.

Roughing

Cuts used to remove large amounts of material from the starting work part as rapidly 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

Which one of the following cutting conditions has the strongest effect on cutting temperature?

Cutting speed

As feed in a turning operation increases, unit power ___________________.

Decreases

Which one of the four types of chip is most likely in a turning operation conducted at low cutting speed on a brittle work material?

Discontinuous.

With which one of the following geometric forms is the turning operation most closely associated?

External cylinder

When using the orthogonal cutting model to approximate a turning operation, the chip thickness before the cut corresponds to which one of the following cutting conditions in turning?

Feed

Normal force to friction N

Force perpendicular to the friction force

Friction Force F

Frictional force resisting the flow of the chip along the rake face of the tool

Which two of the following manufacturing processes are classified as material removal processes? Select all that apply.

Machining and grinding

Variety of part shapes and geometric features

Machining can be used to create any regular geometries, such as flat planes, round holes, and cylinders. By introducing variations in tool shapes and tool paths, irregular geometries can be created, such as screw threads and gear teeth. By combining several machining operations in sequence, shapes of almost unlimited complexity and variety can be produced.

Dimensional accuracy

Machining can produce dimensions to very close tolerances. Some machining processes can achieve tolerances of +- .025mm, much more accurate than other practices

Wasteful of material

Machining is inherently wasteful. The chips generated in a machining operation are wasted material. Although these chips can usually be recycled, they represent waste in a unit operation

Drilling

Machining operation in which a drill bit rotating relative to the work part is fed into the work along the axis of rotation to create a round hole

Milling

Machining operation in which a work part is fed past a rotating tool with multiple cutting edges to generate a plane or straight surface

Nontraditional processes

Material removal processes that use lasers, electron beams, chemical erosion, electric discharges, and electrochemical energy to remove material rather than a sharp cutting tool or abrasive particles

The cutting force and thrust force in an orthogonal cutting operation are best described as which one of the following?

Perpendicular to each other.

Abrasive processes

Processes that mechanically remove material by the action of hard, abrasive particles

The mechanism of chip formation in machining is best described by which one of the following?

Shear deformation

Orthogonal

Simplified, two-dimensional model of machining that neglects many of the geometric complexities, yet describes the mechanics of the process quite well

Among the forces acting on the chip during orthogonal cutting, the friction force is best described as which one of the following?

The frictional force resisting the flow of the chip along the rake face of the tool.

Serrated chip

These chips are semi-continuous in the sense that they possess a saw-tooth appearance that is produced by a cyclical chip formation of alternating high shear strain followed by low shear strain. This fourth type of chip is most closely associated with certain difficult-to-machine metals such as titanium alloys, nickel-base superalloys, and austenitic stainless steels when they are machined at higher cutting speeds. However, the phenomenon is also found with more common work metals (e.g., steels) when they are cut at high speeds

Multiple-cutting-edge tools

Tools that have more than one cutting edge and usually achieve their motion relative to the work part by rotating

A single-point cutting tool is used for which one of the following operations?

Turning

Variety of work materials

Virtually all solid metals can be machined. Plastics and plastic composites can also be cut by machining. Ceramics pose difficulties because of their high hardness and brittleness

Continuous chip

When ductile work materials are cut at high speeds and small feeds and depths, long continuous chips are formed. A good surface finish typically results when this chip type is formed. A sharp cutting edge on the tool and low tool-chip friction encourage the formation of continuous chips. Long, continuous chips (as in turning) can cause problems with regard to chip disposal and/or tangling about the tool. To solve these problems, turning tools are often equipped with chip breakers

Continuous chip with built up edge

When machining ductile materials at low-to-medium cutting speeds, friction between tool and chip tends to cause portions of the work material to adhere to the rake face of the tool near the cutting edge. This formation is called a built-up edge (BUE). The formation of a BUE is cyclical; it forms and grows, then becomes unstable and breaks off. Much of the detached BUE is carried away with the chip, sometimes taking portions of the tool rake face with it, which reduces the life of the cutting tool. Portions of the detached BUE that are not carried off with the chip become imbedded in the newly created work surface, causing the surface to become rough.

Discontinuous chip

When relatively brittle materials (e.g., cast irons) are machined at low cutting speeds, the chips tend to form into separate segments (they are sometimes loosely attached). This tends to impart an irregular texture to the machined surface. High tool-chip friction and large feed and depth of cut promote the formation of this chip type.

Roughing operations are performed at

high feeds and depths. Feeds of .4-.1.25 mm/rev and depths of 2.5-20mm

A cutting tool is

made of harder material than the work material and has one or more sharp cutting edges

Machining is most frequently applied to:

metals

In production machining

one or more roughing cuts are usually performed on the work, followed by one or two finishing cuts