Exam 3 Study Questions

Question 1

Which one of the following is the starting work piece in hot rolling of steel plate and sheet stock?

Answer 1

Slab

Question 2

(T or F) Rolling is a bulk deformation process in which the thickness of the work is reduced by compressive forces exerted by two opposing rolls.

Answer 2

True

Question 3

Which one of the following stress or strength parameters is used in the computation of the maximum force in a forging operation:

Answer 3

Final Flow Stress

Question 4

Which three of the following operations are closely related to open-die forging?

Answer 4

Cogging, Fullering, and Upsetting

Question 5

In metal extrusion, the extrusion ratio is also known by which two of the following terms?

Answer 5

Area Reduction, Reduction Ratio

Question 6

Which of the following stress or strength parameters is used in the computation of rolling force?

Answer 6

Average Flow Stress

Question 7

Johnson’s formula is associated with which one of the four bulk deformation processes?

Answer 7

Extrusion

Question 8

(T or F) The production of tubing is possible in indirect extrusion but not in direct extrusion.

Answer 8

True

Question 9

Flash in impression die forging serves no useful purpose and is undesirable because it must be trimmed from the part after forming.

Answer 9

True

Question 10

In which of the following extrusion operations is friction is a factor in determining the extrusion force?

Answer 10

Direct Extrusion

Question 11

(T or F) Flow curve describes the stress-strain relationship in a metal during the elastic deformation state.

Answer 11

False

Question 12

( T or F) One of the disadvantages of cold forming operations is the requirement of higher forces and power required to perform the operation.

Answer 12

True

Question 13

(T or F) Hot working operations of metals are deformation processes performed below the recrystallization temperature.

Answer 13

False

Question 14

(T or F) Isothermal forming operations refers to forming operations which involves preheating the tools that come in contact with the part to the same temperature as the work metal.

Answer 14

True

Question 15

(T or F) The maximum possible draft in rolling operation depends on the coefficient of friction.

Answer 15

True

Question 16

The property of metal that results in increasing values of flow stress as it is deformed is which of the following?

Answer 16

Strain Hardening

Question 17

The applied force in an extrusion operation is based on which of the following flow stress values?

Answer 17

Average Flow Stress

Question 18

Forgeability is defined as the capability of a material to undergo deformation in forging without cracking. Select the metal which has the highest forgeability.

Question 19

In metal extrusion, the extrusion ratio is also known as which of the following terms?

Answer 19

Reduction Ratio

Question 20

Which Forging process produces flash?

Answer 20

Impression-die forging process

Question 21

Which of these bulk deformation processes produce discrete products?

Answer 21

Forging process

Question 22

What are the desirable properties of metals that are subjected to metal forming operations?

Answer 22

The desirable properties of metals that are
subjected to metal forming operations include low yield
strength and high ductility. These properties for forming
must be balanced against the properties that are
important to the function of the part.

Question 23

What are some of the advantages of hot working relative to cold working?

Answer 23

Advantages of hot working relative to cold working are (1) the
shape of the work part can be significantly altered, (2) lower forces and
power required, (3) metals that usually fracture in cold working can be
hot-formed, (4) strength properties are generally isotropic, and (5) no
strengthening of the part due to strain hardening.

Question 24

How does increasing temperature affect the parameters in the flow curve equation?

Answer 24

Increasing temperature decreases both K and n in the flow curve equation.

Question 25

Why friction is generally undesirable in metal forming operations?

Answer 25

Reasons why friction is undesirable in metal forming include the following: (1) it inhibits metal flow during deformation, causing residual stresses and possible defects; (2) it increases forces and power required; and (3) it increases wearing of the tools.

Question 26

Name the factors to consider in choosing the lubricant for metal working operations. What are the benefits of lubrication in metalworking operations?

Answer 26

Metalworking lubricants are applied to the tool-work interface in many forming operations to reduce the harmful effects of friction. Benefits of lubrication:  Reduced sticking  Reduced forces, power and tool wear  Improved surface finish Factors to consider in choosing an appropriate metalworking lubricant include:  Type of forming operation (rolling, forging, etc.)  Whether used in hot working or cold working  Work material  Chemical reactivity with the tool and work metals (it is desirable for the lubricant to the adhere to the surfaces to be most effective in reducing friction)  Ease of application  Toxicity  Flammability  Cost

Question 27

What are the principles of Design for Environment (DFE)? Summarize the steps that can be taken by a manufacturing company to adopt Environmentally Conscious Manufacturing processes.

Answer 27

Design for Environment (DFE) primarily involves following these two basic approaches: – Design products that minimize their environmental impact – Design processes that are environmentally friendly. DFE inherently involves decreasing waste in all manufacturing. The primary focus should be on improving the efficiency in all manufacturing operations thereby reducing the power requirements. Efforts should be made to reduce or eliminate power sources that require fossil fuels, especially power generated using fossil fuels, burning of which results in pollution of the environment. Products wear out and disposed of in landfills with the associated environmental degradation. DFE Starts from product design stage. Some of the programs that could be implemented could include: – Select materials that require minimum energy to produce – Select processes that minimize waste of materials and energy. – Design parts that can be recycled or reused – Designing products that minimize the use of hazardous and toxic materials – Giving attention to how the product will be disposed of at the end of its useful life. – Adopting good housekeeping practices – keeping the factory clean. – Preventing pollutants from escaping into the environment (rivers and atmosphere) – Minimize waste of materials in unit operations. – Recycling rather than discarding waste materials. – Using net shape processes – Using renewable energy sources when feasible. – Maintaining production equipment so that it operates at maximum efficiency – Investing in equipment that minimizes power requirements.

Question 28

Make a list of parts that can be made by a. Shape rolling b. Thread rolling

Answer 28

SOLUTION Shape rolling Solution: Parts that can be made by shape rolling include railroad rails, I-beams, and other structural channels. Thread rolling Solution: Thread rolling obviously produces bolts and screws, but also can produce threaded surfaces on anything that needs to be assembled through mechanical fasteners.

Question 29

List the possible consequences of rolling at a. Too high speed b. Too low speed

Answer 29

Too high speed Solution: Rolling at high speed is advantageous in that production rate is increased, but it has disadvantages as well, including: * The lubricant film thickness entrained will be larger, which can reduce friction can lead to a slick mill condition where the rolls slip against the workpiece. This can lead to a damaged surface finish on the workpiece. * The thicker lubricant film associated with higher speeds can result in significant oil peel, or surface roughening. * Because of the higher speed, chatter may occur, compromising the surface quality or process viability. * There is a limit to speed associated with the motor and power source that drive the rolls. Too low speed Solution: Rolling at low speed is advantageous because the surface roughness in the workpiece can match that of the rolls, which can be polished. However, rolling at too low a speed has consequences such as: * Production rate will be low, and thus the cost per unit weight will be higher. * Because a thick lubricant film cannot be developed and maintained, there is a danger of transferring material from the workpiece to the roll (pickup), thus compromising surface finish. * The workpiece may cool excessively before contacting the rolls. This is because a long biller that is rolled slowly loses some of its heat to the environment and also through conduction through the roller conveyor

Question 30

List the defects commonly found in flat rolling? How can you prevent them?

Answer 30

Defects in rolled plates or sheets can be present on the surfaces as well as internal structural defects. Defects in general are undesirable not only because they affect surface appearance, but also because they may affect strength, formability, and other characteristics of the rolled products. Surface defects include scale, rust, scratches, gauges, pits and cracks. Oher commonly found defects in rolling operation are shown in Figure 1 (a-d). These are: * Wavy edges * Zipper cracks * Edge cracks * Alligatoring These defects can be prevented by monitoring the quality of the original cast material, rolling conditions and roll surface quality.

Question 31

In rolling of a steel, what are the differences between a bloom, slab, and a billet?

Answer 31

The steel rolling mills uses the cast steel ingot as the starting point. The cast ingot is moved to the rolling mill, where it is rolled into one of three intermediate shapes called blooms, billets or slabs. * A bloom has a square cross section 10 mm / 150 mm (6” x 6”) * A slab is rolled from an ingot or a bloom and has a rectangular cross section of width 250 mm (10 in) or more and thickness 40 mm (1.5 in) or more. * A billet is rolled from a bloom and is square with dimensions 40 mm (1.5 in) on a side or larger. These intermediate shapes are subsequently rolled into final product shapes.

Question 32

What is “sticking” in a hot-rolling operation?

Answer 32

Sticking in hot rolling operation refers to a condition, in which the hot work surface adheres to the rolls over the contact arc. This condition often occurs in the hot rolling of steel and high-temperature alloys. When sticking occurs, the coefficient of friction can be as high as 0.7. The consequence of sticking is that the surface layers of the work are restricted to move at the same speed as the roll speed, and below the surface, deformation is more severe in order to allow passage of the piece through the roll gap.

Question 33

List some of the products produced in a rolling mill.

Answer 33

Rolling process can produce: Plates – for ships, bridges, structures, machines Sheet metal – for car bodies, aircraft fuselages, appliances, containers Foils – for packaging I-beams, railroad rails, architectural shapes Large rings Seamless pipe and tubing Bolts Screws Threaded components