Exam 2

Question 1

Name the two basic categories of casting processes

Answer 1

Expendable & Permanent

Question 2

What are two types of patterns used in sand-casting?

Answer 2

Split & Match-plate

Question 3

What is the difference between a split pattern and a match-plate pattern?

Answer 3

Split: consists of two pieces
Match-plate: consists of two split patterns attached to opposite sides of a plate

Question 4

What is a chaplet?

Answer 4

Metal supports of various designs used to hold the core in place in the sand mold

Question 5

What is the Anitoch process?

Answer 5

Refers to the making of the mold. The mold is 50% sand and 50% plaster heated in an autoclave and then dried. This mold has greater permeability than a plaster
mold.

Question 6

What are the most common metals used in die casting?

Answer 6

Zinc, tin, lead, aluminum, brass and magnesium

Question 7

What is a cupola?

Answer 7

A vertical cylindrical furnace equipped with a tapping spout near its base. Cupolas are used for melting cast irons.

Question 8

Explain the sand-casting process

Answer 8

Involves the pouring of molten metal into a cavity-shaped sand mould where it solidifies

Question 9

What are some of the operations required in sand casting after the casting is removed from the mold?

Answer 9

1) Trimming
2) Core removal
3) Surface cleaning
4) Inspection
5) Repair if needed
6) Heat treatment
7) Machining

Question 10

What are some of the general defects encountered in casting processes? Name and briefly describe three

Answer 10

1) Misruns: the casting solidifies before filling the mold cavity
2) Cold Shuts: two portions of metal flow together but there is lack of fusion at the joint
3) Cold Shots: solid globules of cast metal become entrapped in the casting
4) Shrinkage cavity
5) Microporosity
6) Hot tearing

Question 11

What are the differences between bulk deformation processes and sheet metal processes?

Answer 11

Bulf deformation: significant deformations and massive shape changes surface area-to-volume ratio of starting material is relatively small
Sheet metal: forming and cutting operations performed on metal sheets, strips, and coils surface area-to-volume ratio of starting material is high

Question 12

Extrusion is a fundamental shaping process. Describe it

Answer 12

A compression process in which the work metal is forced to flow through a die opening, thereby taking the shape of the opening as its own cross section.

Question 13

Why is the term pressworking often used for sheet metal processes?

Answer 13

The machines used to perform these operations are presses

Question 14

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

Answer 14

Strength and strain hardening are both reduced at higher temperatures

Question 15

Indicate some of the advantages of cold working relative to warm and hot working

Answer 15

• greater accuracy, meaning closer tolerances can be achieved
• better surface finish
• higher strength and hardness of the part due to strain hardening
• grain flow during deformation provides the opportunity for desirable directional properties to be obtained in the resulting product
• no heating of the work is required, which saves on furnace and fuel costs and permits higher production rates.

Question 16

Why is friction generally undesirable in metal forming operations?

Answer 16

• forces and power to perform the operation are increased
• tool wear can lead to loss of dimensional accuracy, resulting in defective parts and requiring replacement of the tooling.

Question 17

What is sticking friction in metalworking?

Answer 17

The tendency for the two surfaces in relative motion to adhere to each other rather than slide (Sticking).

Question 18

What are the three basic categories of material removal processes?

Answer 18

1) Conventional maching
2) Abrasive processes
3) Nontraditional processes

Question 19

What distinguishes machining from other manufacturing processes?

Answer 19

In machining, material is removed from the work part so that the remaining material is the desired part geometry.

Question 20

Identify some of the reasons why machining is commercially and technologically important

Answer 20

1) It is applicable to most materials
2) It can produce a variety of geometries to a part
3) It can achieve closer tolerances than most other processes
4) It can create good surface finishes

Question 21

Name the three most common machining processes

Answer 21

1) Turning
2) Drilling
3) Milling

Question 22

What are the two basic categories of cutting tools in machining? Give two examples of machining operations that use each of the tooling types.

Answer 22

1) Single-point tools: turning & boring
2) Multiple-edge cutting tools: milling & drilling

Question 23

Explain the difference between roughing and finishing operations in machining

Answer 23

Roughing: used to remove large amounts of material rapidly and to produce a part geometry close to the desired shape
Finishing: follows roughing and is used to achieve the final geometry and surface finish

Question 24

Name and briefly describe the four types of chips that occur in metal cutting

Answer 24

(1) discontinuous: the chip is formed into separated segments
(2) continuous: the chip does not segment and is formed from a ductile metal
(3) continuous with built-up edge, which is the same as (2) except that friction at the tool-chip interface causes adhesion of a small portion of work material to the tool rake face
(4) serrated: 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.

Question 25

Why are metals heat treated?

Answer 25

to effect metallurgical changes that beneficially alter properties

Question 26

What does the term annealed mean?

Answer 26

To heat then cool a material usually for softening and making less brittle

Question 27

Identify the important reasons why metals are annealed

Answer 27

1) to control properties
2) to reduce brittleness and improve toughness
3) to recrystallize cold-worked metals
4) relieve stresses from prior metalworking

Question 28

What is the most important heat treatment for hardening steels?

Answer 28

Martensite formation

Question 29

What is the mechanism by which carbon strengthens steel during heat treatment?

Answer 29

When steel containing carbon is heat-treated, martensite is formed which is a hard and brittle non-equilibrium phase of steel

Question 30

Define hardenability

Answer 30

The relative capacity of a steel to be hardened by transformation to martensite

Question 31

Name some of the elements that have the greatest effect of the hardenability of steel

Answer 31

Chromium, manganese, molybdenum, and nickel