Metal Manufacturing

Question 1

Casting

Answer 1

Process where molten metal flows by gravity or other force into a mold where it solidifies in the shape of the mold cavity

Question 2

Ingot

Answer 2

A large casting that is simple in shape and intended for subsequent reshaping processes

Question 3

Shape casting

Answer 3

Production of more complex geometries that are closer to final desired shape of part or product

Question 4

Advantages of casting

Answer 4

Can be used to create complex geometries, including both eternal and internal shapes

Some are capable of producing parts to net shape. No further manufacturing needed. Some only need some additional shape processing

Casting can make very large parts

Can be performed to any metal than can be heated to liquid state

Some are suited to mass production

Question 5

Disadvantages of casting methods

Answer 5

Limitations on mechanical properties, porosity, poor dimensional accuracy and surface finish for some. Safety hazards to humans when processing molten metal. Environmental problems

Question 6

Mold structural considerations

Answer 6

Contains cavity whose geometry determines shape of cast part. Must be slightly oversized to allow for shrinkage to occur during cooling. Diff metals shrink by different amounts so mold must be designed for a particular metal if dimensional accuracy is critical.

Question 7

Open mold

Answer 7

Liquid Metal poured until it fills the open cavity

Question 8

Closed mold

Answer 8

A passageway called a gating system is provided to permit molten metal to flow from outside the mold into the cavity.

Question 9

Expendable mold

Answer 9

Mold must be destroyed to remove the casting. Sometimes made out of sand or plaster, whose form is maintained by using binder of various casting

Question 10

Permanent mold

Answer 10

Mold that can be used over and over. Most often made of metal that can withstand high temps. Mold consists of two or more sections that can be opened to permit removal of the finished part. Did casting is most familiar process

Question 11

Permanent mold use vs expandable

Answer 11

Expandable can usually create more intricate geometries. Permanent mold have certain economic advantages in high production operations

Question 12

How is the riser designed

Answer 12

Cooling time of metal in riser must be greater than that in main casting. Has a larger volume to area ration

Question 13

What are the steps that cause shrinkage

Answer 13

Liquid contraction during cooling prior to solidification

Contracting during the phase change from liquid to solid called solidification shrinkage

Thermal contraction of the solidified casting during cooling at room temp.

Shrinkage is determined my metals coefficient of thermal expansion

Question 14

What is the cope of a sand cast

Answer 14

The upper half of the mold

Question 15

What is the drag of a sand cast

Answer 15

The bottom half of the mold

Question 16

What is the feast of a sand castle

Answer 16

The box that contains the cope and drag

Question 17

How is the cavity of a sand mold formed

Answer 17

By packing sand around a pattern. Sand for the mold usually is moist and contains a binder to maintain shape. A form, called a core, may be placed inside the cavity to design the interior geometry of the part.

Question 18

Use of downsprue in a gating system

Answer 18

Where metal enters runner

Question 19

Use of pouring cup in gating system

Answer 19

Minimize splash and turbulence as the metal flows into the downsprue

Question 20

What is a riser

Answer 20

A reservoir in the mold that serves as a source of Liquid Metal for the casting to compensate for shrinkage during solidification

Question 21

How do cats permit for air previously in cavity to leave

Answer 21

Sand is porose. Metal ones have small vent holes drilled in

Question 22

Investment casting

Answer 22

A pattern made of wax is coated with a refractory material to make the mold, after which the wax is melted. Capable of making high accuracy intricate detail. Usual,y accomplished by mold ring or injecting the hot wax into a master die with allowances for shrinkage of wax and subsequent metal casting. When complex, several wax pieces must be joined. Then pattern tree dipped into powdered refractory material mixed with plaster. Final mold is achieved by continuing to dip or gently pack around pattern tree.

Question 23

Advantages of investment casting

Answer 23

Parts of greater complexity and intricacy

Close dimensional control tolerances are possible

All types of metals can be cast

Good surface finish

Wax can be recovered and reused

Additional machining not usually required after

Question 24

Disadvantages of investment casting

Answer 24

Relatively expensive as many steps involved

Normally small in size

Question 25

Why is steel unsuitable for permanent molds

Answer 25

The very high pouring temperature unless mold is made of a refractory material.

Question 26

Semi-permanent mold casting

Answer 26

When a sand core is used in permanent mold casting as withdrawal of metal more not possible

Question 27

Process of semi permanent mold casting

Answer 27

Mold is preheated and prayed (preheating facilitates metal flow through gating system and coating aids head dissipation and lubricates for easier separation of pruducg and mold). Mega, pored in a solidifies Mold is opened before appreciable cooling contraction occurs to prevent cracks from developing

Question 28

Advantages of permanent mold casting

Answer 28

Good surface finish and close dimensional control. Rapid solidification caused by metal mold results in finer grain structure so stronger castings are produced

Question 29

Disadvantages of permanent mold casting

Answer 29

Limited to metals of lower melting points Simple part geometries Mold cost is substantial

Question 30

Die casting

Answer 30

Permanent mold casting process where molten metal is injected into the mold cavity under high pressure. Pressure is maintained during solidification. Molds in this process are called dies.

Question 31

What are the two types of die casting

Answer 31

Hot chamber and cold chamber

Question 32

Hot chamber machines

Answer 32

Metal is melted in container attached to machine and a piston is used to inject the Liquid Metal under high pressure in the die.

Question 33

Cold chamber die casting

Answer 33

Molten metal is poured into an unheated chamber from an external melting container and a piston is used to inject the metal under high pressure into die cavity.

Question 34

Cold vs hot chamber casting

Answer 34

Cold chamber cycle rates are usually slower as need to ladle the Liquid Metal in the chamber from external source

Question 35

Ejector pins

Answer 35

Remove the part from the die when it opens

Question 36

Post processing of die casting

Answer 36

Metal fill vents so must be trimmed off. Flash is common in , when metal under high pressure squeezes into the small space between the die halves

Question 37

Advantages of die casting

Answer 37

High production rates Economical for large production quantities Close tolerances possible Good surface finish This sections are possible Rapid cooling provides small grain size and good strength

Question 38

Limitation of die casting

Answer 38

Shape restriction

Question 39

Considerations for casting

Answer 39

Geometric simplicity- simplifying design will improve cast ability, reduces need for cores and and improves strength Corners- avoid sharp as they are sources of stress concentration and may cause hot tearing and ctacks in the casting Section thickness- uniform thickness to avoid shrinkage cavities, thicker sections create hot spots as greater volume requires more time for solidification. These are likely location of shrinkage cavities. Draft- sections that project into the mold should have a draft. For expandable molding, this is to facilitate removal of patter from the mold. In pattern it is to aid removal of part. Use of cores try to reduce need Dimensional tolerances- difference in dimensional accuracy depending on method Surface finish- roughness in sand casting Machining allowances- additional material should be left on casting for machining those surfaces where necessary after