Spin Casting -> Orbital Forging (D)

Question 1

what is CENTRIFUGAL CASTING/ SPIN CASTING?

Answer 1

A method used to make hollow castings without the need for a core. When the cylinder is spun, the centrifugal forces push the molten metal out to the periphery of the internal mold surfaces.

Question 2

CENTRIFUGAL CASTING can be performed horizontally or vertically. Why would one choose vertically?

Answer 2

When you need to create hollow shapes where the diameter to length ratio is large.

Question 3

How is it possible to produce any shape using CENTRIFUGAL CASTING?

Answer 3

By placing individual mold cavities around the central axis. Molten metal is introduced through a central sprue, with radial runners leading to the cavities.

Question 4

What is SLUSH CASTING?

Answer 4

Another permanent mold casting process capable of producing metal parts without a core. A smooth metal mold is filled with molten metal. The metal solidifies first where it is in contact with the metal surface. The mold can be inverted to allow the central part of the melt to flow out.

Question 5

When is SLUSH CASTING used?

Answer 5

When you want a superior external surface finish, but a good internal surface and consistent wall thickness are unimportant.

Question 6

What is SQUEEZE CASTING?

Answer 6

A dynamic casting process (one part f the die moves into another after the pour). The cavity is partially filled, such that the molten metal is forced to flow between the dies, making thin walls feasible.

Question 7

What is FORGING?

Answer 7

An ancient process that uses hammering (or pressing) to shape hot pliable metals.

Question 8

What is the goal of FORGING?

Answer 8

To improve metallurgical properties (to improve the metal’s properties)

Question 9

What is an INGOT?

Answer 9

All metal is initially purified and reduced to a molten state from ore, after which it is poured into a mold to become an ingot.

Question 10

What happens when a metal in an amorphous liquid state solidifies to a solid form?

Answer 10

It goes through a CRYSTALLIZATION PROCESS.

Question 11

What are GRAINS?

Answer 11

Individual patches of crystallization.

Question 12

What are CRYSTALS?

Answer 12

Lattice crosslinking that start from a large number of initiation sites within the liquid metal.

Question 13

What is a characteristic of a CAST STRUCTURE?

Answer 13

Weakness and poor strength. Cast metals undergo slow solidification which allows the grains to grow relatively large.

Question 14

How can the MICROSTRUCTURE of a cast structure be improved?

Answer 14

By reheating the metal below melting temp. but above the recrystallization temp. Then if the metal is hammered/crushed the large cast grains can be broken to smaller ones.

Question 15

How do the elevated temperature and hammering affect the WROUGHT STRUCTURE?

Answer 15

Elevated temperatures prevent micro-cracking and create a strong wrought structure. Hammering drives off impurities such as slag inclusions.

Question 16

What is OPEN DIE FORGING?

Answer 16

Essentially the same process as performed by a blacksmith, but on a larger scale. Generally only produces simple shapes since the main goal is to improve the microstructure.

Question 17

What is EDGING?

Answer 17

A process performed to move metal generally to more advantageous locations in preparation for use in a later process. Concave-shaped

Question 18

What is FULLERING?

Answer 18

A process performed to move metal generally to more advantageous locations in preparation for use in a later process. Convex-shaped

Question 19

How is it possible to create rings/doughnut shapes while OPEN DIE FORGING?

Answer 19

By driving a MANDREL through a block of material. The temperature must be maintained high enough throughout open die forging, otherwise microcracking will inevitably result. It may be necessary to reheat the billet (metal) several times.

Question 20

What is GRAIN FLOW?

Answer 20

The direction that the grains grow in.

Question 21

What is the key to strength, in terms of GRAIN FLOW?

Answer 21

The grain flow should ALWAYS flow parallel to the boundaries of the part.

Question 22

What is CLOSED DIE FORGING?

Answer 22

A hot pliable metal is forced to flow around inside a closed die cavity, where the grains are constrained to flow parallel with the boundaries.

Question 23

What is IMPRESSION DIE FORGING?

Answer 23

Similar to closed die forging. The dies are dovetailed into the base and of the machine, making die removal and replacement easy.

Question 24

What are the two forms of FORGING machines?

Answer 24

PRESSES and HAMMERS.

Question 25

What is a PRESS?

Answer 25

A press uses a slow hydraulically actuated downward movement.

Question 26

What is a HAMMER?

Answer 26

A hammer creates a rapid descending motion generally actuated by a flywheel. Usually smaller and less expensive, but can induce more cracking then presses.

Question 27

What is one issue with IMPRESSION DIE FORGING?

Answer 27

It can be difficult to correctly meter the exact amount of metal into the die cavity.

Question 28

What is the solution to the issue with IMPRESSION DIE FORGING?

Answer 28

Include a FLASH LAND and GUTTER which acts as an overflow system

Question 29

FORGING DEFECTS: not enough metal in the die results in what?

Answer 29

Leaves unfilled areas in the cavity.

Question 30

FORGING DEFECTS: metal in the die is not hot enough resulting in what?

Answer 30

Initial heat may cool too soon, requiring reheat stages.

Question 31

How can a FORGED PART be identified?

Answer 31

Simple passageways, a flash trim line, uneven surface finish, but not uniformly granular (cornflakes on putty).

Question 32

Why must holes be created during FORGING using pins within the die cavity?

Answer 32

Drilling the holes after the forging process will cut through the grain flow and compromise strength.

Question 33

What is COINING?

Answer 33

Coining creates surface designs (usually different) in relief (raised) on both sides.

Question 34

What is EMBOSSING?

Answer 34

Embossing creates the same design on both sides, one in relief (raised) and the other in intaglio (indented).

Question 35

What are BOLTS?

Answer 35

Commonly used in engineering and often in critical strength applications.

Question 36

What is HEADING the bolt?

Answer 36

A process used to form the bolt head by deforming material radially outward.

Question 37

What is ORBITAL FORGING?

Answer 37

A superior and more expensive method of heading. This combines radial and circular motions of the upper punch, which results in a swirling grain flow that is always parallel to the boundaries.