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Flashcards in Chapter 10 Deck (24):
1

Explain the Powder Metallurgy production sequence (2)

Pressing: Compressed to a green compact using punch and die.

Sintering: Green compacts are heated to bond into a hard, rigid mass below melting point.

2

Main benefit of Powder Metallurgy (2)

The process is net shape or near net shape at 97% and very porous.

3

Why is Powder Metallurgy important (4)

Certain metals are difficult to shape .

Certain composites are are only possible thru powder metallurgy

Favorable compared to casting since dimensional control

Economic production because of automated production methods

4

Disadvantages of Powder Metallurgy (4)

High tooling and equip cost as well as expensive metallic powders

Metallic powders degrade over time and are a fire hazard

Metal powders do not flow laterally in the die during pressing

Variations in density

5

What are the work materials used in Powder Metallurgy (

Alloys of iron, steel, and aluminum. Copper, nickel, and refractory metals .

6

What metals can be turned into powders? And how? (3)

All metals.

Atomization
Chemical
Electrolytic

7

How does atomization work?

High velocity inert gas thru an expansion nozzle siphoning molten metal and spraying it into container

8

Explain the conventional powder metallurgy production sequence (3)

Blending - Same chemistry but can be different sizes. Mixing refers to combining different chemistries together.

Compacting - Pressing (opposing punches squeeze powders in a die). After, called green compact since not processed.

Sintering - Temp at .7% to .9% of Tm. Purpose to reduce surface energy. Partial shrinking due to pore size reduction.

9

Go into the specifics of blending

Same chemistry. Then lubricant and binder are added to reduce friction and defects. When sintering, lubricant and binder are removed since it is very porous it is an easy escape.

Note that we use different particle size and material to add strength.

10

What is isostatic?

Compaction and sintering are done at the same time.

11

What are some secondary operations performed on sintered part? (4) And why? (3)

Repressing - Pressing in closed die to increase density and improve properties

Sizing - Pressing to improve dimensional accuracy

Coining - Pressing details into its surface

Machining - Geometric features such as threads and side holes. Not done during pressing.

Increase density, improve accuracy, or accomplish additional shaping

12

What is impregnation?

When oil, other fluids or polymer resins permeate into a sintered powder metallurgy part then solidify to create a pressure tight part.

13

What is infiltration? What is the result?

When the a part's pores are filled with a molten metal.

Melting point must be below that of the PM part.

Increase uniform density. Improve toughness and strength.

14

Name the three other alternatives to Pressing and Sintering

Isostatic Pressing - Hydraulic pressure is applied from all directions

Powder Injection Molding - Starting polymer has 50 to 80% powder content. Polymer is removed and PM part is sintered

Hot pressing - Combined pressing and sintering

15

Name the three common elemental powders

Iron, aluminum, and copper.

16

Name four classes of PM parts

Class I Simple thin shapes

Class II Simple but thicker

Class III Two Levels of thickness

Class IV Multiple levels of thickness

17

Class I

What is the minimum quantity? Maximum porosity?

10.000 units

50%

18

Class II

Requirements for part.

Must have vertical sides. Must not interfere with ejection.

19

Class III

What is possible? Minimum thickness b/w holes and outside wall?

Chamfers and corner radii are possible.

1.5 mm. Hole diameter must also be 1.5 mm

20

Guidelines for Chamfer and corner radii? (4)

Avoid acute angles 45 min.

Use larger angles for punch rigidity

Avoid full outside corner radius since punch fragile at edge. Flat 45 degree edge.

Combine radius and chamfer

21

Difference b/w lubricant and binders (3)

Lubricants such as graphite and stearic acid improve flow and compressibility. Decrease green strength.

Binders reduce flow and compressibility. Increase green strength.

22

Correlation b/w friction and particle (3)

Smaller particle greater friction.

Spherical shapes least friction

Easier flow, low friction

23

Classification of metallic powders

Elemental - particle -> pure element

Pre-alloyed - particle -> alloy

24

Why titanium expensive? (4)

Properties? (4)

High extraction cost

High alloying and ingot casting cost

high processing cost

Typical 10% utilisation

45% lighter than steel
4x corrosion resistant
High strength
Can be welded, forged, machined, etc