Flashcards in Chapter 10 Deck (24):
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.
Main benefit of Powder Metallurgy (2)
The process is net shape or near net shape at 97% and very porous.
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
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
What are the work materials used in Powder Metallurgy (
Alloys of iron, steel, and aluminum. Copper, nickel, and refractory metals .
What metals can be turned into powders? And how? (3)
How does atomization work?
High velocity inert gas thru an expansion nozzle siphoning molten metal and spraying it into container
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.
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.
What is isostatic?
Compaction and sintering are done at the same time.
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
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.
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.
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
Name the three common elemental powders
Iron, aluminum, and copper.
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
What is the minimum quantity? Maximum porosity?
Requirements for part.
Must have vertical sides. Must not interfere with ejection.
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
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
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.
Correlation b/w friction and particle (3)
Smaller particle greater friction.
Spherical shapes least friction
Easier flow, low friction
Classification of metallic powders
Elemental - particle -> pure element
Pre-alloyed - particle -> alloy