Spinning -> PM Processing (H) Flashcards
What is SPINNING?
(https://www.youtube.com/watch?v=43N44ICyuEU)
A sheet metal process used to create circular axisymmetric shapes
MANDREL
Mold with the shape of the internal dimensions and configuration of the desired final part
SPINDLE
Rotates the MANDREL at the necessary speed
TAIL STOCK
Clamps the BLANK cut from the sheet metal against the end of the mandrel
ROLLER/SCISSOR TOOL
Pushes the BLANK over the MANDREL to create the shape
CNC
Computer Numerical Controls
CONVENTIONAL SPINNING
The BLANK remains of constant thickness
SHEAR SPINNING
The BLANK is thinned and the diameter decreases
How to determined it was made with SPINNING?
Tell-tale manufacturing marks will be circumferential (hoop)
DEEP DRAWING and FORMING
Faster than SPINNING
Leave longitudinal marks
PLATE
Metal with thickness of 1/4 in or more
EXPLOSION FORMING (https://www.youtube.com/watch?v=uYL-N01tL-0&feature=youtu.be)
Technique that uses explosions to force metal into dies and molds
EXPLOSION FORMING ADVANTAGES
Shockwaves
Deadens Sound
Cools
Suppresses Flash
Catches Debris
Other examples of EXPLOSION FORMING
EXPLOSIVE BULDGING (
HYDROFORMING (fluid pressure to shape metal)
MAGNETIC PULSE FORMING/ INDUCTIVE PULSE FORMING
Shaping of sheet metal using electromagnetic fields
Types of MAGNETIC PULSE FORMING
MAGNETIC PULSE BULDGING
MANGETIC PULSE CRIMPING
MAGNETIC PULSE FORMING
POWDER METALLURGY PROCESSING
Powdered metal is used as stock material
TUNDISH
Cup which metal is poured through to steady the stream and prevent splashing
Which metals cannot be used for this technique?
TUNGSTEN (high melting point)
TITANIUM (reactive when molten)
COMPACTION
Powdered metal is placed in a DIE CAVITY with the cross section of the desired part, and it is punched by a PRESS
GREEN COMPACT (GREEN STATE)
Powdered metal has been fully PRESSED and highly porous. Intense stress is generated at small points of contact causing limited fusion between particles.
GREEN MEANS INCOMPLETE
CORES
Only straight or tapered holes can be created (no curves or dovetails)
ISOSTATIC COMPACTION (to make stock material for PM)
Powdered metal is placed in a flexible rubber bag and then sealed inside a chamber. Pressurized fluid applied in all directions uniformly densifies the bag.
POLYMER BINDER
Added to metals like Tungsten Carbide to help it stay in a GREEN COMPACT STATE
SINTERING
GREEN COMPACT is placed in a SINTERING OVEN to reduce the porosity
Steps of SINTERING
- PREHEAT ZONE
- HOT ZONE (MAX TEMP -> 1/2 Melting Point)
- COOLING ZONE
SINTERING OVENS need
custom non-oxidizing atmospheres that involve HYDROGEN and/or NITROGEN
PM PROCESSING is mainly chosen because
It can create EXOTIC PROPERTIES due to MIXING and DISTRIBUTION in the DIE
(Two different powders MIXED together or DISTRIBUTED in layers)
IMPREGNATION
Pores are filled with fluid after air is drawn out in a vacuum chamber (OIL IMPREGNATED BEARINGS) (Surface tension prevents oil from coming out)
Another application of IMPREGNATION is
Titanium medical implants, where pores are filled with growth hormone to encourage anchoring by tissue growth. Used for hip and knee implants.
Strength of PM parts is similar to that of FORGING because
The grain size in PM parts is the same as the powder particle size used
PM Advantages
1.No waste
2.Forge-like Strength (small grains)
3.Good for refractory metals(tungsten carbide)
4.Good for reactive metals (titanium)
5.Exotic properties (mixing + distributing powders)
6. Impregnation (bearing oil and implant growth hormone)
7. Porosity (filters, mufflers and light weight)
PM Disadvantages
- High Costs of Powders
- Only simple shapes and straight passageways
- Shrinkage (during sintering)
