What is characteristic for the drawing process?
cold process
lubrication paramount
What materials are drawing dies made from?
tool steels
hard metals (WC-Co)
diamond
Name the components:
payoff reel
lubrication box
die
draw block
motor
drive
what is understood under dry drawing
lubrication with dry lubricant (eg. solid soap powder)
How is the elongation in drawing calculated?
How is the drawing force calculated?
What limits the drawability?
The tensile strain of the wire, which should not break
What is the meaning of beta in this equation?
triaxiality factor
Why is there an optimal angle for the drawing tool?
Because with increasing angle the force of friction decreases and the force needed to push the object through increases. There is an overall minimum.
Describe the pressure distribution over the length of the drawing die.
What explains the increased tensile strength of steel wires after drawing?
dislocation cells and grain allignment in drawing distance
How is the stress of a drawn wire be calculated?
What are the main surface defects in drawing?
Cracks in Martensite
Holes and cavities
Decarburization
What is a chevron crack?
Is the extrusion process generally a hot or a cold process?
Hot process
What lubrication is used for extrusion?
graphitic grease, graphite with MoS2, glass
What are the steps for indirect extrusion?
How can irregular shapes be extruded?
madrel with spiders:
first seperation then welding
Name the two forms of tube extrusion.
Direct extrusion
madrel (Dorn) is attached to ram
Impact extrusion
impact form thin hallow tubes
how is the elongation calculated for extrusion?
How is the specific plastic work calculated?
with beta= triaxiality factor
Describe the pressure distribution over the ram travel way
What are typical values for deformation, working speed and deformation rate for extrusion?
How is the deformation temperature rise calculated in extrusion?
Why is the temperature a limiting factor for the Extrusion process?
The temperature rises additionally due to plastic deformation and can lead to hot shortness and subsequent tearing.
What are defects in the extrusion process?
surface oxides
surface roughness
surface cracks
surface stresses due to friction with the die
ductile cracks
due to hot shortness
What are the limits for selecting the extrusion velocity?
Maximum extrusion load
Maximum extruded heating
Describe the relation between area reduction and opening angle for avoiding chevron cracks
What is the process for the extrusion of Al alloys?
What is the process temperature distribution for a precipitation hardening process?
What is the most common hardening treatment for extrusion dies for Al alloys?
Nitriding
Last changeda year ago
