32 terms

ME 336 Final Exam 3

Describe a process for forming 8-foot section of gray iron pipe
Cast iron parts are made by sand casting; there may be a permanent core down the center
Describe a process for forming 20-foot long sections of rigid PVC sewer pipe
PVC softened using plasticizers; but sewer pipes are not very soft. PVC heat above Tg and extruded into shape.
Describe a process for forming 20-foot long sections of rigid Cu tubing
Ci tubing extruded using a mandrel & annealed or hot extruded with a steel die
Describe a process for forming 10-foot long sections of rigid stainless steel
Stainless steel pipe extruded and annealed; may need to cast if walls are thick
Describe a process for forming 6-foot long sections of laboratory glass tubing
Heat the glass above Tg and extrude it using a mandrel; die can be almost anything because stresses are not too high
Differences in welding cutting and spark machining
Spark machining uses a dielectric fluid to concentrate the arc into a small region & quench the ejected molten material with a pulsed power supply; arc welding doesn't have the dielectric fluid the power supply is continuous
What does thermal activation have to do with viscoelastic strains in polymeric materials?
viscoelastic polymer molecules are in constant thermally activated motion, and their motion is biased on applied stress
What does Tg have to do with viscoelastic strains in polymeric materials?
Tg is the boundary above which there is sufficient thermal energy constant molecular motion, allowing for viscoelastic strain to occur
The first crystals in a metal casting normally form at
the mold wall because the pre-existing surface reduces the energy barrier to nucleation
Coring may occur above the peritectic and
be followed by surrounding at the peritectic
Die castings tend to produce metal objects having very small grains because
the heat is conducted out through the metal mold very rapidly
The driving force for coarsening is
the reduction in surface area and surface energy.
Investment casting uses
a pattern made from a material with a low melting point
The best alloys for soldering
have low solidification ranges
One of the essential functions of the coating on a welding rod is
to provide a shielding gas
Precipittion-strengthened Al alloys are no considered weldable because
the welding process destroys the favorable precipitate distribution
Arrowhead defect may occur in extruded parts when
the surface regions are strained more than the interior regions
The pressure multiplying factor for frictionless axial upsetting is
A metal with a high ductility will have
a large limiting draw ratio when used in a deep drawing operation
Machinability is favored by low
strain rate sensitivity
Cemented carbide cutting tools consist of
WC, TiC, or TaC crystal bound together by cobalt metal
In Taylor's formula for tool life, namely vt^n=C, the exponent, n, characterizes the cutting material. n for high speed steel tools is
smaller than n for coated carbide tools
Ultrasonic machining is really
an abrasive process
Injection molding is suitable for
high-volume production of inexpensive thermoplastic parts
Blow molding is not applicable to simple metals because
metals solidify by a strongly first-order transformation in which a low viscosity liquid changes discontinuously to a rigid solid
A chopped fiber composite can behave like a continuously reinforced composite when
the bonding between fiber and matrix is strong
Bulk molding compounds consist of
chopped fibers in uncured thermoset resins
The green strength of a ceramic powder compact is
mainly due to secondary bonds between ceramic powders and the binder
The isoelectric point is
the pH of an aqueous slurry at which the powder particles have zero surface charge
Mass transport in PVD is
not by forced convection
Cryogenic treatment of tool steels may transform a small amount of retained austenite, but the effect
cannot readily explain practitioners' claims of profoundly enhanced wear resistance
Most of NASA's space based materials processing experiments have
not been run and reproduced well enough to produce good scientific value