Environmental Engineering Reference
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into. a. vapor. or. plasma. form,. which. is. then. deposited. onto. the. substrate,.
typically.in.a.thin.ilm.
.
3.. (Micro-)structure change processes. . Most. often. used. to. modify. proper-
ties.rather.than.geometry,.structure.change.processes.typically.involve.heat.
treatment.to.remove.residual.stresses,.increase.ductility,.and/or.harden.sur-
faces.(e.g.,.precipitation.hardening)..The.process.can.be.used.as.an.interme-
diate.step.in.combination.with.other.processes.such.as.forging.to.enhance.
the.ability.to.create.the.desired.geometry.without.fracturing.the.material..
A. more. recent. variation. on. these. processes. is. ion. implantation,. which. is.
used.extensively.in.the.semiconductor.industry..The.implantation.of.small.
amounts. of. impurity. atoms. changes. the. chemical. structure. and. thus. the.
electronic.and.physical.properties.of.the.material.
.
4.. Deformation processes. . These. processes. require. some. level. of. ductility.
in. the. material.. Constant. cross-sections. such. as. sheet,. rod,. tube,. etc.. can.
be. extruded. through. a. die. of. the. desired. shape.. Other. geometries. can. be.
created. by. matched. die. molding,. forging,. thermostamping,. etc.. In. addi-
tion.to.creating.the.desired.shape,.the.process.can.be.used.to.modify.the.
material,.typically.hardening.the.material.with.repeated.impacts,.such.as.in.
forging..For.metals,.many.deformation.processes.are.combined.with.struc-
ture. change. processes.. The. material. is. softened. with. heat. (annealing). to.
increase.its.ductility.both.before.deformation.and.after.to.reduce.residual.
stresses.
.
5.. Consolidation processes. .Typically.used.for.materials.that.are.brittle.and.
have. high. melting. temperatures,. consolidation. processes. are. commonly.
used. for. ceramics. and. high. melt. temperature. metals.. The. materials. are.
initially.in.a.powder.form,.which.is.then.combined.with.a.liquid.to.produce.
a.slurry.that.lows.into.the.mold..Pressure.and.heat.are.then.used.to.compact.
the.material.and.sinter.the.powders.together.to.obtain.strength.
The.choice.of.manufacturing.process,.or.in.some.cases.the.creation.of.new.pro-
cesses,.depends.on.a.multitude.of.factors,.including.geometry,.dimensional.tolerance,.
number.of.parts,.and.material..Examples.of.some.common.design.decision-making.
aspects.are:
Geometry: complex vs. simple. . Shapes. requiring. constant. cross-sections.
can.be.made.in.continuous.production,.usually.by.forcing.material.through.
a.die.of.the.desired.cross-section..For.example,.electrical.wires.are.coated.
with.insulation.by.forcing.the.conductive.copper.wires.through.a.slightly.
larger.circular.hole.in.the.presence.of.a.molten.polymer,.which.forms.a.thin.
coating. on. the. wire.. Similarly,. large. aluminum. I-beams,. channels,. pipes,.
and.rods.are.extruded.in.continuous.production..Pulling.instead.of.pushing.
is.necessary.for.iber-reinforced.composites;.hence.the.variation.is.pultru-
sion.. One. step. up. in. complexity. is. the. fabrication. of. simple. but. not. con-
stant. cross-section. geometries.. These. shapes. can. be. formed. easily. using.
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