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Flashcards in Powder Metallurgy Review Questions Deck (15)
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importance of PM

  • Mass produced to create net-shape and near net-shape
  • Very little waste of materials
  • PM parts have a specific level of porosity
  • Can made shapes that are difficult for other methods
  • certain metal alloy combos and cermets can be formed
  • Tolerances around +/- 0.13mm
  • PM production methpods can be automated for economical production


disadvantage of PM

  • tooling and equipment cost are high
  • metallic powders expensive
  • difficulties in storing and handling powders
  • limitations in part geometries. powders dont flow laterally
  • variations in metal density throughout part may be a problem


What are principle methods used to produce PM powders







what are three basic steps used to produce PM

  1. blending and mixing of powders
  2. compaction
  3. sintering


what is technical difference between blending and mixing in PM

blending - when powders of same chemical composition but different particle sizes are intermingled


mixing - when powders of different chemistries are combined


what are some ingredients usually added to metallic powders during blending and/or mixing

  1. lubricants
  2. binders
  3. delocculants


what is meant by green compact

Pressed but not yet sintered


describe what happens to individual particles during compaction

Particles are repacked into a more efficient arrangement; followed by deformation of particles as pressure increases


what are 3 steps in sintering cycle of PM

  1. preheat - lubricants/binders burned off
  2. sintering
  3. cool down


What are some reasons why a controlled atmosphere furnace is desirable in sintering

  1. protect against oxidation
  2. provide reducing atmosphere to remove existing oxides
  3. provide carburizing atmosphere
  4. remove lubricants and binders from pressing


What is the difference between impregnation and infiltratrion in PM

impregnation - oil or other fluid is permeated into pores of sintered PM part


infiltration - molten metal is permeated through pore of sintered part


How is isostatic pressing distinguished from conventional pressing and sintering in PM

isostatic pressing - hydrostatic pressure applied to all sides of the mold


conventional pressing - uniaxial pressure


describe liquid phase sintering

two powders are mixed together and heated at a temp higher than the lowest melt temp of the two powders but not the melt temp of the other. melted metal wets the solid particles, creating a dense structure with bonding between the metals upon solidification


what are 2 basic classes of metal powders as far as chemistry is concerned

Elemental - pure metal and used when high purity is needed


Pre-Alloyed - each particle is an alloy composed of desired chemical compositions


why is PM Technology so well suited to production of gears and bearings

  • tolerances
  • near net shape
  • mass production
  • little to no waste material


(1) geometries lend themselves to PM Pressing

(2) porosity allows impregnation