Materials processing Metal parts undergo sequence of processes Primary alter the ( raw ) material s basic shape or form. Sand casting Rolling Forging Sheet metalworking Types of manufacturing processes Deformation Casting Sheet Metal Manufacturing Processes Polymer Processes How is the input material changed? Machining Finishing Assembly Secondary add or remove geometric features from the basic forms Machining of a brake drum casting (flat surfaces) Drilling/punching of refrigerator housings (sheet metal) Trimming of injection molded part flash Extrusion Forging Rolling Bar drawing Wire drawing Centrifugal Die casting Investment Permanent mold Sand casting Bending Blanking Drawing Punching Shearing Spinning Blow molding Casting Compression molding Extrusion Injection Molding Thermoforming Transfer molding Boring Drilling Facing Grinding Milling Planing Turning Sawing ECM, EDM Anodizing Honing Painting Plating Polishing Automated Bonding Brazing Manual Riveting Soldering Welding Tertiary surface treatments Polishing Painting Heat treating Joining Making a thingo Solid Plastic deformation Cold Hot Removal of material Sold state diffusion processes Liquid Casting
Making a thingo Solid Plastic deformation Metals Ceramics Polymers?? What properties allows us to do this? Structural Metals Properties Hardness Brittleness Malleable A metal that can be hammered, rolled or pressed into various shapes without cracking or breaking Ductility Property of metal that allows it to be permanently drawn, bent, or twisted into various shapes without breaking Elasticity Toughness plastic clays Binders added to ceramics powders Structural Metals Selection Factors Strength 5 factors effecting strength are tension, compression, shear, bending & torsion Types of manufacturing processes
FFABRICATIONM METHODS solid P Part/Mfg.Proce essconsiderations D Deformationpro ocesses R Rolling EExtrusion D Drawing FForging SSolid Plasticde eformation R Rolling(ofductile ematerials) R Rolling EExtrusion D Drawing FForging(closed d die) FFORMINGTEMPERATURE M METALFABRICATTIONMETHODS Liquid SSintering m metals/ceramics SSolidification C Crystalsandgrains In nourcaseofsolidifyingmateriaalstheindividualcrystalsgrow aandmeeteacho other Theresultisnoprettycryystalshapes w wecallthese cryystals grains G GrainGrowth G Grains SSolidification:Lett smakeitcrysttalclear! O Oneofthemostimportantphasechanges ofanewphasew withinapre spontaneeousformationo existingp phase
Involves nucleation initiation of the formation of a solid subsequent growth of nucleus into crystals Phase transformations Begin with the appearance of very small particles of the new phase (NUCLEATION) which then GROW until the phase change is complete Note: new solid phase from an existing liquid phase new solid phase from an existing solid phase Homogenous Nucleation Nucleation occurring in a perfectly homogenous material replacement of one phase by another resulting in a decrease in free energy existencee of a surface between the two phases results in an increase in energy Nucleation and Growth T? Degree of supercooling (undercooling) Homogeneous Nucleation: examples Two examples of homogeneous nucleation in the solid state are known. Cu with 1 3% Co can be heat treated to precipitate Co homogeneously. Ni superalloys will precipitate Ni 3 Al homogeneously at small undercoolings because of the small lattice misfit and small interfacial energy. Why only these cases? Small interfacial energy, and small elastic energy difference. Everything else: heterogeneous!
Heterogeneous Nucleation In practice, homogenous liquids rarely exist nuclei formed at a foreign surface container wall, particles, structural imperfections can show r* hetero = r* homo sinδ where δ is a function of the contact angle Practical consequences of solidification From this graph we can see: low T solidification will lead to small grain growth higher T to large grains Solid State Heterogeneous Nucleation Heterogeneous nucleation must occur on some substrate: grain boundaries triple junctions dislocations (existing) second phase particles Consider a grain boundary: why is it effective? Answer: by forming on a grain boundary, an embryo can offset its cost in interfacial energy by eliminating some grain boundary area. Columnar growth Consequences Large ingots (which will cool slowly) require additives to induce heterogeneous nucleation if fine grain size is desired Other problems also encountered first part of ingot to solidify is? the next? and remember, on solidification most liquids shrink (can you think of an exception?) Te m p Growth Rate, G T1 T2 Nucln Rate, N Rate
How do we avoid this? Keep the top of the ingot hot, so the surface does not solidify before the rest of the casting often by adding compounds that decompose exothermally die casting New grains in the solid state recrystallisation of strain hardened brass a) deformed structure (note the slip lines!) b) new grains nucleating along slip planes c) more grains nucleated d) complete recrystallisation Casting Processes Sand casting Die casting Investment casting Sand casting (closed mold) Die casting/injection moulding Investment casting/lost wax Machining Composites Depend on the matrix and reinforcement Particles and short fibres Many of the techniques we have looked at, injection moulding/resin transferr moulding Chopped gun Die casting(squeeze casting) Die casting/injection moulding Plunger Investment casting/lost wax Wax pattern is cast Wax removed by melting Molten metal Sprue Parting line 4-part pattern tree Molten metal solidifies in cast Stationary die Moving die Ceramic mold (hardened slurry) Ceramic mold is removed Ejector pins Much technology relies on placing fibres Pultrusion
Filament winding Hand lay up Vacuum bag SUMMARY Consider the properties of the material Can it be plastically deformed? If not can we make it so? Ceramics for example Do we need to heat it up? Consider the required properties of the thingo Do we need to post heat treat to remove properties we have introduced in forming? Can we use cold working to produce a stronger thingo? Cold drawn copper pipe Does it need post mechanical treatment? Remove parting lines Surface treatment Machining