Lecture 03 Properties - Material Science PDF

 Theory of Materials and Design for Manufacturing Manufacturing Methodologies, 1TE631 Agenda surface characteristics material behavior equivalent stress factor of safety design for manufacturing Surface characteristics Surface texture measures a surface...

 Theory of Materials and Design for Manufacturing Manufacturing Methodologies, 1TE631 Agenda surface characteristics material behavior equivalent stress factor of safety design for manufacturing Surface characteristics Surface texture measures a surface’s overall texture, defined by the surface’s lay, surface roughness, and waviness.  Surface characteristics The integral of the deviation from the mean value is called Ra Surface characteristics Surface properties due to machining parameters An increase in cutting speed decreases surface roughness. This means that the faster the cutting speed, the lesser the surface roughness. With increasing the depth of cut on the CNC machining process, maximum roughness Results for Ti-6Al- depth tends to increase. 4V cut in a lathe by choosing all the other Increasing feed corresponds to an increase in parameters constant, taken average roughness. from doi: 10.1007/s00170- Cutting fluids reduce surface roughness in all 023-12458-y the cutting processes. This occurs by the reduction of tool temperature, which in turn reduces the coefficient of friction. Agenda surface characteristics material behavior equivalent stress factor of safety design for manufacturing Material behavior Isotropic materials Metal alloys larger than millimeter: aluminum, steel, magnesium, copper,... Ceramics: glass, zirconia,... Rocks: concrete, clay, basalt,... Plastics: epoxy, rubber, polycarbonate,... Synthetic wood such as MDF Anisotropic materials Copper in micrometer size (cubic symmetry) Fiber reinforced composites (UniDirectional (UD) laminate sheets are transversely isotropic) Natural wood (assumed to be transversely isotropic)  Aluminum 2011-T8, from matweb.com Isotropic material behavior Linear elastic material Two material parameters are needed Young’s modulus, , and Poisson’s ratio, ν Young’s modulus, , and shear modulus, μ Shear modulus, μ, and Poisson’s ratio, ν  Aluminum 2011-T8, from matweb.com Product design Linear elastic material, 2 material parameters: Describe the loading conditions Perform a simulation with the Finite Element Method (FEM) Determine the equivalent stress Stress-strain relation, monotonous loading Linear elastic material test result, brittle to ductile Glass Concrete Gray cast iron Measurement of limit stress, tensile tests Uniaxial tensile test Three point flexural test Brazilian test, standard and modified versions casting or machining: uniaxial tensile test cylinder shaped rocks, concrete: Brazilian test composite materials: three point flexural test Measurement of limit stress, shear tests Torsion of a pipe Box test Iosipescu test thin walls may buckle in torsion granular material and rocks in box test  Under cyclic loading, fatigue strength Under static loading, no damage The same load under a cyclic loading, damage Brittle material, fracture Ductile material, rupture Al 7075-T651 from doi:10.1016/j.ijfatigue.2007.07.005  Aluminum 2011-T8, from matweb.com Product design Maximum stress allowed in a design: Ultimate tensile strength, if plasticity is allowed Yield tensile strength, if static, elastic deformation Fatigue strength, if a cyclic loading occurs Heat treatment changes the fatigue strength 35CrMo steel, results are taken from doi: 10.3390/met12040688 a) b) c) d) EBSD images showing microstructures a) lath martensite and austenite b) tempered martensite c), d) tempered troostite  Stress value Special case: only one stress component In general, nine components, Equivalent stress reduces to one value, Von Mises criterium (ductile) Tresca criterium (brittle) Normal stress, Colors show the equivalent stress Factor of safety Factor of safety = strength / equivalent stress Strength is yield or fatigue strength Factor of safety examples Only 1.1 for race cars, jet planes Passenger aircraft 1.5-2.5 Between 2-3 for foundation At least 3 and upto 5 for piping Turbine components 6-8 Bolts 8.5 Heavy duty shafts 10-12 Cast iron wheels 20 Highly reliable materials for factor of safety less than 2 Challenging environmental conditions, mostly larger than 3 Agenda surface characteristics material behavior equivalent stress factor of safety design for manufacturing Design for manufacturing Functional design How to manufacture? How many pieces? How to assembly? Design for manufacturing Limitations Material selection Manufacturing methods Assembly Cost analysis Fishing reel A crank, two knobs, a nut, two rivets 25 000 pieces to build Small loads Material will not rust Fishing reel A crank, two knobs, a nut, two rivets 25 000 pieces to build Small loads Material will not rust Affordable: plastic injection molding Market research: fishers dislike plastic Salt-water use, aluminum or stainless steel Die casting or stamping All the same material Best cost: all aluminum, stamping Robot arm gripper Robot arm gripper 1 Body, aluminum, milling 2 Gear 1, nylon, casting 3 Gear 2, nylon, casting 4 Gripper, nylon, casting 5 Linkage, aluminum, stamping 6 Base plate, aluminum, stamping 7 Pin, off-the-shelf 8 Motor gear, acetal/nylon, casting 9, 10 M3, off-the-shelf Redesign for cost saving Truck sheet metal fan cover Redesign to lower the costs Same material and sheet bending is used Labor costs increase 4.9 kr to 5.3 kr Material costs decrease from 75.1 kr to 56.3 kr In total, 25% cost reduction Redesign for cost saving A bracket design, produced by 5 axis CNC Redesign for allowing 3 axis milling Sand casting (even more affordable) Around 2000 kr cost saving per 300 parts a year Redesign for cost saving A sophisticated bracket for milling Cycle time is relatively long Larger radius allow to use a bigger tool 17% of reduction in machining time Reduction of material supply Different parts may be designed to have the same initial geometry All for milling operation and the same material Procurement is then the same block for 3 different parts Less variation in material supply means cost reduction Reduction of tools in milling Different parts may be designed to use the same tools in machining Drilling operation may be done all with one tool Less tool change and less variation in used tools means cost reduction Design for manufacturing Mind setting of considering manufacturing during product design Relatively sophisticated procedure, no magic bullet! General knowledge of the company’s production scheme General knowledge of available materials General knowledge of manufacturing methodologies Smart use of all knowledge together Talk to process and industrial engineers during product design Thanks a lot for the attention!