Unit 6. Selecting processes:

Transcription

1 Unit 6. Selecting processes: shaping, joining and surface treatment New approaches to Materials Education - a course authored by Mike Ashby and David Cebon, Cambridge, UK, 2008 MFA and DC 2008

2 Outline Processes and their attributes Screening by attributes Selecting shape-forming processes Selecting joining processes Selecting surface-treatment processes Exercises 2

3 Manufacturing processes Primary shaping Casting Molding Mould Nozzle Granular Polymer Cylinder PM methods Heater Screw Secondary shaping Machining Drilling Cutting Injection moulding No.8-CMYK-5/01 Machining Joining Welding Adhesives Fasteners Surface Treating Painting Polishing Heat treating Welding Painting 3

4 Data organisation: the PROCESS TREE Kingdom Family Class Member Attributes Difficult! Process data-table Joining Shaping Surfacing Casting Each family has attributes that differ. Deformation Molding Composite Powder Rapid prototyping Compression Rotation Injection RTM Blow RTM Material Blow molding Shape Material Injection molding Size Shape Material Range Min. Size Shape section Range Tolerance Min. Size section Range Roughness Tolerance Min. section Economic Roughness Tolerance batch Documentation Economic Roughness batch -- specific Documentation Economic batch -- general -- specific Documentation -- general -- specific -- general Process records 4

5 Shape classification Some processes can make only simple shapes, others, complex shapes. l Wire drawing, extrusion, rolling, shape rolling: prismatic shapes l Stamping, folding, spinning, deep drawing: sheet shapes l Casting, molding, powder methods: 3-D shapes 5

6 Structured data for injection moulding* Injection moulding (Thermoplastics) INJECTION MOULDING of thermoplastics is the equivalent of pressure die casting of metals. Molten polymer is injected under high pressure into a cold steel mould. The polymer solidifies under pressure and the moulding is then ejected. Shape Circular Prism True Non-circular Prism True Solid 3-D True Hollow 3-D True Physical attributes Mass range kg Roughness µm Section thickness mm Tolerance mm Process characteristics Discrete True Prototyping False Typical uses Injection molding is used. Economic Attributes Economic batch size 1e+004-1e+006 Relative tooling cost high Relative equipment cost high Cost modeling Relative cost index + links to materials Key physical factors in choosing a shaping process (economics always important) fx *Using the CES EduPack Level 2 DB 6

7 Unstructured data for injection moulding* The process. Most small, complex plastic parts you pick up children s toys, CD cases, telephones are injection moulded. Injection moulding of thermoplastics is the equivalent of pressure die casting of metals. Molten polymer is injected under high pressure into a cold steel mould. The polymer solidifies under pressure and the moulding is then ejected. Various types of injection moulding machines exist, but the most common in use today is the reciprocating screw machine, shown schematically here. Polymer granules are fed into a spiral press like a heated meat-mincer where they mix and soften to a putty-like goo that can be forced through one or more feed-channels ( sprues ) into the die. Mould Granular Polymer Nozzle Cylinder Heater Screw No.8-CMYK-5/01 Design guidelines. Injection moulding is the best way to mass-produce small, precise, plastic parts with complex shapes. The surface finish is good; texture and pattern can be moulded in, and fine detail reproduces well. The only finishing operation is the removal of the sprue. The economics. Capital cost are medium to high; tooling costs are high, making injection moulding economic only for large batch-sizes (typically 5000 to 1 million). Production rate can be high particularly for small mouldings. Multicavity moulds are often used. The process is used almost exclusively for large volume production. Prototype mouldings can be made using cheaper single cavity moulds of cheaper materials. Quality can be high but may be traded off against production rate. Process may also be used with thermosets and rubbers. Typical uses. The applications, of great variety, include: housings, containers, covers, knobs, tool handles, plumbing fittings, lenses, etc. The environment. Thermoplastic sprues can be recycled. Extraction may be required for volatile fumes. Significant dust exposures may occur in the formulation of the resins. Thermostatic controller malfunctions can be extremely hazardous. *Using the CES EduPack Level 2 DB 7

8 Finding information with CES File Edit View Select Tools Toolbar Browse Select Search Print Search web Table: ProcessUniverse Subset: Edu Level 2 Find what? Which table? RTM SLS Processes ProcessUniverse Joining Shaping Surface treatment 8

9 Selection of processes l Process selection has the same 4 basic steps Step 1 Translation: express design requirements as constraints & objectives Step 2 Screening: eliminate processes that cannot do the job Step 3 Ranking: find the processes that do the job better Step 4 Documentation: explore pedigrees of top-ranked candidates 9

10 Selection by series of screening stages Browse Select Search 1. Selection data Edu Level 2: Processes - shaping 2. Selection Stages Graph Limit Tree Results X out of 60 pass Process 1 Process 2 Process 3 Process 4 Process 5.. Batch size B Material Shape Ceramic Hybrid Metal Polymer Circular prismatic Non-circular prismatic Flat sheet etc Ferrous Non-ferrous Physical attributes Mass range kg Tolerance 0.5 mm Roughness 100 µm B 1 > B > B 2 10

11 Spark-plug insulator: translation Insulator Translation of design requirements Body shell Function Insulator Central electrode Design requirements Make 2,000,000 insulators from alumina with given shape dimensions tolerance and surface roughness Constraints Free variable Material class Alumina Shape class 3-D, hollow Mass 0.05 kg Section 3-5 mm Tolerance < 0.5 mm Roughness < 100 µm Batch size >2,000,000 Choice of process 11

12 Spark-plug insulator: screening Insulator 1 Select Level 2: Shaping processes Body shell Central electrode 2 Materials Ceramics Hybrids Metals Polymers Alumina B-carbide Silicon W-carbide Translation Physical attributes Constraints Material class Alumina Shape class 3-D, hollow Mass 0.05 kg Section 3 5 mm Tolerance < 0.5 mm Roughness < 100 µm 3 Mass range Range of sect. thickness Tolerance Roughness Economic attributes kg mm mm µ m Batch size >2,000,000 Economic batch size 2e6 - Shape Hollow, 3 D b 12

13 The selection: two shaping processes Powder pressing and sintering Powder injection molding 13

14 Data organisation: joining processes Kingdom Family Class Member Attributes Processes Joining Shaping Surface treatment Adhesives Welding Fasteners Braze Solder Gas Arc e -beam... Gas welding Gas welding Gas welding Material Material Joint Material geometry Joint geometry Size Joint Range geometry Size Range Section Size thickness Range Section thickness Relative Section cost thickness... Relative cost... Documentation Relative cost... Documentation Documentation Lap Butt Joint geometry Sleeve Scarf Tee 14

15 A joining record* Gas Tungsten Arc (TIG) Tungsten inert-gas (TIG) welding, the third of the Big Three (the others are MMA and MIG) is the cleanest and most precise, but also the most expensive. In one regard it is very like MIG welding: an arc is struck between a non-consumable tungsten electrode and the work piece, shielded by inert gas (argon, helium, carbon dioxide) to protect the molten metal from contamination. But, in this case, the tungsten electrode is not consumed because of its extremely high melting temperature. Filler material is supplied separately as wire or rod. TIG welding works well with thin sheet and can be used manually, but is easily automated. Joint geometry Lap True Butt True Sleeve True Scarf True Tee True Physical Attributes Component size non-restricted Watertight/airtight True Demountable False Section thickness mm Typical uses TIG welding is used. Documentation *Using the CES EduPack Level 1 DB Materials Ferrous metals Economic Attributes Key physical factors in choosing a joining process Relative tooling cost low Relative equipment cost medium Labor intensity low + links to materials 15

16 Data organisation: joining and surface treatment Kingdom Family Class Member Attributes Processes Joining Shaping Surface treatment Heat treat Paint/print Coat Polish Texture... Electroplate Anodize Powder coat Metallize... Anodize Anodize Anodize Material Material Why Material treatment? Why Coating Function treatment? thickness of Coating treatment thickness Surface hardness Surface Coating hardness thickness Relative cost... Relative Surface cost hardness... Documentation Documentation Relative cost... Documentation Process records Function of treatment Increased hardness Wear resistance Fatigue resistance Corrosion resistance Oxidation resistance Thermal insulation Electrical insulation Color Texture Decoration. 16

17 A surface-treatment record* Induction and flame hardening Take a medium or high carbon steel -- cheap, easily formed and machined -- and flash its surface temperature up into the austenitic phase-region, from which it is rapidly cooled from a gas or liquid jet, giving a martensitic surface layer. The result is a tough body with a hard, wear and fatigue resistant, surface skin. Both processes allow the surface of carbon steels to be hardened with minimum distortion or oxidation. In induction hardening, a high frequency (up to 50kHz) electromagnetic field induces eddy-currents in the surface of the workpiece, locally heating it; the depth of hardening depends on the frequency. In flame hardening, heat is applied instead by hightemperature gas burners, followed, as before, by rapid cooling. Function of treatment Fatigue resistance Friction control Wear resistance Hardness Physical Attributes Curved surface coverage Very good Coating thickness 300-3e+003 µm Processing temperature K Surface hardness Vickers Typical uses Induction hardening is used.. Economic Attributes Relative tooling cost low Relative equipment cost medium Labor intensity low Documentation + links to materials Key physical factors in choosing a surface treatment *Using the CES EduPack Level 2 DB 17

18 The main points Processes can be organised into a tree structure containing records for structured data and supporting information The structure allows easy searching for process data Select first on primary constraints Shaping: material, shape and batch size Joining: material(s) and joint geometry Surface treatment: material and function of treatment Then add secondary constraints as needed. l Documentation in CES, and 18

19 Exercises: Browsing processes 5.1 Find, by browsing, the Level 2 record for the shaping process Resin transfer molding (RTM) in Shaping: Composite forming. What products, typically, is it able to make? 5.2 Find the Level 2 record for shaping process Abrasive jet machining and cutting in Shaping: Machining: non-conventional machining. Can it be used to cut glass? 5.3 Find the Level 2 record for the joining process Friction-stir welding in Joining: Mechanical welding. How does the process work? File Edit View Select Tools Browse Select Search Table: ProcessUniverse Subset: Edu Level 2 ProcessUniverse + Joining + Shaping + Surface treatment 5.4 Find the Level 2 record for the surface coating process Metal flame spraying in Surface treatment: Surface coating. What are its principal uses? 19

20 Exercises: Searching for processes 5.5 Find, by searching, the record for the rapid prototyping process with the trade name SLS. What classes of material can it handle? File Edit View Select Tools Browse Select Search 5.6 Find, by searching, the record for Flexible adhesives. Which polymers are used for flexible adhesives? Find what: Look in table: SLS ProcessUniverse 5.7 Find, by searching, the record for Vitreous enameling. What Functions can it perform? 20

21 Exercise : Selecting shaping processes 5.8 A process is required to mold ABS components with a solid 3-D shape in large numbers: it should be economic at a batch size of 1,000,000 or more. Use the CES Level 2 Shaping data-table to find possible candidates. Material: ABS (TREE stage) Process: Molding (second TREE stage) Shape: 3-D solid (LIMIT stage) and Economic batch size > 10 6 (LIMIT stage) Browse Select Search 1. Selection data Edu Level 2: 2: Processes - shaping 2. Selection Stages Graph Limit Tree Shape Joining Solid 3-D Process Shape Economic attributes Surface Economic batch size > 10 6 Cast Deform Molding Composite Powder Prototype Results: ü Compression molding ü Injection molding, thermoplastics Material Ceramic Hybrid Metal Polymer ABS CA Nylon PC PE PP 21

22 Exercise : Cutting CFRP sheet 5.9 A process is required to cut flat 4mm CFRP sheet for the face-sheets of a light-weight sandwich panel. Using the Level 2 Shaping data-table to select it. The requirements are Material: CFRP (TREE stage) Shape: flat sheet (LIMIT stage) Section thickness: 4mm (LIMIT stage) Process characteristics: Cutting (LIMIT stage) Browse Select Search 1. Selection data Edu Level 2: 2: Processes - shaping 2. Selection Stages Shape Flat sheet Graph Limit Tree Physical attributes Section thickness <>4 mm Process characteristics Cutting processes Material Ceramic Hybrid Metal Polymer CFRP DMC GFRP SMC Results: ü Abrasive jet machining and cutting ü Band sawing ü Laser cutting ü Water-jet cutting 22

23 Exercise: Joining metal sheet Gillette Sensor 3 razor Browse Select Search 1. Selection data Edu Level 2: 2: Processes - joining 2. Selection Stages Graph Limit Tree A process is required to join 0.6 mm steel blades onto aluminum sheet carriers to form a lap joint. Use the Level 2 Joining data-table to find them. The requirements are Materials to be joined: metals Joint geometry: lap joint Section thickness: 0.6 mm Demountable: No (X) All done with a LIMIT stage Results: ü Brazing ü Power beam (laser, electron beam) ü Resistance welding ü Rivets and staples ü Ultrasonic welding Blades Materials to be joined Metals Joint geometry Lap joint Physical attributes Section thickness <> 0.6 mm Function Demountable The reality: Laser spot welds 23

24 Exercise: Surface treatment of gears Enhancing performance of gears Browse Select Search 1. Selection data Edu Level 2: 2: Processes - surface Emerson Transmission Corp A process is required to improve the wear resistance and fatigue resistance of steel gears. The requirements are Materials: steel Purpose of treatment: wear resistance fatigue resistance Curved surface coverage: very good 2. Selection Stages Graph Limit Tree Function of treatment Wear resistance Fatigue resistance Material Physical attributes Curved surface coverage: v. good Ceramic Hybrid Ferrous Metal Non-ferrous Polymer Results: ü Carburizing and carbo-nitriding ü Nitriding ü Induction hardening and flame hardening 24