Kingdom. Shaping. Process data-table. Surface treating

Transcription

1 Process Selection Manufacturing processes Processes and their attributes Screening by attributes Selecting shape-forming processes Selecting joining processes Selecting surface-treatment processes Case study + demos The text book classified manufacturing processes into three broad categories treatment Each has many sub-categories, which may then be further subdivided into individual processes Many processes are used in combination with others Manufacturing process selection involves identifying which will work best for a particular application More info: s Selection in Mechanical Design, Chapters 7 and 8 ME Winter 2008 Slides 7-1 ME Winter 2008 Slides 7-2 Examples of processes Data organization: the PROCESS TREE Kingdom Family Class Member Attributes Difficult! Sand casting Blow moulding treating Process data-table Surfacing Each family has attributes that differ. Casting Compression Deformation Rotation Molding Injection Composite RTM Powder Blow Rapid prototyping RTM RTM Blow Blow molding molding Injection Injection molding molding Size Size Min. Size Min. Size section section Min. Size Min. Size section section Min. Min. section section Fusion welding Induction hardening Process records ME Winter 2008 Slides 7-3 ME Winter 2008 Slides 7-4 classification Some processes can make only simple shapes, others, complex shapes. Structured data for injection molding* Injection molding (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 molding is then ejected. Circular Prism Non-circular Prism Solid 3-D Hollow 3-D Attributes size 1e+004-1e+006 tooling high equipment high Wire drawing, extrusion, rolling, shape rolling: prismatic shapes Stamping, folding, spinning, deep drawing: sheet shapes Casting, molding, powder methods: 3-D shapes Physical attributes Mass range kg µm Section thickness mm mm Process characteristics Discrete Prototyping False Typical uses Injection molding is used. Cost modeling index + links to materials Key physical factors in choosing a shaping process (economics always important) fx ME Winter 2008 Slides 7-5 *Using the CES EduPack Level 2 DB ME Winter 2008 Slides 7-6 1

2 No.8-CMYK-5/01 Unstructured data for injection molding* Finding information with CES 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 puttylike goo that can be forced through one or more feed-channels ( sprues ) into the die. Mould Granular Polymer Nozzle Cylinder Heater Screw 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 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 are medium to high; tooling s are high, making injection moulding economic only for large -sizes (typically 5000 to 1 million). Production rate can be high particularly for small mouldings. Multi-cavity 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 ProcessUniverse treatment *Using the CES EduPack Level 2 DB ME Winter 2008 Slides 7-7 ME Winter 2008 Slides 7-8 Process Selection Selection by series of screening stages Like materials selection, process selection also has the same 4 basic steps Once a material is selected, it becomes one of the constraints in process selection Step 1 Step 2 Step 3 Step 4 Translation: express design requirements as constraints & objectives Screening: eliminate processes that cannot do the job Ranking: find the processes that do the job most cheaply Supporting information: explore pedigrees of top-ranked candidates Because there are thousands of variants of processes, supporting information plays a particularly important role ME Winter 2008 Slides 7-9 Browse Select Search 1. Selection data Edu Level 2: 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 Ceramic Hybrid Ferrous Metal Non-ferrous Polymer Circular prismatic Non-circular prismatic Flat sheet etc Physical attributes Mass range kg 0.5 mm 100 μm B 1 > B > B 2 ME Winter 2008 Slides 7-10 Example of the Translation step Spark-plug insulator: translation Example: Casing for a capacitance pressure sensor for use as a traffic sensor The sensor lies across the road, covered by a rubber mat. Vehicle pressure deflects top face, changing capacitance between top face and copper conducting strip. Function Constraints Objectives Free variable Casing for road-pressure sensor : Al alloy : non-circular prismatic Minimum section: 2 ± mm Minimize Choice of process Insulator Body shell Central electrode Design requirements Make 2,000,000 insulators from alumina with given shape dimensions tolerance and surface roughness Translation of design requirements Function Insulator class Alumina Constraints class 3-D, hollow Mass 0.05 kg Section 3-5 mm < 0.5 mm < 100 μm Batch size >2,000,000 Free variable Choice of process ME Winter 2008 Slides 7-11 ME Winter 2008 Slides

3 Spark-plug insulator: screening Rank on Processes based on size Insulator 1 Select Level 2: processes 1e8 Constraints Translation class class Mass Section Body shell Central electrode Alumina 3-D, hollow 0.05 kg 3 5 mm < 0.5 mm < 100 μm Batch size >2,000, s Ceramics Hybrids Metals Polymers Alumina B-carbide Silicon W-carbide Physical attributes Mass range kg of sect. thickness mm mm attributes μ m size 2e6 - Desired Batch Size size (units) 1e7 1e Powder injection molding Pressing and sintering Hollow, 3 D b 1 ME Winter 2008 Slides 7-13 ME Winter 2008 Slides 7-14 The selection: two shaping processes Data organization: joining processes Kingdom Family Class Member Attributes Processes treatment Adhesives Welding Fasteners Braze Solder Gas Arc e -beam Gas Gas welding Gas Gas welding Gas Gas welding Joint Joint geometry Joint geometry Size Joint geometry Size Joint geometry Size Joint geometry Section Size geometry Section Size thickness Section Size thickness Section thickness Section thickness Section thickness thickness Lap Powder pressing and sintering Powder injection molding Joint geometry Butt Sleeve Scarf Tee ME Winter 2008 Slides 7-15 ME Winter 2008 Slides 7-16 A joining record* Selection of Processes 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 Butt Sleeve s Scarf Ferrous metals Tee Attributes Physical Attributes tooling low Component size non-restricted equipment medium Watertight/airtight Labor intensity low Demountable False Section thickness mm + links to materials Typical uses TIG welding is used. Key physical factors in choosing a joining process ME Winter 2008 *Using the CES EduPack Level 1 DB Slides 7-17 the most important criteria are: The material(s) to be joined The geometry of the joint Apply these first, then add other constraints ME Winter 2008 Slides

4 Data organization: treatment A surface-treatment record* Kingdom Processes Function of treatment Family treatment Class Heat treat Paint/print Coat Polish Texture Increased hardness Wear resistance Fatigue resistance Corrosion resistance Oxidation resistance Member Electroplate Powder coat Metallize Thermal insulation Electrical insulation Color Texture Decoration. Attributes Why Why treatment? Why treatment? Coating Why Function treatment? Coating Function thickness treatment? of thickness of Coating treatment Coating treatment thickness hardness thickness Coating hardness Coating hardness thickness hardness thickness hardness hardness Process records ME Winter 2008 Slides 7-19 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 work-piece, 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 Attributes Wear resistance tooling low Hardness equipment medium Labor intensity low Physical Attributes Curved surface coverage Very good Coating thickness 300-3e+003 µm Processing temperature K hardness Vickers + links to materials Typical uses Induction hardening is used.. Key physical factors in choosing a surface treatment ME Winter 2008 *Using the CES EduPack Level 2 DB Slides 7-20 Selection of Treatment Processes The main points Processes can be organized into a tree structure containing records for structured data and supporting information treatment the most important criteria are: The purpose of the treatment The material to which it will be applied Apply these first, then add other constraints The structure allows easy searching for process data Select first on primary constraints : material, shape, and size : material(s) and joint geometry treatment: material and function of treatment Then add secondary constraints as needed. in CES, and ME Winter 2008 Slides 7-21 ME Winter 2008 Slides 7-22 The Process matrix The Process matrix A given process can shape, or join, or finish some materials but not others. Process charts have a red dot to indicate that the pair are compatible. Processes that cannot shape the material of choice are non-starters. Figure 7.16 ME Winter 2008 Slides 7-23 ME Winter 2008 Slides

5 The Process matrix classification is the most difficult attribute to characterize. Many processes involve rotation or translation of a tool or of the work-piece. These processes make parts that have axial symmetry, or translational symmetry. Turning creates axisymmetric (or circular) shapes; Extrusion, drawing and rolling make prismatic shapes, both circular and non-circular. Sheet-forming processes make flat shapes (stamping) or dished shapes (deep drawing, bending). Certain processes can make 3-dimensional shapes, and among these some can make hollow shapes whereas others cannot. The process-shape matrix displays the links between the two. If the process cannot make the desired shape, it may be possible to combine it with a secondary process to give a process-chain that adds the additional features: casting followed by machining is an obvious example. ME Winter 2008 Slides 7-25 Some processes can make only simple shapes, others, complex shapes. Figure 7.18 Wire drawing, extrusion, rolling, shape rolling: prismatic shapes Stamping, folding, spinning, deep drawing: sheet shapes Casting, molding, powder methods: 3-D shapes ME Winter 2008 Slides 7-26 The Process matrix The Process Mass - range chart Figure 7.17 The bar-chart on the next page shows the typical mass-range of components that each processes can make. Large components can be built up by joining smaller ones. Therefore the ranges associated with joining are also shown. In applying a constraint on mass, we seek single shaping-processes or shaping-joining combinations capable of making ia part and reject those that cannot. ME Winter 2008 Slides 7-27 ME Winter 2008 Slides 7-28 The Process Mass - range chart The Process Section thickness chart Figure 7.19 The bar-chart on the next page allows selection to meet constraints on section thickness. tension and heat-flow limit the minimum section of gravity cast shapes. The range can be extended by applying a pressure or by pre-heating the mold, but there remain definite lower limits for the section thickness. Limits on rolling and forging-pressures set a lower limit on thickness achievable by deformation processing. Powder-forming methods are more limited in the section thicknesses they can create, but they may be the only ones available for ceramics and very hard metals that cannot be shaped in other ways. The section thicknesses obtained by polymer-forming methods injection molding, pressing, blow-molding, etc depend on the viscosity of the polymer; fillers increase viscosity, further limiting the thinness of sections. Special techniques, which include electro-forming, plasma-spraying and various vapor deposition methods, allow very slender shapes. ME Winter 2008 Slides 7-29 ME Winter 2008 Slides

6 The Process Section thickness chart The Process chart Figure 7.20 No process can shape a part exactly to a specified dimension. Some deviation Δx from a desired dimension x is permitted This is referred to as the tolerance, T, and is specified as mm, or as x = 100 ± 0.1mm or x = mm ME Winter 2008 Slides 7-31 ME Winter 2008 Slides 7-32 The Process chart The Process roughness chart Figure 7.21 The surface roughness R, is measured by the root-mean-square amplitude of the irregularities on the surface. It is specified as R<100μm (the rough surface of a sand casting) or R<0.01μm (a highly polished surface). The bar chart on the next page allows selection to achieve a given surface roughness. ME Winter 2008 Slides 7-33 ME Winter 2008 Slides 7-34 The Process roughness chart The Process -size chart Figure 7.22 Process depends on a large number of independent variables. The influence of many of the inputs to the of a process are captured by a single attribute: the economic size. A process with an economic size with the range B1 B2 is one that is found by experience to be competitive in when the output lies in that range. ME Winter 2008 Slides 7-35 ME Winter 2008 Slides

7 The Process -size chart Figure 7.24 ME Winter 2008 Slides