Process Selection. Manufacturing processes. Classification of processes the Process Tree. Examples of processes. Processes

Transcription

1 Process Selection Manufacturing processes Processes and their attributes The selection strategy Screening by attributes Ranking by economic criteria Case study + demos The text book classified manufacturing processes into three broad categories Joining 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 Fall 2006 Slides 7-1 ME Fall 2006 Slides 7-2 Examples of processes Classification of processes the Process Tree processes Kingdom Family Class Member Attributes Joining Sand casting Blow moulding treating Processes Joining Surfacing Casting Deformation Moulding Composite Powder Machining Rapid prototyping Compression Rotation Injection RTM Blow Min. Min. section section Tolerance Tolerance Roughness Roughness Economic Economic batch batch specific specific general general Fusion welding Induction hardening A process record ME Fall 2006 Slides 7-3 ME Fall 2006 Slides 7-4 1

2 Classification of Process Selection Some processes can make only simple shapes, others, complex shapes. All shapes Prismatic Sheet 3-D 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 Translation: express design requirements as constraints & objectives Circular Non-circular Flat Dished Solid Hollow Step 2 Screening: eliminate processes that cannot do the job Step 3 Ranking: find the processes that do the job most cheaply Step 4 : explore pedigrees of top-ranked candidates Wire drawing, extrusion, rolling, shape rolling: prismatic shapes Stamping, folding, spinning, deep drawing: sheet shapes Casting, molding, powder methods: 3-D shapes Because there are thousands of variants of processes, supporting plays a particularly important role ME Fall 2006 Slides 7-5 ME Fall 2006 Slides 7-6 Example of the Translation step Screening 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. A combination of graph, limit, and tree stages can be used to screen the process universe to reduce the choices Bar charts are better than bubble charts (ranges too wide) All processes Limit stage Tree stage Graph stage Function Constraints Objectives Casing for road-pressure sensor : Al alloy : non-circular prismatic Minimum section: 2 ± mm Minimize Physical attributes Minimum Maximum Mass range 0.6 kg Section mm Tolerance mm Roughness μm Batch size Circular prismatic Non-circular prismatic Flat sheet Dished sheet Solid 3-D Hollow 3-D s Ceramics Metals Polymers Hybrids Economic batch size B B 1 > B > B 2 Free variable Choice of process Screened sub-set of processes ME Fall 2006 Slides 7-7 ME Fall 2006 Slides 7-8 2

3 Example of the Screening step Screening: Limit and tree stages Processes for making the insulator in a spark-plug Specification Function Constraints Objective Free variables Electrical Insulator class Alumina class 3-D, hollow Mass 0.05 kg Min. section 3 mm Tolerance < 0.5 mm Roughness < 100 μm Batch size >1,000,000 Minimize Choice of process Insulator Body shell Central electrode ME Fall 2006 Slides 7-9 Limit stage: Tree stage: Physical attributes Minimum Maximum Mass range kg Section 3 mm Tolerance 0.5 mm Roughness 100 μm Circular prismatic Non-circular prismatic Flat sheet Dished sheet Solid 3-D Hollow 3-D b Select CERAMIC (or Alumina) Rank: bar chart for ECONOMIC BATCH SIZE. ME Fall 2006 Slides 7-10 Rank on Processes based on batch size Classification of processes the Process Tree Joining and treatment processes Desired Batch Economic batch size (units) 1e+008 1e+007 1e Blow Moulding Powder methods Injection Moulding Sheet forming Expanded foam molding Die Casting Compression Moulding Rotational Moulding Rolling and forging Resin transfer molding (RTM) Electro-discharge machining Polymer Casting Sand casting Thermoforming Economic batch size Lay-Up methods Rapid prototyping Kingdom Processes Family Joining treat Class Adhesives Welding Fasteners Heat treat Paint/print Coat Polish Texture Member Braze Solder Gas Arc e -beam Electroplate Anodize Powder coat Metallize Attributes Joint Joint geometry geometry Section Section Purpose Purpose of of treatment treatment Coating Coating hardness hardness ME Fall 2006 Slides 7-11 Process records ME Fall 2006 Slides

4 Selection of Joining and Treatment Processes The Process matrix Joining the most important criteria are: The material(s) to be joined The geometry of the joint Apply these first, then add other constraints A given process can shape, or join, or finish some materials but not others. A red dot indicates that the pair are compatible. Processes that cannot shape the material of choice are non-starters. The upper section of the matrix describes shaping processes. The two sections at the bottom cover joining and finishing. 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 ME Fall 2006 Slides 7-13 ME Fall 2006 Slides 7-14 The Process matrix The Process matrix 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 Fall 2006 Slides 7-15 ME Fall 2006 Slides

5 The Process matrix The Process Mass-range chart 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 Fall 2006 Slides 7-17 ME Fall 2006 Slides 7-18 The Process Mass-range chart The Process Section chart The bar-chart on the next page allows selection to meet constraints on section. 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. Limits on rolling and forging-pressures set a lower limit on achievable by deformation processing. Powder-forming methods are more limited in the section es 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 es 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 Fall 2006 Slides 7-19 ME Fall 2006 Slides

6 The Process Section chart The Process Tolerance chart 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 Fall 2006 Slides 7-21 ME Fall 2006 Slides 7-22 The Process Tolerance chart The Process roughness chart 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 Fall 2006 Slides 7-23 ME Fall 2006 Slides

7 The Process roughness chart The Process Economic batch-size chart 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 batch size. A process with an economic batch 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 Fall 2006 Slides 7-25 ME Fall 2006 Slides 7-26 The Process Economic batch-size chart ME Fall 2006 Slides