EPT 221 Engineering Design Manufacturing Process Selection

Objectives of Lecture Differentiate and select primary, secondary , and tertiary processes Understand and apply methods to select appropriate manufacturing processes Estimate the costs of manufacturing a product.

How would we manufacture a mountain bike ? Handle Bar Top Tube Seat Post Saddle Fork Rear Brake Down Tube Front Brake Rear Derailleur Pedal (Courtesy of Trek Bicycle, 2002)

Manufacturing process decisions How do we choose the specific manufacturing processes? How do the selected materials influence the choice of manufacturing processes? Would product function or performance issues influence our choice of processes? What criteria should we use to select processes? Which criteria are more important? Who will make the final decisions?

Parts undergo sequence of processes Changes? Parts undergo sequence of processes Primary - alter the (“raw”) material’s basic shape or form. Sand casting Rolling Forging Sheet metalworking 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  Tertiary - surface treatments Polishing Painting Heat-treating Joining

Part / Mfg. Process Considerations 1. Production Volume 2. Part Size (overall) 3. Shape Capability (features)/ geometric complexity boss/depression 1D boss/depression >1D holes undercuts (int./ext.) uniform walls cross sections - uniform/regular rotational symmetry captured cavities

Types of manufacturing processes How is the input material changed?

Bulk Deformation To change the shape or form of bulk material caused by compressive or tensile yielding. Rolling Extrusion Drawing Forging

Rolling Two or more cylindrical rollers plastically compress material, forming sheets, bars and rods. Hot rolling requires less work but an oxidized surface finish Cold rolling requires more work but increases the yield strength of the material and produces superior surface finish.

Rolling slab bloom billet sheet coil bar rod structural ingot

Extrusion Heated metal plastically yields as it is pushed through a die, producing long pieces with a constant cross-section. Size: 40-foot in length Economical production quantities: 1,000 to 100,000 pieces Materials: ductile metals (e.g. aluminum, steel, zinc, copper, magnesium) Ram Cross sections Extrusion die Billet

Drawing Process of producing a wire, bar or tube by pulling on a material until it increases in length accompanied with a reduction in its cross-sectional diameter. Size: bar size range 1/8 to 6 inches in cross-section, wire size range 0.001 to 3/8 inches. Material: ductile metals (e.g. aluminum, steel, copper) Pulling force Cross sections Drawing die Billet

Forging (closed-die) Blocked preform Gutter Ram pressure Flash A process in which material is plastically compressed between 2 halves of a die set by hydraulic pressure or the stroke of a hammer. Size: maximum size limit roughly 36 inches Economic production quantity: 1,000 to 100,000 pieces

Casting Processes The process in which molten metal is poured into a cast to solidify. Sand casting Die casting Investment casting

Sand casting (closed-mold) Core Riser Sprue Runner Drag Flask Cope Gate Parting line Uses sand mold. The mold is destroyed to remove the part. Mold size ranges from inches to feet. (e.g. as mold cast for industrial engine blocks as large as 12 feet in cross section and 30 feet long) Economical production quantity: very small i.e. 1 to 10 Material: all ferrous and nonferrous metals Parts produced have a granular surface finish.

Die casting Parting line Plunger Sprue Moving die Stationary die Ejector pins Molten metal Molten metal is injected under high pressure into permanent die set usually made of steel. Die casting is faster than sand casting but can more expensive. Smoother surface finish than sand-cast parts. Size: maximum part size 30 x 30 inches to parts less than an inch. Economic production quantity: over 10,000 Material: low-melting-point metals (e.g. aluminum, zinc, magnesium, brass)

Investment casting (lost wax casting) Molten metal solidifies in a ceramic cast made by coating a wax pattern with liquid slurry, then dried. Wax is melted out and ceramic mold is destroyed after part solidifies. Material: alloy of aluminum, zinc, magnesium, brass, steel, stainless steel. Economic production quantity: less than 10,000 pieces

Investment casting Ceramic mold (hardened slurry) 4-part pattern tree Wax pattern is cast Wax removed by melting Molten metal solidifies in cast Ceramic mold is removed

Polymer Processes Part shapes are created by solidification of thermoplastic polymers or curing of thermosetting polymers. Results in little waste of raw material and require few, if any, finishing operations Compression molding Transfer Molding Blow molding Injection molding

Compression molding Charge Heated mold Part Ram Pressure Charge of thermoset or elastomer is formed between heated mold halves under pressure while the polymer cures. Compression molds are simpler than injection molds (no sprue, runners, risers) Size: minimum part size of the order of 1/8 to ¼ inch in cross-section Economic production volume: more than 10,000 pieces

Transfer molding Charge Ram Heated mold Sprue Part Ram pressure

Molten parison is extruded Blow molding Extruder air injector parison Part is removed Air blown into Mold halves close Molten parison is extruded

Blow moulding A molten parison of thermoplastic material injected with air, then expands to the shape of the mold. Is used to produce hollow parts within thin walls. Size: maximum size of about 3 feet in diameter

Injection moulding Thermoplastic pellets are melted and injected under high pressure into a metal mold. Size: maximum part size less than 24 x 24 inches, minimum part size are of the order of 1/8 to ¼ inch in cross-section Economic production quantity: more than 10,000

Sheet Metalworking The permanent deformation of thin metal sheets by bending and shearing forces produced by mechanical or hydraulic forces. Often called stamping forces. Produces parts of moderate complexity. Size: less than 24x24inches Economic production quantity: more than 10,000 Material: alloys of steel and aluminum Bending Blanking Drawing Punching Shearing Spinning

Shearing : cutting or separating sheet metal along a straight line. Blanking: shearing of a smaller, shaped piece, called a blank, from the stock. Punching: produces slots, notches, extruded holes, and holes. Embossing: forming plastic indentations to form ribs, beads, or lettering on the surface of metal.

Sheet metal drawing Blank Drawn part Clamp force Blank holder Die Punch Punch ram Punch plastically deforms a blank sheet material into a die, forming cupped-, box-, or hollow-shaped parts Products: soda cans, ammunition cartridge casings, and pots and pans.

Solidification processes solid Part molten material freezing Casting Processes Sand Casting Die Casting Investment Casting Centrifugal Polymer Processes Injection Molding Blow Molding ThermoForming Compression Molding Recall Flow (voids, flash) Cooling time (cycle time) Temperature Mold complexity Warpage Post processing Costs (materials, tooling, processing) considerations Add to your notes

Machining The removing of material from the workpiece by a sharp cutting tool that shears away chips of material to create a desired form or features. It is a subtractive process that produces manufactured waste and can, therefore be expensive. Often used as a secondary process to true-up critical dimensions or surfaces or to smooth the surface finish. Often used for low-volume production.

Machining processes ECM : electro chemical machining

Machining – removal of material… Sawing –using a toothed blade. Milling – from a flat surface by a rotating cutter tool. Planing – using a translating cutter as workpiece feeds. Shaping - from a translating workpiece using a stationary cutter. Boring - increasing diameter of existing hole by rotating the workpiece. Drilling- using a rotating bit forming a cylindrical hole. Reaming – to refine the diameter of an existing hole. Turning - from a rotating workpiece. Facing - from turning workpiece using a radially fed tool. Grinding - from a surface using an abrasive spinning wheel. Electric discharge machining (EDM) - by means of a spark.

Machining process considerations solid material machining material removed sawing, turning, boring, milling, drilling, grinding, ECM Recall hardness, strength of material shear forces = strong jigs & fixtures tool/bit wear, replacement size of workpiece, fit machine? volume removed rate of removal, hp needed tolerances operator skill, CNC costs (materials, tooling, processing) considerations Add to your notes

Finishing Preparing the final surface for aesthetics and protection from the environment. Cleaning: wire brushing is used to remove grit and scale, and chemical solutions, including acid baths, are used to remove oily films Protection: polymers and ceramics requires little protection from the environment. Metals, however, require some surface treatment with oil-and-water based painting providing the least expensive coating. Steels are often plated with chrome, cadmium, or zinc). Aluminum alloys are usually anodized (a chemical surface treatment).

Finishing processes protection?

Surface roughness

Assembly The process of putting together all the components of a product before shipping. Operation include handling, insertion, and/or attachment of parts. Handling: grasping, moving, orienting, and placing parts, before insertion or attachment. Attachment: either - Permanent: welding, brazing, soldering, adhesive bonding, rivets, eyelets, staples, shrink fits, press fits, or - Temporary: threaded fasteners such as screws, nuts and bolts, snap fits.

Assembly processes – fastening / joining of 2 or more components permanent?

Process / Material Screening

Product function is interdependent Material Properties Product Function Manufacturing Processes Product Geometry

Are materials compatible with mfg. process? Properties Manufacturing Processes compatible materials & processes

Material-Process Compatibility

Shape generation capability (of processes)

Manufacturing costs Total Manufacturing Cost = Material + Tooling + Processing raw mat’ls molds labor  fixtures electricity jigs supplies tool bits O/H (deprec.) TMC = M + T + P

Material costs per part, cM Let M = total materials costs (raw, bulk) q = production quantity Then material costs per part, cM is cM = M/q = (cost/weight x weight) / number of parts Let’s reorganize the variables in the equation above cM = [cost/weight] [weight/number of parts] = (cost/weight) (weight/part), and therefore cM = cost/part

Material cost per part (continued) Let cw = material cost per unit weight, and wp = weight of finished part ww= weight of wasted material, scrap  = ratio of wasted material weight / finished weight = ww / wp Then the material cost per part, cM is cM = cw (wp + ww ) = cw (wp +  wp ) cM = cw wp (1+ )

Tooling cost per part, cT Let T= total cost of molds, fixtures per production run q = number of parts per run Then tooling cost per part, cT cT= T/q e.g. sand casting cT = ($10,000/run) / (5000 parts/run) = $2.00/part

Processing cost per part, cP Let ct = cost per hour, (machine rate + labor) t = cycle time (hours per part) then cP = ct t e.g. sand casting cP = ($30/hr) (0.3 hrs/part) = $9/part Processing cost: labor, energy, floor space, machine usage Cycle time: time needed to make a part

Total cost per part Cost per part, c = cM + cT + cP c = cw wp (1+ ) + T/q + ct t (6.6) e.g. sand casting c = $1.05 + $2.00 + $9.00 c = $12.05 / part

Example Assume that our company is considering making a part out of low-strength metals or thermoplastics. Three processes appear compatible with the required feature shapes: sand casting, injection, and machining. The marketing department estimates that the company should produce about 5,000 pieces. Data gathered to select the material and manufacturing process are shown in the table below. Determine the cost per part.

Run quantity is important! A-Sand casting B-Inj.Molding C-Machining

How can we lower the cost of parts? c = cw wp (1+ ) + T/q + ct t (6.6)        purchase less expensive materials, keep our finished part weight low produce little manufactured waste design simple parts that result in less expensive tooling make many parts production run (i.e. batch) choose a manufacturing process that has a low cycle time & cost per hour Goal: minimize the sum of the terms! (not any one term in particular)

Case Study- Aero engine

Summary Manufacturing process decisions Deformation processes Casting processes Sheet metalworking Polymer processing Machining Finishing Assembly Material compatibilities / Process capabilities Material costs, Tooling costs, Processing costs