Process Selection - From Design to Manufacture Part 4 pot

//SYS21///INTEGRAS/B&H/PRS/FINALS_07-05-03/0750654376-CH002-1.3D – 59 – [35–248/214] 9.5.2003 2:05PM 1.8CC Plaster mold casting process capabilit y c hart . Plaster mold casting 59 //SYS21///INTEGRAS/B&H/PRS/FINALS_07-05-03/0750654376-CH002-1.3D – 60 – [35–248/214] 9.5.2003 2:05PM 1.9 Squeeze casting Process description . Combination of casting and forging. Molten metal fills a preheated mold from the bottom and during solidification the top half of the mold applies a high pressure to compress the material into the final desired shape. Also known as liquid metal forging and load pressure casting (see 1.9F). Materials . Typically non-ferrous metals, but occasionally ferrous alloys. Process variations . Pouring can be performed automatically. Economic considerations . Production rates low due to mold filling for minimum turbulence. . Long setup times. . Lead time moderate to high. . Material utilization excellent. Near-net shape achieved. . High degree of automation possible. . Economically viable for production volumes of 10 000þ. . Tooling costs high. . Equipment costs high. 1.9F Squeeze casting process. 60 Selecting candidate processes //SYS21///INTEGRAS/B&H/PRS/FINALS_07-05-03/0750654376-CH002-1.3D – 61 – [35–248/214] 9.5.2003 2:05PM . Direct labor costs low to moderate. . Finishing costs very low. Used to minimize or eliminate secondary processing. Typical applications . Aerospace components . Suspension parts . Steering elements . Brake components Design aspects . Complex geometries possible. . Retractable and disposable cores used to create complex internal features. . Large variations in cross section possible. . Undercuts, bosses, holes and inserts possible. . Placing of parting line important, i.e. avoid placement across critical dimensions. . Machining allowances usually in the range 0.6–1.2 mm. . Draft angle ranging 0.1–3  , depending on section depth. . Maximum section ¼ 200 mm. . Minimum section ¼ 6 mm. . Minimum dimension ¼ 120 mm. . Sizes ranging 25 g–4.5 kg in weight. Quality issues . Low porosity experienced. . Low speed mold filling minimizes splashing. . Accurate metering of molten metal required to flashing. . Excellent mechanical properties can be obtained, similar to forging. . Adequate process control important, i.e. metering of molten metal, pressures, solidification times, etc. . Graphite releasing agent and ejector pins commonly used to aid removal of finished part. . Surface detail good. . Surface roughness ranging 1.6–12.5 mm Ra. . Achievable dimensional tolerances approximately Æ0.15 at 25 mm, Æ0.3 at 150 mm. Allowances of Æ0.25 mm should be added for dimensions across the parting line. Squeeze casting 61 //SYS21///INTEGRAS/B&H/PRS/FINALS_07-05-03/0750654376-CH002-1.3D – 62 – [35–248/214] 9.5.2003 2:05PM //SYS21///INTEGRAS/B&H/PRS/FINALS_07-05-03/0750654376-CH002-1.3D – 63 – [35–248/214] 9.5.2003 2:05PM 2 Plastic and composite processing //SYS21///INTEGRAS/B&H/PRS/FINALS_07-05-03/0750654376-CH002-1.3D – 64 – [35–248/214] 9.5.2003 2:05PM 2.1 Injection molding Process description . Granules of polymer material are heated and then forced under pressure using a screw into the die cavity. On cooling, a rigid part or tree of parts is produced (see 2.1F). Materials . Mostly thermoplastics, but thermosets, composites and elastomers can be processed. Process variations . Injection blow molding: allows small hollow parts with intricate neck detail to be produced. . Co-injection: for products with rigid cores pre-placed in the die before injection or simultaneous injection of different materials into same die. Economic considerations . Production rates are high, 1–50/min, depending on size. . Thermoset parts usually have a longer cycle time. . Lead times can be several weeks due to manufacturing of complex dies. . Material utilization is good. Scrap generated in sprues and risers. . If material permits, gates and runners can be reused resulting in lower material losses. . Flexibility limited by dedicated dies, die changeover and machine setup times. . Economical for high production runs, typically 10 000þ. . Full automation achievable. Robot machine loading and unloading common. 2.1F Injection molding process. 64 Selecting candidate processes //SYS21///INTEGRAS/B&H/PRS/FINALS_07-05-03/0750654376-CH002-1.3D – 65 – [35–248/214] 9.5.2003 2:05PM . Tooling costs are very high. Dies are usually made from hardened tool steel. . Equipment costs are very high. . Direct labor costs are low to moderate. . Finishing costs are low. Trimming is required to remove gates and runners. Typical applications . High precision, complex components . Automotive and aerospace components . Electrical parts . Fittings . Containers . Cups . Bottle tops . Housings . Tool handles Design aspects . Very complex shapes and intricate detail possible. . Holes, inserts, threads, lettering, color, bosses and minor undercuts possible. . Uniform section thickness should be maintained. . Unsuitable for the production of narrow necked containers. . Variation in thickness should not exceed 2:1. . Marked section changes should be tapered sufficiently. . Living hinges and snap features allow part consolidation. . Placing of parting line important, i.e. avoid placement across critical dimensions. . The clamping force required proportional to the projected area of the molded part. . Radii should be as generous as possible. Minimum inside radii ¼ 1.5 mm. . Draft angle ranging from less than 0.25 to 4  , depending on section depth. . Maximum section, typically ¼ 13 mm. . Minimum section ¼ 0.4 mm for thermoplastics, 0.9 mm for thermosets. . Sizes ranging 10 g–25 kg in weight for thermoplastics, 6 kg maximum for thermosets. Quality issues . Thick sections can be problematic. . Care must be taken in the design of the running and gating system, where multiple cavities used to ensure complete die fill. . Control of material and mold temperature critical, also injection pressure and speed, condition of resin, dwell and cooling times. . Adequate clamping force necessary to prevent the mold creating flash. . Thermoplastic molded parts usually require no de-flashing: thermoset parts often require this operation. . Excellent surface detail obtainable. . Surface roughness a function of the die condition. Typically, 0.2–0.8 mm Ra is obtainable. . Process capability charts showing the achievable dimensional tolerances using various materials are provided (see 2.1CC). Allowances of approximately Æ0.1 mm should be added for dimensions across the parting line. Note, that charts 1, 2 and 3 are to be used for components that have a major dimension, greater than 50 mm, and typically large production volumes. The chart titled ‘Light Engineering’ is used for components with a major dimension, less than 150 mm, and for small production volumes. Injection molding 65 //SYS21///INTEGRAS/B&H/PRS/FINALS_07-05-03/0750654376-CH002-1.3D – 66 – [35–248/214] 9.5.2003 2:05PM 2.1CC Injection molding capability chart. 66 Selecting candidate processes //SYS21///INTEGRAS/B&H/PRS/FINALS_07-05-03/0750654376-CH002-1.3D – 67 – [35–248/214] 9.5.2003 2:05PM 2.2 Reaction injection molding Process description . Two components of a thermosetting resin are injected into a mixing chamber and then injected into the mold at high speed where polymerization and subsequent solidification takes place (see 2.2F). Materials . Mostly thermosets. . Foamed materials possessing a solid skin can be created by setting up a pressure differential between mixing chamber and mold. . Can add chopped fiber material (glass, carbon) for added stiffness to mixing to produce composites. Process variations . Mold material is usually aluminum. Can also use resin for low production runs or hardened tool steel for very high volumes. . Further heating of resin components before mixing is dependent on material used. Economic considerations . Production rates from 1 to 10/h. . Lead times can be several weeks. . Material utilization good. Less than 1 per cent lost in scrap. . Scrap cannot be recycled. 2.2F Reaction injection molding process. Reaction injection molding 67 //SYS21///INTEGRAS/B&H/PRS/FINALS_07-05-03/0750654376-CH002-1.3D – 68 – [35–248/214] 9.5.2003 2:05PM . Flexibility limited by dedicated dies, die changeover and machine setup times. . Economical for low to medium production volumes (10–10 000). . Can be used for one-offs, e.g. prototyping. . Tooling costs low. . Equipment costs high. . Direct labor costs moderate to high. . Finishing costs low. A little trimming required. Typical applications . Car bumpers . Cups . Containers . Panels . Housings . Footwear . Garden furniture Design aspects . Very complex shapes and intricate detail possible. . Ribs, holes, bosses and inserts possible. . Small re-entrant features possible. . Radii should be as generous as possible. . Uniform section thickness should be maintained. . Marked section changes should be tapered sufficiently. . Placing of parting line important, i.e. avoid placement across critical dimensions. . Draft angles ranging 0.5–3  , depending on section depth. . Maximum section ¼ 10 mm. . Minimum section ¼ 1.5 mm; foamed material ¼ 3 mm. . Maximum dimension ¼ 1.5 m. . Sizes ranging 100 g–10 kg in weight. Quality issues . Thick sections can be problematic. . Care must be taken in the design of the running and gating system, where multiple cavities are used to ensure complete die fill. . Problems can be created by premature reaction before complete filling of mold. . Excellent surface detail is obtainable. . Surface roughness is variable, but mainly dependent on mold finish. . Achievable dimensional tolerances are approximately Æ0.05 at 25 mm, Æ0.3 at 150 mm. Allowances of approximately Æ0.2 mm should be added for dimensions across the parting line. 68 Selecting candidate processes [...]... achievable dimensional tolerances is provided (see 2.6CC) Allowances of approximately Æ0.1 mm should be added for dimensions across the parting line //SYS21///INTEGRAS/B&H/PRS/FINALS_0 7-0 5-0 3/07506 543 76-CH00 2-1 .3D – 79 – [35– 248 /2 14] 9.5.2003 2:05PM Blow molding 79 2.6CC Blow molding process capability chart //SYS21///INTEGRAS/B&H/PRS/FINALS_0 7-0 5-0 3/07506 543 76-CH00 2-1 .3D – 80 – [35– 248 /2 14] 9.5.2003 2:05PM... thickness tolerances are typically Æ0.25 mm //SYS21///INTEGRAS/B&H/PRS/FINALS_0 7-0 5-0 3/07506 543 76-CH00 2-1 .3D – 74 – [35– 248 /2 14] 9.5.2003 2:05PM 74 Selecting candidate processes 2.5 Vacuum forming Process description A plastic sheet is softened by heating elements and pulled under vacuum on to the surface form of a cold mold and allowed to cool The part is then removed (see 2.5F) 2.5F Vacuum forming process. .. //SYS21///INTEGRAS/B&H/PRS/FINALS_0 7-0 5-0 3/07506 543 76-CH00 2-1 .3D – 81 – [35– 248 /2 14] 9.5.2003 2:05PM Rotational molding 81 Tooling costs low Equipment costs low to moderate Labor costs moderate Finishing costs low Little finishing required Typical applications Water tanks Storage vessels Dust bins Buckets Housings Drums Prototypes Design aspects Complexity limited to large, hollow parts of uniform... Process capability charts showing the achievable dimensional tolerances using various materials are provided (see 2.3CC) Allowances of approximately Æ0.1 mm should be added for dimensions across the parting line 2.3CC Compression molding process capability chart //SYS21///INTEGRAS/B&H/PRS/FINALS_0 7-0 5-0 3/07506 543 76-CH00 2-1 .3D – 72 – [35– 248 /2 14] 9.5.2003 2:05PM 72 Selecting candidate processes 2 .4. .. cooled Thermoforming: for thin-walled parts such as packaging Economic considerations Production rates from 60 to 360/h commonly Cups can be produced at 3600/h Lead times of a few days typically //SYS21///INTEGRAS/B&H/PRS/FINALS_0 7-0 5-0 3/07506 543 76-CH00 2-1 .3D – 75 – [35– 248 /2 14] 9.5.2003 2:05PM Vacuum forming 75 Material utilization moderate to low Unformed parts of the sheet are lost and... can occur, particularly at sharp corners Surface detail fair Surface finish good and related to the condition of mold surface Achievable tolerances ranging Æ0.25–Æ2 mm, and largely mold dependent Wall thickness tolerances typically Æ20 per cent of the nominal //SYS21///INTEGRAS/B&H/PRS/FINALS_0 7-0 5-0 3/07506 543 76-CH00 2-1 .3D – 77 – [35– 248 /2 14] 9.5.2003 2:05PM Blow molding 77 2.6 Blow molding Process description... before removal of the part A process capability chart showing the achievable dimensional tolerances is provided (see 2.7CC) Allowances of approximately Æ0.5 mm should be added for dimensions across the parting line Wall thickness tolerances are generally between Æ5 and Æ20 per cent of the nominal //SYS21///INTEGRAS/B&H/PRS/FINALS_0 7-0 5-0 3/07506 543 76-CH00 2-1 .3D – 82 – [35– 248 /2 14] 9.5.2003 2:05PM 82... 2:05PM 82 Selecting candidate processes 2.7CC Rotational molding process capability chart //SYS21///INTEGRAS/B&H/PRS/FINALS_0 7-0 5-0 3/07506 543 76-CH00 2-1 .3D – 83 – [35– 248 /2 14] 9.5.2003 2:05PM Contact molding 83 2.8 Contact molding Process description Glass fiber reinforced material (30 45 per cent by volume) and a liquid thermosetting resin are simultaneously formed into a male or female mold and cured... days //SYS21///INTEGRAS/B&H/PRS/FINALS_0 7-0 5-0 3/07506 543 76-CH00 2-1 .3D – 78 – [35– 248 /2 14] 9.5.2003 2:05PM 78 Selecting candidate processes Integration with extrusion process to produce parison provides continuous operation There is generally little material waste, but can increase with some complex geometries using extrusion blow molding Full automation readily achievable Flexibility limited... mold opening and the product density will tend to vary more than those perpendicular to the mold opening Flash molds do not require that the quantity of material is controlled //SYS21///INTEGRAS/B&H/PRS/FINALS_0 7-0 5-0 3/07506 543 76-CH00 2-1 .3D – 71 – [35– 248 /2 14] 9.5.2003 2:05PM Compression molding 71 Tumbling may be required as a finishing process to remove flash Surface detail is good Surface roughness . 2:05PM //SYS21///INTEGRAS/B&H/PRS/FINALS_0 7-0 5-0 3/07506 543 76-CH00 2-1 .3D – 63 – [35– 248 /2 14] 9.5.2003 2:05PM 2 Plastic and composite processing //SYS21///INTEGRAS/B&H/PRS/FINALS_0 7-0 5-0 3/07506 543 76-CH00 2-1 .3D – 64 – [35– 248 /2 14] 9.5.2003. degree of automation possible. 2.4F Transfer molding process. 72 Selecting candidate processes //SYS21///INTEGRAS/B&H/PRS/FINALS_0 7-0 5-0 3/07506 543 76-CH00 2-1 .3D – 73 – [35– 248 /2 14] 9.5.2003. forming process. 74 Selecting candidate processes //SYS21///INTEGRAS/B&H/PRS/FINALS_0 7-0 5-0 3/07506 543 76-CH00 2-1 .3D – 75 – [35– 248 /2 14] 9.5.2003 2:05PM . Material utilization moderate to low.