Chapter 6 Plastic and Polymer Composite Fabrication Processes Screen on batch size* Molding Processes for PE: Molding Processes for Nylon (30% GF): Desired Batch Size 1e+008 1e+007 1e+006 Blow Moulding Powder methods Injection Moulding Sheet forming Economic batch size Economic batch size (units) 100000 10000 1000 100 Expanded foam molding Rolling and forging Electro-discharge machining Polymer Casting Die Casting Sand casting Compression Lay-Up Moulding methods Rotational Moulding 10 Resin transfer molding (RTM) 1 Thermoforming Rapid prototyping *Using the CES EduPack Level 2 DB Demo: the Process data-table MFA and DC 2005 1
most common (60-70%) Process Plastic pellets are heated in the injection unit and forced through a runner system/gate(s) into a cavity in a mold. Batch Process Equipment Clamping Unit (Ejection System) Injection (Plasticating) Unit Frame Main functions of Plasticating unit 1.Convey solid material/melt 2.Mix to produce homogeneous melt 3.Melt material Range of 300º F (PVC) to 740º F (Polysulphone) Materials Both amorphous and semi-crystalline are done easily Narrow molecular weight distribution With modifications to the equipment thermoset materials and liquid Silicone can be used 4.Develop pressure for injection 2
Parts Three dimensional Can be very complex Multiple cavitation is common (128 cavities) Tooling - Molds Generally steel, but some Aluminum tooling is used High pressure process molds are beefy Plastic pressures around 30,000 psi Weight LXWXH/4 (in inches) Tooling is expensive and can take a long time to create Extrusion Plastic pellets or powders are heated in a plasticating unit and the melt is forced through a forming die. Continuous Process Extrusion Equipment Injection (Plasticating) Unit Frame 3
Extrusion Materials Both amorphous and semi-crystalline are done easily Wide molecular weight distribution Extrusion Parts Two dimensional Sheet Hoses Line Rod Vinyl siding Pipes Extrusion Tooling - Dies Generally steel Aluminum is common though Low pressure process Tooling can be expensive Shorter lead times Sheet is heated and formed to the desired shape Can be a batch or continuous process Some consider Thermoforming to be a secondary process because the material needs to be formed into sheet prior to being thermoformed. 4
Equipment Heating unit Vacuum unit Tool or die 5
Materials Both amorphous and semi-crystalline are done Semi-crystalline are more difficult Wide molecular weight distribution Parts Three dimensional Generally simple shapes Tooling Dies or molds Generally Aluminum, but prototypes are commonly made epoxy, wood, plaster, and composite materials Low pressure process Tooling is relatively inexpensive Shorter lead times Blowmolding 2 basic types Extrusion batch Injection Blow Molding Stretch blow molding (preforms) Injection molding method (indexing) 6
Blowmolding Equipment Depends on type of blowmolding you are doing Extrusion» Extruder» Dies and Blowpins» Clamping system Injection» Preforms (Injection molding machine)» Heating unit» Blowing machine Blowmolding Materials Both amorphous and semi-crystalline are done Semi-crystalline are more difficult Highly Crystalline materials (Nylon) are very difficult Wide molecular weight distribution Blowmolding Parts Three dimensional Generally simple shapes Hollow May need trimmed Blowmolding Tooling Dies or tools Generally Aluminum (some may have brass inserts) Steel Pinchoff areas Low pressure process Tooling is relatively inexpensive Shorter lead times 7
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