Nov 27 Plastics - Coursepack ME 250 Nov 27, 2007 Processing...

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ME 250 Nov 27, 2007 Processing of Plastics Coursepack Section: 13.6 (Injection molding) 13.6.1 – 13.6.5 Section: 13.8 (Blow molding) 13.8.1, 13.8.2 Sections: 13.9 (Thermoforming) 13.10 (Casting-one para) 13.12 (Design issues) Plastics industry Plastics industry contributed $341Billion to the U.S. economy (1.1M jobs) Ranks amongst the top manufacturing industries Plastics play an indispensable role in variety of markets including packaging, construction, home goods, electronics, etc. Advantage of Plastics •A lmos t unlimited variety of part geometries • Plastic molding is a net shape process – Further shaping is not needed • Less energy is required than for metals due to much lower processing temperatures – Handling of product is simplified during production because of lower temperatures • Painting or plating is usually not required Comparing engineering materials + ++ + + +++ joining no + + +++ + +++ Ceramics + ++ +++ +++ recycle + +++ +++ + coloring no + +++ + Polymers Yes/no some + +++ Composites no +++ +++ +++ Glass +++ + +++ ++ Metals conductor? corrosion resistance forming strength/ weight material from Oct 25 lecture Compared to metals Low strength and stiffness – Plastics are not as strong or stiff as metals – Strength-to-weight ratios for some plastics
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Compared to metals Impact Resistance – Capacity of plastics to absorb impact is generally good; plastics compare favorably with most metals Service temperatures – Limited relative to metals and ceramics – Dimensional changes due to temperature changes much more significant than for metals Compared to metals Product degradation – from sunlight and other forms of radiation – due to oxygen and ozone atmospheres – soluble in many common solvents However, plastics are resistant to conventional corrosion mechanisms that afflict many metals Why plastic products Why plastic products? Applications of plastics have increased at a much faster rate than either metals or ceramics during the last 50 years – Many parts previously made of metals are now being made of plastics • High strength-to-weight ratio • Ease of manufacturing • Low cost • Wide choice of colors Plastic Products Plastics can be shaped into a wide variety of products: – Molded parts – Extruded sections – Films – Sheets – Insulation coatings on electrical wires – Fibers for textiles Two Types of Plastics Thermoplastics – To shape a thermoplastic polymer it must be heated so that it softens to the consistency of a liquid – Chemical structure remains unchanged during heating and shaping – More important commercially, comprising more than 80% of total plastics tonnage Thermosets – Undergo a curing process during heating and shaping, causing a permanent change ( cross-linking ) in molecular structure – Once cured, they cannot be remelted
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Video Plastics manufacturing Thermoplastics – Injection molding – Blow molding – Rotational molding
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Nov 27 Plastics - Coursepack ME 250 Nov 27, 2007 Processing...

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