Injection moulding: metal 290-1 plastics

Two examples are used to explain where the use of plastics is appropriate in car bodies, and where metals are more appropriate. Comparisons between plastics and wood are difficult, since different processing methods apply, and certain designs are optimum for each material. A design optimised for injection moulding in plastic (Sections 13.5 and 13.6), is neither suitable for anisostropic materials like wood, nor easy to construct. 

The foundation for this technology is that products are built up layer by layer using laser-fused metal powders of polymers. Thus, rather than casting or machining a metal item or injection moulding a plastic product, this item is created from a series of very thin layers of material. 

When metals are rolled or forged, or drawn to wire, or when polymers are injection-moulded or pressed or drawn, energy is absorbed. The work done on a material to change its shape permanently is called the plastic work- its value, per unit volume, is the area of the cross-hatched region shown in Fig. 8.9 it may easily be found (if the stress-strain curve is known) for any amount of permanent plastic deformation, e. Plastic work is important in metal- and polymer-forming operations because it determines the forces that the rolls, or press, or moulding machine must exert on the material. 

The two major plastics processing techniques of extrusion and injection moulding are used for coating metals. 

All-plastic integrated front-end module for BMW Mini Cooper is injection moulded from StaMax, a LFRT, with no metal support. 

Polyoxymethylene (POM) plastics are highly crystalline thermoplastics that are obtained by polymerization of formaldehyde and can also be in the form of trioxy-methylene oligomers (trioxane). The world-wide consumption in 1997 was 0.5 x 106 t for car parts and other articles processed by injection moulding. Polyacetals are primarily engineering materials being used to replace metals. 

Various approaches exist to increase the electrical conductivity of plastic materials with nanoparticles [70,71]. The precipitation of nanometal particles to the reinforcing fibres is a very effective approach to achieve a good electrical conductivity at low concentrations. Pt was used as a model metal particle to avoid oxidation on processing by extmsion and injection moulding. Stable suspensions of Pt (supplied by Tsutomu Sakai, KRI Inc., Japan) [72] were applied in two concentrations suspension 1 150 mg Pt/L, suspension 2 1500 mg Pt/L, both containing particles of the size between 2 and 5 nm (Figure 5.17). The fibres were immersed... 

The drive sprocket is injection-moulded in rubber-toughened PA6.6, which is resistant to repeated impact over a wide range of temperatures, and which shows excellent abrasion resistance. The plastic sprocket absorbs the shock of gear changes better than metal, causes less wear on the chain, and provides a quieter ride. The polymer is resistant to lubricants and other liquids. Reduced firiction improves power transmission and, coupled with a lower weight, results in better performance. 

Gotzmann [60] discusses methods used in the manufacture of metal plastic hybrid components such as glass fibre reinforced PA around a steel or aluminium profile placed in the mould used for injection moulding plastics. Some applications of such components were examined, and computer aided materials selection, finite element analysis and computer simulation systems developed for use in this technology are described. 

Moreover, there were signs of defects on the plastic inside the metal tube, at a point below the subcritical cracks. They comprised a series of flutes (Fig. 10.26) and a curious wavy line on the inner surface (Fig. 10.27). This combination of features observed on the plastic insert indicated material degradation, because this part should have had a smooth blemish-free surface. Being an injection moulding, the surface had been in contact with the steel core. If the polymer had flowed, then the viscosity must have dropped to allow the material to flow when the product was removed from the tool, showing that the molecular weight was too low. 

This joint is compact and can be accurately made, though it can be expensive -particularly in metal. Nonetheless, it is popular in the manufacture of injection mouldings as it allows the accurate placement of the plastics parts. Such joints may be also made at virtually no extra cost in GRP components, using any of the shaping methods for such parts. 

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