A series of lectures given in the Dept of Polymer Engineering to students at UMIST

S F Bush and J M Methven

Aim

To allow the student to make strategic choices of material and process for polymer-based products.

Learning Outcomes

In the context of applications to the aerospace, automotive, construction and engineering sectors:

• To be able to understand and use the concepts of Utility and Scale in the materials and process selection stage of design;
• To recognise the main features of the various available manufacturing processes and the way in which the shape of product narrows the choice of process;
• To understand the main forms of reinforcement and additive used in polymer composites and their uses in products;
• To understand the application of rapid prototyping and rapid tooling in the making of small quantities of pilot products.

Syllabus

Concept of Utility[1] as a guide to selecting materials. Influence of production scale on process choice. Examples taken from aerospace, automotive and consumer applications using standard production processes including extrusion, injection moulding, resin transfer, filament winding and autoclave moulding.

Continuous and discrete fibre composites:[2] relative advantages and disadvantages. Design of structural components using continuous fibre reinforcements by pultrusion. Control of fibre placement. Composite failure mechanisms. Design of sandwich panels and honeycomb laminates, rubber products: seals, gaskets, springs. Applications to aerospace, building and piping systems.

Concept of Fibre Management[1] for different processes and products. Distinction between thermoplastic and thermoset composites and between speciality and bulk polymers. Common types of polymer and of fibre and their advantages and disadvantages. Minimising weight and maximising recycle in automotive and packaging applications. Mould design considerations in injection moulding applications to aerospace and other panel forms.

Fibre reinforced sheet moulding compounds[2] and processes and their application to large area panels in construction and land transport. Polymer composites made by resin transfer moulding. Lotus cars example. Polymer composites made by continuous fibre pultrusions including microwave assisted methods and their application in fibre optic cabling for terrestrial and aerospace application.

Rapid prototyping and pilot tooling[3] for metal as well as polymeric products. Prototyping techniques based on CAD and Stereolithography; 3-D printing, (laminated object manufacture and laser sintering.) Examples of surgical instruments made this way. Use of silicone moulds as short run production tools.

References

[1] Prof S F Bush

[2] Dr J M Methven

[3] S F Bush/J M Methven

Keynote paper of Composites Manufacturing Technology Symposium 6, Polymer Processing Society 9th Annual Meeting, UMIST, 5th-8th April 1993.

S F Bush

Introduction

The ultimate test of a polymer composite artefact is its entry into commercial production. It is the combination of material properties, geometrical design and manufacturing cost, not any of these separately, which will determine whether this occurs, or, having entered production will stay there.

Polymer products cannot, however, in general be defined in the way their precursor chemical monomers are, by a chemical structure, but only by effects, so that no one process either converting a monomer to a polymer, or a polymer into a solid artefact, is quite like another. More importantly, the effects specified can usually be obtained by several polymeric materials as well as possibly by metals and ceramics. An example is a pipe which can be achieved by man-made polymers, natural polymers, (e.g. wood), metals and ceramics (clays and cements), while the effects demanded may include mechanical, chemical, electrical properties, ease of installation, demountability and so on. Ultimately a polymer product provides a benefit to the customer at a cost which represents the full cost of the pathway from the feedstocks available and feedstocks themselves.

In the design of polymer product and process combinations, cost is thus an absolutely central consideration, every bit as important as material properties and thermodynamics, and without which consideration no sense can be made of the choices made by industry and no realistic view possible of the needs and opportunities for industry-linked research and innovation (Ref 1).

References

[1] R Malpas, Phil Trans Royal Society, London, A322 347-360 (1987)

[2] S F Bush, Development of new processes for the volume production of polymer composite artefacts, I Mech E Conf, Fibre Reinforced Composites, C400/029 237-243 (1990)

See also section on Systems Design & Control.

Paper to the Institution of Mechanical Engineers Conference, Fibre-reinforced Composites, Liverpool, 237, 27th-29th March, 1990.

S F Bush

Synopsis

The paper uses the Utility function introduced in an earlier paper (Ref 1) to analyse from an overall point of view the benefits and disbenefits of some current developments in fibre reinforced polymer composites. Given the raw materials and the end application, the chief influence over whether a polymer composite is actually used in practice is the fabrication process. A particular process is seen as a series of steps along a pathway from raw materials to end-product. Some steps, particularly those connected with fibre-organisation, will be rate limiting in the sense that they introduce a high negative Utility. The development of new processes will thus seek to quantify the disbenefit of such steps and relieve or avoid them.

References

(1) BUSH S F, Utility and complexity in the selection of polymeric materials, 2nd International Materials Engineering Conference, London, 1985, 229-236, Institute of Mechanical Engineers.

(2) GALLI E, Polymers and the IBM Proprinter, Plastics Design Forum, 1985 (May), 17-24.

(3) GIBSON A G, Rheology and packing effects in the injection moulding of reinforced thermoset systems, Composite Processing Conference, UMIST 1988, 6.1-6.15, Institution of Chemical Engineers (NW Branch).

(4) BUSH S F, Extrusion of melts containing semi-coherent fibre structures, 5th International Polymer Processing Conference, Kyoto 1989, Polymer Processing Society.

(5) BAILEY R S, DAVIES M and MOORE D R, Processing property characteristics for long glass fibre reinforced polyamide, Composites (1989) 20, 453-460.

(6) VU-KHANH T and DENAULT J, Effects of processing on mechanical performance of long-fiber reinforced thermoplastics, 5th International Polymer Processing Conference, Kyoto 1989, Polymer Processing Society.

(7) COGSWELL F N, The next generation of injection moulding materials, Plastics and Rubber International Conference (1987), 12 36-39.

Invited paper to 7th Engineering Design Conference, Birmingham, England, 25th-27th September 1984.

S F Bush

Abstract

The paper sets out to examine the relevance of plastics to engineering through the application of particular design concepts. The objective is to provide an overall analytical view of the factors which determine the choice of the material and manufacturing technology combination. Design of a system or artefact is seen as the specification of elemenatary functions and components and their interconnections. The complexity of a system is then characterised as the sum of these. The cost and some major properties of different polymeric materials are related to a simple definition of their chemical complexity.

The application of particular materials is governed by their utility expressed as the sum of their effects on (a) a component and (b) the whole system. To determine this, the manufactured cost is expressed as simple functions of the raw material, process and artefact complexities, and the scale of production. The main advantage of polymeric materials is found through new decompositions of the overall design.