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					Plastics Processes
Plastics manufacturing processes are mostly mass production processes with high volumes of output. The high cost of machinery and tooling is offset by the
speed and volume of production.

Processes                        Advantages                           Disadvantages                          Identifying features                   Products
Injection Moulding               + highly accurate                    - high set up costs                    Injection (sprue) marks, ejector pin   Mobile phone casings are
                                 + very cheap per part                - have to hide visible identifying     marks, split lines, shrinkage marks,   produced by injection moulding.
                                 + very fast                          features                               high quality surface finish, complex   This is because the accuracy of
                                 + excellent surface texture          - flashing has to be removed           form of parts, draft angle, flash.     individual parts can be assured so
                                 + complex shapes                                                                                                   that they can be assembled and
                                 + webs can be added for strength                                                                                   the cost of the parts will be low.
                                 + metal components can be placed                                                                                   The phone casings can also be
                                 inside the mould prior to forming                                                                                  produced quickly in large volumes.

Compression Moulding             + highly accurate                    - high set up costs                    Ejector pin marks, split lines,        Electrical plugs are produced by
(Thermosetting plastics)         + very cheap per part                - have to hide visible identifying     shrinkage marks, high quality          compression moulding. This is
                                 + fast                               features                               surface finish, complex form of        because the accuracy of individual
                                 + excellent surface texture          - flashing has to be removed           parts, draft angle, flash.             parts can be assured so that they
                                 + complex shapes                                                                                                   can be assembled and the cost of
                                 + webs can be added for strength                                                                                   the parts will be low. The plugs
                                 + metal components can be placed                                                                                   also have to be made from a
                                 inside the mould prior to forming                                                                                  thermosetting plastic.

Extrusion                        + fast production (9-60 meters per   - high set up costs                    Long parts with same cross section     Drain pipes and guttering are
                                 second)                              - extrusions will have to be cut and   throughout, lines/scratches along      made by extrusion. The process
                                 + accurate                           assembled to make products (extra      length, shrinkage marks, good          allows them to have the same
                                 + cheap process                      processes)                             surface finish.                        cross section down the entire
                                 + same cross section throughout                                                                                    length and to be produced
                                 + complex cross sections are                                                                                       cheaply. They have to be cut to the
                                 possible                                                                                                           correct size.

Blow Moulding                    + produces hollow parts              - high set up costs                    Small hollow parts, plastic will be    Bottles are produced cheaply and
                                 + accurate                           - only small products can be           thinner at corners, split lines.       quickly by blow moulding extruded
                                 + cheap                              produced due to draw (stretching)                                             tubes. Screw threads on the tops
                                 + fast                               on the plastic                                                                of the bottles can be applied
                                 + screw threads can be added to      - split lines are visible                                                     during the process and they will fit
                                 bottles                                                                                                            well with the lids to form a
                                                                                                                                                    watertight seal because the
                                                                                                                                                    process is accurate.


                                                                                                                                           Fortrose Academy – Product Design
Rotational Moulding   + produces large hollow parts         - slow cooling time limits speed of   Large hollow objects, uniform wall     Large plastic oil drums are
                      + uniform wall thickness makes        production                            thickness, split lines, draft angle.   produced by rotational moulding.
                      products strong                       - high set up costs                                                          They are strong due to the uniform
                      + accurate                            - split lines are visible                                                    wall thickness of the whole
                      + sides can be designed with ribs     - may require further work to                                                product – unlike blow moulding
                      to make them stronger/more rigid      make holes etc.                                                              which is weaker at the corners.

Vacuum Forming        + low cost of machinery makes it      - draw on plastic makes it weaker                                            Plastic sandwich cartons are
                      suitable for small scale production   at the corners                                                               produced quickly and cheaply by
                      + accurate                                                                                                         vacuum forming and the lips fit
                      + cheap                                                                                                            well because the process is
                      + fast                                                                                                             accurate. The bottom corners of
                                                                                                                                         the sandwich cartons will be
                                                                                                                                         thinner and weaker due to the
                                                                                                                                         plastic having been stretched.




                                                                                                                                Fortrose Academy – Product Design
Metals Processes
Metals processes can be described as thermal or mechanical. Different processes are suitable for different forms of material (e.g. sheet materials) and they
all have a variety of advantages and disadvantages.

Processes                        Advantages                         Disadvantages                          Identifying features                   Products
Extrusion                        + fast production (15-40 meters    - high set up costs                    Long parts with same cross section     Copper water pipes are made by
                                 per second)                        - extrusions will have to be cut and   throughout, lines/scratches along      extrusion. The process allows them
                                 + accurate                         assembled to make products (extra      length, good surface finish.           to have the same cross section
                                 + cheap process                    processes)                                                                    down the entire length and to be
                                 + same cross section throughout                                                                                  produced cheaply. They have to be
                                 + complex cross sections are                                                                                     cut to the correct size and bent to
                                 possible                                                                                                         shape as required.

Die Casting                      + highly accurate                  - high set up costs                    Injection (sprue) marks, ejector pin   Wine bottle ‘corkscrew’
                                 + very cheap per part              - have to hide visible identifying     marks, split lines, high quality       openers are produced by die
                                 + very fast                        features                               surface finish, complex form of
                                 + excellent surface texture        - flashing has to be removed           parts, draft angle, flash.             casting. All of the parts will
                                 + complex shapes                   - parts are quite weak                                                        fit together because they
                                 + webs can be added for strength                                                                                 are accurately made and
                                                                                                                                                  there will be a high quality
                                                                                                                                                  surface finish to help them
                                                                                                                                                  look good and stay hygienic.

Sand Casting                     + cheap small scale production     - poor surface texture                 Rough surface texture, draft angle,    Anvils and vices are produced by
                                 + cheap set up costs               - time consuming                       complex shapes.                        sand casting. They are irregular
                                 + very complex parts can be        - needs skilled labour                                                        shapes of varying thickness and
                                 produced                           - needs machined to clean up                                                  will require additional work to
                                 + parts with varying thicknesses   surfaces, drill holes and remove                                              have holes drilled and screw
                                 can be produced                    additional metal                                                              threads applied.
                                 +no wastage of materials           - creates brittle outer shell

Piercing and Blanking            + accurate                         - high set up costs                    Thin sheet material, shear marks.      Car body panels are cut quickly
                                 + fast                             - sheet material only                                                         and accurately from rolls of sheet
                                 + cheap                                                                                                          metal in automated factories. The
                                                                                                                                                  sheet with holes in it is called a
                                                                                                                                                  piercing. The left over metal parts
                                                                                                                                                  are called blacks. Excess material is
                                                                                                                                                  recycled.


                                                                                                                                        Fortrose Academy – Product Design
Press Forming   + accurate                            - high set up costs                Thin sheet material, bends, folds,     Car body panels are shaped
                + fast                                - sheet material only              ridges.                                accurately by press forming so that
                + cheap                                                                                                         all of the individual panels will fit
                + bends, folds and ridges will make                                                                             together. The bends, folds and
                the product stronger and more                                                                                   ridges in the metal sheets make it
                rigid                                                                                                           stronger and protect passengers
                                                                                                                                from impacts.

Drop Forging    + fast                                - not very accurate                Strong parts, complex shapes, cold     Tools like spanners and hammers
                + very strong parts produced (not     - flashing has to be removed       to touch, draft angle, flash.          are produced by drop forging
                cutting grain)                                                                                                  which makes them very strong so
                + varying thicknesses can be                                                                                    that they do not bend or deform
                achieved                                                                                                        when being used.
                + patterns can be added
                + complex shapes can be produced

Turning         + highly accurate                     - high set up costs                Circular/cylindrical parts, highly     Cam shafts and circular engine
                + CNC produces identical parts        - skilled labour (non CNC)         accurate parts, high quality surface   parts which need to be highly
                + CNC can be programmed to            - large volume of waste material   finish, machining marks.               accurate are produced by turning
                produce different parts               - not as strong as drop forging                                           with metalwork lathes.
                + CNC will be fast                    (cutting through grains)

Milling         + highly accurate                     - high set up costs                Complex shapes, highly accurate        Engine blocks which have already
                + CNC produces identical parts        - skilled labour (non CNC)         parts, high quality surface finish,    been cast will have faces milled so
                + CNC can be programmed to            - large volume of waste material   machining marks.                       that they perfectly flat and holes
                produce different parts                                                                                         will be drilled accurately in the
                + CNC will be fast                                                                                              correct position so that all the
                                                                                                                                intricate parts will fit together and
                                                                                                                                be able to move properly.
                                                                                                                                Moulds and dies for injection
                                                                                                                                moulding and die casting are also
                                                                                                                                made by this highly accurate
                                                                                                                                process.




                                                                                                                        Fortrose Academy – Product Design
Woods Processes
Processes for manufacturing in wood usually require a high degree of human input from skilled craftsmen. Please also refer to the sections on assembly and
finishes in wood.

Processes                        Advantages                          Disadvantages                         Identifying features                 Products
Turning                          + cheap process                     - expensive skilled labour (non       Circular/cylindrical parts, good     Banister posts are produced by
                                 + CNC produces accurate and         CNC)                                  quality surface finish, possible     turning on a lathe. The material
                                 identical parts                     - large volume of waste material      machining marks.                     has to be prepared prior to turning
                                 + CNC can be programmed to          - material has to be cut to correct                                        so that it is the correct size and
                                 produce different parts             size and shape in advance                                                  shape. Can be automated with
                                 + CNC will be fast                                                                                             CNC.

Routing                          + cheap process                     - expensive skilled labour (non       Wooden boards with accurately        Decorative edges and slots in
                                 + CNC produces accurate and         CNC)                                  placed holes, decorative edges and   traditionally crafted furniture will
                                 identical parts                     - large volume of waste material      holes with uniform section.          be applied by a router which can
                                 + CNC can be programmed to          - material has to be cut to correct                                        be automated to repeat the same
                                 produce different parts             size and shape in advance                                                  process accurately and cheaply
                                 + CNC will be fast                                                                                             (flat pack furniture).

Spindle Moulding                 +cheap                              - requires skilled labour             Long parts, uniform cross section,   Skirting boards and wooden
                                 + accurate                          - material has to be cut to correct   high quality surface finish.         mouldings are strips of wood
                                                                     size and shape in advance                                                  which have been passed through a
                                                                                                                                                spindle moulder to produce a
                                                                                                                                                uniform, decorative edge along
                                                                                                                                                their length.

Laminating (Boards)              + large, wide boards produced       - expensive manual labour             Wide boards of natural timber,       Dining table tops
                                 which will not bow                  - time and labour intensive           alternating end grain on ends of
                                                                                                           strips.

Laminating (Sheets)              + thin, strong sheets of wood       - expensive manual labour             Thin and strong boards, layering     Skateboard tops
                                 which can be bent to shape during   - time and labour intensive           visible at the edges.
                                 forming for extra structural
                                 strength

Laminating (Beams)               + large, possibly curved beams      - expensive manual labour             Long beams made of smaller           Roof beams in large halls
                                 made from small pieces of timer     - time and labour intensive           individual pieces of timber.
                                 + strong as grain runs throughout



                                                                                                                                          Fortrose Academy – Product Design

				
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posted:7/6/2011
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