Design and Manufacturing Vacuum Forming

Process A sheet of thermoplastic material is clamped around its edges and heated until flexible. A heat-proof mould of the required shape is raised into the softened plastic. The air between the sheet and the mould is evacuated by a vacuum pump. Atmospheric pressure then forces the plastic sheet tightly over the mould. Materials High Impact Polystyrene sheets from 1mm to 3mm in range of colours are available Including clear sheet used for bubble packaging in presentation boxes.

2. The finished former is placed in a vacuum forming machine. THE STAGES INVOLVED IN VACUUM FORMING 1. First, a former is made from a material such as a soft wood. The edges or sides are shaped at an angle/draft of 3º so that when the plastic is formed over it, the former can be removed easily. 2. The finished former is placed in a vacuum forming machine. 3. A sheet of plastic e.g. polystyrene is clamped in position above the mould

MOULDING PROCESS 4. The heating elements are then turned on and the plastic slowly becomes soft and pliable as it heats up. The plastic can be seen to ‘sag’ and as the surface expands 5. After a few minutes the plastic is ready for ‘forming’ as it becomes very flexible or rubbery. Student: An knowledge of construction and manufacturing techniques and processes will be of benefit when considering appropriate ideas / concepts when designing for manufacture. Teachers should model (designing) demonstrate how we think, see shapes and form, use reference materials and mood boards to generate ideas. Also, show how an idea/concept can be developed in design detail and showing constructional details i.e. how the parts intend to fit together. Showing how the pcb, battery are located and secured? 6. The heater is turned off and the mould is moved upwards by lifting the lever until it locks in position.

COMPLETED MOULD 7. The 'vacuum' is turned on and this pumps out all the air beneath the plastic sheet. Atmospheric pressure above the plastic sheet forces it down on the mould. The shape of the mould can now be clearly seen through the plastic sheet. When the plastic has cooled the vacuum pump is switched off. 8. The plastic sheet is removed from the vacuum former. The sheet has the shape of the former pressed into its surface. The dimensions of the wooden blocks will be calculated by the teacher and this is the starting point for the student. Knowledge of the vacuum forming process is important before starting to design. Where possible use 2-3mm rigid polystyrene sheet to accommodate complex shapes which also provides rigidity and a feeling of quality. 9. The excess plastic is trimmed so that only the plastic bowl remains An enlarged view of the final dish is seen opposite.

Mould Manufacture To achieve the desired shape moulds may be made by gluing layers of material together and then shaping using a variety of hand and machine tools such as CNC Routers, Laser Cutting, Scroll Saws, Spindle molding table and Belt sanders . Materials used in mould construction may be MDF, Balsa wood, Modelling clay. MDF is usually used in school and cast aluminum or epoxy resin in industry. Mould strength and rigidity may increased by designing in recesses, grooves or steps. Example of trays or bubble or blister packaging produced by vacuum forming Web site link to commercial blister vacuum forming & packaging http://www.uni-plastic.com/Thermoforming%20&%20Vacuun%20Forming.htm

MAKING A MOULD By using light plywood, aluminum or Perspex sheet as a base layer on your mould, it may be attached using two sided tape so that it may be easily removed and used as the base for your completed project. See example of car mould opposite. When designing a mould it is most important to considering the removal of the vacuum formed shell. No overhanging lips or negative angles. A draft angles of 3° to 5° must be provided on all surfaces of the mould. The formed plastic and the mold is very difficult to seperate and may split or crack. A wooden mould may be dusted with Talcuum powder to aid removal.

Commercial examples of Vacuum Forming

Tips & Tricks MDF & 3mm plywood sheet are cheap and suitable materials used for manufacturing Moulds. Complex shapes can be built up in layers. Two sided tape, coins, dowels, metal crests, car badges, superglue, wood fillers, matches may be used to enhance or personalize a mould. Hole saws, counter sinking bits, counter boring bits, sanding blocks. Existing shapes may be filled with patching plaster to make a mould. Internal holes cavities in a mould must have 2 Ø mm holes drilled through to the base of the mould to all the cavity to emptied by the vacuum pump. Large or complicated shape may be dusted with talcum powder to assist in releasing them from the mould. The base of the mould may be drilled and treaded M6 to allow a handle to be attached to pull the mould from the formed shape.

STEPS in the DEVELOPMENT of the PATTERN Mould Manufacture STEPS in the DEVELOPMENT of the PATTERN 1. MDF block basic shaped to encapsulate the components and support the mechanism. 2. MDF block design refined to hold 9V battery and provide ergonomically designed profiles for Switches, LED & Variable resistors 3. Finished 2 mm Polystyrenes mould ready for motor drilling and fitting of electronic components and pulley mechanism support.

Examples of six Pattern Designs made from the MDF blank

FOUR COMPLETED MOULDS