Design and manufacture of vacuum forming moulds

This paper presents an investigation of the positive vacuum forming process. Previous research has indicated requirements of a draft angle of at least two to five degree and a depth to width ratio of not greater than 1:1. For specific formed geometry that required smaller draft angles and greater draw depths these limitations may make the positive vacuum forming process not applicable. The overall aim of this work was to allow the process to become more versatile. This work focused on three prototype moulds which were designed, manufactured, tested and analysed with a view to over come the present process limitations. Moulds were made of wood with a size of 68 x 68 x 75mm. Air holes of 1 and 10 mm diameter were drilled in to these moulds in different positions. Polypropylene terephthalate glycol (PETG) materials was used to make the final product via the vacuum process. To release the product from the mould a constant 8bar pressure was applied. Proper time to make the final products and the quality of the final product were investigated. It was found that moulds with air holes opening in all surfaces resulted in shorter cycle times, lower air pressure and better quality of formed parts. It was also found in this work that a zero draft angle and as well as 1:1.1 draw depth was possible to achieve in the vacuum forming process.