Rapid Tooling and the LOMOLD Process
Thesis (MScEng (Industrial Engineering))--University of Stellenbosch, 2005.
The LOMOLD process is a new plastic moulding process being researched at the University of Stellenbosch. The process essentially combines injection moulding and compression moulding. Molten plastic is forced into the mould cavity using a plunger. This plunger then forms part of the cavity wall. The plunger face must therefore follow the geometry of the part. Rapid Tooling evolved from Rapid Prototyping. There are two categories of Rapid Tooling: indirect and direct rapid tools. Indirect rapid tools are manufactured by using a master pattern to form the mould cavity. The accuracy of the mould cavity depends heavily on the accuracy of the master pattern. The master pattern is usually produced using Rapid Prototyping technology. Direct rapid tools use Rapid Prototyping technology to build the mould through and additive, layer by layer process or a subtractive process. This research investigates the use of Rapid Tools for the LOMOLD process. Aluminium Filled Epoxy Tooling (AFET) represents the indirect technology and CNC-machined tooling the direct technology. Both of these technologies are available at the University of Stellenbosch. Parts are manufactured on these tools using an experimental LOMOLD machine. These two technologies are compared in terms of part accuracy, tool lead time, tool cost and part cost. The research concluded that the only advantage the AFET has over the CNC-machined tool is a shorter manufacturing lead-time. In terms of tool cost, tool life, part geometric accuracy, part cost and cycle time the CNC tool is superior. Therefore the application of AFET is limited to small volume, prototype or pre-production runs for tool design confirmation, part functional testing and part appearance testing. It is also demonstrated that a cooling system on the AFET tool has no significant influence on the tool performance and should therefore, especially for production runs less than 150 parts, not be included in the tool to save on tool cost. Another conclusion is that the LOMOLD process is not consistent enough for a production process. This statement could be limited to the machine used for the research but to prove this statement wrong, the machine must be improved and more investigation is required.