Dust Extraction Inlet

A client came to us requiring the manufacturing of a number of moulds. These were for a dust extraction inlet unit. Within the unit, there were four individual components that needed to fit together exactly so that the dust could not escape.  

We were asked to make two master moulds that would make four moulded components. Each of the two moulds were required to be designed in such a way that they could be changed over with ease. In normal circumstances, four moulds would have been designed for the four parts, but we understood that we had to develop the design of the moulds so that only two were required with change inserts, so that each would make two parts with interchangeable inserts. 

The surface finish had to be a specific fine grade of VDI18.  

Our design team worked on the first part of the development process to determine which components would suit being moulded from which mould. Through the use of Computer Aided Design (CAD), we were able to make an informed decision regarding this. During this process, we also found that the shape and profile of the components made it difficult to line up so that they would release on ejection and become mouldable. We developed draft angles, and designed the mould so that the features that needed to be aligned were created on a 3D electrode. When this was used to spark erode impressions into steel, it would produce a cavity that was in the correct plane, and the feature would nest together. This also meant holes would be round, not oval.  

We then had to choose what material would be used for these components. Polypropylene was the most suitable for this, due to its high recyclability. There was an uncertainty with this material regarding shrinkage; polypropylene has a tendency to shrink in two directions, the flow direction and the transversal direction. This can cause issues with fit and function, causing potential mismatch with two mating parts, and this project required precision when it came to the finished result.  

We ran a first trial, which went well. The surface finish, which had to be a specific fine grade of VDI18, was perfect, but two of the four components did not fit together. The material had towed in on the side walls, which did not allow the nesting features to fit with one another. 

This led to us making modifications to support the side walls, adding three ribs per side to keep the wall in position. Adding these could potentially create sink marks on the visible surface, which would not be acceptable, but we went ahead with the trial to see the result.  

This modification was successful with very little visible sink marks, and the two parts linked together with ease. There was an issue with shrinkage at the top edge, but not at the sides or the bottom. As such, a second modification was made to increase the plastic on the top edge in order to remove that mismatch and overcome the shrinkage issue.