A concept was brought to us by our client, MEP4 Offsite. This concept was a solution that would connect pressure pipework together quickly in the Build Offsite sector. This concept would allow Offsite to save time, reduce waste, unnecessary emissions, and installation risk, while improving the quality of builds.
There were important requirements for this project; the injection moulded solution needed to be able to withstand extreme forces that would attempt to force the two halves apart. If this was to happen, the boiling liquid inside the pipes would escape at a high pressure, causing a chain reaction of issues further down the line.
It was evident that material selection was going to be key for the best performance of this product.
Our process started with design and 3D printed parts, which were used to determine that the dimensions of the product would work correctly, and the locking mechanism we designed to hold both components of the product together could hold efficiently under pressure, as this was the main part of the product that would carry all of the opposing force. This locking mechanism therefore had to be designed in a way that would add strength, but would not compromise the size of the product, and would continue to hold the parts fully fixed together with no visible gaps between the two mating faces on the main body.
We knew that the mould had to be designed in such a way that we could make changes during the course of development, should it be required. As such, we had to be certain that all critical dimensions were created within the mould using changeable inserts or were manufactured to be ‘metal safe’ so that any changes made would be cost effective. Another challenge was designing the mould for a range of materials, as the post-moulding shrinkage values vary with each. This mould was designed using an average shrinkage rate for a number of materials, so that we had options to trial.
Until we trialled all of the materials, we could not be certain which would give maximum resistance against pressure, or what degree of pressure would cause a failure in the product. Similarly, we needed to make sure that the lockable asset was strong enough made from the same material as the two halves, or if it should be moulded from a different material to give the added strength required.
We trialled this product in the following materials:
Nylon
Nylon + 5% Glass Filled Fibre
Nylon + 15% Glass Filled Fibre
Nylon + 30% Glass Filled Fibre
Acrylonitrile Butadiene Styrene (ABS)
Polyvinylchloride (PVC).
All of the nylon materials processed very well, but ABS and PVC did not. Initial testing allowed us to see that the nylon + 30% glass filled fibre was the strongest of all materials, and the post-moulding shrinkage was also very similar to the percentage of shrinkage used during mould design, therefore no resizing was going to be required.
When the parts were fully cooled post moulding, a small gap that was 0.10mm wide formed as a result of the two halves warping. This is to be expected with a complex design opposed to an even and uniform design.
While the gap did not affect the performance of the product, it could give the impression that the parts were separating under pressure, so we worked to rectify it.
We redesigned and re-machined the mould to create a taper away from the centre. This meant that when the key was turned, it pulled the two halves closer together, closing the gap between them.
