The Challenge: The customer required a completely aesthetic component with a very high gloss finish. This was to be printed as a post moulding process and with no evidence of gate witness, ejector marks, flow lines or sink on the show surface.
The underside (non-aesthetic) had a requirement for four off large bosses to have holes for the retention of the component to the parent part. This resulted in a component design with the four off 8mm diameter bossed protruding from the underside of the aesthetic face that had a wall section of only 3mm. As the customer design was somewhat finalised, the outcome was going to be major sink caused by post mould cooling on the aesthetic face.
Solution
To overcome the above challenges AKI needed to approach the project in two ways.
Firstly, this was by way of working with the customer to instruct them on how to make localised changes to wall sections where bosses met the underside of the aesthetic face to create a wall section ratio over surface area that would result in no sink occurring during post mould shrinkage. The result of this being no evidence of sink or any other surface blemish at the points where the bosses intersects the face.
Secondly, was to produce a tool that would allow for the gating and ejecting of the component from the same side (a reverse gated tool). This type of tooling is not uncommon on none aesthetic components or components with a textured finish on the show face, as this allows any surface finish issues to be camouflaged by the textured finish. Issues such as gates bloom, minor blemishes or distortion.
To overcome the challenge of having the gate in the middle of the back of such a highly critical aesthetic surface, AKI instructed the toolmaker to add additional water channels in key areas of the tool that allowed for the control of tool temperatures over different areas of the tool face. Ensuring that the flow and cooling of the material could be controlled. With this level of control in the tool, in conjunction with the ability to control the injection pressures, speeds and times over up to seven stages through AKI’s state of the art moulding machines the component was produced with no witness marks opposite the gate.
The outcome was a great success.
