Patrick Haney, R&D engineer, MTD Micro Molding
One of the commonest questions in micromoulding is “How thin can you go?” And the answer very much depends on several factors. One of the most important is material choice. Can your component be produced in a thermoplastic material that is better suited to ultra-thin walls, such as liquid crystal polymer (LCP)? Or, does it also require, for example, rigidity, in which case polyether ether ketone (PEEK) might be a better choice but is more challenging for ultra-thin walls? Or, is it overmoulded and therefore requiring the use of multiple materials?
A catheter tip ablation head with 0.009 in. (0.229 mm) wide webbing. The design features challenging long, looping channels that create multiple intersecting flow paths. Preventing one or more of these channels from prematurely solidifying and causing a short shot is only possible using the right micromoulding equipment.
The best and most challenging materials for moulding ultra-thin walled components
Even if you are able to use the best materials available, it should be borne in mind that achieving the desired wall thinness very much depends on the geometry and aspect ratios of the component.
When choosing a material, a key consideration is whether it will flow the distances necessary to fill ultra-thin-wall mould features. Thin flow for short distances is possible using many materials, but thin flow for longer lengths becomes more challenging. Polypropylene is one of the easier-flowing materials, making it a good choice for long, thin walls from a process standpoint.
Producing overmoulded ultra-thin-walled components using challenging materials
If you are using higher heat materials for overmoulding, the secret to achieving ultra-thin walls lies in keeping inserts placed both inside and outside of the mould at mould temperature to allow the material to consistently cooperate. Tools are required to keep inserts at mould temperature outside of the mould. This step is crucial to ensure proper adhesion of the plastic to the substrate as well as combat flow issues.
Other success factors
As well as your choice of material, key to successful and consistent ultra-thin-wall micromoulding is a combination of 1) an exact mould, and 2) material processing parameters. An exact mould is the first step and then it comes down to how the material is processed, keeping in mind the relationship of the two.
The complexity and scale of projects at MTD Micro Molding demand that mould construction is broken down and multiple inserts are produced (like a jigsaw puzzle) to allow for the venting of all thin-wall features. As already mentioned, a hugely important material processing parameter in ultra-thin-wall micromoulding is temperature (i.e. how the mould is cooled and heated).
Building an exact mould and applying the correct material processing parameters is imperative for filling ultra-thin walls.
Equipment also plays an important role in the micromoulding of ultra-thin-wall components. For example, MTD Micro Molding’s presses are highly tuned for such applications, ensuring shot-to-shot consistency and process repeatability.
Summary
The micromoulding field continues to evolve, challenging the capabilities of moulders as well as mould makers and processors. Medical device companies, in particular, are demanding ever smaller components that have ever thinner walls and ever sharper features. Moulders are finding that they must push materials to their limits to achieve these ultra-thin walls and ultra-sharp features, but at the same time ensure that they retain their mechanical properties and meet incredibly tight tolerances.
MTD Micro Molding