Two-Shot and Over-Moulding Specialists

Hymid has 1600 m² of production space dedicated to injection moulding. While we have single shot moulding, we are best known for our two-shot moulding and over-moulding expertise. We can handle low-volume output that is suitable for small production runs, trialling and prototyping, as well as higher volume production.

Two-shot injection moulding

Hymid has become well-known for its two–shot moulding capability (sometimes called twin-shot or 2K moulding). Our facilities and expertise enable us to produce complicated moulded parts from two different polymers.

The key advantage is that, when properly approached, the two injected polymers form a cohesive bond, which provides a level of strength to the substrate component that is not possible with overmoulding or other related manufacturing processes. With two-shot there is a better interface between the plastics, because the initial injected substrate is free from surface contaminants within the mould (enhancing adhesion) and also retains a high level of thermal energy, improving the melt flow of the second shot. Another advantage relates to post-mould shrinkage of the substrate. With two-shot moulding, the substrate commonly remains on the core side of the tool in a fixed and well-indexed location. When the second shot cavity closes against the substrate a highly accurate shut-out is achieved, which is not so feasible within the overmoulding process.

This makes two-shot a good choice for complex, multi-material, and multi-coloured components or products where the cosmetic finish needs to be seamless and free from visual defects.

With two-shot you can achieve:

• reduced unit cost
• faster cycle time
• reduced waste and risk of damage
• single process with no manual intervention
• fewer assembly defects
• enhanced product quality

Overmoulding

Overmoulding is the process of adding an additional polymer layer over an already existing component or part – and is the best option when:

• two-shot is not a feasible option
• a part may require material feeding in a complex format to both core and cavity regions
• an existing component needs adapting or enhancing
• a component derives from a separate manufacturer or process
• prototyping.

It may be the appropriate choice when adding certain characteristics to a component or product – for example, by adding texture, surface resistance, colour variation, or perhaps impact resistance and shock absorption.

The original component is placed in the mould tool, and the new polymer injected. It is important in this process that the new polymer is compatible with the original component, which would typically be a rigid plastic. It is also feasible to consider using elastomeric compounds as the substrate, however this process carries a little more risk and therefore warrants far more planning.

Overmoulding can be more labour intensive than two-shot moulding, and hence more costly, yet can also offer a labour saving compared a similar manual process. These pro’s and con’s need to be evaluated on a case by case basis.

A high level of technical expertise and attention to detail is needed to achieve your goals, and would normally require our involvement at an early stage in the design process.