Overmoulding

Overmoulding injection moulding is a hybrid injection moulding process in which a previously manufactured injection moulded part – the so-called pre-moulded part or substrate – is covered with a second layer of material. This process enables the combination of two or more materials. Typically, thermoplastics and elastomers are used, but Ensinger specialises in thermoplastic overmoulding, especially the combination of two thermoplastics, to optimise components for their application.

1. Injection moulding of the substrate: The base component is produced in the first cavity and cooled.
2. Insertion into the overmoulding injection moulding tool: Depending on requirements, the substrate is inserted manually, semi-automatically or fully automatically into a second injection mould. In the fully automatic process, the substrate is moulded in the second cavity in a single pass.
3. Application of the second material layer: The second material is injected into the mould so that it envelops or fuses with the substrate.

This technique creates durable, multifunctional overmoulded parts with improved properties, e.g. in terms of tribology, strength, appearance and functionality.

Choosing the right materials is crucial for the quality of the injection overmoulding process. The two materials must be able to be joined together mechanically or chemically to create a durable and resistant structure.
Basically, a variety of thermoplastics can be combined with each other. Ensinger offers the following materials in various combinations for the first and second layer: PEEK, PPS, PA, PAI, PVDF, PEI, PET, POM, PPSU, PSU, LCP.

Important factors for a successful overmoulding injection moulding process:

• Melting temperatures: The second material should have a lower melting temperature than the substrate to ensure uniform injection overmoulding, if a mechanical bond is not possible or desired.
• Coefficient of expansion: Different materials expand differently when the temperature changes – this can lead to deformation or detachment.
• Adhesion & chemical bonding: Some materials bond chemically, while others require mechanical interlocking. Plasma treatments or primers are often necessary to improve adhesion.

High-temperature plastics are often combined to achieve higher strength or improved tribological properties. Plastics modified with carbon fibre (CF), glass fibre (GF), PTFE or graphite are often combined with unreinforced plastics, or even the same material in modified form.

Typical combinations are:

Other factors that lead to functional overmoulded parts:

• Form-fit connections such as undercuts, mechanical anchors, gearing
• The use of specialised compounds (e.g. PEEK with bonding agent or modified PPS)

Although overmoulding technology offers many advantages, there are challenges that need to be considered:

• High tooling and set-up costs: Multi-component injection moulds are cost-intensive, so the process is mainly suitable for medium to large production runs.
• Precise mould design required: The mould must ensure even material distribution to avoid stresses and warpage.

Overmoulding is used in many industries, including:

• Automotive industry: production of seals, bearing applications, components in drive technology, thermal management
• Medical technology: overmoulded parts for surgical instruments, medical handles and sterilisable components, device technology (such as 3D ultrasound devices)
• Electronics: Sensor carriers, plug connectors, housings
• Industrial components: Pumps, bearings, gears, thermally and tribologically optimised components

As Ensinger covers all process steps – from concept to implementation – the relevant optimisations can be incorporated into the design of the overmoulding injection moulding component. Ensinger also develops and produces its own compounds, enabling material adjustments for specific components and the development of customised materials. We also recommend suitable material pairings for your specific application.