Overmolding

Overmolding injection molding is a hybrid injection molding process in which a previously manufactured injection molded part – the so-called pre-molded 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 is an established overmolding manufacturer, specializing in thermoplastic overmolding solutions to optimize components for their application.

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

This technique creates durable, multifunctional overmolded parts with improved properties, such as tribology, strength, appearance and functionality.

Choosing the right materials is crucial for the quality of the injection overmolding 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 overmolding injection molding process:

• Melting temperatures: he second material should have a lower melting temperature than the substrate to ensure uniform injection overmolding, 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 overmolded parts:

• Form-fit connections such as undercuts, mechanical anchors, gearing
• The use of specialized compounds (for example, PEEK with bonding agent or modified PPS)

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

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

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

Overmolding is used in many industries, including:

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