Let there be light: Combining PU coating and injection compression moulding

In-mould painting

There is one thing in particular that the automotive industry cannot do these days: A cosy atmosphere thanks to special ambient interior lighting design. For our customer Valeo, we have designed and produced five 1+1-cavity, 2-component insert moulds to achieve this.

The technological basis: injection moulding, polyurethane flooding and a special PU seal design.

Complex visible parts for luxury limousine

Our customer required five different visible components for the luxury car of a Bavarian automotive manufacturer, the basic bodies of which have been produced with our indexable insert moulds since 2024.

The challenge: process-efficient injection moulds for the production of high-quality visible components with a self-healing PU coating, which serve as the basic body for the integration of ambient lighting and integrated function buttons. The components are now used as key design and functional elements in the interior of the saloon.

Based on filling studies to find the ideal injection points, our Hofmann specialists designed the various insert moulds.

Unique polyurethane seal design

Each cavity is filled using the same principle: First, a polycarbonate base is injection moulded and then flooded with polyurethane.

The special feature: Thanks to a special sealing process developed by Hofmann, no burr is created during the flooding process. Thanks to clever design work, a special seal is incorporated directly into the design to prevent the highly liquid PU from running out of the mould.

Our many years of experience in PU coating means that our customers can speed up their processes by reducing the need for lengthy post-processing and reworking: This technology can also reduce the scrap rate to a minimum.

Advantages of PU flooding

• No seams: Thanks to the special Hofmann process, the flooding process does not create any grading or weld lines, ensuring an aesthetically pleasing result.
• No subsequent painting: Painting in the mould eliminates the need for re-coating.
  Less scrap: PU coating typically produces a minimal amount of scrap – significantly less than the approx. 20% scrap associated with conventional painting. This efficient process therefore saves time, material and budget.
• Excellent feel & soft-touch surface: PU coating gives trims a high-quality surface that is pleasant to the touch, which is in high demand in the premium interiors.
• Self-healing, scratch and chemical resistant: PU-finished surfaces use heat, their chemical structure or elastic recovery to repair fine scratches.
• Reduces noise and vibration: PU has a damping effect, reducing creaking noises in the interior. This optimises driving comfort.

Injection compression moulding in combination with PU flooding

There are several key challenges in injection moulding a polycarbonate interior trim with a PU coating. However, these can be overcome with precise process and tooling technology – for a result with high dimensional accuracy, outstanding appearance and optimum feel.

• Low-stress & warp-free components: Material stresses can be minimised through controlled embossing and optimised mouldtemperature control.
• High-quality, weld line free surfaces: Strategic injection points and polished/textured cavities ensure visually perfect results.
• Uniform wall thickness for PU flow: Precise control of the compression path ensures that no dimensional variations.
• Effective venting to elimiate air pockets: Micro-valves or targeted mould venting ensure a bubble-free surface.
• Optimum adhesion for subsequent PU flooding: Mechanical structuring or surface activation improves PU adhesion.
• Fitting accuracy & temperature management: Precise manufacturing tolerances and coordinated cooling processes prevent dimensional variations and distortion.

Injection compression moulding thus enables high-quality production of the PC trim, which can then be optimally flooded with PU. The use of simulations in mould design allows many potential problems to be identified and avoided at an early stage.