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Surface Finishes for Plastic Parts

Injection Molding for Challenging Designs and Functional Integration

When buying plastic products, aesthetics are becoming increasingly important, as are functional properties. Manufacturers of visually appealing and multifunctional parts use our injection molding processes to achieve surface finishes and functionalize plastic parts. With the integration of several process steps in one cycle, you save costs and installation time.

Advantages of Surface Finishes and Functionalizing Plastic Parts
Change design quickly and easily
Image shows surface designs of plastic parts

The injection molding process for film back injection molding allows flexible component design. You can produce the same injection-molded part in different colors, with different surface structures, or with multicolor decorative elements – without changing mold or materials. An example: You want to produce panels in blue and red and with different decorative elements. With the standard injection molding process, you need to change the material and printing. With film back injection molding, you only change the insert film in the mold.

Surfaces with diverse functionality
Image shows plastic component with functionality

In addition to surface finishes, film back injection molding technology allows the integration of various functions into the plastic parts. Some examples: The use of films enables different visual impressions, especially under different lighting conditions. We integrate labels with the help of a carrier film. Preformed films allow complex part geometries. Film back injection molding enables an HMI interface through printed electronic control elements or heating of surfaces in winter to keep sensors functional.

Surface finishes for more sturdiness of plastic parts
Picture shows plastic car parts (exterior)

When parts have to be particularly tough, flooding with a polyurethane coating is the best solution. In the production cell, the plastic carrier is molded first. In a second station, it is flooded with the reactive system. The thermoset PUR protective coating gives parts scratch resistance and impact strength. Self-healing effects allow scratches to disappear. The depth effect created by the coating gives a high-quality look.

Flooding for a haptic experience of the plastic surfaces
Image shows plastic part with haptically challenging surface

Flooding creates haptically demanding surfaces that can have a variety of tactile properties. From rough to smooth, from hard to soft. The clearmelt injection molding process can create different haptic experiences depending on the requirements.

Surface details thanks to heating and cooling in each cycle
Picture shows center console of a car made out of plastic

Variotherm processes are well suited to avoiding larger or smaller weld lines. They are used for high-gloss effects on surfaces and can influence the filling behavior for the smallest details. The processes are based on pressurized water or heat transfer oils and allow hot-cold switching of mold areas. They improve the detail accuracy of parts. Other variotherm processes are based on inductive heating solutions or the partial use of heating elements, among other things.

Visually Appealing Surfaces with Recycled Content
Picture shows plastic part made from recyclate

Decorative processes such as film back injection molding or multi-component processes allow the use of recycled material. A front layer of the part can cover the structural element made of recycled material. In some cases, the use of recycled or bio-based materials is made visible to focus on sustainability. This is achieved, for example, by overmolding the functional surface with a layer of transparent material. The surface of the plastic part remains visually appealing.

More output by linking manufacturing steps
Image shows injection-molded part made from several components

Integrate multiple materials and surface functions in one injection molding process. This minimizes time and costs for further assembly tasks. Thanks to the multi-component injection molding process, production takes place in one production cell. Sequential processes include core-back and sliding table technologies. They enable complex multi-component applications on machines with conventional clamping units. Maximum output is achieved with parallel processes using index, turntable, or insert technology.

Production cell from a single source for increased part quality
Picture shows production cell by ENGEL

We design and manufacture your complete production cell, from the injection molding machine to the robot and conveyor systems, to peripherals. You get everything from a single source, including film or insert preparation and handling, also to clean room standards. This makes it easy to set up production with film back injection molding. You can be sure of best part quality, stable injection molding processes and high productivity of functionalizing plastic parts and surface finishes of plastics.

Picture shows Head of Process Technologies & Digital Solutions at ENGEL Austria
Do you Want to Combine Design & Function in your Plastic Parts?

Take advantage of our expertise, machine engineering and technologies for surface finishes and for functionalizing your plastic parts. We will be happy to advise you on the design of your production cell.

Best-practice Example of Surface Finishes and Functionalizing Plastic Parts
Picture shows Faurecia and ENGEL employees
Faurecia Produces Panels with Multi-component Injection Molding

Manufacturing the center console is demanding. It is a delicate frame structure made of plastic. Three materials are processed simultaneously in one step. The high-gloss lacquer requires an absolutely flat substrate.

Overview of our Plastic Injection Molding Processes for Surface Finishes and for Functionalizing Plastic Parts

Process Product name Industry Applications Procedure
Film back injection molding foilmelt Automotive & mobility, Technical injection molding Trim interior/exterior, Fascias for white goods, Smart panels Create functional, haptic, and decorative surfaces with films
Multi-component injection molding combimelt Automotive & mobility, technical injection molding, medical technology, electronics, packaging Trim interior/exterior, Smart panels Combine different types of plastic in one part
Variotherm technology variomelt Automotive & mobility, technical injection molding, electronics Fascias, white goods, TV frame Create high-gloss surface through alternating mold temperature control (hot-cold)
Flooding clearmelt Automotive & mobility, technical injection molding Trim interior/exterior, fascias white goods, Smart panels Produce high quality surfaces from polyurethane

Details of our plastic injection molding processes for surface finishing and functionalization

Picture shows plastic parts produced by film back injection molding by ENGEL
Film Back Injection Molding

Film back injection molding creates surface finishes with a film layer during the injection molding process. The film layer can add value to your plastic parts thanks to different surface designs or translucent parts, for example. Additional electronic elements give surfaces design accents with special effects or smart functions.

Your Advantages with the foilmelt Process
Complex Effects

Design effects such as a metallic, aluminum, camouflage effect or holograms on the surface of the component are possible.

Flexible Designs

You can implement different designs. Switching to a new design is quick and easy.

One-shot Process

Injection molding production of the surface design in a fully automated production cell. No reworking necessary.

Cost-efficient Production on a Large Scale

Reducing manufacturing and assembly tasks by producing a fully functional component in one production cell. Result: savings in weight, time, and costs.

  • Your plastic part is provided with a film layer through surface finishes and functionalizing

  • The component is visually upgraded

Plastic Surface Finishes with Different Types of Film Back Injection Molding
Film insert molding
Image shows film insert molding process
  1. Preforming the film

  2. Positioning of the insert by a robot

  3. Hot substrate is injected by standard back injection molding and merges with the film

  4. After cooling, the material and film are ejected as one piece

In-mold decoration
Image shows the principle of an in-mold decoration process
  1. Film is inserted into the mold

  2. Film is positioned in X and Y direction and clamped by a sealing frame

  3. Hot substrate is injected using the standard film back injection molding process and merges with the PUR coating layer

  4. After the material has cooled, the film is ejected as one piece

Roll-to-roll in-mold labeling
Image shows roll-to-roll in-mold labeling process
  1. Film is inserted into the mold

  2. Infrared heating and vacuum preforming pull the film into the mold

  3. Hot base material is injected in a standard film back injection molding process and merges with the film

  4. When closing the mold, the film is trimmed with cutting edges

  5. After cooling, the material and film are ejected as one piece

Film Back Injection Molding: Best-practices of Surface Finishes and Functionalizing Plastic Parts
    • technical molding
    • automotive and mobility
    • electronics
    Flexible Process for Fast Design Change

    Film back injection molding on a duo 350 with a roll-to-roll IML application. The film is fed via a roll, thermoformed on the machine, and remains on the component.

    • automotive and mobility
    Production of Aesthetic Vehicle Interior Parts

    Interior door panels for vehicles with different surface properties thanks to film back injection molding

    • automotive and mobility
    Automotive Front Panel with Decorative Film and Polyurethane Coating

    Production on one machine and in one cycle using film back injection molding and flooding. For an efficient and simple process.

Image shows injection-molded part made of several components
Multi-component Injection Molding

Produce innovative molded parts from different materials in a single step.


  • Multicolor parts

  • Hard/soft composites

  • Thermoplastic/rubber composites

  • Thermoplastic/LSR composites

  • Assembly injection molding

Your Advantages with the combimelt Process
One-Shot Process

Produce parts with up to six injection units which can be controlled simultaneously or sequentially.

Save Space and Energy

Machines for composite injection molding with short cycle times.

Design Improvement

The process enables different color variations and haptic experiences.

Reduction of Process Steps

The need for subsequent assembly and printing is eliminated. Different controls are produced in a single cycle.

Best-Practice of Multi-component Injection Molding

Experience combimelt technology first hand. Integration of design and functionality on a tie-barless victory 330H injection molding machine.

Video shows integration of design and functionality on tie-barless injection molding machine >
Picture shows plastic television housing
Variotherm Technology

With the variomelt injection molding process, you heat and cool the mold in each cycle. The injection molding process is suitable for producing housings for modern consumer electronics. Preformed organic sheets can be perfectly overmolded with PC-ABS.

Your Advantages with the variomelt Process
Versatile Application

Ideal for injection molding of modern consumer electronics, light guide panels, lenses, design parts, and more.

Complete Mold Filling

Sturdy housings or transparent parts with thin wall thickness & even surfaces. Reduce visible weld lines and optimize the molding of grains and geometries.

Easily Combined

With other ENGEL injection molding processes such as organomelt, optimelt, coinmelt, foilmelt.

Perfect Finish

Thanks to overmolding with translucent piano black paint.

  • Concealing of weld lines

  • Improved surface impression

  • Easier filling of thin-walled structures

Picture shows operation of a plastic center console
In-mold Coating

In-mold coating technology gives your plastic parts the surface finishes you want during the injection molding process. A PUR top coat gives your product added value through scratch resistance, self-healing surfaces, and a look that has elegance and depth.

Your Advantages with the clearmelt Process
High Component Quality

Scratch resistance, depth effect, and a higher resistance to expansion even with thin coating thicknesses. PUR layer thicknesses from 0.4 mm to 10 mm are possible.

Easily Combined

With other ENGEL injection molding processes such as combimelt and foilmelt.

Innovative Details

PUR-flooded substrates with integrated, capacitive functional film for optimum protection and convenient operation (for example car center console).

  • Scratch-resistant surfaces

  • Self-healing properties

  • Optical depth effect

Flooding: Best-practice for Surface Finishes and Functionalizing Plastic Components
  • Coating with ENGEL clearmelt

    Single-stage Injection Molding Process that Combines Decoration and Scratch-resistant Surface Protection.

  • Capacitive Film Plus Polyurethane Coating

    Production of a center console with integrated control functions, protected by a polyurethane surface.

  • Automotive Front Panel with Decorative Foil and Polyurethane Coating

    Production on one machine and in one cycle using film back injection molding and flooding. For an efficient and simple process.

IML stands for in-mold labeling. The surface finish of the plastic part is achieved by using an inserted film that is back molded. If the film is already preformed, it is often referred to as FIM (film insert molding). Other terms, which often differ according to the type of film, are IMF (in-mold foiling) or PFM (paintless film molding). There are no standardized terms.

IMD (in-mold decoration) is a process in which color is transferred from a carrier film to the part during back injection molding. In this process, the film runs from roll to roll. However, IMD is also used for film insertion. It makes sense to discuss the exact process with ENGEL.

PUR stands for polyurethane. An additive reaction product of polyol and isocyanate, a thermoset. Polyurethane can be adapted to possess a wide variety of properties (hard to soft, self-healing to scratch-resistant).

PUR direct coating or IMC (in-mold coating) means that the PUR coating is applied to the thermoplastic carrier part directly on the injection molding machine without intermediate demolding. A combination of thermoplastic processes with a reactive process for surface finishes of plastic parts is possible.

Discover More Injection Molding Processes for Your Plastic Production

Over 20 Proven Injection Molding Processes for Greater Cost-effectiveness and Different Applications

Picture shows plastic parts manufactured by precision injection molding

Precision Injection Molding

For more geometric accuracy, better surface quality, and low part weight

Image shows transparent part by ENGEL

Optical and Transparent Parts

Injection-molded parts made of transparent plastics for a perfect view

Picture shows lightweight plastic part by ENGEL

Weight and Warpage Reduction

Injection molding process for lightweight plastic components to reduce weight and warpage of your plastic parts

Picture shows plastic part made of special material

Elastomers and Thermosets

A wide range of non-thermoplastic materials such as silicone, rubber, BMC or HTV can be processed by injection molding.

Picture shows recycled material

Injection molding process for recycled materials

More safety and consistently high product quality despite recycled material.

Image shows plastic parts manufactured by ENGEL using injection molding processes

Overview of all injection moulding processes

Over 20 Proven Injection Molding Technologies for More Profitability

Markus Lettau

Molding Industry Business Advisor

+1 (717) 767 2016

Write us

The ENGEL team is happy to support you with extensive knowledge in the field of injection molding.

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