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Lightweight Design worldwide

, Volume 10, Issue 2, pp 30–35 | Cite as

Automation Concepts for Manufacturing Fibre-reinforced Thermoplastic Components

  • Mesut Cetin
  • Christian Herrmann
  • Stefan Fenske
Production Automation

Keywords

Injection Molding Semifinished Product Injection Molding Process Composite Sheet Injection Molding Machine 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Components made of fibre-reinforced composites offer high strength despite their extremely low weight. This gives them advantages that are increasingly in demand, particularly in vehicle manufacturing. For series production of long-fibre-reinforced thermoplastic components, KraussMaffei has developed, implemented and validated various product-oriented automation concepts that allow for extremely short cycle times for high quantities.

Components made of fibre-reinforced composites are very much in fashion. They provide high levels of strength with extremely low weight. These translate into advantages that are increasingly in demand in the field of vehicle manufacturing. Fibre-reinforced components can be manufactured in what are called liquid epoxy resin impregnation methods or by reshaping fibre-reinforced semifinished products. But regardless of which approach is taken, thermoset or thermoplastic matrix systems are used. [1]

The selection of a suitable technology for shell-shaped components usually depends on many different criteria. At the same time, limitations are placed on the selection of the technology by the required quantities, the component complexity and by the required mechanical property pattern [2].

With respect to the manufacturing of shell-shaped fibre-reinforced series components in high quantities, as they are required in vehicle manufacturing, a short cycle time is of critical importance. The FiberForm technology developed by KraussMaffei is perfectly suitable for this. When this method is used, one process combines injection molding with the thermoforming of composite sheets, i.e. plate-shaped semifinished products with continuous fibres made of glass, carbon or aramid, which are embedded into a thermoplastic matrix, made of materials such as polyamide (PA) or polypropylene (PP). The achievable cycle times correspond to typical injection molding processes. The technology also provides the option to implement metallic inserts with a high degree of design freedom and short cycle times.

The manufacturing process encompasses six steps, Figure 1. The preassembled semifinished product is picked up using a gripper system (1) and fed to the infrared heating station (2).
Figure 1

Process sequence of the FiberForm technology (© KraussMaffei)

Then the loader is transferred into the injection mold (3). The reshaping (4) and over-molding (5) take place, followed by demolding of the component (6) with no need for post-mold processing. Parts with integrated organic sheets have significantly better mechanical properties compared to those that are purely composed of short-fibre-reinforced or non-fibre-reinforced injection molding material.

The use of the technology also calls for product-oriented automation concepts for components with various sizes and applications, for example in automotive manufacturing. This primarily applies to heating technology, the positioning of the heating station as well as the selection of the automation kinematic units.

Automation Solutions

For instance, for the use of the FiberForm lightweight construction technology in the automotive industry, different vehicle components were tested with respect to their size and quantity. Then, product-oriented automation concepts were developed based on these tests (Table 1 and Figure 2).
Table 1

Automation concepts for series production of fibre-reinforced thermoplastic components using FiberForm technology for various fibre-reinforced semifinished product sizes (© KraussMaffei)

 

Concept

 

1

2

3

Heating principle

Infrared technology

Position of the heating station

Above the FP*

Automation kinematic unit

Linear unit with two kinematic units (LRX 250 TwinZ)

Linear unit with two kinematic units (LRX 500 TwinZ)

Two 6-axis robots

Semifinished product size (w × h) [mm]

≤ 350 × 350

≤ 850 × 850

≤ 1350 × 850

*: Fixed (mold) platen

Figure 2

Product examples of fibre-reinforced thermoplastic with corresponding production concept using the example of automotive components (© KraussMaffei)

It is typical for all above-mentioned large-scale turnkey solutions to involve positioning an infrared heating station above the fixed (mold) platen. This allows for the implementation of very short transfer distances when inserting the heated composite sheet into the mold. The result is exceptionally short transfer times for moving the composite sheet into the mold, making series production of components possible. The short transfer distance avoids too much cooling of the heated composite sheet. Infrafred technology is used as the heating principle. The advantages of the infrared heating technology in comparison to convection systems lie in the lower investment costs and the high output level of the infrared emitter, allowing for considerably shorter heat-up times. Heating takes place on one side or both sides depending on the thickness of the semifinished product. The infrared heating surface adjusts to the size of the semifinished product and the corresponding injection molding machine. However, it can also be adjusted on an individual basis according to the needs of the customer.

An automation kinematic unit is defined as two decoupled robot units. This means that the heating of the composite sheet and the demolding of the finished part can be decoupled from each other in time, resulting in further shortening of the cycle times. Due to the various component sizes, the robot kinematic units vary with respect to their freedom of movement and load capacities.

Using product-oriented automation concepts at low cycle times for fibre-reinforced thermoplastic components.

In concept 1, Figure 3, and concept 2, Figure 4, the automation kinematic unit is characterised using a linear unit with two kinematic units for material feed and finished part removal (kinematic unit 1 with double gripper) and for heating up and inserting the semifinished products (kinematic unit 2, single gripper). While kinematic unit 1 removes the fiber-reinforced centered semifinished products from the material supply, the reshaping and over-molding of the semifinished products takes place in the mold (first cycle). Before kinematic unit 2 can feed a new heated semifinished product to the mold, the finished part is removed from kinematic unit 1. Then kinematic unit 1 transfers the previously gripped semifinished product to kinematic unit 2. This unit sends the semifinished product into the infrared heating station and transfers it to the mold after reaching a material-specific melting temperature. This allows a new cycle to begin (second cycle).
Figure 3

System concept for series production of fibre-reinforced thermoplastic components for semifinished part sizes of ≤ 350 mm × 350 mm (concept 1); side view above, top view below (© KraussMaffei)

Figure 4

System concept for series production of fibre-reinforced thermoplastic components for semifinished part sizes of ≤ 850 mm × 850 mm (concept 2); side view above, top view below (© KraussMaffei)

In concept 3, Figure 5, on the other hand, 6-axis robot 1 supplies the material and removes the finished component while 6-axis robot 2 heats up the semifinished product and inserts it into the mold. The process sequence is identical up to the point where the semifinished product is transferred. Because of the large semifinished product size (≤ 1350 mm × 850 mm), a centering station is being used here.
Figure 5

System concept for series production of fibre-reinforced thermoplastic components for semifinished part sizes of ≤ 1350 mm × 850 mm (concept 3); side view above, top view below (© KraussMaffei)

Depending on requirements for the process and for the component, additional modular units can be added for quality assurance. This includes the following:
  • ▸ a check upon infeed of the composite sheet cut (contour, fibre orientation)

  • ▸ a check of the heating process (temperature distribution of the heated composite sheet before the mold reshaping)

  • ▸ a finished component check (weight, local fibre orientation, positioning of the composite sheet cut)

  • ▸ the traceability of individual quality metrics and product-specific process data using a QR code.

Implementation and Validation

A validation of the developed automation concepts was carried out at the K 2016 trade show in Düsseldorf, Germany using a compact FiberForm production cell as an example of prototype manufacturing for a holder, Figure 6 (concept 1).
Figure 6

FiberForm system technology (concept 1) for processing of composite sheet semifinished products sized ≤ 350 mm × 350 mm (w × h) (© KraussMaffei)

The complete system was implemented on an area of only approx. 18 m2 and consists of the following:
  • ▸ an injection molding machine CX 300

  • ▸ an LRX linear robot 250 of the TwinZ series with two mechanically decoupled X axes on a joint Z-axis

  • ▸ an infrared heating station

  • ▸ a QR code printing unit.

As described above, by decoupling the process steps, short cycle times and transfer times can be achieved (see process video). Furthermore, the positioning of the material supply unit, the QR code printer and the conveyor belt within the injection molding cell minimises the necessary movement distance of the robot units. As a result, very short cycle times are achieved. An additional safety housing is therefore no longer necessary, which has a positive effect on the space requirements of the production cell as well as on the transport.

Against the backdrop of increasingly intelligent linking of production cells and lossless documentation (Industry 4.0) throughout the manufacturing process, quality metrics and product-specific process data are recorded for each individual component in the process and then stored and evaluated in the system in real time (digital product memory). The evaluation is carried out by DataXplorer, which creates a file for each cycle. In the file, freely selectable process data are stored. DataXplorer is thus a tool for recording, analysing and documenting product-specific process data.

The product-specific process data can finally be accessed using a QR code on the component, Figure 7. In addition to the heating curve and the pressure-time curve of the injection molding process, other component data (e.g. application [-], material [-]) and process data (e.g. heating rate [°C/s], heat-up time [s], transfer time [s], melting temperature of the semifinished products [°C], plasticising current [g/s], max. injection pressure [bar]) can be documented here as product-specific process data.
Figure 7

Traceability of product-specific process data based on a QR code on the finished part (© KraussMaffei)

Summary

The product-oriented automation concepts developed by KraussMaffei, Figure 1, Figure 2 and Figure 3, ensure series production of long-fibre-reinforced thermoplastic components in very short cycle times for large quantities. The reasons for this are the selection of infrared technology as the heating principle, the positioning of the infrared heating station above the fixed (mold) platen as well as the optimised selection of automation kinematic units for various component sizes. All concepts depicted have already been implemented by KraussMaffei for customers in series maturity.

Apart from the automotive industry products used as examples, the FiberForm technology also offers high lightweight construction potential for components from the packaging and logistics sectors as well as sport and leisure. The latter was implemented based on the multi-function stringer, Figure 8, in touring ski binding by the name of “Kingpin” from Marker Deutschland (Penzberg, Germany), in collaboration with S&W (Hebertshausen, Germany) [3]. The FiberForm technology allows for defined mechanical property patterns and functional integration in only two process steps (thermoforming and injection molding) in one injection molding machine.
Figure 8

Multi-function stringers for a ski binding (© KraussMaffei)

References

  1. [1]
    Henning, F.; Moeller, E.: Handbuch Leichtbau — Methoden, Werkstoffe, Fertigung (Engl.: Lightweight construction handbook — methods, materials, engineering). Carl Hanser Verlag, 2011CrossRefGoogle Scholar
  2. [2]
    AVK — Federation of Reinforced Plastics e.V.: Handbuch Faserverbundkunststoffe: Grundlagen: Verarbeitung, Anwendungen. 3. Aufl. (Engl.: Fiber compound plastics handbook: Basics: Processing, applications, 3rd Ed.) — Wiesbaden, Germany: Vieweg + Teubner Verlag, 2010Google Scholar
  3. [3]
    Weber, J.: Komfortabel bergauf und bergab — FiberForm fährt mit (Engl.: Comfort uphill and downhill - FiberForm is along for the ride). AHEAD - the customer magazine of KraussMaffei, 01.2015 issue, KraussMaffei, Munich, Germany. Online: http://service.kraussmaffei.com/media/files/kmdownloadlocal/de/D_KM_AHEAD.pdf. Last accessed: January 2016

Copyright information

© Springer Fachmedien Wiesbaden 2017

Authors and Affiliations

  • Mesut Cetin
    • 1
  • Christian Herrmann
    • 1
  • Stefan Fenske
    • 2
  1. 1.KraussMaffei Automation GmbHOberding-SchwaigGermany
  2. 2.KraussMaffei Technologies GmbHMunich-AllachGermany

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