Simulation, processing and part testing for the new Ultracom semi-finished composite materials
Presentation by Dr. Reinhard Jakobi
Head of Processing Technology
Engineering Plastics Europe
BASF SE, Ludwigshafen
Development platform for composites: Part three of Ultracom
Starting in October 2013, BASF will offer its customers a product and service package under the name Ultracom™ that includes, in addition to composites, i.e. thermoplastic laminates and tapes, and the compounds for overmolding, a comprehensive service component as the third part. The basic idea is to provide an integrated development platform that starts at the concept phase, continues through design, simulation, processing and part testing, and ends in efficient volume production at the customer. The service component of the Ultracom package encompasses design assistance in the form of the Ultrasim® simulation tool, use of the new manufacturing cell for composite part production as well as extensive and expanded capabilities for part testing at BASF.
High-capacity composite production system installed
To gain expertise and provide optimum support for customers when it comes to part development, BASF has installed a high-capacity composite production system in its technical center for thermoplastics processing. Since March 2013, this equipment has been used to produce multifunctional composite test specimens by means of the in-mold forming/overmolding process.
This process represents the most promising approach for production of structural components from laminates and injection molding compounds: forming of the laminate (draping or in-mold forming) takes place in the mold, and is followed by overmolding. If the laminate is heated outside the mold, the cycle time is considerably shorter as the result of parallel process steps. This, however, requires a reliable handling and positioning of the heated laminate insert, which is no longer rigid.
Material, process and part development with CIFO
In order to explore all aspects of composite part design with this new production cell, the company has also developed its own test part: the so-called CIFO part (derived from “combination of in-mold forming and overmolding”) is a multifunctional test specimen for investigating and jointly developing continuous-fiber reinforced composite parts for volume production. It measures about 40 cm x 40 cm, has a height of 4.5 cm and consists of 1.5-mm-thick formed laminates as well as up to 3-mm-thick molded-on functional elements such as ribs and edges. With its approximately 20 individual functions, it allows the characteristic properties and problems associated with actual composite manufacturing to be replicated. Special features of the part include among others overmolded edges, long flow paths to fill the edge and punched or formed holes for use as mounting elements. Additional elements are a rib array for special crash investigations, a variety of different ribs/wall thickness transitions between the laminate and overmolded material, “stitch elements”, i.e. locations in the laminate through which material is injected, and a carrier with ribbed U-profile. The CIFO parts produced require no further processing, they are completely overmolded and no post-molding finishing operations are needed.
The mold (from Georg Kaufmann Formenbau AG) for CIFO part production is highly flexible through use of interchangeable inserts, e.g. to investigate the limits of forming a laminate. The mold is further designed to allow simple and precise handling of the laminate by means of a clamping frame: These clamping frames release the laminate in a controlled manner as the mold closes.
New manufacturing cell with six-axis robot for composite development
In addition to conveyor belts, the magazine for the cut-to-size laminates and a manual loading station for special-cut inserts, the manufacturing cell set-up in Ludwigshafen for near-real-world production of continuous-fiber reinforced thermoplastic composite parts consists of:
- a six-axis robot as central element,
- a station for automatic insertion of the laminate into the clamping frame by the robot,
- an infrared heating station, (all from FPT Robotik GmbH & Co.KG, including automation and programming),
- and a hydraulic injection molding machine (KraussMaffei KM 300 1400C2, 3000 kN clamping force) with controls for the hot-runner system and core pulls as well as interfaces to the robot and temperature units.
Fully automatic process – high degree of simultaneity – short cycle time
The process sequence in the new composite manufacturing cell offers a high degree of simultaneity for the shortest possible cycle time. This means that three clamping frames for laminate handling are used simultaneously in the cell. The steps through which an individual clamping frame passes include:
- inserting the laminate into the clamping frame,
- heating of the thermoplastic laminate,
- loading of the clamping frame into the injection mold,
- forming (draping) and overmolding of the laminate,
- removing the clamping frame and finished part,
- and placing the part on the conveyor and the clamping frame on the laminate insertion station.
While one of the clamping frames is in the injection molding machine, the second frame is holding the laminate in the IR oven (up to 250°C) and the robot is inserting a new laminate in the third frame. The robot inserts the laminate into the clamping frame automatically with high precision and reproducibility. The gripper arm is equipped with suction cups, giving it the ability to insert the laminates carefully and remove the parts in addition to handling the clamping frame.
Numerous trials have demonstrated that cycle times of one minute can be achieved with this manufacturing cell, the equivalent of a standard injection molding process. Thus, a major prerequisite for use of the process in high volume production is satisfied.
Composite design with the Ultrasim simulation tool
As the second part of the Ultracom service package, the capabilities of the Ultrasim simulation tool have been expanded so that the behavior of components made from thermoplastic laminates with woven glass fiber fabrics or tapes and overmolded short glass fiber-filled polyamide can be calculated and predicted reliably through use of Integrative Simulation methods. These capabilities of simulation were first described and used for the Opel Astra OPC seat shell.
The Integrative Simulation offered by BASF incorporates the manufacturing process for the molded plastic part into the calculation of the mechanical behavior of the part. Using rheological FE simulation of the injection molding process and 3-D simulation of draping of the continuous fiber-reinforced laminate, the anisotropic fiber orientation at each location in the molded part is transferred (mapped) to the corresponding region in the mechanical part. For the regions reinforced with continuous fibers, a completely new, expanded numerical material description is being used in Ultrasim that accurately considers the properties typical of the reinforced thermoplastic materials in the mechanical analysis: anisotropy, nonlinearity, shear rate dependence, tension-compression asymmetry, temperature dependence and different kinds of failure.
Equally important as the exact description of material behavior at each location is the design of the part, i.e. correct selection and placement of the reinforcing fibers and the semi-finished product (unidirectionally reinforced tapes or bidirectionally reinforced laminates). Here, the Ultrasim developers are working on enhancing the already used optimization methods. The well-known and acknowledged assistance offered by Ultrasim in the field of short-glass fiber-reinforced materials will also be available for the newly created material class of Ultracom continuous-fiber reinforced materials.
Experimental part testing – now with computer tomography
A wide range of test equipment, including expert know-how, is available for experimental investigation of test specimens, samples and new composite parts. The brand-new computer tomography (CT) system now allows material samples, parts and connections to be tested in a completely new way: CT permits detailed observation of the inner structures and properties of composites in a nondestructive manner like no other technology.
Additional testing capabilities include long-term exposure to temperatures, climates and liquids as well as experiments with quasi-static, dynamic or sudden forces and internal pressures. Individual part structures can be subjected to targeted tensile, compressive, flexural or torsional loads – at different temperatures. In addition, the testing laboratory is responsible for investigating and optimizing joining technologies such as welding, adhesive bonding or bolting – an aspect that is indispensable for multi-material design of thermoplastic composite parts.
For the customer: part development with BASF assistance
In conjunction with simulation and part testing, the new manufacturing cell is now available for customer-specific projects. In addition to the mold, the gripper and clamping frames must then be designed for the customer’s particular part and the robot kinematics modified accordingly. At present, the majority of work involves laminates as the semi-finished product. By the K 2013, unidirectionally oriented tapes consolidated into sheets will be available for use. The first customer projects are already in progress. Optimum interaction of application development with simulation, processing technology and a testing laboratory under one roof ensures assistance for the customer throughout the entire process chain: from material characterization to high-volume parts production. In this way, composite parts can be developed in a joint effort and a highly efficient manner.