Mass production of composites solved

Successfully utilising composite structures to produce vehicles requires substantial improvements in the tools used for end-to-end product development.

Most existing CAD solutions are intended for use with metal and plastic parts of less complexity, and offer no way to track laminate and composite properties, other than manually via spreadsheets.

From a simulation perspective, evaluating the mechanical performance of the proposed design is challenging, because ply and composite parameters must normally be manually re-entered in FEA software - a time consuming and error prone process. Additionally, most of today's FEA software is designed for metallic materials that yield, bend and fold when they fail, whereas composites crack, fracture and delaminate.

In manufacturing, the complex shape of automotive body geometries makes it difficult to predict how composite materials will conform to the mould's complex surface. A major hurdle lies in developing flat patterns that will meet the ply guidelines, without fabric distortion. The prevalent procedure is to cut fabric plies by hand and try to fit them on the mould tool. This process is time-consuming and can lead to costly errors in the positioning of the plies on the mould.

Currently, composite process planning does not take advantage of the product definition embedded in the 3D model. Typically, composite process plans are created using manual entry or finite-element mesh defining plies that do not match the as-built models. While traditional software solutions cover the design, analysis and manufacturing of composite parts, they do not do so using a collaborative process. This inability to quickly analyse the impact of design changes on manufacturing further extends the time needed to deliver products.

To meet these challenges, Dassault Systèmes (DS) has worked in close collaboration with industry leaders to develop end-to-end PLM solutions to design, simulate and manufacture composite structures on a single virtual platform. At the heart of this solution, CATIA provides a dedicated environment for design of composite parts, SIMULIA provides advanced simulation tools and composite specific methodologies to improve the design, and DELMIA supplies digital manufacturing capabilities, from planning to actual delivery to the shop floor.

Complex design process
Composites' numerical definition is complex and involves many different parameters, as compared to metals, which are isotropic. As a result, it's a challenge when modelling composites to find the right balance between the number of parameters necessary and the computation time needed. The CATIA Composites (CPD) solution provides accurate characterisation, based on material property data that allows engineers to quickly define a detailed composite lay-up.

Another challenge is the necessity to quickly explore and test many variants in the preliminary design phase. Critical at this stage is the ability to create and update the composite models within hours of a design change. CPD offers various methods for the automatic creation of plies and provides an association between surface and composite parameters. When surfaces change, the model is automatically updated based on the new surfaces, enabling significant time savings. This approach also offers improved accuracy, reducing the number of prototypes needed.

Designers also need to perform analysis on the composite parts early in the process, in order to understand the behaviour of the various materials and their mutual interaction. CPD delivers a comprehensive set of inspection tools to review a composite structure in detail.

To achieve design weight and strength optimisation, as well as ensure the final product performs as designed, it is necessary to integrate the design, analysis and manufacturing process on a single platform. Metal components are joined either by welding, rivets, bolts or bonding. For composites, the assembly process can be quite different. Designers need to understand the composite material properties and the manufacturing assembly process, as well as the potential impact on the parts they are modelling. With CATIA Composites, productive features are provided, so the designer can take them into account early in the design phase, helping to reduce the design lifecycle and allow manufacturers to go to market faster.

Additionally, designers need to simulate the manufacturing process, in order to visualise the fibre orientation of the material on the shop floor and to ensure that the final product adheres to the original design intent. DS works with technology partners to provide advanced specialised applications that fully integrate with the CATIA environment to improve part quality and prevent delays in production. Engineers can visualise the ply stacking and tweak the laminate structure before the design is sent to manufacturing.

Properties and crash simulation
Composite materials behaviour is complex and more difficult to predict than metals, so reliable simulation applications are key in understanding part behaviour.

Additionally, raw material manufacturers constantly introduce new materials and parameters need to be established. Relying on fully integrated partner products, this solution allows users to quickly define the complete properties of a new material and drape it on the mould.

The loss of information and time required to transfer composite data between CAD and CAE applications often requires data translation. The integration of CATIA information with SIMULIA CAE FEA software overcomes this issue. The ability to directly transfer accurate fibre angles and ply thicknesses from the design to the analysis environment improves simulation accuracy.

Transferring updated design information from analysis seamlessly back to design enables designers and analysts to work collaboratively to ensure the analysed model matches the final structure, and to prevent specifying plies and structures that cannot be manufactured.

Composite assemblies' failure analysis requires a comprehensive analysis of crash worthiness and other severe events inherent to composites, which are all addressed by this solution.

From manual to automated manufacturing processes
Shifting from high-volume metal parts to composite structures is a challenge for OEMs and Tier suppliers. The high cost of raw material, and lack of automated manufacturing processes is preventing composites from being widely used in mass production. DS DELMIA Composites Planning takes properties from the CATIA model to aid the process planning needed to automate manufacturing processes.

With low volumes, a manual process is recommended; for medium to high volumes, an automated process is more suitable. With manual lay-up, automotive manufacturers are reaching a quality limit, because it's difficult to predict the exact final finish of a part on the shop floor. If the operator doesn't deposit the ply consistently and in the same position it could jeopardise the precise initial design.

Utmost accuracy
To help the operator accurately lay the fabrics on the mould, best-in-class industry solutions are fully integrated in the design environment for nesting, cutting and laser projection systems, optimising the ply lay-up of a composites model with the highest degree of accuracy.

With automakers able to implement an end-to-end solution for composites, the industry is increasing its use of fibre-reinforced composites for a wide range of applications, which allows them to reduce their time to market and avoid costly errors, minimise vehicle weight and cost, and prevent overdesign. And that has to be beneficial.

Biocomposites gain momentum
Composite materials derived from natural renewable sources are seeing increased use year on year. This is supported by an increasingly capable supply chain. Despite continuous improvement, the fundamental materials required to make consistent biocomposite parts are readily available from commercial suppliers.

Biocomposites can have specific benefits over synthetic materials including toughness, reduced density and moisture attenuation. Fibres from plant stock or extracted cellulose, including flax, hemp, bamboo and sisal, are processed into yarns and there are a range of matrix materials available including thermoset and thermoplastic. Polylactic acid matrix (PLA) is a 100% bio derived thermoplastic matrix that has already seen widespread use. Thermoset matrix materials include blends of bio derived polyesters or epoxies with synthetic stock to almost fully bio derived resins produced from plant oils.

Products can be successfully produced using common composite processing techniques including resin infusion, resin transfer moulding, compression moulding, pultrusion and injection moulding. The Composites UK - Biocomposites Subgroup brings together interested parties and demystifies biocomposites to help promote the uptake for appropriate applications.

Composites Evolution, a supplier of bio-derived fibres, has seen increasing interest in its materials. It has recently developed a range of lightweight flax fabrics weighing just 100gsm and 200gsm. Developments have been made to the Biotex fabrics to allow for use in applications such as automotive interiors. It uses ultra clear resins and lacquers, creating visually attractive, sustainable finishes. It will be demonstrating its aesthetic part capabilities at the JEC show in Paris this month.

Brendon Weager, managing director of Composites Evolution, says: "Our customers are keen to use Biotex in increasingly more demanding applications, in particular in the marine and construction sectors... We expect to be able to offer a water resistant flax reinforcement in the near future."

Author
Rani Richardson

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