Fibre-Reinforced Plastic (FRP) - Design Process
Functional requirements and economic costs
The design process used in the production of the truck bonnet first starts with the basic materials and requirements of the certain component. This includes several considerations such as the mechanical, physical and chemical properties of components in which the materials used are a large part ensuring the requirements are met. Due to the versatility of FRP/Composites throughout production, materials are able to be optimised/refined up until the final product.
Mechanical properties of the components include the ability to perform as intended under impact, show strength under rotational flexing or stretching and also compressive forces. Physical properties taken into consideration include the hardness and density, dielectric strength, volume resistivity and arc resistance, thermal conductivity, heat distortion and heat resistance, flammability and thermal expansion coefficient.
Chemical properties of the materials include their resistance to acids, alkalies and organic solvents. The ability of the structure to absorb water or any liquid, its ability to withstand the harsh environment; resistance to ozone, ultraviolet radiation and weathering.
Create preliminary plans
The next step in the design process is to establish the cost targets. Evaluation of the economics of a specific application requires an ordered approach so the composite and materials are used sustainably and efficiently until completion. This result however broadens the design process, therefore the comparison of material costs between FRP/Composites and alternative materials is not simple. Such factors provide the plans for tools costs, cooling and heating equipment, machining fixtures and assembly tools. The final cost of machining and assembling includes the costs of component refinement such as trimming, sanding, painting and polishing. Other costly operations require a study and comparison of the products and how they are packaged and stored. Also determining whether the product is of a high standard of quality, therefore the management are able to decide which products are preferential. A thorough economic evaluation plan for the FRP composite application provides three main benefits: Firstly its demonstrates an accurate presentation of the total cost, allowing upcoming design choices more cost effective. Secondly, it displays other cost-savings areas that may have not been obvious and thus can be designed into the product. Lastly, it allows the designer to evaluate exactly how much production is needed, whether the product will be a sustainable long-term product by the company.
Generate detailed plans
At this stage, the designer can now begin the most important stage of the FRP/Composite design process. The designer plays a big part in determining and increasing the value of the end product as they hold the business mentality and understand the wide range of material and process options, coincidentally, well thought decisions here minimise risks throughout the project and therefore avoid excess costs during the development and production period. In many cases, the material and process require a single selection. If sheet moulding compound is chosen as he most suitable material for example, then compression folding is the most logical process. However, in some cases, two or more processes are available, even though definite reinforcement and resin selections have been made. For instance, polyester bulk moulding compound can be either compression or injection moulded. In such a circumstance, other points such as component configuration, fabrication and end-use tolerances, and production volume, may determine the ideal process. Consequently, cost and performance evaluation are most commonly the conclusive factor. Cost of materials, tools, and labour of the product must all be considered and calculated against performance, ensuring that each production method is determined by the company to be the best choice.
Economic and feasibility analysis
This design process is the most commonly used method in determining the efficiency of a project. It is also known as cost analysis and helps in identifying profit against investment expected from a project. To establish the economic feasibility of the initial design concept a mock-up or small scale simulation may be helpful to approximately visualise the finished FRP/Composite component. Mock-ups also help to estimate the cost to determine whether it is feasible and efficient, in addition this also helps to oversee possible problems whether be tooling, assembly inspection or handling. Fixing problems at this stage is also much less expensive than further in the production cycle. Stress analysis or any testing of the composite material/component is also necessary in order to insure a high performing product which is cost efficient and authenticated for the market. Initial sketches are an important factor to stress analysis and are performed through computer programs and software, this is an engineering process used to calculate critical areas of stress concentration. Another method called the 3 - point flexure test is performed through physical testing. As shown in the image below, a sample specimen (in this case a FPS composite) is placed on two parallel supporting pins. The loading force is applied in the middle by means loading pin.
The supporting and loading pins are mounted in a way, allowing their free rotation about:axis parallel to the pin axis; axis parallel to the specimen axis. This configuration provides uniform loading of the specimen and prevents friction between the specimen and the supporting pins. The aim of these methods is to determine the optimum performance of the product to allow for improvements in which are both cost and time efficient.
Determine optimum tolerances
Designing composites is often driven by market demand and cost. As FRP has become the material of choice, based on design potential, conventional methods of analysis, design and manufacturing will not be sufficient. A composite design must be optimised not only for the performance of a finished part but for manufacturability of the part as well. Specifically, analysis and design must be performed in the context of the manufacturing process. A combination of the part geometry, the material form and the manufacturing process affects the fibre orientations within the part; therefore, understanding all three characteristics is critical during the design phase. Fibres that deviate from the analyst’s defined orientations will affect structural performance due to a significant impact on modulus and strength. In addition, in-plane or out-of-plane deformations that occur during production will result in increased manufacturing cost and effort to resolve issues downstream.
Delivering an optimised composite part requires that the fibre orientations of the production part fall within tolerance of an analyst’s desired part, which requires consistent manufacturing. Today, the majority of composite parts are still produced with manual lay-up processes, which introduce the risk of inconsistency. Although consistency increases when automated manufacturing processes are implemented, additional constraints are introduced, which can affect fibre orientations, thus impacting designed performance.
Consistency can be achieved by simulating the manufacturing process in the context of the desired fibre orientations, ensuring delivery of an optimised composite part for performance and manufacturing. When making choices on which processes provide the best outcome, there must be analysis both on the view of the manufacturing and business profits, time organisation and long-term figures.
Prototype
A prototype is a necessary element when coming towards the finished stage of a plan. Composite prototypes in which are made from moulds are far superior compared to most methods, as the completed production mould results in a component close to identical to the original part. The process in creating a mould is lengthy however in concept fairly simple. First the dimensions of the original part are transferred and cut out onto thin foam board, this will be used to act as a flange barrier both adding stiffness to the mould and making it easier to work with. Next the part is applied with a coat of release agent and then two layers of wax, this will ensure no problems when trying to release the mould from the original part. When creating the mould first a gelcoat is applied to provide a layer between the part and the FRP. Lightweight chopped strand matting is used as the fibre, while fibreglass resin is used to bind and harden the layers of the FRP composite. The resin is first applied onto the cured gelcoat, then the fibreglass matting is applied and covered with another layer of resin. After the composite has hardened it is now ready for refinement and application. After the desired prototype is produced, it provides important data to the designers, as a prototype displays the pro’s and cons of the product to determine whether it is a success and should be moved on to the large scale.
Tooling tryout
From the processes prototypes undergo, final adjustments and processes are made to meet the design objective. The tooling is completed, and the design is ready to be manufactured at large scales. Big FRP designers usually organise many machines and operators to keep up with a large-scale production. Thus, they must monitor the temperatures of machines and operators to ensure there is no defects or minor errors in dimensions.
