Determine Functional Requirements
The first stage of the design process starts with determining the functional requirements of the component and assembly being designed. The following are a list of the considerations.
Mechanical properties
Compressive, tensile and flexural strength; impact resistance and elongation.
Physical Properties
Density and hardness; dielectric strength; arc resistance and volume resistivity; thermal conductivity, heat resistance and heat distortion; thermal expansion coefficient and flammability.
Chemical Properties
Resistance to alkalies, acids and organic solvents; water absorption; ultraviolet radiation, resistance to ozone and weathering.
Fitness for service
Cosmetic appearance and surface quality; fabrication, dimensional stability, compatibility with other materials and end-use tolerancing.
Determine Economic Requirements
The second stage of the design process consists of establishing cost targets. Economic evaluation of a specific application requires a system approach for the FRP/Composite component(s) to be viewed in the context its total contribution to the end use. This broadens the design process further than a simple comparison of material cost between FRP/Composites and other candidates. These items should be included in such considerations.
Machining fixtures, tooling cost, including peripheral equipment such as cooling fixtures and assembly tools.
Tolerances outside of normal process capabilities ass cost premium. Process capabilities compared with general fabrication and end-use tolerancing.
Secondary operations, such as machining and assembling.
Finishing cost, such as trimming, sanding planting, painting and polishing.
Other cost-producing operations that require comparing and studying include quality control packaging, storing, inventory control and shipping. These thorough economic evaluations of the proposed FRP/Composite application provide three valuable benefits:
First, a true picture of the total system cost will be presented, making subsequent design decisions more cost effective.
Second, other cost-saving areas are revealed that may not have been obvious initially – saving that can be designed into the product
Third, the designer is able to determine exactly how much performance is worth buying, in projected selling prices or keeping with present and other market considerations.
Determine the Material and Process
With economic and functional requirements established, the designer can then proceed to the most critical stage of the FRP/Composite design process. The designer who understands the process options and wide range range of material will use this step to add a great deal of value to the end product. Good choices here will also minimize cost during the development, project risk and production cycles.the molding method and materials at this of the FRP/Composite part design will effectively define the product performance and economics over the long term.
Partnering together with a material supplier and molder throughout the design process will reward the project engineer regardless of their level of experience, but this step might represent the single most significant opportunity for optimizing cost and performance.
In many cases, process and material involve a single selection. For example, if a piece sheet molding compound is chosen as the most suitable material, compression molding is the logical process. however, in some cases there are two or more process available, even though definite resin and reinforcement selection have been made. Polyester bulk molding compound, for instance, can be either injection or compression molded. In a situation such as this, other factors, such as a part configuration, end-use tolerances, fabrication and production volume, may determine the optimum process.
In every case, performance/cost evaluation should be the deciding factor. Cost of tooling, materials and labor must all be considered and measured against performance. And each candidate method of production must be considered to determine the best choice.
Finally, the basic advantages offered by FRP/Composites should be reviewed. Although the initial design may have had only one or two of these “basics as its goal, opportunities to improve product performance and reduce cost in other areas are often brought to light by considering them all once again.
Create Initial Sketches
The purpose of this stage is to help design engineers make their concepts consistent and focus these basic concepts with end-use requirements. Keeping in mind the basic attributes of processes and attributes of the FRP/Composite materials help avoid producing a direct copy of a part as it can be designed to suit the unreinforced plastics or the characteristics of metals. This is especially important if the savings of a few ounces of a material per part can add up to a significant amount over a large production run and materials are highly cost-competitive.
The designer must decide on an approach that will produce a part sufficiently strong to meet mechanical requirements, withe the thermal, electrical and chemical properties, as well as appearance qualities to meet specifications. Initial sketches are necessary to start the detail empirical design and to perform stress analysis. High-performance FRP/Composite products typically result from effective use of both disciplines, checked with laboratory testing.
Stress analysis involves using engineering equations for calculating stresses at critical areas, resulting in the determination of optimum configuration and minimum part thickness for those areas. These studies are commonly performed using finite element analysis methods and special computer programs that eliminate the tedious manual calculations. This design approach is used for FRP parts where material cost considerations are critical and where performance requirements are severe. Empirical design is based on the designer’s familiarity with processes in related applications and FRP/Composite materials. Assumptions are made concerning surface finish and other features, part thickness and characteristics, based on past experience with similar parts plus all additional available information. And a preliminary cost estimate is usually made which determines whether the design approach meets all production requirements.
Make Detailed Part Drawings
When committing the design to production drawings, many details must be considered and resolved. As elsewhere in the design process, consulting with a reliable custom molder at the point would be a wise decision for advice concerning design details, such as holes, radii, ribs, inserts, bosses, as well as for guidance on surface finish, reduced stress concentration, and other features, molded-in colour, and refinements. This is also a critical point to consider current manufacturing and design methods such as:
Lean Manufacturing
Design for Manufacturability
Design for Six Sigma
Working with the custom molder to optimiza tolerances for performance and cost and to help develop the most efficient production flow concepts will form the basis for near/long-term economic benefits during the production life cycle.
Economic and Feasibility Analysis
As the detailed drawings are completed, a final economic analysis should be prepared to calculate investment, and return on investment, confirm preliminary economic study and to establish the total delivered cost of the FRP/Composite component.
A simulation or mock-up may be helpful to establish the technical feasibility of the initial design concept. This needn’t be a detailed replica or an exact prototype of the part to be molded. An approximation can aid the visualization of the finished FRP/Composite part and its relationship to parts associated within the final product. A mock-up, in addition, helps visualize possible problems involving assembly, tooling handling and inspection. Correcting such problems at this stage is much cheaper than in later stages in the production program.
Develop a Prototype
The next step is a working prototype. One which closely duplicates the expected final design in performance and consideration. The best FRP/Composite prototype is one produced from partially completed production wolds because it will be almost identical to a production part. This can be facilitated with help from molders that are skilled in low-volume FRP/Composite processes that are precisely suited for producing prototype parts economically.
The easiest of prototypes to fabricate are those for applications involving contact molding processes. These prototypes are readily checked against performance and dimensional requirements. Then they are adapted, or the mold is modified and another prototype molded. This mold or the processing technique is adjusted until a satisfactory part is produced.
Through the molding and testing of a series of prototypes and gradually refining the design, the establishments of dimensions and the final configuration. This process produces an FRP/Composite part that will provide the required function and uses the minimum material commensurate with design objectives of dimensional stability, strength and surface finish.
Tooling Tryout
For the final refinements of the prototypes to meet design objectives, the tooling is completed and the design is ready for pilot product. Provisions for cooling and heating are added, and the surface finished are applied to facilitate part release. Twin tools may be built if production volume dictates.
In the time of tool tryout runs, its is essential to control closely the variables of pressure, temperature and cycle times so the parts produced can be assessed in terms of end-use objectives. Such control is also needed to ensure reproducibility of production run pairs.