Reference - Chopped prepregs - A compelling performance and cost alternative material form
| Type | Journal |
|---|---|
| Title | Chopped prepregs - A compelling performance and cost alternative material form |
| Abstract | Chopped prepregs offer another material form for the composite engineers to consider. Some compelling reasons are performance parity, lower total costs, and easier transition from aluminum than continuous fiber composites. Structure - Parts made from chopped unidirectional prepreg will yield similar performance to hand layup continuous fiber composites when knockdown effects are considered. Much of the performance gain for the chopped prepreg material form comes from its low sensitivity to traditional knock down effects. Since the chopped prepreg form has inherent flaws due to stress concentrations at the ends of the short fibers, additional property losses due to holes for attachments, moisture absorption, etc., are minimal. In addition, this chopped material form can be made into complex geometrical shapes that use geometrical stiffening to give it a competitive advantage. Cost - Parts made from chopped unidirectional prepreg can have an advantage over continuous fiber prepreg layups when it comes to labor content. For simple geometries it is much faster to create a random chopped fiber mat than it is to orient and vacuum bag a continuous fiber prepreg layup. In many applications the chopped prepreg form is made into a 3D part that would have required a bonded assembly operation with traditional continuous fiber composites. In order to obtain optimum chopped prepreg structural performance a preform is typically required for complex 3D shapes. The cost trade is two labor intensive continuous prepreg operations (layup/bagging and bonding), for two less demanding chopped prepreg operations (random mat fabrication and preforming). In addition, post processing requirements, such as edge trimming, drilling, insert installation, etc., can be molded to the final condition with chopped prepreg. Eliminating these operations further reduces the cost content of chopped prepreg molding compound as compared with the cost content of continuous fiber prepreg parts.. Re-engineering Aluminum - the chopped prepreg form is much better suited to aluminum replacement with composites because of its 3-D molding capabilities. It is still important to engineer some design tradeoffs to achieve the best cost and performance capabilities with the chopped prepreg, but the changes are typically minor part modifications instead of a total redesign effort. This usually results in lowering the engineering costs associated with converting an aluminum part into a composite part driven by a cost or weight savings effort. |
| Authors |
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| Date | 2009 |
| Journal | International SAMPE Technical Conference |
| ISBN | 9781934551066 |
Welcome
Welcome to the CKN Knowledge in Practice Centre (KPC). The KPC is a resource for learning and applying scientific knowledge to the practice of composites manufacturing. As you navigate around the KPC, refer back to the information on this right-hand pane as a resource for understanding the intricacies of composites processing and why the KPC is laid out in the way that it is. The following video explains the KPC approach:
Understanding Composites Processing
The Knowledge in Practice Centre (KPC) is centered around a structured method of thinking about composite material manufacturing. From the top down, the heirarchy consists of:
- The factory
- Factory cells and/or the factory layout
- Process steps (embodied in the factory process flow) consisting of:
The way that the material, shape, tooling & consumables and equipment (abbreviated as MSTE) interact with each other during a process step is critical to the outcome of the manufacturing step, and ultimately critical to the quality of the finished part. The interactions between MSTE during a process step can be numerous and complex, but the Knowledge in Practice Centre aims to make you aware of these interactions, understand how one parameter affects another, and understand how to analyze the problem using a systems based approach. Using this approach, the factory can then be developed with a complete understanding and control of all interactions.
Interrelationship of Function, Shape, Material & Process
Design for manufacturing is critical to ensuring the producibility of a part. Trouble arises when it is considered too late or not at all in the design process. Conversely, process design (controlling the interactions between shape, material, tooling & consumables and equipment to achieve a desired outcome) must always consider the shape and material of the part. Ashby has developed and popularized the approach linking design (function) to the choice of material and shape, which influence the process selected and vice versa, as shown below:
Within the Knowledge in Practice Centre the same methodology is applied but the process is more fully defined by also explicitly calling out the equipment and tooling & consumables. Note that in common usage, a process which consists of many steps can be arbitrarily defined by just one step, e.g. "spray-up". Though convenient, this can be misleading.
Workflows
The KPC's Practice and Case Study volumes consist of three types of workflows:
- Development - Analyzing the interactions between MSTE in the process steps to make decisions on processing parameters and understanding how the process steps and factory cells fit within the factory.
- Troubleshooting - Guiding you to possible causes of processing issues affecting either cost, rate or quality and directing you to the most appropriate development workflow to improve the process
- Optimization - An expansion on the development workflows where a larger number of options are considered to achieve the best mixture of cost, rate & quality for your application.
