Systems approach to composite materials - A230
A practitioner is always driven by the performance (function) of the product, but constrained by the manufacturing. In the case of composite materials, manufacturing is often challenging. Because of its relatively new emergence, the maturity of the manufacturing of fibre reinforced polymer composites (FRPs) is not as well established as it is for traditional materials such as metals or ceramics. In order to reduce the risk associated with composites manufacturing, a structured systematic approach should be taken towards the development of best practice.
Manufacturing Relationship to Design (MSTEP Approach)[edit | edit source]
As popularized by Ashby, engineering design can be described as the interplay of four classes of choices: the intended function/performance, the choice of material, the choice of shape, and the process that can turn the required material into the desired shape of the product . From this thinking comes a structured approach to selecting the best material and shape for the product, whilst taking into account the feasibility of such material/shape combination through consideration of the process. However, and in particular with composites, the definition of process should be expanded to cover two other items, namely tooling and equipment, that then allow for a full definition of the process.
|Traditional (Ashby) framework for engineering design and manufacturing.||CKN's expanded MSTEP approach to manufacturing.|
MSTE classes[edit | edit source]
The KPC framework is an expansion of the traditional design and manufacturing approach to more explicitly address the process. Traditionally, design can be thought of in terms of the desired function (F), material (M), and shape (S) of the part. The process step (P) is not only a function of the material (M), shape (S), but also the tooling and consumables (T), and equipment (E) that are used. Particularly for composites, the interaction of material, shape, tooling & consumables, and equipment during a process step (abbreviated as MSTEP) is critical in determining the outcome of that particular manufacturing process step, and ultimately the quality of the finished part.
Note that the MSTEP depiction of a manufacturing process represents only a single process step of the entire manufacturing workflow. The complete manufacturing process is a collection of individual process steps that come together to form the factory manufacturing process.
Defining a manufacturing process[edit | edit source]
Discretized, a process is nothing more than a set of equipment and tooling used to perform a specific action (or process step) on the part or material. And a complete manufacturing process is the collection of process steps required to manufacture the finished part from raw material to out the factory door. Defining which steps to perform and which equipment and tooling to use is based on the initial material state and the part geometry to be constructed. In other words, it is the part and material that determine which processing steps must be performed and which equipment/tooling can be used to perform them. The layout of these processing steps are what define the manufacturing workflow.
This is illustrated in the following example, which shows a resin transfer moulding (RTM) process workflow broken down as a collection of individual process steps.
By convention, the composites industry names and classifies manufacturing processes after one or more critical processing steps in the manufacturing workflow or after the material form that is processed. Indeed, many composite manufacturing processes contain very similar steps, however, they may differ in process classification due to differences in a particular process step or the material forms involved. Across the entire manufacturing factory workflow, classified processes might only differ from one another in the arrangement of process steps, inclusion/exclusion of specific steps, and/or differences in the equipment, tooling, part (shape), and material involved.
For examples of typical composite manufacturing processes with a description of the key process step(s) that influence its naming and classification, see the common composite manufacturing processes page.
The manufacturing factory[edit | edit source]
Manufacturing process steps must occur within a physical space in the factory. This is what is referred to as a factory cell, wherein specific equipment and tooling are housed. The production part flows through the factory, taking shape with each successive processing step it undergoes. For each process step there may be a different MSTEP combination. Moreover, there may be multiple process steps that occur within the same physical space (cell) in the factory.
Viewed using a systems level approach, the part being produced moves through several distinct cells within the factory during its manufacturing process. Within each cell, the part is subject to various processes resulting in trackable outcomes. A general factory layout depiction organized by various factory cells is shown below. Example factory layout:
Learn more about the systematic breakdown of a composite manufacturing factory here.
Manufacturing Themes[edit | edit source]
The interactions that occur within each factory cell, as well as the outcomes, can be classified according to processing themes. In the processing of composite materials, there are five primary processing themes. A given manufacturing process may incorporate multiple themes, however this discretized structure can still be used to systematically approach the problem. In order to achieve intended manufacturing outcomes, one must properly control and track all process state-variables across each of the themes. Any outcomes arising in upstream processes (those within TM for example) will influence downstream outcomes (those within RSDM for example).
These themes are, in order of general manufacturing steps:
- Thermal and cure/crystallization management (TM)
- Materials deposition and consolidation management (MDCM)
- Residual stress and dimensional control management (RSDM)
- Machining and assembly management (MAM)
- Quality/inspection management (QIM)
You can learn more about the composite processing themes here.
Manufacturing Outcomes[edit | edit source]
Manufacturing outcomes are the result of the intrinsic material process-structure-relationship associated with composite materials. Outcomes are those parameters that are tracked for evaluation to define quality and producibility. Outcomes that fail to satisfy the set upon manufacturing requirements of the processed material are known as defects.
Manufacturing outcomes may be measured or tracked as:
- Intermediate outcomes – (e.g. temperature seen in a material) changes of a material during a process step.
- Final outcomes – (e.g. final resin degree of cure) usually measured at the end of a process step and independent of any knowledge of process history.
It should be pointed out that manufacturing outcomes are very often dependent on system interactions. For a given manufacturing outcome of interest, upstream dependencies have the potential to be root causes for downstream dependencies as ‘knock-on’ effects.
Click here to learn more about and examples of manufacturing outcomes and their system dependencies, (in the Systems Knowledge volume) where this topic is covered in more detail.
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.
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.