Effect of equipment in a RSDM system - A278
| Effect of equipment in a RSDM system | |
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| Systems knowledge article | |
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| Document Type | Article |
| Document Identifier | 278 |
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Introduction[edit | edit source]
The residual stress and dimensional change of a part is closely linked to the thermal history and consolidation the part experiences during manufacturing. Equipment used for thermal transformation, such as ovens, autoclaves and hot presses, prescribe the cure cycles on the part and have direct influence on the part thermal history. Equipment that applies pressure determines the level of part consolidation. This page explains how equipment can indirectly influence the residual stress level within a part.
Prerequisites[edit | edit source]
Recommended documents to review before, or in parallel, with this document:
- Heat transfer
- Thermal management
- System interactions
- Autoclave
- Oven
- Tooling and consumables (system class)
- Effect of tooling in a thermal management system
- Effect of tooling in a RSDM system
- Effect of equipment in a thermal management system
Overview[edit | edit source]
Equipment can indirectly affect the part residual stress level via thermal uniformity and consolidation.
Thermal uniformity[edit | edit source]
During the thermal transformation stage of a part, the system typically involves the part, the tool, and the equipment such as ovens, autoclaves and hot presses. It is the equipment that applies the thermal boundary conditions to the part-tool combination. In the case of a room temperature cure, the equipment is simply the environment (i.e. the room). The equipment prescribes the thermal boundary conditions, which, in combination with the constituent materials, part shape, and tooling, results in the thermal response of the part. This thermal response may very likely not be uniform during different stages of the curing process, which is one the main sources of residual stress within the part. Please refer to pages in prerequisites regarding the interaction between material, shape, tool and equipment in a thermal management system.
Example 1: a part-tool assembly is placed in a convection oven that has strong airflow above the tool and weak airflow below. The difference in airflow is due to the oven design (having the fan on the top). The top layers of the part heat up more quickly than the bottom layers. The temperature gradient causes the top layers to cure before the bottom layers and create residual stresses.
Example 2: a preform/charge is placed in a tool to be cured in a hot press. The tool serves as the medium of heat exchange between equipment and part via conduction. Due to this nature, the layers of the part adjacent to the tool heat up quickly and remain at a uniform temperature. The center of the part takes longer to heat up because the charge has low thermal conductivity. The temperature gradient will cause a degree of cure gradient which ultimately leads to residual stresses within the part.
Consolidation[edit | edit source]
Equipment such as vacuum pumps, autoclaves and hot presses are commnly used to provide consolidation to composite parts during processing. A more consolidated part typically has higher fiber volume fraction and less porosity. As mentioned in the RSDM homepage, resin cure shrinkage and thermal contraction are two of the major drivers for residual stress and part deformation. So a part that is less consolidated with higher resin content may be more prone to residual stresses and deformation.
Related pages
| Page type | Links |
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| Introduction to Composites Articles | |
| Foundational Knowledge Articles | |
| Foundational Knowledge Method Documents | |
| Foundational Knowledge Worked Examples | |
| Systems Knowledge Articles | |
| Systems Knowledge Method Documents | |
| Systems Knowledge Worked Examples | |
| Systems Catalogue Articles | |
| Systems Catalogue Objects – Material | |
| Systems Catalogue Objects – Shape | |
| Systems Catalogue Objects – Tooling and consumables | |
| Systems Catalogue Objects – Equipment | |
| Practice Documents |
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| Case Studies | |
| Perspectives Articles |
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| About | Help |
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.
