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Transitioning tooling styles between different thermal transformation equipment - P139

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Practice - A6Production Troubleshooting - A251Transitioning tooling styles between different thermal transformation equipment - P139
Transitioning tooling styles between different thermal transformation equipment
Practice document
Document Type Practice
Document Identifier 139
Objective functions
MSTE workflow Troubleshooting

Q: "I am attempting to transition tooling styles, from autoclave to press cure, to increase production rate and am experiencing new quality problems."

A: The problem here is two-fold. The first is that there is a significant change in equipment, from a convection-based one to a conduction-based one. The second is that in order to accommodate the change in equipment, a change in tooling must also be done, from one-sided tooling in the autoclave to two-sided tooling in the press. Often, a hot press will have its platens preheated prior to cure or will heat up quickly in comparison to an autoclave. This shortens the overall cure cycle time, allowing for increased production rate. However, it also subjects the part to a faster heating rate. As a result, the part may experience a much larger exotherm, especially if it is thick. This may thermally degrade the part. Whereas in an autoclave, the part can heat up/cool down from the air, in a hot press, the heat going to and from the part must pass through tooling, which very quickly heats up to the temperature of the platens. Therefore, an increase in tooling thermal mass has less of an effect on reducing the exotherm as compared with a convection-based system.

Other potential sources of quality problems are the change pressure. Hot presses often apply significant pressure to the part. Material systems with relatively low viscosity may experience excessive flow as a result. This can lead to dry spots, poor resin volume fraction, and increased porosity. Moreover, if the part is not designed to be subject to such high pressures during manufacturing, then the part may deform or even break. Another potential source of defects is the lack of vacuum application in hot press curing.

Overview[edit | edit source]

Depending on the equipment used for thermal transformation, the tooling style may change. For example, in hot press curing, two sided tooling is used. That is, both the top and bottom surfaces of the part are in contact with tooling. In an oven or autoclave, however, typically only one sided tooling is used to support the bottom surface of the part (known as the toolside surface). The top of the part is typically covered in consumables, such as release film, breather, and a vacuum bag. This is referred to as the bagside surface. In this latter scenario, the part is subject to vacuum in addition to any external hydrostatic pressure that is applied (in an autoclave for example). In the former scenario (i.e. the hot press cure), no vacuum is applied and all pressure comes from the force of the platens compacting the part. From a systems perspective, the difference between the two scenarios is that the boundary conditions have changed. This includes the part interface boundaries as well as the boundaries of the tool-part assembly as a whole. In the oven/autoclave scenario, the tool-part assembly is subject to convective heating, whereas in the hot press scenario, the tool-part assembly is subject to conductive heating.

Natural convection Forced convection Two sided conduction One side conduction with natural convection

When troubleshooting quality issues arising from a change in equipment and tooling, the root cause of the defects may be from the equipment, the tooling, or the combination of both equipment and tooling.

If the change in equipment is suspected to be the cause of the quality issues, visit the following page for troubleshooting tips:

If the change in tooling is suspected to be the cause of the quality issues, visit the following page for troubleshooting tips:

For both cases, recall that the thermal transformation step (as with all process steps) involves interactions between the material, part shape, tooling & consumables, and equipment. While troubleshooting the tooling (for example) may lead to a mitigation strategy to resolve the quality issues, the ramifications of implementing such a strategy, with regards to the interactions with other components, should be understood. This will prevent further quality issues from arising down the line and allow for a more robust process definition.

Thermal management considerations[edit | edit source]

Link to thermal management

Thermal management considerations for the equipment and tooling are detailed in the links above. A few general points to keep in mind are:

  • For the same thermal conditions, a conduction-based environment will exhibit smaller thermal lags than a convection-based environment. See Conductive heating.
  • Because conduction-based equipment often use fast heating rates, or have their platens preheated (eg. a hot press), along with two-sided tooling, the exotherm potential may be quite high - especially for thick parts.
  • For high temperature processing, the higher the heat transfer coefficient (HTC), the quicker the heat up time and the less the thermal lag. See HTC, high temperature
  • For low temperature processing, a high HTC acts to cool the part. See HTC, low temperature
  • The shape and position of the tool/part in a convective heating system affects the local HTC. See Tooling configuration and Part configuration.
  • Increasing the bagside HTC reduces the part exotherm.
  • Increasing the toolside HTC increases the exotherm if the tool is thermally massive compared to the part. If the tool is not thermally massive compared to the part, increasing the toolside HTC reduces the exotherm. See Tooling substructure
  • Tooling with a higher thermal conductivity/diffusivity will present a more uniform temperature distribution and reduce the part exotherm (assuming the same thermal mass).
  • The higher the thermal mass of the tool/part, the longer it will take to heat up
  • Increasing the thermal mass of the tool will increase thermal lag but reduce part exotherm

To learn more, or to explore these points in more detail, visit the following pages:

Material deposition management considerations[edit | edit source]

Link to material deposition management

Content coming soon

Flow and consolidation management considerations[edit | edit source]

Link to flow and consolidation management

Flow and consolidation considerations for the equipment and tooling are detailed in the links above. A few general points to keep in mind are:

  • An altered thermal profile of the part may also alter the viscosity profile. This, in turn, will alter the flow characteristics of the material.
  • The pressure applied by a hot press is often much higher than that applied by an autoclave. For low viscosity systems, this may lead to excessive resin flow.
  • Lack of vacuum application in a hot press may lead to increased porosity if the part has entrapped gas that does not dissolve into the resin under pressure.

Residual stress and dimensional control considerations[edit | edit source]

Link to residual stress and dimensional control management

  • A large discrepancy in the coefficient of thermal expansion (CTE) between the tool and part may result in significant residual stresses in the part. This may lead to warpage upon demoulding.
  • Generally speaking, a tool with a small CTE is desirable for carbon fibre-epoxy parts.
  • Hot presses often have a minimum force which they can apply. If this force is too high for the part design, it can lead to part deformation or damage.

Related pages

Page type Links
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
Case Studies
Perspectives Articles

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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 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.

The relationship between material, shape, tooling & consumables and equipment during a process step

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:

The relationship between function, material, shape and process

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 relationship between function, material, shape and process consisting of Equipment and Tooling and consumables


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
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