The CKN Knowledge in Practice Centre is in the early stages of content creation and currently focuses on the theme of thermal management.
We appreciate any feedback or content suggestions/requests using the links below

Content requests General feedback Feedback on this page

Effect of tooling in a RSDM system - A277

From CKN Knowledge in Practice Centre
Effect of tooling in a RSDM system
Systems knowledge article
Effect-of-Tooling-RSDM icon-JJBnrDwmVS9r.svg
Document Type Article
Document Identifier 277
Relevant Classes
  • Tooling and consumables

Introduction[edit | edit source]

The residual stress and dimensional change of a part is very closely linked to the thermal history the part experiences during manufacturing. Because tooling plays a crucial role in a thermal management system, it can significantly influence the residual stress and dimensional change of a part. Tooling material, shape, size, the construction, and the design of the sub-structure can all affect the thermal behavior of the tool-part assembly[1], which can consequently affect the residual stress and deformation of a part. In addition, the tooling surface condition can also affect the coupling between the part and tool, as it can facilitate geometrical locking, leading to residual stress build up in the part.

From a manufacturer's perspective, these parameters should be considered during the designing phase of the tool. The tool should be designed to work with the equipment as a system to produce parts that meet to specifications.

Scope[edit | edit source]

This article discuss the impact of tooling on residual stress and deformation of composite parts. The influence of tooling material and their A272(CTE), heat capacity, substructure and surface condition are discussed. The direct impact of tooling on thermal management and its relationship to RSDM is also explained. Please visit Effect of tooling in a thermal management system for more details.

Significance[edit | edit source]

Once a tool is manufactured, the tool undergoes a thermal profiling/characterization stage, where the tool's thermal behavior such as temperature uniformity, and dimensional stability at high temperature are characterized. At this stage, if the tool is unable to produce parts that conform to process specifications (including dimensional tolerance), it is very expensive and time consuming to modify the tool.

Prerequisites[edit | edit source]

Recommended documents to review before, or in parallel, with this document:

Analysis[edit | edit source]

Effect of tooling material on RSDM[edit | edit source]

Since most advanced composites are cured at elevated temperatures in ovens or autoclaves, A272(CTE) of the tool plays an important role in residual stress and deformation, especially in tool-part interaction. The difference in CTEs causes tools made of different material to expand different amounts under the same cure cycle. For example, from the table below, an aluminum tool will expand more that a carbon-epoxy tool which will expand more than an invar tool. Because the composite part usually gels at elevated temperature (partway through the cure cycle), they will take the shape of the hot tool. Adding to the complexity, the composite part is frictionally coupled to the tool and has a different CTE.

CTE values for common tooling and part materials [2][3]
Material CTE (x10-6/°C)
Aluminum 23
Steel 11
Invar 0.6 to 1.5
Epoxy 45 to 62
Polyester 60 to 200
Vinylester 100 to 150
Carbon fibre (longitudinal)

-0.2 to -0.5

Carbon fibre (transverse) 10 to 15
E-glass fibre (longitudinal) 5
E-glass fibre (transverse) 5

Tool part interaction causing warpage is illustrated in the figure below: a) tool expands more than the laminate in in-plane direction upon heating, inducing tensile stress in the laminate close to interface (typically the first and second ply). b) Some tensile stress is released via inter-ply slippage, resulting in a through thickness stress gradient. When the resin gels, the through thickness stress gradient is locked in. c) Part warps upon demoulding.

Tool part interaction schematic-a564e5MGmcRe-V01.png

It is worth noting that while some studies agreed that the higher the tool material CTE, the higher deformation, others did not observe the impact of tooling materials on part deformation [4][5][6][7] . Aside from the A272, tool material density, thermal conductivity and diffusivity play important roles in achieving uniform temperature distribution in a tool, which can affect residual stress development. Please visit Effect of tooling in a thermal management system for more details on how these material properties can affect the temperature uniformity.

Tooling thermal management and RSDM[edit | edit source]

During cure, a thermal gradient across the tool surface can lead to residual stress and deformation of the part. Depending on the tooling material, the unevenly heated tool can expand such that it is out of tolerance, producing a deformed part. A thermal gradient across the tool surface can also cause areas of the part to cure ahead of other areas, generating residual stresses. Because the tool is adjacent to the part, a thermal gradient across the part and the tool in the through-thickness direction (aka the pancake effect) can also generate residual stresses. In general, thermal management is more complicated for parts cured at elevated temperatures because of the additional heat-up stage. For room temperature cured parts, the heat transfer between the part and the tool only occurs when the part exotherms to a higher temperature during polymerization and the tool acts as a heat sink.

As mentioned many times in the Thermal and cure/crystallization management (TM), the interaction between the tool, part, equipment is a complicated system level problem. In the context of residual stress and dimensional control management, ultimately what matters are the actual tool shape (likely at elevated temperature), which shapes the part and the thermal uniformity the part experiences. Please visit Effect of tooling in a thermal management system for more details.

Effect of tooling surface condition on RSDM[edit | edit source]

Tool-part interaction depends heavily on the friction between the first ply of the composite and the tool. The first ply of the part may stick well to a tool with a rougher tool surface. When the tool expands due to thermal expansion, it can impose strain on the ply. The use of non-stick FEP (Fluorinated Ethylene Propylene) films have proven to decrease the amount of deformation on flat laminates compared to using chemical release agent [8]. Sensibly, higher processing pressure also results in greater deformation due to tool-part interaction.

If a peripheral grinding process is used to finish the tool surface, the surface roughness might be different in the grinding direction and the lateral direction. The roughness in the grinding direction was measured to be four times smaller than the lateral direction. As the tool is being used throughout its life, the directional roughness difference will decrease from resin and release agent residual filling the surface[9].

Effect of tooling size on RSDM[edit | edit source]

Tooling size can affect RSDM in two ways: thermal uniformity and the amount of thermal expansion/contraction. In general, the large the tool, the higher the thermal mass, the harder it is to execute good thermal management and achieve uniform temperature across the tool. Hot presses are typically not suitable for very large parts so large ovens and and autoclaves with more powerful circulation systems maybe required. Larger tool will also expands more when heated. The larger the tool, the larger the distortion due to tool-part interaction for flat parts or parts with mild curvature [8].

Effect of tooling on RSDM after gelation[edit | edit source]

The aforementioned sections mainly focused on the effect of tooling on RSDM during the heat-up stage of a cure cycle, mainly before the part gels. As mention in Residual stress and dimensional control management (RSDM), the majority of the residual stresses such as cure shrinkage stress and thermal stress form after gelation when the resin is able to bear stress. The tool behaves as a constraint during the post-gelation stage which prevents the part from deforming freely. Depending on the boundary conditions (surface condition, shape etc.), the tool can impact the final part residual stress levels to different extends.

Another important parameter is the resin modulus. When the resin just reaches gelation, the modulus is relative low. As the cure progresses and resin eventually cools down to room temperature, the modulus increases while experiencing cure shrinkage stress and thermal contraction stress and being constrained by the tool at the same time. When the part is demolded from the tool, it is at a higher modulus compared to when it gelled and the part is allowed to deform freely. The constraints (or boundary conditions) imposed by the tool has large impacts on the final part residual stress and deformation, a flat tool with two layers of FEP will not matter as much as a male C tool with release agent that creates geometrical locking. On a similar note, if a part is removed from the tool once it reaches gelation and proceeds with a free standing cure (while remaining vitrified to prevent viscoelastic deformation), the residual stress and deformation will be different than if it had been kept on the tool past gelation.

Effect of tooling during de-moulding[edit | edit source]

De-moulding can be difficult if the part deforms in a way that stuck to the tool. For example, a composite cylinder made on the outer surface of a mandrel can shrink (radius decrease) onto the mandrel, making it difficult for the mandrel to slide out. A C-shape made on a male (convex) tool can also spring-in and clamps onto the tool. Please refer to Effect of shape in a RSDM system for schematics of the geometries. Therefore, the de-moulding strategy should be considered during tooling design. Proper draft angles, collapsible tooling, dissolvable tooling, release agent or films etc. may be employed to de-mould parts that are susceptible to dimensional changes. More information can be found on Shape Development.

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


  1. [Ref] Fabris, Janna et al. (2018). "Effect of tool design on thermal management in composites processing" (PDF). Cite magazine requires |magazine= (help)CS1 maint: extra punctuation (link) CS1 maint: uses authors parameter (link)
  2. [Ref] Daniel, Isaac M.; Ishai, Ori (2006). Engineering Mechanics of Composite Materials. Oxford University Press. ISBN 978-0-19-515097-1.CS1 maint: uses authors parameter (link) CS1 maint: date and year (link)
  3. [Ref] MatWeb LLC. "MatWeb: Online Materials Information Resource". Retrieved 9 September 2020.CS1 maint: uses authors parameter (link)
  4. [Ref] Kappel, E. et al. (2013). "Process distortions in prepreg manufacturing – An experimental study on CFRP L-profiles". 106. Elsevier. doi:10.1016/J.COMPSTRUCT.2013.07.020. ISSN 0263-8223. Retrieved 15 October 2019. Cite journal requires |journal= (help)CS1 maint: extra punctuation (link) CS1 maint: uses authors parameter (link)
  5. [Ref] Sarrazin, Hugo et al. (1995). "Effects of Processing Temperature and Layup on Springback". 29 (10). doi:10.1177/002199839502901001. ISSN 0021-9983. Cite journal requires |journal= (help)CS1 maint: extra punctuation (link) CS1 maint: uses authors parameter (link)
  6. [Ref] Roozbehjavan, Pooneh et al. (2014), Experimental and numerical study of distortion in flat, L-shaped, and U-shaped carbon fiber-epoxy composite parts, 131, doi:10.1002/app.40439, ISSN 1097-4628CS1 maint: extra punctuation (link) CS1 maint: uses authors parameter (link) CS1 maint: date and year (link)
  7. [Ref] Jain, Lalit K.; Mai, Yiu Wing (1997), Stresses and deformations induced during manufacturing. Part I: Theoretical analysis of composite cylinders and shells, 31, doi:10.1177/002199839703100703, ISSN 0021-9983CS1 maint: uses authors parameter (link) CS1 maint: date and year (link)
  8. 8.0 8.1 [Ref] Twigg, Graham et al. (2004). "Tool–part interaction in composites processing. Part I: experimental investigation and analytical model". 35 (1). doi:10.1016/S1359-835X(03)00131-3. ISSN 1359-835X. Cite journal requires |journal= (help)CS1 maint: extra punctuation (link) CS1 maint: uses authors parameter (link)
  9. [Ref] Erik Kappel (2013). Process Distortion in Composite Manufacturing (Thesis).CS1 maint: uses authors parameter (link)

About Help
CKN KPC logo


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
  • 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.