Composites manufacturing - A215
Overview[edit | edit source]
As explained in the Systems Approach to Composites page, a composite manufacturing process is a collection of process steps transforming the raw material reinforcement and resin matrix constituents into a combined composite material of a desired part shape and geometry.
Composite manufacturing processes are often named according to a particular process step within the complete part manufacturing process. By convention, the process name is in reference to the material (M), part shape (S), tooling (T), equipment (E), or particular action that is involved in this process step (P) (see KPC's MSTEP approach to manufacturing).
In general, the process naming convention highlights one or several of the following manufacturing processing steps:
- Placing and aligning the reinforcement
- Impregnating the reinforcement with the resin matrix
- Transforming the two material components into a solid material
The complete manufacturing workflow, however, includes other necessary steps; starting with recieving and storage of the raw material, on through to the steps mentioned above, and on through to the final part component inspection and out the factory doors.
For a complete list of the generic process steps involved in the manufacturing process, please see the Factory Process Flow page.
To learn about how to identifying process steps, see Practice for Identifying Process Steps.
Common Process Examples[edit | edit source]
As mentioned, composite manufacturing processes are conventionally named after a prominent process step(s) or action(s), often the material deposition step. Examples of some common industrial manufacturing processes, highlighting these critical defining steps, are listed below.
Wet Lay-Up[edit | edit source]
Performed by hand, reinforcement mats, fibre tows or dry fabrics are laid on an open mould. Resin is then spread onto the fibres wetting them. Alternatively, individual fibre plies (layers) are sometimes wetted with resin prior to transfer and laying onto the mould. Compaction of the fibres is usually done by hand with rollers. This wetting and laying process is performed layer by layer until the desired laminate thickness is obtained. Resin curing is carried out at room temperature or in an oven. A limitation to the process is only one smooth surface can be achieved (mould side) and an absence of direct thickness control.
Spray-Up[edit | edit source]
Spray-up involves spraying chopped fibres with resin onto a mould surface with a specialized spray gun. Fibre rovings are fed into to a spray gun, chopping the fibres before spraying. Resin may be applied with a brush or mixed with the chopped fibres in the spray process. Similar to wet lay-up, the resin wetted fibre is compacted by hand with handheld rollers. Resin curing is carried out at room temperature or in an oven.
Autoclave / Out-of-Autoclave Prepreg Processing[edit | edit source]
Pre-impregnated (prepreg) layers of fibre/resin (provided in this form by a materials supplier) are laid up on a mould to the desired shape and thickness. The prepreg stack on the mould is then placed into an autoclave in a vacuum bag setup for curing under heat and applied pressure conditions.
Out-of-Autoclave (OOA) prepreg processing is similar, except curing is carried out with only a vacuum bag setup and oven heating conditions without applied pressure. OOA prepregs are different from autoclave cured prepreg materials in that they are specially designed for curing without the applied pressure provided by the autoclave.
Compression Moulding[edit | edit source]
Compression moulding uses a heated mould consisting of matched dies placed in a press where a charge is placed in between that is pressed into shape when the mould is closed. The charge may consist of bulk-moulding compound (BMC), sheet moulding compound (SMC) or preform mat. Both thermoset and thermoplastic polymers can be processed by compression moulding. After curing (thermoset matrix) or solidification is complete (thermoplastic matrix), the mould is opened and the part is removed.
Resin Transfer Moulding[edit | edit source]
Resin transfer moulding (RTM) is a closed mould resin infusion process carried out in a two or more piece mould. A dry fibre reinforcement stack (preform) is placed into the bottom portion of the mould, after which the top half of the mould is placed to close the setup. Through injection gates, liquid resin is then let into the mould with low to moderate applied pressure up to approximately 7 bar or 100 psi. When mould filling is complete, the resin is let to cure. RTM is generally considered for moderate to high-volume production. It is well suited to small to medium sized parts, limited to large sizes due to injection pressure loads and tool cost.
Vacuum Assisted Resin Infusion / Vacuum Assisted Resin Transfer Moulding[edit | edit source]
Vacum assisted resin infusion (VARI) or sometimes referred to as vacuum assisted resin transfer moulding (VARTM), involves placing a fibre reinforcement stack (preform) on a one-sided tool, sealed with a vacuum bag on top. Vacuum is drawn to compact the fibre stack and to draw resin through the preform. Once the fibre is fully infused with resin, the resin inlet is clamped and vacuum is held until the resin is cured.
Filament Winding[edit | edit source]
The process is characterized by placing resin wetted fibres onto a rotating mandrel tool. Fibre tows are wetted with resin by running dry fibre tows through a resin bath. The resin wetted fibre tows are then deposited on a rotating mandrel. Layers are stacked through rotation of the mandrel until the desired thickness is obtained. Resin curing is then performed.
Pultrusion[edit | edit source]
Fibre tows are wetted with resin by running dry fibre tows through a resin bath. The wetted fibre tows are then subjected to compaction and heating by being passed through a heated shaping die. The pultrusion process requires the fibre distribution and cross-sectional shape be constant across the produced part length.
Bladder Moulding[edit | edit source]
Bladder moulding is a process suitable for hollow structures complex in shape. In this process, prepreg plies are wrapped around an inflatable bladder that is then placed inside a closed mould setup. The bladder is then inflated pushing the prepreg plies outwards against the inside of the mould cavity. After curing with heat, the shaped part is removed from the mould. In some cases, the bladder is removed from the interior of the formed part, in other cases, it may be left in place.
Tube Rolling[edit | edit source]
Tube rolling is a process suitable for hollow tube structures or rods with only a minor taper in geometry (e.g. fishing rod). Prepreg plies of either fabric or uni-directional tape are wrapped around a mandrel. Prepreg patterns may be cut to achieve a desired ply lay-up schedule. The mandrel rolling process compacts and debulks the fibre plies layer by applied layer. Often, the prepreg covered mandrel is covered with a specialized release coated shrink tape. Heated in an oven, the shrink tape applies a uniform compaction force consolidating the fibre plies. Upon curing, the shrink tape is removed with only minor surface mark-off.
Injection Moulding[edit | edit source]
Injection moulding is a popular plastic forming operation used in the plastics industry suitable for both thermoset and thermoplastic polymers. Liquid polymer is pushed with pressure into a closed mould cavity of the desired part shape upon which it solidifies. This process can be used for short fibre reinforced polymers granted the highly viscous liquid polymer can be injected into and fill the cavity. This short fibre injection process is more difficult than with an unreinforced polymer, as the polymer viscosity rises with the addition of the short fibres. The greater the fibre content, the greater the rise in the mixed polymer/fibre blend viscosity.
KPC AIM Event Webinars[edit | edit source]
To learn about composite manufacturing processes from one of our past KPC webinar event recordings:
- Click here to view the KPC AIM Event: Composite materials engineering webinar session 5 - Manufacturing processes – Introduction
- Click here to view the KPC AIM Event: Composite materials engineering webinar session 6 - Manufacturing processes - Prepreg processing
- Click here to view the KPC AIM Event: Composite materials engineering webinar session 7 - Manufacturing processes - Liquid composite moulding
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.