Practice for Identifying Process Steps - P102

Practice for Identifying Process Steps
Practice document
Document Type	Practice
Document Identifier	102
Tags	Integrated product development; Process step;
Cost	Maintain
Rate	Maintain
Quality	Maintain
MSTE workflow	Development
Prerequisites	Integrated Product Development; Practice; Practice for Developing a Product;

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Introduction[edit | edit source]

A factory can be represented as a series of individual steps that the part and material progress through. Each step may contain equipment and tooling which, when combined with the part and material, define the MSTEP system. Similar steps exist for many different manufacturing processes, however it is the arrangement of the factory steps that give individual processes their unique characteristics. For example, the general layout of an RTM or pultrusion factory is mostly similar with the exception that in the former case, dry fibre is deposited, compacted, and impregnated, while in the latter case, impregnation occurs before compaction.

Each step can be discretized into smaller sub-steps, further specifying the factory. For example, the thermal transformation step may be further defined as a cure step (for thermoset polymers) or a crystallization step (for thermoplastic polymers). While this may act to differentiate similar manufacturing processes, the fundamental nature of the two steps is the same (i.e. apply heat to transform the properties of the material).

Scope[edit | edit source]

This document serves as a guide for allowing users to identify the process steps of relevance to them. Various process workflows are provided, along with with a description of individual process steps.

Significance[edit | edit source]

Representing a factory as a series of individual steps is a convenient way to discretize composites manufacturing. Using this thinking allows for a more organized structure when developing, optimizing, or troubleshooting the manufacturing process. Moreover, it allows for a structured, science-based comparison between different manufacturing processes.

Factory Workflows[edit | edit source]

The factory workflow describes each and every stage (step) of the manufacturing process required to produce the composite part, starting from the receiving of the raw material through to final part quality inspection and reporting. A description of each individual factory step is given further down on this page, Process Steps. The part – starting initially as raw material, works its way through each individual factory step on its path to leaving the factory.

The factory workflow is determined by the manufacturing process used to produce the composite part. Defining and evaluating each step within the manufacturing workflow is important as it determines the final produced part outcomes of cost, rate, and quality.

In the general form, the factory workflow steps consist of: Receiving/handling raw materials --> Processing (giving part shape and material thermal transformation) --> Post processes --> Shipping

However, most of these steps may be repeated, altered or even omitted depending on your product and procedures. For example, some parts will require a second thermal transformation step or a second assembly step, or your part may not require any coating before being considered complete and ready for sale.

Many of the required steps in your factory will be dictated by the material system and shape previously selected as well as the functional requirements previously identified. You may also already have equipment available and are aiming to have the new composite part fit into the already existing infrastructure. This may require a reiteration of the material and shape selection in order to have the desired process step be a part of your facility.

Process Steps[edit | edit source]

Below is a description of the general process steps within a composites manufacturing factory. Each step links to the Systems Catalogue, where you will find in-depth information about the contents and inner workings of each step. There will also be a link to the next step in the Integrated Product Development section on the Practice for Developing a Process Step.

Process Steps	Description	Systems Catalogue	Developing Steps
Receiving	The receiving step indicates the portion of the factory where raw materials are received. It includes incoming material inspection and quality tests based on material specifications. Depending on the industry or product, material acceptance plans may demand stringent quality tests or be as simple as visual or tactile inspection.	A179	Practice for Developing a Receiving and Storage Step
Storage	The storage step refers to the conditions under which raw materials or parts are stored. Often, for thermosetting resins this means cold storage. For thermoplastics, core materials, consumables, and other non-temperature sensitive materials, room temperature storage may be appropriate. Humidity is another aspect that should be controlled. It is generally preferable to have low humidity conditions during storage in order to prevent moisture absorption in the material. If notable moisture absorption does occur, a drying step may be necessary.	A180	P155
Formulation	The formulation step is concerned with defining and combining the various chemical agents for the resin. This includes all cross-linking agents, initiators, promoters, accelerators, inhibitors, oligomers, particles, and any other additional additives. Often, for prepregs or high temperature, aerospace grade resins the chemical formulation is predetermined by the material supplier. However, for liquid polyester, vinyl ester, and even some epoxy resins, the end user may have control over the chemical formulation. The material supplier will typically provide some guidance in determining the appropriate formulation.	A181	P156
Impregnation	The impregnation step is where the resin and fibre are combined. Often this is a distinguishing feature between processes. That is, whether the fibre is placed on the tool first and then impregnated with resin, or whether the fibre and resin are impregnated and then placed on the tool. In the case of a prepreg process, the raw material comes pre-impregnated and therefore this step does not exist within the factory workflow.	Material deposition
Deposition	The deposition step deals with placing material on the tool or the tool-part assembly. Multiple deposition steps may exist if individual material systems are deposited and then acted on prior to deposition of subsequent materials. An example is gel coat deposition in a VA-RTM process. Here, the gel coat is deposited and undergoes partial thermal transformation prior to the dry fibres being deposited.	Material deposition	Practice for Developing a Deposition Step
Compaction	The compaction step refers to applying pressure to consolidate the composite in order to achieve the desired fibre volume fraction. Consolidation may occur through application of vacuum or external pressure from a press, caul plate, or other. Similarly, debulking through vacuum application is included in this step.	Material deposition	Practice for Developing a Consolidation Step
Thermal Transformation	In the thermal transformation step, heat is applied to the part/material(s) to transform it into its final form in order to achieve the required in-service properties. The step may be further defined as a cure step (for thermosets) or a crystallization step (for thermoplastics). Furthermore, the step may appear multiple times in a factory workflow if materials are thermally transformed over multiple stages. For example if a gel coat is added, or if a post-cure is implemented (referred to as secondary thermal transformation). While the step represents a heat-activated reaction, it does not mean that active heating need to be applied. A room temperature cure still falls under thermal transformation, although no additional heat is added.	Thermal transformation	Practice for developing a thermal transformation process step
Demoulding	After the part has been cured it needs to be removed from the tool, this is done in the demoulding step. This step has two main features, firstly removing the part and performing minor processing to the part, such as removing excess cured resin or drilling pilot holes. Secondly, the tool needs to be prepared for the next part to be produced on it.	A185	Practice for Developing a Demoulding Step
Trimming and Machining	Trimming/machining occurs after the part has been taken off the tool to remove excess material and drill holes. There are various methods and equipment that can be used for this such as CNC mill, waterjet and diamond saw.	A186	P160
Inspection	For composite parts, extensive non-destructive testing may be needed to ensure part quality has been achieved during manufacturing and post-processing. The inspections methods vary from manual inspection with a flashlight to a coordinate measuring machine (CMM). The amount and accuracy of the inspection step depends on the quality requirements set for the parts. Like most of the other steps mentioned here, this step may also be repeated throughout the manufacturing process to varying degrees, depending on desired set-up.	A187	P163
Assembly	Assembly is concerned with joining completed part components together. This includes adhesive bonding, thermoplastic welding, and mechanical fastening/joining of components. In the former two cases, a second thermal transformation step may be required to cure the adhesive or melt/crystallize the thermoplastic polymers.	A188	P161
Coating	The coating step is where the part achieves its final surface finish, through painting and or other surface modification procedures for aesthetic or preservation purposes. For some products, this step may not be necessary or it is minor and can be achieved in a different step.	A189	P162
Reporting	Reporting deals with documenting and reporting outcomes at the end of the part's manufacturing lifecycle. This step typically occurs immediately prior to shipping.	A195	P164
Packaging and Shipping	Packaging and shipping is the last step in any factory workflow, when the final part is shipped off to the next stage of its life cycle. That may be another factory where it is assembled as part of a larger structure, or the market where it can be purchased by a customer.	A190	P165

Example Workflows[edit | edit source]

The primary difference between the individual workflows involves the details of the processing step, indicated by the dashed box. The differences are largely concerning material deposition management (MDM). Below is a selection of common examples where the process flow is defined by the material deposition step and the surrounding factory layout is the same. Many of the workflows are similar, some are the same. To read more about all the different material deposition workflows follow the link to the systems catalogue Material deposition.

It is important to note that as you are developing your product workflow, you may create unique workflows that do not fit into any of the categories shown in the Knowledge in Practice Centre.

Liquid Composite Moulding (VARTM (VARI)/Light RTM/RTM)[edit | edit source]

The different types of liquid composite moulding processes all contain an optional gel coat deposition step depending on the product. This is followed by a material deposition step that involves placing fibre into/on the tool, which is then infused with resin using pressure as the driving force. The main differences in these process relate to the how pressure is used (positive or negative) to move the resin and the boundary conditions of the tool/consumables (ie. a rigid tool in the case of RTM, or a one sided mould with flexible vacuum bag in the case of VARTM).

Spray-up, Wet Layup & Pultrusion[edit | edit source]

The workflow for these three processes are the same, but with different tools and equipment. Spray-Up and Wet Layup are very similar processes and may also require a gel coat application step before impregnation. Pultrusion has the same concepts, but requires much different tooling and equipment.

Filament winding (Towpreg winding) & AFP/ATL/hand layup prepreg[edit | edit source]

Prepreg filament winding is very similar to other prepreg lay-ups in terms of overarching steps. This is due to the resin already being introduced into the fibres when they arrive at the production facility, eliminating many steps beforehand. The details of the deposition step however, is vastly different between the two types of processes, mainly stemming from a continuous process with winding and a patch by patch approach to layup prepreg. Filament winding with dry fibres can be done by setting up a formulation and impregnation step before the deposition, which can be done in many ways.

Compression Moulding (SMC/BMC) & Reaction Injection Moulding (RIM)[edit | edit source]

Working on the same principle of heated moulds being filled with material, then thermally transformed under pressure, these two procedures are relatively similar. The main difference comes from RIM having the resin injected into the mould to allow for a reaction, whilst compression moulding has resin rich material placed into the mould before compaction.

The primary difference between the individual workflows involves the details of the processing step, indicated by the dashed box. The differences are largely concerning the material deposition management (MDM). Below are a selection of common examples where the process flow is defined by the material deposition step and the surrounding factory layout is the same. Many of the workflows are similar, some are the same. To read more about all the different material deposition workflows follow the link to the systems catalogue Material deposition.

For this Level 2 section, the examples below are expanded to show the sub processes that occur around the main production of the part in more detail, as well as illustrating variations in the later stages where additional steps can be incorporated into various cells.

It is important to note that as you are developing your product workflow, you may create unique workflows that do not fit into any of the categories shown in the Knowledge in Practice Centre.

VARTM (VARI)/Light RTM/RTM[edit | edit source]

Below is an example of a closed mold resin transfer process. In this detailed example there is an emphasis on the preparation of materials around the main process steps. Allowing for tooling, consumables, reinforcement and resin to be prepared in parallel to each other to allow for a coordinated and rapid throughput of products. The resin preparation will have to be timed carefully due to the pot life of the resin, allowing enough time for the resin to go through de-gassing, but processing the part before the gel time is reached. Similarly to the other workflows demonstrated in level 2, there are many inspection steps included

Wet layup[edit | edit source]

In level 1 we see that the workflow for wet layup is the same as pultrusion and spray-up, however, when the workflow is laid out in a more detailed way the differences begin to appear. The largest difference is seen in the impregnation step, where, during wet layup, the deposition and impregnation happen simultaneously on the tool. For spray-up, impregnation happens as the fibres and resin are mixed by a chopper gun spraying onto the tool. All three of these processes can have a gel coat applied to the tool before the fibres are deposited, which is captured in the depiction below. The figure also demonstrates how the placement of fibres and resin is a continuous cyclical process until the desired number of layers is achieved. Also, an optional step for core insert or a second layup is included, where another iteration of the deposition process is required.

AFP/ATL/hand layup prepreg (Autoclave/Out-of-autoclave) processing[edit | edit source]

The first difference to note when comparing to level 1 are the additional preparation cells required for the prepreg layup. Also, the cyclical process of depositing layers of prepreg and debulking to achieve the desired part thickness before applying a vacuum bag for cure. Furthermore, many inspection steps have been added. Depending on the quality requirements of the product, the need for inspection steps must be evaluated specifically for the application. A new step has been added from level 1, the application of a galvanic barrier. This step may be needed if the part has been surface machined and there will be a need to protect the exposed fibres from the environment. It may be sufficient to simply apply a paint layer or a clear coat, however, some applications require a glass fibre layer in addition to a paint layer.

Now that the general layout of the manufacturing process has been established, the next step in the process is to develop each manufacturing step: Practice for Developing a Process Step

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	Composite Production Part Drawing - P169 Material Selection - P153 Practice for Developing a Deposition Step - P157 Practice for Developing a Product - P111 Practice for Identifying Process Steps - P102 Process selection for production scale-up - P171 Selecting Functional Requirements - P152.0 Shape Development - P151.0
Case Studies	Developing for Future Production Scale Up - C113 Lack of Requirements in Product Development - C104 Use of Right Sized Simulation to Aid Decision Making in Thermoplastic Composite Manufacturing Systems - C114
Perspectives Articles	CKN’s Approach to Developing Products with Composite Materials - A332


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