Guide to pre-preg composite manufacturing software

How software can streamline the processes of working with life-based materials


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Working with pre-preg composite materials delivers many benefits to the finished product, but this is often offset by challenges during the manufacturing process, making composite parts more expensive than their traditional counterparts. ERP systems often do not accommodate the unique requirements of a composite shop floor, so what are the common problems and what can you do about it?

Composite part manufactured using CrossTrack

What are the problems when working with composite materials?

Pre-preg composite materials are delivered in rolls on refrigerated trucks and kept in a freezer, usually at around -18c. This gives them an extended shelf life of generally a number of months or over a year. However, take it out on the shop floor and this drops to a life measured in hours. Once the material has expired it can no longer be used and must be discarded – this can be a painful and expensive exercise for material often costing upwards of $100 per square metre.

Tracking is often done by paper, with staff updating it manually as material leaves and re-enters the freezer. When the material is cut into plies to make up a kit of the finished part the problem is compounded further. How do you track dozens or hundreds of plies, especially if some get scrapped and re-made from different material? Furthermore, if you're scrapping a kit due to expired material later on in the production process there's the additional labour and re-manufacturing costs to take into consideration.

Another issue is how efficiently the material is used. Nesting software will create the most material-efficient pattern to maximise the material usage, but the downside of this is that it can often take much longer to unload the plies at the cutting table during the kitting process.

In larger facilities locating material or kits can also prove challenging. Staff may not be aware that a part-used roll is available, taking a new roll instead and leaving the other to quietly (and expensively) expire.



Static versus Dynamic (Just In Time) nesting

Many composite manufacturers will create a nest of all of the plies relating to one kit and then repeatedly cut the same nest as required. This is referred to as static nesting. A major problem is that if you are exclusively static nesting then it's difficult or impossible to use the end of the roll efficiently. If you are cutting several static nests from the same material this will be nowhere near as efficient as if you were to take all of the plies into consideration during nesting.

This process, referred to as dynamic nesting or 'Just in Time nesting', can often generate double-digit percentage savings, with one JETCAM user saving €1500 in the first four hours of using the software due to material efficiency alone. You'll also no longer have the issue of inefficient use of end of rolls, as a dynamic nest can be of any length.

Static Nesting

Single Static Nest example

Re-run multiple times, fixed length. Material selected at time of cutting.

Static nesting involves a single nest, often containing one kit that is repeatedly run. It may be optimized for unloading but will have less material efficiency than a dynamic nest, as it only contains one kit of plies - the more plies on the nest, the greater the potential saving.

If we want to make several instances of this kit we would need to cut the nest X number of times. Many companies often end up with multiple short rolls of material that could be used but for the fact that their shortest kit nest is too long.

Dynamic (Just In Time) Nesting

Dynamic nest example

Created as needed, materialto be used selected before nest created.

Dynamic nesting of an order of plies/kits should select the best material to use first, based on rules that you set (such as remaining life or length of roll). As many plies as possible will then be nested on it. If the material is too short to include all plies, then the next most suitable material will be used, and so forth. Unloading may take longer but considerable material savings can be made. You also use the end of the roll more efficiently, and ensure that material does not expire.

If used in conjunction with automated unloading technologies then you will save on both material and unloading time.

Re-lifing composite materials

The most significant consideration when manufacturing with pre-preg composites is material life. As mentioned earlier, pre-preg material has a different usable life depending on the temperature that it's kept at over the course of its life, and this can differ between material types. Keeping track of this is the issue – especially once the raw material has been cut into hundreds or even thousands of plies and separated into kits. What happens when a ply is scrapped?

Furthermore, material can be 're-lifed'. This is a process whereby a sample of the material is removed and tested for key characteristics (physical, chemical and mechanical properties) that are affected by storage over time and by temperature. If it passes the test then the storage life will be extended by a period determined based on the material's known characteristics.

So, if you have a kit that comprises of 100 plies, spanning three different materials that have different lives, with 3 plies being scrapped and one source material being re-lifed, how do you easily track the actual life of the kit? How do you schedule the various stages of manufacture to occur in such a way as to ensure that no material expires and also in a way that is streamlined an efficient?



Problems with ERP and composite manufacturing

Most companies will have invested heavily in a manufacturing system of varying acronyms – MRP, MRP II, ERP, etc. However, many of these systems are focussed on the financial aspect of the business and are not designed to accommodate the needs of the shop floor. For example, a major ERP system stores materials by batches and overall length. It does not have the concept of individual material stock items. As a result, it is impossible for users to track the life of singular rolls, let alone tracking the life of plies cut from one or more rolls. It also has no concept of individual roll consumption, instead only storing an overall 'batch length'.

A solution to this issue is to use a system dedicated to the requirements of the shop floor that can pass relevant information back to ERP, shaped into the format that it needs, while still providing the traceability needed.

Fragmented information systems

As businesses evolve it is commonplace for a number of standalone solutions to be implemented to solve these localised issues. Nesting software is installed to drive the cutters, with staff often manually importing plies (usually in DXF format) from the CAD system before (again) manually creating lists of plies for nesting. Paper-based or Excel spreadsheets are used to track raw material and kits.

Other systems might be set up to compensate for missing functionality from the ERP system and to meet the needs of staff on the shop floor. The solution is to combine the location, life, consumption tracking of material with integrated nesting and management of processes after cutting. JETCAM's CrossTrack composite manufacturing suite was designed specifically for this purpose.

Back in 2002, after selecting JETCAM Expert with High Performance Nesting, Bombardier Aerospace in Belfast, Northern Ireland, enquired if there was a solution to the tracking of material life and consumption, with CrossTrack following shortly afterwards.

Now in use around the world by companies such as Bell Helicopter, Sikorsky Lockheed Martin, Terma Aerostructures, GE Aviation, Hexcel and Quickstep, CrossTrack and JETCAM have support for virtually every CNC knife cutter available today and also integrate with hardware automation solutions such as laser guidance and automatic unloading systems.

De-skilling complex CAD and nesting processes

CrossTrack takes advantage of JETCAM Expert's Remote Control Processing (RCP) system, turning CAD import and nesting into a fully automatic process. Essentially, JETCAM Expert becomes a 'black box', silently receiving and processing instructions and then delivering the results back to CrossTrack. Users can create lists of CAD/DXF files to be processed, turning them into JETCAM component files that can be tooled for cutting on multiple machines. 'Assemblies' of the part containing all plies are created simultaneously and these are immediately available for nesting. Worksheets of plies or kits can then created for automatic nesting either by simply dragging and dropping them onto the sheet or with tight integration to ERP systems.

Static and dynamic nesting is also elegantly handled. Users can create static nests that they intend to run repeatedly, allocating material at the time of cutting, or choose dynamic nesting. This selects material based on rules set by the customer and then creates the nest(s) to fit.

CAD import for nesting

Real-time example of JETCAM Expert performing CAD import on multiple plies. Plies can be tooled and ready for nesting for multiple machines immediately.

Nest material efficiency versus fast unloading and kitting

As mentioned earlier, the trade-off of savings made through highly optimized nesting is unloading, but there are compromises that can be made. JETCAM's 'progressive nesting' feature allows the nester to nest one kit at a time, meaning that plies are grouped together. The nest won't be as efficient as a truly dynamic nest but it will be significantly better than a static nest and will be far quicker to unload. Alternatively, consider either a laser-guided or robotic unloading system, as these will allow you to fully dynamically nest without impacting heavily on the kitting process.


How Progressive Nesting helps unloading and kitting

Progressive nesting kit by kit of plies on composite nest
Progressive nesting gives a balance between material efficiency and faster unloading, by grouping kits together.

In the above example you can see four kits being progressively nested. Using JETCAM's time-based high performance nesting the first kit is nested, with different patterns tried over a pre-determined period of time. Once done, the next series of plies are sent, and so forth.


Tracking materials through layup

Of course, once you've kitted your plies there will still be several manufacturing stages before the part is finished. Material expiry still needs to be tracked up to the autoclave, especially if plies are damaged and need to be replaced with material from a different roll. Users need complete visibility of where each and every ply of a kit is, bearing in mind that a kit may comprise of multiple materials and therefore different nests.

Additionally, there are further consideration relating to equipment associated with a kit, such as layup tools. You may have multiple tools for the same part, and their location and condition also need to be tracked. CrossTrack solves this elegantly by allowing kits to be assigned either to 'containers' (such as trays within unloading systems) or a layup tool, logging every movement to a traceability report. This not only provides the history of the kit, but of every ply and raw material associated with it.

Real-world scenarios such as a CNC knife cutter stopping part-way through a nest or plies being scrapped and either re-scheduled for nesting or cut by hand are also handled with just a couple of mouse clicks, with all transactions logged. This allows staff to quickly drill down to critical information on-screen, rather than having to hunt down and wade through reams of paper that may span multiple departments and systems.

Layup tracking software

Tracking material life through and beyond layup can be tricky, especially when kits have materials of different life periods.

Example of composite material traceability report

Composite material and kit traceability report

Material/Kit Traceability Report

The CrossTrack traceability report is accessible through the right-click menu on either the material stock screen or the kits screen. Within seconds a highly detailed report is generated in PDF format that not only details the history of each individual kit, but of each ply and associated material. Every operation by every member of staff are time-stamped and logged.

The report also includes a life cycle graph, plotting each operation at the point of the material's life that it occurred.

Short and critical life periods can be defined by the user, and these are also highlighted on the graph.

Integrating nesting and material tracking with ERP software

As the number of software systems grows within your organization it's essential to maintain data integrity between them, avoiding manual entry and duplication of effort. Your ERP system will be the backbone of the company, providing sales, purchasing and accounts with an overview of general shop floor information. However, production-related systems must be able to reliably and automatically exchange data with ERP. With CrossTrack, users have the option of either continuing to use ERP for certain functions, with information being injected into CrossTrack, or taking advantage of CrossTrack's interface that's designed for operators on the shop floor, with the resulting data being safely transferred back to ERP using several available mechanisms.

Every company has a preference to how they view their bespoke data and it may be that your ERP or other system has information that you still want accessible on the shop floor. CrossTrack has the concept of custom fields, which can be created on virtually any screen. If, for example you want to add an alternative supplier stock code alongside your own, simply create a new custom field which will immediately appear on-screen or (if relevant, on the traceability report). Validation rules can also be set up to ensure data integrity.

Reporting and Industry 4.0

Being able to identify trends based on large datasets is an important aspect of decision-making for any business, and having a mechanism to collect shop floor specific data often falls outside of the remit of ERP systems, unless you want to go down the rather expensive customization route. CrossTrack uses Microsoft SQL Server as its database platform. This provides an industry-standard system, with tools that allow for complex reports to be quickly written and available to users throughout the shop floor.

Using a combination of MS Web Services, the ability to create custom fields and CrossTrack's automated 'alerts and triggers' functionality, virtually any system can report back to or receive information from CrossTrack as events occur in real time. This might, for example, be used by sensors automatically updating location status or unloading equipment modifying the status of plies in a kit. An important point to note is that every CrossTrack customer uses the same 'off the shelf' package. There's no expensive customization or bespoke interfaces to write, which also means that upgrades to the software don't 'break' any automation and communication with external systems.



Data Security and the Cloud

While there are many benefits to be gained from cloud computing many composite companies are prevented from storing data in the cloud because they operate under the strict rules (such as ITAR) often found within the aerospace and defense sectors. Although CrossTrack can run in a cloud environment, almost without exception users opt for on-premise installations. There are many reasons for this, not least the fact that if your internet connection goes down then so does your production! Mission-critical systems are only as strong as their weakest link.

The cloud does offer some benefits, such as providing load-balancing for processor-intensive tasks, but for the areas covered within the realms of this document only nesting requires and benefits from more processing power, and this is far more suited to localized on-premise computing.

ITAR regulations restrict sharing of many types of data, right down to innocuous details such as material thickness. This information is shielded within the SQL Server database, so even if data were intercepted between CrossTrack's clients and servers only database record IDs are passed rather than identifiable data.

Summary

Being able to accurately track the usage of pre-preg composite materials demands discipline on the shop floor. Without a system that digitally mirrors the workflow process, companies often end up with a mixture of methods. This fragmented approach drastically complicates the ability to generate traceability information quickly. This is compounded by the losses made through inefficient nesting, maintaining paper-based systems or spreadsheets, material going out of life and time wasted by staff working with different procedures scattered throughout the manufacturing process..

Only a system designed with the unique requirements of the composite manufacturing industry in mind can competently and quickly slot into a working production environment, interface seamlessly with existing MRP/ERP/MES manufacturing systems, provide a simple interface that shop floor staff can work with and deliver relevant real-time information to management.

Find out more about CrossTrack