How Advanced Vacuum Bag Kits Streamline Composite Parts Manufacturing
When they arrived at the customer site, Darren Ingram realized the demonstration would take place directly next to the customer’s production line. This would prove interesting.
“We had just developed a very complex process material bagging kit for a particular customer. We brought one of our engineers to their site to demonstrate the kit application,” he explained.
Ingram is Chief Operating Officer of Velocity Composites PLC, a UK based provider of composite master kits designed to simplify the manufacturing process of composite aerospace components. Velocity partners with Incora™ to bring these composite kitting solutions to the aerospace market.
When the Velocity engineer began the demonstration of the vacuum bag kit, which consisted of four different layers of material, it just so happened that two of the customer’s own operators had begun bagging up a production unit. The race was on. In 14 minutes, Velocity’s engineer, who was not production trained, had bagged up the tool and had it under a vacuum. The customer’s production operators had not yet finished the second layer of material.
This process would normally take 2 hours. So, what allowed this non-production trained engineer to out-perform their own designated in-house operators in just minutes? A highly engineered process material kit.
The manufacturing of complex composite aerospace components is a labor-intensive process, especially the application of the vacuum bag layers needed for consolidation and cure. It requires trained and dedicated operators and a very manual procedure.
Composite use in aircraft is becoming more widespread, with applications expanding to the manufacture of large structural items, like the fuselage and tail systems. The last 15 years have seen composite use by weight in aircraft increase from 15% to 50%, most notably in planes like the Boeing 787 and Airbus A350.
As a result, there is growing pressure from aerospace primes to drive cost out of composite manufacture. New technologies have been developed for the application of prepreg fabric to shape tools, but complex components are still best done through hand layups.
Despite this development in the layup, the vacuum bagging process has remained relatively unchanged. Advanced process material kits offer a chance to change how parts are bagged for debulking and cure, implementing much needed efficiency and repeatability in the manufacture of composite components.
What is an Advanced Process Material Kit?
Advanced process materials kits, along with a structural material kit, make up a composite master kit. A composite master kit is a single kit containing everything needed to manufacture a composite part.
Structural Materials Kit
This is everything that flies. That is, the pre-cut prepregs and film adhesives reverse collated for easy application, with each ply identified and batch traced. Cost savings here come from reducing material waste through advanced dynamic nesting technology.
Advanced software of this type, developed by Velocity, calculates not only how a collection of shapes are best nested on a single sheet. It also calculates how long-term customer demand and material availability will influence the manufacturing strategy around these nests. The result is anywhere from 10-20% material savings, meaning more carbon flying and less in the trash.
Process Materials Kit
The process material kit is comprised of consumable items required for the consolidation (or debulking) and cure stages of composite manufacture. These include:
Woven peel plies
Non-stick release films
Non-woven bleeder fabrics
Non-woven breather fabrics
Nylon vacuum bags
What makes advanced process material kits unique is that they don’t simply contain rolls of flat material that require extensive tailoring at the tool. Each piece is engineered and pre-manufactured into complex shapes that fit precisely over a specific part or tool. The bleeders and breathers are assembled into 3D shapes, the vacuum bags formed into 3D shapes, and the peel plies laser cut to ensure part-specific precision and no frayed edges.
The change advanced process material kits provide to clean room operations is better understood by considering traditional vacuum bagging procedures.
Traditional Vacuum Bagging Procedure
When an operator completes the layup of prepregs onto the mold tool, the part must be debulked and cured. This final stage involves first applying all layers of the vacuum bag materials, then running the part through the autoclave.
The layers of material that are placed over the prepreg layup before consolidation include the following, typically in this order:
- Peel ply: sacrificial material used to create a textured finish on the cured part to aid secondary bonding
- Porous release film: perforated material that controls amount of resin bleeding through
- Bleeder cloth: absorbs excess resin
- Non-porous release film: prevents excess resin from bleeding into breather
- Breather: nonwoven or loosely woven material that acts as a vacuum path around the entire part
- Vacuum bag: the final bagging layer that is applied over the whole part and sealed to the mold tool, to which atmospheric pressure is applied by a vacuum to consolidate the part onto the tool
The vacuum bag compresses the prepreg material solidly together, removing any trapped air, voids, and volatiles that might compromise structural integrity. The traditional application of these layers, however, presents several inefficiencies.
A Time-Consuming and Variable Process
Where this traditional technique becomes labor intensive is in the application of each layer. Operators have flat sheets of material which they cut and fashion to fit the part. For a complex 3D component, this process can take over 2 hours for all materials.
Apart from the time required, application is extremely variable. Having to cut flat sheets of material and create each layer in real-time, by hand, makes repeatability difficult. Even a single operator will be challenged to reproduce each layer exactly across multiple builds.
In traditional composite part manufacturing, clean rooms receive multiple kits of material. This includes a top-level structural material kit along with various sublevel kits, depending on the scale and complexity of the structure. Along with each of these comes a consumable kit. This can mean as many as six or seven kits that must be booked separately through their individual kit numbers. It’s a significant logistical challenge to have all the necessary materials at the point of use when the operator needs them.
On the contrary, engineered process material kits make the debulking and cure process simple, repeatable, and efficient. The operator never has to leave the layup tool prior to the part being available for the autoclave. Furthermore, the clean room management teams know that the correct materials were used in a way approved by the local manufacturing engineering teams.
How Process Material Kits Streamline Vacuum Bag Application
Advanced process material kits turn the inefficiencies of traditional manufacture on their head. Through different permutations of complex 3D vacuum bags, breathers, bleeders, and release films, these pre-manufactured kits allow engineering teams within production areas to produce more repeatable parts, create quicker build times, and de-skill and de-risk vacuum bag assembly.
Highly engineered process material kits streamline composite part manufacture in the following ways.
Since the engineering knowledge is built directly into the kit, everyone will apply the vacuum bag layers in the same way. This makes the technical specifications of that vacuum bag easy to enforce. Done manually, inconsistencies arise. With these kits, repeatability is necessitated. And as the process is developed over time through continuous improvement by customers, the kit is updated to include these improvements in a fully traceable way.
Quicker Part Builds
With composite master kits, everything needed to build a part arrives to the point of use in the form of a single kit. Clean room manufacturing becomes the first stage in the process for customers instead of having to coordinate material forecasts, delivery timings, and kit locations.
Part manufacture starts and proceeds without delay, since the operator never has to step away from the layup tool. While the part in the demonstration above took over 2 hours to fully bag through manual application, the same part took only 14 minutes to bag with a pre-manufactured process material kit.
As Ingram explains: “It is designed specifically for that shape, and it’s pulled on like a sock. You twist it around to make sure the heel is in the right place, seal it down, and you do that time after time.”
This process improvement provides anywhere from 25-75% time savings depending on the complexity of the part. Quicker assembly times means more parts can be placed into the autoclave, leading to the next efficiency.
More Efficient Autoclave Cycles
Pre-manufactured kits result in less excess material around the part, allowing for easier and more uniform heat distribution. Excess material surrounding a part acts as a sort of insulation against heat getting in as it needs to.
By using the advanced process material kits, Bridges notes that “the parts heat up and cool down quicker in the autoclave, your cycles are quicker, and you can get more parts in.” That means faster cycles and more efficient autoclave use. Considering the high costs of running autoclaves, this efficiency is critical.
Higher First-Pass Yield Rate
Being custom-fitted to specific parts, advanced vacuum bag kits allow for more than better heat distribution. Resin flow throughout the part is also more predictable. A more consistent consolidation process results in a significant reduction in scrap rates.
The component used in the demonstration highlighted above initially had a failure rate of 10% due to excess resin bleed, poor consolidation in the internal radii, and poor vacuum performance. After the manufacturer began using advanced process material kits, the failure rate dropped to 0% over three years.
Traditional vacuum bag application requires dedicated operators, being a labor-intensive and highly skilled process. On the contrary, the pre-manufactured 3D shapes of advanced process material kits can be fitted over their corresponding parts “as easily as a sock.” This means that the bagging process can be carried out by almost anyone in the clean room.
“We put reference marks on each of the materials that correspond with your marks on your tool, so that you consistently get the exact repeatable process,” says Ingram. “You’re de-skilling the job by putting the knowledge into the kit.”
By creating a user-friendly process, vacuum bag application is not limited to dedicated operators. This accelerates production and frees highly skilled operators to focus on more critical aspects of the operation.
Consistency of Material Specifications
An added benefit for engineers and operators is that advanced process material kits maintain the same material specifications as existing processes. There is no need to adapt operations to new material specifications. Materials already in use are engineered into the 3D shapes needed, making the use of advanced process material kits a simple, ready-to-go adjustment. In addition, every kit is batch controlled so that each material can be traced right back to source. This makes process adherence and audits much simpler, in line with AS9100 and NADCAP global standards.
The elements above combine to facilitate a more productive workforce. Ultimately, they allow parts to be consistently built in the same manner over a shorter period of time. They also direct the focus of clean rooms directly on part manufacture by eliminating the elements that detract from that focus.
Need for Training
There is an initial need for a small amount of training in the application of advanced process material kits. In the traditional method of vacuum bag application, if an operator makes a mistake in applying a layer of material, it can go unnoticed. That operator can simply toss the scrap material into the trash, walk over to the roll, and cut off another sheet.
Advanced process material kits do not offer the same luxury. Since each layer is uniquely crafted for a specific part, it can’t be immediately replaced if damaged. A 3D vacuum bag takes time and expertise to manufacture. However, each element of the kit is designed to take into account the specifics of its use and application to ensure it can be applied successfully. The simple application of these advanced process materials makes rework easily avoidable. Training of operators on the front-end is all that is required.
Advanced process material kits provide an effective solution for driving cost and inefficiency out of composite part manufacture. They allow operators and clean rooms to streamline their operations in a consistent and reliable way. Considering the growing use of composite materials in aircraft, and pressure from aerospace primes for efficiency, this is a valuable proposition.
Reflecting on the demonstration where his engineer completed the vacuum bag application faster than the in-house operators could finish fitting two layers, Ingram remarked: “It far out-performed even our own expectations. It was a clear demonstration how much the current process can be improved with no impact on the integrity of the finished part.”
This article was written by Daniel Allan, Technical Writer, Incora, (Valencia, CA). For more information, visit here .
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