Composite Manufacturing Overview and Glossary of Terms
Composite material usually consists of a woven fiber material, something like cloth, made of fiberglass, graphite, carbon-fiber, or other fiberous material. This material may be pre-impregnated with a glue or resin. The material can be very flexible, or can be relatively stiff.
Typically the material is applied to a form or mold that represents the shape of the final piece. The material is applied in layers with each layer applied at a different angle to the previous layer. Each composite layer has an isotropic stress characteristic (i.e. is structurally strong in one direction). The layering process makes the finished piece structurally strong in all directions. After the layers are applied the piece is in an uncured or “green” condition.
During material application a bonding-agent (glue or resin) is added to each layer, or it is already pre-impregnated in the material. The “green” piece is then cured to harden the bonding-agent. The curing often happens in a oven, also called an autoclave. During oven “baking” the bonding agent liquefies and flows through the layers of material, creating a single coherent structure.
After curing or baking the piece must typically be cut or trimmed to the final shape, and possibly other machining operations (milling, drilling, turning, etc) must be done to complete it. Composite cutting is also done using waterjet or ultrasonic knife technology.
Composite material can produce very strong and light structures. In many cases they are cheaper to manufacture than metals or plastics, especially where strength and lightweight are required. But composite manufacturing requires complex processes involving chemical, mechanical, and thermal technologies and expertise. And the raw material itself often has critical storage requirements (temperature, humidity, shelf-life, etc). Hence use of composite materials is not wide-spread and can be considered a “new” technology, even though it has been around for many years.
Composite components are used in aerospace, aircraft, and automotive products. They are also present in sports and recreation products such as tennis rackets, golf clubs, bicycles, motorcycles, and various high-end racing components. Composite components are frequently not covered with paint or other coatings, so the composite fibers are visible and create fear and envy in fellow competitors.
Material application processes:
The following processes can be used to create a composite piece.
This process consists of applying a wide strip of composite “tape”. The tape is typically 1″ to 12″ wide (25 to 200mm), depending on the curvature of the mold or form the material is being applied to. Wider tape can can only be applied to relatively flat surfaces, narrower tape can follow more curved surfaces.
The tape is applied from a spool of material. It travels over a “compaction roller” that presses the material onto the form, or onto the previous layers of material, typically with a few hundred pounds of pressure. The tape usually has a “sticky” side that makes it stay where it is placed until the curing process.
The compaction roller is part of a tape head attached to a CNC machine, often similar to a 5-axis head, but with the tape and compaction roller instead of a milling cutter. The tape is pulled onto the form by the compaction roller being rolled over the surface of the form, very similar to apply packaging tape from a “tape gun” onto a box.
The tape can be a simple rectangular strip, or the sides can be trimmed to a specified contour. The contour trimming can be done before the tape is put on the spool, or while it is being deposited from the spool to the form. The tape is cut at any angle.
Machine companies producing tape-laying machines include Ingersoll, Cincinatti, Forest-Line’, and Mtorres.
This process has been around at least since the mid-1980’s in advanced aerospace manufacturing. It is limited to very regular, smooth, and relatively flat shapes. The tape has a tendency to wrinkle or tear if applied to a surface with high curvature. Current applications include wing surfaces and cylindrical rocket and missle sections.
Similar to tape laying, material moves from a spool over a compaction roller onto a form. But in Fiber-placement the tape is typically narrow, between 1/8″ and 1/2″wide (3 to 12mm). There are typically several strands of fiber (called “tows”) that pass over the roller parallel to each other. The CNC machine is capable of cutting and re-starting each tow individually. The individual narrow strips allow the material to be applied over contoured surfaces without wrinkling, tearing, or warping.
This process is newer than Tape-laying, and is much more complex and prone to process problems and errors.
Hand-layup is the traditional process of cutting flat patterns of composite material which is then manually placed or pressed onto a form. The shape of each layer of material must be converted from the 3-dimensional object into a flat pattern. The shape is then cut out using knife cutting machines (either CNC or manual).
The flat material is manually oriented to the form or mold using measurement marks or a laser alignment system.
This process has been around for decades.
Filament winding and weaving
Filament winding is a process where individual strands of fiber feed from spools through a loom or weaving machine and are wrapped around a form. I have only seen this process used to completely encase objects in composite material, such as ski’s, tennis rackets, etc. This is typically a high-production process with dedicated machines producing thousands and thousands of single product.
This process has also been around for decades.
Cutting composite material is a dirty process. The resulting chips or swarf is dust, which is often toxic. Frequently the only way to achieve the desired form and feature is to mill, drill, turn, etc.
However, other cleaner processes are used to cut composite material as well: ultrasonic knife and waterjet. The advantage to each of these cutting technologies is they do not produce dust.
Composite Software FAQs
CGTech is often contacted and referenced by industry publications. Following are few of the questions we’ve been asked. Responses are provided by CGTech’s Product Marketing Manager. Have a question of your own? Ask us!
What are some technical difficulties encountered in composites programming?
I divide the issues into 3 categories: Part, Process, and Machine. A part’s overall shape, and the shapes and directions of the layers of CFRP material that create it, determine the complexity of the process. Dramatically curved part contours limit the direction the material can be successfully laid and also affect how wide a path of material can be laid at once. Additionally, the material has a limit to how closely it can be laid in a particular direction, commonly called the “steering limit.” The patches of material that make-up a layer, known as “plies,” each have their own simple or complex outline shape, called a “ply boundary.” The AFP or tape-laying process can only approximate that boundary.
For a complex-shaped part, the process will consist of many steps of laying material and inspecting each layer before it is covered-up with the next one. If the complexity of each layer is high, then the layer must be closely monitored for failures. The NC program and machine must have a mechanism for dealing with process failures during material lay-down. These recovery schemes can also be complicated.
All machines have limitations, and AFP machines are no exception. Thus the process requirements and machine limitations can sometimes conflict. For example, a curvy part shape with complex ply boundaries may result in the end of a course of material landing on a highly curved region of the part surface. It is very difficult to start a course of material on a highly curved surface, but much easier to end it on the curvy spot, so the NC programmer needs the option to lay the tape course starting at the less curved end. In this case the part complexity, the process requirements, and the machine limitations all come together, and the programming system needs to accommodate them all.
How critical is verification/simulation of complex, expensive composite workpieces?
Expensive workpieces manufactured with complex processes must have reliable and robust verification and simulation tools. Today’s business conditions don’t tolerate any shop floor experimentation, nor very many do-overs. Whether laying a composite part with an AFP process, trimming the laid and cured part with a water-jet cutter, or drilling and fastening a finished composite panel to a titanium structure, failure is very expensive in terms of equipment, materials, man-power, and (probably the most costly) time lost in an always tight schedule.
How do machine providers and users leverage your engineering expertise?
CGTech’s expertise is built into all our products, and our product features are typically based on our customer experiences to-date. We update all our products frequently. But additionally, CGTech directly supports all our products with a dedicated team of sales and technical support staff in several locales around the world.
What software tools does CGTech offer for composites?
Composite aerospace parts, which are typically made from Carbon Fiber Reinforced Plastic (CFRP), can be manufactured in several different ways, but almost all the methods to create the part’s shape involve a molding or forming process. The molded composite parts are sometimes molded to net shape, but more commonly they are “near net shape,” and consequently require additional removal processes such as trimming, some light machining, and maybe drilling. Thus, to ensure the machining is correct, VERICUT simulation is used to simulate the NC programs. VERICUT can simulate conventional milling of composites, but can also simulate trimming with an ultrasonic knife or waterjet cutter, including specific checks for improper use of these technologies. CGTech has been supporting these kinds of machining operations with VERICUT for nearly 25 years.
However, even prior to molding and curing the part, one of the automated fabrication processes commonly used to create the initial CFRP workpiece is Automated Fiber Placement (AFP). AFP uses a CNC controlled machine to lay the initial composite material onto a form or mold surface. The workpiece is built-up with layer-upon-layer of material until the final part shape is achieved. VERICUT Composite Programming (VCP) and VERICUT Composite Simulation (VCS) are specifically designed to program and simulate AFP equipment. In fact VCP and VCS are the first machine-independent software applications in this domain, able to program and simulate AFP machines from any machine supplier in the world.
While we are starting to see AFP being utilized in several industries, it is most commonly used to create airframe components. Once various composite airframe components are fabricated, they are then assembled together to produce the vehicle’s main sections. The assembly process frequently uses CNC controlled automated drilling and fastening machines. To address needs in this domain CGTech created VERICUT Drilling and Fastening (VDAF), for programming and simulating automatic drilling and fastening machinery.
All these products: VERICUT, VCP, VCS, VDAF are built on CGTech’s successful VERICUT software platform, benefiting from nearly a quarter of a century of software development focused on using CNC equipment in aerospace manufacturing.
How do the VERICUT composite tools work with other composites machining software?
CGTech’s products are unique engineering software applications that meet technical needs not being met by the standard PLM or CAD/CAM offerings. They exist to help improve a company’s particular manufacturing processes. VERICUT has simulation features beneficial to complex fabrication processes, including machining composite tooling or composite parts directly, simulating AFP or wide-tape layup, and simulating automated airframe assembly. With desirable features that are unavailable elsewhere, VCP and VCS uniquely established the value of machine and CAD/PLM independence for programming and simulating AFP processes. But VERICUT products have to integrate well in the customer’s engineering and manufacturing environment, and thus interface with various other software applications.
ATL/AFP production is becoming more complex. Is standalone software best able to accommodate the technology?
If by “stand alone” you mean software developed to be used on any CNC machine rather than one specific brand of machine, we certainly think so. The main advantage to universal software is it’s broad usage, especially over time. Software developed for one specific brand of machine is only exposed to a small set of users of that machine. And software enhancements are driven by user requirements more than any other factor. Software exposed to a broad range of user experiences, followed by listening to those users and synthesizing their comments, requirements and requests allows us as software developers to infer new product features. We would not invent the new features, at least not as quickly or effectively, if left on our own or with a narrow band of user feedback. All users benefit from a broad implementation.
And off-line AFP programming software dedicated to a single machine brand is simply not fair or economical for manufacturers. This approach has a tendency to lock them into a single machine supplier, rather than allowing them to select the best machine for the job at hand. Universal CAD/CAM software that can be used on any CNC metal cutting machine is what allows a manufacturer the freedom to choose the best production metal-cutting solutions without having to retool his manufacturing engineers to new software each time. Imagine having to implement a new CAD/CAM system each time you buy a different brand machining or turning center. It’s not unusual to have more than 10 different brands of CNC machines in a single mid-sized workshop.
What features/capabilities are in greatest demand among your ATL/AFP customers?
Most of our manufacturing customers are struggling to apply current AFP technology to complex high-curvature part shapes. It often seems like the machine the customer has is not designed to do it. However it also appears there are new AFP machine technologies being developed to specifically apply material over complex shapes. And innovative NC programming approaches are needed to successfully and reliably fiber-place complex parts while achieving the structural requirements of the laminate.
What are the practical limits of current ATL/AFP technology?
The biggest issue with AFP seems to be production rate vs. part complexity. Fairly complex shapes can be created with a single .125” wide strip (tow) of material. But the production time would be impractically long. So machine builders create 6, 8, 16, even 32 tow AFP systems. But then wide compaction rollers for these systems have difficulty maintaining compaction over curved surfaces. The real practical manufacturing limit is the minimum steering radius of the material, and the software’s ability to deal with it.
Is process simulation a significant part of ATL/AFP control software? Why or why not?
Process simulation is a very important component of AFP process development. And by process simulation I mean simulating from the exact NC program that will be sent to the CNC control of the AFP machine, and producing a simulated representation of the laminate as produced by the NC program. This is the only way to ensure the NC program produces the nominal results desired. Of course there are physical process variations and environmental conditions that cannot be simulated. But it is important to be able to verify that the NC program is not one of the process variables introduced on the shop floor.
How do you see ATL/AFP software evolving over the next five years given current pace and direction of change?
That’s a tough one because I could not have predicted the last two years, let alone the next five. The AFP industry is changing very quickly and there are a lot of smart and creative people involved in it. I think the solution to economically fiber-placing small and complex parts is critical to the success of AFP technology. And the current complex process has to simplify and stabilize so that it is practical for 2nd and 3rd tier suppliers. Until that happens AFP will remain a boutique manufacturing method only available to the highest-end products and companies, not really very far away from the research lab. I think our software approach is a step in the right direction (away from the lab), helping to de-mystify the AFP programming process and make it more approachable for smaller companies.
What are some innovative customer uses of your systems?
This is always difficult to discuss in the composite manufacturing domain. Because composite products and processes are relatively new, at least new compared to the 100+ year history of metal cutting, we often work under proprietary non-disclosure restrictions. One of the most exciting projects we recently completed (that we can’t talk about) utilized CGTech’s engineering and manufacturing expertise to create a novel composite layup using a brand new AFP machine design. CGTech developed the features collaboratively with our end-user customer and the machine supplier, and implemented it on top of our base VCP and VCS products. The project benefited greatly from the solid and proven VCP/VCS foundation, and featured a custom interface where the user enters a set of engineering parameters and the very complicated layup sequence is automatically generated. The implementation ultimately takes a very complex programming process, one that took the end-user several weeks to complete for a single part, and reduces it to a few hours. This extreme time reduction in NC program development allows for many more design and engineering iterations, and much more time to optimize the layup process before it reaches the shop floor.
Send us your own questions.