Automated Fiber Placement (AFP) is an additive manufacturing process that has three different inputs: fiber/polymer tape, heat, and pressure. The end-effector expertly handles the tape and deposits it onto a surface with the help of heat and pressure. The process allows the fabrication of highly customized parts as each ply can be placed at different angles to best carry the required loads. The use of robotics gives the operator active control over all of the process's critical variables, making the process highly controllable and repeatable. This process can result in additively manufactured composites parts that are two times stronger than steel at one-fifth of the weight.

The key components of an AFP system are:

• Manipulator
• Fiber Placement Head
• Heating technology
• Path Planning Software
• Material to run with AFP
• Final checklist before running

Let's go through them and evaluate all the options!

Manipulator

The manipulator is a device used to manipulate the AFP head without direct physical contact by the operator. For AFP applications the goal is to find the right manipulators given the shape of the layup. Here are some guidelines for different shapes:

• Flat layups can be done either by 4-axis gantry with x-y-z and rotational axis-C or by 6-axis robotic arms. For large areas, gantry makes more sense whereas for more variability a robot makes more sense.
• Open 3D shapes can usually be done using 6-axis robotic arms, however, if there are more than one 90 degree turns on the part, an external rotary axis can help rotate the mold and make the layup easier to achieve.
• Close surface shapes (<1 m) can usually be done using a 6-axis robotic arm with an external rotary axis.
• Close surface shapes (>1 m) would require a 6-axis robotic arm with two external axes, one rotary axis, and one linear axis. Adding a linear axis is very beneficial for longer open 3D shapes as well.

Fiber Placement Head

The end-effector is mounted onto the manipulator which repeatably places strips of fiber tapes. The placement head determines what parts and shapes can be laid up, and determined which fiber/matrix material can be used. The order of operations is consistent across all fiber placement heads, i.e. clamp-feed-heat-place(compact)-cut-clamp with a predetermined heat/temperature profile. The automated process ensures accuracy of placement and consistent process parameters during the fiber placement. The fiber placement head can be mounted onto a manipulator/axis combination based on the desired shape requirements. University students have attempted to build their own fiber placement heads with varying degrees of success, but they can also be rented on a monthly basis or purchased from Addcomposites.

Heating technology

Different materials require different heat intensities and profiles for creating enough tack to bond the consecutive layers.

• Thermoset fiber tapes Often thermoset materials are kept in a cold environment (-20°C) and are tacky at room temperature. Often while running the material with the fiber placement technology at a higher speed, the material needs to be heated slightly to 40-50 °C to ensure the right tackiness and bonding between the layer.
• Thermoplastic fiber tapes Thermoplastic is solid at room temperature and requires melting before it can be bonded. Usually, a high-energy focused source of energy like laser or humm3 is needed to quickly melt the tapes for AFP processing. The above-mentioned fiber placement head from Addcomposites is modular and can mount either laser or humm3 depending on the material, production speed, and other safety requirements.
• Dry fiber tapes are often held together with a thermoplastic binder in some format with the melting point of the thermoplastic binder being in the range of 80°C-120°C. For this temperature range, either IR or hot air gun can be used with varying degrees of success.

Path Planning software

Once the hardware is configured there has to be a way to program the robot manipulator and fiber placement head with the heater. We have made our path planning software, AddPath, available for free trials, which can be requested from here. AddPath takes in the CAD model of the mold geometry and automatically generates fiber paths with defined gaps. It also provides robots motion simulation and analysis tools for avoiding collision or other damaging robot operations.

Material

Before running operations, material needs to be secured. Most material is available in sheet format and can be cut down to the desired tape width with the help of slitters for thermoset materials. Some of the main suppliers across Europe and the US are Bindatex, Web Industries, Axiom materials, Kordsa, Thermoplastic tapes are more widely available via Bufa, Victrex, Arkema, SGL, etc. The above-mentioned fiber placement head can work with 1/4'', 1/2'', and 1" width tapes. More complex shape layups require narrow tapes whereas the smoother/flatter surfaces can use 1'' tape for higher productivity. Special widths can also be requested.

Checking and running

By now, we've discussed all the main tangible components required to build an AFP system, however, before running the layup as a laminator all the preparation regarding operation following the placement should be considered:

• Mold: The mold needs to be positioned as accurately as possible with respect to the robot to achieve accurate placement. If the layup is using thermoset material, a mold release agent should be applied prior to placement. This allows for easy demolding after the part has been vacuumed and cured. If the layup is thermoplastic then an in-situ placement approach can be considered to avoid the consequent pressing. With thermoplastic layups, the high-energy laser/humm3 can be used in conjunction with heated molds to ensure more even consolidation.
• Curing/thermoforming: Thermoset material can be cured to achieve complete strength under vacuum pressure in or out of autoclave situation, depending upon the material. Unconsolidated thermoplastic laminates need to be pressed and heated to achieve a higher fiber volume fraction and lower the voids.
• Trimming and Polishing: Once the laminate is cured, it is ready to be trimmed around the edges and ready for bonding with other counterparts. Polishing is the final step and is used for providing a smoother surface finish and a protective coating against the environment.

We converted a used robot to an AFP cell in 2 days

For performing layup on an open 3D shape, the used 6-axis robotic arm was equipped with the AFP-XS (fiber placement head from Addcomposites). The tool was initially used to run thermoset material and was later upgraded to thermoplastic by changing the IR heater to humm3 heating technology.

Build your own AFP

If you are running composites manufacturing-related education, proof of concepts, or industrial production at your facility and would like to build your own AFP to automate your production, reach out to Addcomposites by filling this form.