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:
Fiber Placement Head
Path Planning Software
Material to run with AFP
Final checklist before running
Let's go through them and evaluate all the options!
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.
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. <