One key point of the project was to get the right temperature at the nip-point region where substrate and tape are put in contact. The temperature must be the right one so as to achieve a good bond between the layers.
UBS developed new software to compute the temperature field into the process which depends on the laser power, the laser position and orientation, the roller deformation, and the properties of the materials involved in the project.
The thermal and optical properties of APC2 were taken from literature whereas the thermal and optical properties of PEI were measured.
The new software that has been developed is able to compute the temperature into the process (Figure 1) with the boundary conditions as shown in Figure 2. The software was developed by using MATLAB and ABAQUS to compute the temperature into the process. It is based on process parameters such as laser power, layup speed, compaction force, and robot head parameters based on the process schema shown in Figure 3.
Figure 1: Temperature field into the layers of the hybrid material
A ray-tracing procedure based on the optics geometric was also developed using MATLAB software to determine the heat flux distribution on the composite by taking into account the parameters of the robot head. To compute the thermal history, a fully scripted procedure in Python is developed to allow for fast and efficient pre- and post-processing. From the list of the parameters of the study and the desired number of layers in the laminate, a script generates the corresponding code and is used as input files in ABAQUS according to the flow chart shown in Figure 4. Finally, a user interface made with MATLAB can be used to introduce all the parameters needed to compute a numerical simulation (Figure 5).
Figure 2: Boundary conditions for the 2-D thermal analysis of tape consolidation
Figure 3 shows a schematic illustration of a tape placement head used in AFP machines. This head uses a laser optics module to heat the thermoplastic material at a given optics incidence angle β and laser power PL. The temperature at the nip-point depends on the contact width 2w and the angle tilt of the head θ. The other main parameters are the placement velocity V, the diameter of the roller R, and the laser beam height (working distance wd ).
Figure 3: Schematic illustration of the AFP process with the tilt of the head
Figure 4: Flow chart of NHYTE software
Figure 5: examples of pages of user interface
The software has been used to determine the optimal parameters to control at best the process. ABAQUS has been developed to easily give to the engineer the optimal set of parameters of the process (Figure 6).
Figure 6: ABACUS for optimal laser power control
Figure 7: Process window based on the numerical simulation
Some experiments were conducted at Novotech premises in collaboration with the UBS researchers (Figure 8). These experiments were computed with the new software, whose accuracy has been tested and validated. Finally, based on the numerical simulation a process window is proposed for optimal parameters to well control the process (see Figure 7 above).
Figure 8: Novotech and UBS collaboration for experiments and software validations.