Thermoplastic Tape
A model is only as good as the material it knows. OTOM is fed with the measured characteristics of the unidirectional (UD) thermoplastic tape you actually place: how it reflects and absorbs laser light, how it conducts and stores heat, and how it crystallises.
Thank you for reading this post, don't forget to subscribe!UD thermoplastic tapes (carbon or glass fibres aligned in one direction in a PEEK, PEKK, PPS, PA6 or PP matrix) are strongly anisotropic, optically and thermally. Generic material data misses that, and it is why simulated and measured temperatures often disagree. OTOM starts from the tape.
Reflection, absorption, transmission
When laser light hits a tape it is reflected, absorbed or transmitted. For black-pigmented carbon-fibre tapes transmission is zero, so every photon is either absorbed as heat or reflected elsewhere, onto the roller, the substrate or the incoming tape.
The split depends on the angle of incidence and on the direction of the fibres. The fibre-and-matrix microstructure scatters light in a pattern that is neither mirror-like nor uniform.
Fibre-orientation-dependent and spread around the specular direction. It heats other surfaces or is lost.
Becomes heat at the surface and drives the nip-point temperature that decides bonding.
Zero for black-pigmented CF tapes. It matters for glass-fibre and unfilled tapes.
UD tape characteristics that feed our model
Every OTOM simulation is parameterised with the properties of the specific UD tape: measured where available, from the supplier datasheet or the literature otherwise, and calibrated against thermal-camera trials.
Optical
Measured BRDF reflection patterns as a function of incidence angle and fibre direction; absorptivity through the Fresnel equations; refractive index; and surface roughness from microscopy.
Thermal
Anisotropic conductivity (along the fibre and across it) and temperature-dependent specific heat and density. Contact resistance between layers and convection to the air are included.
Polymer
Glass-transition and melt temperatures, the degradation limit and crystallisation kinetics. Together they set the process window and predict the final crystallinity.
Architecture
Fibre type and volume fraction, tape width and thickness, and the ply orientation of each course, which rotates the reflection pattern and the conductivity tensor.
Mechanical
Transversely isotropic stiffness, thermal expansion and viscoelastic relaxation for the residual-stress model.
Calibration
Simulated temperatures are compared with radiometric IR measurements, corrected for the tape’s emissivity, to close the loop between model and machine.
Why BRDF modelling matters
A simple mirror (specular) or diffuse (Lambertian) model gets the heat input wrong. It puts reflected energy in the wrong place and misjudges how much is absorbed at grazing angles near the nip point. With a bidirectional reflectance distribution function (BRDF) derived from tape measurements, OTOM’s ray tracer reproduces the real reflection pattern of the tape. The result is the correct heat flux on the tape, on the substrate and on the roller, and a temperature prediction you can set the process by.
| Typical UD tape | Why the tape data matters |
|---|---|
| CF/PEEK, CF/PEKK | A narrow window between melting and degradation, and crystallinity sensitive to the cooling rate |
| CF/PPS | Fast crystallisation, with the cooling history driving the final properties |
| CF/PA6, GF/PP | Lower processing temperatures; non-zero transmission in glass-fibre tapes |
Simulate with your tape
Share your tape’s datasheet or a sample. We build its optical and thermal model and show you the process window.