Current context of pultrusion
The development of new manufacturing processes to reduce the operational costs of composite parts is one of the main avenues of study within the industry. This is not surprising, given that 60% of the final cost of a composite part corresponds to manufacturing [1]. Much of this problem is due to the low automation of current composite manufacturing processes and the over-reliance on skilled labour.
Thus, pultrusion’s great advantage over other current processes is its high level of automation and repeatability. However, the nature of the process limits the entry of pultruded profiles in high value-added applications, such as in the automotive industry, shipbuilding or unique civil engineering constructions.
Aware of this fact, the Robtrusion team analysed pultrusion’s limitations with the aim of creating a new innovative manufacturing process capable of covering areas that pultrusion does not cover. Today, it can be said that Robtrusion is a reality and that its differences with pultrusion enable it to achieve what was previously unattainable.
But before we focus on the differences between the two processes, it is important to understand how pultrusion works and what its advantages and limitations are.
What is pultrusion?
In pultrusion, the fibres are fed from a store into a bath, where they are impregnated with resin. They then pass through preforms that guide them to the die inlet, where the profile is heat cured. All of this is driven by an automatic pulling system.
- Strong pulling forces.
- Long heated dies.
- Limited to straight profiles with a constant section.
What makes Robtrusion different?
Pultrusion’s limitations have one thing in common: the profile cures inside the die. Therefore, to overcome them all, Robtrusion cures the profile out of the die.
However, curing the profile outside the die cannot be performed using traditional heat curing. Therefore, Robtrusion uses UV curing, as it has proved to be a fast, flexible and less costly curing technique than the other techniques analysed.
Out-of-die UV curing [3].
Out-of-die curing reduces the pull forces, which allows profiles to be manufactured with a higher percentage of reinforcements in the directions not oriented in the manufacture orientation. This results in higher cross-section mechanical properties.
Finally, the reduction in pulling forces in combination with out-of-die curing allows Robtrusion to manufacture curved profiles with different radii and orientations using a robotic arm. This is one of the main advantages of Robtrusion, since it opens the door to new design and manufacturing concepts.
References
[1] Bader MG. Selection of composite materials and manufacturing routes for cost-effective performance. Compos Part A Appl Sci Manuf 2002;33:913–34. doi:10.1016/S1359-835X(02)00044-1.
[2] Meyer RW. Handbook of Pultrusion Technology. Chapman and Hall; 1985.
[3] Saenz-Dominguez I, Tena I, Esnaola A, Sarrionandia M, Torre J, Aurrekoetxea J. Design and characterisation of cellular composite structures for automotive crash-boxes manufactured by out of die ultraviolet cured pultrusion. Compos Part B Eng 2019;160:217–24. doi:10.1016/j.compositesb.2018.10.046.
Autores: I. Saenz-Dominguez – I. Tena
