How does Robtrusion differ from pultrusion?

Robtrusion is based on the advantages of pultrusion and is designed to overcome its limitations. This has lead to the creation of a high added value, profitable and flexible manufacturing process that is unique worldwide. If you would like to learn more about this process and its differences from pultrusion, please read this article.

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.

Diagram of the pultrusion machine; figure adapted from [2].
Therefore, pultrusion is a continuous and highly automated process for the manufacture of composite profiles with constant section. In addition, profiles with excellent mechanical properties in the pulling direction are obtained [2]. However, it has some limitations:
  • Strong pulling forces.
  • Long heated dies.
  • Limited to straight profiles with a constant section.
Regarding the latter, some variants of the pultrusion process allow the manufacture of curved profiles. However, these processes are restricted to constant radii or greatly reduced flexibility, low productivity ratios, complex dies and high pulling forces. So what does Robtrusion do differently to be able to overcome all these limitations?

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

Out-of-die UV curing [3].

With this new approach, the die is only used to shape the profile and remove excess resin. This means it does not need to be long or heated. In fact, the dies used are no longer than 100 mm in length, leading to lower costs and greater flexibility.
Robtrusion® die.
Robtrusion die.

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.

Curved hexagonal profile manufactured by Robtrusion.
In addition, there are a number of other benefits that we encourage you to discover on the website or by contacting us.


[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