UD3D printing in combination with injection molding

Continuous fiber-reinforced inserts from the 3D printer as internal reinforcement of an injection molded part

Leibniz-Institut für Verbundwerkstoffe (IVW) develops various technologies to transfer novel and more efficient processing methods into applications. One promising approach is the production of continuous fiber-reinforced inserts in a modified 3D printing process. Subsequent overmolding with short-fiber-reinforced injection molding compound in an injection molding process can functionalize these high-strength structures.

The first process step is the automated production of the starting material for UD fiber-reinforced 3D printing (UD = Unidirectional). Here, pre-impregnated tape cut to the appropriate width is formed to round strands in a pultrusion process. The system shown in Figure 1 was designed and built by IVW for this purpose. In addition to engineering polymers, high-performance polymers including PEEK can be processed. Furthermore, various fiber types, such as glass and carbon fibers, can be used.

The finished semi-finished product has a diameter of 1.75 mm and features continuous or endless fiber reinforcement. The strands produced in this way show a high degree of roundness and a low pore content, see micrograph in Fig. 1. The semi-finished product is then extruded on a robotized end effector according to a programmed path. The extrusion process differs from classical 3D printing in the nozzle geometry. The nozzle is conical because of the unidirectional and endless fibers. In addition, fiber reorientations or fiber accumulations must be avoided.

In general, 3D printing ensures high geometric degrees of freedom. In addition, mechanical properties, such as stiffness and strength, are improved by fiber reinforcement. An example is the double-lap loop shown in Figure 2 and Figure 3, respectively, which was deposited from a continuous fiber bundle and demonstrates the feasibility of undercuts.

Double-lap loop forms the inner skeleton of a coupling rod demonstrator for the commercial vehicle sector. For this purpose, an overmolding process encapsulates the load-bearing skeleton structure with short-fiber-reinforced PA6-GF30 in a secondary process step. The bond is ensured by prior heating of the double-lap loop in an IR oven and overmolded with injection molding material. Preheating time and overmolding pressure are main factors to minimize the voids originally present. Further advantages of overmolding are the short-fiber compound supporting the inner structure against buckling and force introduction tasks.

Contact:

Alexander Nuhn, M.Sc.
Leibniz-Institut für Verbundwerkstoffe GmbH
Erwin-Schrödinger-Straße 58
67663 Kaiserslautern
Phone: +49 631 2017-117
E-Mail: alexander.nuhn@ivw.uni-kl.de

Dr.-Ing. Jens Schlimbach
Leibniz-Institut für Verbundwerkstoffe GmbH
Erwin-Schrödinger-Straße 58
67663 Kaiserslautern
Phone: +49 631 2017-312
E-Mail: jens.schlimbach@ivw.uni-kl.de