Description and results

Topic

The present bioreactor coupling hub is currently made of stainless steel (316L) using the SLM process (Selective Laser Melting, metallic 3D printing). For economical reasons, an alternative manufacturing process is strongly recommended.

Image 1: Installation position of the coupling hub with a shaft and a coupling socket

The component must meet the following requirements:

Geometric requirements:

· Standard-compliant M8 internal left-hand thread for connecting the stirrer shaft

· Exact gear geometry to ensure clean form fit with coupling socket

Mechanical requirements:

· Fatigue strength of the gear at least as high as that of the coupling socket made of polyurethane

· Minimum tolerable pull-out torque of the M8 thread: 4 Nm

· Surface pressure at the contact surface to the stirrer shaft within the permissible range

Thermal requirements:

· No deterioration in the mechanical properties during repeated autoclaving (up to 500 cycles at 121 °C with wet steam for 30 min each)

Further material requirements:

· Corrosion resistance, especially due to autoclaving cycles

· Abrasion resistance when pairing with coupling socket

Both the FFF process (Fused Filament Fabrication) and injection moulding are suitable for the production of the machine component. For this reason, it is necessary to determine which process offers the greatest cost-saving potential for a given number of parts. Due to the mechanical and thermal loads as well as the potential need of reworkability for thread cutting, 30% carbon fibre reinforced PEEK (CFR-PEEK) is identified as a suitable material. By integrating the thread into the 3D printing process, reworking can be reduced or ideally completely avoided.

In order to create a clean thread, a standard M8 left-hand thread slightly undersized is printed with the Apium P220 machine. With minor rpost-treatment it is possible to achieve the correct thread size for the machine component.

Results

The pull-out torque is measured to determine the mechanical load capacity of the thread at 19 Nm, which is far above the requirements. In order to analyse the surface pressure and the creep behaviour of the coupling hub at the critical contact surface to the stirrer shaft, a load test is carried out over 72 hours with a torque of 4 Nm. No significant deformation of the material can be detected. The abrasion resistance is verified after a 30-day endurance test under real operating conditions.

Image 2: Micrographs of the 3D-printed clutch hub

Cost comparison of manufacturing processes

Figure 3 shows the manufacturing costs of the coupling hub as a function of the total number of units for different types of production. SRM AG has calculated the costs for the production of the machine component using machining and FFF processes. The SLM and injection moulding costs are calculated by Infors HT and its external suppliers. For each manufacturing process, a suitable material is individually selected for the specified requirements.

It has been shown that the FFF process offers significant savings potential compared to the SLM process, especially in the area of small to medium quantities. Furthermore, due to the high mould costs for this component, injection moulding only has economic advantages over the FFF process in the area of a total volume of more than 1000 units. For small batches of up to 100 pieces, the FFF process also has significant cost savings potential in relation to machining processes, especially for complex component geometries. This is due to the low set-up costs, such as the preparation of the G code and the machine preparation time, as well as the optimum material utilization.

Image 3: component costs of the respective processes

The Apium P220 machine is an industrial material extrusion (FFF) 3D printer that meets the highest quality printing standards and requirements of a variety of industries.