KitkAdd: leveraging Additive Manufacturing and Powder Metallurgy for hybrid manufacturing

In early 2017, nine partners from across Germany came together to kick off the KitkAdd project. The consortium, funded by the German Ministry of Education and Research, set out to explore the potential of hybrid manufacturing. With the target of increasing additive manufacturing’s productivity and reducing cost, the group combines Additive Manufacturing (Laser Powder Bed Fusion or LPBF) with the conventional powder metallurgy process to exploit the benefits of both processes.

The KitkAdd project, which officially wrapped up in March 2020, included several high-profile partners, including Siemens, John Deere and, of course, GKN Powder Metallurgy. Each partner was tasked with a different application and leveraged a different hybrid manufacturing approach to achieve the desired results. In the following article, I will dive deeper into GKN PM’s role in the KitkAdd project, where we combined two of our areas of expertise - LPBF and pressing and sintering - to pioneer a new hybrid AM approach.

How the KitkAdd research project adds value to the manufacturing industry

In our work for the KitkAdd project, my team and I leveraged the benefits of additive manufacturing, including the ability to achieve complex geometries, with those of pressing and sintering, namely, its low cost and precision. By combining the two processes, we were able to utilize AM only where it adds value to the part and subsequently use pressing and sintering to complete the part’s geometry with a high degree of precision.

We demonstrated this technique with the design and production of a gear wheel. Our goal with the application was to utilize Design for Additive Manufacturing (DfAM) to optimize the part’s noise, vibration and harshness (NVH) performance.

To achieve this, we needed to complete a few steps:

• Develop the hybrid manufacturing approach
• Design the part to specifically utilize the benefits of AM
• Conduct the process chain and cost analyses to understand the benefits of using a hybrid manufacturing approach compared to a conventional process chain

The demonstrator component consists of 3 modules and is inspired by product out of GKN Powder Metallurgy's recent portfolio

With the gear wheel, we created the inner part (Module 2) using DfAM to achieve noise reduction. This process resulted in three design concepts. The first, which you can see in the graphic below, was entirely made using AM. In the second design, we integrated internal struts to distribute the noise and break it down into many smaller acoustic waves. In the third design, we printed the gear wheel with holes and subsequently inserted 3D printed capsules filled with metal powder. The idea behind this was to dampen the sound waves and reduce the noise. Ultimately, we saw higher damping ratios with the last two designs.

The design with printed lamellas doubles the damping ratio while the powder capsules realize a 5 times increased damping ratio compared to the reference part.

After producing the additive component of the gear wheel, the printed part was placed into a powder press, where the outer structure (Module 3) was created by pressing the powder onto the internal AM part. Using pressing instead of AM results in a higher degree of precision - in this case, for the teeth of the gear wheel - which results in less post-processing. Another key advantage of using PM for the final construction is that we needed less time to print the part. In other words: As AM is more costly than PM, we strategically used the technology only when it added value. In this case, we were able to reduce the cost by a factor of 3 (lot size 100). Once the part was pressed, it was sintered to achieve a hardened, fully dense component.

Mastering key challenges around material and design

One of the challenges in developing the hybrid manufacturing approach was to find the best connection between the 3D printed part and the pressed powder part. We worked with the AM material 20MnCr5 and the PM material Ancorloy 4 because of its similar hardening properties. Still, we wanted to discover if there was an optimal way to bond the two components together. In this investigation, we experimented with using a copper foil and copper paste to connect the parts. However, the best result was without using any bonding material. By adjusting the process parameters, we exceeded initial requirements of 150 Nm with results reaching over 1,000 Nm tested by a rotation load test.

For joining the AM and PM part, we tried out different strategies. Optimizing the Compaction Process had the best effect for an improved bonding between the AM and PM part

The project’s design stage presented another key challenge: Beyond designing the AM part for NVH performance optimization, we also had to design the part so it could withstand the pressing process. For this, we used topology optimization to generate a design that could withstand the high pressure of the press without risk of deformation, which could cause the two components to break apart. This essentially meant that there were two phases to our design process.

Hybrid manufacturing: a more cost-effective approach

At GKN Powder Metallurgy, the KitkAdd project consisted of exploring the potential of combining additive manufacturing with pressing and sintering - an area where we are a global leader who produces over13 million sintered parts daily. Other KitkAdd partners worked with different hybrid approaches. For instance, Siemens combined casting with AM for the optimization of a turbine wheel. In all cases, however, the goal was the same: to combine complex structures with added value through high quality, high throughput production methods.

Our specific approach enabled us to reduce the part’s cost and lead time through the utilization of AM’sperformance benefits. Crucially, we found that the hybrid process can enable cost efficient serial production of metal parts compared to an AM-only approach. This process chain and cost analysis was conducted in partnership with the Karlsruhe Institute of Technology (KIT).

We performed a simulation to determine the costs per unit and the lead time of the different Hybrid Manufacturing approaches. Compared to the AM process, cost savings up to 70% are feasible.

Now that the KitkAdd project has officially concluded, GKN Powder Metallurgy’s engineering team will continue to refine the hybrid manufacturing process and develop more applications that can benefit from it. A key part of adopting the hybrid approach will be to increase awareness across our own engineering and sales teams so they know how to identify if this process is beneficial solution for a customer’s project. Overall, we want to emphasize the potential for hybrid manufacturing as adding performance value while keeping costs and production times manageable.

At GKN Powder Metallurgy, we are also actively exploring different hybrid manufacturing approaches that combine metal AM with conventional manufacturing methods in various ways to improve the cost-to-performance ratio. The combination of AM and pressing and sintering is just one potential avenue for Hybrid Manufacturing that our customers can take advantage of by working with us.