Full view: Transparent tool enables insight into filling processes of particle foams

The filling of a mold determines the quality of the resulting molded part. But what if insight into the filling process of particle foams is not available and thus control is lacking at this crucial point in the production process? A new transparent experimental mold made of acrylic glass developed by Neue Materialien Bayreuth (NMB) has put an end to this dilemma.

Mr. Schreier, why was it time to develop such an experimental tool?

Peter Schreier: Particle foams have become indispensable in everyday life and in many applications, especially in automobiles and sustainable packaging solutions. It is a widely used material whose life cycle begins with filling a component with particle foam in the molding machine. If mistakes are made during the filling process, this has an impact on the component quality. These errors are difficult or impossible to correct afterwards. Filling is therefore a very important process step in terms of quality, reproducibility and cycle time optimization.

However, the status quo, if you look at the last few years, is that the design of particle foam molds, especially when it comes to setting the filling positions and the fillers, is primarily based on experience from moldmaking. This works well for standard molded parts, but not always on the first try for more complex molds. When the new molds are put into operation, this often results in the need for time-consuming optimization loops. This circumstance was part of our motivation to generate our new test mold.

Are there other factors as well?

Schreier: Yes, there are. The molds for molding with particle foams are made of metal in steam-based processing. I can't look inside. There are sensors installed in it, for example to measure the internal pressure, but it still remains a black box in the broadest sense. If I vary parameters in the filling process on the machine side, I can hardly track their effects due to the lack of transparency and the many subsequent steps (such as steaming), unless I start with the filling process.

And then in the particle foam industry, unlike other industries, there are hardly any filling simulations established yet that can be used to verify the filling processes.

So you developed the transparent test tool. But how?

Johannes Görl: That's where I come in. We wanted to be able to represent and investigate the real process of filling on a classic molding machine. It was important for us to use the tool to represent a high degree of flexibility in terms of filling positions, fillers and part thickness. The background to this is that each of our project partners has different requirements. One wants to fill horizontally, another vertically, the next has a specific geometry that he wants to investigate. That's why we decided to have a monoblock mold made, so that customers don't have to buy a new mold of their own, but can make inserts according to their needs and use them in it. The monoblock tool is constructed from an aluminum frame, with the housing made of transparent acrylic glass.

Ultimately, the design and development of the transparent mold incorporated all of our technical and scientific know-how - we have 20 years of experience in processing particle foams. While it was clear at the beginning that the mold had to be transparent, in the end a very complex mold was created. In addition to the high flexibility, which ranges from various filling positions and different compression options to different component thicknesses, the challenges were the high demands on the mold material. The material must be pressure-stable - it must withstand filling pressures of up to five bar - and transparent, so that we have the largest possible field of view for evaluating the filling process and thus for recording the filling process with our high-speed camera.

What kind of request does a customer now come to you with?

Kristina Schüllner: For example, the customer comes to us with a 3D geometry that he wants to have examined because problems have arisen in the finished component, such as a non-homogeneous density distribution and more material has been compacted in some positions than in others. In order to prevent such a problem as far as possible, we can now use the test tool, obtain precise information and carry out optimizations by, for example, using different filler positions or filling parameters.

Who benefits from your development in the short or long term?

Schüllner: In principle, the entire process chain benefits, that means from the idea to the finished component. The end user from the quality of the product. Research and development, because gaps in the literature can be filled, more information and data can be collected, and research possibilities can be expanded. Indirectly, there are also advantages for the machine builder, who can incorporate the findings into the filling process as an optimization. And this starts with modifications to the silos in which the material is stored before it enters the filling process. The toolmaker has advantages in that he can design his tool differently accordingly. The material manufacturer likewise, because whether the material is elliptical or round also has an influence on the filling process. And of course also the processor, who stands at the machine, by being able to adjust the filling parameters accordingly.

What do you as the NMB hope to gain from this?

Schreier: The first thing is the scientific component: We want to fill the gap on the scientific map, to supplement and fill it, and to investigate the interrelationships between filling parameters and their effects on the component. The second is the economic component: to support our partners and customers with their specific questions, to help them where they get stuck. And thirdly, we want to make our contribution to the further development of particle foam technology and ultimately also give the industry a competitive edge.