Pellet milling system

The challenge

The ‘E-lighter’ is a device that is able to convert diesel fuel into electrical power. It is used as a small, mobile and flexible power supply system which is particular useful off the beaten track. The device operates on limited amounts of liquid fuel.

The E-lighter is based on a thermoelectric generator (TEG); a system that is converts a heat flux directly into electrical energy through a phenomenon called the Seebeck effect. A visualization of the concept is shown below. The generator consists mainly of a large amount of thermocouple elements called pellets. These pellets are produced from pressed metal powder(s) and need to be milled to the correct dimensions.

Demcon industrial systems was asked to develop and realize an automatic solution for the precision milling of the pellets. Due to the large number of required pellets, the required accuracy and the CMR (hazardous) classification of the metal powder, a (semi)manual solution was not considered feasible.

The solution

Demcon industrial systems took up the challenge to develop a fully automatic custom milling solution for the pellets complemented with an appropriate form of quality checks.

The first critical function in the system was the pellet infeed.

This was not trivial as the pellets are relative fragile and small. After some explorative tests, a solution using a bowl feeder from Grimm was found. The individually oriented pellets are picked up at the exit of the bowl feeder using two servo controlled screw spindles and a pneumatic gripper.

The pellet length needs to be within a [+0.05, -0] mm tolerance after processing. Therefore, a Micro-Epsilon laser micrometer measures the length  of the pellet before it is milled to the required length. The pellet is measured once more after milling for final length confirmation. Naturally, during milling the dust is extracted.

Milling can occasionally lead to damages like cracks that would render the pellets useless. To verify the internal integrity of the pellet an electrical resistance measurement is applied.

After this last test, the approved pellet is fed out to the product outfeed box. Any rejected pellets will be sorted out automatically.

The complete solution was implemented on a Smart Machine Base, Demcon industrial system’s own machine platform. It allows the team to focus on the customer solution from day one and reduce the project lead time. For this project, the smart machine base was furnished with an additional dust extraction system with HEPA filters. Overall, it was a technically challenging project with many parameters that had to be tuned during the test phase to ensure satisfactory performance.