Ausrichtmodul beim Fügen der Kernhälften

Accurate Assembly

Steinbeis experts develop multiple assembly system for electric coils

Arnold Elektronik GmbH, which specializes in inductive components and is based in Lichtenau in Saxony, enjoys a long history. Founded nearly a century ago, it has continually moved forward as a business, but the high-precision parts it produces still require intensive manual processes. Until now, the coil cores it manufactures have been assembled by hand. Obviously this has drawbacks, especially with small coils, so Arnold decided it was time to do things differently. The firm has been working with the Chemnitz-based Steinbeis Innovation Center for Drive and Handling Technology in Mechanical Engineering. Together, they have developed an assembly system that makes it possible to automate key processes.

Coils mounted onto other systems consist of a wound coil body and two ferrite halves. These are inserted into the coil body and glued together. Once the two halves adhere, they should leave a gap simply filled with air. The angle of alignment of the core halves dictates coil induction. Offsetting angles by just 100th of a millimeter has an influence on whether induction tolerances can be adhered to and whether a coil works. The ultimate mechanical strength of a coil is achieved by bonding covered copper wires in an oven at 150°C. The adhesive surfaces have to be robust and stable at different temperatures.

One thing that is particularly difficult when handling small coils is that it is almost impossible for the operator to avoid touching wetted gluing surfaces. Aligning the core halves takes ultimate concentration and dexterity, since there are only a couple of seconds to apply the glue while inserting the activator. Immediately after joining the parts, an induction device is needed to measure the coil between specification pins. If a coil does not meet measurement requirements, operators may try to force the core halves together by squeezing them in their fingers or rubbing parts together. Alternatively, they may pull the two halves apart again and use another part instead. This means that the joining areas have to cleaned and re-wetted. If the join on a coil is already too tight, it can only be rejected or destroyed, although a coiled core can sometimes be retrieved and used again.

It’s compulsory for operators to wear gloves when assembling parts, but it is almost impossible to avoid skin contact, since the two connecting pins are extremely sharp and even if somebody is wearing protective gloves, one touch is enough to penetrate the surface. As for miniaturized coils, they are practically impossible to handle with gloves on. Handling parts can cause severe injury to fingertips, and skin damage caused by adhesives is a major contributor to sick leave. The process places high demands on the workforce, also because it is strenuous on the eyes. The quality of coils and the number of rejects depends largely on each individual’s ability to work quickly and accurately.

All of these limiting factors were motivation enough for the project partners to optimize the assembly process. The assembly system developed by the Steinbeis experts in Chemnitz and Arnold Elektronik now makes it possible to mount a variety of coil cores, starting at a core width of 12 to 25 millimeters. All the system requires is an interchangeable workpiece grip matched to the type of coil.

The operator starts the process by inserting up to ten coils, including ferrite cores, into the assembly unit. There are electromagnets mounted on moving magnet carriers, and these are used to remove coil core halves from the coils and swivel them into a wetting position for adhesive to be applied. Once the glue is applied, the core halves are reinser reinserted into the respective coils for joining. The alignment module ensures that the coil cores, which are difficult to position and have to be precise, are carefully aligned to one another. This is an essential part of reproducing accurate adhesive joins.

The new assembly units are already being used as a substitute for the intricate manual process, which required a huge amount of concentration, dexterity, and speed. The produced parts are reproducible and there are fewer rejects resulting from misaligned cores, primarily because the quality of joins no longer depends on individual operators. Operators working on the components at Arnold will no longer have to wear the special protective gloves, as there will be no more direct skin contact with the adhesive. The new assembly system also saves a significant amount of time; up to ten coil cores can be joined and aligned at the same time. Previously each coil had to be mounted manually one at a time. The multiple assembly system has provided Arnold Elektronik with a state-of-the-art, adaptable workstation that will make a big difference in raising productivity and improving product quality.


Prof. Dr.-Ing. habil. Eberhard Köhler
Steinbeis Innovation Center Drive and Handling Technology in Mechanical Engineering (Chemnitz)