Automatic production of carbon brushes
A well-known Japanese company approached KOMAGE to develop a process to automatically produce carbon brushes with a cable connection in large quantities.
Until now, the company has compacted carbon brushes on mechanical presses with a punch: one cavity or part has been created for each stroke. All previous attempts by the company to press several parts per stroke have failed because the tolerances between the individual cavities – i.e. the individual products from one stroke – were too large. This is a well-known phenomenon, since the quality of the results is largely dependent on the even filling of the individual cavities. So in a die with z. B. four openings exactly the same filling quantity can be introduced in order to avoid e.g. to be able to achieve the same densities and heights of the parts.
Higher throughput - Lower tolerances
The Japanese client was therefore looking for a machine and a production process to significantly increase the number of pieces while maintaining the tolerances described. As a further challenge, KOMAGE received a finished part drawing from the client instead of a green body drawing. This means that in the green state, i.e. when the part is only pressed from powder, larger tolerances have to be taken into account because the dimensions change after sintering. However, the customer absolutely wanted to avoid post-processing of the parts after sintering. KOMAGE should come as close as possible to the original or finished part drawing with the weights and heights.
New ways of filling
To implement the task, KOMAGE has now proposed a test tool that was similar to a carbon brush that was already in production. In this way, practical tests could be carried out, since all the equipment from KOMAGE for this process could be made available ad hoc.
KOMAGE then developed a filling device especially for this production test, which evenly fills four small cavities. With the help of this new type of filling device, KOMAGE was now able to add material within very narrow limits.
For this purpose, KOMAGE has designed a device that optimizes the copper-carbon mixture. The mixture runs over a horizontal blade system, which homogenizes and distributes it very finely, so that the fillings in all cavities are as homogeneous as possible.
After a short optimization phase, the evaluation could then begin in the first production at Komage KOMAGE. 50 strokes selected as a random sample and then measured the results individually. Even in this random sample, we actually achieved a constant dimensional difference of 6 hundredths in the entire cavity (test quantity: 50 parts per cavity). This result can be seen as an extraordinary success, since the dimensional deviations including the dimensional tolerances have been plus/minus one tenth.