A Six Sigma project at Ericsson Network Technologies

Abstract: The purpose of the thesis was to find factors that influence the mechanical
characteristics for copper-wire products that are insulated with foamed
polypropylene. This specific insulation material is new to the company and
suitable machine-settings are unknown. The project was carried out as a Six
Sigma improvement project according to the DMAIC-cycle. Six Sigma focuses
on process improvements and reducing variation.

Initially, relevant literature for the area was studied to get a deeper
understanding of the problem. Some of the literature is summarized in the
theory chapter of the thesis. According to the DMAIC-cycle, the process was
then defined and mapped out. Which characteristics to improve were also
chosen, in this case elongation for the insulation, before and after
ageing.

Factorial experiments were conducted later in the process to find out which
factors influenced the chosen responses. The results showed that line speed
and preheating were two important factors for a satisfying elongation. To
maintain the elongation after ageing, the temperature in the main extruder
and the tank position for the cooling bath was discovered to be important.

The suggested factors were adjusted to suitable levels. Factors that did
not influence the chosen characteristics were adjusted to the most
preferable level. For example, a cheaper granulate could be chosen when it
was discovered that the investigated granulates made no difference for the
elongation of the insulation.

To reduce the variation a higher speed is recommended. Unfortunately this
results in a deteriorated surface for the cable. The surface, which was not
in the scope of the project, could also be improved with a tank position
near the extruder head.

The measurement method for elongation was changed according to the method
proposed by UL (Underwriters Laboratories). This resulted in a reduction of
the variation between each tensile test within a sample.

Recommendation for additional research is further investigation of the
effect from different temperatures of the main extruder. Another
interesting area to study could be the factual changes in the polymer
structure from different machine settings. It could also be in the
company’s interest to test if the findings are applicable to other
products.