Particularly broaching tools can be very expensive. Regrinding and recoating of these tools due to excessive wear will not only lead to down-time of the machine but will also add significant costs to the overall process. Therefore improved tool life through optimal tool protection is the key factor for modern broaching processes.
Today we have good evidence that it will be possible to improve tool life and increase process speed / productivity just by optimizing the lubricant as being a key factor for modern broaching processes.
In the past machines were operated at relative low speeds and chlorinated paraffin containing metalworking fluids worked just fine. With the demand on higher throughput, better surface quality of the work piece, lower production costs and improved worker and environment safety, there is a need to introduce new technologies to overcome the problems linked to chlorinated paraffins. Optimized formulations based on special light color low odor sulfurized products combined with antiwear additives can cover a much wider range of cutting speed variations than oils based on chlorinated paraffins.
The compositions of the tested metalworking fluids are shown in figure 1.
Figure 2 shows the wear development over the machined parts at a cutting speed of 24 meters per minute (~ 80 SFPM) in a groove broaching process.RC 12 (Polysulfide + Chlorinated Paraffin) shows the highest wear. Just by the combination of the Polysulfide, that supports the cutting, and a truly inactive sulfurized triglyceride (RC 6) it is possible to meet the performance of RC 12. The additional use of a typical antiwear additive (RC 11 = RC 6 + Special mineral oil free, thermally stable ZDTP) can improve the tool life a further step. The really breakthrough can be obtained by combining special sulfurized products based on reaction products of hydrocarbons and triglycerides with polysulfides (RC 14). The formulations RC 15 and RC 16 are based on the ”sulfur optimized” oil RC 14. In RC 15 we added a thermally stable ZDTP to further improve the tool life. A moderate lower wear was observed. RC 16 is similar to RC 15 but with optimized primary antiwear component. Instead of using a ZDTP we combined Oil RC 14 with an ashless dialkyldithiophosphate.
Despite the discouraging laboratory results in comparison to RC 12 (chlorinated paraffin + polysulfide), the tool life was approx. 20% higher while using RC 14 and doubled while using RC 16. This again is an example how easy laboratory tests can lead to a formulation that shows good performance on laboratory test rigs, but is far from being an optimized metal working fluid.
