Des potentiels de rationalisation résident entre autres dans la combinaison de processus sur une seule machine. S'il est possible d'éliminer ainsi des processus, ceci ne conduit pas nécessairement à des économies de temps, mais permet par contre de réduire de moitié les nouveaux investissements. Comment ceci est-il possible...
KOEPFER : UN NOUVEAU CONCEPT RÉVOLUTIONNE LA STRATÉGIE DE FABRICATION TRADITIONNELLE
17/02/2010 - Oliver Hagenlocher
Automating production processes appears to be the most efficient solution to increase machine availability and productivity rates. A solution that successfully meets all criteria – component quantity, diversity and runtimes – calls for considerable capital investment. At least it does in the case of the machining of pump pinions for hydraulic packs or worms for step-down gears. To date, the central components for gear pumps, for instance, have been turned from bar material and then the profile milled on the gear hobbing machine and shaved on a gear shaver. The subsequent case hardening process with its inevitable quench distortion was followed by grinding of the bearing seats, as the final operation. But it appears that this typical sequence of operations now belongs to the past.
The willingness to rethink and to break new ground
The objective of the transmission manufacturer is, and always has been, to get away with as little handling as possible. In other words, the flexibility that guarantees a rapid reaction to component changes and fast resetting is of greater importance than a manufacturing system that is planned to the last detail. But for cost reasons the manufacturers are presently willing to break new ground with their production techniques. At least, this is how Armin Wacker, Head of Sales at Koepfer Verzahnungsmaschinen, sees it: „In the recent past we have found ourselves facing an ever increasing number of queries from the transmission and hydraulics sectors as to whether it would be possible to switch processes from pre-milling and shaving on two machines to finish-milling or even hard-finishing on a single machine. These queries are coming in from all over the world, but primarily from Italy, Eastern Europe and India. Germany is (still) holding back a little.“ However, the combination of processes such as turning, gear profiling, washing – and maybe also measuring – on a single machine has been recognised as a clear trend for some time. The advantages are obvious: cost and space savings. Opinions are usually revised for good only when there is a need to invest in new machines, i.e. when a hobbing, shaving or grinding machine has reached a certain age, it makes sense to start thinking about the new machining strategy. For one, a gear hobbing machine is considerably cheaper than two machines (hobbing and shaving). And a grinding machine plus a gear hobbing machine would be an even more expensive option. Having all operations on a single machine not only halves the floor space requirement, it also leads to a reduction in operating personnel. It must be increasing competition that results in manufacturers’ willingness to break new ground and to reduce costs to become more competitive. The development of such new machining strategies remains, however, for the most part, the responsibility of the machine manufacturer, especially as loss of quality is unacceptable in the use of stable processes.
Sturdy and of the highest precision – taking on new dimensions
In a current case Koepfer were faced with the need to completely eliminate the shaving process on gear profiles for a renowned Italian manufacturer of hydraulic pumps; bearing in mind that this is a machining method that has to date been used by almost all pump manufacturers across the globe for what are, after all, very similar components.
With a fully automated K 300 Universal Gear Hobbing Machine, using the duplex cut method, Koepfer succeeded in soft finish-milling a pump pinion module 4.0 to quality class 6 DIN 3960/-62. This high degree of precision achieved on the K 300 Gear Hobbing Machine with nine active CNC axes is due, not least, to the machine base in a mineral cast compound, with motion guideways in the linear axes. The closed-loop frame construction offers the highest possible degree of rigidity for tailstock and work spindle, even when subjected to massive clamping and cutting forces. And the diagonal alignment of the hobbing head also offers ideal chip flow conditions for both dry and wet machining operations.
The introduction of a new hard-machining process also leads to an improvement of the surface structure
A successful change to the new manufacturing strategy makes it necessary to make doubly sure beforehand that component quality and process integrity are a given. For instance, in one particular case Koepfer invested a number of years of long-term trials in the development phase. In contrast to this, a manufacturer of gear motors wanted to replace the grinding operation for the gear profiles. This was also done successfully. A K 200 pre-mills the worm – which is then case hardened – and afterwards finish-skives it. Besides being able to complete-machine the component on a single machine, the skiving process has had a pleasant side-effect. The surface finish of the skived workpieces is of a different structure to that produced by grinding, and this has an often very positive effect on the noise that develops in the gearbox. Of course, the prerequisites for such precision are a sturdy machine and the use of high-quality milling hobs in coated solid carbide.
A little incidental detail
The skiving of pump components is considered an interesting alternative to soft finish-milling. The quench distortion generated during case hardening can be eliminated and the surface finish improved by copy-milling the hardened gear. If one puts one’s money on a Koepfer machine to do this, one can carry out the skiving operation on the same machine where the gear profile has been soft pre-milled earlier. All one has to do is equip the machine with the relevant, optionally available automatic positioning sensors.