Setup on a ceiling of 5-axis-Machining Centres - how it is correct
A DMG MORI 5-axis-Machining Centre of DECKEL-MAHO-GILDEMEISTER, weight approx. 130 kN, had been causing problems for 4 years at a large and well-known manufacturer of cleaning devices in Baden-Wurttemberg, Germany. The machine was standing exactly in the centre of a ceiling between two bearers. It was positioned on wedge mounts that were supplied together with the machine. The partly considerable vibrations, depending on the set values, were shown to isoloc. Obviously, they were close to maximum values of the admissible ceiling loads. Because of this, it was run so far with max. 50 % of the possible feeds and velocities. Already during start-up, but also during the following weeks, disproportionately frequent service of a technician from DMG was required on site in order to be even able to operate the machine. During the 4 years the situation has not changed. The expenses were substantial for both sides.
“Different elements were tested” in order to solve the problem. E. g. a competitor of isoloc submitted an offer for an extremely low tuning (mounting natural frequency) with an air spring system that would have costed approx. 30,000.-- €. Before, a measurement for the determination of the natural frequencies of the ceiling on which the machine was standing was carried out. As the customer did not want to realise this costly (air spring) solution the results of the measurement were not disclosed.
Thereupon isoloc was engaged.
Isoloc solution, step 1:
Without exact examination of the situation and knowledge of the basic conditions only a pragmatic first approach to the problem was possible for isoloc. 5 pieces Universal Precision Machine Shoes UMS, equipped with isoloc high-performance elastomers, were chosen that had achieved very good results in similar cases.
Total costs: 775.-- €
The supplied isoloc Machine Shoes UMS18-ASF/I improved immediately the situation and provided enormous benefits. An increase of the values (feeds and velocities) by 30 % was achieved. The customer was contented for a start, especially because of the long history.
By the decision for the isoloc solution instead of the suggested air spring solution of the competitor, 29,225.-- € were saved. The costs of the reduced production and the hours of the technician of the machine manufacturer are not included in the calculation.
Isoloc solution, step 2:
Asked for more optimisations, isoloc proposed a more elastic setup. This was accomplished by an additional layer of the Vibration Insulation Panel IPL I beneath the steel plates positioned at the mounting points on which the machine shoes were standing. These had moved slightly on the floor as no slipping protection between steel plate and floor was existing. Thanks to the excellent static friction characteristics of the isoloc IPL panels also this problem could be solved as additional effect, independent from the elastic setup of the machine. The results of the second test are still pending (status: 2017/06/26).
This example shows that not always the complex and expensive solutions with air spring systems are necessary for difficult setup situations in vibration engineering terms if the communication between supplier and customer is good and experts are entrusted with the analysis. Due to the low rigidity and damping of air springs the operation of machining centres with the desired accelerations and speeds is highly questionable as large vibration amplitudes are to be expected. On the other hand, this case shows that common wedge mounts are in the end more expensive, too, for the machine-tool manufacturer. Presumed cost savings by cheap mounting elements are out of proportion with the risk of getting into trouble by such problems and high subsequent costs - not to mention the damage to the reputation.
How it is correct:
Some months ago, the customer bought a new HERMLE Machine C400 and installed it on the same storey ceiling. In spite of similar local installation conditions and of the machine type, the start-up of the HERMLE machine, which was already standing as standard on isoloc Machine Mounting Systems, could be completed in only one day by the technician from HERMLE. Moreover, no limitations of the machine performance could be perceived.