Complete machining even when cylindrical grinding – in a single chucking operation
Kellenberger’s Kel-Varia in the production hall of Kapp in Coburg: for over a year it has more than proven its worth. The height of its centers is 225 mm, while its between-centers distance is 1500 mm.
When the Kapp firm in Coburg sought to purchase a new cylindrical grinding machine, they wanted one which would combine various work processes such as external and internal cylindrical grinding, face and thread grinding. By dispensing with re-chucking inaccuracies, parts would also benefit from higher degrees of precision. The opinion of Kapp’s machine operators was an important factor in reaching the purchasing decision.
Kapp in Coburg, together with Niles its company in Berlin, is a leading worldwide manufacturer of machines for the hard and soft fine machining of gears and profiles. These companies are complemented by Kapp 2 Technologie GmbH, which specializes in the manufacture of not needing dressing Kapp grinding and coronating tools with a single-layer CBN or diamond coating. Today, profile grinding machines for the fine machining of straight and helical inner and outer teeth are manufactured in Coburg, as are rotor slot grinding machines, coronating machines and special machines, as well as interlinked manufacturing systems – all in all, grinding machines of a very special class. And naturally, their construction requires individual components which need to have a particularly high precision in their own manufacture. It is not without reason that the manufacturing detail for these ‘know-how’ parts is particularly large. And it should be hardly surprising to learn that considerable concerns were raised at Kapp about the flow logistics of this type of manufacturing and the coalescence of work processes.
Combining of machining processes
“The geometrical and dimensional requirements for the workpieces to be manufactured are becoming ever-more demanding” explains Ludwig Bätz, Head of Mechanical Production, “and every customer expects to have short lead times. This has resulted in a complete re-organization of our production operations. The upshot? A reduction in throughput, transportation and idle times, as well as further improvements in quality. The efficiency benefits resulting from the combination of turning, boring and milling operations on turning/milling centers were at least 40% and considerably greater than we had imagined, and this without taking into consideration the hourly machine rate. In rationalizing our cylindrical grinding, the Kel-Varia from Kellenberger caught our attention. Although the savings potential stemming from the combination of machining operations was somewhat smaller for this machine, the advantage lays clearly in gaining higher geometrical accuracies.”
Decision-making input from employees
As is customary, the market was carefully scrutinized, culminating in test machinings on the machines of a few short-listed suppliers, before a decision to buy the new cylindrical grinding machine was made. As a part of this process, employees who worked on similar machines at Kapp were included in the decision-making process. According to Ludwig Bätz, “an employee on the shop floor will know more about the daily demands placed on the individual product than his respective superior”. As a result, the Kel-Varia 225 x 1500 was set up with a higher grinding speed of 45 m/s, as opposed to the earlier 30 m/s, to meet the machining requirements of Kapp. And for internal grinding, the spindle delivers 24 kW at up to 42,000 1/min. This allows sensible stock removal rates, even for larger wheel diameters. However, the overarching consideration for Bätz was that external cylindrical, face and internal cylindrical grinding are all possible in a single clamping. Added to this is the grinding of external threads, with the help of Kapp tools.
“It should be emphasized that the machine offers excellent accessibility”, adds Uwe Horn, Head of Turning/Grinding. “The interior space of the machine is clearly arranged, without any suspended cables or pipework. This was an important factor in the purchasing decision, as this means reduced costs for servicing and preventative maintenance, but also for the setting-up”.
This machine has now been operational for around 13 months. Our experiences to date have been good. Many flanged parts with positional and form tolerances of only a few micrometers no longer present a particular challenge for us. But above all, the coordination-related work and effort has reduced drastically compared to the past. Seen in this light, this grinding machine has already delivered savings similar to those that have already been suggested for other technologies.
A selection of workpieces showing the diversity of grinding in Coburg. In the new Kel-Varia this takes place with a single clamping, which naturally means that, apart from other things, the otherwise unavoidable re-chucking inaccuracies are dispensed with.
Uwe Horn, Ludwig Bätz and decision-making participant Michael Wolf continue to work very closely with one another today. The Kel-Varia has not only solved capacity bottlenecks, it has considerably simplified the compliance with particularly fine tolerances.
The externally and face-ground component can be cylindrically ground internally without being re-clamped. External threads can also be ground in this manner.
A clamped undulating component, ready for external cylindrical grinding
The wheel on the righthand side is used for face grinding.
Specialist software simplifies work
Something that has not yet been mentioned: this machine is equipped with Kellenberger’s KelPos, KelTwist and KelSet software. These programmes – and KelSet in particular – deliver considerable advantages considering to the complexity of the workpieces that need to be ground. When grinding eccentric parts, for I-sections and non-circular contours, it becomes very easy to measure and account for grinding wheel dimensions and their positions automatically. Without this, the contour would deviate. KelSet entirely removes this problem – in spite of the fact that it is highly intricate parts, with particularly tight tolerances, and made, in part, from exotic materials which are being ground on this machine. These are heat-treated workpieces: through-hardened, case-hardened, nitrogen hardened for example. However, components which comprise 97% tungsten and are particularly heavy are also suitable for grinding. There have been instances with the requirement of 3 surfaces to pass alongside one another to within 0.002 mm. The head of mechanical production isn’t minded to divulge the details here. However he does explain that tolerances of 0.2 µm can readily be supplied, and found as well. Ultimately, the cooling lubricant ensures highly effective thermal stability of the machine. And naturally, what’s also being drawn on is know-how, and nuances.
The grinding cell for the fine machining of gears of every type, as they are manufactured at Kapp in Coburg. It goes without saying that the individual components of these high-precision machines need to be manufactured to even smaller tolerances.
The machine basically operates for a two-shift period and is attended to by a single person. Primary processing times have naturally fallen drastically as a result of combining all the grinding processes in this single machine. For workpiece batches of more than one component, the transition to two-machine operation is also possible. This sees the operator also working on an adjacent, conventional grinding machine.
In spite of the current economic situation, Kapp’s order books are full. However plans are already afoot to enable a further market sector to be served soon with a larger machine. Even though the Kel-Varia is currently not being used to its full capacity, a further machine of this type is therefore already under consideration in the company’s plans for the future.
L. Kellenberger & Co. KG