Till now it has been impossible to produce every gear profile in the modular range 0.3 to 3.0 on a single hobbing machine. With the development of a new milling head with corresponding software Koepfer has succeeded in combining soft milling (axial, radial or tangential) with hard milling on a single machine – and to improve component quality many times over.
KOEPFER: The new milling head may be small, but it delivers
04/03/2009 - Oliver Hagenlocher
The crossed axes of worm drives transmit massive forces within a limited design envelope. This is a piece of wisdom that German developers appear to have forgotten about over the years. Then, about three years ago, the Asian market – and in particular the manufacturers of speed reducers – started to call for hobbing machines that allowed them to manufacture worms and to carry out hard peeling operations. The responsible parties at Koepfer Verzah-nungsmaschinen GmbH in Villingen-Schwenningen were facing a choice: to develop a new machine, based on the design of the much larger K 300, or to upgrade the tried and tested K 200 by adding some additional features. The result of their contemplations is a K 200 with a new universal shifting milling head that is extremely efficient, sufficiently small and specially designed for the hobbing of spur gears and the milling of single- and multi-start worms. Its compact design ensures that the milling head can be swung below the tailstock for the milling of the worm geometry – a highlight which is, according to Armin Wacker, head of Sales and Marketing at Koepfer, of enormous benefit, in particular to the typical manufacturer of speed reducers and their sub-suppliers, but also to the tier-1 suppliers for the automotive industry: „The new K 200 has enabled us to open up totally new areas of application and to considerably widen our range. It is now possible for us to also mill worms, which should be of great interest to the manufacturers in this particular field. In conjunction with the new drive technology this allows us to achieve the kind of precision that hitherto has been the domain of the grinding machine. In fact, the resulting component quality now also makes the K 200 an interesting proposition for the aerospace industry with its requirements for safety-critical components.” These high-precision gear profiles are of vital importance, as worm drives with crossed axes have till now been machined primarily by using the dipping method. Although most conventional gear hobbing machines are suitable for the application of this process, no way do they achieve this level of precision. However, tolerances to DIN7 or DIN6 are essential for aerospace components such as those used in the drives for the adjustment of landing flaps. The K 200 is able to meet these conditions owing to the fact that it offers the possibility for tangential milling, using special tools and in-house developed special software. The latter features an exceptionally operator-friendly dialogue programming facility that no longer requires special qualifications to operate.
The demand is growing
By now, European engineers have also climbed on the bandwagon of crossed axes in worm drives. Quite rightly so – as the business analysis shows. The K 200 allows you to soft pre-mill the worm, then hard skive or hard hob it – all on the same machine, and without having to grind it. In other words, the workpiece is hardened to 54 HRC and the gear profile milled into the hardened material. The advantage: highest possible component quality. It is the sum total of the latest developments that make the K 200 the highly efficient and hugely economical machine it is. Meanwhile, the market is following the trend towards the hard-finishing of worms at breakneck speed. Where seven years ago the demand for this type of worm manufacture amounted to a single percent, this has risen to 40 – 50 percent today. In the automotive industry, for instance, the auxiliary drives for window lifts, seat adjusters and sliding roofs all feature crossed axes. By now, the factory at Villingen-Schwenningen equips eight out of every ten K 200s with the universal milling head. Even the sub-contracting gear profilers have found themselves persuaded by the concept.
Automation starts at batch sizes of 30 to 50
The K 200 is designed to handle gear hobbing applications up to module 3, workpiece diameters of up to 120 mm and workpiece lengths of up to 300 mm.
The K 200 can also machine diameters of up to 157 mm and offers higher speeds, but this very much depends on the individual requirement and is something that will be discussed with the customer in detail. The same applies to automation. Even where average annual batch sizes do not exceed 4,000 – 5,000, the K 200 from Koepfer will, almost without exception, feature some automation. Approximately 98 percent of all machines leaving the works are equipped with automation components of one description or another, for instance: gantry loaders with V-gripper, ramp and conveyor belt; or with a multiple separating device and multiple delivery rails; or with a long-term recirculating storage conveyor. Even more telling is the fact that by now other suppliers in the field are also falling back on specific Koepfer automation concepts. For batch sizes of as few as 30 – but especially of 50 and over – and cycle times of one to two minutes, the concept most certainly makes economical sense.
Based on its tried and tested polymer concrete base and a minimum of eight active CNC axes (one of it for the gantry loader) Koepfer relies, as ever, on its closed-loop framework construction. In contrast to U-shaped vertical machines the closed-loop force distribution prevents a possible “deflexion” of the tailstock / main spindle axis – even under the highest clamping and machining forces. With regard to control systems – the K 200 uses the somewhat exotic BWO; but the people in the know believe that it very much has a right to existence in this particular environment. Equipped with touch panel, the control also features a 1 MB memory.
By the way …
Armin Wacker, head of Sales and Marketing:
„A few years ago nobody even thought of developing such a milling head. There really was no call for it then. Today approximately 80 percent of our K 200 Gear Hobbing Machines are equipped with the shifting milling head."
And here is something else that should prove interesting
For existing machines Koepfer offers an angular milling head that serves as adaptor for the shifting milling head used for the manufacture of single- and multi-start worms.
The advantages of the K 200 at a glance
- The universal shifting milling head gives great flexibility and ensures that it can be used for a wide range of workpiece geometries and production processes, such as tangential milling, radial milling, soft finishing or soft pre-machining with hard finishing.
- The Koepfer dialogue programming software is extremely easy to handle and allows for menus to be navigated without problem, even be the unqualified operator.
- Its outstanding precision qualifies the K 200 also for safety-critical applications in, for instance, the aerospace industry.
- The machine’s high degree of flexibility allows for the incorporation of almost any customer-specific solution to automation.
- The integration of the machine into manufacturing cells (e.g. gear hobbing, washing, measuring and damage-free unloading) poses no problem.