IWC Schaffhausen, the Swiss luxury watchmaker, is using a micro-technology index chuck from Röhm to achieve the machining precision required for the Calibre of its luxury timepieces. Calibre is the watchmaker’s term for the centerpiece watch plate of mechanical luxury watches that command prices that can easily run to tens of thousands of dollars and more.
“Today, production of parts for the Calibre is only possible with the help of ultra-modern CNC-controlled precision machines and machining centers,” said Christian Indlekofer, head of IWC’s production of workpieces. “Customers not only expect top-quality materials, superlative design, and functions, like the date, second time zone, and calendar, they also want a valuable wrist watch that exhibits supreme accuracy.”
IWC is able to achieve maximum precision, repeatability, and accuracy in just one clamping for the dozens of machining steps and number of tool changes that are required. “Process reliability and repeat accuracy in production of the individual parts are only possible with the help of machines,” said Heiko Zimmermann, IWC’s head of industrialization. “Assembly, on the other hand, based on a long tradition, still takes place by hand.”
IWC’s Kern Micro ultra-compact five-axis machining center has outstanding automated functions and works accurately right down into the nano-range. A handling robot lays a brass plate measuring 50 × 50 × 3.25 mm in place on the Kern machine. “In the old days, we had to clamp the watch plate on three different machines,” said Zimmermann. “This naturally took a whole lot longer, and also entailed the risk that the final result might have been less accurate than is possible today. After just one measurement of the workpiece, which takes into account the tolerances of the blank, the system gets its zero point.”
The power index chuck from Röhm’s micro-technology series allows IWC to carry out all the necessary operations on the plate in just one clamping position. The processes involved are milling, drilling, thread cutting, piercing, and fine machining of the edges. Even the horizontal drilling for the winding shaft from the outer edge of the plate to the inside can be accomplished without a position change.
The watch plate is the central component of a mechanical watch. This is where all the parts of the watch mechanism will later be mounted from the bridge to the balance cocks, the jewels (rubies are used) and the pins, axles and cogwheels. Depending on the complexity of the design, a watch mechanism of this kind may consist of several hundred very minute components.
Until the point where the index chuck relinquishes the blank as a finished plate ready to be removed, the Kern Micro performs a remarkable 270 operations to a precision of ±2 µm on the works side and the dial with a total of 54 changes of tool. Each tool will be used only once. The machining steps and their sequence are very carefully planned. Because the index chuck turns the plate in less time than it takes to change the tool, one tool always carries out operations on both sides of the plate before a new tool is substituted.
With 101 tools in the easily accessible tool cabinet (which can actually accommodate as many as 209 tools), all process steps are accounted for.
The precision part that is produced results in what eventually becomes a 40-mm diameter watch plate with drilled holes as small as 0.38-mm diameter and threaded holes and space to accommodate the mechanical parts. In some areas as much as 0.5 mm of the material of the blank is abraded. This in turn causes particular problems for the index chuck. If the force applied to the brass workpiece were to cause bending or even breakage, it would be a disaster.
Above all, in connection with the piercing process, the forces in play are not to be underestimated. Any warping would lead to imprecise results. So a workpiece support has to be used—a kind of end stop. This, however, is far from being a simple matter, seeing that the support, which strengthens the plate from below and counteracts warping, must continue to act from below in the just same way after swivelling. For this purpose, Röhm has developed a unique and sophisticated solution which is a world first. “After the chuck has been swivelled, a pneumatically activated clamping yoke rotates through 180° so that it once again supports the workpiece from below,” said Damiano Casafina, managing director of Röhm Switzerland, who was responsible for this innovative and yet simple solution.
And yet here too the devil is in the details. After the clamping yoke has revolved, it cannot be permitted to strike the plate with the full impact of its swing—otherwise the plate could be distorted, or catapulted out of the clamping jaws. To prevent this, Röhm has incorporated a kind of brake, which gently moves the support into position from below on both sides of the plate, slots it into place, and carries out the necessary supporting function. As a result, all machining processes can be carried out with the required precision.
How exactly does this mechanism function? Röhm’s Casafina keeps his cards close to his chest. “Of course that is and will continue to be our professional secret.”
Since October 2015, the Kern Micro has been up and running in combination with Röhm’s swivelling power chuck. “The unit is now productive for something like 140 hours in the week,” Zimmermann reports with some pride. “This forms the basis for manufacturing thousands of plates in the space of a year with complete process reliability and repeat accuracy.”
“Above all, we want to maximize flexibility, as well as increase productivity,” said Christian Indlekofer. “A fourfold [position] chuck with swivel function has been envisaged for the purpose. Kern and Röhm are already working together on the design and expect to achieve the same success with the new device as it has in the past through the close cooperation between the two companies.
For more information from Röhm Products of America, go to www. Röhm-products.com, or phone 770-963-8440.