In an era of domestic and international competitive pressures, gear manufacturers with fabrication sites throughout the United States and internationally are constantly faced with the pains of production challenges and quality control. As a result, gear manufacturers are continually in search of the latest state of the art workholding opportunities. The trend remains in the direction of increased flexibility, efficiency, and accuracy in order to gain the competitive edge. These challenges include, but are not limited to, setup and changeover times, rigidity, and precision. Manufacturing gears is a very intricate process, and that’s why HAINBUCH invests deeply in employee know-how and the latest technologies. We focus on industry needs and strive to be a step ahead of the competition to provide customized solutions with standard products. If you can machine it, HAINBUCH can hold it. Consequently, to ensure this process the company is continuously involved in research and development as it pursues improvements in providing answers to gear-manufacturing challenges.
Workholding Tool Selection
The North American gear industry typically utilizes dedicated or homemade workholding designs. While acceptable, these systems do not provide the most flexible, accurate, or efficient solution. One of the most significant yet overlooked opportunities in which gear manufacturers can gain the competitive edge is by means of improved workholding solutions. The perfect clamping and centering device can minimize the work piece changeover times by as much as 50 percent while concurrently improving quality and machine utilization, increasing the value of machines and profitability.
What to Consider
The ideal workholding solution for gear manufacturers enables quick part-to-part changeovers that can locate and lock on the gear’s pitch diameter, work with pieces having virtually any number of teeth, and can compensate for varying teeth spacing and pitch values. While changeover time is essential, be sure that your workholding system also ensures maximum repeatability and rigidity. “You don’t want to sacrifice manufacturing quality for speed,” according to Sylvia Rall, marketing director of HAINBUCH Spannende Technik. “That’s why our engineers have endeavored to develop and design some of the most innovative systems that give you the best of all worlds, such as HAINBUCH’s CENTREX interface centering system and the MANDO T212 segmented mandrel. HAINBUCH is not only the original designer, developer, and manufacturer of this type of system, but we have been the experts in the field since 1994. We have the knowledge and experience that supports this incredible workholding solution.” Figure 1
The CENTREX Interface Centering System
The need for increased precision and rapid setup times has resulted in the development of the high-precision CENTREX centering system, the compact patented solution and first automatic zero-positioning pallet system already in use with various HAINBUCH products. This simple system uses precision steel ball bearings in a rubber ring in conical positioning elements integrated into the pallet system and guarantees an exact repeatability of less than .003 mm, as well as a perfectly level contact. The four bushings and positioning cones are ready mounted, allowing the pallets to be fitted to each other with exact repeatability. With a mini zero position system in HAINBUCH standard pallets, it will save users space with part specific equipment, time, and money. If you have not seen this centering system in action you will appreciate that a plate fitted with CENTREX is mounted with exact repeatability, and that a dial indicator reading 1 micron shows no deviation. This system allows the changeover of the entire chucks to be performed while retaining process reliability and without alignment. The CENTREX interface system performs the centering function, with accuracy of less then 3 microns. In addition, due to its diversity of applications this system drastically minimizes setup times and interruptions in production.
Here’s how it works:
• The taper bushing is pressed into the carrier pallet, and the taper mandrel is pressed into the base plate.
• If the carrier pallet is positioned onto the base plate, the pallets will initially have no face contact. Under these circumstances the internal and external cones make only indirect point contact through the bearings. If a force is now applied to the carrier pallet, the superficial surface of the tapers deforms in the elastic range.
• The clearance for the bearings thereby becomes greater, and the taper bushing can move in the direction of the base plate until face contact occurs.
• As the superficial surfaces of the tapers have the same hardness universally, the mandrel always has the tendency to move toward the center of the taper bushing.
• Through the use of two CENTREX units, the carrier pallet is exactly aligned between two defined points.
The obstacle to complete machining is often the lack of a sensible workholding device that is able to clamp a work piece from the inside. A jaw chuck offers only limited help, and mandrels currently on the market leave much to be desired regarding accuracy, rigidity, stoke, and usability. The central element is the clamping bushing. Because conventional clamping bushings are made out of spring steel and are only annealed and therefore soft, they have to “bend” to clamp the work piece. HAINBUCH’s segmented bushings are made of chrome/nickel case-hardened steel that is very hard, extremely wear resistant, and rigid. All contact surfaces are ground in one operation, guaranteeing optimum concentricity. Figure 2
The mandrel type T212—known as the MANDO T212—without a draw bolt is just what the doctor ordered to eradicate the pains of the gear manufacturers’ production challenges. The MANDO T212 offers a solid and minimum ID clamping range for blind bore Ø of 8 mm (.31496”) and up to 100mm (3.937”) with pull-back effect. This T212 segmented mandrel has long been in use for customer specific solutions because of its versatility. It can be used in both rotating and stationary applications, and it has an added clamping length, eliminating the need for a projecting draw bolt. The utilization of a pull-back effect provides the powerful holding strength needed for maximum rigidity, while also offering concentric precision of less than 10 microns. Due to HAINBUCH’s own vulcanization process, there is virtually no vibration. The proven mandrel principle is also available as a stock item in a standard series. The T212 is particularly impressive with short distances and expressly for blind bores and small components, including gearing. Since it works without a draw bolt there is no loss of clamping length, and the work piece can be gripped with the pull-back effect in the secure manner gear manufacturers call for and are accustomed to. Also available even with the smallest Ø, a sensational 8mm (.31496”), the new mini mandrel in XXS size naturally has the typical HAINBUCH segmented clamping bushing with the vulcanized rubber to metal connection. The T212 offers maximum accuracy and holding power in the clamping range of 8mm (.31496”)-100mm (3.937”) Ø. Due to the easy-to-operate coupling on the segmented clamping bushing, changeover times are minimal.
Addressing Clamping Range
Small batch sizes are an everyday fact for HAINBUCH, but clamping ranges up to 420mm are the exception rather than the rule. This is exactly the clamping range that was requested by one customer. The international transmission and motor manufacturer builds to order and was looking for a precise, user-friendly setup solution requiring no time-consuming adjustment of the various clamping devices. The company found a solution at HAINBUCH. It weighs an impressive 1.3 tons, and it also has visually imposing dimensions—the largest segmented mandrel ever produced by HAINBUCH. Figure 3
The patented CENTREX centering system in this segmented mandrel, which was developed for China, automatically provides for proper adjustment during changeover, in addition to exact repeatability of the position. The giant mandrel, which has a segmented bushing equipped with a specially developed rubber compound, can clamp gears with an outer diameter of up to 1 meter with concentric precision on the Gleason-Pfauter hobbing machine. In internal tests, the repeatability was even below 0.005mm. “The great challenge was not only the large clamping range, but especially the coordination of the various processes that we were unable to carry out internally,” says Peter Gerster, HAINBUCH production manager. “With more than 200 production orders, the engineering by our team of experts for the end-stop production and nearly 200 external order items—from raw material to the welding construction and heat treatment—all of that has to be managed, and the timing has to be right in the end.” Figure 4
Apparently this was achieved, with a follow-up order involving a Liebherr LC800. Test results have proven that ideal workholding solutions will provide gear manufacturing with the accuracy and rigidity that are essential for product excellence, while easing the pain of production costs and prolonged setup and changeover times. Test results have proven that ideal workholding solutions will provide gear manufacturing with the accuracy and rigidity that are essential for product excellence, while easing the pain of production costs and prolonged setup and changeover times. Figure 5
By simply mounting the MANDO ms dock on the actuating unit you can clamp your work piece manually, precisely, without vibrations, and with a minimum of setup time. This is made possible by the exceptionally wear-resistant segmented clamping bushings, which are made of case hardened chrome/nickel steel. Better still, the same mandrels you’ve used in a rotating application such as a lathe, or other machines can now be used in the stationary mode as well. The stationary MANDO ms dock is ideal for machining centers, measuring machines, parallel and angle plate clamping, or on dividing heads. Highlights include: precise and rigid clamping makes “aggressive” machining possible; it’s possible to draw back against the end-stop, stabilizing the clamping; manual clamping can be actuated with a box wrench; it is extremely rigid, with optimal holding power and minimal setup time; simple construction, thus better power conversion; the shortest clamping length possible; and the minimum clamping diameter is 20mm. Figure 6
In addition, the MANDREX is a mandrel whose clamping elements are laminated with a thin layer of wear-resistant hardened steel, yet still preserving its elasticity. The mandrel has an HSK adapter on the left and is clamped with a SPANNTOP pull-back chuck on the right. The pullback effect creates additional rigidity during turning, which is especially important when working with extremely long work pieces. The MANDREX can be clamped with the aid of a clamping cylinder or manually. The principle of the clamping bushing moving toward the spindle, the so-called pull-back effect, can provide substantial stability to the work piece. Even if the relationship of the clamping diameter and clamping length is obviously disproportionate to the size and the length of the work piece, unbelievable clamping results can be achieved. Figure 7
Mandrel type 212: This version allows an optimal clamping length for blind bores. The minimum clamping diameter is 20mm. With this type of mandrel the segmented clamping bushing moves axially on the fixed mandrel taper. That makes the use of an internal front end-stop possible. Figure 8
Mandrel type 213: In principle, it is similar to the MANDO. The opening of the bushing is achieved through the lip on the clamping bolt, and it is suited for smaller clamping diameters of 18 to 40mm. The clamping bushings are delivered together with the clamping bolt. This version is not suited for short clamping length. When the location surface is not perpendicular to the clamping bore, we recommend the dead-length version. Here the clamping bushing only makes a radial motion, which prevents that the clamping length is shortened. It is typically used on a sub spindle. When the work piece is picked up, the dead-length clamping motion avoids having any pulling effect on the component. Figure 9
Mandrel type 611: Mandrel with a clamping bushing that is absolutely fixed in the axial position. Typical applications are short clamping lengths and blind holes pull-back clamping.
Mandrel type 811: Mandrel with a clamping bushing that is in a fixed axial position. Suited for light duty machining and on smaller clamping diameters, it has a minimum clamping diameter of 25mm. Clamping is achieved by pushing the draw bar.