Designing and manufacturing custom gearboxes for the automotive industry requires the careful combination of opposing criteria if the manufacturer is to increase torque while simultaneously reducing gear noise. An automobile gearbox requires final gears, and also final pinions. In the automobile industry noise characteristics are directly influenced by process technology, therefore transmission gears are ground in a hardened state. In addition to gear quality and surface finish, which also affect noise behavior, the efficiency of the manufacturing process is critical for the gearbox to function at its highest possible capability. For this purpose Kapp GmbH has designed the automated Kapp KX300P Gear Center, a machine that continues to produce excellent results within the automotive industry (Figure 1).
The typical finishing process for mating gears of an automobile transmission on a KX300P can be described as follows: The final gear is a helical gear with 87 teeth, a tip diameter of 310 mm, and a width of 28 mm. The final pinion is also a helical gear with 20 teeth, a tip diameter of 54 mm, and a width of 35 mm. Both mating gears have a module of 2 mm and a helical angle of 26°. After the pre-grind process, the final gear has a stock of 0.12 mm per flank, and the final pinion has a stock of 0.1 mm. The required quality level after finishing is class 6, according to DIN 3962.
In terms of hard finishing, flexibility and efficiency are often a contradiction of terms. Generally, the more options and flexibility a machine design has, the less reliable and efficient its processes are. However, because of its modular component design, the KX300P is able to produce a high level of flexibility, combining various tool and process technologies. The machine optimizes applications as well as specific processes. The KX300P is capable of continuous generating grinding and also discontinuous profile grinding. It maximizes the potential of both processes by allowing them to be combined in one set-up. For the automotive gearbox, both the final gear and the final pinion are ground on the KX300P, using generating grinding technology with a dressing of cylindrical grinding worms worm (Figure 2). The KX300P Gear Center is suitable for external spur gears and helical gears with a module up to 10mm, a tip diameter up to 300 mm, and a gear face width up to 320 mm.
The grinding tool concept for this machine offers many options such as dressable ceramic tools suitable for prototype processing (high flexibility) and also for series production, as well as non-dressable tools for mid-size and series production requiring high efficiency. Either cylindrical grinding worms or one and multi-ribbed CBN profile wheels can be used. The non-dressable tools are made of a hardened steel body with a base profile and galvanically applied CBN plating. Several CBN grinding tools can be mounted on the grinding tool spindle, allowing for shifting in one set-up between roughing and finishing tools. Alternatively, multiple gears may be ground in one set-up.
For the final gear and final pinion the machine configuration uses dressable tools and includes a dressing unit that rotates from a parked position to the dressing position within the work area of the machine. The dressing unit utilizes the machine axes, which facilitates a quick dressing of cylindrical grinding worms as well as profile wheels (Figure 3). A total of six NC-axes position gear and tool, swivel the tool into the crossed angle position, and execute the linear and radial movements required for the grinding process. Both the workpiece and tool spindles have direct drive motors. It takes 0.2 min for the proportionate dressing of one final gear, with a total cycle time of 1.15 minutes. Proportionate dressing for the final pinion is 0.08 minutes with the total cycle time of approximately 0.72 minutes.
The KX300P is equipped with a two-station ring loader that interfaces with a revolving palette transport band for the final gear and final pinion. The ring loader column is mounted onto the machine bed and features two opposing gripper jaws (Figure 4). A pneumatic lifting station picks up the workpiece from the palette transport band, aligns it vertically, and passes it on to the gripper. The opposing gripper in the machine work area removes the ground gear from the clamping device, turns it 180° and passes it on to the lift station, while at the same time the new gear is transferred into the work area and onto the clamping device, ready for grinding. While this gear is ground, the lifting station deposits the finished gear on the palette band and picks up a new gear to be ground. The loading/unloading of the ring loader automation takes 0.15 min for both gear types. The total cycle time (without dressing), therefore, is 1.30 min for the final gear and 0.87 min for the final pinion.
Automation is well worth the investment in the production of final gears and pinions for the automotive industry (Figure 5). At the very least the number of machine operators required for the same workpiece volume is reduced drastically — by approximately 75 percent — and it also expedites the entire production process as well. In addition, the KX300P offers the option of an on-board measuring unit (Figure 6). In conjunction with a Kapp menu-driven user interface of the Siemens Sinumerik 840D, it reduces set-up times for new processing tasks; e.g. should the gear data for the final gear and final pinions change. This machine significantly increases efficiency, and Kapp is committed to support the continuing design of higher precision gearboxes which simultaneously lower fuel consumption.
The KX300P machine will be on display at the Kapp-Niles IMTS booth #B-7030. Along with the KX machine, The Kapp Group will also display its Niles ZE400S Profile Grinder with 400mm capacity (Figure 7).
The S series features an additional 150 mm of stroke length, which provides the machine with excellent internal capabilities and is ideal for finishing internal and external spur and helical gears using either dressable or non-dressable form wheels. It features a cast-iron machine base and column, torque table, and a common CNC dressing device with a high-precision spindle for both internal and external applications. The machine will be displayed with the optional dressable internal attachment. It also features integrated inspection and GMG (grind-measure-grind) technology. Niles’ ZE series profile grinders range from 400 mm to 1,200mm capacity.
Niles, located in Berlin, Germany, offers a complete line of vertical form grinding machines ranging from 400 mm through five-meter capacity. This year Niles shipped the world’s first combination — gear profile grinding and cylindrical grinding — machine. The benefit of the combination machine is that it allows the customer to eliminate a second machine tool and guarantees the concentricity of the gear pitch line to part inside diameter. Additional combination machines will be delivered in 2007 along with Niles’ new ZX630, ZX800, and ZX1000 continuous generating gear grinders.
Kapp-Niles offers a complete process package — machines, tools, processes, and service—supplying its customers with solutions for hard and soft finishing of gears and profiles and specializing in systems for processing external and internal gears and profiles. Kapp-Niles provides customer-specific, optimized solutions and technology support for development and production. It is our mission to help customers realize their goals of safety, higher precision, increased efficiency, and more economical grinding solutions for generations to come.