The quest of the commercial vehicle industry to reduce unit costs and increase productivity in the machining of powertrain components is presenting ever greater challenges to mechanical engineering companies all over the world. Customers demand machines for the complete machining of parts in small batch sizes, using numerous different technologies and achieving optimum machining results in the shortest time possible. The PITTLER PV315, the latest addition to the PV³ machine series for complete machining, has been designed particularly with the requirements of the commercial vehicle industry in mind, and is especially suitable for the complete machining of toothed gearbox parts such as ring gears. Workpieces up to 315 mm are turned, drilled, milled and – uniquely in the field of complete machining – geared inside and out using the Power Skiving method in highly efficient processes.
The advantages of the stock removing complete machining of components for commercial vehicle powertrains are obvious. It reduces costs, since fewer individual process machines are necessary, it reduces the machining time, particularly due to lower retooling, transport and holdingtimes, and it increases component qualitysince numerous functional surfaces can be manufactured in one clamping. It’s no wonder, then, that the commercial vehicles industry – always on the lookout for possibilities of increasing productivity and reducing unit costs – is demanding more and more multi-technology complete machining centres. In view of the relatively small batch sizes compared to the passenger car industry, this presents more and more complex challenges to machine designers.
Complete machining in one single clamping
As part of the DVS TECHNOLOGY GROUP, PITTLER T&S GmbH based in Dietzenbach in southern Hesse is uniting the experience and expertise of the enterprise in the third generation of its complete machining centre series PV³. As well as turning, drilling and milling work, the machines in this series also make thread cutting and deburring work possible and – as the only machine series on the market so far – gearing in complete machining using the Power Skiving method. The PV315, the latest addition to the PV³ family, has been designed especially with the requirements of the commercial vehicle industry in mind, is suitablefor workpieces with a diameter of up to 315 mm and thus ideal for the complete machining of small batches of gearbox components such as ring gears. The inner teeth of ring gears, which are an essential component in the planetary geartrains with crank common in the commercialvehicles industry, are usually cut as straight or helical gearing through involute gearing. Skiving technology, which is mainly used to cut external teeth, cannot be used in this context due to the geometry for inner teeth. Broaching of the gearingis extremely inflexible here, since decisive gearing parameters such as the two-ball dimension and thus the quality of the gearing can be exclusively influenced by the geometry of the broach. The shaping technology usually used for machining small batch sizes is just as inadequate in this case, since the discontinued nature of the process leads to uneconomically long machining times.
Power Skiving within the context of complete machining
The newly developed PV315 which, like allother complete machining centres of the PV³ series is equipped with a multi-function head, Y-axis and tool magazine, gets around the problems of skiving or shaping described above, because it permits inner and outer teeth of quality class IT6 to be manufactured using the continual,CNC-controlled and thus flexible, highly productive Power Skiving method – which has been integrated as a component part of complete machining for the first time. A surface quality with an Rz value of less than 2 μm is achieved on the tooth flanks,while a main time three times lower than if the shaping method were used is achieved. Thanks to the machining processes for both the gearing and the roller bearing seats on the ring gears with concentricity values under 10 μm being carried out with one single clamping, ring gears of an unparalleled quality can be manufactured on the PV315. Unlike a pure gear skiving machine, the tool magazine of the PV315, which has room for up to 20 different machining tools, moves a skiving tool for rough skiving into the machining chamber followed by a finishing skiving tool to work the gearing. This considerably lengthens the tool life of the higher quality finishing tool. Directly afterwards, the gearing can be deburred and chamfered extremely precisely using corresponding tools in the same machining compartment. Completed by toolsfor turning, drilling and milling, the PV315 is the innovative all-rounder for the flexible complete machining of ring gears.In addition to the potential tool cost savings, moving different types of tools into the machining chamber also allows the flexible adaptation of individual steps of the complete machining process at a later date. Since the ring gear is only clamped once during the whole process, reclamping faults can be completely excluded.The retooling, transport and holding times that usually accompany retooling processes are no longer required. Renowned gearbox manufacturers talk about a “Small Factory Unit” in this context – an independent unit which is capable of finalising a component flexibly using several different technologies.
Automation and measuring technology integrated if required
Depending on customer wishes, PITTLER T&S GmbH can extend the PV315 both by custom-fit measuring technology e.g. a post-process measuring station, which can be used to identify deviations and correct these afterwards, as well as by automation solutions which make machine loading by robot or integrated workpiece return possible. As a supplier of a complete Small Factory Unit the Dietzenbach-based company issues a process and cycle time guarantee. Compared with conventional lines with several individual process machines, the lifecycle costs of the PV315 are considerably lower due to both the lower purchasing costs and the lower energy consumption. In addition, the PV315 has a footprint of just about 9 m², significantly less than the space required by concatenated lines.There are other machines in the PV³ series available for workpiece diameters larger than 315 mm: PV630 (up to 630 mm), PV1250 (up to 1250 mm) and PV1600 (up to 1600 mm).
Germany 
