8 October 2013
Where many other manufacturers of roller bearings draw the line, Liebherr really starts to get going. On the Biberach-an-der-Riss site, in southern Germany, large roller bearings ranging from 40 cm up to 6 m in diameter are machined on gigantic carousel lathes and boring machines, often with lengthy machining times and two tools in action simultaneously. Running in new NC programs could previously take days. The deployment of TopSolid'Cam from Missler Software has not only drastically shortened the running-in times, but also accelerated the entire manufacturing process.
The grounds of the Liebherr factory in Biberach are the size of 58 football pitches and lie, like the town itself, on the banks of the river Riss. On 1 January 2012, the two business domains of Liebherr-Werk Biberach GmbH - cranes and drive technology components - were separated into two legally independent companies. Liebherr-Werk Biberach GmbH is now exclusively responsible for the crane manufacturing activity, while Liebherr-Components Biberach GmbH takes care of the development and manufacturing of drive technology components for the Liebherr Group and other customers. These components include not only the aforementioned large roller bearings, but also planetary gears and winches, electrical machines and control technology. The growing number of external consumers include, for example, the manufacturers of wind farms, as well as companies from the maritime domain and other construction machinery manufacturers. The multifaceted crane program of Liebherr-Werk Biberach GmbH includes machines covering all kinds of systems and size classes, and offers the appropriate lifting technology for every job in high-rise construction.
The NC programmers of these two Liebherr companies work with the same CAD/CAM system, since TopSolid'Cam provides optimal support both for the manufacturing processes in crane technology and the manufacturing of large roller bearings and gears. Whereas, in the field of large roller bearings it is turning and boring on 4-axis carousel lathes and 2-spindle boring machines that tend to predominate, in drive technology many gear components are completely machined on modern mill-turn centres. In crane production, large boring machines and machining centres are used. Of the approximately 100 in-house NC machines of various types and manufacturers, the most important have been linked up to CAM programming. For high flexibility and universality, they have almost without exception been fitted out with the same Siemens control system.
Multiple variants and many changes
For those working on the CAM programming and involved in the machining, the multiple variants, the ever-shorter delivery times and the many changes that have to be implemented, often only shortly after the start of manufacturing, constitute a constant challenge. The capability of reacting flexibly to modified requirements is, however, also one of the strengths of the Liebherr production site. In order to improve this still further, and make modifications even more quickly on the machines, the CAD/CAM process chain should be made even more universal. The designers in Biberach have for over ten years been modelling cranes and drive technology components in 3D. For this they use the direct modelling system of PTC. The NC programs for the machining were at first generated using a simple 2D editor, which made the implementation of changes very time-consuming and was prone to errors for complex multi-spindle machining. As such, the workers had to run in new NC programs with the utmost care, since the workpieces may be worth a six-figure sum.
Finding the right system for a universal 3D-CAD/CAM process chain was a demanding task. Liebherr wanted a uniform CAM system for all manufacturing domains, machine types and machining processes. The software had to support, as well as the milling and boring, above all the turning too. It would also have to have powerful synchronisation functions, in order to be able to distribute optimally the parallel machining with two tools on both spindles. Programming with two lathe chisels or two boring spindles brings down machining times considerably and saves money.
Customer-specific postprocessors
Following in-depth market research, they opted for the French company, Missler Software, as partner. Missler Software's TopSolid'Cam is used in Biberach by no fewer than 15 programmers. Liebherr found an efficient partner for the introduction of the program in the form of AdeQuate Solutions. In several stages, the Lahr-based systems vendor linked up the comprehensive machinery pool of the various manufacturing domains to the CAM solution. One of the things that distinguishes this solution in particular is that the user programs in the virtual machine environment.
In all, AdeQuate Solutions has either written or adapted specifically for Liebherr over 30 different postprocessors for linking up the various machine types for crane technology, large roller bearings and drive technology. Liebherr imposes high demands on the postprocessors, in order to achieve the shortest possible machining times while at the same time keeping the programmer effort to a minimum. What is also important is to have reliable and rapid support from the application partner. AdeQuate Solutions has also produced a few special features for Liebherr, such as for the machining of large roller bearing raceways or the manufacturing of winch drums. This has made it possible to consolidate up to 20 individual operations into a single machining sequence, thereby considerably reducing the programming investment.
TopSolid'Cam offers the possibility, for operations such as the tapping, roughing or turning of similar recurring contours, of defining uniform methods that can be used over and over again. For further enhanced efficiency, the Liebherr programmers also use the subroutine technique, in order to have to program recurrent work steps just the one time. The subroutines can then be used on a wide variety of workpieces and are automatically called up by the machine controller.
Link to tool management
Unlike the previous 2D programming system used by Liebherr, the CAM programmers can more easily optimise the machining on the computer with the aid of the 3D models, so that less correction is required when running in the programs. This enables the running-in times for large and complex components in crane technology to be reduced by some 60 to 80%.
In order to be able to reliably simulate turning, boring or milling with TopSolid'Cam, not only are 3D machine models required, but also realistic models of tools and jigs. The users do not, however, generate the tool geometry in TopSolid'Cam; they obtain the corresponding parameters from the separate tool management system, which Liebherr installed at the same time as introducing the CAM solution, in order to improve the overview of the immense tool stock, and so as to have to keep fewer tools in reserve. Currently, there are around 10,000 tools in the solution, with the actual values determined from the tool presetting. In conjunction with the manufacturer, AdeQuate Solutions has linked up the tool management system to TopSolid in such a way that the users, when programming, can access the real tool data. The standard jigs and self-developed jigs are also filed in the tool database.
Liebherr has, moreover, linked up the CAM solution to the PDM system, by means of which the CAD data from design is managed, leading to an enormous improvement in information transparency on the site. The CAM programmers save their NC programs together with premachining drawing, tool list and other item-related documents in the PDM database, so that factory-wide it is possible to see whether or not the manufacturing documents already exist for a particular design. Finished NC programs are called up directly to the machine via a DNC system and, in the event of changes to particular parameters during machining, are resaved, so that the CAM programmers can rework them if required. In this way, Liebherr obtains universal design and manufacturing data management.
Producing the manufacturing documents has also been made considerably easier and quicker with the new system. Accompanying documents such as tool lists, setting sheets or jig diagrams become practically a by-product of the CAM programming. Not only is this beneficial in terms of time savings, but the universality of the data is also significantly improved.
More efficient CAM programming
There is further optimisation potential in the data chain upstream of the CAM system. This relates to the fact that the models from design need to be transferred to the CAM system in a neutral format. These non-parametric CAD models are produced with nominal dimensions, so that the CAM programmers need to convert them following import into median models.
Not only is this time-consuming, but it also has the disadvantage that the NC programs cannot be updated at the touch of a button in the event of subsequent changes to the CAD geometry, because the nominal and median models are not directly linked to one another. There exists the possibility to evaluate two model versions with the aid of the geometry comparison function in TopSolid'Cam, although the processing of the modified topology must be carried out manually. In order to resolve this problem satisfactorily, a more thorough integration of CAD and CAM systems is required.
Despite the gaps in the CAD/CAM process chain, the CAM programming at Liebherr in Biberach has become more efficient and, above all, more secure. For multiple-axis machining, the synchronisation of operations on both axes makes for minimal machine running times and running-in times. The managers at Liebherr are altogether highly satisfied, and the long preparation and introduction phase has been well worthwhile.
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