Higher Productivity through Complete Machining
The length of the respective processing time per machine has become an established yardstick for the performance of manufacturing processes with regard to costs. It is generally accepted that the shorter the primary processing time, the more efficient the process.
The exception proves the rule. The use of multifunctional high performance tools can sometimes extend the production time on a single machine. However, when analyzing the whole process, significant savings are achieved.
This logic applies to a new multifunctional gear cutting system that machine tool maker Liebherr and specialists at LMT have developed together. By integrating tools for various processing steps in one system, producers can finish gear wheels in a single operation. As costly set-up and adjustment times are elimninated, costs per piece drop and productivity increases.
The smooth running, high energy efficiency and exceptional durability of modern gear systems depend largely on the quality of the gear wheels. Their production therefore requires an accordingly high input of resources.
Hobbing has established itself as an extremely economical process for the production of externally toothed gear wheels for the car industry, large gear systems and energy technology. In the past, however, manufacturers have had to carry out the individual work processes of milling, demurring and smoothing with different tools and sometimes even different machines.
Dr. Oliver Winkel, application engineer at machine tool maker Liebherr, approached LMT in 2004 and asked whether it would be possible to combine these work processes using an appropriate tool system.
“In the course of discussions with our customers we had discovered that the total processing time could be significantly reduced by hobbing in one operation,” recalls Winkel.
“ In terms of machinery, our LC series hobbing machines and new control software offered us the possibility of realizing the appropriate movements. We saw that the precise realization of complex tool movements and their combination with the turning of the work piece represented a competitive advantage. What we lacked to be able to exploit this advantage was the appropriate tool.”
The specialists at LMT were the right people to ask. At the end of 2003, the company had already developed the Chamfer Cut, a hobber that could be combined with a gear cutter and was able to demur the facing edge in one operation.
At that time, however, limited software and control capabilities meant it was not yet possible to use this cutter industrially. The Liebherr machines were the first that could move and control the tool and work piece with enough precision.
The Twist Free Hob with Chamfer Cut combines a roughing hob, two tools to demur and chamfer the top and bottom flanks of the work piece and a finishing hob – clamped onto one arbor.
Manufacturers can now produce finished gear wheels in one step using Liebherr gear cutting machines or other installations that permit appropriate movements of the tool holder. Unit costs are significantly reduced by the integration of the different processing operations.
Towards an industry standard
The degree of innovation involved is clearly demonstrated by the integration of the various processing steps.
“During development we concentrated on integrating the different functions into the tool rather than improving each one individually. Of course, that lengthened the processing time on the hobbing machine,” explains Oliver Gerent, and Oliver Winkel of Liebherr adds, “What many of our customers saw first and foremost were the longer primary processing times and higher tool costs. We then had to explain which processing steps, machines and tools they could save by investing in the new technology.”
In addition to the cost-saving potential, with the new tool system Liebherr and LMT also eliminated twisting for the first time, a process-related disadvantage of hobbing compared to scraping. This achievement attracted considerable recognition in the industry. The specialist journal Maschinenmarkt distinguished the tool system with the MM Award, a prize for innovation.
In the meantime, the new tool system has proved itself in everyday practice. Because the tools are designed to meet customers’ specific requirements, it is possible, for example, to modify the pressure angle of the system in a specific way to completely compensate for tooth twisting or to achieve targeted contrary twisting.
Above all, customers that produce high-quality components are demanding greater flexibility and increasingly complex movement profiles. Accordingly, the demands on tools are also increasing.