A visit to STIEBER GmbH in Heidelberg shows that small investments can achieve significant effects in production. In association with the affiliated companies—Formsprag and Marland, STIEBER is a world market leader for freewheels and escapement mechanisms. As part of the ALTRA Industrial Motion Group, a worldwide leading manufacturer of mechanical drive elements, STIEBER uses the ALTRA Business System (ABS). The system’s integrated approach aims to optimise quality, deliverability and costs, with the result of maximum possible customer satisfaction. In pursuit of this goal, the focus is equally on processes, systems, materials and employees. The main motivating forces are Kaizen and the continuous improvement process.
Higher flexibility and lower costs
What, at first, sounds theoretical quickly becomes concrete, when one takes a look at the soft machining department at STIEBER. During a Kaizen event with the ALTRA group management at STIEBER in Heidelberg, Andreas Sandmaier, who is responsible for production controlling, transformed the heretofore conventionally organised soft machining department into a cell production system in which the workpiece passes through all stations of the cell directly, i.e. without lengthy waiting times. “Instead of receiving prepared blanks for sawing, our machining now starts with sawing of the pre-machined part and ends shortly afterwards with the completed part,” Sandmaier explains.
The result is impressive: this procedure reduced the processing times by two to three weeks. Short-term orders can be produced with much higher flexibility. “Today we can respond to customer requirements much more quickly, and the throughput of parts has increased significantly, without putting stress on the employees,” the specially trained Kaizen leader confirms. He and his team were actively involved in the process from the very beginning. “Such a solution requires people who understand and also accept the principle.” Basically, it was a matter of streamlining the organisation and eliminating wastefulness wherever possible. The required machines were arranged to minimise the distances between the stations; all machining programmes were merged; all required tools are now on shadow boards directly at the location of the machine. While one employee operates the machines, the other sets up the next job.
The team recognised early on that the set-up times on the two lathes slow down the process considerably. “There are days when the early shift has to change the set-up six times. That takes between 15 and 20 minutes each time,” Sandmaier summarises. If covers are machined in quantities between five and twelve, the number of set-up processes is even higher. The first step was to equip all existing jaws with bolts and T-nuts, to allow faster changing. “That saves a few minutes, but in the end, each set-up process still takes 12 to 15 minutes.”
One hour of set-up time saved per day
The SCHUNK PRONTO jaw quick-change system finally provided the solution. “We were still in the middle of reorganising when the new change system was launched,” the team leader relates. The first test series already resulted in significant savings potentials. The standard system was further optimised and today, his team needs only two to a maximum of five minutes to change from one product to another. Due to the parts spectrum, usually only the clamping attachments have to be changed, which takes only a few minutes. The savings in set-up times for each lathe add up to at least one hour per day, according to Andreas Sandmaier. “The system increases the productivity on our existing lathes by 10 to 15 per cent, without the necessity for extensive investments. With one small step, we have made huge progress.”
The jaw quick-change system was particularly developed for conventional lathe chucks with bolt-on jaws. It reduces the absolute set-up time for a complete jaw set to only 30 seconds, which is about 95% less than with conventional solutions. It combines serrated supporting jaws (1/16" x 90° or 1.5 mm x 60°) with special quick-change inserts, which allows expansion of the clamping diameter within seconds by up to 55 mm on soft jaws and by up to 45 mm on claw jaws, without having to move the base jaw. That is eight times more than what was achieved with conventional power chucks. All that is necessary for fast jaw change with repeat accuracy is to loosen the interchangeable insert with an Allen key, remove the insert and replace it with another one. This eliminates the risk of incorrect positioning. In locked state, six-sided form-fit clamping ensures maximum process stability and enables high force and torque transfer. Different supporting jaw variants are available for small, medium, and large clamping areas, depending on the particular application. As top jaws, the innovative family-owned company offers hard claw inserts for different diameters and clamping ranges as well as soft interchangeable inserts for finished part machining. Once they have been turned out, the latter can be reused again and again on the system. The clamping depth is variable with the workpiece stop. An adjusting sleeve facilitates the jaw change.
Complete line of quick-change jaws
The jaw quick-change system can be retrofitted on all fine serrated lathe chucks of the sizes – 200, 250, and 315, regardless of the manufacturer. The modular design of the components allows the individual and, therefore, very economical combination of the single components. This also means that the interchangeable inserts are compatible with all supporting jaws; only their position varies. A specially developed set-up cart provides for orderly storage and fast accessibility of all claw inserts, soft interchangeable inserts, supporting jaws with mounted bolts and T-nuts, as well as the adjusting sleeves. A clearly structured table book enables fast selection and mounting of the single components. Provisions were even made for storage in the machine: all parts can be transported on a tray and positioned for mounting directly within the machine by means of a quick-acting connector.
This system is especially advantageous when it is necessary to increase the productivity of existing lathes. “Instead of replacing our existing lathe chucks with quick-change chucks, investing in the jaw quick-change system is a better idea as it helps shorten set-up times significantly,” Sandmaier ascertains.