The precise boring mill KG combines precision and flexibility

Gap between classic boring mill and a jig boring machine closed

The new precision boring mill (KG) of the Union brand closes the gap between a conventional boring mill and a jig boring mill from both, accuracy as well as price-performance ratio. The machining accuracy is significantly higher than that of a classical boring mill, but with a higher level of freedom.

Demanding machining tasks require the adherence of the closest tolerances. Many companies have trouble to meet those with their classical boring mills. Therefore, the KG boring mill unites the advantages of a traditional machine with those of a jig boring machine. The precision boring mill design is based on the reliable Union K-series in planer design, which is the ideal solution for high precision machining results. Many detailed optimizations and the thermal stability, the machine reaches a high level of machining.

The precision boring mill KG sets benchmarks in terms of geometrical precision, positioning accuracy and thermal stability, which is achieved by intelligent temperature compensation. The boring mill offers unique flexibility. Easy access to the work area allows for manual process monitoring. In addition, the machine has an extremely high torque.

To avoid heat development, the main spindle is equipped with a ceramic hybrid bearing. A cooling unit with heating and cooling device, temperature-controlled gear oil cooling and water-cooled main spindle and Y-axis drive ensure the highest thermal stability.

The precision boring mill works with tolerances less than 10 µ/2,500 mm relating to straightness and less than 8 µ/m2 relating to flatness. Simultaneously, the contours deep within the workpiece can be machined with high precision. Compared to a jig boring machine, the KG provides significantly higher level of freedom and thus a wider scope of use while keeping costs down.

Verified precision: Manufacturing of gearbox housing

Thorsten Mehlhorn, Executive Director of RSGetriebe, decided to invest in this precision boring mill. The customized gearbox manufacturer from Sonthofen, Germany, faced a challenge many users know: “The high precision standards we require couldn’t be attained with a classical boring mill. A jig boring mill was no alternative due to the disproportionately high costs on one hand, and the missing high level of freedom on the other”, Thorsten Mehlhorn explains.

Instead, the Executive Director searched for an alternative and found the Union precision boring mill.  Precision is a key factor for the products of RSGetriebe: The company is a specialist in the production of high-quality drive solutions for different industries. The customized high-performance gearboxes are used by leading plastic and machine tool companies and in test stand drives in the automotive industry.

RSGetriebe decided upon an investment in a new large machine tool to expand their production depth. The production possibilities should be expanded and the purchase of components reduced. However, it quickly became apparent that a conventional boring mill would not meet the requirements at RSGetriebe. “In addition to the machined workpieces and the required cutting performance, flexibility was a particularly important factor. On one hand, it had to be possible to manufacture the widest possible range of workpieces - not only milling units but also all gearbox housings. On the other hand, we also needed increased accuracies explicitly for milling head production”, Mehlhorn says. The workpieces must be processed with an accuracy of less than 0.005 mm, which concerns the parallelism and coaxiality of surfaces and bores. “On a conventional boring mill, the accuracies we require - without a corresponding measuring strategy - cannot be produced," Thorsten Mehlhorn explains. "The KG, on the other hand, reliably achieves these accuracies and saved us the investment in an expensive jig boring machine."

With a spindle diameter of 125 mm, the KG machines even the most demanding workpieces with repeatable precision. The new precision boring mill was commissioned at RSGetriebe in 2015. Since then, it has impressively demonstrated its outstanding accuracy and reliability in the machining of housings of milling units for boring mills as well as all types of gearbox housings of the special gearbox manufacturer. Gearbox housings with volumes between 1.5 and 2 m3 and weights of up to 6 tons can now be machined without any problems.

An additional challenge posed to the boring mill at RSGetriebe is the mix of different materials that have to be machined. Accordingly, the precision boring mill is equipped with wet and dry machining capabilities. "With these two machining modes, both steel and cast iron bodies can be machined, which greatly broadens the machine's range of applications," says Thorsten Mehlhorn.

In order to ensure constant temperatures during machining, the precision boring mill was equipped with an air-conditioned enclosure with roof and exhaust. This ensures constant machining conditions even with large temperature fluctuations in the production hall. The operating platform is located inside the climate-controlled enclosure. "From here, the work area is easily accessible and the entire process can be monitored manually. This is a real advantage for our operators in their day-to-day work," says the managing director.

Since efficiency is an important factor in gear manufacturing, a pick-up station for change heads has been integrated. A tool changer provides space for 60 tools. Thorsten Mehlhorn is convinced: "Thanks to the pick-up station, the automatic tool changer and also the various milling units, we were able to clearly reduce the process times".

The precision boring mill has once again increased the production depth. "We have to buy in fewer components. In addition, we have significantly increased the quality of our workpieces and, at the same time, reduced the unit costs. Thanks to the high degrees of freedom in machining, we have been able to greatly improve non-productive times," says Thorsten Mehlhorn. His conclusion is accordingly positive: "The KG series of the Union brand with its increased accuracies is an absolutely interesting investment compared to a jig boring machine. The accuracies of the machines are almost identical with significantly higher level of freedom and larger travel paths".

Technical Data: KCG 125 in Operation at RSGetriebe

X-axis mm 2,000 (79")
Y-axis mm 1,600 (63")
Z-axis mm 1,500 (59")
W-axis mm 550 (22")
Table size mm 1.000 x 1.250 (39 x 49")
Table load t 6
Boring spindle    
Main drive kW 31
Boring spindle diameter mm 125
Tool changer: pockets 60

Positioning accuracy: (according to VDI / DGQ 3441, valid in air-conditioned environment only)

Positioning uncertainty Plinear µm < 8
Average pos. tolerance spread Psmaxlinear µm < 6
Reversal error Umaxlinear µm < 3
Positioning deviation Palinear µm < 4
Positioning uncertainty Prot arcsec < 8
Average pos. tolerance spread Psmaxrot arcsec < 5
Reversal error Umaxrot arcsec < 4
Positioning deviation Parot arcsec < 6
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