Drilling Technology More Process Reliability in Thread Production

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Automated production initially presented Sysbohr with challenges in thread production. Stable automation in unmanned production was only achieved with a change to the process.

Since it was founded in 2004 as a design office, the Fulda-based (Germany) company has developed well. The establishment of in-house production in Hünfeld was not intended to replace contract manufacturers, but to increase production capacity. External manufacturers, some of whom have been supplying Sysbohr for over 20 years, will continue to do so. With production in Hünfeld, the manufacturer can react more flexibly and has its delivery times better under control.

"If a customer requires an additional flushing hole on their drilling tool, for example, this is redesigned in Fulda and manufactured by us according to the requirements," says Production Manager Sebastian Reith, describing one of the company's great strengths: "Tailor-made special designs can be implemented individually and quickly here. Sysbohr supports projects from design to the finished system and optimally adapts drilling systems to the prevailing ground conditions and the requirements of the construction site. Tools and accessories are sold worldwide.

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The portfolio of mainly in-house products includes drill bits, drill pipes, flushing heads and drive units. Typical quantities for special tools are in the single-digit range, but batch sizes of up to 200 units are also achieved for drill bits for the wholesale trade. The majority of customers come from the construction industry, where the tools are mainly used for securing excavations and tunnels. In some applications, the drill bit remains in the borehole and is considered lost. In most cases, however, the drill bit and drill rods are provided with threads instead of an easily detachable bayonet catch.

Production Rapidly Expanded

Production in Hünfeld , Germany, started with a machine from DMG Mori and was expanded very quickly in order to achieve the desired production capacity. In the meantime, six turn-mill centers from this machine manufacturer fill the hall. A turret lathe from Okuma, which has a larger spindle opening, was purchased especially for processing large tubes. All the machines are equipped with robots. Despite the relatively low quantities, automation is worthwhile due to the long running times:

We can completely finish our products on the machines, i.e. ideally, raw part in, finished part out. With ten components, that can add up to five hours of running time. That's a late shift.

Sebastian Reith, Production Manager, Sysbohr GmbH

The workflow is such that the ten employees produce individual parts in the morning and run in one part per machine towards the evening. Robots then take care of the rest in the unmanned late and night shifts.

However, what sounds like cost-effective production initially presented Sysbohr with major problems in the production of trapezoidal threads, which are required for almost all components. The required process reliability was lacking because, especially with thin material thicknesses, vibrations occurred again and again, which left clear chatter marks on the internal threads and produced poor surface qualities. In some cases, automatic production stopped after just a few parts or it ran through completely despite a damaged cutting insert and produced rejects.

We never knew what to expect when we arrived at work in the morning. The pallet may or may not have been processed.

Sebastian Reith, Production Manager, Sysbohr GmbH

The Problems Only Came With Automation

The pavers tried out many things, experimenting with different infeeds and speeds. However, the repeat accuracy in the automated process always left a lot to be desired. Although Ingersoll was represented as a tool supplier in Hünfeld right from the start, the problematic inserts came from another manufacturer. Sysbohr had taken over the process, including the threaded inserts in a special design, from a supplier who never had any difficulties with it. One crucial difference, however, is that the contract manufacturer always has an operator at each machine who can intervene immediately in the event of irregularities before a problem arises. This applies to vibrations as well as chip jams, which also occurred frequently at Sysbohr.

Ingersoll was to provide a solution. Daniel Rudolph, technical consultant at the tool manufacturer, analyzed the problem: "The special threaded insert used to turn the internal thread caused vibrations that built up during the process due to its engagement width and relatively long clamping. Instead of the heavily pressing solid profile plate, we used a grooving tool that exerts less pressure."

As Sysbohr had already had good experience with the Ingersoll cutting insert, it was tried out without further ado. However, because thread cutting is fundamentally different from grooving, existing process sequences could not simply be adopted. The machining speed initially achieved proved to be far too slow. Simply changing the tool was therefore not enough.

"Process reliability was only achieved by completely converting the process," reports Daniel Rudolph.

We not only changed the insert, but also looked at and assessed the entire process, from the cycle to the cutting insert. The machining process was changed and we now do thread cutting rather than thread turning.

Daniel Rudolph, Technical Consultant, Ingersoll

The transition to a 40 millimeter tool shank proved to be very efficient, as application engineer Christopher Hees explains: "Ingersoll chose a larger boring bar in order to achieve a better length-to-diameter ratio. This meant that significantly more infeed could be used and higher cutting speeds were possible. Compared to the first machining tests using the grooving process, machining could be carried out with fewer cuts in half the time. We switched to this precision sintered TDXU 3E-0.3 indexable insert in order to maintain accuracy in the process. In terms of accuracy of fit, the threads now always come off the machine in the same quality."

The multifunctional grooving insert is suitable for radial, axial and internal grooving. With its soft cut, it is suitable for medium to high feed rates. It also produces small chips that can no longer get caught on the tool changer or in the chuck, which contributes to process reliability in unmanned production. In contrast to the previously used solid profile inserts, it is a standard tool that Ingersoll can deliver the very next day if required. Delivery times of three to four weeks were required for the custom-made threaded inserts.

One Cutting Plate For Everything

The pavers have gained a further advantage: The plate to be used is always identical and replaces several special solutions that were previously required for different threads. Sysbohr requires the full-surface threads for all component diameters between 50 and 600 millimetres with different pitches. The universal machining was also made possible by optimizing the programming. In close consultation with Ingersoll and Sysbohr, DMG Mori adapted an existing thread cycle on the machine to the special requirements.

A normal metric thread form, as is usually used for thread production, was out of the question for Sysbohr due to the often harsh operating conditions of its products. "We can't use such pointed threads because you always have to reckon with sand and dirt on construction sites. Nevertheless, an excavator must be able to reliably screw the parts in and out," explains Reith. This also makes it clear why good round thread surfaces are more important for production than the last micrometer of precision.

The user is very satisfied with the results achieved. The machining time has remained practically identical, while the tool life has improved slightly with the Ingersoll tool. Above all, however, it is now also possible to work reliably in the unmanned late and night shifts. This has created the desired production capacity and increased quality at the same time.