22.01.2015

URMA EXPERIENCE - ABB

«Turbo-Reamers» for ABB turbochargers

«Porsche 911 Turbo» is the benchmark for speed, safety and precison on four wheels. The 911 Turbo equivalent in reaming is UrmaCircoTec RX. By using CircoTec RX reamers, ABB Turbo Systems in Switzerland was able to realize advances in manufacturing technology which are simply sensational. Even more important: the process reliability increased remarkably at the same time. ABB turbochargers are important factors for safe and economical propulsion technology for big Cargo ships.

The Porsche 911 Turbo accelerates from 0 to 100 km/h in only 3.4 seconds. That's very good. But it is nothing compared to the acceleration ABB Turbo Systems Ltd achieved in the finishing process of bearing bores for Ship engine turbochargers. Together with the manufacturing experts Thomas Kroker (Manufacturing Technology, Turbocharger Supplies & Production) and Roger Meister (CAM-Programming, both ABB Turbo Systems AG) the Urma Application Engineers worked out a finishing process to machine the main bearing housing for ship-turbochargers in record time, highest accuracy and perfect process reliability. But let's start from the beginning.

Turbos for Cargo ships with up to 80 Megawatt power

ABB Turbo Systems Ltd develops, manufactures, sells and maintaines turbochargers for Diesel- and Gasengines from 500 kW up to 80 MW power. Around 200'000 ABB turbochargers around the world are installed on ships, in power plants, on railroad locomotives, heavy construction machines and mine vehicles. More than 100 service centers all over the world guarantee fast, customer oriented and top quality service – around the clock. Production, central spare part warehouse as well as R&D are located in Baden, Switzerland.

900 employees manufactures 9000 turbos per year

Around 900 people are employed in the business unit ABB Turbo Systems Ltd..They have 38 Machining Centers available in Baden and another 25 in the nearby village Klingnau and manufacture around 9000 turbochargers every year.

Reliability is key factor

According to Thomas Kroker, reliability is the key factor of the ABB turbochargers: "a turbo on a Containership is not allowed to fail. If happens what cannot happen, we have to act immediately. Within 48 hours a spare part has to be at any airport around the world. Most ships manage to reach the harbour because turbochargers are designed redundantly. Big Containerships usually have 2-4 turbos. In a worst case scenario we will have to deliver offshore by Helicopter and assemble the parts right there."

The starting condition

The turbocharger-housing type A100 is made of cast iron and is in production since 2007. It has several bearing positions for the compressor with a distance in between of about half a meter. Depending on the turbocharger model the bore diameter is around 100mm. The tolerance field of IT5 requires highest precision and good surface quality.

Previous machining process: fine boring

According to T. Kroker up till now, the bores have been machined on a machining center "Mammut". Circular milling first followed by several fine boring steps. The "Mammut" has an integrated turning function. The workpiece stands upright on the table as usual on carousel machines. Now the bores are finished with modular boring tools in several passes.

Previous machining: a Machineoperator is absolutely mandatory

T. Kroker explains: „the old process worked ok, but it was absolutely mandatory to have the operator supervise the machining. Due to the strong asymmetric housing we had to run the machine at low RPM, of course with a bad influence to our production time. The long overhang of the boring tool was another problem. We had to monitor the fine boring process very carefully to avoid vibration. That was quite a challenge. In addition we had to make several measuring cuts for each bore to make sure we get the requested precision (remember, it has to be IT5). For these reasons the finishing process was very time consuming. For every measure the operator had to interrupt his work which caused some troubles to the workflow. Thanks to our high qualified employees we were able to keep a reliable manufacturing. We would certainly still produce the same way if we had not found the Urma reamers."

Reamer inserts that rather look like “sawblades”

This is the point where the UrmaCircoTec-RX reaming system comes into the picture. Rene Naef: "meanwhile our reaming system is well-known in the market. When we introduced the system some years ago some customers mentioned: < we need a reamer not a sawblade.>"

First testresults were very promising

T. Kroker: „As a Tool-Expert I always have to be up-to-date. Therefore I watch the tool development progress very carefully. I was already quite familiar with the Urma reamers. In principle a reamer has to be guided. Either by the machine, through guide pads or by the pre-machined bore. However, in ABB we cannot change a process from one day to the other. We have to weigh carefully what advantages we can get out of it. First priority is process reliability. Since we have never used Urma's CircoTec RX reamers before in these challenging turbo housing bores, we made cutting tests in dummy work pieces. The testresults were very promising. But now the internal discussions started. We determined advantages and disadvantages. A critical fact in reaming is: either the bore is perfect or it is not. There is no way to adjust.

Reaming: a very reliable process

Rene Naef: "non-adjustable, fixed diameter is often a reason why machineoperators don't like reaming. They have limited influence to their process. Once the reamer is in the machine, it makes the exact diameter to which it was manufactured. We as manufacturer have to make sure, that our reamers always perfectly match the requested bore tolerance. If you have a tolerance field of 10 µm for instance, we produce the reamer inserts 1-2 µm above the tolerance centerline. The reason is, that a reamer typically looses 1-2 µm in the first few bores and then remains stable. Towards the end of the tool life the wear relatively strong increases - within microns nota bene - and the insert must be replaced. It is not too difficult to define this end-of-tool life point. Therefore we believe this is a very reliable behaviour."

Disadvantage turns into great advantage

T. Kroker:"I can only agree with Mr Naef. The alleged disadvantage – non-adjustable process – is a big advantage for us. Until now we always had to finish and monitor these bores with qualified operators. Today we produce unmanned in ghost shifts. Because of the changed manufacturing process we were able to reduce the machining time by more than 90%."

UrmaCircoTec RX: the «911 Turbo» among reamers

This is made possible by the "911 Turbo" among the reamers. Urma names its reaming system "UrmaCircoTec RX". The Urma reamer for the ABB turbocharger bore is ~600 mm long and has an HSK 100 spindle adaptor. The total length of the solid carbide insert is only 5.3mm and is configured without guide pads for this application. Each insert has 12 cutting edges for this bore size. Currently the ABB experts machine at a feed rate of fz = 0.35mm per tooth, which results in a feed rate vf = 1200 mm/min. Still not enough for Roger Meister: "I believe with a more efficient coolant, we can increase the feed rate even further. But that's a different story. Of course, we had to adopt the CAM-Program to the reamer conditions. Between the bearing positions we speed-up to 30 m/min."