Planetary gear carrier machining in two clamping positions

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Planetary gear carrier machining in two clamping positions

Efficiency has a name: Heckert T45

Voith, based in Garching, Germany, has been manufacturing planetary gear carriers for bus transmissions using a unique, robotic manufacturing plant for more than two years. The core elements of this plant are two Heckert T45 five-axis multifunctional machining centers with turning function. These enable the entire machining process to be carried out in just two clamping positions. The effect is tremendous: in comparison to the previously used conventional manufacturing process which used a total of nine machines, the space required has been reduced to one quarter, machining times have been reduced by 30%, and each component requires only 20% of the previous throughput time.

Imagine that you are riding a public bus through the city: it stops to let passengers on and off, drives off again, accelerates, brakes, stops again – and so on. If you do not notice any juddering movements or switching noises while this is happening, then there is a strong likelihood that the bus is equipped with a Voith DIWA automatic transmission. The “DIWA” is the differential converter (Differenzialwandler in German, hence the name), which enables a smooth start-up across a speed range in which other transmissions would need to shift two or three times.

More than 160,000 DIWA automatic transmissions are currently in operation worldwide. And there is good reason for this: thanks to their innovative design and extremely high quality, DIWA transmissions have become extremely popular with passengers and drivers, and therefore with bus companies and manufacturers as well. As a result of their reduced fuel consumption, they also ensure more cost-effective operation. However, technical innovations are not the only decisive factor for this success. Reliable delivery, flexibility and a competitive price/performance ratio are just as important. “We are constantly monitoring our production processes to find opportunities for optimization,” says Friedrich Oberländer, Director Production Technology at Voith Turbo in the company headquarters in Heidenheim, Germany. “Our focus is on optimizing our level of automation, the technology data in our processes, and how we can intelligently structure those parts of the process that cannot be automated for our employees.”

Friedrich Oberländer, Director Production Technology at Voith Turbo

“Thanks to automation of the manufacturing plant, we are able to manage our resources even more effectively in future, and deploy our qualified workers efficiently.”

Manufacturing concepts on the test bench

The Garching location, where the Voith transmissions are produced, is also affected by these requirements. “We maintain a high level of vertical integration in order to manage our flexibility and costeffectiveness,” explains Vincent Ross, Head of Manufacturing at the Garching facility. “To do so, however, we need to constantly scrutinise our processes for any possibilities for optimization.”

In 2018, the employees responsible for this optimization process identified that the manufacturing plant for the planetary gear carriers installed in the current DIWA transmissions was in need of improvement. In addition, there was a sequential, multi-stage manufacturing process in place at the time, which was no longer in line with current technical capabilities. “It was essential to streamline the process and use innovative technologies,” emphasizes Friedrich Oberländer, who is responsible for these matters across all locations. “We are committed to combining maximum automation with optimized manufacturing technology for series products.”

Friedrich Oberländer, Director Production Technology at Voith Turbo

“We are committed to combining maximum automation with optimized manufacturing technology for series products.”

The Heckert T45 – the key to optimized manufacturing

Oberländer came up with an idea for achieving this when he visited the Starrag stand at the AMB 2018 trade fair. When he saw the Heckert T45 five-axis multifunctional machine with turning function, which was brand new at the time, he recognized the potential for planetary gear carrier manufacturing. “With its robust design and above all its quick, powerful rotary table, this machining centre can handle the entire, previously six-stage manufacturing process on a single machine and in just two clamping positions.” There followed many discussions with the Starrag mechanical engineers in Chemnitz, as well as with other manufacturers of five-axis machining centres. Vincent Ross, who took part in the decision-making process, reports: “We created a structured analysis with integrated risk analysis before the decision was made to use the Starrag plant.” Friedrich Oberländer explains the primary argument: “At the time, Starrag was the only supplier offering a multifunctional milling and turning centre with a 15.8 inch (400 mm) pallet and the speeds and torques that we needed for our application, namely the Heckert T45. Good past experiences also played a role. After all, we have been Starrag customers for a long time now, and we are very satisfied with our Heckert machining centers and the support we have received.”

Vincent Ross, Voith Turbo, Head of Manufacturing at the Garching facility

“For the past 24 months we’ve been able to calculate an OEE of over 90%.”

Successful development partnership

Voith and Starrag worked hand-in-hand on the conceptual planning of the manufacturing plant. Vincent Ross explains: “We considered various concepts, including a transfer system without robotics. However, in line with our strategy of designing automation to be as flexible as possible, we decided to use a solution with an articulated robot. This enables us to not only supply and remove components, but also automate reconfiguration of the machines.”

Starrag brought an external automation specialist on board for implementation. This three-part team created a production cell consisting of two Heckert T45 machining centers and a robot with a load capacity of up to 1102 lbs (500 kg). The robot checks the incoming blanks and loads and unloads both machining centres. When it is time to change to a different series – currently, the plant is used to machine three different planetary gear carriers with a total of 20 variants – it mounts the required gippers, swaps and clamping devices into the machines, without machine downtime. The grippers and the fixtures consisting of pallets, support cylinders and power chucks are already provided pre-assembled in the robot cell. The blanks and finished planetary gear holders are transported into and out of the plant, respectively, on two separate conveyor belts.

Friedrich Oberländer, Director Production Technology at Voith Turbo

“Thanks to the minimal costs and effort involved in changeover between variants, we have become significantly more flexible.”

Key factors: Employee expertise and commitment

“Together, we were able to install a completely new manufacturing system for planetary gear carriers, with a level of efficiency that continues to impress hugely,” says Vincent Ross. The key factors in his point of view: the people involved. “The high level of expertise, specialist knowledge and commitment of the Voith employees and Heckert specialists have made our idea for automated complete machining on a single machine with two clamping positions a reality.” Ross acknowledges that the path to achieving this was not without its rough patches. The installed Heckert T45s were the first series models of a newly developed machine that had not previously needed to contend with this kind of continuous operation. As such, the rotary transmission initially suffered premature wear, though this problem was mitigated to everyone's satisfaction by means of a design adjustment. Starrag also made successful improvements to the toothed belt magazine: the material used for the belt turned out to be sensitive to the cooling lubricant used by Voith, and was replaced with a different material following appropriate testing.

Friedrich Oberländer also mentions that there were problems with the retaining force in clamping position OP 20, which were subsequently rectified via a special coating on the collets. “We worked together to look for, find, and above all carefully implement solutions to every problem,” Oberländer confirms. “This is what makes partners like Starrag stand out.”

Output per area unit increased many times over

Vincent Ross agrees with this, and is pleased with the uptime that has now been achieved: “After more than 24 months, we have verified an OEE of over 90%.” Using this new plant, his team is able to manufacture planetary gear carriers in five-figure quantities each year, which is roughly equivalent to the previous output. However, the space required is approximately 75% less, and the throughput time has been reduced by around 80%. This is primarily due to the significantly lower set-up and idle times. In addition, net processing times have been decreased by approximately 30%. “The greatest impact with regards to cost-effectiveness is in assignment of employees,” adds Friedrich Oberländer. “Thanks to automation of the manufacturing plant, we are able to manage our resources even more effectively in future, and deploy our qualified workers efficiently.”

New perspectives

The effects for customers are extremely important. “Thanks to the minimal costs and effort involved in changeover between variants, we have become significantly more flexible. We can respond much quicker to customer requirements,” says Friedrich Oberländer. “In addition, this solution has opened up new perspectives for us,” Vincent Ross states with conviction. “In our new cell, we can manufacture not only the planetary gear carriers for the DIWA 6 but also the successor product, the DIWA NXT 7-gear mild hybrid transmission, which is perfect in terms of process reliability and costs. Even a changeover to future generations of transmissions or comparable components will not pose a problem.”