Partnering with a Tier 1 supplier for decades results in 15 parts per million quality defects for global production

Shifting focus to e-mobility

ZF Friedrichshafen AG (ZF), a well-known Tier 1 German automotive supplier, is known for its innovation and quality. Their success dates to the first gearboxes for the legendary Zeppelin dirigibles in 1915, followed by many automotive component firsts, including the first five-speed transmission for a Lotus Formula 1 car in 1961.

Building on its reputation as an industry leader for high-quality transmissions, like the 4HP and the 9HP for internal combustion engine (ICE)-driven powertrains, ZF is shifting to electrification, delivering quality hybrid and electrified components and subsystems to most major automotive original equipment manufacturers (OEMs) globally. This focus on electric mobility (e-mobility) includes innovative products for a wide range of electric vehicles (EVs) throughout the global automotive EV ecosystem as well as marine, heavy equipment and industrial machinery.

Building on a history of success

As a senior expert and acoustical engineer at ZF, Franz Knoppik’s key responsibility is to help guarantee the quality of thousands of automatic transmissions and electric drive units (EDUs) coming off the lines globally, which has evolved into a serious process internally. Over the years, a key tool that he and his team count on to support their process is the Simcenter™ Anovis™ system, an end-of-line (EOL) test bench solution, which is part of the Siemens Xcelerator business platform of software, hardware and services.

“I started at ZF almost 24 years ago working on the original 4HP automatic transmission and gearbox technology, and we’ve used a version of Simcenter Anovis since then,” says Knoppik. “It was advanced for its time with some online capabilities and was a modular, flexible measuring system.

“This is still the case today. It is still easy to work with Simcenter Anovis and integrate it with other systems. This is a huge advantage.”

Simcenter Anovis can be easily integrated into EOL test benches or production lines to ensure product and process quality. ZF already incorporated Simcenter Anovis globally in over 50 EOL test benches and could easily reach 100 or more.

Additionally, as a complete noise and vibration testing system, it combines all the necessary sensors, accurate sound and vibration signal recording hardware and smart signal analysis and flexible test bench integration software to precisely perform noise and vibration-based pass or fail checks and deliver formal proof that
the tested part meets specifications.

“When we started working on electrification, we thought it would be easy because we know how to handle complex engineering thanks to our 8HP work,” explains Knoppik. “Today, there are still some challenges, and the mix between normal gear-box technology and electric drives is not as easy as we thought.

“There is no masking anymore. With an electric driveline, you hear everything, and you need to find the root cause and a fast solution.”

Introducing fresh ideas

Today, ZF has onboarded young engineers and specialists who have the “old-school” understanding of noise, vibration and harshness (NVH) and acoustics engineering from the ICE world, as well as experience and insight into the new world of electrification.

“The newer team members see other possibilities for using Simcenter Anovis to get the right results faster,” says Alexander Neis, an NVH engineer and coordinator for the Simcenter Anovis partnership at ZF. “Our partnership is vital. We have weekly or biweekly meetings with our colleagues from Siemens where we share ideas and experiences from the field.

“If we sense we need new features or a solution to an issue, I’m in direct contact with everyone on the ZF-Siemens team, and we work together to implement these features in the end-of-line tools and software.”

“We have had a working relationship with Siemens’ Simcenter Anovis team for more than a decade or two,” says Andreas Steffensky, team leader at ZF. “We are always on the lookout for how we can be more efficient and sensitive when it comes to quality issues. We talk regularly with the Siemens team about new Simcenter Anovis features and add-ons. After a positive test result, which is usually the case, we roll these new Simcenter Anovis features out to the company.”

Meeting tougher customer requirements

Nils Mueller, team lead for NVH in the quality department at ZF who brings electric motor development experience to the team, points out another quality driver: tougher customer requirements from OEMs.

“We already have tight limitation zones regarding product specification requirements from our customers when it comes to quality and specifically e-driveline noise,” says Müller. “We are expecting these limits to be tighter in the future.”

Although preventing production waste and unwanted recalls and repairs drives quality at ZF, what Mueller is referring to specifically has a price tag. Tier 1 companies are generally required to pay penalties for items that do not meet the OEM’s quality specifications. Depending on the item, this ranges from $100 to $5,000 United States dollars (USD) per rejected item. When referring to hundreds of thousands of parts, subsystems and systems, a small mistake, overlooked metrics, ghost orders in gears or other unexpected or unexplainable phenomena in NVH engineering, which, if not caught and solved on the production line, can add up quickly to fines over $150,000 USD. This could also damage the company’s reputation.

Creating a catch-it-all process

The normal quality process is a “catch-it-all” process, as Knoppik calls it. Using Simcenter Anovis, depending on the gearbox product and production process, engineers can apply a certain tolerance envelope. They can then analyze discrepancies and swap parts to see if the issue was a one-off. For example, if there were issues in the machining or material quality.

“If we are still seeing issues after a part swap, then we need to put Simcenter Anovis and our advanced analysis capabilities to work,” says Knoppik. “We can look at the entire spectrum with Simcenter Anovis and see effects that we wouldn’t normally even see with a classic end-of-line test bench. It does help us catch it all. We have an overall 15 PPM or 0.0015 percent. Metrics like this make us happy, make the customer happy and prevent overall production waste.”

For clarification, 15 parts per million (PPM) is a measurement of the number of defects in the ZF production process worldwide. “This means that, for a major OEM, we only have 15 complaints per million pieces on a very high tech and successful transmission,” says Steffensky. “This covers all the locations worldwide. Of course, this varies from project to project, but only slightly. Our challenge right now is to have the same result with e-drives. It’s a new area for everyone involved. The expectations are high, and our collective experience is still growing.”

Inventing time-saving and easy-to-use metrics

With quality requirements like these, ZF puts high expectations on metrics and the Simcenter Anovis solution loops. With assistance from Siemens Digital Industries Software, ZF’s quality team developed numerous custom analysis processes. ZF’s excellence and expertise in transmission and gear quality form the perfect synergy
with the Siemens team’s skills and experience in digital signal processing.

For example, the team codeveloped a bespoke order-based cepstrum metric for EOL fault detection, which they can use instead of classic order spectral-derived metrics for detecting potential issues.

“I think it was about a decade ago we sat down together because we were having a few challenges with Siemens Anovis, namely identifying issues on the line,” says Knoppik.

Together, the team came up with a way to identify and synchronize certain spectral data in a unique, limited acoustics curve that eventually became a dedicated analysis function in the software called the order cepstrum curve. This analysis, originally handcrafted by the ZF and Siemens teams, is a common signal processing technique. Its algorithm-driven analysis capability is used to catch hard-to-identify gear failures during EOL testing.

“It took all of us on the team, along with the Siemens experts, days of analysis work and troubleshooting in the past,” says Knoppik. “Today, in Simcenter Anovis, a novice can do this special type of cepstrum analysis work. All they have to do is set the limits correctly and use the cepstrum curve and it works in ten minutes.”

Moving to e-mobility

For ICEs, ZF can easily change their singular setup between component and system orders for various OEMs; however, they know e-mobility will continue to grow and plan on replicating the same successful quality process when it comes to the expanded EOL testing for e-drives.

“We use one master setup and only change some parameters when we run tests on various products for OEM customers,” says Steffensky. “It is very straightforward. We want to use the same method for e-drives. Of course, this is just the beginning of the electric revolution, but as we focus on electrified powertrain quality, this is our goal.”

As electrification starts to mature, ZF engineers will continue to drive progress and quality for the e-mobility industry.

“At ZF, we have the right experience from our various OEM projects,” says Knoppik. “We are seeing firsthand, as a team, what works and what doesn’t. We are using our experience to make sure new e-drive projects work for our customers, and we will continue to work together with our customers, everyone on the e-powertrain quality team and Siemens to make sure the next ZF e-drive projects will continue this success story.”

“From a technical perspective, for years, we had the time and resources to solidly prepare and plan for a new project, even the most complex ones,” says Steffensky. “Today, the pace is different. It is extremely fast.

“As German engineers, we must be fast, faster than our competitors. This is why our partnership with Siemens, weekly meetings and weekly alignments are so important. We already did the hard work; now we just need to benefit from the fast support and fast changes we can implement as a ZF-Siemens team in the software.”