In the driving seat

Tillsonburg has come a long way since Canadian country music legend, Stompin’ Tom Connors thrust the small Ontario town and its tobacco fields into the spotlight with its namesake song. Today, Tillsonburg is part of a thriving automotive region, home to the THK Rhythm automotive plant that serves global manufacturers including BMW, Ford and Daimler Mercedes Benz. A tough, competitive landscape meant THK Rhythm needed to make its offering stand apart from competitors. To give its products the edge, the company enlisted the support of Sandvik Coromant and its new steel turning grades.

The THK Rhythm automotive plant specializes in suspension components found in vehicles worldwide, along with ball joints and ball studs for these components. Being a global automotive player demands stringent quality and cost-optimization measures, which is evident in the THK facility.

THK’s quality policy, which is prominently displayed at the plant’s entrance, reads: right the first time, right every time, continually improve. And it’s more than just a catchy mantra. Several manufacturing improvement practises evidence this policy, including Kaizen, Japanese for continuous improvement, which focuses on optimizing efficiency, productivity and overall equipment effectiveness (OEE).

A challenging machining process

Despite THK’s crystal clear efficiency goals, reaching productivity targets and controlling cost was a challenge when producing the front lower tension arm, a component that goes into the suspension assembly of a car. “The front lower tension arm requires the removal of a lot of material during several steps including drilling, roughing and finishing a bore,” explained Adrian Dabrowski, a process engineer at THK Rhythm.

The component is made of a forged ISO P steel that is particularly abrasive, with a high tensile strength. Machining this part requires a specialist tool with a number of inserts that are staggered or stepped — meaning they are not all of the same diameter. The original machining process for the front lower tension arm was designed to make 140 parts per tool, however, THK could only produce about 92 pieces on average before one of the inserts on the largest diameter failed, which caused the entire tool to fail.

Frequent failure meant operators had to change tools far too often. The machines in the THK Rhythm workshop are set up in a way that if one tool breaks, a spare tool is brought in automatically so that machines can keep running. With frequent tool failures, however, there were not enough spare tools to keep production flowing.

Chip control, a vital consideration for any steel turning operation, was also a concern. "When the tool failed, chips would often get wrapped around it; so, we had to physically take the tool out and remove the chips,” revealed Gary Martin, a machine operator at THK. “These chips were sharp and could cause finger cuts and injuries.”

Dabrowski further highlighted the pains of tool failure: “We were running the machines with just a single tool and when that tool broke, the operators had to physically take it out, manually change all the inserts and put it back in the machine. That equates to around five-to-six minutes of downtime per machine, which quickly adds up.” On average, operators oversee three machines. So, if one machine is down, in essence all three are down. “On good days, we had just one breakage per shift,” continued Dabrowski. “On these days, downtimes were as frequent as three-to-four times per shift per machine.”

Using the previous inserts there was a lot of downtime, which made meeting daily productivity targets difficult.

The search for a solution

In search for the right solution, THK tried to adjust the machines on a daily basis, fine-tuning feed rates and revolutions per minute (RPM). The team also tried out different inserts and geometries from a couple of tool suppliers, but nothing hit the mark. That was until THK turned to Sandvik Coromant.

Sandvik Coromant added two high performing carbide insert grades, GC4415 and GC4425, to its existing range at the end of 2020. The inserts have a broad range of applications and are recommended for both continuous and interrupted cuts. While GC4425 delivers improved wear resistance, heat resistance and toughness, GC4415 complements GC4425 where enhanced performance and better heat resistance is needed. For THK Rhythm, GC4415 was a fitting addition to its machining process.

Both grades contain the second generation Inveio® coating technology. “What makes this tool coating particularly unique is that it can be examined at the microscopic level,” explained Rolf Olofsson, product manager at Sandvik Coromant. The material’s surface has a uni-directional crystal orientation. Each crystal lines-up towards the cutting edge, creating a strong barrier that improves crater and flank wear resistance. Heat is also lead away from the cutting zone more quickly, which keeps the cutting edge in shape for longer time in cut.

“GC4415 and GC4425 can machine a larger number of pieces, while contributing towards extended tool life, eliminating sudden breakages and reducing reworking and scrap. For THK, the GC4415 insert is the remedy to its turning troubles,” continued Olofsson.

Driving forward

Since introducing GC4415 to its machining operations, THK has seen shop floor productivity change for the better. In fact, because it runs at higher cutting rates, THK witnessed an 11% increase in productivity as soon as operators started using the insert.

During the first four months of 2021, THK used roughly 3,800 inserts of their previously-favoured grade. When the GC4415 grade was introduced in May 2021, the workshop used just 3,000 of the new inserts in the same timeframe — an 18% decrease in the number of inserts used, dramatically improving overall cost-per-part.

Change isn’t just about numbers. “On the shop floor, our operators are happier as they can focus on loading parts and not having to worry about frequent tool changes or chip jams,” concluded Dabrowski. “The new grade has helped save 194 hours of production time per year. Thanks to GC4415, the THK Rhythm workshop now experiences far less downtime, and more reliable production.”

Following the success of the GC4415 insert grade in machining vehicle front lower tension arms, THK Rhythm now plans to test and introduce the grade in other parts of its production line, such as ball studs and ball joints.

If your workshop faces similar productivity challenges, speak to Sandvik Coromant and find out how its range of steel turning grades can transform your machining process.