Nakamura Creates Solution for ‘Impossible’ One-Hit Project

Shannon Precision Engineering Ltd (SPE) is a major subcontract machining business on the Emerald Isle with a world-class AS: 9100 and ISO: 9001 certified manufacturing facility that meets the stringent demands of its high-profile client list. To be at the pinnacle of Irish subcontract machining, SPE has invested heavily in industry leading machine tool brands like Nakamura-Tome from the Engineering Technology Group (ETG).

The Nakamura SC100X2

With more than 38 machine tools on the shop floor, the Shannon based company frequently works on high-profile projects for Airbus, Lear, Bombardier, Collins Aerospace, Liebherr, Safran, Spirit, Ametek and many other leading names in the aerospace, automotive, offshore, rail and power generation sectors. To meet the stringent quality levels the company sets, it has recently invested in two Nakamura-Tome mill/turn centres from ETG, the WT150II and the SC100X2.

The 80 employee manufacturer puts the stability and performance of its machine tools of paramount importance. With the company winning a significant automotive contract and a major contract in the aerospace sector, SPE needed a new strategy in its mill/turn department.

Recalling the situation, Dominic Murphy, the Managing Director at SPE says: “On some projects, we have been struggling with repeatability when machining particularly difficult materials. We won a contract to machine electro-mechanical connections for the aerospace industry from nitronic 40 and titanium, and we needed to be very responsive with our changeovers and lead times.
With regular batches from 200 to 500 and up to 20 different part families in the series, the project has some very ambitious cycle time targets with tolerances of +/-5 and +/-10µm on many features. We didn’t want to be chasing tolerances – we needed a more robust process.”

It was the Nakamura WT150II that won the day with cycle times more than 20% faster than its rivals. “We gave ETG and other vendors a series of components as a prove-out. ETG built a machine set up around the family of components and they delivered a turnkey solution that was best suited to our requirements. Unlike many machine tool brands, Nakamura is a specialist in mill/turn centres, their pedigree stands out.”

The next level

With the success of the Nakamura WT150II proven, ETG Ireland Managing Director Jamie Fletchmore was visiting SPE and Dominic mentioned an extremely complex automotive part that required machining on three machine tools – a 4-axis HMC and two single-spindle turning centres. With an annual output of 40,000 units, the steel-forged automotive tensioning assembly component is permanently absorbing the capacity of all three machines. The solution suggested by Jamie was the Nakamura-Tome SC100X2.

The ETG Ireland team with Spe and MTDCNC

Discussing the project, Jamie says: “We were notified that other machine tool companies said the part could not be machined in one-hit. When I first saw the part, I was trying to think of ways that we could machine the job in one operation. I took inspiration from the technology from Nakamura – and also the art of Japanese origami. I wouldn’t accept that the part could not be machined in one hit, so I conducted my own origami project in the office where I took a sheet of paper and started tearing strips on the paper and folding it to get an impression of the particular part and how it might work. I moved the paper around my hands to replicate the spindles and how target points could be put on the centreline. Once I understood this in my head, I went back to Nakamura, they worked out a plan and the component is now used as one of their sales tools to demonstrate how this type of complex part can be produced on a Nakamura machine.”

Confirming Jamie’s comments, Dominic adds: “We’ve run this family of parts for more than 2 years and we have investigated the market for a solution on numerous occasions – without success. There just hasn’t been a machine on the market that can do the parts in ‘one hit’ – until now. The challenges have included the turning of two spigots on either side of the part that are 40-50mm off-centre. Added to this, we have to mill features that require long-reach tools to overcome interfering features.”

The solution

To explain how the part is machined on the Nakamura-Tome SC100X2, Jamie says: “Once we determined that we could handle this part inside the machine in one operation complete, the next challenge was workholding. Workholding is so fundamental to the process and we knew that if we didn’t get good clamping and repeatability, the project wasn’t going to work. We went to the workholding manufacturers and developed the solution. So, what we have on the left spindle is an offset three-jaw chuck with hard gripper jaws that have been designed so the part sits off centre – this means the main spigot is sitting on centreline.”

With forgings known to be inherently inconsistent in their precision, ETG Ireland developed yet another solution for this challenge. As Jamie states: “Inside each of the chuck jaws are two inserts with teeth that are both independent and rock. With the independent teeth and the rocking motion, this counteracts the inconsistency of the forging, as the teeth provide six points of clamping contact that is even – every time we clamp.”

The challenging automotive components now produced on the Nakamura SC100X2

With a long spigot and groove turning on the face of the component, ETG was faced with yet another challenge. Discussing this, Jamie continues: “Overcoming this issue was largely down to the tooling. Once again, we had to do some work on the design with some trial and error on how to overcome the overhang. We put a small tool in a thin toolholder that would run from the driven tool station. The holder takes up the bulk of the 8mm diameter end mill and it has been designed for us to get as close to the shaft as we can to create the internal groove form. The benefit of completing the part in one operation with all turning, milling and synchronisation between the two spindles was that the milling time became less important – as we have saved time in other areas. Overall, we have saved 50% cycle time on this part alone. When that is multiplied by the quantities required, the saving is significant.”

Looking at the sub-spindle processes, Jamie adds: “What we had to do on the sub-spindle with the offset was use the ability of the X-axis on the sub-spindle, as it has its own axis. This allowed us to move the sub-spindle down to position. Once again, this came down to a specialised clamping design on the sub-spindle. We picked the part up ‘off-set’, so when it is transferred to the
sub-spindle, we then brought the X-axis back to 0, so the second operation spigot would be running on the centreline. This meant we could do a full operation and transfer eccentrically to the sub-spindle – giving us the ability to complete the part in one hit.
We also have superimposed machining to further reduce the cycle times.”

Taking Turnkey to Another Level

The off-centre clamping turning of the automotive part on the Nakamura SC100X2

With the ability to machine components that other machine tool vendors said could not be done in a single operation, ETG more than proved its pedigree. As Jamie continues: “We completed this project at the ETG base in Wellesbourne. Once we had the concept, our engineers proved out the parts and the process. Another cycle time saving arrived from the lower turret, where we have a fixed head on the left-hand side. We were able to synchronise machining to further optimise the cycle time by using the superimposed turning in conjunction with the synchronised. That means that if we are tracking on the top turret and then want to come down to do independent machining, we can use the lower turret where the sub-spindle will work independently on the lower turret. This gives us the best cycle time solution.”

Alluding to this, Dominic adds: “There just hasn’t been a machine on the market that can do the parts in ‘one hit’ – until now. The challenges have included the turning of two spindles on either side of the part that is 40-50mm off-centre. Added to this, we have to mill features that require long-reach tools to overcome interfering features. ETG has overcome these issues with the SC100X2. ETG has also cut the cycle time by almost 50% from 14 minutes to 7.26, but more importantly, the Nakamura-Tome SC100X2 has freed the capacity of two single spindle turning centres and a 4-axis HMC whose capacity we desperately needed. We’ve reclaimed three machines and two employees and massively improved our throughput. We are delighted with both the new Nakamura-Tome machines.”