Medical Shop Increases Tool Life with Hex Broaching

A manufacturer of spinal implants and surgical instruments achieves immediate results in a switch from rotary broaching to hex broaching.

by Chris Felix
Editor-in-Chief, Production Machining

Small changes can make a big difference. Shopfloor personnel who have been in the business for a long time usually know this. A new CNC machine or a complete overhaul of procedures isn’t necessarily the only way to make a substantial impact on the shop’s output. And it’s a good thing. Sometimes a simple change in tooling can be just the ticket to the next level of success.

When a shop is a relative newcomer, resources might not yet be available to invest in additional machine tools, and processes are often still being established. But even when a shop is young, it’s still often the beneficiary of well-trained and even well-established operators and engineers, along with knowledgeable suppliers. And these individuals are the right people to look toward for instituting changes that will make a difference.

With seven Nexturn Swiss machines on the floor (six 20-mm machines and one 32-mm machine), Amendia is able to tackle a wide range of screw production. Four of the company’s Nexturns are the SA-20e, which handle the majority of the hex and Torx broaching.

A Medical Upstart
Amendia (Marietta, Ga.) opened its doors in 2008 with a mission to design and build spinal implants and instrumentation in the spinal device market. The company designs and manufactures its own cervical and lumbar implant devices and markets them to its distributors and direct sales force, who service spine surgeons at hospitals or surgery centers.

The company currently has about 65 employees, all but two of them work the first shift. Those two employees work the second shift, and the third shift is totally lights-out. Unattended operations are continuous throughout the night, 6 days per week. The well-maintained shop floor has a lineup of Mazak Integrex and Multiplex machines that are used to manufacture implants such as interbody devices made from PEEK.

In the Swiss area of the shop floor, four Nexturn SA-20e Swiss machines, two SA-20b machines and one SA-32e crank out hundreds of lumbar and cervical screws per day, along with other components needed for the implant system. “Several things are going on to make up the entire system that is used in surgery,” Application Engineer Steve Selvia says. “You have a screw, a tulip, a saddle and a set screw. Cycle times and quantities vary, but we run these around the clock in the Swiss Department.” Horn USA supplies much of the tooling in this area.

The Swiss department at Amendia includes seven Nexturn machines, from 20 mm to 32 mm. Michael Morgan (left) discusses the Horn broaching system with Steve Selvia, applications engineer at Amendia.

Challenges
All of the parts produced in the Swiss department are from implantable-grade titanium, which is strong and light, but also tends to be very unforgiving and tough to machine. And, of course, some parts present more challenges than others. According to Mr. Selvia, the most challenging parts are the pedicle screws.

“They’re a double-lead thread,” he says. “We have to whirl that thread, which requires a double-lead insert and is kind of tricky to make just right to produce the thread you need.” But the more remarkable part of the process, which Amendia recently adjusted, is broaching the hex form.

Originally, the parts were being produced with a full-form broach made from cobalt steel, which generated about 300 to 400 parts per tool. The process was not every predictable. The tool life was fair, but the unpredictable way the tools would break down was not very favorable. Mr. Selvia felt sure a better method was available.

About 3 months ago, Horn USA Application/Sales Engineer Michael Morgan was in the shop discussing tooling options in some other processes. Mr. Selvia happened to notice the N105 carbide broaching tool in the Horn catalog. “It was exactly what I thought we needed to make the hex,” he says.

This tool is not a full form, but rather a 60-degree form that pecks at the workpiece and creates the form one side at a time. The gradual forming process enables it to be more controllable, and the material is, therefore, more forgiving on the tool. “I’m now getting about 10 times the tool life from a tool that costs half as much as what we used before,” Mr. Selvia says.

As part of its implant systems, the shop produces about 300 lumbar screws and 500 cervical screws a day from implantable-grade titanium. The screws are shown here with the broaching tool on the right.

Broaching a Hex
Mr. Selvia says the new broaching tool works better for Amedia because the entire tool form is not forcing itself into the titanium at one time. Instead, only a piece of the tool goes in and scrapes a small amount of material away with each pass.

“Imagine a shaper tool,” he says. “As it creates a hex hole, it’s only touching two of the six sides at a time. It removes material at about a thousandth at a time down to the right size, and then indexes 60 degrees. It pecks away at the material without too much pressure on six sides of the tool.”

Because only two sides of the hex are machined at a time, the process is considerably slower. But Amendia performs the broaching operation on the subspindle while the other machining takes place on the main spindle. Running simultaneously, the broaching is completed first anyway.

“This process doesn’t cost us any time,” Mr. Selvia says. “And it saves us money and increases our throughput.” The improved performance and longer tool life have enabled Amendia to run unattended through the night with more confidence, which has further increased the production capabilities. “With the previous process, the tool would break unpredictably,” Mr. Selvia says. “That’s no longer the case.”

The icing on the cake is that the quality of the finished parts seems to be better, as well. The improved surface finish can be partly attributed to more efficient and effective chip removal. With the full-form, six-sided tool, a large chip would be pushed down to the bottom of the hole and then often would need to be dug out with a drill.

The broaching process, by pecking away only a thousandth at a time with each pass, creates very small, fine chips that clear away without complication. Also, according to Mr. Morgan, the Horn broaching tools are sharper than a wobble broach or rotary broach, and by shaving the material away rather than pushing it, a smoother, shinier finish can be achieved.

Other Advantages
The broaching system has led to other improvements in the process for Amendia, as well. Because only one corner of the hex shape is being cut at a time, the process has more adjustability. If the machine is misaligned, for instance, or if the hex is undersized, additional taper can be added or an additional pass can be added to the program. With rotary broaching, the operator has only one shot at getting it right. If the form is not right, the part is scrap.

Amendia has also realized significant savings in setup time. The broaching tools can utilize the same toolholder as any Horn USA boring bars or face grooving tools or any others from the 105 Series. The operator simply replaces one insert for another one, without any need for

Customer Satisfaction
Although it’s a completely different approach with a different tool, the process has fit in well at Amendia. “Everything about it has been an advantage over the old method—cost, speed and finish,” Mr. Selvia says. “We’re very pleased with it.”

With plenty of experience, he feels that learning how to best use the tool was pretty straightforward. He wrote a macro program to peck the hex out to the right size based on the variables that applied to each screw design.

“Just drill the hole to the right size and use the tool in a common sense way,” he says. “Anyone with some experience with CNC Swiss wouldn’t have a problem with it. It didn’t take us long at all to get it incorporated into our system.”

Amendia is regularly broaching on three of its Nexturn machines for anything with a hex in it. Currently that includes pedicle screws, cervical screws and set screws. The company also uses the Horn broaching tools for Torx work on a variety of cervical screws.

The hex and Torx tools bring the same advantages, but simply use a different form. With Torx, material removal is done one lobe at a time, as opposed to the hex doing one corner at a time. A common method for the Torx form is milling using a very small-diameter mill. While effective, this method can be time consuming because the small diameter end mill requires close attention all the way around the periphery of the form.

Overall, the company’s relationship with Horn has developed nicely, and Mr. Selvia is considering moving to Horn tooling for some other jobs as well. “We’re happy with the way Horn USA operates,” he says.

“Michael (Morgan) is knowledgeable and very available when we need him. Their network is very responsive and easy to work with. They don’t hesitate to adjust their stock if we need them to.”

And who can argue with a tool life increase of 10 times? Besides the obvious savings in tooling costs, it also carries over to better production rates, reducing the frequency of machines being stopped for tool breakage. With fewer broken tools that go unnoticed, scrap has been reduced, as well. And the door has been opened for successful lights-out machining.

So the results speak for themselves—a simple change in tooling has had a big impact on production savings.