MARKETPLACE: ENGINEERING INSIGHT
The Right Tool(s) for the Job
A spinal implant manufacturer relies on high-tech multi-axis machining systems to develop its products
EASING BACK-PAIN IS BIG BUSINESS, but developing devices
to treat the problem is anything but simple. For one thing, spinal
implants and the surgical tools associated with the devices often
must be customised to meet specific requirements. For that reason, spinal implant manufacturer NuVasive Inc. (San Diego, CA,
USA; www.nuvasive.com) produces prototypes and proof-of-con-cept pieces of its Fusion implants and surgical tools, explains Jeff
Castleberry, Machine Shop Manager. “The products are eventually manufactured in large-run production shops, but in-house
machining is a vital part of our product development, testing and
client support.”
Investing in the future
In 2001, Castleberry set up an 8 × 15-ft machine shop,
housing just a manual lathe and knee mill. But the company
quickly expanded and outgrew its modest in-house machining
setup. Castleberry relocated and upgraded the shop to CNC
capability with a VF- 2 vertical machining centre from Haas
Automation (Zaventem, Belgium; www.haascnc.com). After
outgrowing two more locations, the company’s machine shop
now has six experienced machinists and new CNC equipment
from Haas. The machines include a VF- 2, two Mini Mill and
two Super Mini Mill vertical machining centres, all equipped
with 4- or 5-axis HA5C indexers. There are also two TL-1
Toolroom lathes and also a Super Mini Mill 2 fitted with a
TR-110 trunnion.
“‘Cheetah Speed’ is the motto we often have to work by and
we have about one-and-a-half machines for every machinist,”
Castleberry notes. “We
rely on the Haas VMCs
fitted with rotaries to
give us the full 4- and
5-axis capabilities we
need. But, importantly,
they save us time by let-
ting one single-mount,
multi-axis positioning
operation handle jobs
that would other-
wise require multiple
operations and multiple
setups. Working with
‘always configured’
Haas vertical machining centres use a
single-mount, multi-axis positioning tool
to perform complicated tasks in a single
operation.
Nuvasive’s Fusion implant line includes precision-machined plates, rods
and screws.
multi-axis Haas machines means that there is little time lost to
setups,” Castleberry says.
Medical and material demands
“None of our work is simple, because virtually everything the
shop produces will be used to slide in and out of a human body,
and is handled by surgeons wearing easily damaged latex gloves,”
says Castleberry. He explains that sharp edges must be avoided,
requiring the surfaces to typically have 30-μm or better finishes.
“We carefully configure our CAM postprocessing to take advantage of the 15K spindle and high-speed look-ahead capabilities of
our Haas VMCs and trunnions. Getting a smooth finish right off
the machine reduces post-finishing,” Castleberry adds.
NuVasive does a lot of work with 17-4 stainless steel, which
is heat treated in-house and then machined hard to get a clean
finish and predictable final dimensions. To prevent potentially
harmful reactions within the human body, the stainless steel and
titanium pieces are passivated. “Our tools often go as small as
0.020-in. ball mills,” Castleberry explains. “Machining titanium
with such small tools is especially tricky as pieces tend to distort
when heated. Therefore, we must produce large chips to carry
away the heat.”
Although NuVasive standardises equipment and procedures
as much as possible, almost all of its products are unique. “Engi-
neers are used to ‘drop that, go with this’ requests,” Castleberry
concludes. “Having exactly the right tools—reliable multi-axis
machines configured and ready to go—makes our type of work
possible.” 1
