In-house
"Doctoring" of Setup Process Reduces Throughput Time
Reductions in machine tool setup time
typically come in small increments. However, this is not the case on the four
vertical machining centers used by the instrument department of Howmedica
Osteonics, a leading maker of replacement hips and knees. The instrument
department reduced setup time of standard jobs from over two hours to only five
minutes - and eliminated $1 million of inventory - by implementing a
quick-change pallet fixture system, tooling carts and Renishaw's NC1 non-contact
laser tool setter.
Pallet fixture systems and tool carts
are setup timesavers used in a wide variety of shops. However, Howmedica
Osteonics is at the forefront of using Renishaw's non-contact laser technology
for quicker tool setting. The NC1 tool setter is commonly used for in-cycle
broken tool detection, but Bob Mykytka, Howmedica Osteonics manufacturing
engineer, found it just as helpful for hands-off setting of tool length and
diameter, thus satisfying one of the new setup procedure's key time-reduction
objectives.
"Machine shop floors are a buzz of
activity, and it's often difficult to stop and examine how current procedures
can be improved," says Mykytka. "But it was readily evident that long setup
times were killing throughput of our short-run jobs and rapidly increasing
backorder. Our setup procedures needed significant upgrading," he says.
Howmedica Osteonics' instrument
department produces over 4000 different parts for 1000 tools and devices used
for shaping bones and installing orthopedic devices. The range includes
specialized broaches, reamers, drill guides and clamps. Most of the parts are
machined from 17-4 or 300-series stainless steel. The instrument department
produces them using four verticals, three horizontals, four lathes, three screw
machines, two grinders, and a few small manual mills. Most of the parts are
processed on the verticals, so Mykytka focused on those machines for the new
setup program.
Long setup time means low
productivity
According to Mykytka, the previous
setup procedure was typical of many shops. An operator with part order sheet in
hand would collect tools from the tool crib; assemble tools in a tool holder;
install, indicate and tram fixture in the machine; and then manually perform
tool offset and diameter compensation and dry-run the program. This took over
two hours for standard machining jobs, which is inefficient for small production
runs, he stresses.
Mykytka assembled a team in early
2000 to brainstorm ideas for reducing setup times. "We wanted something similar
to an automotive industry flexible manufacturing cell, with all machines
in-line, all fixtures already mounted, rail delivery to machine, etc., but this
was obviously beyond our budget," says Mykytka. "So we set out to design the
poor-man's flexible manufacturing cell."
Mykytka had the idea of using
standardized pallet fixture tooling on all the verticals, and was surprised to
find such a system covered in dust in the tool crib. The Siegel tooling pallet
was part of an attempt at a quick-change fixture system program initiated the
prior year that never gained momentum. The system uses a pallet receiver that
mounts permanently in the machine bed and receives an aluminum plate onto which
is mounted the fixture. The plates slide on and off the receiver in seconds,
providing positioning repeatability to 0.002" without need to tram or indicate.
Mykytka began testing the quick-change fixture system on one of the pallets on a
dual pallet machine. That way, when the machine was needed for production, he
simply changed-out the test pallet, allowing the other to be used for a job,
ensuring no production time was lost.
With the first piece of the setup
puzzle in hand, Mykytka began investigating ways to automate the tool setting
procedure to allow single-button cycle start with a "hands-off" tool
compensation procedure. For that, Mykytka turned to Renishaw's NC1 non-contact
laser tool setter. "We heard good things about non-contact tool setters offered
by a few different companies and went to the Eastec show to check them out,"
says Mykytka. "We were familiar with Renishaw's name and reputation for product
support, and were impressed with its new cost-effective system, so we purchased
one for testing."
The NC1 allows setting of both tool
length and diameter to be carried out at normal spindle cutting speeds, enabling
identification and compensation of errors caused by radial run-out of the tool
and tool holder, notes Mykytka. The NC1 can measure tools anywhere along its
laser beam (up to two meters in length), eliminating a positioning move
specifically for measurement and minimizing cycle times. The laser tool setter
can measure tools as small as 0.2mm (0.008") with system resolution of one
micron (0.00004").
NC1 non-contact laser technology is
designed for easy installation and low maintenance. A compact and robust
laser-based transmitter sends a visible beam to a receiver unit. System
electronics detect when a tool breaks the beam, and output signals are sent to
the machine's control, allowing the position of tips, teeth or cutting edges to
be instantly established. No additional M-codes are necessary for basic system
functionality, simplifying installation.
A continuous stream of air flows
through special apertures, Renishaw's MicroHole, to protect the NC1's optics.
There are no moving parts in the protection mechanism. The NC1 runs off a single
air supply and requires no adjustment or cleaning once installed.
"The NC1 is simple and reliable,"
says Mykytka, "and is right at home in the belly of a machine tool surrounded
with coolant and metal chips." Mykytka admits that it took time for the
operators to feel comfortable watching the tools rapid-down to the NC1 for
touch-off. "The guys were a little nervous seeing the tool move so quickly down
to the NC1, and some even had their hands on the E-stop 'just in case,'" says
Mykytka. "Of course the NC1 always detected the tool and they never had to hit
the button."
Once he proved-out the fixture and
NC1, the real work began, installing the receiver plates and NC1 on each of the
verticals and converting the 4000+ jobs going to the verticals. The tool room
worked to mount all the fixtures to the plates, while the programming department
updated the part programs with an NC1 macro so the operator could just push
cycle start and the machine would touch-off tools. This stage of the project
took one year to complete. The shop continued to use the dual pallet machine
which had both old and new setup systems until all machines were converted. All
but three jobs now use the plate system (there is a height restriction for those
three jobs). Some even use indexers, vices, double vises, and other such fixture
devices mounted on the plates.
The final step was streamlining tool
retrieval and installation. Tool carts were purchased which allowed operators to
have all the tools selected and waiting for them to install in the machine,
instead of wasting time at the tool crib picking out tools while the machine may
be sitting idle.
The department also started keeping
most commonly used tools permanently installed in the tool magazine. Most
machines had 20-tool capacity, so tools 11-20 were strictly end mills of all
different sizes that are used on almost every job. This way, the operator may
have to load only half as many tools. The tools are only removed when they are
broken.
Now under the new setup procedure
system, the operator goes to the cart parking area to choose a job/cart, loads
tools into the machine, quickly slides in fixture plate (no need to tram or
indicate), and hits cycle start. The NC1 macro in the program automatically
touches-off all the tools, then the machine starts making chips.
"This was a high-profile project, so
prompt service and support from Renishaw was especially essential as this was
our first experience with non-contact laser tool setters" says Mykytka. "Renishaw
was helpful and quick to respond whenever we called on them."
Needless to say, management was
thrilled with the project's results. Mykytka made a presentation at a quarterly
meeting about success of program, and the system was presented at the company's
annual best practices meeting in Germany.
The company recently transferred
Mykytka to the femoral knee department, where he has been charged to implement a
similar setup system there. The femoral department currently has one NC1 mounted
on a robo-drill, which is used not only for tool setup, but also for broken tool
detection. Replacement knees are made from Vitalium, Howmedica Osteonics' own
cobalt chrome material, as well as titanium, and tool breakage is common when
drilling these tough materials. "If a drill breaks during a drill and tap
routine and the machine continues, all the tools after the drill (tap, counter
bore) would also break," says Mykytka. "A quick check with the NC1 between
cutting routines ensures this does not occur."
For more information contact:
Dave Bozich
Renishaw Inc.
5277 Trillium Blvd.
Hoffman Estates, IL 60192
847-286-9953
Fax: 847-286-9974
E-mail:
dave.bozich@renishaw.com