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Retooling Machines Lowers Machining Costs
Manufacturing News Center
Sandvik
Coromant CoroMill 390
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Abstract -- Milling - Retooling Machines Pays Off Big for Bosch
Retooling brand-new machines isn't anybody's favorite pastime. It's likely
to raise eyebrows with general management. But sometimes it's the smart
thing to do. At least that's the experience at Bosch Automotive Diesel,
Charleston, SC in the manufacture of injector rails. They mill the rails
on nine brand spanking new Hueler Healy horizontal machining centers.
By switching cutters for the rails' mounting-pad milling step, they saved
$471,000/yr in machining costs and eliminated a serious production bottleneck
within months of startup. "The labels hadn't even worn off the original
tooling, but if you've got a problem and a solution, better to act sooner
than later," says Don Meredith, Bosch process engineer.
Original Tooling Came Up Short The problem with the original tooling was
excessive flank wear on the inserts in a shell-type cutter. Projected
to last 60 pc/edge, the edges failed after 10-40 pc, wasting 45 minutes
per shift and running up a $162,000 annual bill for replacement inserts.
So Mr. Meredith called in Sandvik Coromant's Freddie Wilson for ideas.
Mr. Wilson suggested the CoroMill 390 square shoulder milling cutter with
1025 grade inserts. The two men then arranged a trial with a 40 mm diameter
cutter, modifying the original cutting data to 1000 RPM (415 SFM), at
24 IPM feed in the 4140 steel forging at 275 Brinell hardness. Tool life
immediately improved dramatically, from 10-40 parts per edge to over 400.
The increase in tool life resulted in savings of $150,000 per year in
tool cost alone.
Although the 4140 steel forging isn't regarded as difficult to machine
by itself, the Bosch setup in a 4-up "tombstone" type fixture complicated
things. It required a long unsupported reach for the cutter, raising the
risk of chatter and instability. For that reason, the original machining
plan based on the shell cutter was conservative: two light passes.
Turning Off The Heat
Sandvik Coromant's Mr. Wilson also noticed that the root cause of failure
of the original insert was overheating. The giveaway was flank wear. So
he suggested reducing the speed and increasing the feed rate. "These changes
move the heat from the insert to the chip," he explains. "The positive
rake design of the CoroMill 390 cutter creates a freer cutting action
which helps keep the insert cool," Mr. Wilson adds.
The two men tweaked the operation further to improve surface consistency
and edge life. "Throughput wasn't our priority here, as we had ample capacity
to make 400,000 rails a year with the original tooling," adds Mr. Meredith.
"Lower insert costs and ultimately machining costs for the injector rail
as a whole, was what drove us to make a change."
The workpiece is basically an 18 inch long by 1.5 inch dia. cylinder with
four mounting pads that need milling on both sides. The fuel rail is designed
to be standard for a broad line of diesel truck engines.
Starting Over
The new process went into operation in December 2002. Previously, due
to the instability of the setup, Bosch was forced to make two passes to
machine the mounting pads. Due to the light cutting action of the CoroMill
390, Bosch is now able to mill the pads in one pass. The modified cutting
data is slightly slower than the original data of 1250 RPM (515 SFM) and
32 IPM. Even though the new data is slightly slower, eliminating the second
pass reduced part cycle time from 40 to 23 seconds. Machining cost for
the mounting pad milling operation dropped from $1.09 to $0.79 per part.
Bosch produces over 400,000 of these fuel rails per year. Taking into
consideration lower insert cost, tool change time, and machine cost, annual
savings for this operation totaled $1.20 per part, or $480,000 per year.
In addition with the reduced cycle time, Bosch is now able to take advantage
of increased productivity and machine capacity. "We're getting 400+ pieces
per edge now and with further tweaking should get it up to 550," says
Mr. Meredith.
New Cutter, Close Up
The cutter that "turned it around" for Bosch is the Sandvik Coromant 390
square shoulder, extra close-pitch facemill with six positive axial rake
inserts. It had been on the market about two years at the time of Bosch's
tooling switch. Its compact design permits milling very close to fixtures.
Positive rake seat pockets and inserts create a free-cutting action, reducing
cutting forces and instability in such long-reach applications as Bosch's.
Cutting fluid or compressed air can flow through a center hole in the
cutter to clear chips. Although it was available when Bosch bought the
nine new machines, the 390 cutter was never brought to their attention
during the machine procurement cycle. "Manufacturers buying new machines
often miss out on potential savings by overlooking or deferring the tooling
decisions until after they've made the machine purchase decision," says
Mr. Wilson. "By then it could be too late. In fact, the right choice of
tooling on a new machine can swing the machine's capacity and throughput
by 30% or more." You can produce more with less machine.
In the Bosch case, planning to mill the pads in one pass from the start
could have reduced the machine capacity required to produce the 400,000
rails per year. "As goes cycle time, so go machine requirements," Mr.
Wilson adds.
Tips For Machining The New Machine Right
Based on his experience with Bosch and dozens of other companies tooling
nearly new machines, here are Mr. Wilson's key suggestions for tooling
them right.
1. Recognize that your tooling choice can make a 30% difference in productivity,
capacity, machining economics and ROCE of that big-ticket machine.
2. Don't treat the tooling as an afterthought. Tooling can affect a machine
tool's productivity as much as software does on a computer.
3. Integrate tooling decisions into the machine procurement process.
4. Get tooling suggestions from full-line tooling suppliers - early on
as part of the process. The support is free, and the tooling supplier
is inherently more current on what's available and what will work.
5. Resist the temptation to use existing tooling simply because you have
it. Every new machine creates an opportunity to optimize an operation,
and the tooling is an integral part of it. If it's not the most productive,
you lose an opportunity to save money with every part you make and the
chance to be more competitive.
6. If the tooling you're considering for that new machine has been on
the market for more than five years, take that fact as a yellow flag.
On average, today's tooling is at least 25% more productive than the best
of 1998.
"We followed these guidelines with our nine nearly-new Heuler Healys,
and are saving about half a million dollars a year as a result," says
Bosch's Don Meredith. "In the future, we'll certainly apply those same
guidelines on new machines, so the savings kick in sooner. The right tooling
can exert a surprising impact on machining process economics."
To further the cause of tooling new machines correctly, Sandvik Coromant
recently introduced "ProPak," a package of tooling, manuals and hints
aimed specifically at new machines.
Besides saving Bosch more than $100,000 a year in inserts, the switch
to the Sandvik Coromant 390 cutter also cut cycle time for the mounting
pad milling operation in half. All told, savings by switching saved more
than $400,000 a year.
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Source: Sandvik Coromant
For more information contact Hakan Hellstrand of Sandvik Coromant (Fair
Lawn, NJ) at (201) 794-5000 or via e-mail at hakan.hellstrand@sandvik.com.
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