Conroe Machine is doing what most machine shops only dream of — hard
turning a family of parts around the clock in an unmanned cell that
operates a “self controlled” process. The company is proof that the
dream is achievable for any shop ready to use the talents of today’s
young automation experts to exploit new technology.
In this case,
the new technology is Renishaw's programmable Equator gauge. The turning
cell, with software and programming developed by CNC programmer James
Wardell and robotics technician Jeff Buck, integrates a Fanuc robot with
the Equator gauging system, using Renishaw EZ-IO software to provide
comprehensive communication for 100 per cent part inspection and
auto-compensation of a twin-spindle Okuma 2SP-250 lathe. The cell also
boxes and palletizes finished parts. According to the company, the cell
paid for itself in 18 days.
The same automation team has gone on
to create an unmanned part measurement/sorting cell for a customer, this
time combining two Equators, a Fanuc robot, a vision system and
multiple lanes of low-profile conveyor. In both applications, the
Equator demonstrates the value of programmable comparative inspection by
quickly measuring a family of bearing races, doing it cost effectively,
and without fixturing or problems from a shop floor environment.
Conroe
Machine is a relatively young company, founded by Murray "Tippy"
Touchette in 2000, with the expressed objective of producing parts with
the best manufacturing technology available. The company grew rapidly to
about 150 employees operating in a climate-controlled
65,000-square-foot plant. While it is a general-purpose shop, Conroe’s
location near Houston, Texas, results in a high percentage of business
from the oil and gas industry, principally for drilling components. One
of the company’s continuously running jobs for the industry is
manufacturing thrust bearing races for downhole mud motors. These parts
are produced by the thousands each week, around the clock.
Moving up the automation ladder
The bearings are currently roughed out on four Doosan Puma lathes that
originally did both roughing and finishing, and were served by four
operators. These machines are now split into two cells, loaded/unloaded
by Fanuc robots, doing only the roughing operation. The semi-finished
parts are sent out to be case hardened to HRC 65 at a depth of 1.7 mm
before the finish turning.
“Our production plateaued at 800 to
1,000 total parts per day with these two cells,” explains James Wardell.
“We had a single operator loading the machines and inspecting the
parts. However, you can rely on an operator to correctly inspect only so
many parts with this kind of volume, and we needed even more output.
“For
our next step up, we conceived a fully automated process for the finish
machining, with automatic part loading, post-process measurement,
automatic tool compensation, part engraving, and boxing/palletizing the
parts,” he adds. “We had pretty good ideas for the components of such a
system, except for the part measurement technology, CNC type and
software for tool compensation. Inspection must be fast to keep up with
the cycle times on the parts, which can be as short as 98 seconds.
Originally, we looked at white light laser inspection because of its
speed, but the parts are too reflective. We also looked at hard gauging
and shop-floor CMMs. Hard gauging was very expensive and required setup
attention, and the CMM gave no speed advantage. While working with
Renishaw on other projects, we were introduced to the Equator as a
possible solution.”
Process-control tools and software
The
Equator is an alternative to dedicated gauging. It uses the comparison
method of measuring. A master part with known measurements taken on a
CMM is used to "master" the Equator, with all subsequent measurements
compared to the master. Repeatability is 0.002 mm immediately after
mastering. To compensate for shop temperature changes, the Equator can
be re-mastered at any time. The Equator uses an SP25 probe for touch and
scanning data collection, at speeds of up to 1,000 points per second.
Styli are stored in an integral six-port changing rack, and the system
is programmed through MODUS Equator software. The Equator can be used
manually with push-button ease, but its EZ-IO software for automation
also makes it ideal for integration into cells like Conroe's.
“We
attended an open house at Hartwig in early 2012 and saw the Equator in
action, along with Okuma’s twin-spindle dual-gantry lathe,” says
Wardell. “Apart from being automation ready for parts of our type, the
lathe’s Windows-based OSP dual-path control has an open-architecture,
PC-based operating platform, which was important in our plan for
developing our own auto-compensation software.”
Gauging as part of the automated cell
Wardell and Buck went on to install a cell consisting of the Okuma
2SP-250H, a single Equator, an engraving machine and a Fanuc M20iA
six-axis robot. In practice, the lathe’s two-part carousels are loaded
with raw workpieces, approximately 300 parts. The lathe’s dual gantry
loaders feed the spindles and place finished parts on a chute leading to
a conveyor for pickup by the robot. The robot places the part on the
Equator for measurement and, if acceptable, transfers it to the
engraving machine, and finally boxes/palletizes the finished parts.
“We
developed our own tool compensation software to run on the OSP
control,” Wardell adds. “This software uses measuring results from the
Equator, transmitted in the form of a CSV file, to offset the tools when
the part deviates from tolerance.”
Machining removes about 0.38
mm from each side of the part, with the tightest tolerance at ±0.025 mm
and a 0.5 micron surface finish. Parts range in size from about three to
six inches O.D.
“The Equator is easily able to measure within our
tolerances with a high margin,” says Wardell. “Our OD/ID stays spot on,
with perhaps a couple of tenths variation on radius. We batch-process
parts by size, so changeovers of chuck jaws and other tooling are
minimized. The Equator’s speed allows it to easily keep pace with the
process. We re-master only once a day, because our shop is climate
controlled to 22.2 degrees C."
Inspection principles and automated flexibility
The measuring methodology for the parts is surprisingly simple.
“We
made an aluminum block with a hole in the center, which is placed in
the center of the Equator fixture plate,” Wardell explains. “We use this
to determine our center and set our co-ordinate system. Each part is
placed in the center of that block. We touch to get a center on the
part, then surface scan for everything else. We planned the measurement
process to work without a part fixture or stylus changing. The robot
chooses, through the Equator's EZ-IO software, which measuring program
to run for each type of part. We know the critical features we must
measure to ensure the part is within tolerance.”
Measuring/sorting used parts
The hard turning cell currently produces about 600-700 finished parts
per day, and it led to a followup project involving a parts sorting cell
for a customer. Based on a concept sketched out by Touchette, Wardell
and Buck are developing a measurement and sorting cell for used
mud-motor thrust bearing races.
In oil field service shops, used motors are disassembled, refurbished and put back into service.
“The
customer was visually inspecting used races to determine if the parts
were reusable, and they knew they were throwing away some good parts —
and money,” says Wardell. “We wanted to give them a plug-and-play
measurement and sorting system that takes human judgment out of the
process, so more good races can be salvaged.”
Still in development
when this article was written, Buck and Wardell are assembling a cell
that consists of two Equators, a Fanuc LRMate 200iC six-axis robot,
multiple lanes of low-profile conveyor, a Fanuc iR Vision system and an
ATI quick toolchanger for the robot’s end-effectors. The vision system
tells the Equator what part number is being presented and what
measurement program to run. Good parts are subsequently placed on the
appropriate conveyor, and bad parts are placed on a scrap conveyor.
“We
designed this system to be trucked in for delivery as a unit, and user
friendly for the motor shop people – just turn on the power and load
parts onto the conveyor,” Buck says.
“For our machining cell,
there was no other cost-effective, shop-floor measuring tool comparable
to the Equator,” Wardell adds. “And we hope that our venture into cell
integration for a customer opens a new business avenue in this area for
our entire company.”
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