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The resulting
coordinate point cloud of millions of points is then compared with the
original CAD model of the part using Geomagic QUALIFY Inspection Software
that provides a graphical comparison between the Scan Data and the CAD
model. “We can see in a second on the screen exactly how the first
article compares to the design intent,” said the company’s Process
Improvement Specialist. “ Using graphical imagery we can quickly see if
the part is warping, which is normally a process problem, or if it is out
of tolerance, which means that we may need to modify the tool. The new
process reduces the time required for first article inspection from two to
three weeks to one or two days, which is huge when you consider that we
often have machine tool worth half a million dollars sitting waiting for
the inspection results.”
The
company’s market-leading brand of NEMA-type electrical distribution and
industrial control products, systems and services are found in all types
of residential, commercial and industrial construction, in a wide range of
manufacturing and processing facilities, and in or on the products of
other manufacturers.
Switching from
CMM to laser scanning
“We are the
world’s leading manufacturer of circuit breakers, a product distinguished
by the fact that even one failure is unacceptable,” the Process
Improvement Specialist said. “Our continuing success depends on the our
ability to maintain extraordinarily high levels of quality. As a result
we are continually evaluating our inspection processes and searching for
better ways to achieve our high quality standards.” The use of CMMs to
inspect injection moldings in the past was time-consuming because of the
need to generate the program to move the machine probe into position for
each individual point to be measured. As the geometrical complexity of
the company’s parts increased, the number of points needed to fully
characterize the geometry skyrocketed. Even though operators spent several
weeks generating points one by one, they could never be sure that they
hadn’t missed a critical feature. After the points were captured and
converted into dimensions, they were exported onto a spreadsheet. Then
the designer had to go over each location, line by line, and determine if
the probed dimension was in or out of tolerance. If a problem was
identified, it took even more time to identify the cause. Typically,
series of points would be out of tolerance but it would be very difficult
for the designer to detect a pattern, such as that they were all part of a
boss that had been mis-positioned.
The company’s
search to improve the process led to the technology of high accuracy 3D
laser scanning which works by projecting a line of laser light onto
surfaces, while cameras continuously triangulate the changing distance and
profile of the laser as it sweeps along, enabling the object to be
accurately, digitally scanned in 3D. The SURVEYOR Scanning System
collects up to 15,000 coordinate points every second at a higher level of
accuracy and repeatability than is possible with contact measurement
methods. 3D Laser Scanning allows for a complete check of all the
geometry of complicated parts more consistently and error free than
conventional, time-consuming CMM inspections. Non-Contact scanning of the
parts means that the results are independent of the skill of the
operator. The company looked at several different suppliers of laser
scanners and selected Laser Design’s Surveyor Model DS 2020 because they
were impressed by the fact that Laser Design’s process inspection
standards were as high as theirs. The Laser Design scanning system offers
accuracy to 8 microns on small parts and scanning speeds up to 15,000
points per second. The customer ran measurement standard assurance tests
on the equipment and verified that it provides measurements that are
repeatable within 0.0003 inch. The customer said that Laser Design
provided a turnkey system that was so easy to set up and use that, even
though they had never used a laser scanner before, they were generating
accurate point clouds in less than two hours.”
Evaluating the
resulting point cloud
Laser Design
partners with Geomagic, which provides a software package that
also plays a key role when implementing this inspection system. Geomagic
Qualify software allows the user to create a graphical comparison (Color
Error Map) of the manufactured part vs. the CAD model, by displaying
differences between the two in a range of colors, indicating the magnitude
of the variation from the design intent. By visually comparing the CAD
database to the point cloud of the first article generated by the laser
scanner, the customer can now instantly see differences and make an
evaluation of the impact or seriousness of the deviation. For example,
consider the case where a feature, such as a boss, is not machined
correctly in the injection mold. If the top of the boss is highlighted in
red, chances are it’s either too short or long, as red is used to indicate
a deviation outside acceptable tolerances. It could easily take hours to
see the same pattern looking at individual numbers in a spreadsheet. On
the other hand, suppose that the part has warped. This is an entirely
different problem that requires making changes to the molding process
rather than the mold itself. With the graphic you can easily see where
the part has twisted out of shape during the cooling process. It is very
difficult to identify the location of the warped feature by only looking
at numbers on a spreadsheet.
“If you are
viewing a single dimension on a spreadsheet, you can see if it is good or
bad but you have no way to see it in the context of the entire part
geometry,” the Process Improvement Specialist said. “By viewing the
deviations on the computer screen, the designer can make an informed
decision as to whether the deviated feature has any impact on the
performance of the part.” The new software also makes it easy for design
engineers to evaluate the seriousness of the variations. Often, tolerances
are assigned to broad areas of the component even though they have no
functional significance. The Geomagic QUALIFY software provides Feature
Measurements of single or hundreds of typical GD&T measurements
graphically displayed and listed in a Spread Sheet for conventional part
measurement reports. These Spread Sheet reports and the Color Error Maps
can be saved and automatically applied to subsequent part scans for
automated report analysis and output further saving large quantities of
time for multiple part tool inspections. This assures that each part is
measured identically. This new highly automated process further minimizes
the need to created detailed drawings as part of the design process. In
the past, the only time the detailed drawings were normally used was to
inspect the first article. The drawings are no longer needed now that the
inspection can be carried out far more efficiently on the model itself.
Since the drawings take as long to create as the model itself, their
elimination reduces design time by 50%.
“The time and cost savings are enormous,”
according to the customer. “It used to cost $25,000 to $30,000 to hire an
outsourcer to perform a complete inspection of a first article. Or we
could spend two to three weeks ourselves to capture maybe 1300 points and
compare them one by one to the part specifications,” “Now, when I receive
the first article, within just 15 minutes I can scan it and generate a
point cloud containing millions of points that is sufficient to define
every contour regardless of its complexity. I then export the point cloud
and turn it over to the person who knows the part the best, the design
engineer. You don’t need to be an expert to use the software. The user
interface is intuitive and follows a simple workflow: align, compare,
evaluate and report. Using this approach in less than a day he can
completely characterize the first article and determine what, if any,
corrections need to be made to the process or tool at a cost of only a few
hundred dollars. The time savings are just as important as the cost
savings since while the inspection process is occurring the injection
molding press is normally sitting idle.”
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