Service Bureau Completes Laser Scanning Job in a Quarter the Required Time
To reverse engineer and replicate its cast bronze seal faster and cheaper, the University of Cincinnati outsourced the laser scanning process.
Laser scanning made it possible for the University of Cincinnati to relatively inexpensively reverse engineer and replicate its cast bronze seal for several upcoming open space projects. The last time the university hired a sculptor to create art for a university seal was 1963 and that original seal was salvaged from a building demolished a few years ago. This time the university needed a slightly smaller seal for its University Plaza project.
The University of Cincinnati Master Plan reasserts the campus as an active pedestrian precinct conducive to human interaction, study and play. It recognizes that the physical environment strongly influences the educational experience. A key element of the Master Plan is the development of gateways at the entrance to each campus that tie all of them together with common design elements. A critical element of each gateway is the university's seal. The seal also is needed for a new open space that is being developed in front of the University Pavilion, called the University Plaza. The centerpiece of this plaza is a one hundred-foot long granite water fountain that accommodates two, albeit smaller, bronze seals on the south end of the granite water fountain.
In due course, the university took advantage of the ability of laser scanning to capture the geometry of the original seal in a 3-D electronic file that allows it to be reproduced and scaled up or down with such a high level of accuracy that it can hardly be distinguished from the original. Rather than purchasing and operating a laser scanning machine, the university shipped the salvaged original seal to a service bureau, Laser Design, Inc. (Minneapolis, MN) that scanned the seal into a CAD file and managed the complete process of creating the new seals involving several other companies.
One company created a rapid prototype model from the CAD file, then a pattern shop cast a pattern from the rapid prototype to fix imperfections in the original and cast a perfect pattern which, in time, was supplied to the foundry that cast the actual seals in bronze. The seals will be mounted on a University Plaza water fountain and on selected sandstone gate walls found at the university's campus entrances. Total cost was about $10,000 for four castings and includes an electronic file that could be used to recreate 3-D seals of any size and a pattern that could be used to produce additional copies at a much lower cost.
Challenge of Replicating a Seal
Mauricio Luzuriaga, architect and planner with the Office of the
University Architect, faced the challenge of replicating the seal for
this and other upcoming projects, "Finding a sculptor to recreate a
seal at this point in time would have been very expensive and time
consuming. This time we decided to see if technology that had been
developed since the last time we hired a sculptor could do the job
faster and cheaper. We fairly quickly zeroed in on laser scanning. The
technology looked appropriate, but it hardly would have made sense for
the university to purchase a laser scanning machine for this one
project." So Luzuriaga, assisted by student Millind Surve, looked for a
service bureau that could handle the project, "We were connected with a
company that was extremely helpful, not only in their laser scanning
capabilities, but also in their expertise in a wide range of reverse
engineering technologies. Laser Design explained the entire process,
helped us select from the various alternatives and ended up providing a
complete solution that gave us excellent quality at a fraction of the
cost."
A key advantage of using a service bureau is that it makes it possible to take advantage of the latest equipment. Greg Hertzler, director of engineering says that recent advances in laser scanners have made it possible for the company to dramatically reduce the cost of the scanning service throughout the last five years. "A new data acquisition architecture has been developed that makes it possible to take advantage of the incredible speed of today's laser probes," Hertzler explains. "The key is the ability to collect the laser scanner profile data in real time with the laser's positional location moving over the part at a fast scanning speed. We also are using faster processors and more RAM to collect the point data, making it possible to acquire more than fourteen thousand points per second. With this newer equipment we can typically complete a scanning job in a quarter the time that was required a few years ago and pass the savings on to our customers."
How It Was Done
"The project began when the university shipped the existing seal to us
and told us they needed the new, smaller seals back in two months,"
explains Larry Carlberg of Laser Design. "Our first step was to scan
the seal using our Surveyor 3-D scanning system, which collected
millions of X, Y, Z coordinate points on the original casting creating
an accurate, detailed 3-D surface model that can easily be converted
into a CNC program. Since there is no probe that must stay in contact
with the part, laser scanning is able to replicate the smallest details
without concern over whether the probe is small enough to fit inside
them. In about two hours, we completely scanned the original model to a
degree sufficient to create a perfect reproduction of the seal. We
would have been almost done except that there were some imperfections
on the original casting that needed to be corrected."
Carlberg continues, "First, we generated a file in STL format that included the complete surface geometry of the seal. We scaled down the model because the university wanted a smaller size seal to fit the specifications of the water fountain. We sent that file to QuickParts.com, a service bureau that specializes in stereolithography (SL). The SL process carves the CAD model up into thin layers about one-tenth of a millimeter thick. Then a laser paints the layers one by one, exposing plastic in the machine and hardening it. The process was repeated layer by layer until the model of the seal was complete."
But SL does not produce a perfect replica of the design that was captured during laser scanning due to the stairstep nature of the process. Carlberg arranged for the rapid prototype to be shipped to Vick Pattern and Mold (Bloomington, MN), which began by eliminating several cracks that were in the original, and removing the stairstepping of the SLA model with hand tools and skilled expertise. Once that process was completed, they took a picture of the improved SLA pattern and sent it to Luzuriaga at the university for review. After he approved it, the company cast a reverse-image mold from the modified pattern and used it to create a new pattern with all of the imperfections corrected and replicating the texture on the original seal. This pattern was then sent to St. Paul Brass and Aluminum (St. Paul, MN)—the foundry responsible for casting the actual brass parts. This foundry took the pattern, built a plywood frame around it, and filled the frame with sand and a hardener that makes the sand stick together when the pattern is removed. Four duplicate molds were created and used to cast the bronze seals needed by the university.
"The pieces look great, even better than the original," Luzuriaga says. "The price also was great. We ended up buying four castings for less than $10,000 and that includes an electronic file and a pattern that we can use whenever we need additional copies. The delivery time for the project was better than I expected. We received the seals almost exactly two months from the time we issued a purchase order. Laser Design managed the entire project from start to finish. These new seals are being implemented at several very important projects that are critical to the university's Master Plan. This experience has demonstrated that using a laser scanning service bureau is the way to go for geometrically-complex, architectural details that need to be reproduced to high levels of accuracy."
