Geomagic DSSP Helps Get Full Power Back

By Bob Cramblitt

The top image shows the interior of a pump used to generate hydraulic pressure to start a steam turbine at a Kentucky power plant. The bottom image shows a closeup of the damage sustained by the impeller. Using DSSP, a new impeller was manufactured and the pump was back in action in twoweeks, enabling full-capacity power generation for 26,000 customers. (Images courtesy of RER)

A centrifugal pump might seem an odd thing to be grateful for on Thanksgiving, unless you are John Allen, maintenance superintendent for Owensboro Municipal Utilities in Kentucky.

  It seems that a couple of weeks before Thanksgiving of 2006,  a centrifugal pump used to generate hydraulic pressure to start a steam turbine in the Owensboro power plant had a major malfunction. Half of the shroud was destroyed and the tops of the impeller blades were sheared.

  Without the pump, the generation unit couldn’t operate,  reducing the power plant’s capacity to provide electricity to its 26,000 customers by a third. There was no backup for the pump, since under normal conditions it can perform for 40 or 50 years without needing replacement. Nor were there CAD models or documentation to help rebuild it.

  Under pressure to replace the pump, Allen turned to long-time contractor Rotating Equipment Repair (RER, Sussex, WI). RER has nearly 25 years of experience and a 38,000-square-foot facility housing the latest in pump repair and manufacturing equipment. The company also has partners nearby with unique credentials: Advanced Design Concepts (ADC), a company that specializes in digital shape sampling and processing (DSSP) for Harley-Davidson, Briggs & Stratton, Simons-Voss; and Signicast, which operates one of the largest, most innovative foundries of its kind in North America.

From the left: An ADC engineer used a Cimcore head and Romer arm to scan the damaged impeller. This is raw point-cloud data from the scan. Geomagic Studio automatically wraps pointcloud data to form a polygon model that can be used in Pro/ENGINEER software. This is a pattern of the master vane. ADC used Pro/E to pattern the master vane,making exactcopies around the axis. (Images courtesy of ADC)

Traversing physical and digital worlds
The pump project began on an evening two weeks and a day before Thanksgiving, when RER received the severely damaged pump from the Owensboro plant. The next day, RER disassembled the pump and began preparing it for reconstruction.

  Based on the original dimensions of the pump, the damaged impeller, and its experience in pump design, RER built a 2D model of the impeller in AutoCAD and obtained cross dimensions from it. Over the weekend, a pattern maker used clay to build up one of the damaged impeller vanes to match original specifications. 

  Five days later ADC received the impeller with the built-up vane and the AutoCAD dimensional drawings. ADC was a natural fit for this project. It is less than seven miles from RER, but more importantly, the company has used DSSP to recreate everything from classic Harley-Davidson gas tanks to cylinder head ports for Nextel Cup race cars.

  DSSP can enable companies to navigate easily between physical and digital worlds. This capability helps companies speed development of products based on legacy designs, conduct accurate engineering analysis with digital models that replicate manufactured parts, inspect faster and more precisely, and continuously improve products over their lifespan.

  Accelerating the design
Since the impeller vanes were identical, ADC only needed to capture one vane, then recreate it for the CAD model. By noon, Justin Ebbe, an ADC engineer, had captured the impeller geometry using a Cimcore scanning head with a Romer arm.

  Geomagic Studio software was used to automatically align the scan data, then “wrap” the point cloud with a polygon model. The Geomagic Wrap module eliminates time-consuming and labor-intensive surface reconstruction work by mathematically wrapping a polygonal surface around point-cloud data. The patented process is automatic, but gives users control to fine-tune the model if necessary. Wrap creates watertight polygonal models without approximation. The RER polygon model was saved as an STL file that could be used as a guide for the CAD model.

“Geomagic enabled us to align the scan data easily and quickly create an STL model that accurately depicted the part in a form that Pro/ENGINEER CAD/CAM software could handle,” says Chris Mulhall, the ADC design engineer who managed the project. “This allowed me to model the part and simultaneously compare the model to the scan data in a time-efficient manner.”

  The Geomagic model served as the basis for building a parametric model of the impeller in Pro/ENGINEER. Mulhall overlaid the scan data onto the Pro/E model of the master vane as it was being created to ensure accuracy. Exact copies of the master vane were then made and patterned around the impeller’s axis. Geometry from the shroud on the bottom of the impeller was used to recreate a model of the top shroud.

  The initial plan was to produce a two-part model, which could then be machined, assembled, and welded. But some quick adjustments by RER led to a more time-efficient solution.

This is a cutaway image showing the modelderived from scan data of the damaged impeller.

The CAD model of the impeller prepared by RERfor quick investment casting.

This image shows the completed cast of theimpeller. (Images courtesy of ADC)

Casting the quick way
RER had originally planned to do a sand-cast mold of the impeller. This requires intricate wood molding boxes that are handmade and filled with casting sand or a mixture of sand and clay. The process is labor intensive, and the resulting metal castings are rough, usually requiring a fair amount of hand work — including hammering, grinding, and sanding — to make them suitable for manufacturing. They also take a lot of time, a luxury RER didn’t have.

“It can take four to six weeks to get foundry time for a sand casting, then another two to three weeks for the foundry to complete the mold,” says Eric Kirschling, the RER mechanical engineer who headed up the impeller project. “The standard turnaround time is 8-to-12 weeks, which we couldn’t afford.”

  To shorten the turnaround time and increase accuracy of the mold, Kirschling looked into investment casting. In this process, a wax mold is coated in ceramic and placed in a furnace, where the ceramic hardens, and the wax melts away, leaving a finished ceramic mold. RER found a way to further accelerate the process by working with Signicast in nearby Hartford, WI.

  Signicast manufactures molds directly from the CAD model with a Mori Seiki rapid milling system. A hard coating is applied to the mold,  and then the liquid metal is poured into the casting to form the part.

“The end product is of better quality than a sand casting,”  says Kirschling, “it’s smoother and has tighter tolerances.”

  Mulhall had finished the two-part CAD model of the impeller when Kirschling contacted him with the change in plans, which now required a one-piece model.

“It took Chris about an hour to switch gears and create the one-piece model,” says Kirschling.

The entire digital reconstruction of the impeller — from scanning to geometry processing to CAD — lasted just a day and a half. RER now had the solid model from ADC, ready for Signicast’s process, sometimes called quick casting.

A reason to give thanks
Signicast did the rapid prototyping and created three investment castings in a week. RER heat-treated the castings that night, then machined and balanced them the next day, Thanksgiving eve. The pump was fully assembled and shipped by the end of Thanksgiving day.

  The combination of DSSP, MCAD work, and quick casting saved anywhere from 6 to 10 weeks of time, according to Kirschling’s estimations.

  At Owensboro,  John Allen had a reason to give thanks. Although the pump replacement was only part of his problem, it was a major part, as an entire energy-generating unit was out of service until it could be replaced. While work was being done on the pump, Allen and his team were busy cleaning the tank in which the pump was submerged and repairing damage in lube oil piping caused by the parts of the pump that blew into pieces.

“We didn’t have a spare part, so it was important to replace the pump as quickly as possible,” says Allen. “RER met our needs to get the pump back and working as soon as possible, and now we have a couple of replacements if ever needed.”

More Info:
Advanced Design Concepts
Pewaukee,WI
adcinc1.com

Geomagic
Research Triangle Park, NC
geomagic.com

Mori Seiki
Rolling Meadows,IL
moriseiki.co.jp

Romer Cimcore
Wixom. MI
us.romer.com

Rotating Equipment Repair
Sussex,  WI
rerpump.com

Signicast
Hartford,WI
signicast.com

Bob Cramblitt owns Cramblitt & Company in Cary, NC (cramco.com), and writes about design, engineering, and IT technologies. Send e-mail about this article to [email protected].