Providing Value With 3-D Scanning
One case study shows how 3-D scanning can trim lead times by quickly developing tooling for complex castings while ensuring dimensional accuracy.
Glenn McQuarter, Bay Cast Inc., Bay City, Michigan
(Click here to see the story as it appears in the November issue of Modern Casting.)
A casting buyer needed a large, curved component as part of a new project, but the design’s size (1,200 lbs.) and curved shape presented specific challenges that severely limited the available methods of manufacturing. Not only that, the turn-around time for the project was relatively short.
The customer approached Bay Cast Inc., Bay City, Mich., which specializes in heavy-sectioned castings and large-format machining services.
This specific project highlighted how metalcasters can provide added value with 3-D scanning as a method of ensuring the accuracy of first article castings and minimizing tooling work. The customer needed 16 large castings in a 1030 steel alloy, including 10 large elbows (1,200-lb. castings with a maximum envelope size of 132 x 58 x 15 in. and a maximum wall thickness of 1.44 in.) and six small elbows (500-lb. castings with a maximum envelope size of 93 x 42 x 8 in. and maximum wall thickness of 1.12 in.).
3-D scanning involves the use of a three-dimensional data acquisition device to acquire X, Y and Z coordinates (or points) from the surface of a physical object. The conglomeration of these points, known as a point cloud, then can be used to create a 3-D mesh and, eventually, a solid model in various CAD formats. These models then can be used in inspection, analysis, rapid manufacturing and reverse engineering efforts.
The customer initially pursued casting the parts, which were part of a new project, because of the difficult design. The only other viable method for production required rolling and shaping approximately 18 individuals pieces and then welding them together. Casting this component as a single part had the potential to lower costs and reduce lead times, as long as they could be cast to the desired shape.
Capabilities & Concerns
Timing on this particular project was critical because these castings were part of larger fabrication assemblies. Figure 1 shows the elbow piece in its final application. Bay Cast’s engineering department, with a minimum amount of experience with these castings’ geometry at the time, had major concerns about casting this particular project:
- Will parts with this much surface area and so little weight encounter a restraint to contraction on the large open sides?
- Can the length of the longest overall dimension be held to a consistent tolerance?
- Will the overall pattern shrinkage factor hold true on the critical surface of the casting (shown in Figure 2)?
The customer requested an overall tolerance of plus or minus 0.25 in. on all dimensions, so the initial plan was to produce a one-off first article large elbow from single-use polystyrene pattern tooling, inspect it and then make the necessary adjustments on the balance of the pattern equipment. Bay Cast decided the castings would be produced in CNC-cut polystyrene tooling from customer-supplied CAD models so any necessary adjustments could be made quickly. Also, if major changes were required, a pattern could be immediately recut. A 0.19-in. pattern shrinkage allowance was selected, but with 0.25 in. of stock added to the perimeter of the pattern so some extra material would be available for fit adjustments during finishing.
Producing a First Article
The three-axis geometry of the elbow pieces made traditional layout of the rough castings nearly impossible to achieve, especially with foundry rigging still attached. To get a better idea of the geometry of the casting at shakeout and move forward on first article approval, the metalcasting supplier decided to outsource a complete 3-D scan of the part. The casting was sent to Diversified Tooling Group, Sterling Heights, Mich., to utilize the company’s equipment and software for high density white-light scanning of surface geometry. The results were then converted into an .STL file and analyzed against the original build model using mesh processing software. In the case of the elbow piece, the surface geometries of the scan data and the build model were compared in a “best fit” scenario.
The results were submitted to the customer for review and preliminary approval. These parts were originally intended to be manufactured from bent and rolled fabrications. Bay Cast discussed with the customer dimensional requirements and preferred reporting method to facilitate approval on all of the castings. Based on the data, only the cope edge was beyond the 0.25-in. tolerance originally requested, which could be remedied easily by removing the extra material from the surface prior to shipping. From the customer’s standpoint, the surface scans provided an excellent visual tool with regard to the shape of the casting. The customer also requested analysis of the section views (in inches) based on a supplied 2-D drawing.
One of the drawbacks of analysis software is in slicing the models to compare cross-section geometries. Although no additional scanning work was necessary, this additional request required conversion of the scan data into a CAD file to overlay the build model and analyze the required sections.
Inspection performed on the first article small elbow piece showed similar results with additional material (0.4 to 0.6 in.) along the cope edge of the casting. Both large and small first articles were brought into tolerance by removal of the excess material during finishing. Additionally, tie bars were introduced to maintain dimensional stability through heat treatment (shown in Figure 4).
Ensuring Accuracy
After making the required adjustments to the patterns, Bay Cast poured the remaining castings which were again inspected utilizing the same criteria as the first articles. All of the results were within customer requirements, and dimensional variations from casting to casting were minimal considering all of the pieces were poured from a separate polystyrene pattern. A summary of the variations are shown below in Tables 1 and 2.
3-D point cloud scanning has been used for a variety of applications in various industries. For the metalcasting industry in particular, the technology can be a tremendous tool in verifying a pattern’s dimension and inspecting a first-article casting for shrinkage and warpage.
From a machining standpoint, especially in large format jobbing operations, 3-D scanning technology can be used to qualify castings for rough or finish machining with an additional purpose of optimizing a machining strategy. This allows for “level machining,” which means that CNC milling equipment can be programmed based on a part’s scanned geometry. As a result, less spindle time is spent cutting “air” during the rough machining process, which potentially increases throughput and reduces costs.
In the case of the two different elbow castings, the data from 3-D scanning provided general insight into the metalcasting process with respect to dimensional repeatability of unusual geometries utilizing polystyrene pattern equipment. By casting these components, and ensuring they met required tolerances via 3-D scanning, the customer eliminated complex layout and assembly processes at its facility. The scan data provided proof that the component met its required shape.
This article is based on the paper, “Practical Application of 3-D Scanning in a Jobbing Foundry,” presented at the Steel Founders’ Society of America’s 2014 Technical & Operating Conference.
ncountering a scenario in which you are forced to suddenly and immediately suspend melting operations for an extended period can be a death sentence for many metalcasting facilities. Small to mid-size businesses are the backbone of the industry, but many do not survive when forced into extended downtime. One disaster-stricken metalcaster, however, found resilience through its own perseverance and a circle of support from peers, friends, suppliers, teams from installation and repair providers, an original equipment manufacturer and even competitors.
Tonkawa Foundry, a third-generation, family-owned operation in Tonkawa, Okla., was entering its 65th year of operation this year when a significant technical failure ravaged the power supply and melting furnaces on January 17. Thanks to the textbook evacuation directed by Operations Manager Carrie Haley, no one was physically harmed during the incident, but the extent of emotional and financial damage, and just how long the event would take Tonkawa offline, was unclear.
Tonkawa’s power supply and two steel-shell furnaces would have to be rebuilt. No part of the reconstruction process could begin until the insurance company approved removal of the equipment from the site. The potential loss of Tonkawa’s employees and customers to competing metalcasters seemed inevitable.
Within two days of the incident, repair, installation and equipment representatives were on site at Tonkawa to survey the damage. Once the insurance company issued approval to begin work, the installation team mobilized within 24 hours to remove the equipment and disassemble the melt deck.
Since the damaged equipment was installed in the 1980s and 1990s, Tonkawa and an equipment services and repair company quickly strategized a plan and identified ways to enhance the safety, efficiency and overall productivity of Tonkawa’s melt deck.
“The most critical issue was for our team to organize a response plan,” said Steve Otto, executive vice president for EMSCO’s New Jersey Installation Division. “We needed to arrive at Tonkawa ready to work as soon as possible and deliver quickly and thoroughly so they could get back to the business of melting and producing castings, and minimize their risk of closing.”
Several years after Tonkawa’s melt deck was originally installed, an elevation change was required to accommodate the use of a larger capacity ladle under the spout of the furnaces. Rather than raising the entire melt deck, only the area supporting the furnaces was elevated. As a result, the power supply and workstation were two steps down from the furnaces, creating a number of inconveniences and challenges that impacted overall work flow in the melt area. Additionally, the proximity of the power supply to the furnaces not only contributed to the limited workspace, but also increased the odds of the power supply facing damage.
The damage to the melt deck required it to be reconstructed. It was determined to be the ideal opportunity to raise the entire deck to the same elevation and arrange the power supply, workstation and furnaces onto one level. The furnace installation company provided the layout concepts, and with the aid of Rajesh Krishnamurthy, applications engineer, Oklahoma State Univ., Tonkawa used the concepts to generate blueprints for the new deck construction. The results yielded a modernized melt system with an even elevation, strategically placed power supply, enhanced worker safety and increased operator productivity.
“Eliminating the steps and relocating the power supply farther from the furnaces was a significant improvement to our melt deck,” Tonkawa Co-Owner Jim Salisbury said.
Within four days of insurance company approval, all damaged equipment had been removed and shipped for repair.
The insurance company required an autopsy on the damaged furnace before any repair work could begin. The forensic analysis was hosted by EMSCO in Anniston, Ala., in the presence of insurance company personnel, as well as an assembly of industry representatives from the companies who had received notices of potential subrogation from the insurance company.
Tonkawa’s furnace was completely disassembled while the insurance company’s forensic inspector directed, photographed, cataloged and analyzed every turn of every bolt on the furnace over a nine-hour workday. The coil was dissected, and lining samples were retained for future reference.
While the furnace sustained extensive damage, it did not have to be replaced entirely.
Structural reconstruction was performed to address run-out damage in the bottom of the furnace, a new coil was fabricated and the hydraulic cylinders were repacked and resealed. Fortunately, the major components were salvageable, and ultimately, the furnace was rebuilt for half the cost of a new furnace.
“The furnace experienced a significant technical failure,” said Jimmy Horton, vice president and general manager of southern operations, EMSCO. “However, not only was the unit rebuilt, it was rebuilt using minimal replacement parts.”
Though work was underway on the furnaces, Tonkawa was challenged with a projected lead time of 14 weeks on the power supply.
When accounting for the three weeks lost to insurance company holds and the time required for installation, Tonkawa was looking at a total production loss of 18-20 weeks. From the perspective of sibling co-owners Sandy Salisbury Linton and Jim Salisbury, Tonkawa could not survive such a long period of lost productivity. After putting their heads together with their furnace supplier, it was determined the reason for the long turnaround on the power supply could be traced to the manufacturer of the steel cabinet that housed the power supply.
The solution? The existing cabinet would be completely refurbished and Tonkawa would do the work rather than the initial manufacturer. This reduced the 14-week lead time to just five weeks.
Tonkawa is the single source for a number of its customers. Although lead-time had been significantly reduced, the Tonkawa team still needed a strategy to keep the single source customers in business as well as a plan to retain their larger customers.
Tonkawa pours many wear-resistant, high-chrome alloys for the agriculture and shot blast industries. Kansas Castings, Belle Plaine, Kan., which is a friendly competitor, is located 50 miles north of Tonkawa. Kansas Castings offered Tonkawa two to three heats every Friday for as long as it needed.
“We made molds, put them on a flatbed trailer, prayed it wasn’t going to rain in Oklahoma, and drove the molds to Kansas Castings. We were molding, shot blasting, cleaning, grinding and shipping every Friday,” Salisbury Linton said.
Others joined the circle of support that was quickly surrounding the Tonkawa Foundry family.
Modern Investment Casting Corporation (MICC) is located 12 miles east of Tonkawa in Ponca City, Okla. Though MICC is an investment shop and Tonkawa is a sand casting facility, MICC’s relationship with Tonkawa dates back years to when Sandy and Jim’s father, Gene Salisbury, was at the helm.
“Gene was always willing to help you out,” said MICC owner, Dave Cashon. “His advice was invaluable for us over the years, so when the opportunity arose to support Sandy and Jim, we volunteered our help.”
MICC offered to pour anything Tonkawa needed every Friday in its furnace. Tonkawa brought its alloy, furnace hand and molds, while MICC provided its furnace and a furnace hand for three heats. Many of the specialty parts Tonkawa produces were completed with MICC’s support.
When Salisbury Linton approached Cashon and asked him to issue her an invoice to cover the overhead Tonkawa was consuming, Cashon told her if she brought in six-dozen donuts every Friday morning they’d call it even.
“We’re all kind of like family,” Cashon said. “We’re all part of the same industry and though we may be friendly competitors at times, you don’t want to see anybody go through what they’ve gone through and it could have just as easily been our furnace that failed. While we all take the appropriate measures and perform maintenance to prevent these scenarios from occurring, they unfortunately still occur from time to time in our industry.”
Tonkawa had recently added steel work to its menu of services and Central Machine & Tool, Enid, Okla., was able to take Tonkawa’s patterns and fulfill its steel orders so it would not fall behind with those customers, while CFM Corporation, Blackwell, Okla., took three of Tonkawa’s employees on a temporary basis and kept them working during the downtime. Additionally, a couple of Tonkawa’s major suppliers extended their payables terms.
Thanks to Tonkawa’s suppliers, friends and its personnel’s own passion, persistence and dedication, the business is up, running and recovering—placing it among the few shops of its size to overcome the odds and remain in business after facing calamity.
Nearly eight months after that devastating Saturday evening in January, Salisbury Linton reflected on the people and events that helped Tonkawa rise from the ashes. “We certainly would not have the opportunity to see what the future holds for Tonkawa if it weren’t for all the kind-hearted people who cared about what happened to us. Everyone still checks in on us.”