Laser Scanning Accelerates Inspections at Rochester Metal Products
In-depth analysis of castings brings the big picture into view.
For 75 years, Rochester Metal Products has been manufacturing castings in Rochester, Indiana. Starting as a captive supplier to two manufacturers of hand-push lawnmowers, the enterprise has grown to produce 50,000-plus tons of gray and ductile iron castings every year. Their customer base includes companies in the rail, heavy truck, construction and agricultural industries. Although approximately 30% of their business is comprised of automotive suppliers, their coast-to-coast client base is truly diverse with the largest customer only accounting for 11% of sales.
Their 200,000 square foot facility is designed to serve a wide range of casting requirements from 0.75 to 50 pounds. The company supplies Class 25, Class 30 and Class 35 gray iron with a capacity of more than 70 tons of saleable castings per day. They also supply 65/45/12 as cast, 80/55/06 as cast and 60/40/18 heat treated ductile iron with a capacity of more than 166 tons of saleable casting per day. Additionally, they provide design engineering assistance for new product development from original concept to prototyping and final production. The company is vocal about their focus on customer service and equally committed to quality assurance backed by the use of state-of-the-art measurement solutions.
Metrology Comes Into View
Rochester Metal Products does not hesitate to invest in technology that will add value to their product offering. During the 1990s, the ISO9001:2008 certified company purchased a bridge coordinate measuring machine (CMM) to aid in their quality inspections. Though primarily a first stage foundry and their castings are rarely used as finished products, they still meet tolerances of ±0.03 inch or 0.8 millimeter to reduce scrap when their customers machine the castings.
Roughly ten years ago, the company purchased a portable CMM articulating arm which not only provided added versatility, but also allowed them to compare inspection results to the nominal CAD model. Over time, the PCMM’s flexibility made it the main method for layouts with the bridge CMM becoming a backup unit. The PCMM was used primarily for PPAP (Production Part Approval Process) to verify sample castings for Rochester Metal Products’ customers. This was a time consuming process depending on the number of data points that needed to be checked using manual hard probe touches. Some customers have over 130 check points on their more complex parts. To improve their rate of throughput, the company began to explore other options.
The Complete Picture Emerges
Rochester Metal Products wanted to learn more about the benefits of laser scanning. Output generated from laser scanning creates a 3-D model, or “point cloud,” of an object’s surface. The dense coverage of data, potentially millions of individual points, creates the point cloud. These results are then compared against nominal CAD values. During CAD-to-part comparison, large point clouds are overlaid on the CAD model for fast visual inspection of deviations. The result is sometimes referred to as a “color map.” Surfaces that are extremely complex with lots of curvature and difficult to access features benefit the most from scanning.
The company purchased the ROMER Absolute Arm with a factory calibrated, integrated laser scanner roughly one year ago to bring a whole new level to their inspections. Instead of manually taking individual points, the scanner is passed over the part almost as though the operator were “painting” it. Making scans at different angles ensures all the relevant geometry is captured. After scanning, the Layout Department overlays the point cloud with the CAD model to see if the part has diverged from the original design intent. Additionally since all their work must be traceable back to NIST (the National Institute of Standards and Technology), the length standard and calibration sphere included with the ROMER portable CMM guarantees the laser’s accuracy.
The time savings from non-contact scanning was an immediate benefit to the company. When the operator needed to take manual points, he had to figure out how to fixture the part. Now he simply sets it on a table and scans. There are no concerns about the part moving, which would cause him to start over, and the whole process moves quicker. This speed is most apparent when Rochester Metal Products makes sample molds when working with a new pattern. Once the Layout Department verifies all measurements are correct back to CAD, the Engineering Department is notified that the tool build was successful and the PPAP moves forward. This process used to take up to a week, but with the laser scanning capability it takes approximately a day or two.
Another area that sees constant use of the arm is the wear review rack. To get an accurate baseline when a new pattern arrives, the Layout Department measures the first castings produced off the new tool to obtain a permanent record of its original state. After a certain number of molds, castings are sent to the wear review rack where they are re-measured and the results are compared against the original data. This shows where the sand has been wearing away at the pattern and whether or not they are still within the tolerances from the initial run. If the castings do show wear, Rochester Metal Products notifies the customer to make the decision to either repair or replace the pattern. Wear reviews started to pile up when points were taken manually. Today they are performed as orders are produced, providing instant feedback on their quality.
With laser scanning capabilities, Rochester Metal Products does not simply report on the highs and lows of a few dimensions as compared to the CAD model. They can provide a comprehensive assessment of a casting. Their inspections are much more proactive with in-depth measurement of features that are difficult to measure such as wall thicknesses and cross sections. They can create cross-sections of the casting in a virtual environment without physically doing so. One such cross-section showed wear that wouldn’t have otherwise been detected. After inspection, they discovered a frequently run part had a square corner starting to round off. Since wear reviews only require a certain number of dimensions, that corner was not called out in the blueprint. The wear was not visible to the naked eye, but would eventually have caused their customer problems in the machining process.
Most of the time, the arm is stationed in the Layout Department. However, its lightweight construction and magnetic base allows it to be moved from the lab to the foundry floor. On the floor, Rochester Metal Products checks alignment on the machines that put patterns and molds together. This capability saves on maintenance costs and ensures a uniform casting without shift. The thermal stability of the arm enables it to function in temperatures ranging from 0 and 50 C (32 to 122 F) with no warm up period or homing procedures. The operator simply turns it on and starts measuring.
Worth a Thousand Words
Laser scanning has given Rochester Metal Products an improved method of communication to share valuable information with their customers. The color map inspection reports show more than just a handful of dimensions. Now a complete view of the product can be seen. With over 2,000 parts that the company produces annually, they do not feel customers fully understand how much scanning is going to help. As Ron Spencer, their quality manager, states, “Now we are able to see the entire footprint of the part instead of best-fit circles and planes generated from the CMM and portable CMM.”
One of the biggest stumbling blocks for Rochester Metal Products has been the technology’s newness to the industry. At first, a customer is understandably apprehensive. They now receive a rainbow colored picture of the casting instead of the more familiar inspection reports containing 2-D linear coordinate relationships, part and probe information, and raw inspection data. Once the customer sees the hundreds of thousands (or even millions) of points represented, the value quickly becomes apparent. As they pass through the learning curve, customers actually favor these reports. At a glance, the picture tells them everything they need to know.