Case Studies: CMMs Mow Down Quality Bottleneck
January 2, 2008
Richardson Manufacturing (Springfield, IL) is in the heart of earth-moving country, and their primary customers are the makers of enormous machines that push, haul and scrape dirt. During their 50-year history, Richardson has become a fully integrated engineering and production metalworking company. They accept CAD drawings from customers, then manage the parts from prototyping through production, and along the way make whatever fixtures are required to build them.
Given who its customers are, Richardson’s niche is the enormous part. They supply axles, wheel hubs, differential carriers, anchor brakes, and brake hubs for earth-moving trucks that have gross operating weights from 0.5 million to nearly 1.4 million pounds. Engine ratings are what one would find on a small ship, often in excess of 3,000 hp.
To handle the huge torques and shock loads that go with moving ore and overburden, parts for these trucks typically weigh many tons. For instance, a rear axle for one truck is 7 feet long and weighs almost 8,500 pounds. But size is not a problem for Richardson. With turning tables that measure up to 120 inches, they can process parts that would make most machine shops quake. Machining a single rear spindle of a mining truck even produces a ton of chips for the recycler.
No Room for ErrorLarge as they are, these components must be machined to surprisingly tight tolerances. Earthmoving equipment is no longer assembled using the “bigger hammer” approach-if two pieces did not fit, then the builder made a “fine adjustment.” Today, the culture of quality is the same as it is in Detroit. Most parts are machined from cast iron or cast steel to tolerances that are as tight as ±0.002 inch.
The reason for this is that precision is directly related to reliability. Flanges and bearings and mounts must fit well with mating components because poor fits distribute loads unevenly across bolted joints. Assemblies such as axles and transmission housings would leak or crack from overloads. And in earthmoving, reliability is even more important than gross hauling capacity.
“We are known for making big parts, but also quality parts,” says Justin Bishop, quality control manager for Richardson. “We rarely experience rejects. With items this big, it pays to be precise.”
Years ago, the company instituted a strict quality program, and at the heart of it was a conventional coordinate measuring machine (CMM) that occupied a large portion of the metrology lab. To check part dimensions, technicians would bring a forklift to the machining table, load the part onto the lift, drive it to the metrology lab, then position it so that the CMM could measure key dimensions. After measurements were taken and checked against specifications, the piece had to be reloaded on the forklift and returned to production. Average time for checking one part-including loading, hauling and programming the CMM to follow the part contours-was about two hours.
This bottleneck in the Richardson throughput was about to change.
Step Change in Throughput“One of our customers told us about a new instrument, a miniature CMM, that they were using on-line to check assemblies in their plant,” explains Bishop. “Parts didn’t have to be carried anywhere-the instrument could go to the parts. We saw a demonstration of it and immediately recognized that it could improve our work flow.”
That instrument was the Faro Gage, a compact version of the Faro Arm from Faro Technologies Inc. (Lake Mary, FL), designed to be carried anywhere and set up in a moment to take measurements of any structural feature. Like its larger sibling the Arm, which Richardson also has on hand, the gage operates via articulating links that are joined by rotational joints. It can be extended to measure any 3-D object within its 48-inch spherical reach. It can reach in, around and over most surfaces, to touch a spot to be measured.
Gage software makes the instrument simple and versatile. Little or no training is required to take measurements, and anyone with a modest exposure to computers can come up to speed on it quickly. Also, no unique programming is required to inspect parts of various shapes.
Measurements are taken by touching the probe on the gage’s tip to a particular point and clicking a button on the handle to capture a point. Points are retained in the software as a file. After this is done, the program can compare measured values to dimensions in the original blueprints in order to evaluate the flatness and parallelism of planes, hole or boss position.
The gage becomes a pipeline to customers, too. As a history of the measurements is compiled during a production run, these can be formatted as geometric dimensioning and tolerancing or statistical process control reports-in tabular and graphical forms-for customer evaluation.
“We regularly e-mail quality reports to customers, for a particular lot of parts, or for their continuous supply stream,” says Bishop. “These reports let everyone know what’s going on in our production.”
Although not designed specifically for them, the gage has proven to be ideal for metalworking shops. Sealed joints keep out contamination and the housing is designed to accept the abuse that is common in machining and sheet metal shops. With an optional magnet clamp built into its base, the gage can be attached to almost any jig or production machine and inspect parts as they travel down a conveyor.
Richardson is no exception. Technicians employ the gage all over their plant. At one moment, technicians use it to check dimensions on a part on a milling machine. The next, they carry it to the area where they build up assembly fixtures, to check the position of surfaces on a building tool. In their metrology lab, it will be used to qualify other assembly gages and standards.
“With the Faro Gage, all these functions are relatively simple,” says Bishop. “No one has to be called in to write a program to do a particular function; it’s pretty much touch and shoot.” Quality control personnel at Richardson discovered that it was in such demand around their plant that they ordered a second one.
Time CompressionAn instrument that is simpler and faster than what it replaces not only increases throughput, but also can improve the overall quality posture of a company. More points are inspected on a greater percent of production. But it is the boost in throughput that gets management’s attention.
Richardson has experienced a huge decrease in time-to-inspect parts. “Although the gage is easy to use, the biggest benefit to us is how it has streamlined our production,” affirms Bishop. “On average, our old technique for inspecting parts took two hours. With the Faro Gage on the floor, we don’t drive parts to the CMM and back, and our inspection time is down to 20 minutes, not two hours.”
- Faro Technologies Inc.