Case Studies: Riding the Rails to Quality
Therefore, high precision in measuring wheel bore diameters during machining so that the wheels can be fitted perfectly to an axle is critical to the successful and smooth performance of train wheels. According to Mike Russell, quality assurance manager at Progress Rail’s plant in Jackson, SC, comparing the new and old ways of measuring bore diameters has shown a 10-fold increase in accuracy with the newest instrument recently acquired by the company.
GR&R at 15%Consistent quality is also key for the success of this leading supplier of rail, rail anchors and track-work components.
“The optimum fit between the axle and the wheel bore is critical, and it is necessary to hold a tolerance of 0.002-inch on the wheel bore,” he says. “We formerly used a stick micrometer for measuring these wheel bores and it wasn’t very reliable.”
Today the company uses an electronic pistol-grip bore gage from the Fred V. Fowler Co. (Newton, MA) to get its readings. The Bowers XT Holematic Pistol Grip Bore Gage allows a wide measurement range of ¼-inch to 8 inches without the need to change anvils. It has two preset memories, self-centering heads and an RS232C output. It has a tungsten carbide measuring face on all three-point heads from 5 inches and provides constant measuring pressure.
“In studies of gage repeatability and reproducibility (GR&R) with the old stick gage, we showed 159% or no better than 1.59 times the tolerance. This meant that it was impossible to hold the 0.002-inch tolerance effectively. Most manufacturers like ourselves look for a 30% GR&R and prefer it to be near to 10 percent if possible. With the Bowers Gage, we achieved a 15% result,” Russell says.
Fewer misfitsThe company’s previous experience in fitting wheels to axles had shown a “misfit” rate of 1%, but during August’s first half Russell says the rate dropped 0.65%. Further, the new gage has eliminated the factor of operator fatigue. Such fatigue contributes to unreliability in meeting Progress Rail Services’ quality standards. The time it took per measurement has dropped from 30 seconds to 5 seconds.
“When we worked before,” Russell adds, “three different operators gave three different readings. Now, they are all on target and give us greater confidence in our methods.”
The importance of the low misfit rate, according to Russell, has to do with the standards set by the Association of American Railroads (AAR). When the wheel is mounted it either must meet the minimum or maximum tonnage requirements stipulated by AAR. “That is why our goal is not to have any misfits,” he says.
To enable the new gage to provide optimum results, Fowler supplied the company with special spherical anvils to accommodate the intentionally rough surface finish in the wheel bores. This enables the operator to place the gage into the component by resting the squaring collar on the wheel face to obtain an instant reading by releasing the pistol trigger. The spherical profile on the anvils takes care of any misalignment of the gage and the axis of the bore.
Russell is recommending the other company wheel shops in California, Texas, Indiana, Kentucky, Nebraska, South Carolina and Canada switch to the new bore gage. “It takes variability out, assures accuracy and is easy to use,” Russell says. “Training time is minimal.”
Fred V. Fowler Co. Inc.
- The company improved its GR&R from 159%, or no better than 1.59 times the tolerance, to 15%.
- The misfit rate dropped from 1% to 0.65%.
- The new gage reduced operator fatigue that contributed to unreliability.