Case Studies: Amazing Optical Measurement
When lives could be endangered by the failure of a part, making that component takes on a new importance. “Our components are what we call life critical,” says Joe Kinsella, president of Pointe Precision Inc. (Plover, WI). “Consequently, we take inspection very seriously.”
Since 1995, Pointe has specialized in producing critical tolerance parts for fuel control systems, primarily for the aerospace industry. The company also makes precision parts for medical and industrial applications. A mid- to low-volume contract manufacturing operation, the company is focused on making parts with a high degree of precision.
When a part is processed at Pointe, a feature-based inspection criteria guide is created for every dimension at every operation. Every machine workstation is equipped with surface plates and the necessary inspection equipment to allow operators to perform consistent and reliable in-process inspection.
On-Time, In-Tolerance“Our customers’ tolerancing is becoming very stringent,” says Kinsella. “Right out of the chute you have to deliver perfect parts. We have learned that our inspection systems must quickly, repeatedly ensure that the many critical dimensions and features on our machined parts are well within tolerances.”
One of the busiest pieces of inspection equipment is a Starrett HD400 optical comparator. Optical measurement is a noncontact technique that graphically displays and measures parts with dimensions and shapes that would be difficult to measure with regular gages.
Pointe has found an edge by trimming time from the production cycle for each product it produces with no compromise in quality. The lathe operators have found significant timesavings in the use of the Starrett HD400 for visual verification on the shop floor.
While the plant depends on a state-of-the-art, climate-controlled metrology lab for some measurements, shop floor inspection is an integral part of the production process at Pointe. The Starrett HD400 is stationed on the manufacturing floor in the center of its turning operation, which is comprised of a dozen lathes. The Starrett HD400 is equipped with a Metronics (Bedford, NH) QC200 digital readout device used to produce geometric dimensioning and tolerancing (GD&T) calculations.
“The Starrett HD400 allows us to verify a wide variety of product characteristics very quickly,” says Chris Spranger, quality assurance manager with Pointe Precision. “We measure many features, including angles, outside diameters, runout, hole sizes, corner breaks, threads, radii and shaft lengths on parts measuring 2 inches or less.”
Spranger says the Starrett HD400 “drastically shortens our in-process inspection time, as well as our changeover time between manufacturing work orders.” Spranger also says that if the company used conventional gages to verify all the features it measures on the optical comparator, inspection times would be two to four times longer.
Visual Versatility“We use the Starrett HD400 to get the measurements quickly and easily,” says Spranger. “We also have measured the distances between holes with the HD400 by placing pins in the hole for easy location.”
The Starrett HD400 is a busy machine, with 12 machinists using it more than 20 times per day as they verify complex parts.
“We like the comparator a lot,” says Marty Cattanach, level 3 operator. “The quick release fixture on the table is a huge time saver vs. a manual crank handle. The screen rotates very easily for checking different angles. Plus we can check distances and concentricity with the Starrett, which we couldn’t do on our previous system.” Cattanach also says that the HD400 has sharper, clearer optics than the previous system, allowing more precise edge inspection.
“The Starrett comparator has more bells and whistles than its predecessor,” says Randy Grezenski, manufacturing engineer. “We actually use it for some measurements that previously required a CMM [coordinate measuring machine] located halfway across the plant in an inspection room.”
Increased ThroughputAccording to Spranger, minimizing setup time is a critical factor in keeping the company competitive. Some runs involve as few as 50 pieces. Others may involve a thousand. By placing the Starrett HD400 on the shop floor in the machining area, Pointe eliminated time-consuming trips to the inspection room. And if the company had to inspect its parts using only micrometers, indicators and other conventional gages, inspection time would be much longer.
Spranger estimates the Starrett HD400 has reduced overall inspection time by up to 75%, depending on the complexity of the part.
Each one of Pointe’s 12 turning centers is set up for its next job two to seven times in a 24-hour period. Setups are usually completed between 30 minutes and three hours after they are started. The company estimates that 10% to 25% of the setup time is absorbed by the first-article verification process. “You can easily see the impact of an inspection process that took three or four times longer to complete,” says Spranger.
He points out the turning department not only has the Starrett HD400, but also Starrett surface plates and other gages located near the machine for use with each lathe. Even first-article inspection is frequently done on the shop floor rather than in the CMM/inspection room.
“We have found optical, noncontact measurement to be an integral part of our turning operation,” Spranger says. “The Starrett HD400 provides a more reliable, repeatable and far faster method for inspecting parts, including setup and the all-important first-article inspection.”
The L.S. Starrett Co.