Dimensional & Calibration Laboratories Inc. (Hackensack, NJ) is a 17025-accredited dimensional inspection laboratory. The laboratory’s services include calibration of metrology instruments and first-article inspection.
The laboratory had a first-article inspection job that required the measurement of interior dimensions of a small pressure-actuated switch for a medical device customer. The part was cylindrical with small radii and the customer wanted measurements of the ramps around the center radius. The measurements were requested as part of a reverse engineering initiative.
Dimensional & Calibration Laboratories found that its metrology equipment could not measure the part without destroying it. This led the laboratory to contact its sister company, Dengel Associates (Hackensack, NJ), a distributor of metrology equipment, for a nondestructive solution.
To measure the interior dimensions of the part nondestructively, the lab found that the solution lay in producing a casting of the part’s interior space. This would convert the part’s hard-to-measure negative space to a positive casting that would be accessible to the laboratory’s metrology instruments.
Reprorubber from Flexbar (Islandia, NY) was the product of choice. Reprorubber is a metrology-grade, self-curing casting material that can provide replica castings of both internal and external forms. It produces reproductions in less than 10 minutes and does not require a release agent in most applications. The material consists of a two-part base/catalyst system that produces rubber-like replica castings ranging from 30 to 50 durometer on the Shore A-2 scale.
The part that needed to be measured was very small, so the Reprorubber had to be used in such a way as to keep the casting from being damaged when it was removed from the part. Clay was used to create a dam to contain the Reprorubber, making it easier to pull the part out after the casting was set.
“The beauty of the Reprorubber is that you don’t have to use a release agent such as wax or silicone,” says Mike Reinhart, president of Dimensional & Calibration Laboratories Inc. “Some hard casting materials require a release agent, which don’t always work and can interfere with reproducing very small part features.”
After Reinhart had the Reprorubber casting of the interior of the part, he used a video measurement machine to obtain the needed measurements. Reinhart says that other than the use of Reprorubber, the only other way to obtain the measurement nondestructively would be with a specialized coordinate measuring machine (CMM) designed to measure small IDs.
Reinhart estimates the use of Reprorubber and a video measurement machine represent a total investment of approximately $50,000. If he were to invest in a specialized CMM for the same types of measurement, that figure would jump to approximately $150,000.
Dimensional & Calibration Laboratories uses Reprorubber for casting undercuts and grooves when such features cannot be accessed with other equipment without destroying the part. “Some of these parts are prototypes and they could be one of a kind,” says Reinhart. “So if we can provide customers information without destroying their part, it is of value to them.”