Redditch-based seal energising spring manufacturer, Clifford Springs, is using a new, highly accurate, automated procedure on a Nikon Metrology iNEXIV VMA-4540 CNC video measuring machine to determine the length of an irregularly shaped loop of welded coil. The result is equivalent to the circumference of the spring when it eventually strengthens a circular seal.
The iNEXIV is more accurate than the former hard gauges. Up to 1,000 successive coordinates around the loop are recorded automatically and subsequently linked to create a series of small, straight lines which are added together to find the length. To correct for the fact that it is the arcs between the points that should really be totalled, Nikon Metrology’s engineers calculated a small correction factor running to eight decimal places that increases the measured length to arrive at the true circumference.
The new process has the added advantage that the number of coils per unit length of spring can be counted automatically, which predicts its load deflection characteristics. Compared with the present method of manually counting the number of coils in a given length and using a formula to extrapolate the total number for the whole spring, the optical method will be more precise. Furthermore, measuring the angle between successive coils in a spring and their distance apart will be more accurate and reliable as well as much faster than current manual procedures on a shadowgraph from a profile projector.
Managing director John Clifford commented, “Customers are increasingly asking for reports with numerical values from inspection of the springs we manufacture. The Nikon Metrology machine has allowed us to print off actual readouts of spring diameter and soon coil count and geometry will be included. It has enhanced the perception of our metrology expertise amongst our customers and increased the confidence they have in the reports we produce.”