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NOVEL METHOD FOR MEASURING THE LENGTH OF FREE-FORM SPRINGS

How do you determine the diameter of a seal energising spring after manufacture, while it is still an irregular loop of coil with its ends welded together and not yet formed into a circle by the seal it will eventually strengthen? The standard options are traditional circular go / no-go gauges for a specific size of large spring or a conical step gauge rising in one millimeter increments for a family of smaller sizes. However, Redditch-based Clifford Springs has established a more accurate process using a Nikon Metrology iNEXIV VMA-4540 CNC video measuring machine, installed in May 2016.

Nikon Metrology 1173-2
To a repeatability measured in single-figure microns, the optical measuring equipment automatically determines the length of a free-form loop of coiled spring to determine what its circumference will be when it is circular, after which dividing by pi produces a precise result for the diameter.

Clifford Springs now plans to use the iNEXIV VMA-4540 to count automatically the number of coils per unit length of spring, looped or unwelded, which predicts its load deflection characteristics in use. 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, as well as much faster, than current manual procedures using an optical profile projector. Another important benefit is that an automated system eliminates the risk of human error.

Managing director John Clifford commented, “Customers are increasingly asking for reports with proof of the numerical values from our inspection of the springs we manufacture, but only transcription of manually measured results was previously possible.

“Since May this year, the Nikon optical measuring 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 our products and reports.”