Page 31 - MetalForming June 2010

for an edge. Your strip may be too thin for the edge to affect the inductive or photo- electric field and the sensor may be blind to its presence within its sensing field.
Metallurgy—A common item often overlooked is the metallurgy of the target. When using inductive proximity sen- sors, this can make or break the appli- cation as most such sensors are ideally presented in the catalogs using pure iron as the material being detected in the sensitivity charts and specifications. Iron gives the best performances by these sensors in terms of sensing-field ranges and sizes. Well, I have yet to see pure iron being stamped in our industry. From stainless to copper to aluminum, every type of material seems to find its way into stampings except pure iron. With a few exceptions, inductive sensors will have a different range based on the metallurgy of the target. We will detail this challenge in a future installment of this column.
Why are the above factors so impor- tant? Consider the environmental real- ities of the stamping process (our next topic). The die and press are vibrating and shaking while the atmosphere with- in the die may be filled with an oil mist. If you do not have enough of an edge, surface, detection-field area or proper metallurgy for detection then you may be setting yourself up for the proverbial “nuisance stops.” You’ll irritate produc- tion personnel as the sensor, seemingly at random, stops the stamping or assembly process. The sensor you chose may have worked well on the test bench with the minimum target requirements, but placed within a die or assembly machine, where the environment caus- es the target to become unstable, the sensor may fail to make its detection.
It is paramount that your target selec- tion satisfy the needs of the sensor and the realities of the mechanical process with- in which the detection will take place.
The next installment will address the metallurgical, reflective and refrac- tive properties of targets and how to best match a sensor type to them. MF
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