In-Die Analog Sensors Can Assure High Product Quality

Using analog sensors to measure important part features during the stamping process can reduce the need for time consuming in-process checks, expensive attribute gages, and costly part sorting.

However, just as important, maintaining part quality through the use of sensors and control systems can ensure that out-of-tolerance parts are identified and contained before they get to the customer‚’s good-parts bin. This goal is often accomplished using analog output sensors. 

Analog sensors work well in part-measurement applications, because instead of simply indicating part presence, a specific feature of the part can actually be quality checked and ‚“measured‚” by its proximity to the sensor. 

An analog sensor (below) checks a part for correct bend angle.  Even though at setup and initial inspection the part is acceptable, the tool may begin to wear or fatigue, the material thickness may change slightly from coil to coil or soften, or the ram of an older press might back off.

All these events can enable the 90o bend to relax, causing a quality issue.  If a bad part is discovered, depending on the technology available in the press controller or PLC, the press can be stopped, the part can be diverted to a scrap bin after it exits the die, or by using movable sections, the form blocks can open or close to tighten or loosen the form as necessary.

Below, an analog proximity sensor measures depth of draw.  The sensor is mounted directly under the pressure pad, aimed at the bottom surface of the can.  At the bottom of the stroke, the sensor will send an output based on the distance between the bottom of the draw and the sensor face.  If the dimension is wrong, a number of problems could be present:  The draw could actually be shallow, a foreign object between the strip carrier and the die could be standing the part off, the shut height could be set too high, or the draw punch could be damaged.

By Drew Stevens at drew.stevens@balluff.com
www.balluff.com/metalforming