Common Die Protection Mistakes

They say that experience is the best teacher, but it is much more efficient to allow others to fail, and learn from their experience. This article describes several of the most common mistakes made by both new and experienced sensor users:

Using sensors without bench testing first
Companies embark on sensor implementation programs and have varying levels of success. Whether it's a big-budget plant-wide program involving a team of people, or a one-person 'pay-as-you-save' ROI-based implementation, some programs succeed while others fail. All programs and approaches are a little different, but there is one ubiquitous step among the successful users: Bench Testing.

The best way to ensure that a sensor will work in the die is to try it out on the bench first. A well-stocked sensor lab (this will be covered in a future article) will likely pay for itself the first time that one of those ideas that 'looked good on paper' proved to be ineffective in practice. The worst (and most expensive) place to prove out sensors is in the press when the die should be in production.

Forgetting about the environment where the sensor will be installed
Try to anticipate all failure modes when you install your sensors. All too often, sensors are destroyed by the very event they're supposed to detect when that event occurs in an unanticipated fashion.

Here's an example:
The best practice for checking stripper position at BDC (usually to detect pulled slugs) is to install inductive proximity sensors in the bottom die to ensure that the stripper comes all the way down at BDC. Occasionally, a user will buck this trend and install the sensors in the upper die behind the stripper. The sensors are installed so that they will actuate at BDC if the stripper is too high by one material thickness. This method will be effective for detecting pulled slugs, but the sensors will be crushed when anything larger than one material thickness (like a piece of broken punch) ends up under the stripper.

Installing "Yellow" sensors in the upper die
A "yellow" sensor is a sensor that is normally open, and that only actuates when a problem exists. If you install a yellow sensor in the upper die, the wire to the sensor will eventually break due to repeated flexing. To a die protection control, a yellow sensor with a broken wire looks exactly like a yellow sensor not detecting a problem. A normally open sensor (that only actuates when there's a problem) can often be 'converted' to a normally closed "Red" sensor (that is always actuated, and turns off when there's a problem) by selecting the normally closed instead of the normally open output. The die protection control will immediately detect a broken wire on a Red sensor, and stop the press.

Trying to use one type of sensor for every application
Standardization is good... to a point. The various types of electronic sensors have their own advantages and limitations, and not all are suited for every application. Try to avoid the natural inclination to stick with what has always worked rather than trying something new. Bench testing in a well-stocked sensor lab will help you to know when it's time to try something new. If you can barely get something to work on the bench, it is unlikely that it will be reliable in a production environment.

Trying to use sensors that do not meet the electrical requirements of the control
There are many output options available when you're ordering electronic sensors, and not all outputs are compatible with all controls. If you are unsure if a particular sensor is compatible with your Wintriss die protection system, a quick call to 1-800-586-8324 will give you the answer.

Not planning the wiring before installing sensors
More sensors are replaced because of cable damage than any other reason. This can be avoided by using die mounted junction boxes and carefully planning the sensor wiring so that the cables are protected. Often, the most difficult part of installing a sensor is figuring out how to get the wiring from the sensor to the junction box. If you wait until the die is assembled and the sensor is installed, it is probably too late. All new die designs should have the sensor wiring on the CAD drawing.