General Die Maintenance
General die maintenance is a very important part your overall roll forming system preventative maintenance program. Production losses due to die breakage, feed problems, or other die related issues can make it very hard to compete in today’s economy. Periodically maintaining the die set can greatly reduce the frequency of these problems.
Operators – The operator is your first line of defense against line stoppages due to die problems. The operator has the ability to visually inspect the die set and the parts being produced. Prior to starting up the line, the operator should visually inspect the die (without removing it from the press) and look for chipped punches or buttons (if visible), or any items that appear to be loose. The operator should also check the parts coming off of the line and look for excessive burrs on the punched material. If the die was set up properly, there should be a fairly consistent burr around the punched hole. If the operator notices that there is a heavy burr on one side of the hole, this would typically indicate that a punch or button has chipped and should be serviced.
Die Configuration / Design - The configuration or design of the die should never cause unexpected shut downs. If you are having problems with broken springs, pulling die posts or die section breakages, this may indicate a problem with the initial design, or previous die maintenance. For example, a die spring has a life expectancy based on the ratio between preload, compressed length and free length. Almost every die spring manufacturer will give you the recommended distances for long life right in their catalog. Use this information to make sure your springs are the correct replacements as recommended by the die manufacturer. Pulling die posts or bushings is typically caused by a vacuum that is created during the die cycle. Die posts and bushings have minimal clearances to help maintain alignment of the tools. At times this clearance does not allow air to pass by at the same rate in which you are cycling the press. Adding a vent hole to allow the air to exhaust as the die cycles should eliminate this problem.
Documentation - All good maintenance programs start with good documentation. Any work completed on the die set should be recorded along with the number of cycles the die set had completed prior to being serviced. There is no need to record the number of strokes down to the last stroke, but the more accurate you are the better you will be able to set the frequency for your regularly scheduled maintenance on the die set. The recorded information can also be useful in determining the best punch or button materials, coatings or even the effects of various types of coolants for the application.
Die Maintenance – When performing maintenance on your die set, you should always check for loose bolts and dowel pins. A bolt or dowel pin that comes loose during a production run can be very damaging to your die set. Also when grinding punches and buttons it is very important to select the proper grinding wheel. If the wrong wheel is selected, you can generate additional and unwanted heat due to the wheel not breaking down properly. Generating too much heat when grinding your punches and buttons can ultimately reduce the hardness of your tool or even cause tiny stress cracks if it is cooled too quickly after the heat is generated. It is also important to remove any burr generated by the grinding of the punches. This should be done with a fine stone or emery cloth. In some applications it is also a good practice to slightly break the sharp edge created by the grind (based on material thickness and type). A sharp edge on a punch will typically dull faster and chip more frequently than a punch that has been slightly blunted.
Written by Robert Nelson