Page 30 - MetalForming June 2010

George Keremedjiev has been writing this column for more than 20 years. He regularly consults with metalforming companies worldwide and provides metal- formers with training on the appli- cation and implementation of sen- sors for die protection. For more information on his seminars and consultancies, contact:
Tecknow Education Services, Inc. P.O. Box 6448
Bozeman, MT 59771
phone: 406/587-4751
fax: 406/587-9620
www.mfgadvice.com E-mail: gk@mfgadvice.com
Starting with this column and con- tinuing for the next five install- ments, I will address some of the most important fundamental topics crucial to the proper application of electronic sensors for metalforming and assembly. The applied science behind sensors is not hard, but it is critical to one’s success when it comes to die pro- tection and the error-proofing of assem- bly operations. There is no magic or luck involved. Instead, a clear under- standing of the basics followed by trial and error will lead to many successful sensor applications plant wide.
We begin with targets. It is para- mount that a clear definition of the exact target be made in order to facil- itate the appropriate “best guess” as to what sensor to try, followed by a bench test to verify the robustness of the choice. No matter how big or small the part, die component or assembly tooling, the target area is to be fully defined in both its metallurgical and dimensional aspects. Future install- ments will address the environmental conditions surrounding the target, but for our purposes here, we will limit our discussion to the target itself, inde- pendent of its immediate environment.
Edges—There are an infinite num- ber of edge types within our industry. One could be faced with the challenge, for example, of the proper detection of a short feed. The edge of the strip that will be detected for this may be a nice- ly cut straight edge, a rough cut edge, a curved hole edge or steeply angular, say within a triangular hole. The edge of interest may be smooth or burred. It can be slightly tapered. The edge itself may have coined sections. Why think about all of this? Well, consider for example that inductive proximity sensor catalogs
are based on edges being perfectly smooth, flat and traveling in a perfect perpendicular fashion sideways into the inductive field. In later installments, we will look into the sensing-field shapes of the various sensor types. But in all cases, the edges are expected to be ideal.
Surfaces—The target surface entering a sensing field (be it inductive or photo- electric) is expected to be perfectly flat, solid and in a perfectly straight head-on trajectory as the target penetrates the sensor’s detection field. Your stamped part may have target surfaces that are round, gently tapered, steeply angled, punched with holes, dimpled, coined, slotted, etc. Again, the ideal expectation as shown in the sensor catalog will not be met in many surface-detection applications. The same holds true for tooling-component detection. The returning cam surface that you wish to monitor may be angled instead of being the ideal flat. The punch you wish to monitor for breakage may have some fairly intricate surfaces as would the detection of a tap surface, deeply threaded as it is, being detected during an in-die tapping application.
Area—The target entering the sen- sor’s detection field must have a mini- mum amount of area in order for the sensor to react. Again, the catalogs assume that this is a given but it may be far from so with your chosen target. Be the sensing field inductive or photo- electric, there must be a minimum amount of material that the field needs to react in order for the sensor to turn on or off. If this minimum is not present then the sensor may work erratically or not at all. This is true for edge or sur- face detection. You may have a deeply drawn part that is small in diameter and consequently presents a small surface area for detection. The same holds true
METALFORMING ELECTRONICS GEORGE KEREMEDJIEV
Sensor Fundamentals, Part 1 Targets: Edges and Surfaces
This CD-ROM presents dozens of George’s columns as well as papers and exclusive new presentations covering all aspects of die protection and part-quality inspection, starting and maintaining sensor programs, the role of controls in in-die sensing, and the benefits of a sound sensor program. Order it online at www.metalformingmagazine.com.
28 METALFORMING / JUNE 2010
www.metalformingmagazine.com