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50 Tips For Better Die Protection

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This presentation provides you with fifty ways to improve the way you protect your metal stamping dies. Everything from improving the press stopping time, to selecting and wiring sensors is covered here.

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50 Tips For Better Die Protection

  1. 1. 50 Tips for Better Die Protection Jim Finnerty Product Manager Wintriss Controls Group LLC jim.finnerty@wintriss.com
  2. 2. #1 – Know the Critical Angle  The “critical angle” is the last point in the press cycle where an E- stop will stop the ram before the die closes  The goal of die protection is to stop the press before the die can be damaged  You should know the critical angle for every die, in every press that can run it.  To prevent die damage, the control must be finished checking the sensors before the critical angle.  SmartPAC PRO’s Brake Monitor can help you to establish the critical angle
  3. 3. #2 – Improve the Press Stopping Time  The faster the press stops, the more time a die protection system has to detect problems  In addition to regular brake maintenance, the following things can improve the press’s stopping time:  Quick dump valves on older clutch/brake units  Properly, or better, automatically set counterbalance pressure  Valves properly sized to the press
  4. 4. #3– Use The Proper Clutch Air Pressure  Set the clutch air pressure according to the press manufacturer’s recommendation.  Many presses are running with the clutch air pressure set too high.  Excessive clutch air pressure adds to the stopping time, giving the die protection system less time to work.
  5. 5. #4 – Know When to Top Stop  Your die protection control should be set to E-Stop the press for virtually every die-threatening event  The exception is for events that occur after the critical angle in presses without hydraulic overload protection  The only thing worse than crashing a die is crashing a die and sticking the press on bottom.  If the press is equipped with hydraulic overload protection, use E-Stop all the time
  6. 6. #5 – Use Variable Stop When Appropriate  Some die problems can occur both before or after the critical angle – long feed cycles for example.  An E-stop can cause the press to stick on bottom, a top stop can allow unnecessary damage.  Variable Stop (a.k.a. “Smart Stop”) gives E-Stop protection right up to the critical angle, and then switches over to top stop.
  7. 7. #6 – Eliminate Nuisance Stops  A press stoppage initiated by a sensor when no real problem exists is called a “nuisance stop”  If there are too many nuisance stops, the system usually ends up bypassed or disabled  The ONLY time a sensor should stop the press is when there’s a real problem  Sensors that require adjustment during set up cause nuisance stops.
  8. 8. #7 – Keep Sensors Out of the Upper Die  Any wire that is repeatedly flexed will eventually break  Simple wiring is good wiring – Sensors in the top complicate the wiring  Sensors in the upper die are far more likely to be damaged by excessive shock
  9. 9. #8 – Use Normally Closed Static Sensors  A static event is a condition that is never supposed to occur while the press is running normally  High loop, end of material, and low lube are examples of static events  When you have a choice of using a normally closed or normally open sensor, use the Normally Closed  A controller cannot tell when you forgot to plug in a normally open sensor.
  10. 10. #9 – Start With The Strip Layout  When looking for a place to install a feed sensor, start with the strip layout.  Select a feature that can be detected by a sensor.  Select a location in the die where the sensor will detect that feature only when the strip is fully fed.  Bench test.
  11. 11. #10 – Half Feed for High Speed  If the feed cycle is long enough, or the press runs fast enough, full feed won’t occur until after the critical angle.  If this happens, your full feed sensor needs to top stop the press to avoid sticking it on bottom.  Die damage can result…. But … Don’t stop there.  Install a sensor to detect the strip ½ way through the progression (or early enough to E-stop).
  12. 12. #11 – Know Your Feed Tolerance (and use it)  If you try hard enough, you can detect a misfeed of 0.0005”.  Don’t do this.  Your pilots have the ability to align the strip if the feed is not perfect.  Determine how hard you want to allow your pilots to work, and use the “slop”.  Don’t make your feed detection too precise.
  13. 13. #12 – Feed Sensor Placement  It’s often necessary to install separate shortfeed and overfeed sensors  The best place for a shortfeed sensor is at the end of the die  The best place for an overfeed sensor is at the beginning of the die
  14. 14. #13 – Get The Feed Moving  The sooner the feed starts, the sooner it can finish.  Get the feed started as soon as the pilots have cleared on the upstroke.  Give your die protection a chance to work.
  15. 15. #14 – Call the Sensor Companies  Sensor companies only advertise a fraction of what they make in their catalogs  If you need something different, call the sensor companies  Sensor lengths  Cable lengths  Outputs  Other materials (both construction and detection)  Detecting distances
  16. 16. #15 – Avoid Adjustable Proximity Sensors  Adjustable (separate amplifier) prox sensors are more expensive, and offer no performance advantage over self contained sensors  The amplifier must be put into an enclosure on the die  If there’s an adjustment that can be made, someone will make it whether it needs to be adjusted or not.
  17. 17. #16 – Stick With Shielded Prox Sensors  Shielded proximity sensors can be flush mounted in metal, unshielded sensors cannot  Shielded sensors can be better protected  Use unshielded sensor only when you need extra range from a smaller sensor
  18. 18. #16 – Stick With Shielded Prox Sensors  Shielded (flush mountable)  Unshielded (non-flush mountable)
  19. 19. #17 – Sensing a Hole With a Proximity Sensor
  20. 20. #17 – Sensing a Hole With a Proximity Sensor
  21. 21. #17 – Sensing a Hole With a Proximity Sensor
  22. 22. #18 – Spring-load Proxes for Hole Detection Sensor Spring Bushing Strip
  23. 23. #19 – Use Powerful Photosensors  The most popular through-beam photosensors used for die protection have a 7-meter (23’) range  Typically, these are installed with the emitter and receiver less than 1 foot apart.  The extra range (excess gain) allows the sensor to “burn” through lube, scratches, and grime on the sensor lenses.
  24. 24. #19 – Use Powerful Photosensors RE Max. 23’
  25. 25. #20 – Make Your Own Apertures  Apertures make through-beam photosensors more precise.  Most applications require them  The sensor companies sell aperture kits.  If you make your own, you can make them the exact size and shape that you need for your application.
  26. 26. #20 – Make Your Own Apertures Aperture (also called a “slit plate”) No aperture - Wide effective beam Aperture installed - Narrow, more precise effective beam
  27. 27. #21 – Sensing Color Differences  Mechanical convergent photosensors can detect differences in color  Also called “V-Axis” sensors  Much less expensive than specialized color detection sensors
  28. 28. #21 – Sensing Color Differences Emitter Beam Receiver Viewing Area Detecting Area
  29. 29. #22 – Sensing Near a Background  Trying to use a diffuse or direct reflective photosensor to sense an object near a background can be tricky.  If the background is larger or more reflective than the target, the sensor will detect the background instead of the target.  Use an Optical Convergent or Optical triangulation sensor instead.
  30. 30. #22 – Sensing Near a Background Emitter Beam Viewing area receiver #1 Viewing area receiver #2 Viewing angles are adjustable Focal Area (shifts when viewing angles are adjusted)
  31. 31. #23 – Infrared-Only for Part Ejection  Do not use visible light mini light curtains or visible light diffuse reflective sensors for air-ejected parts.  Often, a blast of air will carry some lube out of the die.  The lube can “fool” a visible light sensor into thinking the part came out.  Infrared sensors are much less susceptible to oil in the sensing field.
  32. 32. #24 – Use IP-67 Rated Sensors  A sensor’s IP rating tells you the kind of environment that the sensor is designed to tolerate  The higher the number the better  An IP 67 rated sensor is dust-tight and can be submerged in liquid to a depth not exceeding 1 meter.  Do not use a sensor with a rating below IP-65
  33. 33. #25 – Use a Diffuse Sensor “Screen” to Detect Part Ejection  When air-ejected parts fly out of the die with an unpredictable trajectory, a single sensor may not cover enough area  You can “stack” diffuse reflective sensors, and wire them in parallel to a single control input  (My record is 8)
  34. 34. #25 – Use a Diffuse Sensor “Screen” to Detect Part Ejection Diffuse Reflective Sensors Sensing Area
  35. 35. #26 – Protect the Lenses  The lenses of most photosensors are made from plastic  It’s high-quality plastic, but is no match for a sharp burr on a metal part.  When mounting the sensors, take steps to protect the lenses from damage
  36. 36. #27 – Avoid Fiber Optic Sensors  The main enemy of photosensors (especially fiber optics) is lube build-up.  Lube on the ends of the fibers reduces the amount of light coming out of the emitter and into the receiver  Since fiber optics have a short range to start with, lube build-up reduces it to nothing, causing nuisance stops.
  37. 37. #28 – Use Lenses on Fiber Optic Sensors  If you must use fiber optics sensors, look for fibers that accept lenses  Although expensive, the lenses can increase the range of some fiber optic sensors by a factor of 5.  Sensors with lenses are less susceptible to nuisance stops caused by lube build-up/
  38. 38. #29 – Part Ejection Sensors Close to the Die  Mount part ejection sensors as close to the die as you can, while still ensuring that the part is out  This is particularly important for top knock-out dies  Too much distance between the sensor and the die can cause a late detection.
  39. 39. #30 – Mount Sensors to Avoid Rewiring  If possible, sensors should be installed so that they don’t have to be removed during routine die maintenance  More sensors are damaged during handling than during use  When wires are disconnected and reconnected, they tend to get shorter, and shorter…
  40. 40. #31 – Throw Away The “L”-Brackets  Many sensors come with sheet metal “L”- brackets for mounting  Throw them away.  This is metal stamping, stuff is going to get knocked around.  If you think you’ve overdone the robustness of the mounting brackets, you’re on the right track.
  41. 41. #32 – Epoxy Prox Sensors into Removable Inserts  Smooth-barrel proximity sensors should be epoxied into a slip-fit hole.  Often, it is necessary to remove sensors when working on the die; so the sensors should be installed in removable inserts.  If possible, “key” the inserts so that they can be installed only one way.  If installed in a die section, make the insert thinner than the die section and shim it as needed.
  42. 42. #33 – Anticipate All Failure Modes  When mounting sensors, ensure that they will not be destroyed if something goes awry. For example:  Do not mount stripper position sensors behind the stripper plate.  Make sure a big over feed will not destroy your overfeed sensor.  Make sure a big material buckle will not tear your material buckle sensor off the press
  43. 43. #34 – Don’t Use Set Screws
  44. 44. #34 – Don’t Use Set Screws
  45. 45. #35 – Recess Proximity Sensors  The ends of most proximity sensors are made from plastic  When installing the sensors, recess the face slightly to protect it.  Relieving the edges of the mounting hole gives more consistent detection
  46. 46. #35 – Recess Proximity Sensors
  47. 47. #36– Use Loctite Green on Threaded Proxes  Install threaded proximity sensors without Loctite for the first run or two.  When you’re sure the sensor is in the right place, apply Loctite green  Loctite green wicks into assembled parts
  48. 48. #37 – Standardize… Carefully  Standardization (on sensors, controls, and wiring accessories) is good.  Standardizing on junk is bad.  Thoroughly test all items (for months if necessary) before you standardize.
  49. 49. #38 – Protect Your Sensor Cables  Keep sensor wire runs as short a possible  Run wires through metal tubing  Run wires in channels machined into the die set
  50. 50. #39 – Plan Die Wiring Ahead of Time  Die wiring is an important but often overlooked aspect of sensor installation.  Sometimes, running the wires is the most challenging part of installing sensors.  Over the long term, the wiring can “make or break” the effectiveness of sensor implementation.
  51. 51. #40 – Use Die-Mounted Junction Boxes  The single most important thing you can do to preserve the sensors is to use a die mounted junction box.  Most sensors have to be replaced because of damage to the cables.  Press-mounted junction boxes force you to keep long lengths of cables coiled up on the dies.
  52. 52. #41 – Mount Junction Boxes Carefully  If driven very deliberately, a fork truck can destroy almost anything.  Die mounted junction boxes should be installed in or on top of the die shoe.  Avoid mounting anything on the underside or edges of the die set.
  53. 53. #42 – Don’t Be Afraid to Use More Than One Die-Mounted Junction Box  Die mounted junction boxes are strongly recommended.  For large dies, it may make more sense to use more than one junction box.  Trying to wire everything into one box can be time consuming, expensive, and a maintenance nightmare.  The large connectors required for complex installations can be very expensive and hard to wire.
  54. 54. #43 - Know Your Control’s Input Requirements  Sensors must match the input requirements of your controller.  It is much easier (and cheaper) to select the proper sensor up front than it is to add adapters later on.  Most sensors are available with several output options, if you are unsure which to use, call your control supplier.
  55. 55. #44 – Use Auto-Enable if Available  There are times when the sensors need to be disabled.  Among experienced sensor users, a contributing cause to most die crashes is running the press with the sensors disabled  Many control systems offer “Auto Enable” based on a stroke count; i.e. the sensors will be automatically enabled after “X” strokes.
  56. 56. #45 – Avoid Chlorinated Water-Based Lube  Many water-based lubes are chlorinated to reduce algae, fungus, and bacteria growth.  These additives can ruin the plastic housing and cables of sensors.  Ask you lube supplier to formulate the lube without chlorine.
  57. 57. #46 – If You’re Not Going to Bench Test, Don’t Bother Trying to Implement Sensors  Seriously, save your money  The worst time to find out that a sensor location is wrong is when you’re trying to run parts.  Avoid debugging sensors in the press.
  58. 58. #47 – Be Creative
  59. 59. #48 – Do the Worst Die First  If you’re just starting out with die protection, don’t pick an “easy” die to start.  Install sensors on the die that crashes the most.  It gives you the quickest return on investment.  When the worst die stops crashing, you’ll win converts.  It’s no harder to install sensors on a die that crashes all the time than on one that never crashes.
  60. 60. #49 – The Most Common Mistakes  Using sensors without bench testing first.  Using sensors that need to be adjusted  Forgetting about the environment where the sensor will be installed.  Trying to use one type of sensor for every application.  Trying to use sensors that do not meet the electrical requirements of the control.
  61. 61. #50 – Stay Current  When it comes to technology and electronics (including sensors), knowledge is obsolete almost as soon as it is gained.  Stay current:  Sensors Magazine - www.sensorsmag.com  Wintriss Die Protection Knowledge Base

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