50 Tips For Better Die Protection

50 Tips for Better Die Protection
Jim Finnerty
Product Manager
Wintriss Controls Group LLC
jim.finnerty@wintriss.com

#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

#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

#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.

#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

#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.

#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.

#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

#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.

#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.

#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).

#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.

#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

#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.

#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

#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.

#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

#16 – Stick With Shielded Prox Sensors
 Shielded
(flush mountable)
 Unshielded
(non-flush mountable)

#17 – Sensing a Hole With a Proximity Sensor

#18 – Spring-load Proxes for Hole Detection
Sensor
Spring
Bushing
Strip

#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.

#19 – Use Powerful Photosensors
RE
Max. 23’

#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.

#20 – Make Your Own Apertures
Aperture
(also called a “slit plate”)
No aperture -
Wide effective beam
Aperture installed -
Narrow, more precise
effective beam

#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

#21 – Sensing Color Differences
Emitter
Beam
Receiver
Viewing
Area
Detecting Area

#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.

#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)

#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.

#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

#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)

#25 – Use a Diffuse Sensor “Screen” to
Detect Part Ejection
Diffuse Reflective
Sensors
Sensing Area

#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

#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.

#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/

#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.

#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…

#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.

#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.

#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

#34 – Don’t Use Set Screws

#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

#35 – Recess Proximity Sensors

#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

#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.

#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

#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.

#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.

#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.

#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.

#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.

#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.

#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.

#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.

#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.

#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.

#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

50 Tips For Better Die Protection

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