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.
The Codex of Business Writing Software for Real-World Solutions 2.pptx
50 Tips For Better Die Protection
1. 50 Tips for Better Die Protection
Jim Finnerty
Product Manager
Wintriss Controls Group LLC
jim.finnerty@wintriss.com
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. #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. #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. #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. #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. #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. #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. #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. #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. #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.
13. #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.
14. #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
15. #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.
16. #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
17. #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.
18. #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
23. #18 – Spring-load Proxes for Hole Detection
Sensor
Spring
Bushing
Strip
24. #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.
26. #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.
27. #20 – Make Your Own Apertures
Aperture
(also called a “slit plate”)
No aperture -
Wide effective beam
Aperture installed -
Narrow, more precise
effective beam
28. #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
29. #21 – Sensing Color Differences
Emitter
Beam
Receiver
Viewing
Area
Detecting Area
30. #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.
31. #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)
32. #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.
33. #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
34. #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)
35. #25 – Use a Diffuse Sensor “Screen” to
Detect Part Ejection
Diffuse Reflective
Sensors
Sensing Area
36. #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
37.
38. #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.
39. #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/
40. #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.
41. #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…
42.
43. #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.
44.
45. #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.
46.
47. #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
50. #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
52. #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
53. #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.
54. #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
55.
56. #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.
57. #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.
58. #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.
59.
60. #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.
61. #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.
62. #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.
63. #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.
64. #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.
66. #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.
67. #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.
68. #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