Tonnage Monitors-101 - A Basic Guide for Stamping Press Load Monitoring

© 2018 - Wintriss Controls Group - All rights reserved
Tonnage Monitors 101
Jim Finnerty
Product Manager – Wintriss Controls

Tonnage Monitoring
 What is it?
 A system that monitors the force being
exerted by a press during the working
portion of the cycle
 Compares the actual working force to
preset limits, and stops the machine when
the limits are exceeded
© 2018 Wintriss Controls Group LLC- All rights reserved

Tonnage Monitoring
 How do Tonnage Monitors work?
 Sensors called strain links are mounted on the frame of
the press in known locations where strain is proportional
to load
 The strain links measure the deflection of the press frame
under load
 A calibrated controller converts the strain link signal to a
tonnage value

Deflection
 When the press is under load, the frame deforms
 It will either stretch or compress depending on the shape
of the frame and the location on it
 The columns of straight side presses get longer under
load
 The inside front portion of a gap frame press stretches
under load
 The back of a gap frame press compresses under load
 Deflection is measured in “microstrain” (parts-per-million)

Straight Side Presses
 A straight side press is constructed like a sandwich
 The base and crown are the “bread”, and the columns are the “meat”
 There are big threaded rods called tie rods inside the columns that
hold the whole thing together
 The tie rods have nuts at each end that are tightened to pre-stress
the whole machine
 The columns are permanently compressed when the press is
assembled
 Tonnage monitors measure the columns “relaxing” slightly under load

Calibration
 Calibration is the process that enables the tonnage
monitor to read the actual force being exerted by the
press
 Load cells are used to measure the actual force under
the ram, then the tonnage monitor’s output is dialed in to
match
 Once the tonnage monitor is calibrated, the press itself
becomes a force-measuring instrument
 Calibration isn’t 100% necessary, but it provides some
benefits

Zero Cam
 The press frame expands and contracts with changes in temperature
 The strain links measure this change, but we really wish they wouldn’t
 The load monitor cancels out the temperature change by reading the
strain link output during a non-load generating portion of the stroke
(i.e. TDC), and subtracting this reading from the overall load
 The “Zero Cam” is a latching magnetic limit switch (LMCS) that
provides a timing signal to the tonnage monitor through the top of the
stroke
 The LMCS tells the load monitor where in the stroke to zero out the
tonnage

Setpoint Limits
 Setpoint limits are thresholds that are set for each tool
 When a setpoint limit is exceeded, the tonnage monitor
stops the machine
 High Tonnage Limit – If the peak tonnage exceeds this limit, the
press will stop
 Low Tonnage Limit – The peak tonnage must exceed this level
or the press will stop

Setpoint Limits
High Tonnage Limit
Press
Stops!

Setpoint Limits
Low Tonnage Limit
Press
Stops!

Nuisance Stops
 It’s normal to see gradual changes in the peak
tonnage value thought the day
 Your high and low setpoints must allow for this
variation or nuisance stops will result
 This makes it impossible to monitor small tonnage
variations with only high and low setpoints
 Fortunately, there is a 3rd setpoint type

Repeatability Limit
 Gradual changes in tonnage are normal, but abrupt changes
usually mean trouble
 The Repeatability Limit is the maximum allowable variation in
tonnage from one stroke to the next
 High and low limits can be relaxed to prevent nuisance stops,
but still protect the machine and die
 The Repeatability Limit can be set to a very precise value
(often in the tenths of tons) without causing nuisance stops

Repeatability Limit
Press
Stops!

Reverse Load
 As regular (forward) load increases, the press frame loads up
like a giant spring
 When the punches break through, the spring suddenly
releases, and the load direction reverses
 Presses are designed to withstand forward load, but not
reverse load (20% of capacity max).
 Excessive reverse load damages bearing cap bolts, and the
ram adjust mechanism

Tonnage Monitor Benefits
 More repeatable setups
 Reduce off-center loading
 Detect loss of lubrication
 Detect material variations
 Detect tool wear

Your Insurance Policy
 Even if you utilize other forms of monitoring such as die
protection sensors or in-die measurement systems, tonnage
monitors are still an important part of the overall monitoring
package
 Unlike those other devices, a tonnage monitor requires no tool-
specific sensors or programming
 The tonnage monitor becomes your “insurance policy” against
machine or tool problems that are unusual or unforeseen – the
things you would never install a specific sensor to detect

AutoSet Load Monitors
 Wintriss Controls offers a series of accurate and
reliable stand-alone press tonnage monitors suitable
for any application
 The basic model 1500 provides economical
protection for any machine
 The 1500 Plus and 1504 Plus models provide
advanced features that are extremely easy to use

AutoSet Load Monitors
 AutoSet 1500
 2 inputs, high tonnage limit only
 AutoSet 1500+
 2 inputs, high and repeatability limits, reverse load display
 AutoSet 1504+
 Same as the 1500+ but with 4 inputs

AutoSet 1500
 This is the simplest and cheapest tonnage
monitor we make
 Available with either an enclosure or
panel mount
 The AutoSet 1500 uses auto-setpoints
 It reads the tonnage during a sample
period, and sets the high limit “X” percent
above the highest reading

AutoSet 1500
 Setpoint limit percentage is set by the user with a rotary switch
on the board
 The sample period is either 1 or 15 strokes.

AutoSet 1500/1504 Plus
 The “Plus” models have both high and
repeatability setpoint limits
 There’s a momentary pushbutton on the
front panel that allows the user to display
reverse load
 The AutoSet 1500+ has two inputs
 The AutoSet 1504+ (shown) has 4 inputs

Contact Us
Backed by 60+ years of manufacturing
experience, Wintriss has the expertise to help
you protect your presses and keep your
stamping operation performing smoothly and
efficiently.
Contact us by:
 Calling (800) 586-8324
 Submitting this simple form

Tonnage Monitors-101 - A Basic Guide for Stamping Press Load Monitoring

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Tonnage Monitors-101 - A Basic Guide for Stamping Press Load Monitoring