How to monitor stamping presses, stroke by stroke

A plant should track six things on every stamping press: strokes, the stroke rate, the parts each stroke makes, stops long enough to act on, die and coil changes, and scrap. Capture strokes and run state with a vibration sensor on the press frame, count finished parts with a beam at the exit, and read the press control's counter where you need the die number or the last stop's reason.

This guide is for plant managers and process engineers running mechanical presses of mixed ages. It works one hypothetical 200-ton press through a shift, computed two ways, so you can see what each number catches.

What should you track on a press?#

A press makes its output one stroke at a time, so most of what you need follows from counting strokes and timing the gaps between them. The table lists the six numbers and the question each one answers.

Strokes per minute differs widely from press to press. One press maker lists its 2,000 kN gap-frame crank press at 25 to 45 SPM with its longest stroke and 40 to 85 SPM with its shortest.^[1] The same maker's 220-ton link-motion press for progressive dies runs 50 to 120 SPM, and its 660-ton model 30 to 70.^[2] Record a rated SPM for each die, not for each press, because the die sets the speed.

Strokes are not parts#

A stroke count becomes a part count only after you multiply it by the parts the die makes per stroke. Parts per stroke is that multiplier, and the glossary entry for quantity per cycle defines the same setting for any machine.

The die type decides the multiplier:

• Single-hit die: one blank in, one part out, so the multiplier is 1.
• Progressive die: the strip advances through several stations on its own, and each stroke finishes one or more parts at the last station.^[3] A progressive die making one bracket per stroke is 1. A two-out die is 2.
• Transfer die: independent dies at each station, with mechanical arms moving the part between them.^[3] It finishes one part per stroke unless the last station drops two.

A count that reads exactly double or half is a multiplier setting, or a press that rings twice per stroke, not a counter fault. For example, a two-out progressive die set to 1 reports exactly half the parts the bin holds. The guide to part counting methods covers how each counting method turns a signal into a count.

A stroke also isn't a good part. A misfeed stroke moves the ram and makes nothing usable, and the carrier strip of a progressive die is engineered scrap that never counts as a part. Scrap to track is parts that left the die and can't ship, logged with a reason.

How do you capture strokes and parts?#

You capture strokes and parts in one of three places: on the frame, at the exit or in the press control. Each one sees something the others don't.

A vibration sensor on the frame feels each stroke as a sharp impact, well above the level of an idling flywheel. It counts strokes and reads running or stopped from outside the press, with nothing wired into the control. Mount it on the frame near the ram, never on a guard, which rings on its own.

A beam at the exit counts each part that breaks it on the way down the chute. It counts parts that cleared the die rather than strokes, so a misfeed stroke doesn't add one. It needs a chute where parts fall one at a time.

The press control already counts. A die protection unit from one press-control maker keeps parts, batch and total-hits-on-a-tool counters, and detects improper part ejection, misfeeds and material buckling before die damage occurs.^[5] Reading it gives you the die number and the reason the press last stopped. A connection to the control is a security concern for many plants, and IT usually reviews it first.

The sensor-based versus PLC comparison lays out what each approach sees on any machine, with its sources.

Which method fits which press?#

The press's speed, its feed and how its slide moves decide which capture method fits. Use the table as a starting point for each press on the floor.

A servo press needs the extra column. One press maker says its servo presses achieve a wide variety of stroke lengths and slide movement profiles,^[4] so the same press can run a slow draw job in the morning and a fast blanking job after lunch. Record the rate for each job, and read the job from the control when the press runs several.

How do you separate short stops from downtime?#

You separate them with a short-stop cutoff: a stop shorter than the cutoff counts as running time, and a longer one reaches the downtime record and gets a reason. Without it, every pause between strokes is a stop, and a shift becomes hundreds of one-minute rows nobody can classify.

Set the cutoff from two numbers on each press:

• The longest pause that belongs to the rhythm: the operator reaching for a blank, the feed indexing, a part clearing the chute. On a press these run from a fraction of a second to a second or two.
• The shortest stop you'd act on: usually the coil change. If coils take 8 minutes to load, a 10-minute cutoff hides every one of them.

The cutoff goes between them. For example, a coil-fed press at 40 SPM with 8-minute coil loads takes a 5-minute cutoff. A hand-fed press needs a lower one, because operator pauses are the loss you want to see.

The guide to micro-stops covers where these short stops land in OEE. The press setup guide gives a starting cutoff band by stroke rate.

Track die and coil changes separately#

A die change and a coil change are both changeovers, but they need separate reasons, because each one has its own fix and its own owner. A die change swaps the tooling for a new part number. A coil change reloads material for the same part.

Time a die change from the last good part of the old run to the first good part of the new one, as the guide to measuring changeover time explains. The SMED method aims at a changeover in single-digit minutes, under 10,^[6] and the element log is where you find the minutes to move outside the stop. Die setting itself is governed by OSHA's mechanical power press rule, 29 CFR 1910.217, which this guide doesn't cover.^[7]

Coil changes are predictable, so you can check them against arithmetic. For example, a 3,000-foot coil fed 4 inches per stroke lasts 9,000 strokes, which is 225 minutes at 40 SPM. A press that stops for a coil every 90 minutes is running a shorter coil than you think, or losing material somewhere.

Build each reason by creating a downtime category for it, so die change minutes and coil change minutes never mix.

A 200-ton press at 40 SPM#

The numbers below follow one hypothetical press through one shift, computed two ways: from the clock and from the counter.

The two methods answer different questions. The clock says the press stood for 60 minutes, and the reasons say die changes cost most of it. The counter says it lost another 39 minutes while it was supposedly running, in stops too short to log and strokes slower than the die's rate.

Split by OEE factor, that's availability of 390 ÷ 450 = 86.7%, performance of 14,040 ÷ 15,600 = 90.0% and quality of 27,800 ÷ 28,080 = 99.0%. The OEE calculation guide works through each factor. Without the stroke count, the 39 minutes would vanish into a run time that looks like 390.

Monitor presses with IoTFlows#

IoTFlows puts a SenseAi on the frame of each press. It attaches magnetically in seconds, calibrates in under five minutes and reads each stroke from outside the press, with no PLC or controller access.

The Discrete w/o Merge algorithm counts every stroke at 10 to 120 strokes a minute, times the parts per stroke you set for each die. One operation per die keeps each die's output separate. The Downtime Threshold keeps the gaps between strokes out of downtime, and operators tag die changes and coil loads in a tap.

A BeamTracker at the exit chute counts parts that cleared the die instead. On Enterprise, the IoTFlows edge device reads the press control, and it reads only the controls you choose to connect. Validate the count against a stroke count by hand before you trust the shift goal.

Set up monitoring on your presses#

1. List every press and every die

   Write down each press with its tonnage, its feed (hand, coil or transfer) and every die it runs. Record each die's rated SPM and its parts per stroke.

2. Pick the capture method per press

   Put a vibration sensor on the frame of every press first. Add an exit beam where misfeeds are common, and plan a control connection only where a question needs the die number or stop reason.

3. Validate the count over an hour

   Run the press for one to two hours and compare the count with run minutes × SPM, or with the press counter. A count that reads exactly double or half is a parts-per-stroke setting or a press that rings twice.

4. Set the short-stop cutoff

   Place it above the pauses that belong to the stroke rhythm and below the shortest coil change on that press.

5. Create the press reasons

   Add separate reasons for die change, setup and adjustment, coil change, misfeed and die repair before anyone classifies a stop.

6. Compare clock and counter weekly

   Each week, compare counted strokes with run time × rated SPM for each die. A gap that grows is short stops or slow running, and a rate that falls on one die points at its tooling.

7. Rank the losses after four weeks

   Rank classified stops by hours and work the largest reason first. If die changes lead, time them by element next.