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Power Presses by the Numbers
Force, energy, stroke and speed: screw, crank, hydraulic and servo presses, flywheels, frames, shut height, feeding, stopping time and choosing a press
Choose, set and check a power press with numbers: tonnage curves, flywheel energy, frame deflection, hydraulic and servo drives, shut height, feeding, stopping time and cost.
Start readingAbout this book
A power press is a machine for delivering a large force over a short distance, quickly and repeatably, to a die that cuts or forms sheet metal. How it does that decides what it can do. A screw press stores energy in a spinning flywheel and spends it in one blow. A crank press converts a flywheel’s rotation into a stroke of fixed length, with a force that depends on where in the stroke the work is done. A hydraulic press pushes with a force set by its pressure, at any point in its stroke, at a speed set by its pump. A servo press drives its crank with a motor that can be told how to move. Each has a number that limits it, and choosing or running a press without knowing which number it is leads to stalled presses, broken dies and parts that cost more than they should.
This book works through presses with numbers. It starts with what a press must deliver, then looks at energy machines through Hodgson’s 1903 examples, the crank press’s force curve, flywheel energy, frames and their deflection, hydraulic and servo drives, fitting a die, feeding the strip, stopping the press and guarding it, and finally choosing a press on its whole cost. Each chapter follows one running case, includes a plausible mistake and how it was found, and ends with an exercise and its worked answer.
It is for production engineers, press shop supervisors, toolmakers, maintenance staff and the people who buy presses. It assumes school algebra and physics. The dies themselves, their cutting force, clearance, stripping and wear, are the subject of the Library’s companion book, Blanking and Piercing Dies by the Numbers, whose MP-40 die is one of the two jobs in this book’s case.
The running case
Every chapter follows one fictional decision. This is an illustration. A manufacturer of electrical enclosures is choosing a press, called Press 4 here, for two jobs:
- MP-40, a flat mounting plate made from 2.0 mm steel strip in a three-station progressive die, 60,000 a year. The die needs 192.8 kN to cut and 28.5 kN for its stripper springs, 221.3 kN in all at the bottom of the stroke, and is 204 mm high when closed.
- AB-75, an angle bracket formed from a pre-cut 3.0 mm blank in a wiping die, loaded by hand, 20,000 a year. Its die maker’s trial shows the forming force rising from first contact 25 mm above the bottom of the stroke to 65 kN, and then to 180 kN in the final millimetre as the bend is set.
The main candidate is a 400 kN gap-frame mechanical press with a 60 mm stroke, a crank radius of 30 mm, a connecting rod of 250 mm between centres, a geared flywheel with a moment of inertia of 4.0 kg·m² turning five times for each stroke, a speed range of 40 to 120 strokes a minute, and a shut height adjustable from 240 to 300 mm. Hydraulic and servo presses of the same rating are the alternatives. The manufacturer, the jobs, the presses, the prices and the mistakes are invented. None describes KEVOS® work, a real business or a real press.
How to use the book
Read Chapter 1 first: it sets out the five numbers every press is judged on. Chapters 2 to 4 deal with force and energy, Chapters 5 and 6 with the machine’s structure and drives, Chapters 7 to 9 with running a press, and Chapter 10 brings the decision together. Every calculation was checked by running it, and values are given to more figures than a shop needs so that the arithmetic can be followed.
Source limits and professional responsibility
The relationships in this book are standard mechanics, and the press specifications, stopping times, prices and job forces are illustrations. Real presses are chosen and run with the maker’s data, the die maker’s figures and trials. Power presses cause amputations and crush injuries. Their guarding, controls, inspection and maintenance are governed by Australian work health and safety law, the regulators’ guidance and the Australian standards for presses, and are designed and verified by competent people. This book teaches how presses work and how to check them. It is not advice for any particular press or installation, and qualified review governs real work.
Who this book is for
Production engineers, press shop supervisors, toolmakers, maintenance staff and buyers who choose, set up, run or check power presses for sheet metal work.
What you will learn
- Read a press's specification and test it against a job's force, energy, stroke, speed and die space.
- Calculate the force a crank press can deliver at any height above the bottom of its stroke.
- Work out a job's energy per stroke, a flywheel's slowdown and why speed changes the energy available.
- Size a hydraulic press's cylinder, speed and power, and compare mechanical, hydraulic and servo drives.
- Fit a die, time a feed, understand how stopping time sets guard distances, and choose a press on whole cost.
Inside this book
Chapters
- 01What a press must deliverThe five numbers a press is judged on, how presses differ in what limits them, tonnes and kilonewtons, Press 4's two jobs set against its specification, and a press specified by tonnage alone.
- 02Screw presses, fly presses and drop hammersEnergy machines and the principle of work: Hodgson's copying press and fly press restated in SI, force against stopping distance, drop hammers, and a slip in a 1903 worked example.
- 03The crank press and its force curveWhy a crank press loses force with height above the bottom of the stroke, the rating point, Press 4's curve from 400 kN at 3 mm to 184 kN at 25 mm, and a pad it could not carry.
- 04Flywheel energy and slowdownEnergy per stroke for MP-40 and AB-75, the flywheel's stored energy and slowdown, why a variable-speed press has far less energy at low speed, motor power, and a press that stalled on the bottom.
- 05Frames, deflection and off-centre loadsGap and straight-side frames, how a gap frame tilts under load, what that does to a 0.15 mm clearance, breakthrough shock, off-centre loads, and a die on too flexible a press.
- 06Hydraulic and servo pressesSizing a 400 kN hydraulic press's cylinder, pressure, speed and power, its cycle time for MP-40 and AB-75, servo-driven presses, and the energy a compressed oil column releases at breakthrough.
- 07Shut height, the bolster and fitting the dieShut height, adjustment and daylight, fitting MP-40's 204 mm die to a 240–300 mm press with a riser sized for its regrinds, the bolster's drop-through opening, and parallels that blocked the blanks.
- 08Feeding the pressCoil lines and roll feeds, the window when MP-40's strip may move, feed speed at 120 strokes a minute, coil changes, shuttle feeds, and a feed that ran into the pilots.
- 09Clutches, brakes, stopping time and guardingClutches and brakes, stopping time, the order of guarding measures in Australian guidance, how stopping time sets a light curtain's distance, and a brake that wore past its guard.
- 10Choosing the press on its whole costThree 400 kN presses tested on all five numbers, ten-year costs excluding GST, the choice and its acceptance tests, and a comparison that mixed GST-inclusive and exclusive prices.
Apply This in Practice
Use these KEVOS® tools to try the method from this reading with your own numbers.
Applies this method
Flywheel Energy and Speed Fluctuation
Calculates a flywheel’s inertia and the energy it releases between its maximum and minimum speeds.
Used in Flywheel energy and slowdown
Applies this method
Hydraulic Press Cycle Check (Regenerative Approach, Pressing Force, Return, Cycle Time, Motor Power)
Checks a hydraulic press’s force at relief, approach, pressing and return speeds, cycle time and motor power, with a standard or regenerative approach.
Used in Hydraulic and servo presses
Applies this method
Mechanical (Crank) Press Capacity Above Bottom
Works out a crank press’s force curve from the crank’s dimensions and its rating.
Applies this method
Punch and Shear Flywheel Sizing
Sizes a flywheel and motor for punches and shears from the energy each stroke takes.
Used in Flywheel energy and slowdown
Related Tools and Examples
Useful alongside
Forging Hammer Efficiency by the Heim Lead Cylinder Test (Work per Blow and Efficiency)
Measures the work a hammer blow actually does, by the Heim lead cylinder test, to set against the stored energy this chapter calculates from the tup weight and drop height.
Related to Screw presses, fly presses and drop hammers
Useful alongside
Hydraulic Press Gauge Pressure for a Pressure on the Work (Capacity and Pressure on the Material)
Carries this chapter’s force from pressure times piston area on to the pressure the ram puts on the area of the work, and the gauge pressure a required pressure on the work needs.
Related to Hydraulic and servo presses
References and source notes
The manuscript and worked examples are original KEVOS® writing. References inform particular concepts; their authors do not endorse this book. Web references were consulted on 26 October 2026.
- R. B. Hodgson, The Technical Publishing Co., Manchester. Machines and Tools Employed in the Working of Sheet Metals (1903). Supplied source, out of copyright, read as a subject map for screw, fly and power presses, press frames, clutches, feeds, stamping and the power of presses and stamps. Its worked examples of the work stored in a fly press's balls are restated in SI and checked in Chapter 2, where an arithmetic slip in the original is noted. No text, figures, tables or exercises are reproduced; the case, numbers and checks in this book are its own.
- Serope Kalpakjian and Steven R. Schmid, Pearson. Manufacturing Engineering and Technology (2014). University text used for the general classification of presses by how they deliver force and energy, and for the mechanics of shearing and bending that the companion book develops.
- WorkSafe Victoria. Controlling risks from power press machines (2026). Regulator guidance on power press hazards and controls: fixed and interlocked guards, presence-sensing systems where guards are not possible, chocks, inching, daily checks of clutch and brake mechanisms and test runs. It names AS 4024.3001 and AS 4024.3002. Used in Chapters 7 and 9.
- WorkSafe Western Australia. Power presses (2024). Regulator guidance giving priority to tooling and stroke limits that prevent access, automatic feeders and interlocking guards, stating that two-hand controls alone are not an acceptable means of protection, and describing foul strokes from brake or clutch faults. Used in Chapters 8 and 9.
- Safe Work Australia. Model Code of Practice: Managing the risks of plant in the workplace (2024). The national model code that state guidance on presses refers to, for managing plant risks, guarding, maintenance and inspection. Readers are directed to their own regulator to confirm its status in their jurisdiction. Used in Chapters 9 and 10.
- United States Occupational Safety and Health Administration, via Cornell Law School Legal Information Institute. 29 CFR 1910.217 Mechanical power presses (2026). A publicly readable regulation whose simple safety distance formula, Ds = 63 inches per second × the press's stopping time, is used in Chapter 9 only to show how stopping time sets the distance of a presence-sensing device. It is a United States rule; Australian presses are guarded under Australian law and standards.
- Standards Australia. AS 4024.3001 and AS 4024.3002 Safety of machinery: mechanical and hydraulic power presses (current edition). Named by number and scope as the Australian standards for the safety of mechanical and hydraulic power presses. No values are quoted from them.