KEVOS® MAKEOS · Hydraulics
Hydraulic Press Gauge Pressure for a Pressure on the Work (Capacity and Pressure on the Material)
What gauge pressure must my hydraulic press run at to put a given pressure on the area of the work, what force and pressure on the work does it give at the gauge pressure I set, and can the press reach it?
Hydraulic press capacity and pressure on the work by the rules the handbook gives: the press force is the gauge pressure on the ram area (C = 0.00039 D² P tons in the inch form, 0.7854 D² P in pounds), the pressure on the material is the press force divided by the area being pressed, and the gauge pressure for a required pressure on the material is that pressure times the area of the work divided by 0.7854 times the square of the ram diameter. In SI units with force in kilonewtons and tonnes-force, checked against the most pressure the press system may run at.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Press | ||
| Ram diameter | mm | Diameter of the press ram (piston) on which the oil pressure acts. |
| Gauge pressure applied | bar | Gauge pressure you set or read on the press. |
| Most gauge pressure the press may run at | bar | Most gauge pressure the press, its pump and relief valve may run at, from the press rating plate. |
| Work | ||
| Area of the work under pressure | mm² | Area of the material actually being pressed, measured in the pressing direction. |
| Pressure wanted on the work | MPa | Pressure the process needs on the material, from your process data (coining, compacting or bonding pressure). |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
Press
What this means: Ram diameter
- What it is
- Diameter of the press ram or piston on which the oil pressure acts.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 5000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 250 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Press force grows with the square of the ram diameter.
- Get it right
- Take it from the press rating plate or cylinder drawing, not the rod diameter.
What this means: Gauge pressure applied
- What it is
- Gauge pressure set on the press or read on its gauge during pressing.
- Units and format
- Enter a number in bar: bar (1 bar = 100 kPa). The form accepts 0.000001 bar to 3000 bar. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 200 bar as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Press force and pressure on the work grow in direct proportion.
- Get it right
- Read the gauge while the press holds the load, not during the fast approach.
What this means: Most gauge pressure the press may run at
- What it is
- Most gauge pressure the press, its pump and relief valve may run at.
- Units and format
- Enter a number in bar: bar (1 bar = 100 kPa). The form accepts 0.000001 bar to 3000 bar. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 250 bar as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Sets the press capacity and the reach check.
- Get it right
- Take it from the press rating plate; the relief valve should be set no higher.
Work
What this means: Area of the work under pressure
- What it is
- Area of the material actually under pressure, seen in the pressing direction.
- Units and format
- Enter a number in mm²: square millimetres. The form accepts 0.000001 mm² to 100000000 mm². Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 20000 mm² as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The pressure on the work falls as the area grows.
- Get it right
- Use the area in contact with the punch or die face, not the blank outline if only part is pressed.
What this means: Pressure wanted on the work
- What it is
- Pressure the process needs on the material, such as a coining or compacting pressure.
- Units and format
- Enter a number in MPa: megapascals (1 MPa = 1 N/mm²). The form accepts 0.000001 MPa to 10000 MPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 40 MPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Sets the gauge pressure needed.
- Get it right
- Take it from your process data or trials for the material and operation.
Method and formulas
- Ram area = 0.7854 D².
- Press force C = gauge pressure × ram area (handbook inch form: C = 0.00039 D² P short tons).
- Pressure on the material Pa = press force ÷ area of the work (handbook: Pa = 2000 C ÷ A).
- Gauge pressure for a pressure on the work P = A × Pa ÷ (0.7854 D²).
- 1 tonne-force = 9.80665 kN; 1 short ton-force = 8.8964 kN.
- Example: a 250 mm ram at 200 bar gives 981.75 kN (100.11 tf), 49.087 MPa on 20000 mm²; 40 MPa on the work needs 162.97 bar.
Limitations
- The force is the ideal hydraulic force on the ram; seal friction, a return spring or the weight of the platen change it slightly.
- The pressure on the work is an average over the area; the local pressure varies with the shape of the tooling.
- The gauge must read the pressure at the cylinder; long lines or a restrictive valve can make it read differently while the press moves.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Set the press gauge for a pressing, coining or compacting pressure
- Find whether a press can reach the pressure a job needs on its area
- Convert a gauge reading into the force and pressure on the work
Who it is for
- Press operators
- Tooling engineers
- Manufacturing engineers
What you get
- Ram area
- Press force at the gauge pressure set
- Press capacity at the most pressure allowed
- Pressure on the work at the gauge pressure set
- Gauge pressure needed for the pressure wanted on the work
Interpreting the result
- Pressure on the work rises with the square of the ram diameter and falls with the area being pressed: a press that coins a small part easily may not reach the pressure on a larger one.
- Set the relief valve no higher than the most pressure the press may run at, and keep the working gauge pressure below it.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 3224. Topic reference; no source tables or recommended settings are reproduced.
Learn the Concepts Behind This Tool
These KEVOS® Library readings explain the method this tool uses, with worked examples.
Useful alongside · KEVOS® original book
Hydraulic and servo presses
In Power Presses by the Numbers
What it covers: Sizing 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.
KEVOS® tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.