A guillotine shear, a punch press or a press brake mostly run on hydraulics or electric drives: compressed air only serves auxiliary functions, and air use stays low. What matters is a pressure that never falls below the minimum in the manual, and dry air, because these machines stop on a fault when the air runs short. For a sheet metal shop and its tools, a 7.5 kW 4-in-1 screw compressor such as the K 75 is often enough; move up to the K 110 when grinders run on the same network.
This article covers sheet metal machines. Hand tools and plasma cutting are on our page on compressors for metal fabrication.
Where does the air go on each machine?
The guillotine shear. Depending on the model, air drives the rear sheet supports, scrap ejection and, on some mechanical shears, the clutch and brake. It uses air in bursts, at each cut.
The punch press. On a CNC punch press, air drives the clamps that hold the sheet, the lifting ball table, slug blow-off and sometimes mist lubrication of the punches. Blow-off and lubrication can run continuously for the whole sheet.
The press brake. Air is mainly used for pneumatic tool clamping, when the machine has it, and sometimes for sheet supports. Clamping uses very little, but it must hold pressure at all times.
Each manufacturer gives the air use and the minimum pressure in the manual, in the pneumatic supply section. Without those two figures, do not size anything.
The calculation, step by step
Example of a fabrication shop, with manual figures to replace with your own:
| Machine or tool | Air use | Use | Counted |
|---|---|---|---|
| CNC punch press (clamps, blow-off, lubrication) | 200 l/min | continuous | 200 l/min |
| Guillotine shear (supports, ejection) | 40 l/min | in bursts | 20 l/min |
| Press brake (tool clamping) | 20 l/min | continuous | 20 l/min |
| Air nibbler | 300 l/min | in bursts | 150 l/min |
| Blow gun | 150 l/min | in bursts | 75 l/min |
| Subtotal | 465 l/min |
Tools that work in bursts are counted at half, as in our configurator, because the receiver absorbs the peaks. Then:
- 25 % safety margin: 465 × 1.25 = 581 l/min.
- 20 % margin for growth: 581 × 1.2 = about 700 l/min.
The K 75, 1.1 m³/min at 8 bar with a 420 L receiver, covers this. If two grinders at 450 l/min also run on the same network, the requirement goes past 1,800 l/min with margins: you then need the K 150, 2.2 m³/min at 8 bar. One extra grinder stays within the range of the K 110.
What pressure for sheet metal machines?
Note the minimum pressure in each manual, often around 6 bar, and keep the highest. Add the losses through the dryer, filters and network: a setting of 7 to 8 bar suits most cases. There is no point going higher: a screw compressor delivers less flow as pressure rises. The K 75 goes from 1.1 m³/min at 8 bar to 0.95 m³/min at 10 bar. Our article on calculating compressor pressure details the method.
If the shop adds a laser cutter, which needs a much higher pressure, that is a different need: the L series combines compressor, 16 bar receiver, dryer and precision filtration for that use alone.
Pitfalls specific to sheet metal machines
- The safety pressure switch. Many machines monitor their inlet pressure and refuse to work below the minimum. A pressure drop while a grinder runs can stop the punch press mid-sheet. Feed the machines with a large enough pipe, in a ring main if possible.
- Water in the solenoid valves. Machine valves and cylinders do not like water. Dry air prevents sticking and rust. Our article on which air dryer to choose compares the options.
- Tool oil on the wrong line. If the shop uses a lubricator for its hand tools, fit it at the tool's station, never at the head of the network feeding the machines.
- Leaks overnight. A machine left under pressure leaks through its fittings. Close the inlet valve at night and check the network: see detecting and fixing leaks.
- The pneumatic clutch. On mechanical shears and presses that have one, air pressure and quality affect how safely the machine stops. Follow the manufacturer's manual strictly.
To size your shop, enter your machines and tools in the configurator. Send us your machine manuals with a quote request: we will check the flow and pressure with you.
For your trade: Compressor for metalwork and fabrication shops.