Compressed Air Consumption of a 1160 Vertical Machining Center

• 1
  Where a 1160 vertical machining center actually uses air
• 2
  Typical air flow by circuit
• 3
  Why air consumption shows up as a machining problem
• 4
  How to measure your own machine
• 5
  Step by step: from measurement to a smaller air bill
• 6
  Air consumers on a 1160 vertical machining center

A 1160 vertical machining center is a mid-size vertical mill, roughly 1,100 mm of X travel, with a 40-taper or similar spindle. Nothing about the cutting process needs air. The machine needs air for everything around the cut: clearing chips, holding tools, opening the tool changer, and keeping coolant and swarf out of places they should not be.

That distinction matters when you size a compressor. Air demand is not proportional to spindle load or to metal removal rate. It is proportional to how often the machine changes tools, how often the operator opens the door, and how well the pneumatic system holds pressure.

On a typical 1160 the pneumatic consumers fall into four groups: the tool changer, the spindle air purge and taper cleaning, the workholding and door circuits, and the chip and coolant air blast. Each one draws at a different moment in the cycle, so the peak is higher than the average by a wide margin.

The spindle purge is the one people forget. It runs a small, steady bleed of air through the spindle nose to keep fine chips and coolant mist out of the taper. That bleed is present whenever the spindle turns, which on a two-shift schedule is most of the day.

Published figures vary by builder, but the orders of magnitude are consistent. A tool changer on a 40-taper machine is the largest single draw. It fires in short bursts, often under two seconds, and then stops. If you average that burst over a five-minute cycle, the tool changer looks small. If you look at the instant it fires, it is the reason your header pressure dips.

Spindle taper cleaning and purge sit in the middle. They are modest flows, but they are continuous during cutting, so they dominate the air bill over a shift. Workholding and door cylinders are intermittent and small unless the machine runs a heavy fixture that vents constantly.

Air blast for chip clearing is the variable you control. A short blast after each roughing pass adds up fast. Many shops leave the blast on a fixed timer that is longer than needed, and that single setting can account for a fifth of the machine's air use.

A useful rule: on a 1160 class machine running a mixed job shop schedule, total air consumption usually lands in the range of 200 to 400 litres per minute when averaged over a shift, with peaks three to four times higher. Your number depends on cycle time, tool count and how the blast is programmed, so measure rather than copy a table.

Low air pressure rarely stops a machine outright. It shows up as symptoms. Tools fail to clamp cleanly and you get runout or a pulled tool. The tool changer hesitates, alarms, or drops a tool. The spindle taper collects chips because the purge is weak, and then the tool seat is not true.

These symptoms get blamed on the machine, the tool holder or the operator. In practice the cause is often a header that was sized for one machine and now feeds three, a filter that has not been changed, or a 6 mm line running 15 m to the machine.

Pressure drop is the mechanism. Every fitting, hose, filter and regulator costs pressure. A compressor set at 0.7 MPa delivering 0.45 MPa at the machine will still run the spindle, but the pneumatic logic gets slow and unreliable.

There is another cost that does not show up as a fault code. Compressed air is one of the most expensive utilities in a shop per unit of energy delivered. Leaks and oversized blasts are paid for every hour the compressor runs, whether or not a part is being cut.

The cleanest method is a flow meter installed in the drop to the machine, logged over a full shift. That gives you average flow, peak flow and the shape of the demand curve. If a meter is not available, you can still get useful numbers from the compressor load.

Log compressor loaded and unloaded time with no other machines running. Loaded time as a fraction of total time, multiplied by the compressor's free air delivery at your pressure, gives a rough average for the machine. It is not precise, but it is enough to catch a 30 percent leak.

For leaks, isolate the machine at the end of the shift with everything off and watch the meter or the compressor. A machine that draws air with no cycle running has a leak. Common spots are the tool changer arm cylinders, the door cylinder, old push-in fittings and the regulator drain.

For the blast, watch one complete cycle and time how long the solenoid is open. Then ask whether each blast actually clears the chip. On most jobs a shorter, better aimed blast does the same work with less air.