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Material thickness and cutting accuracy in comparison - laser / plasma / EDM / waterjet

Higher accuracy can be achieved with waterjet cutting than with a thermal cutting or plasma cutting system. Furthermore waterjet cutting systems can cut greater thicknesses of material than laser systems.

Moreover waterjet cutting systems have numerous additional advantages available compared to other solutions

Which water quality is required?

The following minimum requirements for the water quality apply:

  • pH value 7.0 – 8.5
  • Carbonate hardness 20 – 60 ppm corresponds to 2 – 6 ° dH
  • Calcium carbonate (Ca) 35 – 107 ppm
  • Chloride content (Cl) ? 100 mg/l
  • Infeed temperature for feed water 10 – 25 °C
  • Electric conductivity at +25°C 450 µS/cm
  • Filtrate dry residue 350 mg/l
  • Free, dissolved chlorine 1 mg/l
  • Feed water admission pressure 0.2 – 2.5 MPa

Deviations from these values lead to shorter service lives of the high-pressure seals of the pump and of the nozzles. Therefore, we recommend a water analysis and if necessary an appropriate water treatment.

What accuracy of cut can i expect when cutting with waterjet?

More than 80% of waterjet system users throughout the world cut with an accuracy of ±0.1mm or less.

Should I cut under water?

The biggest advantage is the reduction of cutting noise to less than 75 dBA. A negative aspect of underwater cutting is that during cutting one can hardly see or even not see the workpiece at all. Workpiece handling is also carried out underwater – unless one has a water level control in the water tank. Furthermore it should be mentioned that the cutting process suffers an approx. 5% reduction in performance with 1mm water coverage.

Up to what thickness can I cut?

Up to 200 mm thick steel and titan are cut under production conditions. There are cases in which thicknesses of 300 mm and 400 mm have been cut. The majority of users however cut material with a thickness between 10 mm and 60 mm.

Must I drill a starting hole?

The waterjet creates its starting hole (connection) itself without any additional effort. For several composite materials the pump pressure must be reduced and a special vacuum connecting device employed.

What electrical connection do I require?

Per abrasive cutting head installed a power rating of 37 kW must be allowed.

When and how do I employ one or more cutting head?

You employ multiple cutting heads if you want to manufacture a lot of identical parts. A second cutting head is either mounted to the existing Z axis or a second Z axis installed to which additional cutting heads can be attached. In this respect it is important that each individual cutting head is provided with the same pressure and same flow rate in order to achieve a uniform cut.

How long is the service interval for the high pressure pump?

The high-pressure seals must be replaced if they leak! With a constant working pressure of 400 MPa the seals should be replaced after 400 to 1,200 cutting hours.

Which abrasive should I use?

Garnet sand is the most frequently used abrasive by far. It is advantageous as far as purchasing costs, cutting speeds, mixing head service life and health hazards are concerned. Other abrasives contain olivine sand, aluminium oxide and several synthetic minerals.

How much abrasive do I need?

For optimal cutting performance at 400 MPa working pressure one requires:

  • Nozzle 0.15 mm / focus 0.6mm 150g/Min
  • Nozzle 0.25 mm / focus 0.8mm 350g/Min
  • Nozzle 0.35 mm / focus 1.0mm 450g/Min

How long does the water nozzle last?

A sapphire nozzle lasts for 25 cutting hours. A diamond nozzle (the best nozzle quality) lasts for far longer but costs up to 30 times more and is normally used only for pure waterjet cutting.

How long does the workpiece support last?

The supporting grates last for a good many cutting hours provided one does not always cut in the same place. The grids can be moved, exchanged and inverted same as with laser or plasma cutting systems.

How long does the focusing tube last?

Focusing tube of good carbide ceramics last around 100 hours. Focusing tube of the highest carbide ceramics last around 30% longer than focusing tube of other materials.

Such a focussing tube can achieve up to 150 cutting hours with an increase in diameter of 0.5 mm. Many of our customers utilize partially used foci for manufacturing parts where great accuracy is not required.

Are waterjet cutting systems easy to program?

StM waterjet cutting machines with standard CNC equipment are not more difficult to program than other cutting machines.Standard CAM software easily converts .DXF files into a cutting program. The cutting speed is determined depending on the type and thickness of the material.Programming is even easier when you are using EasyCut Software. In other words, projects that are programmed and cut can be made quickly and accurately.

How do I clamp the part to be processed?

Since the force working on the workpiece is very small (under 1 kg for precision cuts and under 5 kg for average cutting) elaborate clamping devices can be dispensed with. Most users utilize simple light weights to hold their workpieces securely.

How wide is the kerf?

The width of kerf is around 15% wider than the diameter of the focussing tube. With an 0.8 mm focussing tube the width of kerf is 1.0 mm. With increasing diameter of the focussing tube the width of kerf also increases.

How much water is used when cutting with 4000 bar?

This depends on the power of the high pressure pump and the water nozzle respectively.

High pressure pump:

  • 19 kw: 1,9 l/min
  • 37 kw: 3,8 l/min
  • 45 kw: 4,6 l/min
  • 75 kw: 7,6 l/min

Water nozzle:

  • 0,1:   0,32 l/min
  • 0,15: 0,71 l/min
  • 0,2:   1,22 l/min
  • 0,25: 1,87 l/min
  • 0,3:   2,66 l/min
  • 0,35: 3,57 l/min
  • 0,4:   4,60 l/min
  • 0,5:   6,82 l/min

Why should I cut with waterjet instead of laser?

Laser cutting is an extremely productive process. Nevertheless the waterjet has several advantages over the laser:

  • No thickness limitations
  • No problems with reflective materials such as brass and aluminium
  • No heat factor and therefore no burning and no changing of the material structure through heat
  • With the waterjet heat-sensitive materials such as plastics, rubber or composite materials as well as glass, stone and extremely hard
  • ceramics can be cut
  • Changes of material: only the cutting speed is changed Neither gas nor optics must be switched
  • Additional cutting heads can easily be mounted for an expanded production
  • Maintenance of laser systems is specialized and more difficult to carry out
  • Distance between nozzle and material is nowhere near as critical
  • Waterjet systems are less capital intensive to purchase than lasers

Why should I cut with waterjet instead of EDM?

EDM is extremely accurate but also extremely slow. It also needs an electrically conducting material and causes changing of the material structure through heat.

Why should I cut with waterjet instead of a milling machine?

If one cuts through the edge of the material or holes or wants to manufacture blind holes and threads the abrasive waterjet is usually a lot faster, easier to program and also cheaper than a milling cutter.

This can be ascribed to the fact that we cut through in one pass and that we do not create any metal chips. Additionally should be noted that waste in complete form is worth more than in the form of chips.

Why should I cut with waterjet instead of a plasma?

Plasma cutting is a heat process. It introduces huge amounts of heat to the workpiece and leaves a heat-affected zone.
The surface created by a waterjet is generally superior. No edge is created on the underside of the material and consequently post-processing is not necessary. The abrasive waterjet is not subject to any limitation of depth of cut and several workspaces of a jet can lie in close proximity to each other.

What is the abrasive price?

Abrasive price is 350-450€ per Ton.

What happens in case of pushing your hand under a jet of water?

The jet has enough power to cut the bones. The safety equipment around the machine is therefore constantly being improved. Operators on water cutting machines and operators of various machines in other industries are subjects to stricter safety requirements .

Can I reuse the water?

Water, as well as the abrasive can be recycled by OneClean system.

Should the water be clean?

Yes. Most customers use tap water. In front of the high-pressure pump the water must be filtered to 0.5 micrometres. Deionizing as well as osmotic systems are not recommended. Such systems clean the water too much – and waster which is too clean is extremely aggressive which leads to increased wear of the high-pressure system.

How loud is the waterjet cutting?

The noise development when waterjet cutting is dependent upon the clearance of the free jet to the workpiece surface – i.e. the distance in which the waterjet travels through the air at supersonic speed. If one cuts under water the noise level sinks to under 75 dBA. If one cuts above water the noise level rises depending on the distance of the cutting head to the workpiece surface to as much as 105 dBA. In extreme cases the working area is totally covered.

What to do with the waste water?

Neither the water nor the garnet sand contain toxic substances. Consequently the water can be discharged into the drains after the suspended solids have settled or rather been filtered out. The abrasive can be disposed of as building waste. If the processed material is toxic or hazardous to health waste water and abrasive must be disposed of as hazardous waste!