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Cool cuttings - the waterjet option

Editorial
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There are several different ways to cut metals. For small to medium operations that value versatility and economy over speed and precision, waterjet cutters are one of the best options. Matt McDonald writes.

When most people with a passing interest in metal work hear the words ‘metal cutting’ their minds head quickly to lasers.

And this is fair enough. Laser cutters have come a long way in recent years and they do what they do very well. When it comes to speed, nothing can touch them and they have transferred the words ‘lights out manufacturing’ from a concept into a reality.

But lasers aren’t the whole story. Other technologies, such as waterjet cutters have a role to play. In fact, they can do some things that laser cutters can’t.

And waterjet cutters offer a number of their own advantages. First off, they are relatively cheap. They cost about a quarter the price of laser cutters and also cost less to run.

Versatility

Waterjet cutters were developed in the 1930s and were originally used to cut soft materials like paper.

According to Matt Weaver, waterjet applications specialist at Headland Machinery, these days they can can cut anything except toughened glass. (He explained that this tricky product will shatter when hit by a jet stream).

So they can handle all metals, from aluminium to brass to steel.

Weaver told Manufacturers’ Monthly waterjet cutters are “good for exotic materials”. This is important because there is not much else out there for machining such materials.

In comparison, said Weaver, “lasers and plasmas are more restricted in what they can cut. They can only cut certain materials and up to certain thicknesses...”

Lasers generate a lot of heat and therefore they can’t cut anything much thicker than about 25mm. Waterjet cutters, in contrast, can cut metal with a thickness of 50mm, 100mm, or even 200mm.

Weaver added that “you can go from cutting 2mm thick aluminium to cutting 200mm thick tool steel… completely different parts, in under a minute.”

In other words, they are versatile. They are great for smaller businesses which haven’t identified speed and volume as their top priorities. (Those who are chasing speed should choose laser cutters).

Although, as Weaver added, “A lot of people have both. A lot of laser shops are investing in laser jets because it gives them the versatility.”

In addition, waterjet cutters can handle complex shapes. As Prashant Gokhale, Machine Tools Sales Manager at Applied Machinery told Manufacturers’ Monthly, they can even cut three dimensional shapes.

Gokhale pointed to 5-axis technology which has facilitated new waterjet cutting options.

The normal axes on a waterjet are named X (back/forth), Y (left/right) and Z (up/down). The 5-axis system adds two new axes – an A axis (angle from perpendicular) and C axes (rotation around the Z-axis) – and in so doing opens up a range of cutting options.

“You can do spirals,” Gokhale explained. Or you can do “impellers for turbo charges or it could be blisks or…turbine blades.”

Cold cutting

Another advantage of waterjet cutting is that it doesn’t compromise the material being cut.

“That’s why it’s great for things like the aerospace industry because they can’t have any alterations to the mechanical properties of the material...because it adds stress,” Weaver said.

He explained that this is because it uses a cold-cutting process. “It’s basically high speed erosion... It’s the abrasive that’s doing the erosion and the water is the carrier for the abrasive which does the cutting.”

“You’re not putting heat into the material and you’re not hardening the edge the way you are with a laser or a plasma... It’s virgin material on the edge,” Weaver continued.

Water is a scarce resource so it’s pertinent to ask how much water waterjet cutters use.

“We basically use four litres a minute. Six litres a minute if you include the cooling circuit,” Weaver said. “But that’s only being used while the nozzle’s actually on.”

So when you’re just setting up, loading sheets, or having lunch you’re not using any water at all.

And it is also possible to re-use your water. “We do closed loop systems which recirculate the water. So you fill it up once and that’s it. It will just recirculate,” he said.

Software

The latest machines come with powerful software systems. For example, one of Headland’s offerings the Omax60120 includes the Intelli-MAX software suite which was developed to ensure the waterjet is controlled at all times and the finish is optimised.

According to Weaver, its automated programming software is intended to allow the user to go from loading a drawing to cutting parts in just five steps. And pre-drawn designs are input with a USB stick.

According to Gokhale, right now waterjets are unable to cut very large objects; they can’t handle massive big plates, large water tanks and so forth.

And waterjet cutting is still a fair way behind laser cutting in terms of automation. According to Gokhale, while software now comes with monitoring capabilities, “you cannot use lights out machining with waterjets at the moment.”

Automation may come in the future but at the moment, the operators of waterjet cutters have to load and unload all the sheets.

In any case, as Matt Weaver explained, the demand for such automation is currently not there anyway.

“At the moment the majority of our systems are sold to fairly small businesses, because it’s cheap, because it’s versatile, because it’s easy to run,” he said.

“The attraction is what the Americans call the ‘Mom and Pop shop’.”

And they’re not interested in lights out operation. They are more interested in the versatility and reliability that waterjet cutters provide.

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