Compass cutting warped material
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The Importance of Standoff Height, Especially with Bevel Cutting

Standoff height, the distance between the tip of the mixing tube and the material you are cutting, is important when cutting parts on a waterjet. In a previous blog I provided recommendations for proper standoff height. In general, stand off height should be about 0.100” (2.5 mm), or as thick as a dime. When your jet is perpendicular to your part, straight up and down, then raising the standoff will increase noise, mess and round the top edge of the part. You will lose a little cut power as well.

It’s important to maintain stand off under conventional waterjet cutting.

How Waterjets Work
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Tough Applications Where Waterjet Shines

It is true that waterjets are used for common materials such as steel, aluminum, gasket, and foam. But many people feel the tougher applications are where waterjet really shines. In this post I’ll highlight some that I believe best illustrate waterjet and abrasive waterjet capability.

  1. Stone
  2. Composites
  3. Exotic metal: Titanium and Inconel
  4. Thick insulation
  5. Cement board

The first three are abrasive waterjet related, and the last two use pure waterjet.

Waterjet Jobs
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The Waterjet Masters: Mohamed Hashish

What makes a technology take hold?  Technologies come and go; even some that seemed so permanent at the time, such as kerosene lamps, typerwriters and record albums. One of the reasons waterjet has remained one of the fastest growing major machine tool processes in the world for the past 20 years is due to adaptability.  The waterjet process was invented in the 50’s by Dr. Norman Franz, but it didn’t begin commercial use until the 70’s with the explosion of disposable diapers (which in this case is a good thing).

Then ultrahigh-pressure water was adapted to hard material cutting (metal, stone, composites, ceramics) with the invention of the abrasive waterjet in the late 70’s, really beginning industrial use in the mid 80’s. This important technology was invented by a team of engineers and research scientists led by Dr. Mohamed Hashish.  Here is a brief excerpt of the abrasive waterjet master’s tale.

Waterjet Masters
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Marketing Your Waterjet: Getting the Most Out of Your Quote

In Part 1 Jessica covered marketing your waterjet on the internet.  In this second part of a two post series I will cover some basic suggestions we’ve picked up over the years from successful job shops, concentrating on maximizing the power of your quote.

Of all the collateral you have as a job shop, it could be argued that the most important is your quote.  Nothing else you create will be scrutinized as thoroughly and compared side-by-side to your competitors as often as your quote.  Is your quotation setting you up for a simple price/delivery war with your competitors, or is it separating you from the pack by showing all the value you give beyond that price and delivery?

Marketing Your Business Waterjet Jobs
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Why Not Ultrahigh-Pressure Slurry Jets?

A reader asked about Slurryjet, and why there are no ultrahigh-pressure units out there in the world today cutting in production.

First of all, let’s make sure everyone who has not studied the subject understands what we’re talking about here.  Abrasive waterjets today are created by pressurizing water, forcing it through a small jewel orifice where the pressure is converted to velocity, and then the abrasive particles are metered into a mixing chamber and accelerated like a bullet out of a rifle down the mixing tube.  Abrasive slurry jet is where a water/abrasive slurry is pressurized and pushed through an orifice.  It is inherently more efficient because the water and abrasive are going the same speed, and no momentum transfer from the water to the abrasive is taking place.

How Waterjets Work Pump Technology Waterjet Technology Overview
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The Waterjet Control: Inside the Brain Behind a Waterjet

In 1984 the abrasive waterjet was released as a commercially available product. It was powerful, it was incredibly versatile; but it took a special operator to run it.  Someone who was into it – who had caught the waterjet bug. Why? Because at the time, waterjet wasn’t all that easy to run.

I had the unique opportunity to be such a waterjet operator by getting into abrasive waterjet just one year after it was released.  While in undergrad and grad school running the waterjet laboratory and demo center I could reference basic cut speed tables for what was believed (at that time) to be the best operating parameters. The table included water pressure, orifice size, mixing tube size, abrasive size, abrasive flow rate and the maximum cut speed for a dozen common materials at one or two thickness levels.

How Waterjets Work Programming Waterjet Technology Overview
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Standoff Height: How Close Should You Be?

The standoff height is the distance between the tip of the mixing tube and the material. A standoff too high causes dimensional problems and alters the top edge created by the jet as it gradually widens in open air.  Standoff too low risks scratching material on rapid traverse between cut paths, or snapping the tube causing downtime, cost, and angry operators.  Standoff height should be approximately the thickness of a coin (varies depending on your nationality, obviously) – about 0.100” (2.54 mm).

Standoff Height

I guess I could end the blog right here, but I think there are a few more things you might want to know about standoff height.

Waterjet 101 Waterjet Technology Overview
Dynamic Waterjet
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Dynamic Waterjet: The Story of a Problem Worth Solving

Taper left on a part was by far the biggest complaint from our customers across the world. As we have learned in prior posts, the faster you cut through a material with an abrasive waterjet, the greater the v-shaped taper. At the time, the only solution was to slow down your cut speed. The problem was, slowing down only minimized the taper – but rarely get rid of it; and slowing down costs shops a lot of money per part.

Waterjet Technology Overview
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So, What Is Stream Lag & Taper?

A waterjet stream acts like a beam when cutting, much like plasma cutting and laser cutting. These types of non-rigid cutting tools have to address the beam flexing and changing within the target material to minimize part cutting errors.

What is taper?

Taper in waterjet cutting is when the entrance width of cut is different than the exit width of cut.

Taper_v2

What is stream lag?
Stream lag causes corner damage when the exit point lags behind the entrance point, shown in the bottom of the part below.

Plasma cut parts often exhibit an upside-down V-shaped taper where the width of cut is wider at the bottom. Laser and waterjet exhibit a normal V-shaped taper (more narrow width of cut at the bottom). Plasma, laser and waterjet can all yield stream lag errors when cutting a part.

How Waterjets Work Waterjet 101 Waterjet Technology Overview