Quality Waterjet Newsletter – 04/12/2005

How to Measure Waterjet Cut Parts?

For people who are used to deal with parts cut with traditional milling machines or EDM machines, it is important to know that there is something special about parts cut with abrasive waterjets. The difference lies in the fact that an abrasive waterjet beam is neither a rigid nor a cylindrical cutting tool. That is obvious, isn’t it? But the true shape of a part cut with an abrasive waterjet isn’t so.

If you look at a picture of a typical kerf cut with an abrasive waterjet, the walls on both sides of the kerf appear relatively straight and parallel. But if the picture is stretched horizontally to a significant scale, you will see a shape like a flower vase with two narrow sections, one near the top and the other at the bottom. Between the two narrow sections is the belly. The very top edge (usually less than 0.025 inch in depth) is rounded from the impacts of scattered particles around the core of the jet. Dimensional measurements done on this section of the kerf will be misleading. The neck section is more representative of the true diameter of the jet while the bottom is a reflection of the cutting speed (the slower the wider). For most parts, the bottom is narrower than the neck. Exceptions are parts that are either very thick or cut very slowly. For the purpose of dimensional tolerance control, measurements should be done at the narrower section, usually the bottom. However, for geometric tolerance control, measurements should be done at both the neck and the bottom sections to determine the taper error, and probably also at the belly section, to determine geometric errors such as flatness or cylindricity.

Evaluation of a complete part usually requires more than one measurement. For example, a circular part may require several measurements equally spaced around the circle to detect dimensional and geometric variation caused by cutting speed variation, jet out-of-roundness, jet perpendicularity, as well as motion errors of the machine.

Regarding selection of a measurement tool, a micrometer is always favored over a caliper. A caliper tends to deform the fine features of the cut surface, unique to abrasive waterjet cutting, and the result is subject to the level of force applied to the tool.

Surface roughness measurement is another topic on its own and will not be addressed here.

Unusual Cut

Over the years there have been many applications for HP/UHP pumps, intensifiers, and the mirage of systems that go into the diverse systems. You have probably run into some unusual uses for the systems or have a funny antidote about unusual situations. When you received this newsletter, return you story to QualJet LLC for consideration.

Mike Gracey writes, "My friend Mr. Fred Machol of Acme Cleaning told me about a request that came from Produce Row in Houston, Texas. The manager of a salad manufacturing plant that prepared slaw, carrots and peeled potatoes for the restaurant trade was interested in speeding up his operation. Fred brought a sack of potatoes back to his shop and tested several flows and pressures. He found that potatoes cut very quickly at 10,000 psi and can be peeled using a fan jet at 3,000 psi. The plant manager wanted a demonstration and liked everything except the cost of the machines and conveyors. Fred learned another thing when the potatoes did not turn brown after hours in the sun. The inner transparent skin was not being removed from the potatoes so they did not oxidize and turn brown".

Beyond High Pressure

· Waterjetsor parts for sale (www.qualjet.com/UsedWaterjets.htm ):

o Two brand new Flow pumps (Husky S-200, 100hp) for sale, $85K each or Best Offer; contact wyattb@nedcorp.com.

o 4'x8' FLYING BRIDGE, 55Kpsi, 50hp, dual paser 3 heads, newly rebuilt 7xpump; contact glh@laserindustries.com.

· Industry jobs: www.qualjet.com/IndustryJobs.htm

QualJet LLC

Quality Waterjet

Spare Parts Specialist

· Quality Waterjet Spare Parts

o Meets/exceeds OEM standards

o 30% longer operation life time than competing products

· Extensive Parts Coverage for:

o Flow style, IR Style

o 40K/55K pumps

o Intensifiers

o On/off valves

o Cutting head

o Swivels

· OEM Expert

o 20+ year waterjet OEM experience (via OH Precision)

o Accept small OEM order

Q2 Promotion

· 20% discount for any in-stock inventory

· Contact info@qualjet.com for details.

Quality Waterjet Bricks

· HDPP rather than softer HDPE material

· 4”x6”x48”, 6”x6”x48”

· 5mm wall thickness

· Available in 900 g/m² standard density and 1,200 g/m² heavy duty density

· Contact info@qualjet.com for details.

QualJet LLC

12819 SE 38th Street, #240

Bellevue, WA 98006

1-866-QUALJET (782-5538)

Fax: 425-378-7776

Email: info@qualjet.com

Website: www.qualjet.com

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