Which Slat or Grate Support System is best for waterjet cutting?

WARDJet offers 7 different styles of grate support systems. Why and how do you benefit from this research and design built into our waterjets?

It appears that most waterjets are sold with a support system made up of slats of steel that are forced into tension by offsetting the slats in staggered toothcomb supports. Yet WARDJet do not seem to push this as a method of supporting parts. So why are there different ways to support your material, and although WARDJet offers slats, why do WARDJet take a different route as a first choice?

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Typical slat support system	WARDJet Job Shop Grating Systemâ„¢

So you are being told you only need slats!

The reasons given by salesmen as to why slats are a good choice are:

• Slats are easy to make and replace if one is worn out and others are not
• By forcing the slats to be installed in a wavy fashion, the back spray that will occur if you are cutting directly over a straight slat for some time will be reduce
• You can make them yourself

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Slats with toothcomb support	Slats with forced tension
Slats with mesh support underneath	Slats supported with welded bar

And the above are true. We used to push the same things when singing the praises of slats. What changed WARDJet was when we were the 6th largest capacity job shop in the USA, cutting parts in real time, for real survival against the competition. We found we were hitting our head against several barriers, all eroding our bottom line faster than we could compensate for with all our attempts to improve efficiency, scheduling, handling and programming. (The job shop was sold in 2003 when we decided to focus solely on building waterjet machines. Many aspects of WARDJet's waterjets can be attributed to the hands on experiences gained in operating a 24 hour per day job shop).

A study into increasing performance revealed the answer. The dead time lost in cutting while loading and unloading the table was unacceptable.

Success of the waterjet job shop was going to hinge around hearing the "hissing" sound of waterjet cutting. No "hissing" sound and it was safe to assume that no revenue was being generated. We had to get a continuous "hissing" ringing in our ears. We had to be able to achieve the following if we wanted to excel in the waterjet job shop business:

• Finish cutting a part
• Move the cutting head to the next part and start cutting
• Then go back and unload the previously finished part
• Load the next part, without stopping cutting the other part
• We also had to be able to interrupt the cutting of a part, go and cut something else, then return to the interrupted part and continue where we had left off.

Limitations of Slats

• You can grab a slat with your hand and shake it which is not a good idea while cutting a part that is supported on the slat.


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• This means if you really want to make sure your part does not move around while being cut, you cannot rely on clamping the part to the slats. You need to somehow come up with a way of clamping the part to something that does not move, like the wall of the tank. BUT beware, not all tanks are equal and most tanks, because of the way they are built, have vibration and resonance issues. (see the CHALLENGE on ‘Should the cutting tank be separate from the gantry motion system?)

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Material clamped to the side of the tank


• Although slats may start out level, flat and parallel to the travel of the cutting head, as the slats vibrate in the toothcomb support, abrasive may get between the underside of the slat and the toothcomb support. The result is the abrasive will force the slat upward. Now you no longer have a flat surface to cut on, and if you don't have a height sensor, this will affect cutting drastically in that you will end up running the nozzle higher off the part, and hence lose cutting power and be forced to cut slower.

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• If you want to interrupt cutting a part, move away and cut another part, then return to the original part you had started on, it is critical the initial part is exactly where you left it! So the initial part needs to be clamped and fixed to the support system, so it does not easily move. Slats do not make this easy as they move.

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• If you intend to load the table while still cutting another part, the process will typically result in some bangs and bumps to the loading surface. If using slats, and depending on how the tank is built, this could result in the part being cut at the time moving, which will affect its final shape and accuracy. It is important that the part being cut is isolated from loading and unloading of other parts as much as possible. We found that slats did not work well for us as a job shop and limited our options.


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WARDJet's RESOLUTION

WARDJet offer 7 support systems, all interchangeable with each other. They are:

1. WARDJet Job Shop Grates™
2. WARDJet Heavy Duty Grates™
3. WARDJet Pure Water Cutting Grates™
4. WARDJet Concrete Grates™
5. WARDJet External Loading Platform™
6. Slats...like everyone else... but not so easy to be interchangeable
7. Stainless steel chain and honeycomb

Why would you want to use a support system other than slats? We will look into the options of supporting your parts, along with some cutting characteristics, clamping, fixturing and how to measure the results of your support decision with real data you can collect yourself.

The Ideal Modular Grate Support System

To be efficient in our job shop cutting, we needed to ensure the following.

• The surface of the grates supporting our parts had to be flat and parallel to the travel of the cutting head.

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• We needed to be able to take a part, place it anywhere on the table surface and clamp it into position.


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• We needed to be able to load multiple different parts on the table simultaneously, anywhere on the table, and clamp it down.


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• Parts when clamped must have the least possibility of moving with loading and unloading of other parts
• When interrupting a job that might be many hours of cutting, to go and cut another more urgent job, we needed to know with confidence we could go back and pick up the previous job and finish it. The support and clamping of the waterjet system needed to give us assurance this would be the case. Slats had proven this was not acceptable.

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• As a job shop, materials cut in one day could vary from 10" thick stainless, to ½" aluminum, to 6" foam, to ¼" acrylic, to lining up a mold to within a few thousands and cutting a shape into it, to finishing off the day with a marble design inlaid into some granite with glass.
• We wanted a grate support system that allowed us to change from cutting rubber, to foam, to glass, to stone, to steel all seamlessly with ideally no loss in time.

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The challenge we had was different materials do not all cut at their best on the same support system.

Different Grates All At The Same Level

The ultimate was to have grates that are easy to swap out with each other, as well as have different types of grates installed on the cutting bed at the same time. It would be ideal if a part of a table could be set up for cutting 10" thick steel, another part for general cutting, and another for cutting foam and rubber. Then ideally we need to be able to take a large sheet of material and lay it across all the different grates at the same time. Now this would be fantastic!

Loading Different Grates On Top Of Each Other

Another wish of loading some grates on top of others quickly and easily, would really give the ultimate in efficiency. With 12" of travel on the Z, even if we loaded some 4" thick grates on top of the presently installed grates, we would still have 8" of travel to play with.

It was these requirements that led to the design, testing and implementation of the range of WARDJet grates.

1) Cutting General Job Shop Work With Abrasive - WARDJet Job Shop Grates™

You want to cut everything that is thrown at you with ease. You need to be flexible, light on your feet, and be able to have 10 different materials on the table at the same time. You want to be able to jump from the one material - say ¼" stainless, to the 1" thick copper, to the ½" aluminum jobs. Some of the material is 4" x 8". Some of the material is an off-cut no bigger than 6" x 7". While a WARDJet height sensor will automatically sense the height of the material and set the cutting nozzle at the optimum stand off from the material, it is still vital all these different materials can be easily loaded and clamped down into position.

And hence the birth of the WARDJet Job Shop Grates which proved to be the ideal Job Shop cutting support system. Made of 1/16" x 5" strips the grate has a standard spacing of 4" x 4" with 8 welds per joint. 4 welds at the top and 4 at the bottom as the grates are reversible. The grates are rigid and do not flop over as would anyone trying to make a 5" high grate with 1/16" material. In fact the 1/6" material is fantastic when it comes to reducing kick back and damage to the underside of the material. As the stream comes through the material and travels over a typical slat it will bounce up and can damage the underside of the material being cut.

With the 1/16" wide supports on the WARDJet Job Shop Grates™, the stream tends to jump over the grates when the stream hits it, as opposed to digging right into the material. All the grates are built to be reversible and flipped over and used again. So if looked after, it could be possible to use the grates up to 4 times, extending the life of the grates substantially, and certainly, based on experience, far in excess of slats.

The clamps that are used with the grate system allow material to be clamped down anywhere on the table in seconds. Suddenly every part you place on the table is secured in seconds, quickly and easily, reducing the chance of bad parts because they moved on the table.

The grates are modular and the same size as the WARDJet Heavy Duty Grates™ and can be placed in a tank side by side with each other. The Job Shop Grates™ once welded are then checked for flatness and put in a press brake to ensure that they are flat. Securing the grates into a WARDJet tank is easy as the entire system is designed to have easy to use clamps lock the grates down onto the grate support system.

It took us over 1 year to perfect the WARDJet Job Shop Grates™. We consider this to be as important as the rest of the waterjet. Something most manufacturers literally leave you in the cold on with a bunch of slats that are stuck into a tooth comb looking support that shake around, can change in vertical position relative to each other and relative to the position of the cutting nozzle. We ask, would you buy a car and then put plastic wheels on it? Never. You would want the best to protect your investment. The WARDJet Job Shop Gratesâ„¢ are critical to your efficiency, growth, quality of parts cut and peace of mind.

2) Cutting Thick Steel And Alloys - WARDJet Heavy Duty Grates™

If the material is 4" to 12" thick, you are of course cutting slowly. This means the stream will be more likely to cut deeper into the support grates. The latter is unavoidable, but a grate support system that is easy to repair, and has the strength to hold heavy loads and openings that limit the number of supports being cut, would be ideal. Hence the birth of the WARDJet Heavy Duty Gratesâ„¢. These grates are made of 5" deep x ½" bars. They have as much open space as possible to limit damage to the grate itself. It is easy to repair any cuts, and theoretically, the grates could be used indefinitely with repair.

The grates are made the same MODULAR SIZE with the dimension of the grate being the same as the equivalent other options, making it possible to have a portion of the tank surface as a heavy duty grate. We have proven this to be a fantastic way to cut thick material, and far superior to the slat system. Securing the grates into a WARDJet tank is easy as the entire system is designed to have easy-to-use clamps to lock the grates down onto the grate support system.

3) Cutting with Pure Water And Cutting Very Small Parts With Abrasive - WARDJet Pure Water Grates™

Yes, as a job shop you may want to cut very small parts at times with abrasive. There may also be many times that you will be asked to cut foam, rubber, plastic, leather, cloth, paper, wood, fiberglass, carbon fiber and so on. Here the WARDJet Pure Water Grates™ are ideal. They offer a flat surface in a frame that is 5" high. This means you can have a set of WARDJet Pure Water Grates™ right next to a set of Job Shop Grates™ and Heavy Duty Grates™. The Pure Water grates are made of corrugated plastic on edge, almost like cardboard, with openings of about 1/16" to 1/8". The plastic "bricks" are then mounted in a frame that is easy to pick up by hand and slide into position. The Pure Water Grates can be slid on top of the Job Shop Grates in minutes, meaning it is easy to have Job Shop Grates in for normal cutting, and then quickly put the Pure Water Grates on top of the Job Shop Grates™ and still have 8" of travel to do that special job where these are ideal.

We don't know how other job shops can be anywhere as efficient as you flip flop from one material to the next without this kind of built in flexibility.

4)Intricate Inlays in Stone - WARDJet Concrete Gratesâ„¢

So right in the middle of everything, someone wants to have a few tiles cut with their corporate logo inlaid. A piece of cake with the WARDJet Concrete Grate™ system. Having done small and very large jobs in stone and tile, porcelain and ceramic, we quickly saw there was a good margin in this kind of work if we could get it cut and completed easily.

And the WARDJet Concrete Grateâ„¢ was born. Easy to load and use, and of course modular to fit in with the other grates, the system reduces the chance of the small parts falling into the tank. By using an anti-back spray device, the water, abrasive and eroded material is caught and allowed to drop back onto the material being cut. This then fills up the opening that was created by the waterjet stream in the cutting process. In turn this locks the smaller parts together and helps hold them in place while the rest of the job is completed. It is then possible, if all these parts could fit on a single WARDJet Concrete Grate™, that the entire concrete grate could be picked up off the table, and the small parts removed. If there were more than one concrete grate, and these were loaded on a WARDJet External Loading Platform™ the entire platform could be removed at once. For more on this, see the next section below.

5) Loading / Unloading Several Jobs Off The Waterjet - WARDJet External Loading Platformâ„¢

There are times, when no matter how you look at it, you will not be able to cut parts because you have to unload the table and then load it up again. Unless of course, you have the ability to preload a table outside of the table itself. Like on a separate platform. So imagine loading several different jobs and types of material onto the platform, then lifting the entire platform and dropping it into position in a matter of minutes onto self-centering guides in the tank. Then to be really efficient, having a second platform, so that as soon as all the cutting is completed, you just lift out the platform in the tank, then load the second platform into the tank and off you go cutting again. And after this move, you turn around and start to unload and the reload the platform while the jet is cutting. Now that would be the ultimate in efficiency. It is also called the WARDJet External Loading Platform™. The actual dimension of the platform is 84" x 163" and can be dropped vertically into position on any Z-813 size machine.

The platform can be retrofitted onto any machine in the field with ease. So even if you started without it, but decided you needed to go this way, it is easy to get this set up and installed.

6) Slats

Yes, there is a place for slats. There are WARDJet machines that have slats as the support system. These have been installed when there has been a very specific reason to have slats. The one specific application was when the opening needed to be less than 1", the parts could not be tabbed, there were thousands of parts cut each day, 24 hours per day, 7 days per week, and it was the right way to go.

The raw material was such that it was repetitive and fitted into a set fixture. The machine had 6 cutting heads, and 24 parts were loaded on the table at any one time. (12 in the front and then 12 at the back).

So yes, if you wanted slats, we can provide them and the machine is built to take this easily. We would however want to make sure that this was the right way to go. We are more interested in you making the right decision for your application and it could be that slats are best. If this is the case, we will certainly tell you.

7) Stainless Steel Chain And Honeycomb

When cutting with pure water, there are times when the use of stainless steel belt chain, or honeycomb is ideal. The selection will depend on the material and size of the parts. This would not be suitable for abrasive as the grates would be cut up and this would not be good.

The chain is often used either as an overlay, or of course with a chain feed system that will automatically load and unload the table. Such a system can be integrated into a Pinch Feed Roller system that is synchronized with the travel speed of the chain.

The CHALLENGE

• Look at what the primary use of the waterjet will be
• Understand the functions of the different grate supports offered and decide which one or combination you would prefer
• Know the effects, characteristics and consequences each support system will have on the finished parts and select your grates accordingly
• When looking at waterjet cutting, try to estimate the dead time you will have between loading and unloading the machine, put a financial cost to this, and make sure you figure out a way to reduce this to a minimum.
• Don't underestimate the value and importance of the support system under your cutting material. Never think of the tank and grate support system as just a "tank and some slats" to hold things up while cutting.

Consider the support system to be as important as the rest of the entire waterjet system, and ensure that you are prepared to bet your home, your loan and last $ on it. We did!