Waterjet questions

[YoDoug]

We are considering a waterjet for some of the larger plate parts we machine. They are almost all .75" thick 6061 aluminum. I am looking for accurate feedrates to hold +/-.005 and consumable cost per minute/hour of runtime. I put these questions out to our local machine tool dealer but I am looking for a second opinion.

[Shazam/TPP]

+/-.005 on .750 aluminum will be a tall order. we farm ours out but the thickness is .250 and under. at that thickness the +/-.005 is still hard to hit. good luck but have them physically prove it

[Tim Johnson]

We purchase our waterjet parts but 1/2" stock is between .005"/.010" taper.

[YoDoug]

+/-.005 on .750 aluminum will be a tall order. we farm ours out but the thickness is .250 and under. at that thickness the +/-.005 is still hard to hit. good luck but have them physically prove it

Taper doesn't matter as long as it is consistent. It is +/-.005 on the profile we are looking for. We finish machine all surfaces that the waterjet will cut and we use knife edge clamps so they will dig in regardless of taper. The only issue is the travel of the clamps is limited so repeatable size is preferred. Truthfully we could probably live +/-.01

[MIL-TFP-41]

+/-.005 is not that tough, depending. Sometimes when cutting large parts out of a sheet, the sheet will stress relieve & you can get some movement. Not really noticeable on small parts. But on really small parts out of 3/4 sheet, it becomes the same story. Like cutting a 1/2" hole in that thickness of material, it just won't be pretty. Taper isn't an issue on newer/fancier machines, the head auto-tilts to a certain extent to overcome this.

I can dig deeper to find out consumable cost, but they are not cheap to run. Very high maintenance machines.

[gcode]

Very high maintenance machines.

and not as well built as CNC mills
we had a half dozen plates of an irregular shape (144" x 50" with pocket cutouts and some big holes) water jet out of 1" mild steel plate.
The machine's X and Y axis were not perpendicular and the Y axis had accuracy issues.
We gave the water jet house a +.25/-000 tolerance and he scrapped 10 of them before he produced a good part.

The machine was cutting a parallelogram with the Y axis nearly a 1/2" out of square with the X
They were checking the parts with a yoyo and they checked fine.
Once we put them on a mill trying to machine them to size, the defect was obvious.

He was a small mom and pop shop and eating 6 of those plates plus the repair expenses for his waterjet machine  nearly killed him.

[YoDoug]

We outsource a fair amount of waterjet parts now and they normally hold really decent size. I guess they must have a higher quality machine.

We run all our machines unattended over night. We struggle with chip build up in the machines. We are exploring the idea of water jet blanks to minimize the roughing time and chip build up in the machines over night. Also being able to nest parts will save us some money.

[MIL-TFP-41]

and not as well built as CNC mills

True statement. The things are built out of extrusion bolted together, like an erector set. (well a little more robust than that, but not much) That being said, we have never had problems like you describe. The maintenance comes in things like rebuilding intensifier pumps every x amount of hours. The media isn't cheap. And depending on usage, cleaning the tanks of spent media is labor intensive and time consuming. I believe our shop rate for those machines is higher than it is for our larger bridge & boring mills.

[CADCAM396]

they tend to self destruct. shootin water past the part, you have to support said part some how
they create massive humidity and noise
nobody puts top operators on them
maintanence is very high, cleaning, media build up, water, power
the water jet has a curf, curel, swarf around radius motion
on a good day +/-.03. best use i have seen is nesting titanium 3 inch thick cutting +.25 cheating tight corners out +.5 stock.
they have there place but precision aint it.

[Rstewart]

I can disagree with most of the statements here. We routinely hold about +/- .01 on 1/2" aluminum plate, but it's a 200k$ flow WJ.  We have two of them with the dynamic head.  Yes, they're maintenance hogs but I do machine parts that come off of them using talon jaws.  Find someone who has a 90kpsi intensifier jet and the 3/4 plate goes fairly swift.

[YoDoug]

Doug - these are your own in-house product, yes?
If so, how about waterjetting bolt down holes in the parts (tooling holes)?
No need for talon grips just bolt through and hit it all in 1x?

We finish 100% of the part so bolting through the part requires an additional op to finish the face after the bolts are removed. We currently do it in 2 ops. In the pic below, the plate holding the accessories is the part in mind. We make a coupe hundred a month.

[Tim Johnson]

Doug - these are your own in-house product, yes?
If so, how about waterjetting bolt down holes in the parts (tooling holes)?
No need for talon grips just bolt through and hit it all in 1x?

That's what we do here. One and done.

[YoDoug]

Update; I was at a local fab shop we use for sheet metal work and he was cutting aluminum on his CNC plasma. I had no idea how far along CNC plasma machines had come, especially in aluminum. We have gotten some test cuts done and they look like they will work. The tolerance is decent, or at least repeatable where we need it to be for clamping and the speed/consumable costs blows away a waterjet. We have a few quotes for different CNC plasmas and I think we may go that route. The link below is the machine we were able to go personally watch a test cut of our parts.

https://akscutting.com/aks-cutting-machine-products/plasma-cutting-systems/

[mkd]

Got a customer that claims +/-.001 on their modern water jet. Obviously a bunch of qualifications follow that spec.
 Surface finishes rival EDM. They have a 5 axis head to comp for the kerf.

[Jeff]

Update; I was at a local fab shop we use for sheet metal work and he was cutting aluminum on his CNC plasma. I had no idea how far along CNC plasma machines had come, especially in aluminum. We have gotten some test cuts done and they look like they will work. The tolerance is decent, or at least repeatable where we need it to be for clamping and the speed/consumable costs blows away a waterjet. We have a few quotes for different CNC plasmas and I think we may go that route. The link below is the machine we were able to go personally watch a test cut of our parts.

https://akscutting.com/aks-cutting-machine-products/plasma-cutting-systems/

Do you have a ballpark price on that plasma by chance?