Waterjet and
Abrasivejet pictures (Page 7):
For
this page of pictures, we will
look at one of the very first abrasive waterjet parts ever cut, and
compare it with what a modern machine and controller can do today...
Way back in 1980
(give or take a few years), waterjets (pure water)
were fairly well established for the purposes of cutting diapers,
cardboard, candy, paper and other soft material separation
applications. However, waterjets were incapable of cutting
metal.
Sometime around
then, experiments were being performed regarding
introducing abrasives into the stream of water, with the hopes of being
able to cut harder materials such as steel, stone, and glass.
One of the very
earliest parts ever made with an abrasive jet is the
part that you see below:
It is likely
that the above part is the oldest abrasivejet part in
existence. The Chinese character that you see means "Cheung",
which is the last name of Dr. John Cheung, who also happens to be my
boss and the president of OMAX (yea, I stole the part from his desk :)
). Ok, I'm not 100% sure this is the oldest part in
existence, but
it is
definitely one of the oldest. It is the oldest part that I know
of, anyway. Although the cut looks very ugly, this
is a very impressive part. At the time, it was revolutionary to
be
able to cut metal at all. In this case, 1/2" (13mm) thick
stainless
steel.
Above: the same
part as seen from the backside. Yes, it's really
ugly! This is why I wanted to show it to you. Many early
abrasivejet parts were this ugly and extremely imprecise.
Advances in controllers, pressure regulation, nozzles, and other
technologies are the reason most modern parts don't still look like the
above.
Looking at this
part made me think, "how does this compare with the
state of the art in waterjet machining today?". So, I thought that it
would be cool to use the latest in technology to reproduce this same
part, and see how much things have improved in the last 20+ years.
Since I didn't
have a handy DXF file of this part, I started out by
scanning the original part using a flat-bed scanner. (Actually,
my co-worker Debbie M. did the scanning, then gave me the .jpg file,
since I don't have a scanner myself.)
Next, I traced
over the image in OMAX Layout
(waterjet CAD software) to
reproduce the drawing with clean lines and arcs. I then used this
to
generate a tool path for the controller:
Above: Partly
traced image. (In case you are wondering why the
photo in the background is so dark, it's because I dimmed the original
image to make it easier to see the lines as I drew them.) I did
not use any automatic "raster to vector" conversion software to convert
the photograph into a vector outline, because in this case it would
have been more more work than I wanted to do, and I also wanted to make
sure that the ugly boogers of the original part were not faithfully
reproduced in the new one. (Automatic scanning software is generally
better suited for artistic stuff where edge quality and tolerance is of
no concern.)
From my CAD
drawing, I then generated a tool path and loaded that into
the machine. I told the machine that the material is 1/2" (12mm)
stainless steel, and let it figure out how to apply a cutting model to
compensate for the sloppy and floppy abrasive waterjet:
Above, the part
in OMAX Make (Controller) ready to machine. The
colors represent cutting speeds automatically assigned by the
controller based on a built in cutting model. The idea there being to
optimally only slow down for the areas where it is needed to move
slower to maintain the user's desired results. (A luxury that was
not available when the old part was made!)
Above: Tool path
loaded into the controller.
I then loaded in
some 1/2" (12 mm) material into the machine, and told
it to "begin"
Below is a
picture of the part as it is being cut. Note the
articulated "Tilt-A-Jet"
cutting head, which tilts the cutting opposite of the taper produced by
the jet, so the edges of the part are perfectly parallel (More on
tilting on the next picture page):
It's fun to
watch the tilting head, because it dances all around as it
cuts. Watching it, you would suspect that something was wrong and
that it is tilting way too much, but amazingly the parts turn out great.
As I write this,
tilting cutting heads are just being introduced into
the market. They offer the advantage of being able to produce
nearly taper-free parts, which expands the range of parts possible to
make with an abrasivejet. I would expect that in 10 years they
will be standard equipment on nearly all waterjets. Of course, it
is possible to make nearly taper free parts without such a cutting
head, but it requires very careful setup from an experienced operator,
and requires slowing the cutting process way down. The tilting
heads allow for making the same part without having to slow down nearly
as much.
Below is a
picture of the final part (right) next to the historical
part (left):
As you can see,
there is considerable improvement!
Above: A
close-up picture of the back side of the new part. The
back-side of abrasivejet machined parts are the most difficult areas to
make good because when you cut with a "floppy tool" any problems are
magnified on the backside. It is only with the introduction of
sophisticated control that such good results can be achieved. As
you might notice if you study the part carefully, the part is not
perfect, but it is darn close to it!
Above: The front
side of the new part, with the tool path in the
background.
So, how has this
processed improved since the original part was
made? Here are some areas:
- It was very easy to program this part. I estimate that it
took me less than 10 minutes to draw the part in CAD and create a tool
path ready to cut.
- The surface finish and quality of cut improved dramatically.
- The part has virtually no taper now, thanks to the tilting
cutting head
- The tolerance of the part has improved from, say +/- 0.060" or so
to +/- 0.002" or so due to sophisticated control
technology, modern nozzles, and tilting cutting head.
- The part was probably cut much faster than the original.
Unfortunately, I don't have the time of the original for comparison,
but I do know that through software, part cutting times have increased
in speed by a factor of perhaps 2-4 times since this first part was
made, and through hardware part cutting times have decreased by perhaps
another factor of 2 or three.
- Lots of other parts of the process have improved as well, but the
above are the main points.
If you have
pictures you would like to share, send
them by with a short description of what it is, what it is made of,
and any special or interesting notes on how it was made.
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Olsen Software, LLC