Way back in 1980 (give or take a few years), pure waterjets were fairly well-established for cutting diapers, cardboard, candy, paper and other soft material applications. However, waterjets were incapable of cutting metal.
At that time, experiments were performed on 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 earliest parts ever made with an abrasivejet
“It is likely that the above part is the oldest abrasivejet part in existence,” said Carl. “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 (yeah, I stole the part from his desk). I’m not 100% sure this is the oldest part in existence, but it is definitely one of the oldest. 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, ½” (1.3 cm) thick stainless steel.”
The same part as seen from the backside, where the water stream exited
“Yes, it’s really ugly!” said Carl. “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 got Carl to thinking how that primitve technology compares with modern waterjet machining in 2004. So Carl decided to use the latest in 2004 technology to reproduce this same part, and see how much things have improved in the last 24 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,” said Carl. “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.”
The partially traced image of the part
“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,” said Carl, “and I also wanted to make sure that the ugly parts 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 the CAD drawing, Carl then generated a tool path and loaded that into an abrasivejet machining system. After setting the material to ½” (1.2 cm) stainless steel, the machining software applied a cutting model to compensate for the abrasive waterjet stream.
The part in OMAX Make (abrasivejet machine controlling software) ready to machine
In the above image, the colors represent cutting speeds automatically assigned by the controller based on a built in cutting model. The goal of the controller is to only slow down for the areas where it needs to move slower to maintain the desired precision.
Tool path loaded into the abrasivejet machine controller
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.
The part being cut with a tilting head
“It’s fun to watch the tilting head, because it dances all around as it cuts,” said Carl. “Watching it, you would suspect that something was wrong and that it is tilting way too much, but amazingly the parts turn out great.”
The final part (right) next to the historical part (left)
As you can see, there is considerable improvement in the quality of the part.
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,” said Carl, “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!”
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. Carl estimates that it took 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 approximately ±0.060″ (1.5 mm) to ±0.002″ (0.05 mm) due to sophisticated control technology, modern nozzles, and tilting cutting head.