Week 16, Wildcard (Waterjet)

Individual assignment:: Complete the safety and operations training for the waterjet; Characterize the waterjet cutter cut quality and accuracy; Cut a brittle material on the waterjet

For Wildcard week, I decided to explore the waterjet machine. I have used a waterjet to make metal, plastic, and even wood parts. However, I wanted to explore the waterjet in a different way by exploring brittle materials.

The result was that I was able to cut the bottom out of coffee mugs to upcycle them into planters, and I was able to cut CDs to make diffraction grating to test for my final project.

Finished upcycled mug planters cut with the waterjet.

Cutting CDs to use for diffraction grating in week 10

About the Waterjet

At the UNCC SFL we have an Omax Global Max 1508 waterjet. It has a 4' x 3' cutting area and uses 30,000psi water and garnet abrasive to cut through a variety of materials. It uses two pieces of software to create and run jobs. OMAX Layout is a minimally feature CAD program that also creates the machines paths for each job. OMAX Make drives the machines and runs the jobs and is where the user sets their user zeros for all of the axes and controls the machine.

The UNCC SFL waterjet in the machine shop.

Safety Training

I started by completing the safety training. Since I run the lab and have used a similar machine for a number of years, I delivered the training and safety session to David and my new intern. I showed them how to turn the machine on from the water at the wall to the computer, to the high pressure pump. I showed them how to home and zero the axes, how to move the head of the machine and how to setup art.

I showed them how to draw shapes and setup toolpaths using OMAX Layout. This tool has crude CAD functions to make 2D art. To test run the waterjet, I made a small rectangle (about 4" x 2") with a hole in the middle. We ran the file using the OMAX Make program and cut the shape out of 1/8" thick aluminum. I intentionally made the shape small enough so that it would fall to the bottom of the tank. Then I showed them how to go back into Layout to add a tab so that the perimetter would not cut all the way through and the part could be bent out of the sheet after the cut.

I also showed them proper safety techniques for the machine. First and foremost, operators and bystanders always need to wear safety glasses when the machine is being operated as agregate and sharp pieces can be discarged from the perimeter of the tank. I also showed them where the e-stops on the machine are and the pause buttons are in the software. Generally waterjets are safe to operate and my only injuries have been from moving sharp metal pieces into and out of the tank.

Characterize the Waterjet

Then we did a characterization exercise to see how accurate the water jet is and to investigate the taper. We started by creating a new cut file which was a 2" x 1" rectangle with a .75" hole inside of it.

Setting up our calibrated test piece. Note the tab at the top of the art that was added so the part does not fall into the water.

Then we setup the job with a small tab and ran it at a quality of 1 (the fastest machine setting which is the fastest speed) Once we had the piece, we deburred the edges and then measured it with calipers. We noticed that the lengths of the sides were slightly larger than the as-drawn dimensions.

We started by observing the taper. The waterjet loses energy as it passes through the part so the bottom of the part is wider than the top of the part. It was a bit hard to tell on a piece that was only 1/8" thick, but it was barely noticable.

Then we used calipers to measure each side. The 1" side came in at 1.005" and the 2" side came in at 2.010". So they were just a bit larger than the as-designed part. As I was not going to build anything to assemble in this body of work, it is good to know for future work on this machine.

Cut Something Brittle

It is quite easy to cut metals and plastics on the waterjet as they are very forgiving to be abrasively cut like this. However, brittle materials can be a bit of a challenge.

A couple of weeks ago, I was browsing the university surplus warehouse. While there, I found a box of unused coffee mugs that were garbage as they had the old university logo. As we are also working on some Fab City intiatives, I thought it would be interesting to try to repurpose them somehow. I took 5 of them back to my lab. Then I thought a good use for them would be to make planters out of them. The problem is how to get a hole in the bottom. I thought the waterjet could do the job.

First Iteration

For the first iteration I decided to cut a single hole in the mug. As I was unclear how this would all go, I started simple with the art.

Setup

The first challenge was fixturing the mugs. Since they are round, it would be difficult to use our sliding clamps to lock them down to the waterjet table. So, I took a piece of aluminum sheet, flipped the cup upside down and used hot glue to bond the mug to the metal. Then I used a clamp to pin the sheet metal to the metal grid in the waterjet.

Setting up the mug in the tank before cutting.

Then I made a cut file. I started with a simple .5" circular hole. I drew the circle in OMAX Layout. Then I drew a second circle about 1" diameter around the first hole. I did this to trick the machine into making the cut path on the inside of the hole and so that I could make the starting point of the path in the center of the inner circle.

Then I created the path and exported it into OMAX Make. Before cutting it, I added a pause in the path after the inner cut on the traverse to the outer cut. This way the machine would autmatically stop and I could cancel the job before it cut the outer.

For the material I chose "Plate Glass Soda Lime Silica Glass" in the OMAX material library. I thought this was a good a place to try as any. I measured the mug and estimated that the thickness of the floor of the mug was .30"

Measuring the mug to estimate the thickness of the bottom

Running and Result

I zeroed the X and Y axis of the machine. I moved the tip of the waterjet to a position that looked close to the center of the bottom of the mug. Then I used the gauge tool to set the height of the Z-axis to the correct height above the top of the mug.

Then I ran the job. I really had no idea if it would cut or what would happen so I made sure to hover my hand over the pause button. Fortunately, the job ran just fine and in about 30s there was a well-formed hole in the bottom of the mug.

Second Iteration

Bouyed by the success of the cut, I decided to try to do a more intersting shape that could not be done with a drill and made a 6 lobed shape that was vaguely flower shaped.

Setup

I used SolidWorks to sketch the shape. I made the 6 lobed shaped to have something that looked more interesting than a circle but still was a continous shape (so that the jet would not have to pierce more than once). Then I exported the file as a dxf. I brought it to the waterjet computer and imported the geometry. I used the clean function to tidy up the art. Then I setup the job with the same settings.

I used the same piece of metal sheet as the first iteration and hot glued a new mug to it. Then I clamped it down to the grid in the machine in the same way.

SolidWorks File of the Cut Shape

Cut Shape DXF

Running and Result

I estimated the X and Y zero and reset it to the center of the new mug. Then I ran the job. The new shape cut well, but was just a bit off center.

The first cut of the star shape. Note it is just a little off center.

Third Iteration

I thought I could center the art on the mug better, so I made a jig to help.

Setup

I measured the OD of the nozzle of the waterjet and the diameter of the bottom of the mug where it starts to curve up. Then I used the OMAX Layout software to make a ring with those dimensions. Then I cut the shape on the waterjet out of 1/8" aluminum.

I took a third mug and glued it down to the same piece of sheet metal in the same general location. Then I slipped the newly cut ring over the nozzle. I moved the nozzle over the top of the mug until the OD of the ring matched up with the shape of the mug. Then I zeroed the X and Y position of the nozzle in that location and ran it again.

Running and Result

I ran the job in the same way. However the result was a bit strange. The cut was well centered, however the cut was very messy. Observing this run, I noticed that the sheet metal holding the mug was moving up and down a lot during the cut. I felt this motion was causing the cut to not look very good.

Fourth Iteration

My suspicion was that the jet of water was bouncing off of the sheet metal under the mug and causing it to bounce. I noticed that there was some wear underneath the area the cuts. So I decided to cut a hole out of the sheet metal under the mug to allow it to dump smoothly out into the tank.

Setup

I sketched a 2.5" circle in OMAX Layout and then cut a hole in the area under where I have been cutting the mugs. Then I took a 4th mug and hot glued it down over the new hole. Then I clamped the sheet metal back in the machine and made another run.

Running and Result

I used the same locating jig to set the X adn Y zero. Then I ran this iteration was run the same way as the last 3.

Observing this run, the sheetmetal was still bouncing like crazy and the cut shape was still jagged,

Cut shape after the 4th iteration. Note the jagged shape.

Fifth Iteration

I only had one more mug to try. So I took special care with the last setup.

Setup

For the final run, I added additional clamps on the sheetmetal near the mug. I also added a heavy chunk of steel to weigh it down to keep it from moving.

Running and Result

This cut started badly but ended up coming out well. I initially set the Z zero a little bit too low and the nozzle clogged. This caused the ceramic to splinter a little bit. Once I cleaned the nozzle and reset the Z zero the job ran well. The sheet metal stayed stable and the rest of the cut ran cleanly.

Fifth iteration after the cut. The pieces left inside the shape pushed out easily.s

Full Suite

Below is a shot of all five iterations in order from left to right.

Cutting CDs

For my final project exploration a few weeks ago, I used the waterjet to cut rectangles from old CDs. I did this to make pieces of diffraction grating to try to make rainbow projections for my camera device.

This work is documented in Week 10, Output Devices

I initially tried to cut the CDs with a Zund cutter but quickly moved to waterjetting. Since CDs are made from polycarbonate, they are not suitable to cut with a laser cutter, so the waterjet was the most efficient way to create rectangle shapes that I used to make rainbow projections.