Fab Academy 2017

Molding and casting consists of three steps: the design and the preparation of it to be milled on wax, the preparation and production of the silicon using the wax, and lastly the casting process using the resin and having your final design.

For this week, I wanted to make a small model of Michael Jackson. For the design I used Fusion 360. Also, for the preparation of the milling process of the design on wax, I used the CAM process of Fusion 360.

So, the first step was to import a picture of Michael Jackson in one of his famous dancing moves using the canvas option of Fusion. Next using the sketch function, I did the outline of him and then extruded the different parts on different heights. After, I designed a box with the dimensions of the wax block we had in the Fab Lab which were 142x92x36mm³ and I placed MJ on top of the box after I created a pocket of at least 15mm from the MJ design. This thickness is needed because the silicon should have a thickness below the design so that we can be able to cast.

More information of how to use Fusion 360 can be found on "Computer Aided Design" and "Computer Controlled Machining". After the design was ready, I could proceed on the CAM process.

The first step after entering the CAM environment of Fusion is to make a new setup. After that, a window pops up. On the setup of that we set the home point of the milling process being careful to select the right orientation. On the stock I made sure to select the relative size box option as I designed my design box with the same dimensions as the block of wax that was available.

After this point, there are two processes that take place. It is the rough cut of the design which cuts through the desired depth without taking so much time. For the roughing process we usually use a bigger diameter tool than when we use for the final cut. The final cut process is used to smoothen the design that needs to be casted.

So, for the roughing I used a 6mm tool and for the end cut I used a 2mm tool.

For the roughing of the design, I chose the Adaptive Clearing under the 3D menu. On the window pop up, the only things I changed after I chose the appropriate tool to use, were the Spindle Speed to 15000rpm on the tool menu and the final stepdown to 0.5mm on the passes menu. Nevertheless, below you can see all the settings I used just in case I forgot to mention something.

For the end cut, I used the Parallel tool under the 3D menu. On the pop up window I used a Spindle Speed of 5000rpm on the tool menu because if I put a higher spindle speed the wax would melt. I also chose the right tool of the 2mm. On the geometry menu, I selected only the design of MJ to be milled. On the tool containment, I chose "Tool outside boundary" but if I were to do it again I would not choose it as the final result was not as flat as I wanted from the back side. Finally, on the passes menu, I changed the fine stepdown to 0.2mm for a better smoother result. Below are the settings used:

After all the parameters are set, I made the simulation of the cut under the menu of Actions. After I pressed for the simulation to start, the program calculated the collisions that may occur during the cutting process. Sometimes, not all the collisions are happening. For that you have to look carefully through the collisions to see if it is an actual collision or not. In my case, there were no actual collisions despite the fact that so many collisions were stated. It was probably showing me that there were collisions just because the tool was touching the surface because of the fillets that existed on the surface.

So, after everything was ready, I right clicked on each process separately and extracted the .gcode. In order to extract the .gcode, I right clicked, chose Post Process and I made sure to chose MDX-40 by changing the no to yes and deactivate the yes-es to no-es.

After the extraction of the .gcodes from Fusion, I used VPanel (a program that can control the movement of the Rolland mill we have in the lab). First thing after we open the Vpanel is to find the origin point of our design and adjust the block of wax accordingly. The origin point that we should set in the Rolland mill is the bottom left. For the XY coordinates we use the high speed but for the Z coordinate we use the low speed and the 10 steps when the tip is near the block of wax. When we find the origin point we press apply. Also, the rpm should be changed to 15000 and 5000 accordingly depending on the process we launch.

After finding the origin point I have to upload the .gcode. To do that, I chose cut, I delete all then I add my process I choose it and then press Output. After that, the machine will start milling.

I launched- as referred before- two processes separately as I extracted two G-Codes from Fusion. After the enf of the first process I had to change the tool from the 6mm one to the 2mm one. Below, you can see the result after the milling of the wax. Because I did not like quite the surface around the design of MJ, I sandpapered it in order for it to be a bit more smooth.

For the making of the silicon mold, I firstly had to determine the mixing ratio of component A to B, the pot life (the time before we have to cast the silicon; before the silicon starts getting hard) and the process of them. So, I followed the below descriptions taken from the silicon description.

It has to be noted that component A was a little bit hard to pour into the container because of its high viscosity. We tried to pour it using pumps but as it was of no use we just took the liquid with the container directly. After pouring the right amounts, the pot life started after the mixing of the components. After mixing them really well, we put it into the vacuum in order to get rid of all the air bubbles in the mix. After we turned on the vacuum, we pressed the button so that the air in the chamber starts coming out. We can stop the process when the bubbles collapse and the small LCD indicator of the vacuum chamber indicates 0. When we turn it off, we have to first release the air and then open the door of the chamber otherwise it is impossible to open. Be careful with the air release though. Quite powerful!!

After the silicon is ready we start pouring it in the wax starting from the lowest point. After we pretty much covered it sufficiently, we put the wax to the vacuum chamber again once more for any leftover air bubbles. After all that is ready, then we have to simply wait at least 12 hours before we cast the resin.

After the silicon is ready to be used again, we put some air in it using the air compressor so that we could take out the silicon. When I took the silicon out, I could see that unecessary silicon was created along the edges of my design because of the cutting outside borders as before-mentioned. Nevertheless, it turned out fine! :)

So, after the silicon mold was ready, it was finally time to cast the resin. I tried once without a colourant and once with one. Again, before starting I had to read the datasheet to determine the mixing ratio, the pot life and the process of how to use them. I firstly poured component A and then component B, it being the hardener.

For the colourant, component A was poured, then 5% of the colourant related to component A, these were mixed together very well and then component B according to the dose of only A without the colourant.

Important note after the resin was used, it has to be written when last used on the back of the bottle because of the expiration date of it once you open it.

After the resin is ready, we pour it carefully into the silicon mould starting again from the lowest point of the mold making sure that once poured it is flat and nicely looking. After we have to wait for 30- 60 min for the resin to harden completely until we will be able to take the design out. In order for this process to be faster, we can put it in the oven to 70^o for 20- 30min and the design will finally be ready! After it was ready my design had some leftovers around but i easily took it off with a cutting knife while it was still hot out of the oven.

Some people guessed it was an angle, some a sea horse, some an island (one of the many in the Aegean :D) and some guesses a chicken wing (I think these were just hungry!).. But, I can still see just MICHAEL JACKSON!!!