Molding and CastingFor Molding and Casting I´ve decided to design a double lens, because I like this shape. I`ve created the shape in Fusion 360:
First, create a square plane. Stop sketch and extrude. Create sketch again and choose front vertikal face. Draw a circel, stop sketch and extrude/cut the channel until half of the block. Create sketch again, and choose the profile of the channel in the center of your cube. Disable the body view and create a sector of a circle. Stop sketch and revolve around an axis you have set before. Now, create sketch again, choose the upper face. You have to create pins for fitting. Draw two circles, stop sketch and extrude negative to create two poles with 3,5mm depth. Mirror the this cube but create it 3mm more flat. Draw again two circles in mirroring positions and extrude them positive about 3mm high. And create around these pins flat channels. Now you are ready to prepare for molding.
Download the intermediate result :Lense File:FinalLens Fusion360 file
As we have to do it in three steps, I redesigned everthing, as seen below:
Preparing for moldingNow, the object above had to be prepared for cnc milling. Marcel and me did this session in KampLintfort, and I have to say we spent a richfull day there with Daniele instructing us in a perfectly balanced manner for learning: instructing us and admonishing us to do it on our own.
For the milling prozess I had to combine all bodies in one. Under Menue 'modify' you can find 'combine'. Then I switched the working plane to 'cam'.
I checked all dimensions in view of the milling tools we are going to use, probably, and regarding to the dimensions of our wax blocks I`ve bought. I´ve only removed the collar around the holes they weren´t necessary because we´ve decided to use flat nose cutter.
Please, see the proceeding list as follows:
- In 'cam' modus choose Menue/Setup/ New Setup. Setup window is popping up.
- In the Setup layer choose operation type 'milling', Orientation: Model Orientation, Stock Point: Box Point and Model: Body
- In the Stock layer set Mode: Relative size box, Add stock to sides.. and set all Offsets to Zero. Check below the dimension in comparison to your wax block. Click 'o.k.'.
- In Fusions Menue you can find 'Manage' -> 'Tool Library'. The Tool Library will pop-up.
- There is a list on the left side of the window, go to 'Local' and click on 'Library'.
If you can´t see the Library Tree click on this sign
- Then choose in the menue 'New Mill Tool', we have to define the tools in Fusion we are going to use.
Again, a new window will pop up and we had to measure the cutting tools and set them in this window as seen below and click ok.:
If you bought you can also write the vendor and product ID.
- Then go to 3D Menue choose 'Adaptive Clearing' for your first quite rough and fast milling prozess. A window will pop up.
- Set Tool and Passes layer as seen below. Remove 'Stock to leave'. Click OK.
- Select in menue: 'Actions: Simulate' and check with the greenish processline at the bottom of the window, the pathlines. Are all holes done?... Check also the pop up window: 'Simulate' on the 'Info'layer for any collisions. Close simulate window.
- Now, select the next processing strategie for getting everything smoth and fine. I chose Morphed Spiral as my farvorites: Spiral and Scallop didn´t work out.
- Again, the pop up window appeared for Morphed Spiral: I`ve set everything like seen below in the same procedure but with a different tool.
- After simulating the second process I selected 'Actions':'Post Process' for sending it to the milling machine. Please see below the settings for Roland machine.
- Save every single process on USB stick, by clicking on o.k. of the post process window, saving window will pop up with .rpm
Milling the shape on cnc-machine: Roland MDX-40A
I've used the following wax block: Regina Formwax bought in the german artist supplier Boesner for abaout 6Euro each. You have to take care which one you buy as there are wax blocks which melt in your hand very good for modulating by hand. This one is suitable for higher temperature. This is the wax block I was going to mill:
After placing it on the working bench and clamping the first milling tool (6mm in diameter) for rough cut, I had to set the xy-origin. See screeshot below. Afterwards, I had to set the z-Axis with a sensor.
If you click on 'Cut' at the bottom of the window, a new window will pop up to ask you which file to import for cutting job. Choose your rough cut file first.
For fine milling you don´t have to and you shouldn´t set xy-origin anymore, it is allready stored. Just change the cutting tool, click 'Move to XY Origin' and set z-axis by using sensor again.
To get a more durable molding I casted my form in silikon, like my colleagues did. We mixed a two component silikon material in proportion 10:1 as recommended on the instruction label. We had to mix ist very well. The substance for component A is silicon rubber (Polydimethylsiloxan with reactive groups und Plati nkatalysator) and component B is Methylhydrogenpolysiloxan (cross linking agent for creating Elastomere).
Datasheets for comp A and B: KompA silikon rubber, KompB1 cross linking agent
You can find more information here: ProtoSil245
The procedure: First you measure silikon rubber in an chemical resistant cup, it depends on the volume you have to fill. For me it was about 200g. Then you add 10%, for my form it was about 20g. You have to mix it very well. But with mixing you add a lot of air in you substance. To get rid of air bubbles we hat to put the silikon filled wax blocks in a vaccuum chamber.
Here you can see Daniele, our Guru, and Marcel and in the picture below Cesar and me, measuring and pouring the mixture
Afterwards we brought our wax blocks with fluid silikon in the vakuum chamber to get out the air. We had to to wait until the air wass sucked out to 1hpa (nearly vacuum) and wait 5 minutes. Then we had to wait for additional 12 hours until the mixture cured.
You have to close the door and shut the air pipe. Then turn the machine on an extract the air until you can see 1hpa (0.00bar) on the screen. Wait for 5 minutes and slowly and carefully open the pipe. You will here the sucking the air into the chamber, don´t do it to fast. As soon as the air pressure is normal again you can open the door and turn off the vacuum machine. Above you can see the air bubbles coming out of my and Cesar 's block.
Demolding after 12h.
Third step was casting acrylic resin. Take care to use a chemical resistant bin for mixing and fresh air, because of acrid fumes. Wear gloves and a work coat, the resin is acid.
First step was painting my negative form with releasing agent. Then I prepared the mresin mixture.
I used a fluid resin from 'sculptare' also bought at Boesner. After pouring and measuring the resin,
I've added 2% of the reacting resin hardener into it. If you use 50g resin, then pour 1g hardener into it and mix it with a flat stick. A round stick won´t work.
After filling up the form I left it for 3 days. Even it was cured after 60 minutes, the instruction manual recommends to leave it up to 3 days.
It was easy to demold, because of the releasing agent on negative form.
There was still some sticky agent left I had to remove. And I had to polish my lens.
Download Final File:FinalLens Fusion360 file