Design a 3D mold, machine it, and use it to cast parts
I decided to design a chocolate mold using Fusion 360. I base my design on Tux, the linux penguin.
As a chocolate mold does not really require sculpting tools; I sketched a simple design using the sketching tools in Fusion 360.
At this time do not worry about dimensions, the image can be scaled up to the size of the wax block to use for the mold.
After checking that all lines are closed, extrude the design according to the desired effect.
Next I draw a construction line of the dimensions of the wax block. Then I use the scale feature, under modify, in Fusion 360 tool panel.
Fillet as necessary and reshape anything in the original sketch, Fusion 360 will parametrically update the extruded figure.
Then create a box of the dimensions of the wax block.
MEASURE the wax block with a caliper, take the biggest measurement from two of the ends of the width, height and length.
WAX BOX SIZE ------------ 142.9mm length 92.6mm width 36.9mm height
After measuring the wax block, position the positive design inside the block; leaving at least 1cm clearance height for the molding creation process.
Now, the mold is ready for the CAM process. Fusion 360 has a CAM functionality compatible with the printer in our Fablab; the Roland MDX40a.
Fusion 360 provides a module for CAM processing.
In CAM mode, first create two new tools in the tool library - these, must match the tooltips available for use.
The first tool I will use for the rough cut will be a 3mm flat end mill.
I introduce the measurements of the tool following the highlighted guidelines of Fusion 360.
Next, I create a new tool for the finishing job. It is a ball-end tool, suitable for the tux design.
In order for the machine to be able to mill the design correctly; the coordinates of the milling machine must be set. This is indicated by the xyz arrows in the design.
Next, the stock size is selected. In my case, as I already positioned the design manually on the stock - the mode selected is relative size box.
Next, I proceed to create a 3D milling job. Adaptive cut is used for rough jobs. I set the spindle speed to Roland MDX40a's maximum and the cutting feedrate to 1000.
I also disable the coolant option.
Next, I proceed to select the passes settings.
I set the maximum roughness step-over to 5mm and optimal load to 1mm.
After toolpath is calculated I simulate the job. No collisions are detected; hence, the first rough cut is ready for processing.
Before generating the output file, I set up the finishing job. For my particular piece, scallop seemed most suitable.
Similarly to adaptive clearing, I select my tool for finishing. In this case, a 3mm ball-end tool.
Additionally, spindle speed is set to 10,000rpm.
Now, I simulate the whole job by first selecting SETUP and then clicking on Actions/simulation.
The operation did not contain any collisions; hence, the whole job is ready for milling.
The next step is to post-process the job. By post-processing, fusion 360 generates the gcode for the machine. Make sure you select the machine, in the picture below choose generic roland RML and Deselect as NOMDX15or20 and select YES to MDX40. The machine in our fablab is the MDX40a, however, the MDX40 setting in fusion360, works just fine.
Give a program name or number and then click on post.
This will save the job in a new file.
Now it is necessary to go to the Roland MDX40a machine control GUI. There, the first thing to do is to set the origin points of the machine.
Next, click on the cut button and select the file generated by Fusion 360 and launch the job.
The post processor will export the files in .prn format, which can be easily imported into the Roland's Vpanel.
File is imported, the origin xyz axis is found in the machine and the block of wax positioned and fixed carefully inside the machine.
With the wax ready, proceed with the silicone negative of the wax.
Mixing ratio of A component to B is 10 to 1 and pot life is about 80 minutes (see Product information.)
Mixture is carefully poured in the wax piece.
Next step is to take the piece to a vacuum machine.
The vacuum machine will remove the bubbles so the silicone mold is smooth as possible for casting.
The mold looked as follows after the vacuum process:
Final mold and wax piece:
I contacted the silicon manufacturer to find out whether it is food safe. A customer service representative replied that their silicon has not been tested with food products; so I decided to not cast chocolate on the mold.
For the casting process I used Neukadur protocast 195. The datasheet can be found here.
The mixing rate is of 70 of compound A to 100 of compound B.
The casting process is as follows:
The mold is pre-heated to 70 degrees celsius and protocast A to approximately 40 degrees and put into a vacuum machine for 30 minutes.
Next, components A and B are mixed throughly and put into the vacuum to 100mbar.
The result was unexpected, stil with bubbles. Perhaps, the temperature wasn't ideal. However, the colour and texture were satisfactory.
I decided to try with another casting compound, the Neukadur Multicast 8.
This casting material offers low viscosity, fast-cast system with shorter curing times.
Datasheet can be found here.
I used as a hardener, the Neukadur ISO 2 hardener.
The process of casting was more simple than with the protocast 195 compounds.
A ratio of 1 to 1 was mixed of Multicast 8 and the hardener.
Next, it was carefully poured onto the silicone mold.
Afterwards, it was promptly taken to the vacuum machine in our fablab to remove air bubbles. Note that the process must be fast as the pot life of the materials is significantly shorter than of protocast 195. Pot life is approximately 5 minutes at room temperature.
Next, the mix is let to rest in the silicon mold for around 150 minutes.
After 150 minutes, the casting process is finished.
This time the result was very satisfactory. The level of detail is excellent and the appearance is homogeneous.
Below a final picture of the casted penguin.
Learned to create a mold with a positive 3D design.
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