Week 12
Molding & Casting
Group assignment Review the safety data sheets for each of your molding and casting materials. Make and compare test casts with each of them
Individual assignment Design a 3D mould around the stock and tooling that you’ll be using, mill it (rough cut + (at least) three-axis finish cut), and use it to cast parts.
Group assignment
- Review the safety data sheets for each of your molding and casting materials. Make and compare test casts with each of them.
- find the limits of the materials
- safety sheets and instructions are in the box, if not google them.
- find out which casting to use for my own cast, since we were not allowed to use Crystal Clear 202EU nor Tarbender for the try outs i still don’t know what to use but will find out more from Henk and my fellow students this week.
Basics
I was really looking forward to this week, fun and creative so let’s first get the practical things out of the way. We are doing 3 steps casting this week:
- first cut out the design in machinable wax with the ShopBot
- cast a flexible mold from the 1st mold
- cast the final cast from the flexible mold.
Rubbers and silicons are made of 2 components which you mix together in a paper or plastic cup.
Things to think about :
- make sure you have pin or other connections to make the pieces fit
- think about the pouring and airhole for the last cast (airhole should be the highest point)
Air bubbles are to be avoided as much as possible so stir very gently and every know and then tap the cup on the table. If you end up having air bubbles you can try to use a vacuum chamber, the one in the Waag is a beautiful home made version. The valve on the left is for closing the lid and releasing the air when finished.
Here you can see the bubbles appearing
Releasing the air pressure performed by Erwin “egeltje”
Before you do this always read the instructions and safety sheets that are in each of the boxes, if not there then google it because the variations of ways to handle the materials are numerous.
On the box itself you can find the simple info such as:
- Ratio for mixing described as 1A:1B which is the fluid ratio not the weight ratio, that’s listed separately.
- Pot Life: the time the material is still good to work with after mixing it together
- Cure Time: the time it takes for the material to dry (after this you may still have to dry it further in an oven)
- Shell Life: the time the material is still good to work with after opening
- Shore Hardness the hardness of the material - it’s measured with a shore durometer
Fun fact: i am a rhythm skater and we use the same scale for wheels hardness, mine are 86A
Fume extractor is what you would think if you hear the name, a box where the fume gets extracted and you can work with materials that are hazardous for your health.
Mold release (release agent) is a spray you can put on the mold to make it easier to take the cast out, if this is needed for the specific material you can find out by reading the instructions.
To find out how much material you need you can fill the mold with water and weight it.
Make sure you always have gloves, glasses and if needed a respirator close by, when reading the safety sheet through you will find out if you will have to use them for your specific material, since it is a chemical reaction that takes place between components it will always be different depending on the material chosen.
Testing the molding materials
Moldstar Silicone Rubber
This seems like a very standard widely used mold which could help with casting compatibility.
- Ratio:
- by Volume: 1A:1B
- by Weight: 100A:96B
- Potlife: 45 min
- Curetime: 6 hrs
- Color: blue
- Shore Hardness: 30A
- Site
After filling the cup we realized that the LEGO was starting to float.. so Lucia rushed to the wood workshop and made a quick solution to keep the lego down.
OOMOO Silicone Rubber
OOMO als seems to be one of the standard and no so hazardous molds to use, a bit shorter potlife but that’s fine for what we are doing.
- Ratio:
- by Volume: 1A:1B
- by Weight: 100A:130B
- Potlife: 30 min
- Curetime: 6 hrs
- Color: lavender
- Shore Hardness: 30A
- Site
PMC Urethane Rubber
The Urethane rubber needs a bit more precautions to use, more toxic fumes so we treated it more carefully and under the extractor. We used a release agent and brushed it in, as suggested on the site/manual.
- Ratio:
- by Volume: 1A:1B
- by Weight: 1A:1B
- Potlife: 30 min
- Curetime: 16 hrs
- Color: clear amber
- Shore Hardness: 30A
- Site
Casting material try out
Pigmentable Smooth-Cast 325
We noticed that there was one Pigmentable resin which ofcourse we wanted to try, so together with Erwin and Lucia we started the experiment. It has a very short pot and cure life so we could watch it dry.
- Ratio:
- by Volume: 1A:1B
- by Weight: 115A:100B
- Potlife: 2.5 min!!!!!
- Curetime: 10 minutes!!!!!
- Color: milky clear or colored with pigment
- Shore Hardness: 72D
- Site
The 3 experiments still in their molds, you can see that the cat was the last one to be filled.. the resin was already passed the pot life by then.
Since i want to work with a led inside my cast we checked with the bicycle light from Lucia’s bag if the light would go through.. it does :)
The not pigmented material seems to blend better with the pigmented material then when they are both pigmented but this could also be due to the thickness of the resin since the pot life was only 2 minutes. Below some miniture versions of the Waag, mold made by a student from a previous year.
Which resulted in a cat that as Erwin mentioned would appear in your nightmares.
Making the machinable wax mold
To make the first mold we use the shopbot to cut out the design. Since we already used this machine in week 07 i will stick to explaining the basic steps and explain a bit better whats specific for this week.
Vcarve
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Open Vcarve software
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New file
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Fill in set dimensions.
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Import 3D model (STL file)
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Center to the model (in model size window)
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Zero Plane position - a little under the red line so that the top layer is also milled off. Which is only done by the finishing toolpath.
when you press ok here you can’t go back anymore
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Go to edit/move and check if there is really one vector not several on top of each other
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I would suggest to measure one of your paths to make sure nothing has gone wrong with importing
3D roughing toolpath
- Fill in your milling bit specifications
- in the Waag this is set for us using the 5mm - 2 flute.
- Spindel speed 6000 & Feedrate 50mm/sec (both lower for wax then with wood)
- Machine limit boundries: material boundries
- Machine Allowance: 0.5mm allowance
- Rampling move unchecked (you can use this when you have a hollow mill)
- SafeZ 6mm ???? is this the layer thickness
- Name it and calculate
3D finishing toolpath
- Fill in your milling bit specifications
- i would like to use a 2mm bit … ended up using a 5mm bit so i didn’t have to stop in between the 2 toolpaths to save time and keep my life as simple as possible.
- Spindel speed 6000 & Feedrate 50mm/sec (both lower for wax then with wood)
- Stepover 0.5 (10% of the mill)
- Area machine strategy: offset
- Name it and calculate
in preview you can see how it’s gonna mill
- green lines are where the mill lands
- blue lines are the paths
- red lines is airpaths
The simulation in VCarve seems to not work properly so do check for strange things but keep using your own logic.
If needed cut off the pieces sticking out from your material.
Prepare the machine
- place your machinable wood which should be just slightly smaller then your design to avoid unneeded machine time.
- Screw a corner of 2 pieces of wood of 90º on the sacrificial layer.
- Place your block on the sacrificial layer in the corner
- Press another wood against it and screw it down
- Do the same with the 4th piece of wood
- Measure the milling bit width to check
- Put the collid in the nut
- Insert the mill in the nut - measure it, minimum 2 cm should stick out.
- Lower the skirt by undoing the wing bit
- Put the nut in the spindle with 2 english key & wrench (one has the key from the machine attached to it)
- Clean the working space.
- Switch the machine on (only the red knob on the side of the shop bot) For machinable wax we don’t wanna put on the dust collector, we actually wanna keep the wax to be able to re-melt it.
Open Shopbot software
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Check the direction off your material on the machine (think about the direction of your design)
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XY home
- the machine will make an alarm sound and moves to the origin of the machine, i think you can also just move it to the right place and zero the axis but i got used to this rythm.
- Adjust it with → ↑ ↓ ← to the exact corner of you block.
- If needed you can move Z down pg up - pg down to make it easier visually and to not bumb into the wax.
- Take a picture of the values just in case because the numbers got to zero after the next step.
- Go in the top menu to zero-zero-XY-azis
- Popup screen with the message ‘tool is now Zeroed in X and Y axis will appear (strangely enough sometimes this doesn’t appear)
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Press K for keyboard (if you wanna be sure that you set it right you can go to the little green screen and set the the x/y to zero and see where it moves to, if done right it doesn’t move)
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Setting the Zaxis
- Move the arm with → ↑ ↓ ← to a position where you think the block will be the flattest, for sure not the corners.
- → ↑ ↓ ← and pg down - pg up are the single ones, not the one from the numeric.
- Put the metal small plate underneath the mill exactly in center of the mill, make sure there is no dust, tap it against the mill to check if the green dots reacts (otherwise it will keep on going down because it will not create a closed circuit)
- Z axis
- When confirming the first pop up screen the machine will sound an alarm and move the mill down to the metal plate, keep your hand on the space bar to pause in case it goes wrong.
- Confirm the second pop up and remove the alligator clip which is apparently how they call the little metal plate.
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Press K for keyboard - with pg up move the mill a bit higher so you can remove the alligator.
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Put the milling on with the key on the side.
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Adjust the speed to what you’ve put in Vcarve.
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open stl file
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Pop up
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Ok and hands on the space bar - the machine will sound a alarm and start milling
if you are using 2 different mills then you will have to export the tool parts to 2 different stl files and execute them separately the rough on first of course.
individual assignment
- Design a 3D mould around the stock and tooling that you’ll be using, mill it (rough cut + (at least) three-axis finish cut), and use it to cast parts.
- keep the design simple enough so that i can make the molds etc without getting confused. If i have time i would add some electronics to it.
- as always google for ideas and tutorials online.
- understand more of the process.
Ideas
As a lightdesigner the first thought with casting would be “hmmm.. what if i put a LED in there..?” so thats exactly what i am gonna do. Focusing first on making the mold and if that all works out i can continue with the electronics, if time is finished i can always just hold a 3V cell battery between the pins.
Since the lightbulb is my favorite shape (even have a tattoo of one) i have lots of them lying around so could break this one to check if it’s really as ‘easy’ as i thought.. and yes, just a LED and a Resistor.
Designing in Fushion
Although i am getting more comfortable in Fushion i still make a mess when i do not understand fully what i am doing, pretty sure next time i will not be so scattered and messy in my timeline.
Found out a fun trick how to keep a sphere parametric in relation to the other objects:
- create a component from your sphere
- make a sketch point on the placement on the object you want it to be attached with (use constraints so that it moved when you change the parameters)
- create a rigid joint from the center point of the sphere and the placed point
- DONE seems a bit like a work around but it works
a version of the stamp, which is cleaner because i understand better the logic.
On the left on of the first ideas before i realized the mill is 5mm thick.. and holding the recycled material in front of the screen to see if i got the proportions right.
Milling with the Shopbot
Above you can find out how i used the Shopbot, starting to feel a bit more comfortable with the machine and software. It was a bit tricky to keep my model within the wax since my model was so big.
i missed out on 1 millimeter on top, if i would have placed the model a tiny bit lower i would have had the pin connections going through the wax but thats easier to fix then a not fully rounded bulb. But no more time so this is what it is for now.
There was one tiny point on which i had less then 5mm according to the machine, but when i checked it’s actually exactly 5mm so next time go for clearing space of 5.1mm with a 5mm mill. It was really easy to take away with a stanley knife.
Then time for the missing top.. i made a little wooden plate with the laser cutter on to off my wax to have a bit of space for the Oomo to go higher so it’s a thicker wall. Attached it with double sided tape and then later on melted the wax a bit to avoid cracks.
Melting the wax with the heatgun.
Making the mold with OOMO
With the group assignment i thought the OOMO was the most comfortable to work with texture and pot life wise, although Moldstar gave the same feeling but that’s almost finished and with my big mold i don’t wanna end up having not enough material.
Big fan of the vacuum pump, but don’t use it with your mold i learned the hard way because with less pressure the fluid expands and of course overflows, i could have figured that out without trying :)
After 6 hours of waiting (well actually 3D printing) it was time to get them out, the wooden top was still a bit more sticky then the rest of the mold even though i used a release agent.
When the first one came out i realized it didn’t dry it properly before filling. There was a bit of water left in the little holes which now did not hold so much of OOMO, but good enough to connect.
A day later both of the sides where ready - as you can see i payed more attention to drying the mold the second time i filled it.
Making the stamp
Since i could not create detailed line with the Shopbot i decided to 3D print my stamp/top lid to hold the wires from the LED. Designing it was fairly easy, had a few version of the top before decided to go with the champagne cork version.
Wiring the LED
Soldering the LED and the resistor together.
Trying out the tilt switch.
Trying out Crystal Clear 202
When reading the instructions for Crystal Clear they mention that you can only use it with a mold made in MoldStar.. but together with my partner in crime Lucia tried an OOMO test run anyways. The only other option at the Waag was Tarbender and those safety sheets and requirements seemed a bit to extreem for a first try. So before Henk was heading to the shop we gave it a try and hoped for the best.
- Ratio:
- by Volume: NOT LISTED
- by Weight: 100A:90B
- Potlife: 9 min
- Curetime: 90 min
- Color: clear
- Shore Hardness: 80D
- Site
On the left the first try with OOMO combined with Crystal Clear, even tried half of it with no release agent which didn’t seem to matter, but there are not so much details in this left over from the cup created mold (patented by Lucia). So tried the puzzle piece from nadieh to see how it dealt with details, passed the test with bells on :)
It takes 5 days for the maximum cure time, meaning that then i really has reaches all the properties as described in the datasheet.
Molding with Crystal Clear
So now that i know it can work it was time to prepare my mold, i skipped the part of preheating since it didn’t seem to have affected the puzzle piece also. Taped the whole thing just in case, in retrospective i didn’t need it, the material stayed beautifully in the mold. The second clamp on top is just there to round the top cylinder again, the 1st one is need to hold the molds together.
When i took the stamp of i realized i did not fill it to the top, it looked like it but by the looks of it i missed 1mm, that’s gonna give me issues with the montage of the fitting but no time to waste. Got the stamp off very gently and was able to see the damage..
Even with the missing 1mm and slightly flattened sides i still love it!
Making a fitting
How to make this fit? I wanted to make a insert to my recycled fitting to be able to connect every thing together and hold the tilt switch. The first try out i made the wall a bit to thin, trying to safe space has bit me in the ass. The 2nd try worked out fine.
Making the bottompart.
I printed the first and only version of the bottom part together with the first version of the fitting, so also here the walls where to thin but it only effected the little upstanding cylinder, for now this will have to do. Maybe i can make a new one next week when i have time (hahaha as if i ever have extra time these last months)
Putting it together
Back home i put everything together, because of the missing 1 mm i ended up having to use acryllic kit to make it fit, but as long as it fits i don’t mind, this is a try out version :)
Before glueing it together i checked if the LED & tilt switch still worked, better safe then sorry.
Also in daylight on my desk it functions fine :)
Retrospective realisation
During the regional Quentin pointed out that maybe i should have checked the material condustion & resistance, good point.. didn’t even think about that.. oeps, but since it’s only 3V not much can go wrong.
Also Luc made me aware of the way that an LED actually already in epoxy.. Crazy to realize that, here is a picture of it:
At the beginning of week 13 i still wanted to try some pigment in the bulb, not sure if i like it better but funny to see how easy it is to create fluffy clouds.
- Great week, finally feel free to use more of the tools i’ve learned during fab combined.
- understand better what i am making before going digital (fushion) - maybe i should start to make more detailed sketches on forehand.
- dry the mold & fill the mold till the top (duh)
- find a way to make sure the led stays in center, maybe only non flexibele wires at the bottom of the stamp - i gave 2mm of freedom..
- find other ways to control a light instead of a normal switch