Molding and Casting

Design a mold around the stock and tooling that you'll be using, mill it (rough cut + three-axis finish cut), and use it to cast parts

Documented how you designed your 3D mold and created your rough and finish toolpaths for machining, including machine settings

Shown how you made your mold and cast the parts

Described problems and how you fixed them

Included your design files and ‘hero shot’ of the mold and the final object

Group assignment:

Review the safety data sheets for each of your molding and casting materials, then make and compare test casts with each of them

Group assignment

The molding and casting materials I used for this assignment summed up:

Smooth-On Ecoflex 00-30

Ecoflex 00-30 is a platinum-catalyzed silicone rubber that is soft, strong, and stretchy. It is mixed 1A:1B by weight or volume and cures at room temperature (negligible shrinkage). It is translucent and can be pigmented for color effects. Ecoflex is suitable for making prosthetic appliances, orthotic cushioning, and special effects applications. It is also certified as skin safe. Here's a summary of the main points for using Ecoflex 00-30 silicone rubber :

Use in a properly ventilated area and wear safety gear.
Cure inhibition may occur with certain contaminants, so test compatibility with a small-scale application.
Applying a clear acrylic lacquer or release agent can help prevent inhibition and make demolding easier.
Mix Part B thoroughly before starting. Combine Parts A and B in a mixing container at a 1A:1B ratio by weight or volume. Mix for 3 minutes, scraping the sides and bottom of the container.
Vacuum degassing is recommended to remove air bubbles. Use a vacuum pump that can pull at least 1 Bar / 100 KPa and leave space for material expansion. Continue vacuuming until the material rises, breaks, and falls. Vacuum for 1 additional minute after the material falls.
Pour the mixture in a single spot at the lowest point of the containment field and let it seek its level over the model.
Cure at room temperature (23°C, never less than 18°C) and post cure for attaining maximum performance properties quicker (After curing at room temperature, expose the rubber to 80°C for 2 hours and 100°C for one hour).
If using as a mold, no release agent is necessary when casting wax or gypsum, but a release agent is recommended when casting polyurethane, polyester, and epoxy resins.
THI-VEX can be used to thicken Ecoflex for vertical surface application, and Silicone Thinner can be used to lower the viscosity for easier pouring.
Clean and dry the mold before storing it on a leveled surface in a cool, dry environment.

Mixing component B and A (1A:1B). White color. Quite heavy bubbling occured while vacuuming.

Pouring it into a mold.

Cures to be very soft.

Removing it is very easy.

Very soft and stretchy, but always going back to it's original form without permanent deforming.

NEUKADUR ProtoCast 105

Main characteristics

Very good flowability
Very impact resistant
Very good colorability
High heat resistance
Cures to white color
Only suitable for vacuum casting

Component	Color	Mixing Ratio by Weight	Density (20°C) g/cm³	Viscosity (25°C) mPa∙s
NEUKADUR ProtoCast 105 Component A	Slightly yellowish	100	1.05	650
NEUKADUR ProtoCast 105 Component B	Slightly yellowish	200	1.16	160

Mixture Properties (approximate values)	PC 105 A / PC 105 B
Mixing Viscosity (25°C) mPa∙s	325
Density (20°C) g/cm³ DIN 53479	1.13
*Processing Time (25°C) Minutes*	5
Demolding Time (70°C) Minutes	60
Hardness Shore D DIN 53505 after storage 2 Hours at 70°C	82
Cured Color	White
Recommended Layer Thickness mm	5

Processing Instructions:

NEUKADUR ProtoCast 105 Component A must be thoroughly homogenized prior to processing. The containers must be carefully sealed after each use. After 30-60 minutes, the cured material has not yet achieved its full impact resistance (which is achieved only after approximately 1-2 hours at 70°C), so cautious demolding, especially for thin parts, is recommended. It's recommend pouring NEUKADUR ProtoCast 105 Component A/B into preheated molds at 70°C (e.g., made of ProtoSil RTV 245) and tempering for at least 1 hour at 70°C before demolding. Recommended casting thickness: up to a maximum of 5mm.
It's recommended evacuating NEUKADUR ProtoCast 105 Component A for 15 minutes at the highest possible vacuum, then relaxing to 20-25 mbar before adding NEUKADUR ProtoCast 105 Component B. If the vacuum drops below 20 mbar, severe foaming may occur when both components are mixed.

Mixing component B and A (1A:2B). White color

Some bubbling occured. But there was another problem. The potlife of this (5min) was so short, that it turned hard while vacuuming.

Hard as stone - almost.

So I just vacuumed one component and mixed it without vacuuming again. Bubbles were quite strong.

All tst cast of Neukadur 105 hardened. (Below were cast in Smooth-on mold, above was cast in Protosil mold)

Removing was very easy, because the negative molds were very soft and stretchy. But Neukadur is stone-hard, the hardest of all the materials tested. If the negative molds wouldn't have been so soft, it might have been a lot harder to remove.

Luma!

ProtoSil RTV 245

Main features

Shore hardness A 40
very good flow properties, translucent
shrinkage-free vulcanization at room temperature
can be made thixotropic
high resistance to initial tearing and tear propagation

Properties in the non-crosslinked state	ProtoSil RTV 245 Comp. A	ProtoSil RTV 245 Comp. B 1 (dry surface)	ProtoSil RTV 245 Comp. B 2 (oily surface)	NEUKASIL Thixotropic Agent SN 200
Colour	colourless	colourless	colourless	colourless
Mixing ratio p.b.w.	100	10	10	0.1 – 0.3
Density 20 °C (approx.) g/cm3	1.1	0.95	0.96	0.98
Viscosity 20 °C (approx.) mPa·s	60,000	320	400	1,000

Properties of the mixture (approx. values)	Mixture A/B
Mixed viscosity	35,000 mPa·s
Pot life (1000 g)	80 minutes
Demouldable after	12 hours
Shore A hardness points	DIN 53505 40
Service temperature	200 °C

Minimize air incorporation during stirring. To achieve a bubble-free vulcanized material, evacuate the crosslinker-containing formulation prior to processing. Expect the mixture to expand 3-4 times its original volume and form bubbles during vacuum creation. Processing is complete once the bubbles have collapsed and the mixture returns to its original volume. Pour the prepared material over the object to be cast with care.

Test cast of Protosil (right) compared to the following test cast of Epodex (left)

Protosil cures to be a bit soft still, while Epodex cures to be very hard.

EPODEX ECO System

Evacuate component A for 15 minutes at maximum vacuum and then relax to 20-25 mbar before dosing component B.
Mix NEUKADUR ProtoCast 105 components A and B together at the recommended ratio (2:1 by weight).
Make sure that the mixing is done as thoroughly as possible.
After casting, allow the material to cure at 70°C for at least 1 hour before demolding.
For thin sections, use caution during demolding, as the material may not have achieved its full toughness yet.
Recommended casting thickness is up to 10cm.

20g of component A.

Vacuum component A (no bubbling occurs)

Mixing component B (10g) to A, but this caused air to be trapped in the mix again.

So vacuuming again. Now small bubbling occurs.

Pouring it into the mold.

Hardened over th weekend.

A bit harder to remove, but it worked without any primer.

The result: very clear cast, still not completely stone-hard, but almost.

_{End of group assignment.}

Operating the vacuum chamber

Connect it's power adapter to a power outlet.

Turn on the main switch.

Open the door and put inside / take out what you need to.

Turn on the vacuuming by turning this switch.

Wait until the air pressure (in hPa) drops to one or zero. Please note that it takes exponentially longer the lower the air pressure already is.

Use these two black handles to tip over the platforms inside, if you need to. This is needed when you have to mix the epoxy/resin under vacuum.

Pull this lever towards you to let the air back in. And you're done!

Designing a mold in Fusion360

Download my Fusion project file

I decided to make a Luma keychain (from Super Mario Galaxy) for this weeks assignment. For the Luma model I used a design from models-resource.com.

This model was a mesh though, so I first had to convert it to a solid body in Fusion. Right click on the mesh in the browser and choose Convert.

Mesh (right) vs solid body (left).

I created a box that is the exact same size as my stock.

At the places where I wanted my negative mold to be, I cut smaller boxes into the big box. I added a few spheres as the registration pins used to really make the mold stay in place when casting. I also created a small step surrounding each box, so the mold will be easier to remove later on. (Even though this got milled away more or less, because of a collision of the end mill with the wax)

Now I used the split body tool to cut the solid Luma model in half to have one side for each part of the mold (two part mold). After placing one half of Luma in each shell, I used one of Lumas feet as the place to pour in the resin while the other one is used to let the air out. I added small tubes to the legs to create a connection to the outside.

Head over to the Manufacture workspace.

First, create a new setup.

Select all the bodies. Make sure the stock point is on one of the upper points of the box. You might want to check which axis is which on your CNC.

Make it a fixed sized box. It is also very important to have the lower edge of you model to be at the bttom of the stock box. I gave my box the dimensions of my actual wax block, so it was automatically at the bottom.

Adaptive clearing

After you are done with your setup settings, you can start with your milling toolpaths. The first one "Adaptive Clearing" is very good for rough milling the majority of the unneeded material.

First, you want to select your tool.

Creat a new one, make it a flat end mill.

These are the settings of this tool.

Settings 1 (Make sure Rest Machining is ticked off)

Settings 2

Settings 3

Settings 4

Settings 5

You can let is simulate to check for any warnings/collisions or to see how much gets milled away.

Scallop

Next milling strategy is Scallop. This is optimal for finetuning and round surfaces.

Settings 1. I am using a 2mm flat end mill tool for this as this allows for much finer milling.

Settings 2

Settings 3

Settings 4

Simulation:

Parallel

Last milling strategy is Parallel. This is optimal for finishing passes.

Settings 1. I am using a 3mm bull nose end mill.

Settings 2

Settings 3

Settings 4

Settings 5

Simulation:

Post Process

I used scallop and parallel twice to get a really smooth finish.

When you have set up you milling strategies, you can create their respective NC programs. You need one for every different tool. I chose the post processor of the Roland MDX as I worked with this CNC for this assignment.

3D Milling

I used 3 different end mills during the whole process. 6mm flat end mill, 2mm flat end mill and 3mm bull nose end mill. Wax block is 15 cm x 9,1 cm x 3,7 cm (LxBxH)

Adaptive clearing milled away most of the wax and also made quite the mess, but I easily cleaned this with a vacuum cleaner.

Scallop as the first finer milling process.

Parallel milling:

The finished wax model looked very nice. It had a very good level of detail and was quite smooth! Time to make the molds.

Molding and casting

Let's start with the materials I actually used. First off is Smooth-On Ecoflex, I used this to make a negative mold.

ProtoSil was also used to make a negative mold.

I used Neukadur to cast Luma!

And these colors along with it to give Luma a yellow-ish color.

My work station for now, with all the materials, a scale and I am wearing gloves of course!

I started with ProtoSil. I mixed component A and B under a vacuum.

Since one side of the wax got milled away, I used acrylic glass as the missing wall. I poured the vacuumed mix inside.

The cured mold looks like this, it was very easy to remove and sturdy while also being a bit bendable. Just like in the Group assignment test casts.

I repeated the same process with Smooth-On Ecoflex and this is the result, a super stretchy negative mold.

Now mixing Neukadur, as I already learned from the test cast, you have to mix this very fast, as the pot-life is 5min or less. It took me a few tries to get this right.

Vacuumed it as well. I didn't actually measure the time, but it felt as if this mixture had a slightly prolonged pot life compared to the test cast. I have a hunch that maybe the color I added might have caused this.

Now pouring it in! As you can see I use one hole for pouring and the other for letting air out. I had to use hot glue to seperate the two holes, because in my first attempts he mix would get into the second opening as well. I also used the hot glue to really seal the seam of the two touching negative mold parts.

The fully cured model looked very nice. It had a very good level of detail and was quite smooth! Now only a bit of painting is left and it's done!