13. Molding and Casting - Week 13


13.1. Assignments

Molding and Casting

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

  • compare mold making processes

individual assignment:

  • design a mold around the process you’ll be using

    • produce it with a smooth surface finish that

    • does not show the production process toolpath

    • and use it to cast parts

  • extra credit: use more then two mold part

13.2. Group Assignment

Group Assignment Page

Group Page about Material Safety

13.2.1. Mold making processes

We tried out 2 processes (how to make the positive):

13.2.1.1. Milling

When milling, we use the part we want to make and first decide, how many sides we need. In our case it was just one side. Then we model the positive in combination with a cavity, which also needs to be slightly angled for the mill, so it can reach the bottom of the mold cavity.

IMAGE_MODEL_WITH_CAVITY

Then to generate the G-Code, I’ve chosen FreeCAD. It is a bit tricky to generate a rough and a fine path in a fast way. It’s way easier and faster to generate it in Fusion 360.

For Machine Settings, we used following:

Method

Feedrate (mm/min)

RPM

Rough

1000

5000

Fine

500

10000

Fusion 360

Also Ferdi made a tutorial for doing it in Fusion 360: Ferdis Doc

FreeCAD

See below on how I generated the G-CODE.

13.2.1.2. 3D Printing

For 3D printing there are 2 possibilities to produce a smooth surface:

  • SLA Printing (event though it is not perfectly smooth, but extremely)

  • normal FDM printing and then post process the print

We used FDM printing to get used with the process.

There you have the possibilities of applying some material on the print to make it (like paint or similar) or you use a material, that smoothen the current print by reacting with it and dissolve it. We used the 2nd approach with ABS and Aceton-Fume, where the Aceton fume reacts with the ABS and smoothens the surface, when applied correctly:

IMAGE_PRINTED_TU

IMAGE_ACETON

You need:

  • Aceton

  • A closed container (which optionally can be heated)

  • the part on something, you can attach on it (to get the maximum surface that should get smooth)

  • OPTIONAL something to heat the container

IMAGE_PARTS_FOR_SETUP

I then put a good amount of Aceton in the container. The I used a professional and completely normal Setup for keeping it in the container:

IMAGE_THE_SETUP

And then occasionally rotate the piece. And it its to slow, you can heat up the aceton-container (we use a portable stove top).

After a while, it gets quite smooth:

IMAGE_ACETON

But I should have left it in there a bit longer.

13.2.2. Casting A mold

For the Mold, we used some silicons from smooth-on and also mix gelantine with material from a supermarket.

IMAGE_TABLE

13.2.2.1. Silicon

The material consists out of 2 components, which increase their viscosity as time increases (the mixture ‘cures’) and the point, where it’s no longer pourable, is called ‘Pot Life’ and the time it take to be solid is called ‘Cure Time’.

IMAGE_2_COMPONENTS

Then we need to mix the components thoroughly (while trying not to scoope):

IMAGE_MIXING

Next we mixed the components by checking the mixture rate with a scale to get a 1:1 mixture:

IMAGE_COMPA

IMAGE_COMPB

IMAGE_CAST_SCALE

Then we mixed it very thoroughly (also no scoope), so that everything can get solid:

IMAGE_COMPA

IMAGE_COMPB

And then we degased it with a vacuum chamber:

IMAGE_VACUUM

After that, we poured it into the wax…

IMAGE_COMPA

IMAGE_COMPB

IMAGE_COMPB

…and then again degased it again:

And after that, let it dry:

IMAGE_FINISHED_CAST

And after a while it was time to remove it:

IMAGE_TU_MOLD_HARD

IMAGE_TU_MOLD_HARD

Which came out really nice: IMAGE_TU_MOLD_FINISHED

13.2.2.2. Gelatine

Then to mix a gelantine mold you need:

Ingredients

Gelantine

Glyzerin

Water

Mixture

1

1

2

IMAGE_GELANTINE

IMAGE_GELANTINE

Then mix everything together

IMAGE_GELANTINE

IMAGE_GELANTINE

Heat it up but not to hot!!! :

IMAGE_HEAT_UP

Then again create a positive (in this case a 3d print with aceton improved glued to a yogurt) and fill it:

IMAGE_GELANTINE

After filling, slap it a bit to get the air out (or again use the vacuum chamber):

IMAGE_GELANTINE

…FREEEZING…

Then to get it out it’s easiest with high pressure under the mold:

IMAGE_FABBY_MOLD

And then make some cuts on the side to get it out:

IMAGE_FABBY_MOLD

13.3. Individual Assignment

13.3.1. Creating a Space Mold Model

For my assignment I wanted to make a mold for making chocolate and I made it in the style of the logo from our hackspace (again).

13.3.1.1. Inkscape Preparation

First I needed to improve the path of our Logo, because I wanted the get the outline of the path.

To do this, I:

  1. Merged the path above (those lines, that make the font a bit thicker are actually seperat paths) with: Path -> Combine and then

  2. Made the outline of the stroke to a path (so the path looks like the actual font) with: Path -> Stroke to Outline

IMAGE_PATH_MENU

IMAGE_SPACE_PATH

IMAGE_SPACE_PATH

Then to create a cool outline as the base for the chocolate, Ferdi showed me the Dynamic Outline in Inkscape:

  1. Create a copy of the path

  2. Go to Path -> Dynamic Outline and use it on the copy:

IMAGE_SPACE_OUTLINE

IMAGE_SPACE_OUTLINE IMAGE_SPACE_OUTLINE

13.3.1.2. FreeCAD Modelling

First I imported the SVG in freecad and resized it (it was made in the size of a banner).

IMAGE_BIG_SPACE

IMAGE_SMALL_SPACE

Then to make a mold casting mold, I created a cube, added steep walls and extruded the font and outline:

IMAGE_MOLD_MODELL

IMAGE_MOLD_MODELL

IMAGE_MOLD_MODELL

Here I first used the ‘Draft’ Workbench to convert the SVG path (only outline here) to a sketch (Draft to Sketch) and adjusted the size a bit in the sketcher.

IMAGE_MOLD_MODELL

And here the same, but with the other path.

13.3.1.3. FreeCAD Path Generation

First you go to the CAM Workbench, presse JOB Setup and setup the needed tools, workpiece and initial feed rate and RPM. (Ignore the Arch-Logo behind the model ;])

IMAGE_JOB_SETUP

IMAGE_JOB_SETUP

Select and add the body to the job

IMAGE_JOB_SETUP Add tools to the job and set the machine settings

IMAGE_JOB_SETUP

Change the processor the one used on the mill (in our case mach3/4)

IMAGE_JOB_SETUP Adjust the stock material and set the origin point on top of the model to mill!

And don’t forget to set up the tools with the right dimensions:

IMAGE_TOOLS_MENU

IMAGE_TOOLS_MENU

IMAGE_TOOLS

IMAGE_TOOLS

For creating the Path, it’s not as easy as in Fusion but I tried to mimic the way fusion generates a path (at least for the adaptive clearing). I first added a roughing job with the ‘Adaptive Clearing’ (which is not as powerful as as in fusion) for everything above the model:

Clearing

IMAGE_ADAPTIVE_CLEARING

Select the outer edge for the clearing: IMAGE_ADAPTIVE_CLEARING

Set the step down: IMAGE_ADAPTIVE_CLEARING

And Adjust the operation to your liking: IMAGE_ADAPTIVE_CLEARING

Which then results in this path: IMAGE_PATH

Then I did the same for the rest next to the SPACE symbol:

Select the bottom side and also the outline of the cast which helped for the generation of the clearing. IMAGE_ADAPTIVE_CLEARING_2

Set the stepdown high enough, so its only one operation: IMAGE_ADAPTIVE_CLEARING_2

IMAGE_ADAPTIVE_CLEARING_2

Getting this path: IMAGE_PATH

3D Pocket

Next I used the ‘3D Pocket’ operation to remove the side walls. The nice thing about this operation is, that it can calculate the already removed material (‘Use Rest Material’) and then it does not generate a path there.

IMAGE_3D_POCKET

IMAGE_3D_POCKET

IMAGE_3D_POCKET

IMAGE_3D_POCKET Here setting the ‘Use Rest Material’ is very important for time.

The path, making the sides steep and also make the first outline of the cast: IMAGE_PATH

Then I made the same operation but this time on the surface of the cast structure and the bottom but with the finer tool.

IMAGE_3D_POCKET2

IMAGE_3D_POCKET2

IMAGE_3D_POCKET2

The path hase some little corners which came frome the calculation of the resting material being not perfect (those movements where unnecessary -.-). IMAGE_PATH

Important

Because the calculation of the resting material is not perfect, I did the following steps to get the path above for the finished G-CODE calculation:

  1. Calculate all operation in the normal sequence

  2. Move the 2. ‘3D Pocket’ operation one above

  3. Recalculate ONLY this operation

IMAGE_ORDER

Profile

And to finish I made a last ‘Profile’ operation around the text with the finer tool.

IMAGE_PROFILE

IMAGE_PROFILE

IMAGE_PROFILE

IMAGE_PROFILE

A normal profiling path: IMAGE_PATH

Combined

IMAGE_ALL_PATH

Simulation

Even though there is a Simulator in FreeCAD, I wanted to test CAMotics(Git).

And it’s more accutare than the one in FreeCAD and it also calculate a time estimate. IMAGE_CAMOTICS_PATH IMAGE_CAMOTICS_SIM

So about 40min., let’s see how accurate this is.

13.3.1.4. Milling the Mold

Then like always use the Carvera to mill it. First I set the origin so that other molds fit into the wax and started milling:

Rough

Fine

It actually took 25min :D.

IMAGE_WAX_MILL

IMAGE_WAX_MILL

IMAGE_WAX_MILL

And after milling a bit of manual cleaning:

IMAGE_WAX_MILL

13.3.2. Casting a Mold

Again, first stirring and mixing:

IMAGE_STIR

IMAGE_STIR

IMAGE_STIR

IMAGE_STIR

IMAGE_STIR Then we used a vacuum chamber to degas:

And again after filling the wax:

IMAGE_STIR

…12 houres later…

IMAGE_MOLD_FINISHED IMAGE_MOLD_FINISHED

Nice

13.3.3. Casting Chocolate

For casting chocolate, the temperature is very important. To have a nice cast of chocolate, where the inside and outside get solid, you want to:

  1. Heat up the chocolate to ~45°C so the sugar crystals deform and don’t transform to caramel

  2. Cool it down to ~28°C so the sugar crystals are about to form again

And a machine that simplifies this process is a Sous Vide.

We have this sous vide

So first we did the previously mentioned procedure:

IMAGE_HEAT_CHOCOLATE

Then we cut up the bag to cast the chocolate into the mold:

IMAGE_HEAT_CHOCOLATE

And casted:

IMAGE_HEAT_CHOCOLATE

Then to remove the air inside we just bumped the mold onto the table and used our fingers to shove it around:

IMAGE_BUMP_CHOC

IMAGE_BUMP_CHOC

IMAGE_FINISH_CAST

IMAGE_FINISH_CAST

We where messing around with it a lot :]

Then we put it into the freezer for some time and finish:

IMAGE_FINISH_CAST

And then carefully removing and voilà:

IMAGE_FINISH_CAST

Nice!
Not perfectly without air bubbles and also some chocolate was stuck in the mold.

I should have brushed something on the mold before casting the chocolate and maybe also use the vacuum chamber to degas it.

13.3.4. Casting Plaster

Then I also casted with plaster:

So first mix plaster (German ‘GIPS’) with water.

IMAGE_PLASTER

IMAGE_PLASTER

And then, if the plaster is still a bit viscous, cast it into the mold:

IMAGE_PLASTER_CAST

IMAGE_PLASTER

The workplace:

IMAGE_PLASTER

Waiting…

And:

IMAGE_PLASTER

Nice, again, maybe should have used the vacuum chamber to get the bubbles out.

13.4. Notes

  • matt wax for milling

  • for metal casting

    • cerrotru (tin)

    • zamak

  • mixing

    • use 3 glasses to mix without sheering

  • when casting, think about air, should entweichen

  • use a watch because of the cure-time

Parts of casting

  • sprue: da wird reingegoßen (konisch)

  • runner: distributes the casting material

  • gates: connects runner to part

  • riser: out for the air while poring

  • part

Materials Easy:

  • GIPS

  • WAX (candle)

  • Chocolate

  • Nougat

  • Soap

  • Silikon

    • use quickly all material after bought -> datasheet -> unusable after a time (splits material, hard to rühren etc…)

  • always 2 components because of the hardening

  • Pot Life: time you have, until it should be casted

  • Cure Time: time until hardened

  • mixed ratio: for the 2 components

Safety infos

  • what happens when on skin/mouth, how to treat, safety equipment needed

2 components

Designing 2 Sided Molds

  • rahmen zum verbinden

Becher

  • Rührstab nicht zu dünn, stabil wegen umrühren -> chopsticks good

  • stabil, flacher Boden

  • molds should be high enough -> we use 1cm -> when entgasen dann 3x volume

  • think about air comming out -> needs to have holes

  • Sachen mit Öl einreiben, damit sie leichter rausgehen

13.5. Design Files