12. Molding And Casting

WEEK'S GOAL:Design a 3d mould, machine it and cast parts from it.

Procedure:
0. Assignment Go
1. What I Need Go
2. My Final Virtual Mould Go
3. Milling The Mould in MDX-20 Go
4. Urethane Mould (Negative Mould) + Data Sheet Go
5. Casting The Mould In Grey Plaster + Data Sheet Go
6. Final Result Go
7. Using Liquid Plastic Go
8. Problems Accounted (respiradero, esferas, subir la pieza, cubos, ). Go
9. Other Virtual Moulds Designed Go
10. Download Files Go

0. Assignment

Design a 3d mould, machine it and cast parts from it.

Learning Outcomes:

Design appropraite objetcs within the limitations of 2 axis machining
Demonstrate workflows used in mould design, construction and casting

Have you...?

...explained how you designed your 3d mould and created your rough and finish toolpaths for machining?
...shown hoy you made your mould and cast the parts?
...described problems and how you fixed them?
...included your design files and 'hero shot' photos of the mould and the final project?


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2. What I Need

For this week's assignment, I will need a lot of material considering that I will make first a wax mould with the MDX-20 milling machine, then the silicone mould to cast the final product. These are the different materials concerning the whole process:

• Milling Machine MDX-20
• 3mm mill for both 'Rough Cut' and 'Finish Cut'.
• 15x8'90x3'70cm machineable wax block
• Urethane Rubber Compound VytaFlex 50 - Smooth-On
• DM wood (recycled)
• Gloves (x2)
• Table and Scale's Protection
• Plastic Cups For Silicone and Plaster
• Cardboard Cups For Resin
• Body Protection
• Melting Glue
• Double-faced Tape
• Breathing Protection if resins used
• Grey Plaster Smooth-Cast® ColorMatch® 325 Series
• Liquid Plastic - White - Smooth-On

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2. My Final Virtual Mould

After experimenting with different moulds, I decided to create my personal chess. Starting with the knight, I am looking for a clean design made out of triangles, except for the base, that has an hexagonal shape with a curved surface.


AS I do not have that much time, I am going to concentrate in this piece, moulding it and casting it to learn the whole process first before designing the other chess parts.

DESIGNING THE MOULD

Starting with a quick plan of my wax piece, first I divided the piece in two parts + creating a 1'20 cm wall for silicone to stay strong while curing itself and casting the plaster.



After realising the material limitation that I had, I started designing my piece from the base upwards. Very important to know the maximum height of my possible piece. Auxiliary lines (purple and red) drawn to make sure I did not have trouble later on.

First I thought about a cylindrical shape and experiment with the revolving tools that Rhino has.



Then, while building up the figure, I decided to turn into a triangle-shaped piece:







The I built the shape was really simple: starting with multiple auxiliary lines joined together creating the figure. Just below you can see how I built the head:



I had to change several times the shape, as first I had a dog shape rather than a horse.

Finally, happy with the design, I decided to change the base as the cylindered shape was not what I was looking for. The final base has a hexagonal shape based on the initial cylindrical base.

Final virtual piece:





Joining all parts together, I had no problems having a closed polysurface:

CREATING THE VIRTUAL MOLD

Starting drawing the wax mould ( 150x89x37mm) + cutting the knight in half, corresponding one half to each side.





Very important to mention: I needed a good ventilation so air does not get trapped inside the mould while casting the plaster. On the horse's nose, I have designed a cylindrical shape to let the air come out while pouring and filling up the silicone mould. At first, I had a minimal ventilation pipe, but after discussing with my instructor, I made it bigger one to assure the air does not get trapped.



(small ventilation cylinder)



Bigger Ventilation



Here is a top view so far...



and a side view



Considering the amount of material the milling machine has to take from the mould, my instructor suggested me to elevate both figures to the maximum possible height to save more time. As I will need to use DM wood to stop the silicone from spilling over the mould, I can reduce the amount of material being milled from the machine by rising the DM's height when curing the silicone.



THE 1ST COMPLETE MOULD





As I am the last one of my lab to mill the mould for this week's assignment, some of my colleagues have had problems with the spherical joints. Therefore, I considered to instead of being spherical, to be cubed so the mould comes together without moving one piece from the other.



CALCULATING THE VOLUME NEEDED



To calculate mould's volume, Rhino's is very quick. We have a negative copy of our mould and calculate its volume with 'Analyse-->Mass Properties-->Volume'.







In total: 410 cm3 of material will be used.

CHECKING ON FAB MODULES

To make sure everything is going the right way, I entered Fab Modules and loaded my .STL file onto it.



After converting the inches to mm, everything seems to be OK.

CHANGES

Once finished, my instructor and me had a look to the last version of the mould and we thought it would be best to have a larger joint. The cubes that substituted the previous spheres for joining one piece with the other are not enough to keep both parts together. Therefore, we talked about having a joint just on the perimeter that fits perfectly one piece with the other.

In this first picture, we can see the new joint on the mould's design. In the second one, the negative silicone mould + its volume. The last picture the final mesh..







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3. Milling The Mould in MDX-20

PREPARING THE WAX MOULD AND THE MACHINE

I am ready for milling the mould. I am going to use a blue wax to create my piece with the modela MDX-20 Roland Mill.

First, I glued with a double-faced tape and hot glue the way blue piece to the modela's bed to make sure it does not move during the milling.

I took the bed from the modela and started working on it.



Making sure everything is glued correctly!



Everything is ready! Let's go!

Milling With The Modela

Turning on the modela and starting the connection with the server with './fab_modules':



Open Firefox + fab modules: input-->mesh (.STL) + 'Calculate Height Map'.

ROUGH CUT

Once calculated all the map: output format--> 'Rolland Mill' + process--> 'Wax Rough Cut (1/8)'.



Parameters I have used:

INPUT
file: mould7_mesh_final_mm.stl
triangles: 36468
units/inches: 25.4
dimensions: 150x89x37mm (5.906x3.504x1.457 inches).
dpi: 1000

OUTPUT
machine: MDX-20
speed (mm/s): 20
x0 (mm): 35
y0 (mm): 31
z0 (mm): 0
zjog (mm): 2
xhome (mm): 0
yhome (mm): 152.4
zhome (mm): 60.5

PROCESS
server: 127.0.0.1:12345
bottom z (mm): -37.008
bottom intensity (0-1): 0
top z (mm): 0
top intensity (0-1): 1
direction: climb
cut depth (mm): 1
tool diameter (mm): 3
number of offsets (-1 to fill): -1
offsrt overlap (%): 10
path error (pixels): 1.1
sort path: yes
sort merge diameter multiple: 1.5
sort order weitht: -1
sort sequence weith: -1

MILLING

'Rough Cut' Done - Result

During the process of milling the rough cut, I had a big issue with the machine as suddenly we lost internet connection. The machine stopped. Please see 'Problems Accounted' lower in this page.

FINISH CUT

After completing the 'Rough Cut' with the small problem that I had, I continued with the finish cut. I knew that I had to do it in both directions (XZ & YZ) as I have different surfaces in different directions. In order to have a proper detail, I needed time and patience to finish the mould successfully.

As before, I entered 'fabmodules.org' and selected my mesh (.STL) and calculated the 'Height Map'. After that, I selected the Roland Machine, MDX-20 and 'Finish Cut'.

XZ DIRECTION

Parameters used:

INPUT

file: mould7_mesh_final_mm.stl
triangles: 36468
units/inches: 25.4
dimensions: 150x89x37mm (5.906x3.504x1.457 inches).
dpi: 1000

OUTPUT
machine: MDX-20
speed (mm/s): 20
x0 (mm): 35
y0 (mm): 31
z0 (mm): 0
zjog (mm): 2
xhome (mm): 0
yhome (mm): 152.4
zhome (mm): 60.5

PROCESS
server: 127.0.0.1:12345
bottom z (mm): -37.008
bottom intensity (0-1): 0
top z (mm): 0
top intensity (0-1): 1
tool overlap (%): 90
direction: XZ
type: flat end
path error (pixels): 1.1



Pictures taken during the process:



Starting with the horse's head (left) + Continuing with the horse's body (right)

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Piece with XZ direction 'Finish Cut' finished.

CHANGING TO YZ DIRECTION

The parameters used are the same as the XZ direction, changing the direction of the cut to YZ.

Final Result - XZ and YZ Directions Done - Wax Mould Finished

Detailed picture with the knight's design. The basement has come out with very interesting textures that hopefully will come out with the silicone.

(Ignore the water drops)

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4. Urethane Mould (Negative Mould) + Data Sheet

The material I am going to use for the negative mould is VytaFlex 50 - Liquid Urethane Rubber Compound from 'Smooth-On'.



DATA SHEET

TECHNICAL INFORMATION

A:B Mix Ratio by Volume: 1:1
A:B Mix Ratio by Weight: 1:1
Pot Life: 60 minutes
Cure Time: Overnight/16 hours

MEASURING AND MIXING

Important: Pre-mix the Part B before using. After dispensing equal amounts of Parts A and B into de mixing container, mix thoroughly for at least 3 minutes making sure that you scrape the sides and bottom of the mixing container several times.

Pour mixture in a single spot at the lowest point of the containment. Let the rubber seek its level up and over the model. A uniform flow will help minimise entrapped air.

SAFETY

Wear safety glasses, long sleeves and rubber gloves to minimise contamination risks.

Part A is a TDI prepolymer. Use only with adequate ventilation. Contact with skin and eyes may cause severe irritation.

Part B is irritating to the eyes and skin.

SAFETY DATA SHEET

Harmful if swallowed/causes skin irritation/causes serious eye irritation, may cause respiratory irritation/do not eat, drink or smoke when using this product/Non-Flammable/ Respiratory protection is not normally required when using this product with adequate ventilation.

LET'S START!

MOULD'S DM FRAMEWORK TO CREATE NEGATIVE URETAHEN MOULD

Based on the wax piece I have designed on Rhinoceros, I added the new parts of the Framework to contain the Urethane while curing.



Next step was to save it in .dxf file and import it on the Lasercutter's program.











Here is the result: the different parts of my DM container that I am going to use with hot melted glue to stick them together.

Building Process - Framework

Making sure they are no errors

CALCULATING VOLUME OF URETHANE NEEDED

Although I had calculated previously the volume I needed of urethane, I wanted to make sure it was correct by pouring water inside and confirm it.

On Rhinoceros, volume needed: 410,82 ml (1ml = 1g of water)

Reality

What I did was to fill the whole mould with water and then pour it into a plastic glass. The final volume used is 356 ml (50 ml error).

CALCULATING URETHANE'S VOLUME - PART A & PART B

As now I have the exact amount of volume needed and having a 1:1 ratio by volume on the urethane I am going to use, I divided the amount of water in two smaller cups.



Each cup has exactly the amount of Part A and Part B needed for it to work correctly. Now I mark with a permanent pen its height and go to the next step: creating the negative mould.

PREPARING THE NEGATIVE MOULD

Opening Part B



Having both Part A and Part B Ready to be mixed after stirring Part B as data sheet tells to do so.



Pouring Part B first in the bigger cup



Mixing together both parts for more than 4 minutes thoroughly, including sides and bottom.



Pouring the mixture on to the wax mould making sure no air gets trapped.







Final Result: the left part was done first, and it can be appreciated that it has a more homogenous mix while the right hand side looks differently. Although I noticed it instantly, I thought it was because at that moment it did not have enough time to settle.



Here is the same picture done 30 minutes later. It seems as if the mixture has been done correctly, but still there is a small difference between both sides.

Curing

20 hours later...



Let's start!



Having the Negative Urethane Mould Done Successfully




Mould's detail

Getting Ready for the Plaster

I opened again my computer and analysed the volume needed for my little piece.



As the file is in mm, there are 19886.7 mm3 of material needed for my knight. A huge problem that I had is that, instead of reading 19.89 cm3 (the real value), I read 198.89cm3, exceeding by 10 times the amount needed. Instead of doubting, as a normal person would do, I was so excited to create my first piece that I completely ignored and did not pay the attention to it.

What happened --> HUGE quantities. I could have done 9 more knights with that amount of material.

CALCULATING THE MATERIAL NEEDED

Starting with a volume of 198cm3 of material, for plaster to work I needed the same volume of water (199cm3) + the corresponding plaster based on 38:100 ratio (for 38 units of water, I needed 100 units of plaster).



I decided to do everything by weight, having 199ml of water and 522 grams of plaster + a 13 grams plastic cup.



The total amount of plaster that I needed was of 522 grams.

Mixing

Pouring the material inside the mould. I had to pay attention at this special moment as the bottom part of the knight (the one receiving material first) is the most delicate part of all my piece (corresponding to the head, nose and mould's ventilation).

What I did was pour a little amount of material, shake it and continue like that until filling completely the mould.

TAKING THE PIECE OUT OF THE MOULD

While drying the plaster, I had to make sure it did not come out from the bottom part of the mould:







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6. Final Result: The Knight Ready To Fight!

Here is my plaster piece, with l details and ventilation included! I need to take that off.







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7. Using Liquid Plastic

Having successfully completed the knight made out of plaster, I wanted to continue and discover new material. I decided to try Liquid Plastic, from Smooth-On, but this time using the correct amount of material.

For this material to be mixed properly, a 100:90 ratio is needed for A:B (by volume).

CALCULATING THE AMOUNT OF MATERIAL NEEDED

Total volume of material needed: 19.89 grams

Total amount of A: 10.43 grams

Total amount of B: 9.37 grams.

Cup's weight: 9 grams

PREPARING THE WORKPLACE

Pictures while making the Plastic Liquid Piece:









Plastic once it has solidified + bottom part of the mould.

TRYING TO SEPARATE THE PIECE FROM THE MOULD

When starting to take the piece from the mould, I found myself with a mould that has been glued together. When mixing Part A and Part B creates an exothermic reaction, reaching 100 degrees Celsius, it has melted surprisingly the urethane mould together.

FINAL RESULT - MY FIRST MOULD DESTROYED

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8. Problems Accounted

Mould's Ventilation

The knight's head needed ventilation as air would have been trapped inside. At first, I did design a ventilation pipe, but it had a really small diameter: 1.2 mm. Discussing with my instructor, it would be better to have a larger ventilation pipe. I created a new one that had 2.7mm diameter



Once the negative mould had been done and experimenting with the plaster, I was not sure it would work correctly. Therefore, while pouring the plaster inside little by little, I made sure to move the liquid enough to make sure all the air came out. Surprisingly, the whole piece came out as one without any bubbles on the head. Meanwhile, at the base, it had a few bubble of air that had been trapped.



On the other hand, the joint between one side and the other did not came out as expected. It is difficult to notice at first as the finish product looks very good and detailed, but paying attention to the joints, is not as good as it should be.

The main reason is once the mould has been filled with the materia, I applied pressure on both sides with DM wood that did not cover completely the mould, so the pressure did not distribute homogenously through the piece, slightly bending it.

Negative Mould's Joints

As I have been the last one of my fablab group to complete this assignment, my colleagues' experience has been really useful. Álvaro recommended me to not create the spheres the way he did, as the joint he produced was not strong enough giving him problems. What I did was to create a boundary that snapped together one piece with the other. It worked really good for the plaster, but as good for the liquid plastic, as some of the material came out while drying.



(bottom side of the mould)

MACHINE STOPPED WHILE MILLING

During the process of cutting the 'Rough Cut', the computer lost internet connection causing the machine to stop. So far, it had milled 90% of the process.

Discussing with my instructor what we should do, if to repeat the 'Rough Cut' or continue with the 'Finish Cut', we decided to have a go with the 'Finish Cut'. Just a few minutes it started to mill, the modela had problems to mill the excess of material. I had no choice but to repeat the 'Rough Cut' again.

Urethane's Mixture

After successfully finishing the plaster piece, I continued and tried it with 'Liquid Plastic' and everything went wrong. The urethane mould stuck together when the mixture was poured in.

Discussing with my instructor what happened, we thought that I have missed a step while curing the urethane. As it is a different material than the silicone rubber, an additional step could have been required that I have not done. Going back to the data sheet, you can optionally heat the rubber to 65 degrees Celsius for 4-8 hours, but no additional apart from let it cure for 16-24 hours.

Our conclusion was that I did not mix both Part A & Part B together successfully, having a sticky mould after the 16 hour cure.



In this picture it is visible how the right hand side has a different texture from its opposite.

Conclusion:

The mix was not done properly. Although it was done for more than 3 minutes thoroughly, making sure to scrape the sides and bottom of the container.

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9. Other Virtual Moulds

When I started this assignment a few months ago, I wanted to do something related to my Final Thesis Project. I am designing the new Medical Research Centre for Ramon y Cajal's Hospital in Madrid in an existing building. This building is a gold piece in Madrid's industrial architecture from the 60s, built by the known architect: Alejandro de la Sota. It is an important building as in that moment it used several structural developments that made it possible to investigate in new spatial features to make the building work. Therefore, I am doing my first mould based on the building and a 2d point perspective. For designing the virtual model, I used Autocad 2d and Rhinoceros to create my STL document. First, I took the cross sections I have from my project and started creating the 3d shape of the building. Then, with the virtual 3d model, I took a 'vectorial picture' of the 3d view and turned it into a 2d document to make some smaller extrusions and have that 3d perspective. Then I completed one of the sides with PFC (Final Project Thesis - 'Proyecto Final de Carrera') to related my project with this moment.

First Mold

M2nd Mold - by juangarciamaestro on Sketchfab

Make It Simple

Example by juangarciamaestro on Sketchfab

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10. Download Files

Download: Rhinoceros File (knight, mould, frameworks, etc)
Download: Rhinoceros File: Mould for Modela .STL

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