10. Molding and casting¶
All this information is refered to Molding and Casting class.
Assigment¶
- Design a mold around the stock and tooling that you’ll be using.
- Mill it (rough cut + (at least) three-axis finish cut).
- Use it to cast parts.
Group Assigment¶
- Review the safety data sheets for each of your molding and casting materials.
- Make and compare test casts with each of them.
The Machine¶
ShopBot Buddy
The ShopBot Buddy is designed for industrial, commercial, or residential applications cutting in wood, plastics, aluminum and other materials. The Buddy incorporates many of the same features as ShopBot’s full-size industrial systems, yet weighs less than 600 lbs. and occupies as little as 16 sq. ft. of floor space — and it comes with optional casters that allow you to move the tool easily for different applications in your shop. That makes them useful on the shop floor. They can be configured and reconfigured for specific production needs—Buddys are the agile production CNC solution.2.
The Mill¶
I used a ball nose endmill, wich are highly recomended for 3D milling operations, cause they don’t cut the higher layers during the finishing operation. Eventhough you can do this same process with and Flat Endmill and a 3 axis operation. At the end of the experience I am going to analize the results and define if it was the correct desicion.
3D Design¶
The objective is to design a Wooden Star Puzzle:
A Brain Teaser Puzzle thats formed by 6 equal pieces.
I downloaded the piece from this link, so I just could center in the molding design.
The Mold¶
To get a hard piece result you wil need a flexible mold, and to make a flexible mold, you will need a hard mold. In order to get this to work, I’m going to use Machinable Wax for the first hard mold, silicone for the second one and poliurethane for the final part.
Design advices¶
Before I started designing the mold, the lab instructor gived us some advices to make an optimal mold:
Where:
- d1, d2, d3,= 5 mm
- 3 mm < d4 < 5 mm
- Ang1 = 15°
3D Design¶
This mold has to have the “positive” figure, in order to give the negative form to the silicone mold and then get from it our finall piece.
The mold is composed by 2 parts:
First and upper one:
Second and lower one:
In the models you can see 2 key parts:
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Tubes: One is designed as a entrance for the material in the silicone mold, and the other one as a escape of the air when the material enters.
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Unions: They are designed with a plug-in logic, to make sure the molds fit each other.
This process is really confusing, because you have to really understand the transformation your diferent molds and pieces are going to have, to make this easier I used the bolean tools that Fusion 360 has:
In order to make this process, you need to have you wax mold already design.
Then I will create a new body, as a box that uses the hole volume of my mold:
You have to make a sketch at one plane on the mold, and create a new body that goes from one face to the other one.
After you have make the second body, you go to Modify => Combine
There you choose the New Body (Body2) as Target Boodie and the Mold (Body1) as Tool Body, and cut as the operation. With this process, you will substract the mold from an object using its whole area, so you will just get the free spaces.
This allows to see our Silicone Mold:
Finally, I made an assembly to check how the silicone molds would feet together.
For me the most usefull part of the final assembly of the two molds was the analizing interferences. In order to do this, you go to Inspect => Analize Interference.
As I dont have interferences, I can asume that the molds should work.
Fusion CAM Processor¶
In order to make the G-Code for the machine I used the Fusion 360 CAM processor.
1.- Setup:
In the setup there are three key parameters to define:
- Model Orientation: The model orientation gives our CAM the coordinates in wich our Stock is going to be installed, coinsidering the machines axis.
- Stock: Gives to the CAM the measures of our Stock, this is really important in cases where the model to cut is smaller than the stock we have. You can see the stock as a gray rectangle that goes through all the model.
- Part 0: You have to define where the parts 0 is going to be, this is rally important, because you’ll have to input this parameter to the machine.
3.- Tool Library:
Fusion gives the user the posibility to build their own tool library:
Defining their geometry, so you can anticipate colisions between the shaft and the stock.
I also allows you to configure the feeds, RPM, and speeds wich you will use to work. Is important to distinguish that this parameters are just defined as a functions of the mill, and aren’t coinsidering the material you are cutting, so some times you will have to re-define them.
Those are the parameters I used to cut Machinable Wax.
2.- Roughing: Adaptative Clearing
If you want to learn more about this operation click the name and go to the Fusions tutorial.
To define an operation in Fusion, you will have to define the faces you are goint to work with:
Then we define the diferent working planes:
If you need to know what does each plane represent, you can put the mouse over the name in Fusion or go to their learning center.
After that, you will set the working parameters, as the step-down, the direction, the stock to leave, etc.
The final step, the software will show us the toolpaths:
4.- Finishing: Scallop Finishing
As a finishing process, the first steps are pretty much the same, but we dont have to make multiple passes, our toolpath will finish like this:
Fusion Simulator¶
After defining our operations, we can simulate the result before sending it to the machine:
José Tomás Domínguez (Joseto) on Vimeo.
Molding¶
Milling¶
The first step in the molding process is the milling the wax mold. To understand the process of milling, just refer to Week 8.
The result:
I want to analize the results of the finishing operartions of Fusion 360, The first mold (aslha) uses the scallop operation and the second one (aksasb) uses the parallel. Non of them satisfied me a lot, I was talking to Alexander Demers who is going to test other operations in order to find the best one. Also I could have used a flat endmill to make the operations, with a fine stepover, this way I should have better results in the plane area.
Silicone Mold¶
I used a Sorta-Clear 37 silicone, thats food safe, so I could test diferent materials.
Safety Data Sheet¶
From the SDS I got the following key safety precautions:
General Precautions:
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P101: If medical advice is needed, have product container or label at hand.
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P102: Keep out of reach of children.P103: Read label before use.
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P103: Read label before use.
Exposure controls: Respiratory Protection: Should a respirator be needed, follow OSHA respirator regulations 29 CFR 1910.134 and European Standards EN 141, 143 and 371; wear an MSHA/NIOSH or European Standards EN 141, 143 and 371 approved respirators equipped with organic vapor cartridges.
Hand Protection: Wear any liquid-tight gloves such as butyl rubber, neoprene or PVC.
Eye Protection: Safety glasses with side shields per OSHA eye- and face-protection regulations 29 CFR 1910.133 and European Standard EN166. Contact lenses are not eye protective devices. Appropriate eye protection must be worn instead of, or in conjunction with contact lenses.
Other Protective Clothing/Equipment: Additional protective clothing or equipment is not normally required. Provide eye bath and safety shower.
Comments: Never eat, drink, or smoke in work areas. Practice good personal hygiene after using this material, especially before eating, drinking, smoking, using the toilet, or applying cosmetics. Wash thoroughly after handling.
Key Steps:¶
1.- Spray demoldant to your wax mold, so the two molds are easilly separated, I have to use the Ease Realease 200.
2.- Mixing the two parts: Silicon molding is a reaction of two diferent materials, as the instructions says, you have to mix them for 3 minutes. In this case particularlly, yuo also have to mix the Part B first.
3.- In order to remove bubbles, the mixture is inserted in a vacuum system.
4.- After this, the mixture is poured into the mold:
As you can see in the pictures, the mixture has lots of bubbles, so I reinserted in the vacuum system:
5.- Curing: the curing time depends on the material. It can be accelerated using an external heat enviorment, as an oven. In this particular case, it is 4 hours.
6.- The Result:
Poliurethane¶
For the last step and the definite piece, I used Smooth-Cast 300.
Safety Data Sheet¶
From the SDS I got the following key safety precautions:
First Aid Measures:
Inhalation: Remove source(s) of contamination and move victim to fresh air. If breathing has stopped, give artificial respiration, then oxygen if needed. Contact physician immediately.
Eye Contact: Flush eyes with plenty of water occasionally lifting the upper and lower eyelids. Check and remove any contact lenses if safe to do so. Continue to rinse for at least 15 minutes. If irritation develops, seek medical attention.
Skin Contact: In case of skin contact, wash thoroughly with soap and water. Continue to rinse for at least 15 minutes. Chemical burns must be treated promptly by a physician.
Ingestion: Do not induce vomiting unless instructed by a physician. Never give anything by mouth to an unconscious person. If material has been swallowed and the exposed person is conscious, give small quantities of water to drink. Stop if the exposed person feels sick as vomiting may be dangerous. if vomiting occurs, the head should be kept low so that vomit does not enter the lungs.
Most important symptoms and effects, both acute and delayedIn case of inhalation of decomposition products in a fire, symptoms may be delayed. The exposed person may need to be kept under medical surveillance for 48 hours.
Exposure controls:
Respiratory Protection: Respiratory protection is not normally required when using this product with adequate local exhaust ventilation. Where risk assessment shows air-purifying respirators are appropriate, follow OSHA respirator regulations 29 CFR 1910.134 and European Standards EN 141, 143 and 371; wear an MSHA/NIOSH or European Standards EN 141, 143 and 371 approved respirators equipped with appropriate filter cartridges as a backup to engineering controls.
Hand Protection: Wear any liquid-tight gloves such as butyl rubber, neoprene or PVC.
Eye Protection: Safety glasses with side shields per OSHA eye- and face-protection regulations 29 CFR 1910.133 and European Standard EN166. Contact lenses are not eye protective devices. Appropriate eye protection must be worn instead of, or in conjunction with contact lenses.
Other Protective Clothing/Equipment: Additional protective clothing or equipment is not normally required. Provide eye bath and safety shower.
Key Steps¶
The first key steps are pretty much the same as silicone, but the pouring process is diferent:
In this step I used a siringe to pour the plastic into the mold:
Foto jeringa
To press uniformly the mold I design a simple wood box, so the curing process will have a better quality:
And after 1 hour, I can get my part out of the mold:
The Piece:
Post Process:
After getting the parts out of the mold, I cut all the “extra material” that the part had, so I could get finally the form I wanted.
Main Problem and Steps for the Future:
I made 7 pieces for the whole puzzle, but never could get one without any bubble, I tried different strategies; getting the mold into the vaccum system, making, shacking the mold, or calmly use a syringe to get the mis into the mold.
FOTO FINAL
After making 6 of them:
