Molding and Casting

MOLDING

Molding is the process of manufacturing by shaping pliable raw material using a rigid frame or model called a pattern.
A mold is a hollowed-out block that is filled with a liquid like plastic, glass, metal, or ceramic raw materials. The liquid hardens or sets inside the mold, adopting its shape. A mold is the counterpart to a cast. The manufacturer who makes the molds is called the mold maker. A release agent is typically used to make removal of the hardened/set substance from the mold easier.
Typical uses for molded plastics include molded furniture, molded household goods, molded cases, and structural materials.

Injection Molding

Injection molding is used for creating high-quality three-dimensional objects, that can be commercially reproduced. The molding process begins by melting plastic in a hopper. Then the plastic is injected into a tightly closed, chilled mold. The plastic quickly takes the shape of the surrounding mold. Once it has completely set, the mold is opened and the plastic object is released. Yogurt pots, butter tubs, toys and bottle caps are made using this process.


GIF Source~ https://giphy.com/gifs/isopoly-111nFzlkBckNC8

Blow Molding

Blow molding is a process used for making piping and milk bottles. Plastic is heated until molten. Then it is injected into a cold mold. The mold has a tube set within it, which has a particular shape when inflated. So, while the plastic is molten, air is blown into the tube and the plastic is formed around the tubing. It is then left to cool and removed from the mold.

GIF Source~ http://i.imgur.com/lRKZO64.gif

Compression Molding

The most labor-intensive type of molding process is compression molding. Therefore, it is only used for large-scale production purposes, and not for mass production. For example, boat hulls and car tires are made using this method. Molten plastic is poured into a mold. Then a second mold is pressed into it. This squeezes the plastic into the desired shape before being left to cool and removed from the mold.

GIF Source~ https://makeagif.com/gif/compression-molding-3-drKFTq

I made one part mold here for my design did not require a two part mold. Although it could be made uing a two part mold too.

Source- https://sciencing.com/types-molding-processes-7651143.html

Casting

Casting is a manufacturing process in which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process. Casting materials are usually metals or various cold setting materials that cure after mixing two or more components together; examples are epoxy, concrete, plaster and clay. Casting is most often used for making complex shapes that would be otherwise difficult or uneconomical to make by other methods.

Design Process

Inspiration

For this week I wanted to design some jewelery sort of thing after looking for various intricate and complicated designs
I came across this picture of a snowflake and I wanted to make something like this in any form of wearable

I thought to make a pendant shaped like this with my own little skills of designing.

Started off making with some lines in that fashion as picture
The I made a feature of it and patterned it.

I added some text then exploded it and add some extruded length to give it a custom form.

Now for making a moold I've to make a positive
So that when I pour silicon my silicon is the negative
And the feature at last when I pour epoxy is the final positive.
For that just make a rectangular box and extrude it to some lenght actually the length doesn't matter

Now finally you have to use the combine feature to make it all as one body which is ready for milling

As my size design was a bit oversized
so I scaled it down about a scaling factor of 0.5 in Fusion 360.

Creating Toolpath For the MOld

Software Used- Modela Player 4

Steps to proceed-

After selection of the process it's required to select the tool the tool should be decided according the design considerations.

After roughing select another process of finishing and go through the same steps as did for roughing.


Now set the Origin for SRM-20 in the V-panel software and in the modella player click on the bottom toolbar to start the process of milling.

Issues-(Things need to take care of) The only thing you need to take care is that after roughing process is over you need to manually start the finishing process by clicking again on the bottom toolbar to start the milling and make sure the origin is not disturebed.
For my first iteration the mdf board was displaced from the SRMs sacrificial bed as the double side tape lost it's adhesiveness and the mold did no turn out to be any good.

Design Considerations that I took into account and that I omitted


Draft angle

Adding draft to parts is essential for manufacturing processes that involve a mold; cast parts, injection molded parts, and thermoformed parts come to mind. That’s why it’s important to be able to not only add draft, but to also verify where draft angles are insufficient or missing completely.
Well not going to the very technicality of the design so I included a draft angle of about 0.5 degree so that the casting is easy basically.
Above Image Source~link

Registration Points (Omitted)

Sice my design included only one part mold so I did not include registration points, But
If you are planning to make a multi part mold or two sided mold registration points are required to get a better hold and remove the flashes in the final casted part.

Making negative Silicon Mold and Casting Positive resin

But Fist Let's Consider Some Safety Precautions

The chemical used for making the silicon mold-

Features:
  • Since silicone alone can't get hard it needs a hardener or a curing agent to get hard
  • The propotion adviced is 3-5 gms of hardener in 100gms of the silicone. I used the same proprtion.
  • Fast curing. Cures at room temperature within 8-12 hours.
  • Good tensile and tear strength, low shrinkage.
  • Appearance : white
  • Mixing proportion of curing agent : 3-5%
  • Operating time (@ 25 °C ) : 5-15 Min
  • Curing time (@ 25 °C ) : 2-5
  • Hardness : 25 A°
  • Density : 1.09 g/cm3
  • Viscosity (@ 25 °C ) :20000±2000 cps
  • Tensile-strength : ≥43 kgf /cm2
  • Tear-strength : ≥26 kgf /cm
  • Elongation-break : ≥ 500 %
Further info about the product and it's afety features you can visit the manufacturers website.
https://www.chemzest.com/liquid-silicone-rubber/
Source- https://www.chemzest.com/liquid-silicone-rubber/
Amazon.in product specs

First Aid Measures

Referenced from the safety Datasheet
Go to- Safety Datasheet

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. If irritation persists, seek medical attention. Skin Contact: In case of skin contact, wash thoroughly with soap and water. Ingestion: Do not induce vomiting unless instructed by a physician. Never give anything by mouth to an unconscious person

Fire-Fighting Measures Use water spray to cool fire-exposed surfaces and to protect personnel. Shut off “fuel” to fire. If a leak or spill has not ignited, use water spray to disperse the vapors. Either allow fire to burn under controlled conditions or extinguish with foam or dry chemical. Try to cover liquid spills with foam. Because fire may produce toxic thermal decomposition products, wear a self-contained breathing apparatus (SCBA) with a full face piece operated in pressure demand or positive-pressure mode.

Handling and Storage Keep container(s) tightly closed and properly labeled. Store in cool, dry, well ventilated place away from heat, direct sunlight, strong oxidizers and any incompatibles. Store in approved containers and protect against physical damage. Keep containers securely sealed when not in use.Containers that have been opened must be carefully resealed to prevent leakage. Empty containers retain residue and may be dangerous. Avoid water contamination.

Exposure Controls / Personal Protection

Hand Protection: Wear any liquid-tight gloves such as butyl rubber, neoprene or PVC.
Eye Protection: Safety glasses with side shields eye- and face-protection regulations 29 CFR 1910.133 and 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.

Casting Resin


Haksons Ultra Clear Grade 1 Epoxy Resin And Hardener

Go to the - Safety Datasheet
    Some features:
  • Water-like transparency and UV resistant.
    • Best results comes when pour 8 mm max thickness in one pour
  • 100 ml covers a 1sq.ft area with a 1mm thickness. Ratio 3:1 by weight |

They have a blog about the product you can checkout here
https://www.bohriali.com/blog/

Safety 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. If irritation persists, seek medical attention.
Skin Contact: In case of skin contact, wash thoroughly with soap and water.
Ingestion: Do not induce vomiting unless instructed by a physician. Never give anything by mouth to an unconscious person.

Making the mold

Pouring Silicon on Weighing scale
Adding the hardener in 100gms 3-5 ms hardener.
Stirring them well to remove any bubbles.
Pouring them on the MDF milled positive.


Pouring Resin on Weighing scale
Adding the curing agent the ratio is 3:1 by weight
Pouring them in the silicon mold in such a way to form the minimum bubbles
Leaving it to settle the curing time is almost 24 hrs.

Issues Faced

As you can see the output is not very satisfying to me as the milling was done using 3mm endmill and my features include
intricate exploded texts that would have been casted If I would have used 1mm endmill, then my features could have come out better.
But anyhow there was a lot of learning through the week and as I design a mold around the stock and tooling I milled it (rough cut + (three-axis finish cut). Although the finishng was not good as the tool selected was not apt.
I moved on the next week as I was way behind for the next weeks assignment, I hope to make this correction with 1mm bit(Once I have it) or may be i'll try the v-bit(The one in LAB from which we make the circuits)

Learning Through the Week

I learned that it is important to consider the the cutting tool at the first place at then design the 3d mold accordingly so that if the model of the mold is complex then you have to choose the tool accordingly.
The week was very interesting. I had the chance to experiment a lot of new materials and their reactions
It was my very first time to experience the material used for molding & casting such as the liquid rubber and liquid plastic, also how to mix, stir, pour and the to go through the technical datasheet and safety sheet for the respective materials as well.

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