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.

 

 

Assignment:

Individual

-Design a 3D mold around the stock and tooling that you'll be using,

 machine it

-Cast using the mold created

 

Group

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

 

Software :

-AutoCAD

-Fusion 360

-Mods

 

Materials :

-Machinable Wax

-Smooth-on VytaFlex 40 (Urethane rubber mold)

-Smooth cast 300 Liquid plastic(Plastic cast)

-Smooth cast 325 Liquid plastic(Plastic cast)

-Lubricants

 

Accomplised

 

-I understood the ideology behind molding and casting

-explored different methods of molding

-Understood and designed a mold(Positive and negative part)

-Made the mold using urethane rubber

-Learned about different materials(strength, cutting time, making them)

-Casted parts using the mold I created

 

 

 

Group Work

 

Download Files

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.

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.

Rotational Molding

 

Toys, shipping drums, storage tanks and items of consumer furniture are made using rotational molding. Each object is made by coating a mold from the inside. A mold is held in place between two mechanical arms. Then, the arms rotate the mold constantly at the same level, while molten plastic is placed inside. As it turns, the plastic coats the inside of the mold to create a new hollow, plastic object.

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

I wanted to design this tile that I had seen

But then I wanted to mill both the positive and the negative part of the tile. This was like an added challenge because understanding how the mold would come out is not easy. A lot of factors have to be taken into consideration, like how the cast is going to be poured, what height must the blocks be in etc.

I took to AutoCAD to draw the basic outline of the model and to understand how to model the mold. It took some time for me to understand how to make the mold and I referred my predecessor's work to understand. I use AutoCad as a pen tool as it is easy for me to make rough sketches using this software.

 

Initial CAD design

Once I had the basic idea in 2d I imported that in Fusion to make a 3d model of it.

Importing in Fusion 360

 I extruded all the surfaces keeping my maximum height as 25mm. The model started shaping up quite well, but I had to reconsider my height and think about the cast when it is being poured into the mold. I have designed in such a  way that there should be any extra frames to hold the cast.

3D Model

Once I was done modeling I needed to export the file as .stl(binary) because that's the mesh format understood by fab mods. Now fusion does not have STL format in the export option so I used the print option to export it as STL.

Exporting STL

I opened up fab mods and from the input format selected .stl. I chose my file and once the file is chosen the mesh of the file is suppose to appear, but in my case just saw a blank screen. I clicked on show mesh and nothing happened. I took me awhile to figure out what was wrong. I had worked my 2d and 3d drawings in mm. 25mm(thickness) was transferred to inches which made the thickness as  635mm resulting in scaling up of the model.

Problem with MODs

Another important factor I realized was that the material (molding wax) available at the lab was only 80mmx60mmx40mm so I decided to mold the positive and negative parts separately. I went back to fusion and modified my design. Made the model in inches and split the model into two.

Final Model

I exported the model again and took it to fab mods. I was faced with the same problem. I couldn't find out the source of the problem. So as an alternative I exported the model from fusion as a .step(the other formats didn't work) file and opened it in Rhino(other formats, the mesh was not correct) adjusted the model and exported it .stl file. This time file was perfect.

Importing in MODS

Clicking on calculate height map shows the objects in different colors depending on what height they are in

Height Map

The following gif explains how to load an STL file-choose output format and the process

Input and Output

I then selected the machine that I wanted to use, and in this case Roland MDX-20.

Now before I start milling I needed to first sent my stock and drilling bit in place. I started placing double sided tapes on the molding wax. It is very necessary to secure the stock firmly on the plate.

Securing Stock

NOTE: While milling there shouldn't be any disturbance for the spindle to move. Any slight disturbance from its regular movement will make the spindle very cranky causing to damage the model.

 

Milling happens in layers and in processes. First, the machine understands and splits the Z-axis into layers. The layer height can be manually entered which is also known as the cut depth.This is the rate at which the drill plunges into the material at each pass.

In this stage, the model is first as contours. This is called rough cut and is usually don't with a flat end mill. This gives hard edge finish.

Then once the rough cut is finished its time to shift to finish. This is done with ball nose end mill. This smoothen the edges left by the rough cut giving a more finished look. The finish cut can be run in both directions xz and xy if the finish needed is very fine.

 

I used a 1/8th (flat and ball nose)bit for rough cut and finish cut.

Drill Bit

I secured the stock on to the drilling plate and set Z zero

Securing Stock to plate

Setting Z -Zero

All other parameters I left it at default, as I was quite happy as they were. I usually change the error to 0 but doing so will increase the milling time to almost double, so I left it at 1.1. I then hit the calculate button. The calculation takes time, as the program calculates each pass and its movement in each pass.

Configuring Cut parameters

Once done I sent it for milling

 

Error testing

 

It's always good to test or prototype before going for final milling. As there was a shortage of material I couldn't risk a bad mill. So milled a test piece before going for final in a waste wax that was already used.

Test Cut

Having seen that it was fine I milled my final model. I used a vacuum cleaner to remove the milled wax.

 

Milling

Once I had the dust removed there lay my model. It had come out quite neatly.

Positive Rough cut mill

Now I have to change the drill bit and run the smoothing operation. So on the top menu, I changed the option from rough ti finish cut. At the bottom, I checked the xz and yz direction and clicked on ball end and hit calculate.

Configuring Finish parameters

Configuring Finish parameters

There was an error in the toolpath. The program calculated an extra portion of the stock which was not in the drawing.

Configuring Finish parameters

I reloaded the file and tried again resulting in the same error. Also, the finishing time had gone up drastically. I wasn't sure what was the problem but began the milling process anyway.

Changing mill bit

Apart from milling the actual model, the machine wasted time in milling extra portion of the stock, but anyhow the model looked fine.

Milled model

I followed the same procedure for milling my negative mold.

Configuring Cut parameters

Rough Cut

I made a mistake while setting the drill bit height. During the last pass, the collar was rubbing against the stock. Make sure enough drill bit height is provided while setting the Z zero

Wax Melted

Once the roughing was done I ran the finish cut, having selected two axes and ball end.

Configuring Finish parameters

Configuring Finish parameters

Again I was faced with the same problem of having the toolpath running extra stock and the time was alarming 397 mins.

Configuring Finish parameters

 I tried tweaking the setting a little but of no use so I began the milling. To mill in one direction took about 45 mins and I stopped the milling then as the model already looked neat and it would be a tremendous waste of time having it mill in the other direction as well,

Final Mill

Final shots after milling both the parts,

Positive and Negative Mold

Rubber Mold

 

To pour the rubber mold I had to make a small box. I Picked up some waste ply pieces lying around and fixed them on all four sides of the mold.

Support

Chandini Chabra, a student of fabacademy who graduated last year was there to help me with the rubber molding process. Lubricating the mold was very vital as the rubber mold would stick to the edges and would be a great challenge while demolding. So I used grease, lubrication oil, and soap, mixed them together as lubricants.

Lubricant mix

I applied them to the surface of the ply and in the corners where the wax meets the ply.

Lubrication

For rubber molding, I used Vytaflex 40 a urethane rubber compound from Smooth-on company. All instructions on how to mix and use are provided on the label of the bottles.

Product Page :

https://www.smooth-on.com/products/vytaflex-40/

Vytaflex 40

I mixed the compound by weight. I first placed my mixing cup on the scale and set 0. Now I have to mix in 1:1 ratio, hence poured Part A first, set 0 again and then poured in part B.

Rubber Mold mix

As per Instruction, the mixture needs to be mixed well for 3 mins and then poured.

Mixing and Pouring

I then allowed it to settle. The curing time is 16 hours.

Milled model

I left the mold overnight to cure. Once cured removing the supports and the rubber mold from the model was fairly simple.

Demolding

Due to the lubricant, the rubber did not stick to the sides and came out quite smoothly. The Rubber mold was perfect and the rubber had actually gone through all the small gaps as well.

Demolding

There was a small problem however that I had missed during the milling process. One of the gaps were too small and the milling bit couldn’t pass I guess. So this left that particular edge not deep enough, regardless the mold came out fine.

Final Mold

Casting

 

To cast my model I decided to use smooth-cast liquid plastic 300 series

Product Page :

https://www.smooth-on.com/product-line/smooth-cast/

300 is opaque and fast setting where 305 is opaque with medium setting.

Which means to cure 300 would take about 10 mins and 305 would take 30 mins. 325 is transparent and pigments can be added to it. I chose 300 for my purpose because my mold is small and using 300 I can cast it quickly.

All this is completely new to me hence I wanted to try it out first before using my mold to cast parts. I used an old mold to test the liquids and lubricants.

Test Cast

From my testing of lubricants it was evident that vaseline would be the right choice, also the finish of the plastic was not all that great, I don't know if it was the mold or was it because of the material cause it was quite old. Anyhow having finalized my material and lubricant I went on to cast my parts. I coated the inside of the mold with vaseline and with the help of a stick coated all the tricky corners.

Lubricating Rubber Mold

Now to cast.

 

NOTE: Wearing gloves while mixing the chemicals is mandatory. The process is highly exothermic and once the two liquids are mixed they must be poured into the mold immediately as it starts setting quite quickly.

Smooth-Cast Liquid Plastic

As per the label the ratio PartA 1: PartB 1 if measured by volume and if by weight it was 100A:90B. as I had tested earlier 1:1 by weight worked perfectly fine for me. Once the liquid is poured into a cup its necessary to mix them properly. When they mix the liquids slightly turn milky at first and then into a clear liquid. This is the indication that the liquids have mixed properly.

Mixing Plastic Cast

Once I poured the mold it took about 2 mins for the reaction to start and then solidified quickly.

Demolding wasn’t very easy this time. Despite using enough lubricants there were some corners that the vaseline couldn’t reach but plastic could.

Removing Cast

Removing cast

The casts were not very clean. I don’t know if it was because of the material or the mold. The mold actually seemed fine. Another guess would be the lubricant.

I made a couple of more casts and some with 325.

Final Cast

Here are the final images of the cast I made.

Week 10 Group Work:

 

The assignment was to read the safety data sheet for different casting material and make a test cast with them. To make a mold we used one of the previous year’s wax model. We secured acrylic panels on all four sides of the model and then poured urethane rubber (PMC 780). Allowed it to cure for about 48hrs.

Each of us were assigned different materials and I was assigned USG Drystone and USG Hydrostone. The material was readily available in the lab and the safety data sheet for the same was available online in the product website.

https://www.usg.com/content/usgcom/en.html

The usage of the product was quite easy but the ratio was quite odd. For example, in drystone for 100parts of drystone the water that needs to be mixed was only 18-20 parts. So when I started mixing the mixtures seemed really dry at first. The trick is to add water slowly and mix it continuously. Once all the parts are mixed in right proportions it forms a neat paste. The same result in both the cases.

Additionally I was in-charge of documenting the group website.

Conclusion

 

The week was very interesting. I had the chance to experiment a lot of new materials and their reactions. Like for one instance, while making a plastic cast(exothermic reaction) we mixed with it a textile dye as we did not have the actual tint that was supposed to be used, the reaction was unexpected. The dye did not mix with the solution and due to the exothermic reaction, the whole content started frothing and emerged up which later cooled and solidified to form an interesting structure. There were a few problems I faced during the week like few milling problems and material insufficiency. But overall it was a great week and had a lot of fun experimenting though it did not turn out as expected.

Files

 

All files can be downloaded from HERE

WEEK 10

This week is about molding and casting. This week seemed quite interesting as there were so many new things to explore and the whole process of doing it was very intriguing. Neil started the lecture by introducing different types of molding techniques and the on to the vendor. At first, I didn't care much about the vendor list but made sense when I started using them. Then we discussed different materials and their properties like curing, storing etc. To make the mold and mill it, we spoke about 3d milling and the software for them.