Molding and Casting

Reading the safety datasheet

This is an important part of the the process as it will provide information about the correct use of the material as well as important safety measures that need to been taken.

Make sure you are on a well ventilated area to work with these materials

Silicone Rubber 6255

This is a 'safer' material, but is highly recommended to use protective gloves and safety glasses to minimize contamination risk, also be sure to mix it properly.

• Always wash you hands after manipulation this product.
• Flush with abundant water on accidental contact with you skin.

EpoxAcast 690 - Smooth-On

After reading though the safety datasheet that covers handing and storage, fire fighting measures, and first aid measures among other topics. Is important to remember these points:

• Use protective gloves, eye protection and a breath mask.
• Always wash your hands after manipulating this product.
• On an accidental contact with skin and/or eyes flush with plenty of water, use soap if on the skin.
• If inhaled, move the victim to fresh air, if needed provide artificial respiration and oxygen. Contact a physician immediately

How to use the material

• The proper mixing ratio is 100 parts of EpoxAcast™ 690 resin to 30 parts hardener by weight.
• Mix thoroughly for 3 minutes making sure that you scrape the bottom and sides of the container several times.
• Mixed EpoxAcast™ 690 is exothermic, meaning it generates heat.
• Let cure for 24 hours at room temperature. Castings that are ¼ in. thickness or less will cure more slowly and may require up to 48 hours to fully cure at room temperature.
• Pour mixture in a single spot at the lowest point of the mold or enclosure. Let the mixture seek its level.

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Design!

At first I didn't know what object use to mill, mold and cast. Then I saw my desktop background, a low poly tree that I made while learning Blender, the idea is to make a low poly tre with clear material and embedded LED lights, it will be a night lamp.

I use Blender to model the 3D object, considering the future moldering process I create a tree that can be 3D machined. To have an idea of the size I make a bounding box, to make the 'leaves' I use icospheres and deform them avoiding the overhangs.

Get the .blend file Get the .stl file

Working with Artcam 2018

I use Artcam to make and simulate the toolpaths based on the previously modeled tree, to do this I first crete a 100mm to 100mm workspace and import (Relief>Import>Import 3D model)my .stl file, then I set up my material at 20mm, and start with the toolpaths generation, but as we will be using 1/2 inch end mill for rouging and a 1/4 ball mill for the 3D milling, after I simulate the final result wasn't great there was places were the mill coundt reach.

To improve the toolpaths I modify my model to fit the tools we will be using to make this assignments. I add a small 90 degree 3mm space on the back of my model and also scale it up to 14 cm of height. This help to make a final set of toolpaths that won't take that much time, and also leave a great final product, you can see the simulations.

I also save some time by only applying the surface finish paths to the model area with some offset. The clear strategy can affect the finish result, espial or two raster offsets by 60 degrees work well.

Artcam toolpaths settings

Toolpath	Mill bit	Feed Rate	Plunge Rate	Step over	Step down
Roughing	End mill 1/2 inch	50 mm/s	30 mm/s	10.16 mm	4 mm
Surface finish	Ball Nose 1/4 inch	30 mm/s	30 mm/s	0.953 mm	3.175 mm
Edge finish	End mill 6 mm	40 mm/s	30 mm/s	2.54 mm	3.175 mm

Milling!

Firs we start by reviewing our feeds and speeds with our instructor, the we place the material on the CNC router bed, 30mm MDF of at least 18cm by 18cm was used to make this mold.

We first attach the 1/2 roughing mill to make our rough cuts and get the idea of the shape. Then we make the surface finish, with the first pass the surfaces was great on some faces and other have some lines, after the second pass offset by 60 degrees it was completed.

The final edge pass was made with a flat end mill that allow a sharper edge. You can see the difference below.

Molding

This is the process of making a flexible mold that capture the detail of the 3D milled piece, and allows you to cast a solid material that will have tha shape generated before.

We use Silicon Rubber 625, to make the mold. As it is a two component mix we first estimated the amount needed and add the corresponding catalyzer, after mixing it with a wood stick we pour it on top of the MDF pieces.

The MDF pieces was sealed using wood sealant and some linseed oil as a release agent. When we poured all the rubber some parts were still visible so using a plastic cup places were the mold would not be affected we reduce the overall volume needed to fill the cavity.

After 48 hours the silicone was cured and I remove it from the MDF piece, I add a small cut on the base to fit the cables of the embedded LED's and hold them in place during the casting.

Casting

This is the process were you fill you flexible mold with the desired rigid material,I would use Clear Epoxy because I want a translucent pieces with embedded LED lights.

The first step was to prepare the space and my self, I use some old paper to cover the table that is on a well ventilated area outside my house. Put all the safety gear on and prepare the measure cup by using water and a marker to indicate the appropriate levels.

Then I mix the two parts of the resin, mixing thoroughly for 3 minutes and the pouring to fill all the 'leaves' and half way to the trunk, I then places the LED's and finish with other layer on top to seal it up.

After 24 hors of harden time, the resin wasn't hard enough, but as the that sheet points, casts that are smaller than 1/4 inch on thickness can take up to 48 hours, after that I demould the piece, it was a bit flexible though, it took another 48 hours to completely harden, This ma be because the resin mixing was made by volume and not by weight.

Final Result!

Conclusions

On this week I was thrilled when the CNC router was making my own design to something physical and tangent, I decide to use Blender to make the 3D model on a more 'artistic' way, I'm also excited about the embedded LED that will be inside the casted part.

Due to supply and time issues this assignment wasn't completed on time, but all the waiting time was worth the result, when I finally programmed and the light turn on, all the effort and planing was finally rewarded.

Have I?

• Linked to the group assignment page
• Reviewed the safety data sheets for each of your molding and casting materials, then made and compared test casts with each of them
• Documented how you designed your 3D mould and created your rough and finish toolpaths for machining, including machine settings
• Shown how you made your mould and cast the parts
• Described problems and how you fixed them
• Included your design files (.blend) and ‘hero shot’ of the mould and the final object

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