Skip to content

10. Molding and casting

This week we had following objectives

  • Group assignment: review the safety data sheets for each of your molding and casting materials,then make and compare test casts with each of them

  • Individual assignment:design a mold around the stock and tooling that you’ll be using,mill it (rough cut + (at least) three-axis finish cut),and use it to cast parts

Research

Learning from earlier year student page

This week was a completely new skill to me. I never heard about moulding and casting. So i started with what previous year studnets has done. Starting with my instructor pages Rahul Gautam

So going through the page Rahul explains how he designed a chess queen object in fusion. As i was already comfortable in fusion but the approach of molding design seems to be a bit different. It seems i need to design a 3d object and then use some geometry operations like union, cut to create some impresssion in a rectangular box. Create some holes for liquid to pour in which will be used for casting. This reminded me of my childhood candle making process which i used to do after Diwali where i picked up all the remaining wax afer diwali, liquify it and then use to create a new candle using a hole in sand. It seems may be i have done this before and only differenc is now i have a new fancy name which is molding and casting.

So as next step i started surfing through internet on tutorials on how to design a mold. So i found couple of good video tutorials that were quite helpful for me in this week.

Tutorial Create One Part Mold

Tutorial Create Two Part Mold

Understanding molding and casting

Tutorial on Smoothon website was quite useful and they have a handy booklet that explains the molding and casting process and material. Also i found a good PPT that explains some of the details around 1 part mold, 2 part mold and draft angles in a very simple way.

Group Work

  • This week’s group assignment was to review the safety data sheets for each of the molding and casting materials at our lab, and then to make and compare test casts with each of them. In addition to the group activity, we had to individullay design a 3D mold and use it to cast parts.
  • The materials we have at our lab are Aditya 1010 RTV liquid silcone & Aditya Easy Cast Transparent Epoxy Resin -33

Understanding Data Sheet

  • Aditya Silione Rubber RTV – 1010 is a condensation cure type Silicone Rubber. It comes in 2 parts. One is Silicone Rubber and second is Curing Agent.
  • DataSheet Silicone Rubber
  • Curing Agent is mixed into Silicone Rubber in a given ratio (40-50 ml in 1kg of silicone).It cures at room temperature. Plaster, Resin, Epoxy Resin, Polyurethane, Wax and other resins can be casted into the cured silicone mould.
  • Easy Cast Transparent Epoxy 33 can be casted into moulds of Silicone Rubber to Create Transparent Crafts, Lockets, Jewellery and Trophies. Pigments are available to make Opaque Colour Castings. It comes in Part A and Part B.
  • DataSheet Curing Agent

Features Silicone Rubber

Specially created Silicone Rubber to make molds of Murties, Statues, Crafts, POP Cornices, Medallions and items which have deep under cuts. - Low Viscosity - Low hardness - Easy demoulding - Can be made paste to apply with brush also

Features Curing Agent

  • Low Viscosity
  • Transparent
  • No grinding or sanding after casting
  • Can Cure in 30 minutes if heated at 65 degree centigrade and poured
  • Part A 100 parts : Part B 50 parts mixing ratio
  • Non-Yellowing

Technical Properties

  • Viscosity - .10000 Pi
  • Curing Agent / Hardener Ratio 4 %
  • Curing Time - 6 Hours
  • Colour - Milky

Test Parts

Silicone

  • For epoxy the mixing ratio of the Silicone and the curing agent was mentioned on the pack. The ratio was 40-50ml in 1000ml of silicone i.e 4-5% of curing agent in measure amount of silicone
  • First batch didn’t turn out perfect, we added about 5% of curing agent. The silicone set in about 3 minutes which is not ideal. For the next batch we decided to add a little less curing agent at about 4%.
  • For the second test 4% was used and it worked perfect. We used syringe to add curing agent to the silicone. This helps us to add the correct weight drop by drop.

Curing Agent

  • Ratio for epoxy was also mentioned on the pack. The Proportion for Epoxy –> 2:1 i.e. for every 2 parts of Compound A we have to add 1 part of compound B.

Getting Started Mold Design

For this week objective was not simply doing a one part or two part mold but do a three part. First i need to create a mold using flexible material and then use it to cast the actual object.

Fusion design

So i started with the design i already made in 3d printing week which was a knight i designed. Sound like a good testing ground for my own chess pieces. So from laser cutter i can create a board and from molding and casting i can have chess knight, Pawn etc.

Steps

  • Import the knight design in a new design in fusion

  • Create a rectangle around the 3d design

  • Use extrude to get some depth

  • Use combine operation (Join) to merge both rectangle and knight

  • Export as STL file by right click and save as STL

Learning New Software Modella For Milling The Mold

I use Modela software for the same which is used to mill the mold on SRM 20.

Import STL file in Modela player and select a new process

Roughing operation

Enter the diameter of the tool

Set the Cutting Parameters

Finishing Operation

SRM VPanel

SRM Operation Video

Final Mold

Used silicone rubber and curing agent as 100 gm and 3 gm combination

Mistakes made

After the silicone mold was made i realised my design mistakes. I left a hole at the top and no way to join these molds.

How i corrected design mistakes

There was no point in redesigning whole piece again as miling and settling of silicone rubber could have taken me two days to fix. I think we anyways learn better by mistakes. So the design mistakes i tried to correct using tape to wrap the two pieces together and using nails to join two molds together. Its not a neat way to do it but work as a backup option.

Preparing the Chemicals for Casting

Next step was to pour resin by mixing chemicals and left for 24 hours.

Resin

Curing agent

Mixing

Pouring into Mold

Issues

While mixing i realised that i tried to shake the mixture and it results in bubbles formation. I think this is the mistake i did. To correct the mistake i tried to mix the solution gently. Its very important otherwise the final product will have bubbles inside it and won’t get smooth finish.

Final Product

Overall Learning Outcome

  • Molding and casting scope is huge in terms of what we can build
  • I learnt to design a mold in fusion. The approach to design is different
  • I learnt new feature of autodesk fusion like Combine geometry to create mold design
  • We come to know how SRM can be used for creating mold and not just PCB design. So explored one more feature for SRM machine
  • Lot of chemicals are used in molding, so its important that we use it after reading proper instructions and manual for our safety and also it made me curious how we can do this process without use of harmful checmicals.
  • I was curious to learn more about molding and casting after this week so i went to local industrial place in delhi to see how injection molding machine works. Here are some snapshots of that visit.

Mold made of iron using Lathe machine

Injection molding machine that uses mold like above to create plastic products

How a Product like a handle in this case get made