UNDERSTANDING MOLDING AND CASTING

WEEK10: Molding and Casting

ASSIGNMENTS:

 

Individual assignment

  • Design a 3D mold around the stock and tooling that you'll be using, machine it, and use it to cast parts

   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

 

  • This week's assignments, I have started with fundamental process of molding and casting and materials involved in this.
  • Fundamentally molding and casting is manufacturing process to give shape to liquid raw material by pouring it into rigid frame known as mold.
  • One understanding this clearly, by going through process of molding and casting

Process:

  • This involves 3 step process, some industrial application are being practiced in two step only.
  • A) Making positive mold : By machining of hard material such as wood, plywood, wax blocks,  etc
  • B) Making Negative mold from positive: This can be made by pouring liquid and somewhat flexible material or with such material that can be used to make multiple parts (casted) out of it. For example Rubber mold
  • C) Making positive pieces in mass from negative mold: Here negative mold can be used to cast multiple part out of it by pouring end product material such as liquid plastic, ceramic etc.

OUTLINE OF MY WORK FLOW OF THIS WEEK

 

  1. Decide what to make: Sketch the end product with general dimensions.
  2. Design the mold: Based on machining tool and material
  3. Making toolpath for cnc milling
  4. 3D milling on shopbot CNC
  5. Making of Rubber mold from CNC mold
  6. Cast multiple objects from rubber mold
  7. Additional Aluminum metal casting for final Project
  8. Learning outcome and observation

STEP01: SKETCH THE END PRODUCT

 

  • After spending sometime by referring previous year's students work and some projects in my lab I got an idea how people are using molding and casting to make something.
  • Finally I have decided to make Table-stationery pot. That can be used on office table to keep mobile, pen drives, pins, pen, and general stationaries.
  • Also the advantage here is I can make multiple pieces and gift those around to my colleague and friends in my office.
  • Initial size I chose is 150*120mm and height of 35mm.

STEP02: DESIGNING THE MOLD

 

  • Having decided what to make, next thing is I have to prepare 3D CAD design of model. I have decided to make 35 mm height object so, I will prefer to do machining by Shopbot CNC with stack of water proof MDF material.
  • I have designed the 3D CAD model in Rhino, with wall thickness of 5mm and sketched dimensions.

STEP03: MAKING TOOLPATH FOR 3D CNC MILLING

 

  • Once the design got ready I have exported it into STL for 3d milling.
  • For 3d milling on shopbot CNC I have used partworks 3D software to make toolpath.
  • Partworks3D interface consist of 5 steps with different set of instructions:
  • 1) Job orientation,
  • 2) Material size and Margin
  • 3) Roughing toolpath
  • 4) Finishing toolpath
  • 5) Toolpath preview and save
  • Load 3D file (STL) right after you open partworks3d software
  • In Orientation and size step we have to set model size, cutting surface and unit.
  • In Material and Margin step one have to set origin point, material size and machining margin. I have chose down corner as origin and 5 mm as margin.
  • Next step is to generate Roughing toolpath, where one has to select right tool and its cutting parameters. I have used 1/8th inch 4 flute endmill.
  • Roughing toolpath preview
  • Next is calculate Finishing toolpath. For finishing toolpath one need to use ball nose milling bit. I have used 1/8th inch 4 flute ball nose bit. Accordingly set the cutting parameters for finishing the already cut part.
  • Once both the toolpaths are being calculated, next step is to check preview  of cutting. If there is any correction required we can go back to particular toolpath and change the parameters
  • If all looks good, next onse has to save both toolpath in different .sbp files, as we need to use different tool for types of cutting operations..

STEP04: MILLING ON SHOPBOT CNC

 

  • First we have to run roughing toolpath so I have mounted 1/4th inch 4 flute endmill on spindle.
  • I have prepared my material from 12 mm thick water proof mdf sheets, by gluing 4 sheets together. It took 24 hr under compression clamps have permanent strong bonding. And I mounted this material on cnc bed with screws on sides.
  • Turn on the CNC and set origin point in my material.
  • Once right origin set, I run roughing toolpath and start milling.
  • After completion of roughing toolpath, I have removed key and changed tool with 1/8th inch ball nose milling bit. And turned back to defined origin.
  • Once tool and origin are set I loaded finishing toolpath, and start milling.
  • It took 2 hour in total.
  • I have prepared my material from 12 mm thick water proof mdf sheets, by glueing 4 sheets together. It took 24 hr under compression clamps have permanent strong bonding.
  • First we have to run roughing toolpath so I have mounted 1/4th inch 4 flute endmill on spindle.
  • Turn on the CNC and set origin point in my material.
  • Once right origin set, I run roughing toolpath and start milling.
  • After completion of roughing toolpath, I have removed key and changed tool with 1/8th inch ball nose milling bit. And turned back to defined origin.
  • Once tool and origin are set I loaded finishing toolpath, and start milling.
  • Finished CNC milled mold.

STEP04: MAKING RUBBER MOLD (NEGATIVE) FROM CNC MOLD (POSITIVE)

 

  • Now  in order to make rubber mold from cnc machined mold, I have to pour liquid rubber material into cnc mold and cure it.
  • Here I have decided to make rubber based mould that can be used multiple times to cast again and again different parts.
  • Step by step process I have followed here, explained below.
  • So, first thing I have done here is make sides on mold so that rubber mold have certain base height. After that I have applied lubricant on sides of water proof mdf mold so that rubber dont get stuck with material after solidification.
  • Now, as rubber mold material I have used Vytaflex-40 rubber compound, so first I have measured part A and part B and mixed it to make right rubber mold mixture.
  • Once mixture got ready I poured into cnc mold and put it on straight surface on stable condition for 24 hour to cure it.
  • Once rubber mold was out I washed it to remove grease and lubricant from surfaces although there were some black stains on rubber mold.

STEP04: CASTING MULTIPLE PARTS (POSITIVE) FROM RUBBER MOLD (NEGATIVE)

 

  • For casting I have decided to use liquid plastic materials of two types. 1) smooth cast-300 white and 2) smooth cast-326 transparent
  • Procedure step by step I have explained here below.
  • To initiate Casting to make multiple pieces out of rubber mold by pouring different material and take out solidified part.
  • First I have decided to cast with liquid plastic i.e. smooth cast-300 white. The setting time for this is very fast, it takes 10 minutes to settle and get solidified.
  • Before pouring liquid plastic mixture material into rubber mold, I have applied Vaseline (After many trials of different material such as cutting oil, machine, oil, talc,vaseline etc, Vaseline was working fine) so that plastic dont get stick with rubber mold
  • I removed the casted part once it got solidified. It took around 12 minuted to settled properly.
  • I Once it get solidified, it easily came out due to Vaseline and rubber flexibility.
  • Next material I have tried to cast part is smooth cast-326 transparent (pigment-able). This is medium settling liquid plastic so it took around 30 minute to get settled.
  • Once done all part looks like this. CNC mold, rubber mold and two casted parts out of mold.
  • Once done all part looks like this. CNC mold, rubber mold and two casted parts out of mold.

ALUMINUM CASTING FOR FINAL PROJECT

 

  • For my final project I have to make heater and nozzle assembly module. There is no metal machining machine available in my fablab and I cant go for 3d printing plastic because it essentially should be metal to transfer heat.
  • For this purpose I have decided to design this module in rhino, 3d print it in plastic, go for sand molding, and then aluminum casting.
  • For this I went to local fabricator setup and requested to make aluminum casted part.
  • 3D CAD Design of heating element, which has slots for heater, melting zone and nozzle to extrude material from front..
  • 3D Printing in PLA material.
  • CAD design iterations
  • Final 3D Printing for sand mold
  • Sand molding with 3d printed part
  • Casting of Aluminum metal
  • Casted part came out
  • C3D Printed module and aluminum casted part

LEARNING CONCLUSION

 

  • After going through this weeks assignments and exercise I got clear idea about process one need to go through for manufacturing something by molding and casting.
  • I have learned critical design parameter we have to take into consideration for designing mold such as draft angle, vents, press fit slot for double sided part etc.
  • I have learned about nature of materials to use as mold and casting, and different behavior of those materials while cutting and while under liquid mold compound like some hard material get stuck with flexible material while settling.

Original Files:

  • Original files which of molding and casting can be downloaded here as package

INDIVIDUAL CONTRIBUTION TO GROUP WORK

 

  • For molding and casting group work, we have tested various types material on single type of mold.
  • We have worked in group to make mold from PMC780, and individually I have tested two types of materials casting i.e. ultra clear epoxy resin and smooth cast-300.
  • I have used Haksons ultra clear high epoxy resin and Hardner in 3:1 ratio.
  • Its curing takes about 24hrs with the pot life of 30 mins.
  • After 24 hrs the material had hardened nicely. But unfortunately removing the cast from the mold was very difficult because first time we have not applied any lubrication. So, its highly recommended to use lubrication and draft angle in mold.
  • Smooth cast-300 part A and part B needs to mix in 1:1 ratio. Curing time for this material is  7 to 10 minutes.
  • For smooth cast it is advisable to pour your mixture in a single spot at the lowest point of the containment field and let the mixture seek its level. This will help minimize air entrapment

For detailed documentation on tests of different types of material is done on lab website

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2018 | Tanvir Khorajiya