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Week 13

Assignment - Moulding and Casting

  • Group assignment:

    • Review the safety data sheets for each of your molding and casting materials
    • Make and compare test casts with each of them
    • Compare printing vs milling molds

  • Individual assignment:

  • Design a mold around the process you’ll be using, produce it with a smooth surface finish that does not show the production process toolpath, and use it to cast parts.

See Assignment Details

Group Documentation

Safety Data Sheets

Test Casts

  • Jesmonite

Steps

  • Weigh out 56g of liquid and 144g of plaster (based on starter kit example mold provided), or use something like jesmonitecalculator.com.
  • For AC1000, the ratio is 1:2.5 (powder:liquid), as follows:
material materialDensity ratioOfPowder ratioOfLiquid Pigment
AC100 1.75 1 2.5 0.02
AC730 1.95 1 5 0.02

Measuring the various sample moulds gives( with water technique):

measured mold mold nickname material density total combined how much liquid how much jesmonite powder
(g, water) density, g/cm^3 g ratio, 1:2.5 ratio, 2.5:1
67 flowerpot (each in set of 3) AC100 1.75 117.25 33.5 83.75
108 coaster AC100 1.75 189 54 135
52 10x10 square 3D printed AC100 1.75 91 26 65

I originally measured the 3D printed mold as 66g water (or 91g combined gpc). Though when I measured out the jesmonite liquid, I only had 26g left, so I adjusted the total amount and calculated only 52g water, which would fill the mold less.

I found a wider disposable container and mixed in that. I stirred with a wooden stirrer. But unfortunately the powder spilled, and the mix started drying immediately. I stirred until it was homogenous anyway, but it was too thick to pour,

  • Hot Glue Injection

(See mold design below)

  • XTC-3D (Paint-on Smoother PLA)

Individual Assignment - Mold Design

Designed an FDM printed mold.

Mould Idea

Tried some models from Printables.com

They were too intricate. So, I used ShrinkWrap in Rhino to reduce the mesh.

Rhino ShrinkWrap

I measured a hot glue gun, and made a grasshopper script around automatically subtracting the mould adding sprues and splitting into two parts.

HGG Tracing 1

HGG Tracing 2

HGG Model

And I measured the material, a small gluestick refill, which was 7mm diameter and 98mm long.

HGG Material

Idea, instead of cutting in Grasshopper:

Cut in PrusaSlicer

I used Prusa’s Connector Features to add alignment divets (this is part of the Cut tool). This actually gives you a neat way to add and position them when setting up the job and to test different tolerances.

Prusa Connector Features to add alignment

…Which gives:

Preview

And the intention is to make a more complicated pipeline that can take a variety of meshes.

Test Homme32 ideas

But unfortunately at the moment, looks like this, because of mesh problems.

Test Homme32 model

I found that if you made the mesh of two adjacent boxes in Rhino/Grasshopper, the mesh triangles already aligned with the cut tool and didn’t create any naked edges, so I added that to my script.

Version 2

In version 2, I made adjusted the nozzle tolerence, and made the injection point closer to the model. I made a panel in Grasshopper to show you what number to use in the “Cut” tool in PrusaSlicer. And copied the “pin” to another location, but I’m not sure if the adjustment is needed while also adjusting the overall tolerence.

I also made the settings for the alignment pins in PrusaSlicer shallower frustrum shapes with a 0.3mm tolerence setting. In this case, I had to cut at 15.013mm.

This mightn’t have been the correct move, it puts the injection point on the line of the seam.

Files