Weekly Assignments Final Project About me

WEEK 14

Moulding and Casting

How the week started

Moulding and casting sounded fun, but the machine part meant learning another new machine. I knew I had to design fast.

How the week ended

I chose resin, and I felt it was a good decision. Otherwise, finishing this documentation would have been hectic. Well, here I am editing it a day after the week ended.

Week 14’s Assignment

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.
  • Compare mold making processes.

Link to group assignment

Individual assignment:

  • Design a mold around the process you will be using, produce it with a smooth surface finish that does not show the production process toolpath, and use it to cast parts.
  • Extra credit: use more than two mold parts.
  • Extra credit: make your own materials.

Individual Assignment

This week I designed a paper plane in Fusion - pattern. I resin printed the pattern and 3D printed the mould casing -flask. I placed the pattern inside the flask and poured silicone into it to get the mould. After it was cured, I poured resin into the -mould cavity.

Introduction

Moulding and casting are familiar terms. Yet the key difference between these words is something I had to search about it. From that I understood that casting is something we have all done at some point in our lives.

Ice cream example

If I am making ice cream, the mixture that I pour is the casting material, and the container I pour it into is the mould.

Puttu maker example

For Malayalis, it is like adding the puttu mix into the puttu kutti or puttu maker.

In these cases, I can choose any mould I want. For the assignment I designed the frame and flask. After pouring the silicone into it I got the mould

Types of moulding and casting processes

Injection moulding:

The plastic pellets are first added into a hopper feeder. From there, they pass through a heated barrel where they are melted. An injection ram then pushes this molten plastic into the mould at high pressure. This ensures that the material fills every part of the mould cavity accurately, resulting in a precise final form.

Injection moulding machine

source: Kuraray Injection Molding

Gating system:

The gating system defines how the molten material enters the mould. In high pressure systems, the entry point where the molten material is first poured is called the pouring basin. From there, the material flows through the sprue, moves into the runners, and finally passes through the ingates to enter the mould cavity.

This is important to understand while designing moulds. In a two part mould, runners are required to guide the flow of material. For silicone moulds, these runners act as channels through which the resin is poured.

Pressurized gating system diagram

source: Gating System

In my case, I am designing a one part mould. Instead of adding a separate runner system, I am using the base of the model itself as the opening for pouring the material.

The red color in the diagram shows the flow of the molten material. When the material is injected under pressure, the air inside the mould cavity needs to escape. For this purpose, vents are provided in the mould design.

To speed up the cooling process, water channels are often built into the mould. Water flows through these channels, helping the mould cool faster and improving production efficiency.

Runner and gating flow diagram

source: Runners, Gates, and Vents Overview

Rotational moulding:

Rotational moulding, also known as rotomoulding, is a process mainly used to create hollow plastic objects. In this method, the polymer material is added inside a closed mould. The mould is then rotated continuously while being heated, allowing the molten material to coat the inner surface evenly. After the heating stage, the mould is cooled, and the final object is removed from the mould cavity.

This process is economical for short production runs and is commonly used for manufacturing hollow products such as tanks, containers, and playground equipment.

Rotational moulding process

source: BPF Rotational Moulding

Overmolding:

Overmolding is a manufacturing process in which one material is moulded over another material to create a single part with multiple layers or properties. This process is commonly used to improve grip, durability, appearance, or flexibility in products.

Overmolding Process Video Reference

References:

Casting Terms and Pattern

Casting Common Terminology

Reference for Overmolding

Here, I am required to design the object or shape I want. I have designed a 3D model of a crashing paper plane. I will resin print a master so that I can create a flexible silicone mould from it. I will then pour resin into the silicone mould.

PATTERN - Fusion

Short story

I designed a paper plane, it was straight. The instructor said it was too simple. So what is not a straight plane? "A crashed paper plane."

Dimensions 40x40x15mm

1 / 3 I drew the outline of the fold on one plane. Then I drew a curved spline line and a perpendicular line to it.
2 / 3 I used the loft tool. I selected the plane I drew first and the tip of the spline. It initially created a straight surface.
3 / 3 Then I selected guide greater than centerline and chose the spline as the centerline. This gave the form of the crashed paper plane.
I drew the outline of the fold on one plane. Then I drew a curved spline line and a perpendicular line to it. I used the loft tool. I selected the plane I drew first and the tip of the spline. It initially created a straight surface. Then I selected guide greater than centerline and chose the spline as the centerline. This gave the form of the crashed paper plane.

Resin Print - CAD - CHITUBOX

I used the ELEGOO Saturn 4 Ultra printer to print the pattern. CHITUBOX was used for the CAM process.

1 / 6 Setting the model upright to get more surface area.
2 / 6 The exposure time is adjusted to give a longer curing time.
3 / 6 Here, the rest time for each submerge is set.
4 / 6 The raft is the base where the model rests. The raft is given an angle so it is easier to scrape off from the bed. The supports are not placed too close because they sometimes bind together.
5 / 6 The file is sent to the machine.
6 / 6 The estimated time duration was 2 hours and 29 minutes, but on the machine it showed 3 hours and 55 minutes.
Setting the model upright to get more surface area. The exposure time is adjusted to give a longer curing time. Here, the rest time for each submerge is set. The raft is the base where the model rests. The raft is given an angle so it is easier to scrape off from the bed. The supports are not placed too close because they sometimes bind together. The file is sent to the machine. The estimated time duration was 2 hours and 29 minutes, but on the machine it showed 3 hours and 55 minutes.

ELEGOO Saturn 4 Ultra - An LCD (mSLA) 3D Printer

ELEGOO Saturn 4 Ultra resin printer

Image source: What is an MSLA 3D Printer?

ELEGOO Saturn 4 Ultra is an LCD (mSLA) 3D printer. It prints in liquid resin layer by layer. mSLA stands for Masked Stereolithography Apparatus. There is an LCD screen below the vat which masks the UV light and allows light to pass only through specific areas. The resin solidifies where the light passes through. The build plate moves a few millimeters up and down as the model is formed layer by layer.

The printer has smart levelling and requires the liquid resin to be around 30°C to ensure smooth printing.

Know more about or buy the printer

Resin Print - ELEGOO Saturn 4 Ultra

1 / 7 ELEGOO Saturn 4 Ultra and the exhaust machine on the left.
2 / 7 The pattern is attached to the bed. The resin is left to drip into the vat.
3 / 7 The pattern is still on the bed and was scraped out later.
4 / 7 Post processing. The scraped out pattern is then dipped into the IPA solution.
5 / 7 The pattern is placed inside the Formlabs washing machine and set for a 2 minute cleaning cycle. This removes the excess resin.
6 / 7 Then it is placed inside the Formlabs UV cure machine. The heat was turned off as the temperature in Kerala is above 35°C. The timer was set for 9 minutes. After this, the pattern can be handled without gloves.
7 / 7 After UV curing, the pattern comes off easily from its supports. I placed the pattern on top of the supports as it had already come off before I took the photo. The pattern finish was flawless.
ELEGOO Saturn 4 Ultra and the exhaust machine on the left. The pattern is attached to the bed. The resin is left to drip into the vat. The pattern is still on the bed and was scraped out later. Post processing. The scraped out pattern is then dipped into the IPA solution. The pattern is placed inside the Formlabs washing machine and set for a 2 minute cleaning cycle. This removes the excess resin. Then it is placed inside the Formlabs UV cure machine. The heat was turned off as the temperature in Kerala is above 35°C. The timer was set for 9 minutes. After this, the pattern can be handled without gloves. After UV curing, the pattern comes off easily from its supports. I placed the pattern on top of the supports as it had already come off before I took the photo. The pattern finish was flawless.

3D Printed - A1 Bambu

I did the flask in Fusion with reference to the paper plane model. I offset the flask slightly bigger than the model. Well, I would say I should have gone slightly bigger with more clearance towards the sides.

1 / 3 The initial idea was to have a 2 part flask held by binder clips so I can reuse the flask.
2 / 3 I applied 0.15 mm tolerance on one side. Later, Ali told me that I could have done it in Bambu Studio and got a better model.
3 / 3 Printed in A1 Bambu.
The initial idea was to have a 2 part flask held by binder clips so I can reuse the flask. I applied 0.15 mm tolerance on one side. Later, Ali told me that I could have done it in Bambu Studio and got a better model. Printed in A1 Bambu.
  1. The brim is cut off.
  2. The pattern is placed inside to check the fit.
  3. The pattern is stuck to the flask using super glue.
  4. The flask is secured using painter's tape so that no leakage occurs.

Mould Making - Using Silicone Rubber

Casting silicone is ratio and time sensitive. I had taken the hardener in a 1000:25 ratio. By the time I took it out of the vacuum chamber, it had begun to thicken. From the next person onwards, we tried 1000:22 and 1000:20 ratios. The lower ratio gave a better time interval to pour the resin without trapping air bubbles.

The silicone will begin to set if the pouring is delayed.

The total curing time for resin is 17 to 18 hours.

1 / 11 Workflow. Drawn using Draw.io.
2 / 11 Water is poured into the flask and pattern to get the volume of silicone needed. The water is poured into a transparent cup and the measurement is marked.
3 / 11 Compressed air is blown into the flask to clear any water droplets and it is left to dry.
4 / 11 I placed an empty transparent cup and set the weighing scale to zero. I poured the silicone into the cup until it reached the same level as the water level.
5 / 11 The silicone hardener ratio is between 1000:20 and 1000:25. I took 1000:25. Using the ratio calculator, I got the value as 1.2 g.
6 / 11 I poured 1.2 g of silicone hardener after calculating the ratio.
7 / 11 Mix the silicone and hardener in a to and fro action. This avoids air bubble formation.
8 / 11 Keep the mixture in the vacuum chamber. This pulls out the trapped air bubbles. Wait for the silicone to rise and fall, then the bubbles are gone.
9 / 11 Spray the flask with releasing spray.
10 / 11 Pour the mixture into the flask. Here, the mixture is time sensitive.
11 / 11 I poured the silicone to cure around 10:45 PM on April 27th.
Workflow. Drawn using Draw.io. Water is poured into the flask and pattern to get the volume of silicone needed. The water is poured into a transparent cup and the measurement is marked. Compressed air is blown into the flask to clear any water droplets and it is left to dry. I placed an empty transparent cup and set the weighing scale to zero. I poured the silicone into the cup until it reached the same level as the water level. The silicone hardener ratio is between 1000:20 and 1000:25. I took 1000:25. Using the ratio calculator, I got the value as 1.2 g. I poured 1.2 g of silicone hardener after calculating the ratio. Mix the silicone and hardener in a to and fro action. This avoids air bubble formation. Keep the mixture in the vacuum chamber. This pulls out the trapped air bubbles. Wait for the silicone to rise and fall, then the bubbles are gone. Spray the flask with releasing spray. Pour the mixture into the flask. Here, the mixture is time sensitive. I poured the silicone to cure around 10:45 PM on April 27th.

Workflow drawn using Drawio. Ratio calculator used: Ratio Calculator.

Post Processing - Silicone Mould

The silicone mould was removed the next day around 11 AM. I cut the painter's tape and took apart the flask.

1 / 4 The silicone rubber has hardened. The curing time taken was 12 hours.
2 / 4 A thin layer of silicone seeped under the pattern and covered it. There are flash lines along the two sides where the flask joined.
3 / 4 I removed the pattern from the silicone. The seeped line has to be cleared for easy pouring of resin.
4 / 4 I removed the excess silicone layer with a handy cutter and scissors.
The silicone rubber has hardened. The curing time taken was 12 hours. A thin layer of silicone seeped under the pattern and covered it. There are flash lines along the two sides where the flask joined. I removed the pattern from the silicone. The seeped line has to be cleared for easy pouring of resin. I removed the excess silicone layer with a handy cutter and scissors.

Casting - Resin

Aditya Ultra Clear Cast Epoxy – 37 – 1 Kg

Epoxy used is transparent clear resin. The mixing ratio is Easy Part A 100 parts : Part B 50 parts. The curing time taken is 24hours. It does not need grinding and sanding after curing. It does not turn yellow over time.

1 / 7 The volume of the mould cavity is measured by pouring water into it and then pouring it back into the cup. Measure the volume in the cup.
2 / 7 Aditya Ultra Clear Cast Epoxy Easy Part A is poured to the same volume as the water.
3 / 7 The resin Part A weighed 38.8 g when measured.
4 / 7 19.5 g of Ultra Clear Cast Epoxy Part B was poured, according to the 2:1 ratio. This time, the weighing scale was not brought to zero. Therefore, the weight shown was 58.3 g. This gave a more accurate reading.
5 / 7 The resin mixture also has to be mixed in a to and fro motion. This avoids the formation of bubbles.
6 / 7 The resin mixture is kept in the vacuum chamber to remove the bubbles. Wait for the resin to rise and fall. This would take less than 2 minutes or so.
7 / 7 I squeezed the mould while pouring the resin into it, as it is very thin. This was done to ensure that the resin enters the tiniest parts.
The volume of the mould cavity is measured by pouring water into it and then pouring it back into the cup. Measure the volume in the cup. Aditya Ultra Clear Cast Epoxy Easy Part A is poured to the same volume as the water. The resin Part A weighed 38.8 g when measured. 19.5 g of Ultra Clear Cast Epoxy Part B was poured, according to the 2:1 ratio. This time, the weighing scale was not brought to zero. Therefore, the weight shown was 58.3 g. This gave a more accurate reading. The resin mixture also has to be mixed in a to and fro motion. This avoids the formation of bubbles. The resin mixture is kept in the vacuum chamber to remove the bubbles. Wait for the resin to rise and fall. This would take less than 2 minutes or so. I had sprayed the release spray inside the mould. I squeezed the mould while pouring the resin into it, as it is very thin. This was done to ensure that the resin enters the tiniest parts.

The complete curing time for resin is 24 hours. In 4 hours it begins to set. This window can be used when pouring different colors or adding another element between the resin layers. I poured the resin at 1 PM on April 28th and was able to take the resin out of the mould around 1 PM on April 29th, the next day.

Hero Shot

I have to accept that trying to remove the resin from the mould was a Hercules task. I used compressed air blown into the mould to release the resin cast. From this, I understood that I should have designed a bigger flask so that the mould edges would not have been too thin.

1 / 2 The resin had spilled outside and cured. When I removed the mould, I had to scrape off the excess using a handy cutter. You can also see the bulge in the resin cast caused by trapped air inside the silicone mould during pouring.
2 / 2 The two outcomes. The transparent one is the first cast. I poured a second resin cast using red dye. The cast came out looking good.
The resin had spilled outside and cured. When I removed the mould, I had to scrape off the excess using a handy cutter. You can also see the bulge in the resin cast caused by trapped air inside the silicone mould during pouring. The two outcomes. The transparent one is the first cast. I poured a second resin cast using red dye. The cast came out looking good.
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