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. Compare mold making processes

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

Group assignment

Group assignment page

13. MOLDING AND CASTING

Molding is a manufacturing process that involves shaping a liquid or pliable material using a rigid frame known as a mold or matrix. This technique is used to form materials such as plastic, metal, glass, or ceramics into specific shapes and products. Depending on the material and desired outcome, various molding methods can be employed, including injection molding, compression molding, blow molding, and rotational molding. Each technique offers unique advantages and is selected based on factors like the complexity of the shape, production volume, and material properties. Molding is widely used in industries ranging from automotive and aerospace to consumer goods and packaging.

Types of molding

Injection Molding : In this process, molten plastic is injected into a mold under high pressure. After the material cools and hardens, the mold opens, and the finished product is released.

Blow Molding: Used mainly to produce hollow plastic objects like bottles. It involves extruding a molten plastic tube (parison), which is then expanded within a mold using air pressure to match the mold’s shape.

Compression Molding: Ideal for forming thermoset plastics and rubber. A preheated material is placed into a heated mold cavity and then compressed between two mold halves until it takes the desired form.

Rotational Molding: This process creates large, hollow parts by placing powdered plastic in a mold that rotates biaxially. The heat melts the powder, which coats the mold’s interior to form the part.

Extrusion Molding: A continuous process in which heated material is forced through a shaped die, producing long products with consistent cross-sections like pipes or profiles, which are then cooled and cut to length.

Thermoforming: Involves heating a plastic sheet until it becomes flexible, then shaping it over or into a mold. Once formed, it is cooled and trimmed into the final product.

Casting: A simple yet versatile process where liquid material such as metal or resin is poured into a mold and allowed to solidify. Once set, the mold is removed, revealing the final shape.

Die Casting: A precise method of forming metal parts by injecting molten metal into a metal mold (die) under high pressure. It is commonly used to produce components with high dimensional accuracy and a fine surface finish.

Silicone molding

Silicone molding, also known as silicone rubber molding, is a flexible and precise manufacturing process used for creating detailed, durable parts, particularly in prototyping and low-volume production. The process begins with a master pattern, either a premade object or a custom model that serves as the positive shape for the mold. Silicone rubber is then mixed and poured over the pattern, ensuring it covers the model adequately. Once cured, often using a vacuum chamber to eliminate bubbles and speed up the process, the mold is removed. After final curing, the master pattern is gently extracted, leaving behind a reusable mold cavity. Casting materials such as resin or wax can then be poured into the silicone mold to replicate the original design.

Making a Mushroom

1. Design in Fusion 360

.AS mushroom is symmetrical , I used a single positive mold which can be used to make two negative silicon molds. A machinable wax of dimension 3"x3.5"x1.5" was given. So I started by drawing the block. The intial sketches of both the mold and mushroom were made.

Then I used revolve tool to create the 3D mushroom and extruded the rectangle to create mold.

I added appearance to get a realistic look.

The design time line is shown below.

2.Computer aided manufacturing

Computer-Aided Manufacturing (CAM) is a process that utilizes specialized software and automated machinery to control and optimize the production of physical products. By transforming digital models from CAD (Computer-Aided Design) software into machine-readable instructions, CAM directs tools like CNC machines to execute precise manufacturing tasks. I used fusion 360 for CAM. The first step was to change the workspace. Select manufacture workspace.

We can add custom libraries in fusion. I added tool library which consisted the tools available in the lab. Manage -> tool library(right click) -> Import libraries

From setup, select new setup

In setup we can choose the orientation and where to set origin, stock and stock dimensions.

From 3D option, we need to set adaptive clearing, pocket clearing and scallop.

Adaptive clearing in Fusion 360 is a roughing strategy designed to efficiently remove large amounts of material while maintaining a consistent tool load and speeding up machining time. 3D-> Adaptive clearing. The settings I used are given below. I used a 6mm flat 4 flute end mill.

Pocket clearing is a toolpath strategy primarily used for roughing out large areas of material, specifically in pockets (cavities) and open areas.I used the same 6 mm flat end mill for pocket clearing. The settings I used is given below.

The toolpath of pocket clearing is given below

Scallop is used to create a consistent surface finish by removing material along a surface. This approach is particularly effective for finishing areas with complex geometries, ensuring a smooth and uniform surface finish.

The toolpath of scallop is given below

To generate G-code, Actions-> post process.

CAM simulation video is given below. For simulation, actions->simulate

3.Creating the positive mold

TRAK DPM RX2

The picture of TRAK machine is shown below

First we need to set the origin. Click DRO on the right panel of TRAK screen. We need to move the machine manually using the wheels.I used edge finder to set x and Y axis, the edge finder is rotated and moved near the machinable wax. Once the probe touches the wax and is aligned, take the next misaligning point to set origin.Instead of entering zero we need to enter -2mm which is the radius of the probe. Once set, click the ABS SET. For 'Z' axis, we can choose a reference point on the machine table. Use the jog controls to move the Z-axis in the desired direction. Remember to click return after completing the jog.

Using a pen drive transfer the G-code to the machine. Place the machinable wax and tighten it to the vice. Change the tools using the IN and OUT buttons in the top left corner of the machine. Select PROG IN/OUToption in the screen.Now select the “TOOL TABLE” and add the details of the tool that you are using. I was using a 6mm rough end mill in the begining.

After completing the 6mm end mill processes, here the result.

Then I changed the tool to 3mm ball mill. I got a smooth finish. Here is the result.

4. Creating the negative mold

To create a negative mold, first we need to know the volume. For that I filled the mold with water and poured it to a glass. The level of water is noted. The water is then removed and filled with silicon in the same level. Hardener is added to the silicon. To get the amount of hardner, ratio calculator is used.

When weighted, it was 164.7 gm. So I added 5 gms of hardener.

I mixed the silicon with hardener and placed it under a vaccum chamber to remove bubbles. It is then poured into the mold and let it rest for 24 hrs.

Next day I detached the silicon mold from the positive mold.

5. casting

The next step is to pour epoxy resin into the mold. I wanted to make a fridge magnet. To make it work, I had to add magnet to the mushroom head. As I wanted the mushroom in two colour, resin were mixed as two parts. Magnet was attached to the mushroom head. To make it stay intact an external magnet was attached. An acrylic piece was cut to close the negative mold.