MOULDING & CASTING

This week was about moulding and casting — taking a 3D design, machining it into a physical positive, making a flexible silicone mould from that, and then casting a final part in a hard material. It is one of those weeks where you start with a CAD file and end up holding something real and solid, which is always satisfying.

Assignment

Group

• Review the safety data sheets for each of the moulding and casting materials
• Make and compare test casts with each of them
• Compare mould making processes

Individual

• Design a mould 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
• Extra credit: Use more than two mould parts
• Extra credit: Make your own materials

What is Moulding and Casting?

Moulding and casting is a manufacturing process for reproducing the same shape multiple times. The core idea is simple, you make a mould once, then use it to produce as many copies of a part as you need. It is one of the oldest fabrication techniques humans have used, from bronze-age metal casting to modern industrial injection moulding.

The process has two distinct stages:

Moulding is the process of creating the mould itself which is the the negative cavity that defines the shape of the final part. In Fab Academy, we machine a positive form into wax using a CNC mill, then pour a flexible silicone rubber over it. Once the silicone cures, it peels away as a reusable mould that holds the exact shape of what we machined.

Casting is the process of filling that mould with a material that will harden into the final part. The casting material can be almost anything that starts as a liquid and solidifies — resins, plaster, concrete, metals, chocolate. We typically use urethane resin or hydrostone in the lab because they are safe to handle, cure at room temperature, and produce rigid, durable parts.

The reason this process is so useful is the decoupling it creates. The hard work happens once, at the moulding stage, getting the geometry right, machining it cleanly, producing a good silicone. After that, casting more parts is fast and repeatable. The silicone mould can typically be used dozens of times before it degrades.

In Fab Academy, we go through the full chain: design a part in CAD → machine the positive in wax → cast silicone to make the mould → cast the final material → demould the finished part. Each step depends on the one before it, so understanding the whole process before starting the design is important.

Design

For my individual assignment, I decided to design a decorative candle mould.

A cylinder is a clean, simple form that translates well to casting, but I wanted it to have some character, so I added embossed surface decorations using SVG artwork before working out the mould strategy.

Adding the Decorations

I started with a cylinder body in Fusion 360 representing the candle.

To add the decorative elements, I used the Insert SVG workflow. Fusion lets you place an SVG file directly onto a face or curved surface as a sketch, which you can then use as a profile for embossing.

Embossing the Decoration

With the SVG sketch on the surface, I used Fusion 360's Emboss tool (Create → Emboss) to raise the cloud profile off the cylinder surface.

The Emboss tool takes a sketch profile and either raises or recesses it relative to the face of a solid body by a specified depth. It handles the geometry of wrapping onto curved surfaces automatically, which would be very difficult to do manually.

Splitting the Body

A solid cylinder cannot be demoulded from a single-piece mould, the curved walls would trap the cast part. To solve this, I used Split Body to cut the cylinder in half along its central axis.

After splitting, I had one half of the candle with the embossed cloud and sun decorations on the curved side, and a clean flat face where the cut was made. This half became the positive for my mould.

Creating the Mould Box

The final step in the design was encasing the candle half inside a rectangular box. This becomes the mould housing that will be machined into wax.

CAM Setup

With the mould design finished, the next step was generating the toolpaths that would drive the CNC machine. Fusion 360 handles both design and CAM in the same file, you just switch workspaces.

Switching to the Manufacture Workspace

I switched from the Design workspace to the Manufacture workspace using the workspace dropdown at the top left. The Manufacture workspace is where Fusion generates toolpath strategies.

It reads the same 3D body from the design but now interprets it as a stock to be machined rather than a shape to be built.

Importing the Lab Tool Library

Before creating any toolpaths, I needed to set up the correct tools. Rather than manually entering tool dimensions, our lab provided a pre-configured tool library, Academy_Fusion360_Tool_Library_updated, which contains all the bits physically available at the lab with their exact dimensions and cutting data already set.

I opened the Tool Library from Manage → Tool Library.

Inside the Tool Library, I right-clicked on Library under the Local section in the left panel and selected Import libraries. This opens a file picker where you can load a .tools library file. The lab had shared their library file which I selected to import.

Once imported, the Academy_Fusion360_Tool_Library_updated library appeared under Local with all seven tools pre-configured with correct dimensions and cutting data:

• Tool 1 — ⌀3.175mm 30° V-bit (Engrave/Chamfer)
• Tool 2 — ⌀0.4mm Flat end mill
• Tool 3 — ⌀6mm Single Flute flat end mill (40mm flute, 70mm overall)
• Tool 4 — ⌀6mm Single Flute flat end mill (42mm flute, 70mm overall)
• Tool 5 — ⌀6mm Single Flute flat end mill (32mm flute, 60mm overall)
• Tool 6 — ⌀3.175mm Single Flute flat end mill (25mm flute, 50mm overall)
• Tool 7 — ⌀3.175mm Ball end mill (18mm flute, 58mm overall)

Having the lab library loaded means I can pick tools by name when setting up operations, and the cutting speeds and feeds are already calibrated for the machines in the lab.

Creating a New Setup

With the tool library loaded, the next step was creating a Setup. In Fusion's Manufacture workspace, a Setup is the first and most important step before generating any toolpaths.

It defines the stock material, the orientation of the part on the machine, and sets the Work Coordinate System (WCS) zero point, which is the reference position the machine uses for all its moves.

I clicked Setup → New Setup to create one.

Setting the Stock and WCS Origin

After creating the setup, Fusion displayed the mould model surrounded by a stock bounding box. The tan-coloured box represents the wax block that will be physically placed on the machine bed. The white dots around the corners and edges are the stock point handles, which let you choose where the WCS origin sits.

The WCS origin (shown by the X, Y, Z axis arrows) tells the machine where zero is. By default, Fusion placed the origin near the top of the model.

I moved the origin to the bottom-left corner of the stock box.

The Orientation dropdown under the WCS section controls how Fusion determines the X, Y, Z axes relative to the model. I opened the dropdown and selected Z axis/plane & X axis. This lets me manually pick an edge or face for the Z axis and another for X.

After selecting that option, the Z Axis and X Axis fields appeared as Select buttons, ready for me to pick edges from the model to define the coordinate system.

I selected edges from the mould box for both axes.

The 3D view updated to show the WCS origin at the front bottom-left corner of the stock, with X pointing right, Y pointing up, and Z pointing toward the front face making sure that the machine will approach the mould from the correct direction.

The Stock tab defines the physical wax block the machine will cut into. I set the mode to Relative size box with all offsets at 0 mm so the stock matches the mould body exactly.

Post Process Settings

The Post Process tab sets the program number that will be written into the G-code file header, and the WCS offset which tells the machine which coordinate offset register to use. I left the program number as 1001 and the WCS offset at 0, which are the standard defaults for the lab machines.

Toolpath Generation

With the setup configured, I moved on to creating the actual toolpaths. I used a 3D Adaptive Clearing strategy, this is a roughing operation designed to remove large amounts of material efficiently while keeping the tool load constant at every stage to avoid breakage.

Adding the Adaptive Clearing Operation

I selected 3D → Adaptive Clearing from the toolbar.

Once created, the operation appeared in the CAM browser as Adaptive1 nested under Setup10, ready to be configured.

Tool — Selecting the Cutter and Feed Rates

Opening the Adaptive Clearing dialog shows the Tool tab first. This is where I selected the cutter and set the cutting speeds.

I chose tool #5 — Ø6mm flat (6mm Single Flute) from the lab library.

On the Geometry tab I set the machining boundary to the inner rectangle of the mould box cavity. This restricts the tool to the area inside the cavity walls and prevents it from cutting outside the pocket. Tool Containment was set to Tool inside boundary. The stock definition was set to Remaining stock from previous operation(s), so if a second pass is added later it will only cut what is left over.

The Heights tab controls how high the tool travels between cuts and how deep it goes. The coloured planes visible in the 3D view correspond directly to these values:

• Clearance Height: Retract height + 10mm — the safe travel height when moving between passes
• Retract Height: Stock top + 5mm — where the tool pulls back to between cuts
• Top Height: Stock top + 0.25mm — where cutting begins, just above the surface
• Bottom Height: Model bottom + 0.25mm — the deepest the tool will go, leaving a thin floor

The Passes tab sets how the tool moves through the material on each cut:

The Linking tab controls how the tool moves when it is not cutting, that is, retracting between passes, leading in and out of cuts, and ramping into the material:

• Retraction Policy: Minimum retraction — keeps the tool as low as possible between passes to reduce air time
• Allow Rapid Retract: enabled — uses rapid feed rate when retracting, speeding up the overall cycle
• Maximum Stay-Down Distance: 30mm — the tool stays down instead of retracting if the next cut is within 30mm
• Lift Height: 0.2mm — tiny lift over obstacles when staying down
• No-Engagement Feedrate: 900 mm/min — feed rate during non-cutting moves
• Ramp Type: Plunge — the tool enters the material by plunging straight down
• Ramp Clearance Height: 2.5mm — how far above the stock the tool positions before plunging

Simulating the Toolpath

With all the tabs configured I right-clicked the operation in the CAM browser and selected Simulate. Fusion's simulation replays the tool moving along every toolpath, shows the material being removed from the stock in real time, and highlights any collisions between the tool and the remaining stock.

Second Adaptive Clearing

The Ø6mm tool clears the bulk of the wax quickly but its diameter is too large to reach into the tight areas around the embossed cloud and sun details. To machine those zones I added a second Adaptive Clearing operation using the smaller #6 — Ø3.175mm Single Flute tool.

The Passes settings are scaled down for the smaller tool — the optimal load and stepdown values are proportionally reduced to keep chip load safe on the 3.175mm cutter.

Pocket Clearing — Decoration Edges

I added a third operation — 3D Pocket Clearing — to clean up the material immediately around the embossed cloud and sun outlines. Adaptive Clearing can leave small ridges next to raised features because the tool steps over in wide arcs. Pocket Clearing traces the boundary contours directly with smooth offset passes, which removes those leftover cusps cleanly.

Flow — Surface Finish

The final operation was a Flow finishing pass using the #7 — Ø3.175mm ball end mill. Flow follows the isocurves of the selected surfaces with evenly spaced passes, which produces a smooth finish on curved geometry. I targeted the three curved faces of the candle body with a 0.15mm stepover and 0.01mm tolerance to bring the surface quality up to a level that will produce a clean silicone impression.

Full Simulation

With all four operations configured, I right-clicked Setup10 in the CAM browser and selected Simulate to run the entire toolpath sequence in one pass.

Machine Setup & Milling

With the toolpaths verified in simulation, I moved to the CNC milling machine.

First you have to specify the stock point on the wax block.

For this I first secured the wax block on the machine. I made sure that it was properly clamped.

Then I loaded the Edge Finder tool in the spindle collet.

I used the edge finder to locate the edges of the wax block and set the origin accordingly.

After loading the tool, the screen shows the coordinats of the tool in real time. We have to set the X and Y coordinates to 0 at the stock point.

For this, first I lowered the tool through the screen. Then I manually adjusted the Z height using the levers.

With the origin set, I started the first tool run, the roughing pass to remove the bulk of the wax material.

After the roughing pass, I ran the finishing pass to get the smooth surface finish required for a clean silicone mold.

Once both passes were done, the wax mold was complete. The cavity came out clean with no visible tool marks.

Before pouring the silicone over the mould, I needed a way to hold the two wax halves together when pouring the wax into the silicone. For this, I designed two interlocking acrylic frames in Fusion 360 and laser cut them.

I filled the assembled frame with water first to measure how much silicone I would need before mixing it. Then I poured iut into a transparent glass and marked the water level using a tape.

Then I emptied the glass, made sure there were no water left behind and poured in the silicone.