Moulding and Casting

Introduction

This week focused on the transition from digital design to physical manufacturing using moulding and casting techniques. The objective was to design a 3D mold, produce it with a smooth surface finish, and use it to cast high-quality parts.

I used SOLIDWORKS for the entire design process, focusing on lofted geometries and boolean operations to create a functional negative mold cavity.

Objectives

Tools & Equipment

Design & Hardware

• SOLIDWORKS: For 3D modeling and mold design.
• Production Equipment (FDM 3D Printer): Crucial settings were kept high-resolution to minimize steps.
• Silicone / Resin: Casting materials.

Safety Gear

• Nitrile Gloves
• Safety Goggles
• Respirator Mask (for chemical vapors during resin mixing)

Workflow & Implementation

2D Sketching

I started by creating a 2D sketch on the Top Plane. I used the Circle and Rectangle tools to define the footprint. I used Trim Entities to clean up the intersections.

Initial circle sketch on Top Plane

Adding rectangle geometry and geometric constraints

Trimming entity intersections to form a single continuous profile

Base Extrusion

The sketch was converted into a 3D base using the Extrude Boss/Base feature with a height of 1.50mm.

Base extrusion feature setup in SOLIDWORKS

Adding Reference Planes

To create a lofted shape, I needed a second profile at a higher elevation. I added a Reference Plane offset from the Top Plane.

Creating an offset reference plane for lofting

Sketching the Top Profile

On the new plane, I sketched a smaller circle. This serves as the end point for the lofting transition.

Sketching top circle profile on new reference plane

Initial lofting preview between top and bottom profiles

Lofted Boss/Base

I used the Loft tool to connect the base sketch to the top circle. This creates a smooth, tapered organic shape which is ideal for easy demolding.

Completed lofted positive feature model

Creating the Mold Cavity

Once the "positive" part was ready, I designed a rectangular block around it. Using boolean operations, I subtracted the part from the block to create the Negative Cavity.

Boolean subtraction creating the internal negative mold cavity

Final 3D Review

The final design shows the mold ready for production with smooth surfaces and proper draft angles.

Final 3D mold render with verified draft angles

Machine Preparation & Toolpath Settings

The mold was imported into Creality Slicer 4.8 to prepare the print files and configure explicit parameters to minimize manufacturing artifacts:

Imported STL geometry ready for slicing parameters setup

• Layer Height: 0.12 mm (Fine resolution to minimize stair-stepping)
• Infill Density: 20% Gyroid (For structural rigidity under casting compression forces)
• Print Speed: 45 mm/s (Slower speed to increase outer wall precision)
• Wall Count: 4 lines (Ensures no structural seepage or chemical leaking through microgaps)

After configuring the print profiles and support structures, the model was successfully sliced with an estimated print time of 33 minutes.

Sliced preview rendering estimated print time and layer paths

Post-Processing for a Smooth Surface Finish

FDM prints inherently present subtle layer ridges which will bind to casting materials or ruin structural aesthetic. To achieve a perfectly smooth finish free of production lines:

1. Mechanical Sanding: I progressively sanded the interior cavity using 400-grit, 800-grit, and finally 1200-grit wet sandpaper.
2. Surface Sealing: Applied a microscopically thin coating of low-viscosity epoxy glaze coat to fill remaining microscopic ridges and allowed 12 hours to cure.
3. Release Agent Application: Applied a thin spray layer of Universal Mold Release to prevent physical material adhesion.

Results

• Completed a precise 3D mold design in SOLIDWORKS.
• Ensured smooth surface finish by choosing appropriate lofting techniques and meticulous post-processing validation.
• Verified all dimensions for casting material volume calculation.

Hero Shots

Fabricated 3D printed negative mold

Final cast resin part with smooth surface finish

Challenges & Solutions

1. Non-manifold Geometry

Cause: Overlapping lines in the initial sketch.

Solution: Used the "Trim Entities" tool to ensure a single closed loop.

2. Surface Ridges

Problem: Rough transitions in the loft.

Solution: Adjusted the "Start/End Constraints" in the Loft property manager to "Normal to Profile".

3. Micro-Adhesion Demolding Issues

Problem: Cast pieces initially snagged on un-sanded perimeter layers.

Solution: Integrated a uniform draft angle of 3 degrees into the design files and performed the micro-sanding regimen outlined in post-processing.

What I Learned

• Difference between positive and negative mold design structures.
• Importance of Draft Angles for clean demolding without ruining parts.
• Using Reference Geometry (Planes) for complex 3D shapes.
• Safety precautions when handling casting chemicals (MSDS metrics, mandatory PPE usage, local ventilation parameters).

Downloads & Design Files