12. Molding and casting

Group assignment requirements

The group assignment for this week is the following: - 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

All molds used in testing different materials and techniques were sourced from the lab’s inventory, having been previously created by other individuals and past graduates of the Fab Academy

Material 1: Gypsum

Safety

• Wear eye protection and gloves when handling gypsum powder.
• Avoid inhaling gypsum dust by working in a well-ventilated area or using a dust mask.
• Follow the manufacturer’s safety recommendations provided on the packaging, or general saftey and instructions from other manufacturers.

General information

• Type: Casting gypsum
• Mixing ratio: 2:3 (water to gypsum) by weight
• Work time: Typically 10 minutes (depends on many factors like temperature and type)
• Cure time: Typically 30-60 minutes.
• Cured material state: Solid, opaque, white.
• Resources: Link

Process steps & Pictures

1. Measure the required amount of gypsum powder according to the mixing ratio (2:3). Use a scale for accuracy.

1. Gradually add the measured gypsum powder to clean water in a mixing container. Stir continuously to avoid lumps and ensure thorough mixing.

1. Continue mixing until the gypsum mixture reaches a smooth and homogeneous consistency, free from air bubbles, then pour into mold.

1. Tap mold ro remove trapped air bubbles, then carefully remove excess material if necessary.

1. Leave gypsum to cure and set in the mold.

1. Carefully remove cured part from mold.

Result

Opinion: Gypsum is a versatile casting material suitable for a variety of applications. It offers ease of mixing and casting, with relatively short curing times compared to other casting materials. However, it may require careful handling to achieve the desired consistency and avoid air bubbles in the final cast.

Material 2: Mold Max 60

Safety

• Wear appropriate personal protective equipment, including gloves and eye protection, when handling.
• Ensure proper ventilation in the working area.
• Follow all safety guidelines provided by the manufacturer.

General information

• Type: Silicone mold rubber
• Mix ratio: 100A:3B by weight
• Work time: 45 minutes
• Cure time: 24 hours
• Cured material state: Flexible, blue, translucent
• Datasheet and sources: Mold Max 60 Technical Bulletin

Process steps & Pictures

1. Weigh the required amount of Part A and Part B components according to the mix ratio.

1. Thoroughly mix Parts A and B together until uniform.

1. Pour the mixture into the mold.

1. Tap mold ro remove trapped air bubbles, then carefully remove excess material if necessary.

2. Leave silicone to cure and set in the mold.

1. Carefully remove cured silicone from mold.

Result

Opinion: Mold Max 60 is a versatile silicone mold rubber that offers good flexibility and tear resistance. It is suitable for a wide range of casting applications and provides reliable results with minimal shrinkage.

Material 3: Smooth-Cast 305

Safety

• Wear appropriate personal protective equipment, including gloves and eye protection, when handling.
• Ensure proper ventilation in the working area.
• Follow all safety guidelines provided by the manufacturer.

General information

• Type: Polyurethane casting resin
• Mix ratio: 1:1 by volume
• Work time: 2.5 minutes
• Cure time: 10 minutes
• Cured material state: Solid, white
• Datasheet and sources: Smooth-Cast 305 Technical Bulletin

Process steps & Pictures

1. Measure equal parts of resin and hardener.

1. Mix vigorously for 30 seconds.

1. Pour into mold.

1. Tap mold ro remove trapped air bubbles, then carefully remove excess material if necessary.

1. Leave resin to cure and set in the mold.

1. Carefully remove cured resin from mold.

Result

Opinion: Smooth-Cast 305 is a quick-setting resin that produces solid, white casts suitable for various applications. Its short work time makes it ideal for rapid prototyping, but careful mixing and handling are necessary due to the quick curing process.

Printing vs Milling Molds

For this comparison, we used the 4-finger mold from Naim’s individual assignment to demonstrate the differences between 3D printing and CNC milling for creating molds.

3D Printing:

• Machine: Ultimaker S5
• Time: Approximately 22 hours for each half.
• Process: Slicing the model using slicing software, such as Cura, to generate printable layers. The printer deposits material layer by layer to build up the final object. Extra fine layer thickness (0.6mm) was chosen to allow for the best possible surface finish for the mold.
• Result: Relatively smooth surface finish, suitable for intricate designs.
• Accuracy/Resolution: High, especially with fine layer heights.

CNC Milling:

• Machine: Shop Bot
• Time: Approximately 45 minutes for each half of the mold.
• Process: Generate toolpaths using CAM software like Fusion 360. The CNC machine carves the mold out of a solid block of wax material, following the specified toolpaths.
• Result: Precise and accurate, suitable for functional prototypes.
• Accuracy/Resolution: Excellent, depending on the milling bit used and machine calibration.

Comparison:

• Speed: CNC milling is significantly faster than 3D printing for creating each half of the mold.
• Surface Finish: 3D printing provides a smoother surface finish suitable for detailed designs, whereas CNC milling offers a highly precise finish ideal for functional parts.
• Material Use: 3D printing builds objects additively, layer by layer, which can result in less waste. CNC milling is a subtractive process, removing material from a solid block, which can produce more waste.
• Design Complexity: 3D printing is better suited for complex, intricate designs due to its layer-by-layer approach. CNC milling excels in creating precise, functional prototypes with excellent resolution, depending on the bit used and machine calibration.