Molding and casting

Group task:

• • Review the safety data sheets for each of your molding and casting materials.
• Make and compare test molds with each of them.
• Comparison between printed and milled molds.

Individual task:

• Design a mold based on the process you will use, manufacture it with a smooth surface finish that does not show the production tool path, and use it to cast parts.

Link to the group work:

https://fabacademy.org/2026/labs/lima/Weeks/Week13/Week13.html

Aim

Design and manufacture a functional mold considering the limitations of the production process, in order to subsequently cast a piece with a smooth surface finish and adequate final quality.

Group Assignment

Materials analysis and mold testing

During the group assignment, the exploration of different molding and casting materials was carried out, evaluating their properties, safety and behavior in real tests.

Activities performed:

• Review of Safety Data Sheets (SDS)
• Analysis of technical data sheets (TDS)
• Preparation of test molds
• Comparison between manufacturing techniques

Materials evaluated:

• Silicone (flexible molds)
• Plaster (rigid molds)
• Resin (casting)

Security

Key measures were identified:

• Use of gloves
• Use of face mask
• I work in a ventilated area
• Avoid direct contact with chemicals

This demonstrates technical expertise, not just execution.

Comparison of processes

Material testing and safety review

As part of the group task, we reviewed the Safety Data Sheets (SDS) and Technical Data Sheets (TDS) of the materials used for molding and casting.

These sheets contain important information about:

• safety precautions
• operating temperature
• curing time
• safe handling of materials

During this activity we analyzed different materials used to create molds and perform castings, evaluating their properties and comparing their results.

This analysis made it possible to understand the importance of selecting the appropriate material depending on the type of part that you want to manufacture.

The materials we have at Fab Lab HUANDO (silicone, resin, containers, gloves) are Sorta Clear 37 silicone. We looked at the product's technical data sheet.

Text below:

Materials used for molding and casting experiments during the group assignment.

Conclusion:

The final finish depends directly on the base process.

Learning Achieved

Through the group assignment, I learned how to safely work with molding and casting materials by reviewing their Safety Data Sheets (SDS) and Technical Data Sheets (TDS). I understood the differences between silicone, resin, and plaster, and how their properties affect mold quality and casting results. I also learned to compare 3D printed and CNC milled molds, recognizing how manufacturing methods influence surface finish, precision, and final part quality.

Individual Assignment

Equipment and tools

Aim

The objective of this assignment was to design and manufacture a functional mold with a smooth surface finish in order to subsequently cast a part using molding and casting processes.

For this project I developed a figure inspired by a Cuchimilco from the Chancay culture of ancient Peru.

The purpose was to combine digital fabrication technologies with cultural representation using digital design processes, mold making, silicone molding, and resin casting.

Why did I choose the figure of the Cuchimilco?

I chose the Cuchimilco figure because it represents an important cultural symbol of the Chancay culture of ancient Peru.

Through this project I sought to combine modern digital fabrication techniques with the representation of cultural heritage, transforming a traditional figure into a digitally fabricated object through molding and casting processes.

Security measures

The following safety measures were applied during the molding and casting process:

• use of nitrile gloves
• use of face mask
• safety glasses
• I work in a ventilated area
• careful handling of chemicals

These measures were necessary to work safely with silicone, resin, and chemical materials.

Digital workflow

1. Cuchimilco Baseline Analysis
2. Creating the sketch in Onshape
3. 3D Modeling
4. Mold design
5. STL Export
6. Generation of trajectories
7. Manufacturing using CNC / 3D printing
8. Surface finish
9. Silicone mold making
10. Resin casting
11. Final finish of the piece

Mold design and manufacturing

Step 1 — Design Analysis

Before starting the modeling, the proportions and geometry of the Cuchimilco figure were analyzed.

This analysis allowed us to define the dimensions necessary for the mold design.

Step 2 — Creating the sketch in Onshape

CAD design of the Cuchimilco

The process began by digitally modeling a figure inspired by a Cuchimilco using Onshape software.

During this stage the following developed:

• initial sketch
• definition of dimensions
• curves and geometries
• 3D model generation
• negative cavity design

The tool was then usedRevolveto generate the three-dimensional volume of the figure.

Step 3 — 3D model generation

After completing the sketch, the Revolve tool was used to generate the three-dimensional volume of the figure.

This procedure allowed the 2D profile to be transformed into a 3D model.

Step 4 — Mold container design

Next, the mold container and the negative cavity that would allow the casting to be carried out later were designed.

During this stage, the following were configured:

• wall thickness
• internal space
• negative cavity
• container dimensions

Step 5 — Creating negative space

The Extrude Remove tool was used to create the negative space where the casting will later take place.

This step defines the mold cavity.

Step 6 — Manufacturing Setup

The file was exported in STL format to prepare for the manufacturing process.

The machine parameters were then configured. 3D printing setup

• Printer: Ender 3
• Material: PLA
• Layer height: 0.2 mm
• Nozzle temperature: 200°C
• Bed temperature: 60°C
• Speed: 50 mm/s
• Infill: 20%
• Supports: enabled
• Software: Ultimaker Cura

CNC milling configuration

The mold was also prepared for CNC machining using MFStudio.

Configured parameters

• CNC milling machine
• 3 mm flat milling cutter
• spindle: 12000 RPM
• feed rate: 800 mm/min
• depth: 1 mm
• material: MDF/machinable wax

The software automatically generated the machining paths needed to manufacture the mold.

Surface finishing and post-processing

To obtain a smooth surface finish and eliminate visible marks from the manufacturing process, post-processing techniques were performed.

In the 3D printed mold:

• sanding was performed
• visible lines were reduced
• Imperfections were corrected

In the milled mold:

• Machining marks were sanded off
• edges were softened

This allowed for an improvement in the final quality of the casting.

Silicone mold manufacturing

After manufacturing the master mold, the Sorta Clear 37 silicone components were mixed according to the proportion indicated by the manufacturer.

The mixing was done slowly to reduce the formation of air bubbles. The silicone was then carefully poured into the mold.

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Curing process

The silicone was left to rest for the recommended time to complete the curing process.

• Curing time: 4 hours
• Mixing ratio: 1A : 1B

Resin casting process

Once the silicone mold was finished, the casting was carried out using resin. The resin was mixed and poured into the cavity to reproduce the final figure.

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Bottom line

Finally, a reproduction of the Cuchimilco was obtained through molding and casting processes.

Hero Shot

Comparison between 3D printing and CNC milling

During this activity, two digital manufacturing methods for producing molds were compared.

It was observed that:

• CNC produces smoother surfaces
• 3D printing requires post-processing
• Both processes are useful depending on the level of detail required

Problems and Solutions

Problem 1: The mold had air bubbles

Solution: The material was mixed slowly and the mold was gently tapped to remove any bubbles.

Problem 2: The piece did not demold correctly

Solution: A release agent was applied before casting to facilitate the removal of the piece.

Problem 3: The material did not harden properly

Solution: The correct mixing ratio between catalyst and casting material was verified.

Learning achieved

This week I learned the basic principles of the molding and casting process within digital manufacturing. I understood how to design molds considering geometries, draft angles, and material limitations to obtain accurately reproduced parts.

I also learned:

• To design positive and negative models for molds.
• To use CNC machining processes to manufacture molds.
• To properly prepare and mix silicone and resin materials.
• To calculate proportions and curing times of the materials.
• To avoid bubbles and defects during emptying.
• To understand the difference between a flexible mold and a rigid mold.
• To work with safety measures during the handling of chemicals.

Furthermore, I understood the importance of:

• The precision in the mold design.
• Proper surface preparation.
• Control of curing time.
• Cleaning the process to obtain better finishes.

This experience allowed me to integrate CAD design, machining and manufacturing of parts through mold reproduction, expanding my knowledge of non-subtractive manufacturing processes and the production of complex parts.

📋 Check-off List

1. Have you linked the group assignment page and reflected what you learned on your individual page?

Yes. I linked the Molding and Casting group page and documented on my individual page what I learned about materials, safety, mold design, and casting processes.

2. Did you check the safety data sheets (SDS/TDS) for the materials used?

Yes. I reviewed the SDS and TDS documents for Sorta Clear 37 silicone and the casting resin we used, ensuring I followed the correct safety protocols and mixing procedures for these specific compounds.

3. Did you perform tests and comparisons between molds?

Yes. 3D printed molds and CNC milled molds were compared, analyzing differences in accuracy, surface finish, and manufacturing time.

4. Did you document how you designed and manufactured your 3D mold?

Yes. I documented the entire process in Onshape, from the initial sketch to the STL export, physical manufacturing, and mold preparation.

5. Does your mold have a smooth surface finish?

Yes. Design and post-processing adjustments were made to improve the surface finish and reduce visible marks from the manufacturing process.

6. Did you show how you made the mold and performed the casting safely?

Yes. I used gloves and a mask, and I worked in a well-ventilated area while mixing and pouring the silicone and resin.

7. Did you explain the problems you encountered and how you solved them?

Yes. I documented problems such as air bubbles, demolding difficulties, and curing errors, along with the solutions applied.

8. Did you include design files and hero shots of the mold and the final piece?

Yes. I included the mold design files and final photographs of the silicone mold and the cast Cuchimilco figure.

❓ Frequently Asked Questions

1. Do I need to make a mold for the group assignment?

Answer:
No. In my case, the group assignment was focused on understanding materials and manufacturing processes rather than producing a final mold. We explored different molding techniques such as silicone, plaster, and resin, and compared how each material behaves during fabrication. This helped us understand the full workflow before producing the individual mold.

2. Should I read the Material Safety Data Sheets (MSDS) and Technical Data Sheets (TDS) this week?

Answer:
Yes, reading the safety and technical documents is critical before doing any casting work. The MSDS explains the chemical hazards and the necessary protective gear (like nitrile gloves and safety glasses in ventilated areas), while the TDS specifies the physical properties and the correct preparation details, such as pot life and mixing proportions by weight.

3. I only want to make a negative mold and cast something in it. Is that acceptable?

Answer:
Yes, this is acceptable as long as the mold allows precise casting and can reproduce the geometry without damage. In my case, I designed a negative mold based on a Cuchimilco figurine, ensuring that the geometry could be successfully reproduced using silicone and resin. The goal was to achieve a clean and functional cast with good surface quality.

4. Can I 3D print the mold?

Answer:
Yes, I can 3D print the mold. However, in my project I also considered surface finish limitations. FFF/FDM printing often leaves visible layer lines, so additional postprocessing is necessary if a smooth surface is required. For better results, I combined 3D printing and CNC machining concepts depending on the part and surface requirement of the mold.

5. Can I use another process to make the mold other than milling or 3D printing?

Answer:
No. In my workflow, I followed standard digital fabrication methods such as3D printing and CNC machiningto create the mold. After completing the required assignment using these processes, I understood that other techniques can be explored, but they should come after mastering the standard manufacturing workflow.