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10. Molding and casting

Introduction

This week’s assignment is to make a mold and cast something in it. Designing and making molds is my area of expertise, so I documented one of the projects I worked on this week. I work in a casting factory as a mold designer and maker, managing two CNC machines: one for metalwork and the other for woodwork.

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To make this mold, I used the woodworking CNC 3-axis milling machine with 18mm thick MDF. The cover needs to be 40-42mm thick, so I glued together two sheets of 18mm and one sheet of 6mm MDF. I aimed to create a manhole cover based on a specific drawing with a few modifications.

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Foundry

A foundry is a factory that produces metal castings by melting metals into a liquid, pouring it into a mold, and removing the mold material after the metal solidifies. Common metals include aluminum and cast iron, with others like bronze, brass, steel, magnesium, and zinc also used. This process allows for the creation of parts in desired shapes and sizes.

Pattern Making

In sand casting, a pattern is a replica of the object to be cast, used to make a negative cavity for the molten metal. Patterns can be made from wood, metal, plastics, urethane, or silicone rubber. They vary in complexity from single-piece patterns to multi-piece or match plate patterns. Patterns must often have a draft angle to facilitate easy removal from the sand mold, with typical angles ranging from 1 to 3 degrees for external surfaces and 5 to 8 degrees for internal surfaces. CNC Machining

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For roughing, I used a pocket toolpath with a 16mm end mill and a 12mm shoulder. For finishing, I used a 10mm bullnose end mill, combining parallel and contour toolpaths. Although Fusion 360 offers a steep and shallow toolpath that combines these, I prefer separate toolpaths for efficiency and ease of use in NC Studio.

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Metal Melting

In our factory, we use a 400kg induction furnace. The furnace consists of a crucible surrounded by a coil of copper wire. An alternating current flows through the wire, creating a magnetic field that induces eddy currents in the metal, heating it by Joule heating and, in ferromagnetic materials, by magnetic hysteresis. The eddy currents also cause vigorous stirring, ensuring good mixing.

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    • Melt
    • water-cooled coil
    • yokes
    • crucible

Sand Casting

Sand casting involves using sand as the mold material. It is a cost-effective method suitable for steel foundry use, mixed with a bonding agent like clay. The sand mixture is moistened to develop strength and plasticity. Sand casting involves placing a pattern in sand, creating a mold, incorporating the pattern into a gating system, removing the pattern, filling the mold with molten metal, allowing the metal to cool, and finally breaking away the sand mold to remove the casting.

Mold Forming and metal pouring

  • Place a pattern in sand to create a mold.

  • Incorporate the pattern and sand in a gating system.

  • Remove the pattern.

  • Fill the mold cavity with molten metal.

  • Allow the metal to cool.

  • Break away the sand mold and remove the casting.

  • The metal is poured into the mold through a hollow channel called a sprue. The metal and mold are then cooled, and the metal part (the casting) is extracted

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Conclusion

The molding and casting process is both simple and complex, requiring attention to small details that are crucial for achieving the desired final result.

Files

3d model