Introduction


This week’s assignment is to make a mold and cast something in it. To be honest designing and making molds is my work.
so I go around and document one of the projects that I‘m doing this week.
I’m working in a casting factory as a mold designer and maker. For that, I have 2 CNC machines under my control one
of them is for metalwork and the second one for woodwork.

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to make this mold I will use the woodworking CNC 3 axis milling machine.
I’m going to use 18mm thickness MDF. obviously the cover is the 40-42mm thickness and I need to steek together 2 shits
of 18mm and a 6mm thickness MDF.
I’m going to make manhole cover from this drawing with few changes.

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foundery

A foundry is a factory that produces metal castings. Metals are cast into shapes by melting them into a liquid, pouring the metal into a mold, and removing the mold material after the metal has solidified as it cools. The most common metals processed are aluminium and cast iron. However, other metals, such as bronze, brass, steel, magnesium, and zinc, are also used to produce castings in foundries. In this process, parts of desired shapes and sizes can be formed.

pattern making

In the process of sand casting, a pattern is a replica of the original object to be cast. This pattern is used to make a negative cavity into which molten metal is poured during the casting process. Patterns typically used in sand casting include wood, metal, plastics and urethane or silicone rubber. Patterns are made of wood, metal, ceramic, or hard plastics and vary in complexity. A single piece pattern, or loose pattern, is the simplest. It is a replica of the desired casting—usually in a slightly larger size to offset the shrinkage of the intended metal. Gated patterns connect a number of loose patterns together with a series of runners that will be detached after shake-out. Segmented or multi-piece patterns create a casting in several pieces to be joined in post-processing. Match plate patterns are patterns with the top and bottom parts of the pattern, also known as the cope and drag portions, mounted on opposite sides of a board. This adaptation allows patterns to be quickly pressed into the molding material. A similar technique called a cope and drag pattern is often used for large castings or large production runs: in this variation, the two sides of the pattern are mounted on separate pattern plates that can be hooked up to horizontal or vertical machines and pressed into the molding material. When the parting lines between the cope and drag are irregular, a follow board can be used to support irregularly shaped, loose patterns. Sweep patterns are used for symmetric molds, which are contoured shapes rotated around a center axis or pole through the molding material. A sweep pattern is a form of skeleton pattern: any geometrical pattern that creates a mold by being moved through the molding material. When the pattern is to be removed from the sand mold, there is a possibility that any leading edges may break off, or get damaged in the process. To avoid this, a taper is provided on the pattern, so as to facilitate easy removal of the pattern from the mold, and hence reduce damage to edges. The taper angle provided is called the Draft angle. The value of the draft angle depends upon the complexity of the pattern, the type of molding (hand molding or machine molding), height of the surface, etc. Draft provided on the casting is usually 1 to 3 degrees on external surfaces (5 to 8 internal surfaces).

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for roughing I used pocket toolpath. I used a 16mm end mill with a 12mm shoulder. in finishing toolpath, I used a 10mm bullnose endmill. finishing I have done with two combined toolpath parallel and contour. There is one toolpath in Fusion 360 which is combining parallel and contour automatically that is named as steep and shallow but personally I don’t like it because it didn’t reduce machining time and make g code bigger and difficult for NC studio to run it.

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Metal melting

in our factory we are using 400kg induction furnace.An induction furnace consists of a nonconductive crucible holding the charge of metal to be melted, surrounded by a coil of copper wire. A powerful alternating current flows through the wire. The coil creates a rapidly reversing magnetic field that penetrates the metal. The magnetic field induces eddy currents, circular electric currents, inside the metal, by electromagnetic induction.[9] The eddy currents, flowing through the electrical resistance of the bulk metal, heat it by Joule heating. In ferromagnetic materials like iron, the material may also be heated by magnetic hysteresis, the reversal of the molecular magnetic dipoles in the metal. Once melted, the eddy currents cause vigorous stirring of the melt, assuring good mixing.

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  • 1 - Melt
  • 2 - water-cooled coil
  • 3 - yokes
  • 4 - crucible
  • Sand casting, sand mixture

    Molds made of sand are relatively cheap, and sufficiently refractory even for steel foundry use. In addition to the sand, a suitable bonding agent (usually clay) is mixed or occurs with the sand. The mixture is moistened, typically with water, but sometimes with other substances, to develop the strength and plasticity of the clay and to make the aggregate suitable for molding. The sand is typically contained in a system of frames or mold boxes known as a flask.


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    Sand casting and mold forming

    Sand casting, also known as sand molded casting, is a metal casting process characterized by using sand as the mold material. The term "sand casting" can also refer to an object produced via the sand casting process. Sand castings are produced in specialized factories called foundries. Over 60% of all metal castings are produced via sand casting process. There are six steps in this process:

  • 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.

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    Conclusion

    Molding and casting process is very simple and at the same time is a complicated process with small tricks which are very essential for the final result.