SAND CASTING

Step 1:Making the Pattern of Desired part

This technique utilizes reusable pattern with the same details as the desired finished part. There is thermal contraction or shrink allowance also provided.

Step 2: The second step is to set up the metal delivering system.
The pattern produced in previous step, in which the metal pathways that will feed the desired cast product design with appropriate gating and risers. This drives the inevitable thermal contraction to desirable regions(someplace apart from the actual desired finished product), and manages the metal flow with required gas venting.

Patterns are made of different materials like wood, metal, synthetics, etc. Which depends on the required volume and tolerance values.

Step 3: Mold Creation

The important part in this process is developing the mold.

A high temperature refractory material which is stable at high temperature (sand, in our instance) is formed across the pattern. The material must be sturdy enough to hold the weight of the molten metal throughout casting and resistant to any reaction with the metal, yet brittle sufficient enough to be in ease to get removed away by breaking it from the solidified metal after the casting cools.

Alternatively, the mold can be created through machining the desired shaped cavity directly into the block of sand. This approach is broadly used during product development because design modifications can be controlled and implemented fast, or for parts with infrequent utilization to avoid the storage or preservation of a physical pattern. The mold is typically produced in two pieces, the top half [which is called as “cope box”] and the bottom half [called as “drag box”]. Once the sand is set (either using the traditional or non-machined method), the halves are separated, and the pattern is removed. A refractory coating is provided additionally for better surface finish and protect the mold from the turbulence of the poured metal. The halves are positioned back together, leaving a cavity in the shape of the pattern.

The mold can also contain “cores”, which are used to produce internal passage ways in the final product as desired by the clients requirements.

Step 4: Pouring the molten metal
Molten metal is poured directly into the static mold. It fills the cavity of both the finished part and risers. The risers gets filled with an available supply of liquid metal. As they are designed to cool and solidify last, the shrink is concentrated in the riser rather than in the desired part. There are numerous alternate ways of “tilt pouring” are available. It is a procedure designed to allow metal to flow effortlessly into the casting, eliminating turbulence. Less turbulence can assist preventing the creation of oxides and other casting defects. For those materials mainly reactive with oxygen, a procedure such as argon shielding may be employed to keep air away from the molten metal.

Step 5: Shakeout
The casting, which includes both the desired part and the additional metal required to create it, solidifies and cools. The sand is broken away in a shakeout manner. Much of the sand which is used to create the mold is collected, reconditioned, and can be utilized again.

Step 6: Post machining operations.
This is the final step of this casting process. The gates, runners, and risers are shrug off from the casting, and if vital, final post-processing sandblasting, grinding, etc., are performed to finish the casting process. Sand castings often require atleast a few additional post machining to reach final dimensions or tolerances.