Manufacturing process

How Cast Iron Products Are Made The World of Sand Casting

STEP 1 Creating the Pattern (Model)

The first step is to create a pattern that matches the shape of the final casting.
These models are typically carved from materials such as iron, aluminum, or wood.
In recent years, 3D-printed resin patterns have also become common.
The accuracy of this pattern greatly influences the final product.

STEP 2 Making the Sand Mold

A sand mold is created to form the shape of the casting.
At Yoshiwa Kogyo, we use a method called the “green sand process.”
This involves mixing sand with clay and water, then compressing it firmly to form a strong mold.
The pattern is pressed into the sand to form a cavity in the desired shape, which will later be filled with molten metal.

STEP 3 Melting the Iron

Next, cast iron is melted at high temperature.
Cast iron is a material made by adding a few percent of carbon (graphite) to iron.
It becomes liquid at around 1,200°C. This molten metal is called yōtō (molten iron).
Because of the extreme heat, it is melted in a special furnace and transported safely in a container called a ladle.

STEP 4 Pouring the Molten Metal

The molten iron is carefully poured into the sand mold, a process called chūtō (pouring).
Inside the mold, the metal slowly cools and solidifies.
The cooling speed and method affect the mechanical properties of the casting, making this a critical quality control step.
Once cooled, the metal takes the shape of the mold.

STEP 5 Removing the Casting (Shakeout)

After the casting has solidified completely, the sand mold is broken apart to remove the casting.
Although the mold is destroyed, the sand is recovered and reused for new molds.
At this stage, the casting still has gates and risers attached, and requires further finishing.

STEP 6 Finishing and Inspection

The surface of the casting is cleaned, often using a shot blasting process where small steel balls are used to remove surface residue.
Excess material (burrs, flashes) is removed using grinders.
Some processes now use automated systems for precision finishing.
Finally, the casting undergoes inspections for appearance, dimensions, hardness, and other quality criteria.
Only after passing these checks is the casting considered ready for use in everyday products.