Gravity casting and sand casting are two different casting process, their differences are mainly reflected in the following aspects:

1. different principles: gravity casting is the use of gravity to make molten metal flow into the mold to form the casting process, while sand casting is first made of sand casting molds, and then pour the molten metal into the molds, to be solidified after the metal to take out the casting.

2. Different mold materials: gravity casting generally use metal molds, such as copper, iron, etc., while sand casting uses sand as the mold, sand can be made according to the need, common quartz sand, natural sand and so on.

3. Different scope of application: gravity casting is suitable for the production of large castings and high-precision castings, such as ships, aerospace and other fields; while sand casting is suitable for the production of small and medium-sized castings and castings of complex shapes, such as automobiles, machinery and other fields.

4. Different production efficiency: gravity casting production efficiency is higher, can achieve continuous production, while sand casting production efficiency is lower, need to make molds and cleaning molds, production cycle is longer.

5. Different cost: gravity casting mold cost is higher, but can be used repeatedly, lower production cost; and sand casting mold cost is lower, but need to be replaced frequently, higher production cost.

In summary, the difference between gravity casting and sand casting is mainly reflected in the principle, mold materials, scope of application, production efficiency and cost, etc., choose the appropriate casting process needs to be based on specific production needs and product requirements to decide.