Investment vs Sand Casting

Investment casting would give you a better surface finish and dimensional accuracy than sand casting.

In investment casting, the pattern is made by injecting liquid wax (or similar materials) into a metal mold in the shape of the pattern. Several such patterns are attached together to make a "tree". This "tree" is dipped in a refractory slurry repeatedly, which forms a skin around the pattern accordingly. After this the entire tree is placed in an oven until the wax has melted away. You get a mold of the required shape. Several of these are attached to a common sprue (or similar gating system), and molten metal is poured into it. When the metal solidifies, the mold is hammered, and the casting is removed.

Whereas:

In sand casting, the mold is made usually with moist sand and baked until adequate strength is achieved. Impressions of the pattern are obtained in the mold sand by rapping it around the pattern (in the cope and drag). Cope (upper half of mold box) is also provided with a pouring basin, risers and vents. Molten metal is poured into the pouring basin -> sprue -> runner -> gates -> mold cavity. Cope and drag are separated, and the solidified casting is withdrawn.

You can minimize the chances of blow-holes by using certain die-casting methods.

Thank you very much.