Common precision casting defects have bubbles, the bubbles is refers to the individual location precision casting present lubrication hole defect.Bubbles are usually talents were found after machining.Dongguan precision casting technology personnel separation workshop consumption experience for many years, presents the cause of the bubbles in the precision casting:A, constitute the reason:1. Most of the cases present bubble is mainly due to the fine casting exterior shell roasting is not abundant, when pouring molten steel shell suddenly produce a large number of gas cannot successful eduction, which constitute a bubble in liquid metal into the;2. Because of the cause or shell mold material shell making technology, shell permeability is poor, is difficult to exhaust gas in the cavity, into the metal liquid in a bubble;3. When pouring into fails to discharge the air in the molten steel castings bubbles to form.