At present, China’s high-grade CNC machine tools needed in important fields such as automobile, aviation, railway and national defense depend on imports for a long time. The poor machining accuracy and precision retention of machine tools is one of the important reasons why they can’t resist imports. Cast iron bed is the key basic component of machine tool, and its dimensional accuracy and accuracy retention are the key to affecting the machining accuracy and accuracy retention of machine tool. Machine tool and precision mechanical castings working under low stress state usually fail not due to fracture failure, but due to poor dimensional stability of castings.
ZHY casting is a bed casting of horizontal machining center exported to Japan. The material brand is HT300. The casting structure is complex, with a mass of 11940 kg and a size of 4060 mm × 2 970 mm × 1 440 mm, with main wall thickness of 20 ~ 110 mm.
Molten iron is melted in a 10 t cupola with chemical composition of W (c) 3.1% ~ 3.2%, w (SI) 1.6% ~ 1.8%, w (MN) 0.8% ~ 1.0%, w (P) ≤ 0.1%, w (s) 0.06% ~ 0.1%. Two 10 t pouring ladle are used to pour the casting. The tapping temperature is 1 490 ~ 1 510 ℃, the pouring temperature is 1 370 ~ 1 400 ℃, and the pouring time is 70 ~ 100 s. The inoculant is 75sife, the addition amount is 0.5% ~ 0.6%, and the boxing time is more than 120 h.
The production results show that the metallographic structure of the guide rail surface of the bed is A-type graphite, the volume fraction of pearlite is more than 98%, the tensile strength is 310 ~ 340 MPa and the hardness is 180 ~ 200 Hb.
In recent years, although nodular cast iron, vermicular cast iron and various light alloy castings have developed rapidly, due to the unique multiple superior properties and relatively cheap price of gray cast iron, its dosage is still large and its application is still wide. Therefore, further strengthening the research of gray cast iron and giving full play to its potential functions is still an important topic that the casting industry must continue to study.