灰铸铁和球墨铸铁前托架钻削性能评价

从导热系数、铁屑形貌、钻孔内表面粗糙度、钻头顶部温度、钻削负载(扭矩、进给力)等方面,评价了QT450和HT250材质拖拉机前托架的钻削性能,并分析了钻削性能与微观组织的关系。结果表明,对HT250和QT450前托架钻削加工时,两者钻削负载没有明显差别;与HT250相比,QT450的石墨对基体的分割作用小,其基体组织中较多的铁素体,造成钻削加工时断屑和排屑困难,导致钻孔内表面粗糙度大;QT450导热系数低、铁屑与钻头摩擦严重,使得钻头温度较高;QT450有较小的切削力和铁屑对钻头较大的摩擦力,在这2个力作用下,QT450钻削负载与HT250基本相同。

Drilling-ability Evaluation for Grey Cast Iron and Ductile Iron Front Brackets

The drilling-ability of HT250 and QT450 used in front brackets of tractors has been evaluated in terms of thermal conductivity, chip shape, surface roughness in the drill hole, temperature of drill top and drilling load (torque, feeding force). The relationship between the drilling-ability and microstructure is analyzed. Experimental results show that drilling load of two front brackets was roughly same. Compared with the HT250 tractor front bracket, the one of QT450 has a larger surface roughness in the drill hole and a higher temperature of drill top. This is mainly because QT450 has a weaker graphite segmentation effect to matrix and a higher ferrite content, there is certain difficulty in chip breaking and chip removal during drilling, which leads to the larger surface roughness in the drill hole of QT450. The smaller heat conductivity coefficient and severer friction between the drill and chip result in the higher temperature of drill top. Moreover, QT450 has a smaller cutting force and a larger friction force between the drill and chip. Under the comprehensive function of the two forces, QT450 has nearly the same drilling load as HT250.