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方管的成型方法

1、实弯

　　实弯，顾名思义是压实了弯折，实弯时内外辊与管坯内外壁双向压实。

　　1)实弯的优点是反弹小，成型准确，而且只要辊型准确，内角成型的R比较准确。

　　2)实弯的缺点是有拉伸/减薄效应。靠前，实弯会使弯折处产生拉伸，拉伸效应使弯折线纵向的长度缩短; 第二，实弯弯折处金属会因拉伸而变薄。

2、空弯

空弯是通过外辊与管坯外壁的单向接触形成弯矩使带料弯折，空弯会使弯折线产生压缩，压缩效应使弯折线纵向伸长，弯折处金属出现堆积变厚，这就是空弯的压缩/增厚效应。

1)空弯的优点是可以在无法进行实弯时进行边长的弯折，比如方矩管的上边/侧边同步弯折和精整。空弯还可以弯折R<0.2t的内角而不致管壁发生断裂。

2)空弯的缺点是在上边/侧边同步空弯时，由于上辊和下辊同时产生压力，成型力容易超越临界点，造成边部失稳内凹，并且也会影响到机组稳定运行和成型质量。这也是方矩管和圆管空弯成型时不同的特点。

Forming method of square pipe
1, solid bend
Real bend, as the name implies, is compacted, inside and outside roller and tube billet inside and outside the wall bidirectional compaction.
1) The advantage of solid bending is that the rebound is small, the molding is accurate, and as long as the roller type is accurate, the R of the inner angle molding is relatively accurate.
2) The disadvantage of solid bending is the tensile / thinning effect. First, the real bending will cause the bending to produce a stretch, and the tensile effect will shorten the length of the bending line longitudinal; Second, the metal is thinned by stretching at the actual bend.
2, empty bend
The empty bend is formed by the unidirectional contact between the outer roller and the outer wall of the tube billet to make the material bend. The empty bend will cause the bending line to compress, the compression effect will make the bending line lengthen vertically, and the metal at the bend will accumulate and thicken. This is the compressive / thickening effect of the empty bend.
1) The advantage of an empty bend is that it can be bent when it is impossible to make a real bend, such as simultaneous bending and finishing of the top/side of the square moment tube. Empty bends can also bend R & lt; 0.2 T of the internal angle without fracture of the tube wall.
2) The disadvantage of the empty bend is that when the top / side is synchronized with the empty bend, due to the pressure generated by the upper roller and the lower roller at the same time, the forming force easily exceeds the critical point, resulting in the instability of the edge, and it also affects the stable operation of the unit. And molding quality. This is also a different feature of the square tube and the circular tube when they are formed.