The drawing process is a common method in the forging production process. The drawing process of the forging blank is a forging process in which the cross section of the blank is reduced to increase its length. The function of drawing is to obtain a shaft forging with a smaller cross-sectional area and a longer axial length from a blank with a larger cross-sectional area. Perform local deformation as an auxiliary process. In fact, it is similar to the repeated heading process. The drawing process of forging production is to compress and deform the blank by successively feeding and repeatedly rotating it, which eliminates many man-hours.
1. Main quality problems and deformation flow characteristics during pulling
(1) Quality problems: cracks, surface folding, end face concave, uneven structure and performance.
(2) Deformation characteristics when pulled out for a long time:The deformation of the blank during drawing is somewhat similar to that of upsetting. It is upsetting with undeformed metal at both ends. When drawing, the attention should be paid to the effect of drawing speed and drawing length on the quality of forgings.
In addition to affecting productivity, the feed amount also affects the quality of forgings. When the feed amount is too small and the thickness of the blank is relatively large, there will be a phenomenon that the forging is not penetrated. The internal deformation of the billet is small and axial tensile stress will be generated, which may occur. Causes cracks inside the forging. Excessive feed amount will cause external transverse cracks and internal longitudinal cracks. Therefore, the feeding amount also needs to be considered based on the thickness of the blank.
The reduction amount refers to the difference in thickness of the blank before and after deformation. The reduction amount for each hammering should not be too large. Generally, the width-to-height ratio of the section after pressing should be less than 2 to 2.5 times. Otherwise, it will be reversed by 90° during the second forging. Will produce bends resulting in folds. During the drawing process, the temperature of the forging blank is moderate and uniform. The hammering must be fast, and the severity of the hammering shall
be based on the ability to penetrate the forging.
2. Preventive measures for defects when the blank is pulled out for a long time:
① Surface transverse cracks and corner cracks. The former is caused by excessive feed and excessive compression; the latter, in addition to deformation, is mainly due to temperature loss at the corners and the
production of temperature stress, causing excessive surface tension. big.
②The surface folding is mainly due to the feed amount being too small.
③The internal transverse cracks are also due to the fact that the feed is too small, resulting in double drum-shaped features, causing axial tensile stress.
④ Internal longitudinal cracks are caused by excessive feed and small reduction, resulting in central tensile stress.
⑤ The concave end face is caused by the feed amount being too small, the surface metal deforming greatly, and the axis not having time to deform.