January_2021_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | J A N U A R Y 2 0 2 1 3 9 portion of the wheel flange to save blank weight and forging is divided into two steps, pre-forging and final-forging (Fig. 1). During forging, a constant pressure production mode was used with pres- sure set to 5500-7000 tons, the working speed of the slider was 8-15 s/mm, and the pressure holding time was 0-6 s. Lu- brication settings were 0-1500 ms for the upper die center area, 0-2000 ms for the other upper die area, and 0-1000 ms for the bottom die area. Results of the actual production included zero defects in the groove of the pre-forging flange, and good blank quality. However, the fi- nal-forging became folded in the groove of the wheel flange and was distributed for one week, which was apparent to the naked eye. A deep fold crack was discovered in the cutting sample of the wheel (Fig. 2). DEFECT ANALYSIS Based on this defect, the authors concluded that the design of the ini- tial and final forging steps is incorrect. More specifically, they suspected that the pre-forging design was causing metal to backflow and create folds. To verify this, a simulation analysis was conducted using DEFORM software from Scientific Forming Technologies Corp., Columbus, Ohio. Analysis results are displayed in Fig. 3. Metal flow con- ditions exhibit the following features: (a) flow is normal; (b) a metal flow prob- lem has occurred, with the flow direc- tion of the flange moving upward, the flange position pressed down by the mold, and the metal flow at the flange position flowing back, forming a fold; (c) the folding position moves to the outside of the flange; and (d) the fold finally moved to the outer corner of the flange, con- sistent with actual production results. According to both the physical production defects viewed on site and the simulation re- sults of the DE- FORM software, it appears that the folding of the rim groove is caused by the flow of metal in different directions during forming. In order to achieve bet- ter metal utilization, the design of the fi- nal-forging blank must be as consistent as possible with the shape of the final product. The flow direction of the metal can only be controlled by adjusting the shape of the forging blank to avoid met- al backflow at the flange. Fig. 3 — Analysis of metal flow direction in rim groove: (a) flow direction is normal; (b) and (c) problems with flow direction appear; and (d) final shape. (a) (b) (c) (d) Pre-forging Final-forging Fig. 4 — Three positions on the flange required adjustments. Fig. 5 — Problems during adjustment. Pre-forging Final-forging Fig. 6 — The solid line indicates the final blank, while the dotted line shows the initial blank.