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 8 A s lightweighting has become an im- portant trend in automotive manu- facturing over the past several years, the wheel industry has followed suit. Because aluminum alloys feature low density, light weight, high corrosion resistance, and good heat transfer per- formance, they are widely used to make wheels. Casting and forging are the pri- mary methods used to manufacture alu- minum alloy wheels. Casting imparts moderate mechanical properties—good enough to meet the needs of most wheels—while the rate of finished prod- ucts with few defects is high, and the cost is low. Wheels produced by forging fea- ture high mechanical properties, in- cluding tensile strength 1.3 to 1.5 times that of cast wheels, elongation 1.2 to 1.5 times greater, and weight reduction of 5-10% versus a cast wheel with the same specifications. Although forged wheels provide a lightweighting advan- tage over cast wheels, they are more ex- pensive due to higher equipment costs and more involved production steps. However, due to the performance ad- vantages of forged wheels, certain au- tomotive categories such as bus fleets often use them. And with recent growth in the forged wheel market, prices are becoming more competitive with cast versions. As the market is expanding, factors such as metal utilization rates are becoming increasingly import- ant—with rates for forged wheels now climbing above 60% in some cases. With bus wheels, a grooved struc- ture exists at the junction of the wheel’s rims and spokes. Some wheels have a deeper shape than others, and weight can reach as high as 2 kg. To achieve efficient metal utilization, the groove shape must be forged when the blank is forged. During production, the groove is a location where folding defects are easily generated. How to solve the fold- ing problem at this spot is a perplexing issue for the entire wheel industry. To address this defect, the authors used modeling as the primary tool to ana- lyze and optimize the process. PROCESS DETAILS The process of forging wheels be- gins with using a large press to apply pres- sure to aluminum alloy bars to generate plastic deformation to make wheel blanks. During production, a spray disc is used to deliver lubricant before bar is placed into the mold. The press is then run un- til the mold is closed. Finally, the press opens the mold and removes the wheel blank. According to factors such as spe- cific wheel requirements and the type of forging equipment, specific steps in- cluding pre-forging and final-forging are often involved. In this study, a forged aluminum bus wheel design is explored. In order to improve the metal utilization rate, the groove is designed at the indented DEFECT ANALYSIS AND PROCESS OPTIMIZATION FOR FORGED ALUMINUM WHEELS Modeling and simulation are used to solve the problem of folded grooves, a common occurrence during aluminum wheel forging. Jing Li, Qinhuangdao Discastal-Xinglong Wheel Manufacturing Co. Ltd., China Jian-fang Liu, Research Center of Light Alloy Wheel Engineering of Hebei Province, China Fig. 1 — Forging process design steps include pre-forging and final-forging. Pre-forging Final-forging Fig. 2 — (a) pre-forging flange; (b) final forging flange; and (c) section after cutting final forging blank. (a) (b) (c) ok