Brief Introduction To The Production Process Of Forged Aluminum Wheel

In general, all deformed aluminum alloys can be used for forging, but because the wheel forgings take strength as the main indicator, aluminum wheels should choose deformed aluminum alloys with high strength and easy heat treatment, such as 6061, 6082, and so on.

The blanks of forged aluminum wheels are generally cast rods with a diameter of 8 inches (26.7cm) or other specifications. The size, weight, chemical composition, microstructure, appearance quality, and hydrogen content of the blanks should be checked before use, and special attention should be paid to reducing the harmful effects of metal and non-metal impurities in the materials as much as possible. The harmful metal impurities in 6061 alloy are mainly Fe, and Fe forms FeAl3 in the alloy, which is harmful to the performance, especially to the elongation; Non-metallic impurities are mainly hydrogen and oxide film, one of its sources is the water in the refined gas, because water and aluminum will react, if there is hydrogen and oxide film, heat treatment after solid solution product inspection will be unqualified, in addition, they are also very harmful to the performance, will significantly reduce the elongation.

The forging of an aluminum wheel is the process of plastic deformation of the cast billet material in the hot state. Compared with the low-pressure casting, the production process has obvious differences.

The production process of forged aluminum wheels is generally: preforming → forging → spinning → heat treatment → machining → painting.

(1) Breakage: The primary process of the forging aluminum wheel production process is billet making, using swing rolling (rotary forging) technology to make cylindrical bar material into cake material, providing suitable billet for subsequent forging forming.

Swing rolling technology uses an upper die with a cone to locally process the blank by applying a tilt force to the rotating blank to achieve molding. This way can greatly reduce energy consumption under the premise of ensuring efficiency. Swing rolling can complete the work of more than 3,000 tons of ordinary press under the pressure of 250 tons. Another advantage is that the material inside the bar can be evenly distributed to the surface of the blank, forming a unique spiral metal flow line, thereby improving the overall surface and performance quality of the forging process. The initial temperature of the billet can be set above 500℃, and the preheating temperature of the mold is about 450℃.

(2) Forging: The forging process is to preheat the blank after high temperature, and forge the spinning front blank of the wheel after the press forging, mainly forging the wheel spoke and window parts. The press generally needs to choose 4,000 tons or higher tonnage equipment according to the different pressure required for wheel forming.

According to the different degrees of wheel forming difficulty, the forging process needs to consider the number of forgings, that is, several forgings on a press or initial forging and final forging on two presses. The overburning temperature of 6061 aluminum alloy is about 590 °C. Considering the temperature difference of the heating furnace is ±20 °C, the temperature of the forging blank should be controlled at about 500 °C. In order to prevent the production of large grains during the solution heating process, the final forging temperature is generally controlled below 450 ℃. The material of the forging mold is generally H13, and the mold temperature should be controlled at about 400 ℃.

(3) Spinning: Because of the structure of the wheel itself, the rim part of the wheel is difficult to forge, and it is necessary to rely on the subsequent spinning process to form the spinning process is to process the short rough rim part of the forged blank into the final wheel rim structure.

Spinning equipment generally chooses a vertical three-wheel strong spinning machine, or a horizontal spinning machine. Germany's vertical three-wheel strong wheel spinning machine rotary wheel head can be positive and negative two-way high-speed work feed, in one step can complete the rough spinning and finishing process, fewer auxiliary processes, supporting loading and unloading robots, turnover belt, is the key equipment in the forged aluminum wheel large-scale production line, production quality and efficiency are very high. According to the difficulty of forming the rim, the cold spinning or hot spinning process can be used.

By the pinning process, higher material density can be obtained, and mechanical properties can be significantly enhanced. The rim thickness of aluminum wheels can be reduced from 4.0 ~ 6.0mm (cast aluminum wheels) to 2.7 ~ 3.0mm (forged aluminum wheels).

(4) Heat treatment: Heat treatment is a process method to change the internal organization of the blank by heating it in the solid state, holding heat, and cooling it, to obtain the required mechanical properties.

Forged aluminum wheels generally use the T6 heat treatment process, that is, first solid solution treatment, and then artificial aging. Using this process, the tensile strength of each part of the 6061 forged aluminum wheel can reach more than 350 MPa. In actual operation, on the one hand, the solution temperature is increased to make the strengthened phase Mg2Si fully dissolved in the solid solution treatment, and the artificial aging temperature is correspondingly increased to precipitate Mg2Si to obtain the maximum strengthening effect.

(5) Cutting processing: the inner and outer surfaces of the wheel blank after spinning need to be cut by a CNC lathe, and the bolt holes and valve holes need to be processed by a vertical machining center. The CNC lathe and vertical machining center required for aluminum wheel cutting are special equipment for wheel processing.

(6) Surface treatment: The surface treatment process of aluminum wheels is divided into full coating, polishing, electroplating, finishing, etc.

Full coating production line, more equipment, large investment, but the production efficiency is high, suitable for mass production. Full coating is the most used surface treatment process for aluminum wheels, which refers to the wheel in the automatic production line using a high voltage electrostatic spray gun and a high-speed rotating spray gun for spraying, with coating thickness and color luster uniform, good surface quality, and saving paint. Paint needs to use environmentally friendly powder and water-based paint approved by customers. The wheel is pre-treated before spraying to form a chemical conversion film, which can improve the adhesion performance of the coating. The pre-treatment is an environmentally friendly chromium-free treatment.

Polishing process is recommended for forged aluminum wheels. Because the forged aluminum alloy has a dense structure and superior surface quality, it can achieve an appearance effect comparable to electroplating after polishing, and also avoid the environmental pollution of electroplating.