With the development of automobile industry and China's accession to WTO, the quality and cost price of automobile forgings in domestic and international market are becoming more and more demanding, such as draft angle, weight tolerance, size, machining allowance and other requirements are very high, and the price is not ideal, but the batch is very large. In order to meet the market demand, this paper analyzes and practices the technology repeatedly, and finds an ideal technology, which is of great significance to the production of similar products.

　　Product introduction and determination of process plan

　　Product introduction

　　The arm is a part used for the brake pump of heavy duty vehicle, and its structure is shown in Fig. 1. There are several difficulties in forging: (1) the draft angle is small, only 3 ° outside and 5 ° inside, while the ejector has only one place in ∮ 62 hole; (2) the machining allowance is small, and only boring and broaching are used for machining ∮ 62 and 23.2mm square groove; (3) the 10 nails of 10 - ∮ 6.2 * 5 are full of difficulties and have high position requirements, and the root fillet of the nail is r0.2, which makes the mold wear faster and the production flow faster In the process, it is easy to bump and cause deformation.

　　Determination of process plan

　　In order to adapt to mass production and improve efficiency, we have determined the following processes: (medium frequency furnace) heating / (cross wedge rolling) blank making / (25000kN hot die forging press) bending / pre forging / final forging / (3150kN double point press) punching / trimming / normalizing / shot blasting / precision pressing. In the technological process, two pieces are used at a time for heating, the part handle is long and thin, and the efficiency of free forging single piece is low. Use wedge cross rolling blank (as shown in Figure 2), and cut into two pieces on the rolling mill at the same time. Because the cross-section of the part changes greatly, from ∮ 55 to ∮ 23, it needs two wedges to complete, so it is difficult to process and repair the rolling die.

　　In addition to ensuring the size of pressing head and handle, it is more important to correct the position of 10 nails, the fillet of root and the bending of handle. Therefore, two standard pressing plates with five holes are used to ensure the position of the nail and the round corner of the root, thus improving the service life of the forging die.

　　Key points of mold design and manufacture

　　Generally, in the design of the press bending die, only the shape bending of the extruded blank is considered to be consistent with that of the forging. Because the thickness difference between the big end of the arm and the handle is large, when the pre forging die is put in, the handle of the bent blank will be suspended. During the pre forging, the transition between the handle and the big end will be folded. Because the handle of the bent blank is suspended, the metal flow in this part is too large during the pre forging. Therefore, the design of the bending blank must make the bending blank on the pre forging die to make its shape consistent with the pre forging die.

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