Screwdriver is one of the on-board tools of 150 series high-power and high-speed diesel engines, and most of its forgings are not machined. As shown in figure 1, the forging blank of the screwdriver is a long shaft forging with small cross-sectional area and simple shape. The forming process of forgings is: blanking → heating → die forging → trimming → grinding → heat treatment → inspection. The key of this process is die forging, and the key of die forging is die design. The original insert forging die hole was designed with 1 die hole for rolling extrusion and 1 die hole for final forging. When the blank is made by rolling and extrusion, because the forging is long and the cross-sectional area is small, the cooling speed of the blank is fast, but the blank making efficiency is low; Compared with other vehicle-mounted tool forgings, it has poor dimensional consistency and low qualification rate; In the production process of screwdriver, about 80% forging dies are scrapped due to wear and plastic deformation, and the service life of forging dies is short. Therefore, reasonable forging die design is the key to improve quality, forging efficiency, service life and reduce the cost of forging dies and forgings.

Figure 1 Screwdriver Forging Blank Figure

1 Optimal design of insert forging die The main failure forms of hammer forging die are wear, plastic deformation and fracture. There are many methods to prevent the premature failure of forging die, improve the service life and performance of forging die, and reduce the cost of forging die and forgings. The optimal design of forging die with dual-mode cavity is an effective method. The forging die diagram of 1. 1 was optimized and improved. The forging die for the plug-in screwdriver bit is shown in Figure 2. The structure of the insert forging die is 1 drawing die and 2 final forging dies. The working process of die forging is as follows: firstly, one end of the blank with reasonable material selection and reasonable heating is stretched, and then the stretched blank is put into any final forging die cavity for final forging.

Fig. 2 Forging die diagram of screwdriver insert

1.2 the design form and parameters of the drawing die hole are different from the traditional design introduced in the relevant forging literature, and are superior to the original design function of the rolling extrusion die hole blank. According to the shape characteristics of forgings, a simple wedge-shaped platform drawing die cavity is specially adopted (the upper die drawing die cavity is designed with a drawing inclination of 2), which can reasonably distribute the deformation of metal, obtain fine and uniform flash, and make forging fibers evenly and continuously distributed along the shape of parts, thus effectively improving the blank drawing efficiency, improving the material utilization rate and obtaining good forging performance. 1.3 The working conditions of the final forging die bore are poor and the service life is short. Wear and plastic deformation failure account for about 70%, and fracture failure (mainly fatigue fracture) accounts for 25%~30%, and its service life depends on the service life of the final forging die bore. The forging temperature of the forging blank is 850℃ ~ 1200℃. When the blank is forged in the final forging die cavity, the final forging die cavity is suddenly heated by high temperature, and the temperature can reach 400℃ ~ 600℃. The process of fatigue fracture of forging die is: stress concentration → crack generation → new stress concentration → crack propagation → final fracture.

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