Cold die forging process and die design of the hot

Drive gear cold die forging process and die design

1 Introduction

drive gear is an important part of automobile motor, and its shape and size are shown in Figure 1. In the past, the process of processing drive gears was: first forging blanks on a 3000kN friction press, then turning, and finally machining the tooth shape. Due to the characteristics of the part structure, the tooth shape can only be processed by gear shaping, and the tool withdrawal groove needs to be processed before gear shaping. In this way, not only the material consumption is high, the processing time is long, but also the strength of parts is not high, so this processing technology is relatively backward

Figure 1 drive gear parts

with the rapid development of the automotive industry, cold die forging is more and more used. In addition to having high accuracy, it is more urgent to solve complex shapes, while constantly improving the internal quality of parts, reducing the consumption of raw materials and machining hours, improving productivity and reducing product costs

cold die forging technology is a new die forging process developed and popularized in recent years. Its basic principle is that in the closed cavity, the upper and lower dies are used to upset and extrude the blank. It can make the blank obtain the complex shape blank free forgings in one stroke of the forging equipment, and its dimensional accuracy and material utilization rate are significantly improved. At the same time, it saves the edge cutting process after forging, reduces energy consumption, and improves the productivity

2 process branch the company has conducted joint tests with two of the four major German automobile companies. It is analyzed that the driving gear parts are made of medium and high strength alloy steel 20CrMnTi, which has high strength, large deformation resistance, poor plasticity in the state of supply, and work hardening, making it difficult to carry out cold die forging with large deformation. However, if the blank is fully softened and annealed to reduce the deformation resistance and improve the plasticity index, the cold die forging process is completely feasible

the forming dimensional accuracy of cold die forging process can reach it7 ~ it8, and the surface roughness can reach ra=0.4 ~ 0.8 μ m。 The tooth surface roughness of the straight tooth of the drive gear is R. the adjustment of the impact point of the falling hammer is realized through the up and down, rotary movement of the rocker arm and the radial movement of the automatic hammer lifting mechanism along the arm. A=1.6 μ m. Therefore, the cold die forging process can meet the technical requirements of the part

3 process design

cold die forging process design is the first step of cold die forging design, which is directly related to the quality, cost, production efficiency and die life of parts

3.1 formulation of cold die forging drawing

according to the basic requirements of drive gear part drawing and cold die forging process, the following problems should be considered and solved in the design:

(1) determine the parting surface position and excellent durability. In order to make the cold die forgings easy to take out from the die, and to obtain good results of upsetting, extrusion and filling, and considering that the workpiece is left in the lower die when opening the die, according to the shape of the part, the position of the parting surface should be selected at the maximum outer diameter, as shown in Figure 2 A-A

(2) allowance, allowance and tolerance. Two end plane and undercut requiring machining after cold die forging φ 28mm, knurled groove φ 54mm and center inner hole φ 46mm, and the hole diameter φ 18mm considering that the mold is easy to break, add more blocks to make blind holes. Considering the tolerance of blank size, 1mm allowance is added to both ends of the height of the workpiece, and the tolerance of other dimensions is within the tolerance range of the part. Refer to the manual for allowance and tolerance

(3) die forging slope. In order to prevent the punch from sticking with the central inner hole of the workpiece and facilitate demoulding, in φ A die forging slope of 5 ° is set at the 46mm inner hole

(4) fillet radius. The fillet radius at the sharp corner of cold die forgings directly affects the metal flow, cavity filling, cold die forging force, die wear and streamline cutting at the corner of the workpiece during cold die forging. Refer to the manual according to the size of the part

especially PP and PE with low viscosity are more difficult to shear. According to the above data, the drawing of cold die forgings of drive gears is drawn, as shown in Figure 2

Figure 2 Diagram of cold die forgings of drive gears

3.2 selection of deformation speed

domestic and foreign data and relevant tests point out that in order to make the precise shape of spur gear surface, higher deformation speed must be used to extrude. Because higher deformation speed can improve the plastic deformation degree of metal, there are two reasons: first, the deformation speed is higher than the cold work hardening speed, so that the material can continue to plastic deformation without cracking; Second, the friction coefficient between the metal and the mold cavity decreases with the increase of deformation speed, which accelerates the metal flow speed and is easy to fill and form. At the same time, it also reduces the deformation resistance and reduces the non-uniformity of deformation. At present, the ch83-50 hydraulic die forging hammer manufactured by Jiangsu Hai'an Weihong Forging Machinery Co., Ltd. is used. Its strike speed is 6m/s (more than 3 times faster than that of the mechanical cold extrusion machine), and the number of blows is 60 times/min

3.3 selection of blank size

in the big end diameter of cold die forgings of drive gears (Fig. 2) φ 58mm and straight tooth end diameter φ A size between 40mm is selected as the diameter of the blank. This dimension can not only meet the requirements of allowable deformation, but also be used as the positioning dimension of the blank in the cavity. According to this design principle, after the required volume calculation, the diameter is selected as φ 57.8mm, and the blank length is 22mm

3.4 calculation of allowable deformation degree

using the cold die forging process, the extrusion allowable deformation degree of the material must be checked first, and the section reduction rate is generally used ε F indicates. The allowable cold extrusion deformation of 20CrMnTi alloy steel can be 65% - 70% according to the experimental data. According to the blank size, after calculation ε F=(F0－F1)/F0 × 100% =45%, which is less than the allowable deformation degree of cold extrusion. The test proves that the cold die forging process can be allowed for the drive gear

3.5 blank making treatment

according to the requirements of cold die forging process, blank materials must be processed, which includes softening treatment, surface treatment and lubrication treatment. The process is introduced as follows:

(1) softening treatment. The hardness of 20CrMnTi alloy steel in the supply state is greater than 200hb, the material grain is coarse and uneven, the plasticity is poor, and the deformation