| Engine connecting rod fracture splitting technology is the newest method for producing connecting rod in the world at present. Compared with traditional methods, it has many advantages such as fewer procedures and inexpensive equipment investment, lower costs, good-quality products, high assembly precision, strong loading capacity, etc. The technology marks the development of engine connecting rod manufacturing in a country to a certain degree. The study and application of connecting rod fracture splitting technology and its equipment play a vital role in automobile and engine industries in China. Connecting rod fracture splitting is precision processing technology and influenced by many factors. Therefore, studying the effects of those factors on fracture splitting quality is very important to the development and application of the technology. In response, this paper makes research from following aspects:1. Tensile experiment is carried out on C70S6 used extensively in the world. The result shows that the material has obvious yield point and its yield stress and tensile stress are 585MPa and 945MPa. Fracture toughness of the material is measured by fatigue testing machine. Critical fracture toughness KIC at room temperature is 39.74MPam1/2. Due to the fatigue pre-crack, which provides an extremely high stress concentration at the crack front, material exhibit brittle fracture without any visible plastic deformation. This shows the material has strong cracking sensitivity and is fit for fracture splitting technology. Different loading speeds v=0.1, 10, 100, 200, 500mm/min are adopted to measure the sensitivity of strain rate at room temperature. Corresponding to loading speeds mentioned above, yield stress is 575, 583, 601, 620, 643MPa and tensile stress is 965, 972, 1014, 1004, 1001MPa respectively. Thus it can be seen that yield stress increases gradually as loading speed increases; while tensile stress has little change. A perlitic microstructure with small portions of ferrite is received by electron microscope. Ferritic structure rests at the grain boundary of the perlitic base structure. Pearlite and ferrite are in the proportion 9:1.2. Software MARC and ABAQUS are employed to establish finite element model of Jetta car connecting rod. Through analysis, the curve between J integral at crack front and loading on movable block is established. According to the relationship between J integral and stress intensity factor and tested critical stress intensity factor, separation force of fracture splitting are gotten. The values are 81954N and 83217N respectively. Compared with loading which is 85136N obtained from fracture splitting experiment, the errors are 3.738% and 2.254%. Separation forces of 53d and 56d bevel split big end connecting rods are determined by above numerical analysis method. Compared with loading obtained from fracture splitting experiment, the errors are below 10%.3. Starting notch of Jetta car connecting rod is processed by broaching, laser and wire cutting. After fracture splitting processed by those three methods, plastic deformation of the big end bore and level error of separation surface are tested and fractured surface is also analyzed. Results show that in laser processing method, the big end bore deformation and level error after fracture splitting are the smallest and brittle fractured surface is obtained almost without plastic deformation. However, the above two errors in broaching processing method are the largest and partial plastic deformation occurs at the root of starting notch. Among the three methods, the two errors in wire cutting processing method are in the middle. According to the results, laser processing method has more advantage. Furthermore, broaching and laser processing methods are fit for massive production due to high productivity. In contrast, wire cutting processing method has low productivity and is only fit for products development.4. Orthogonal experiment method and numerical simulation are employed to analyze how geometry parameters of starting notch influence separation force. Curvature radius r ranges from 0.05mm to 0.3mm, open angleαfrom 0°to 90°, notch depth h from 0.4mm to 1.2mm. Variance analysis is also adopted to get the significance levels of three parameters during their influence on separation force. Results show that notch depth influences separation force most and curvature radius takes second place and open angle has little effect.Taking numerical analysis experiments and practical production into consideration, optimal geometry parameters ranges of starting notch are put forward. For starting notch processed by broaching, suitable range of open angleαis between 60°and 90°, in whichα=90°is commonly used. For starting notch processed by wire cutting, open angleα=0°is often adopted and curvature radius r is between 0.1mm and 0.3mm, in which r=0.2mm is commonly used. To car connecting rods, notch depth h ranges from 0.4mm to 0.5mm; while notch depth h of truck connecting rods is between 0.6mm and 0.7mm.5. Numerical simulation is adopted to study how backpressure affects fracture splitting quality of Jetta car connecting rod. It is shown that separation force increases as backpressure becomes larger. Plastic deformation at fractured surface decreases with the increase of backpressure. When backpressure is below 20KN, plastic region narrows dramatically with backpressure increased; when backpressure is above 20KN, plastic region narrows slowly. Big end bore deforms increasingly with backpressure increased and when backpressure is above 25KN, big end bore deforms too much. Therefore, when backpressure ranges from 20 to 25KN, that is 1/4~1/3 of separation force, both fractured surface and big end bore have ideal deformation and good fracture splitting quality can be obtained. Studies on 53d bevel split big end connecting rod also prove that fracture splitting quality is fine when backpressure is 1/4~1/3 of separation force.6. ABAQUS is employed to study the influence of loading speed on fracture splitting quality. Combine displacement method and numerical simulation to find out displacement of nodes near crack front. Relation between stress intensity factors obtained by displacement extrapolation method and time at different loading speeds is established. It is shown that stress intensity factors decrease and plastic region narrows as loading speed increases. When loading speed is above 130mm/s, plastic region decreases slowly.7. Study the influence of forging parameters on mechanical properties and fracture splitting quality. According to the experiment results, the more quickly cooling speed, the higher hardness and strength of connecting rod become under the same heating temperature. Hardness and strength decrease with the increase of heating temperature under the same cooling speed. After being forged, the structure of the material changes with cooling speed. Ferritic structure increases and the size of grain becomes larger and hardness decreases as cooling speed decreases. When heating temperature is 1150℃and strong wind cooling method is used, fracture splitting quality is better than other forging methods. However, under those conditions, tools for processing connecting rod are easier to be worn. Taking fracture splitting quality and later processing quality into consideration, it is better that heating temperature is from 1150 to 1250℃and cooling method is weak wind.8. Quality requirements for connecting rod fracture splitting and common defects are introduced. The cause of defects and effect factors are analyzed and suitable technological parameters are also determined to avoid defects.
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