| Different from the machining of composition plane between rod and cap for traditionalconnecting rod, fracture splitting (FS) connecting rod adopts controllable cracking to separatethe cap from the rod, which greatly simplifies the manufacturing procedures of the compositionplane and bolt holes. It has offered a list of remarkable merits in good product quality, lowmanufacturing cost, high production efficiency and material usage rate, saving equipmentinvestment, etc. It is of great significance for enhancing engine performance, reducingautomobile production cost and boosting our country automobile competitiveness. FSconnecting rod has high competitiveness and development potential. Consequently, it will be thedevelopment trend of connecting rod manufacturing industry.The key technologies are the core of FS technology, while the complete equipment withhigh efficiency and precision is application foundation of FS technology. Until now, some keytechnologies during FS processing of connecting rod are still in the exploring stage. Meanwhile,there still isn't complete equipment for machining FS connecting rod with intellectual propertyrights in our country. Therefore, the research on key technologies and the development ofcomplete equipment have important realistic significance. This thesis is supported by nationalscience-technology tackling project and doctoral degree fund. This thesis aims to investigate theapplication of FS technology, to develop the complete equipment with high efficiency andprecision, and to accelerate the industrialization application of connecting rod FS equipment.The major researches are summarized as follows:1. The processing methods of SN including mechanical broaching, wire cutting and pulselaser notching are investigated. The tension test with samples maded by the three methods iscarried out, and the lowest fracture load and notch sensitivity factor characteristics of pulse lasernotching are determined. At the condition of vertical cutting, the finite element (FE) simulationsand physical tests of laser notching process with typical material C70S6are achieved. Thesimulating morphology and experimental morphology of starting notch (SN) are obtained. Thechange laws of notch depth, notch width, continuity, opening angle and curvature radius of SNare investigated. At the condition with an actual cutting angle, the orthogonal tests are carriedout. Based on the experiment results, the sequence of importance of the processing parameterson SN dimension is determined. According to the requirements of notch depth for differentconnecting rod, optimum ranges of process parameters for car and truck connecting rod arepredicted.Some conclusions can be drawn from FE simulation and physical tests as follows: laserparameters show apparent influence on macro morphology of SN. At a small negativedefocusing amount, perfect macro morphology of SN can be obtained using rational laser parameters. Among the influence factors of notch depth, the sequence of importance is shown as:pulse power> pulse time> scanning speed. Among the influence factors of notch width, thesequence of importance is shown as: pulse time> pulse power> scanning speed. Among theinfluence factors of opening angle, the sequence of importance is shown as: defocusingamount> pulse power> pulse time. Scanning speed and pulse frequency are the main factors ofSN continuity. While ablation phenomena is mainly caused by pulse power, pulse width andscanning speed.2. In order to obtain the constitutive relations of C70S6steel, the material performancetests is carried out. The numerical model of con-rod fracture splitting is constructed. Based onthe numerical analysis method, the influence of loading speed on the stress relation isinvestigated, as well as the distribution of stress and strain under different loading speeds. Thus,the influence of loading speed on FS quality is studied. The numerical analysis results show thatstress intensity factors decrease with loading speed increasing. When loading speed is above87mm/s, plastic region width decreases slowly. At this time, Low-stress fracture likely occurs, andthe deformation of con-rod big end bore is within a reasonable range.3. After the mathematical model of FS circuit is constructed, some influencing factors onloading speed of FS cylinder are analyzed by using hydraulic simulations. Based on thesimulation results, the optimal hydraulic and component parameters are determined. The virtualprototype model of FS station is constructed. At the optimal hydraulic and componentparameters, the simulations with constant input and displacement feedback input are achieved,then the loading speed characteristic of FS station under the above two simulations are gained.The detection system of FS station is constructed. At the optimal hydraulic and componentparameters, the actual loading speed and working pressure characteristics of FS station aregained.Some conclusions can be drawn from the co-simulations as follows: In the simulation withthe constant input, the loading speed of FS cylinder is about118mm/s, and the working pressureis about12MPa. In the simulation with displacement feedback input, among the four designcurves, the elliptic curve input shows the most obvious deceleration characteristic during thestroke of FS cylinder, therefore the actual loading speed can be controlled referring this curve.The detecting experiment shows that the curves of load speed and working pressure duringloading process are the same as those during un-loading process. The actual loading speed of FScylinder is about110mm/s, and the actual superior vena pressure is about12MPa, which cansatisfy the basic requirements of connecting rod FS process. The trends of loading speed andworking pressure obtained by the detection system are similar to those obtained from the virtualsimulations, which illustrates that the models used in this thesis are feasible and reliable. Thesimulations can reflect the actual situation of hydraulic system approximately.4. The virtual prototype models of the equipment are constructed. The dynamic simulationsare achieved towards the mechanical system key components. Then the functionality andpracticability of the key components are gained, and the effectiveness of design plan is verified.The conclusions can be drawn from the simulations as follows: the laser cutting head asway mechanism works with stability, reliability and good cutting effect under the condition withappropriate process parameters (hydraulic pressure:2.5MPa, throttle valve's dischargecoefficient:0.2). The initial assembling bolts station (IABS) after optimum structure cantransmit bolts from the feeding hopper into the bolt holes of connecting rods automatically. Thewhole transmission and split transmission of straight connecting rod and oblique connecting rodcan be accomplished through the straight pincer (SP) and oblique pincer (OP) after optimumstructure respectively, which illustrates that the structure design of these pincers are reasonable.5. The total design scheme of FS complete equipment is accomplished, the developingstrategy is investigated, and the initial design work is fulfilled. The basic content of initialdesign contains the planning of the equipment performance parameters, the determination ofworking stations, the structure design of mechanical system based on UG software, and theworking processes planning of the equipment. The physical prototype of the completeequipment is constructed for the first time. In order to guarantee the machining accuracy andwork efficiency of the prototype, some debugging experiments are done. Based on thedebugging results, some improvements are done, and it is expected that the product quality ofFS connecting rod and the stability of the equipment could be improved. Some conclusions canbe drawn from the debugging experiments as follows: after the compensation of backlash forlaser notching station (LNS), the transmission accuracy of servo-controlled axis has beenimproved. At the reasonable working parameters, the laser cutting head asway mechanismworks with stability and reliability. Tightening experiment at the parameter of22Nm isconducted, and the error of torque between the detection value and the set value is less than1%.The physical prototype of the complete equipment can work with coordination, and the workingtime is about22s.6. The FS processing experiment is achieved using the physical prototype towards type Acon-rod. The FS process parameters are determined, including the laser notching parameters,parameters of FS procedure and bolts assembling parameters. Then some important parametersduring the three core procedures are detected. The causes for some common defects areinvestigated, and the solving methods of the defects have been proposed. Mass production oftype A con-rod is carried out using the physical prototype, the information of product quality isobtained.Some conclusions can be drawn from the FS experiment as follows: the notch depth is inthe range of0.46~0.55mm, notch width is within the range from0.19mm to0.21mm, whichsatisfy the basic requirements of SN. The deformation value of big end bore is less than0.07mm, the extending oversize of FS line is within the range of±1mm, and the area of droppinggranule is less than2×1mm~2, which satisfy the requirements of FS procedure.20Nm+95°ischosen as the final tightening parameter, under this parameter, the axis pre-tightening force ofbolt is within the region of30380±980N, and the bolts work in the plastic range. Someconclusions can be drawn from the mass production as follows: The primary production yieldreaches98.8%, and the total quality rate reaches99.78%. Among all defects, the mismatchdefect takes75%. Mass production indicates that the complete equipment developed by this study can be competent enough to fulfill the FS processing task, but the deslagging ability of thecomplete equipment is in urgent need of strengthening. |
