Main Defects Of Connecting Rod Fracture Splitting And Calculation Method Of The Allowable Size

In the manufacture of engine parts, connecting rod is a typical sectional classificationparts whose manufacturing process is very complex. Engine connecting rod fracture splittingtechnology is produced in the late20th century，which is the latest method for producingconnecting rod in the world at present. Compared with the traditional connecting rodprocessing, it has many advantages such as fewer procedures and inexpensive equipmentinvestment, lower costs. Moreover, connecting rod fracture splitting technology improves thecarrying capacity, shear capacity, also significantly improves the positioning precision of theconnecting rod and lid, so that it greatly improves the assembly quality. And it plays animportant role in improving the level of engine manufacturing technology and performance.Therefore it also has become the development direction of sectional classification partsmanufacturing technology.With the application and promotion in the domestic fracture splitting technology, someprocessing quality problems arise. It is also prone to all kinds of machining defects in theactual connecting rod fracture splitting manufacturing. The position and reason of crackingdefects, the detection method and the allowable value, which are not very clear. So currentlyconnecting rod manufacturing companies develop their own standards, based on experienceor the counterpart of data, which are a large difference. This paper figures out the defects andreasons of connecting rod fracture splitting. Moreover, according to the strength ofconnecting rod bolts, subsequent machining process, and requirement of connecting rodbearing capacity, it describes and analyzes the main defects of connecting rod such asfracture line offset, big end hole out of round, fracture surface area of the defect. Theallowable size has carried on the preliminary calculation to provide a reference for qualitycontrol standards of connecting rod fracture splitting. The major research work and achievements of this paper are summarized as follows:1. Based on the practical machining and the core process of connecting rod fracturesplitting, the kinds of defects and the method of detection are analyzed. The main defects ofthe groove processing including: insufficient length/cut more, relative position precision andsurface defects due to processing in a different way, etc. The main defects of the fracturesplitting process including: fracture line offset, defect of fracture surface area, the big endhole out of round, what is more serious is that single side crack and not crack. The maindefects of bolt tightening process including: slag, misalignment, lack of bolt pre-tighteningforce, etc.2. Analyzing and summarizing the main reasons for the fracture splitting processdefects and preliminary related control measures are given. Based on the whole fracturesplitting machining process such as connecting rod forging, fracture splitting notch process,fracture splitting process, bolt tightening process, the affecting factors of processing qualityare summed up by causality diagram: materials, equipments and design of process. Theinfluences of fracture splitting processing quality including: composition of material, forgingtechnology, equipment and fixtures, performance parameters of fracture splitting mechanical,fracture splitting notch.3. Based on the requirement of connecting rod bolt strength, analysis of fracture lineoffset and the allowable deviation angle of fracture splitting process is given. Under the limitstate of fracture surface defects, this article analyzes the shear stress of connecting rod bolt.According to the checking formula of bolt shear strength, the angle of fracture line offset isderived under the bolt security strength. Then checking intensity of three types of connectingrod bolt, the purpose is to acquire the limit angle of fracture line offset. The results conformto the requirement of actual production, namely, the allowance requirement of fracture lineoffset is increased with the development of connecting rod weight.4. Based on the requirement of finishing allowance in the actual production ofconnecting rod, the formula of maximum loss of circular is given. The formula is to calculatethe big end hole out of round. Then the cars are generally0.1mm, while the medium-dutytrucks are generally0.19mm. The results are larger than the actual experience. 5. This paper puts forward a calculation method for connecting rod fracture surface area,which is based on reverse engineering. Compared with the traditional mechanical processing,it determines the size of fracture surface defect. Firstly, according to the laser scanningsystem to acquire connecting rod fracture surface data, the area of fracture surface iscalculated based on STL solid model file. The results show that the area of con-rod jointsurface obtained by fracture splitting is13.1%larger than obtained by machining. Withoutreducing the bearing capacity and usability, the area of fracture splitting connecting rod jointsurface defect is4.4×4.4mm2. The fracture splitting surface defect size is standardized andthe allowable size is greatly increased.