The Experimental Research Of Laser Processing For Typical Material Fracture Splitting Notch

Fracture splitting technology is a new technique which occurred in 1990's, it is first used in auto engine connecting rod. and simplified structural design of bolt hole and whole process technology. The technology has lots of advantages, few working process, small equipment investment,low manufacture cost, good product quality ,high assembly precision, strong carrying capacity and so on. The field is dilated to Crankshaft bearing caps, Crank shaft flange, Cam disk, Strap, Bearing for printing machine etc.Notching as one of the most critical and core process of fracture splitting, demands on processing technology,accuracy and quality of notch. YAG solid laser notching is an technology,but the choice of laser processing parameter depends on experience mainly. Due to all kinds of materials,physical dimension of parts,. in order to obtain the rationality choice of the parameter,the experiments were needed.C70S6 and HT150 were tested for notching as the most representative material of connecting rod and cylinder block of engine by YAG laser in this thesis. Based on the experiments,the mechanism of laser cutting fracture splitting groove was researched,The influence of laser processing parameter on geometry of fracture splitting groove were analyzed corresponsive ,the change of material microscopic structure,micro-hardness and the depth of hardened case were measured,which can provide a scientific reference and practical data of the optimization of laser processing parameter and follow-up machining .In this thesis,The main research are carried and results obtained as follows:1. the impact on fracture splitting notch dimension of cylinder bearing and connecting rod was confirmed,though the change of laser pulse power,scanning speed and impulse width , which have offered basis for the optimization of parameter. Educed from experimental result: The range of laser scanning speed is 12-18mm/s, the range of impulse width pulse is 0.3-0.5ms, laser impulse power can be confirmed according to the size of the cylinder bearing or connecting rod. Under the same laser parameter and processing parameter, HT150 material notch was smaller than C70S6 materials in depth width,because HT150 roughness is relatively low, which caused the laser absorption rate smaller than before.2. After laser processed, fracture splitting notch can be divided into three parts: Melting part, abnormal phase hardening part and base metal. In the room temperature,the microscopic structure of melting part are arborization crystal(M +A ')and lamellar structure eutectic ledeburite (M+A'+Fe3C),in abnormal phase hardening part are martensite + remain austenite +graphite in flakes +little phosphorus eutectic. the character of C70S6 melting part was columnar crystals. Air vents and cold crackle were found in fracture splitting notch of both materials,they have bad influence on fracture splitting quality.3. Hardening depth of two kinds of materials was measured separately, One was between 0.232mm-0.625mm,while the other was between 0.372-0.897mm.Among laser processing parameter, pulse width exerted a largest influence on hardening depth, pulse power took second place, scan speed was minimum to influence the depth. It offer the consulted data for ensure of follow-up machining surplus. Consulted data was offered for making sure follow-up machining surplus.4.The micro-hardness of material was obviously improved,after processed by laser. Toward HT150 material, micro- hardness was higher in the melting part than abnormal phase hardening part; And that to C70S6 material , abnormal phase hardening part had higher micro-hardness than the melting part. The micro-hardness increased with the increase of the laser pulse power, reduce with the increase of laser scanning speed.5.Smaller pulse width was choosed , and other laser processing parameter was coordinated for C70S6 material, in order to reduce the emergence of fracture splitting defect; The defocus amount and incidence laser incidence angle were guaranteed to avoid the unilateral fracture phenomenon .To gray cast-iron material, a lot of defects in cast one was existed, it is less sensitive than C70S6 material to breach effect.