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《Science & Technology of Welding & Joining》2013,18(8):683-693
AbstractIn order to understand the temperature fields, cooling rates and mixing in the weld pool, a comprehensive, three-dimensional heat transfer and fluid flow model is developed and tested by comparing model predictions with two sets of experimental data. The first set of data was taken from the literature. The experiments varied the separation distance between the heat sources for three arc current levels at a constant laser power. The second set of experiments analysed the effect of varying laser power for a constant heat source separation distance. The results demonstrate that the distance between the two heat sources significantly affects the cooling rates. The calculated results showed that the hybrid weld pool was very well mixed with strong convection currents resulting from the interaction between the electromagnetic and Marangoni forces. The calculated and experimental results showed that hybrid welding increases the weld pool width and gap bridgability when compared with laser welding. The weld pool depth in hybrid welding was affected mainly by the characteristics of the laser beam. Hybrid weld pool penetration depth is maximised at an optimal distance between the arc electrode and laser beam. The cooling rate increases significantly when the heat sources are separated beyond a critical distance. At close separation between arc and laser, calculations show that the arc radius must be decreased to achieve the observed weld depths. 相似文献
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为了能够反映固液相变过程中潜热等对熔池动态行为的影响,基于旋转高斯体热源与高斯面热源相结合的混合热源模型,分析了相变潜热对焊接熔池温度场和熔池形状的影响.计算结果表明,在铍材激光钎焊过程的温度场和流场分析中,潜热的影响不是总可以忽略的,其误差取决于材料在物相转变时交界面温差的范围及材料熔解体积的大小.与不考虑相变潜热的情况相比较,考虑相变潜热时显示出较低的最高温度、较小的熔池范围和较窄的热影响区.通过对铍材焊接温度场、焊缝断面形状模拟结果与实际热循环曲线以及焊接接头形状的对比,表明,考虑潜热的计算模型会得出更精确的结果. 相似文献
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The effect of ultrasound on heterogeneous nucleation in a tungsten inert gas(TIG) weld pool of 2195 Al–Li alloy has been investigated by a series of experiments. An ultrasonic vibration was imposed on the surface of base material before turning off the welding arc during the TIG welding implemented at a fixed point. The results suggest that ultrasound could promote heterogeneous nucleation in the TIG weld pool of 2195 Al–Li alloy. The grain around the fusion zone is changed from a column grain to an equiaxed grain after applying the ultrasonic treatment. To study the influencing mechanism of ultrasound on heterogeneous nucleation, further investigations were implemented where the welding arc was turned off after turning off the ultrasonic power. The results show that the equiaxed grain around the fusion zone disappeared gradually with an increase in heat input after turning off the ultrasonic power. It suggests that ultrasound could promote the heterogeneous nucleation particle to nucleate in advance before turning off the welding arc and the crystal nucleus could again be melted with an increase in heat input after turning off the ultrasonic power. Moreover, the effects of the welding current and ultrasonic amplitude on heterogeneous nucleation in the weld pool of 2195 Al–Li alloy were also investigated. Possible influencing mechanism of the welding current and ultrasonic amplitude on heterogeneous nucleation was discussed. 相似文献
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以Al-Zn系铝合金LB-VPPA(激光-变极性等离子弧)复合焊接焊缝成形机理为研究对象,分析了LB与VPPA耦合效应对复合热源特性及其焊缝成形的影响规律.结果表明,LB与VPPA相互耦合不仅提高了激光吸收率,在变极性等离子弧根部形成一烁亮区,并且在VPPA反极性期间此效应更为显著.适当减小VPPA电流幅值,增加离子气流量,匹配合适的激光功率,可获得总热输入小,穿透力更强的热源,从而能够克服单VPPA平焊位置不易形成穿孔熔池的难点.8 mm厚Al-Zn系铝合金LB-VPPA复合热源焊在Iz=115 A、If=155 A、离子气流量q=3.0 L/min、激光功率P=1 000 W时可获得良好的焊缝成形. 相似文献
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VPPA-MIG复合焊集VPPA穿透力强和MIG焊熔敷效率高的优点,弥补了单VPPA焊工艺区间窄且需立焊和MIG焊熔深浅的不足. 使用Red Lake Y4高速摄像获取6 mm厚2A12铝合金VPPA-MIG复合焊接熔池图像,建立了熔池受力模型. 对比分析了复合热源不同能量配比对焊缝成形和熔池形貌的影响及VPPA-MIG与单MIG焊缝成形特点. 结果表明,VPPA-MIG复合热源相比单VPPA热源易保持焊缝成形稳定性. VPPA电流接近穿孔阈值时,配合较低功率MIG热源可以获得6 mm厚2A12铝合金良好焊缝成形;VPPA能量比例过低时,小孔较浅,熔化效率较低,不能起到增加熔深的作用;VPPA能量比例过大,易使熔池失稳,焊缝成形不良. 热源输入功率相同时,VPPA-MIG复合焊比MIG焊显著增加焊缝熔深和深宽比,提高生产效率. 相似文献
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通过熔池的动态观测可以获得焊接过程的稳定性和连续性等信息.熔池的动态观测目前基本上停留在试验室阶段,焊接现场对熔池进行观测在改进工艺和指导生产等方面更具意义.针对焊接现场焊接电源不能修改,非计算机可控,电流电压波形未知等问题,在焊接现场建立了一套焊接熔池图像动态检测系统.根据焊接现场脉冲GTAW的特点,采用"外同步取像"方式确定了焊接现场取像的关键制约因素--取像时刻;并利用电弧光谱分析建立了减小弧光干扰的复合滤光系统;在适合的取像时刻,CCD摄像系统配合复合滤光系统,在焊接现场检测到了清晰的熔池图像. 相似文献
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以圆圈形运丝为研究对象,利用数值模拟与试验相结合的方法研究了在MIG焊接过程中的温度场分布规律,讨论了温度峰值影响接头显微组织及断裂位置的规律.结果表明,对于圆圈形摆动工艺来说,由于熔池区内左侧的材料经历了周期性的二次加热,导致焊缝左侧及热影响区材料经历的温度峰值均高于右侧;摆动工艺的熔池区温度峰值高于不摆动工艺.与直线运丝相比较,摆动焊焊道内的等轴晶较大,而相邻焊道界面处的柱状晶较小.不同工艺下拉伸试样的断裂位置与焊缝区经历的热循环密切相关. 相似文献
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《中国焊接》2018,(4)
The temperature field and flow field were analyzed to solve the problems of unstable penetration and poor forming quality,which always happen in asymmetric fillet welding. In order to explore the effect of the welding parameters on welding and improve the quality of forming,a three-dimensional mathematical model of asymmetric fillet welding was established by using the finite element software COMSOL and the coupling equation. The model was considered about the surface tension gradient,the electromagnetic force,gravity and the effect of temperature,radiation and convection heat on physical properties of the material. The flow field and the growth pattern of the weld pool were analyzed,and the weld pool geometry under different welding currents was compared. The results show that,the thin metal was preferentially penetrated,and with the welding process the weld width expanded until the weld beam was fullpenetration. The heat affected zone was got from weld experiments,its shape and size agreed well with the simulation results,which verifies the validity of the theoretical analysis. 相似文献
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以TA15钛合金为研究对象,采用自行研制的红外光辐射信号监测系统,研究了在激光焊接过程中红外光辐射信号的特征以及焊接热输入与熔池红外光辐射信号和焊缝熔宽的关系.结果表明,对于整条焊缝红外光辐射信号可明显分为三个阶段,分别对应焊接起始阶段、准稳态阶段和焊接收弧阶段;当热输入增加(功率不变焊接速度降低)时,焊缝熔宽变大,红外光辐射信号相对强度随之增强,熔宽与红外光辐射信号相对强度之间存在相同的变化规律,因此利用红外光辐射信号可以相当准确地监测焊接过程的熔池的变化,进而监测焊接过程的稳定性. 相似文献
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《Journal of Materials Processing Technology》2014,214(9):1844-1851
A rotary-Gauss body heat source was employed in the study to model the laser welding of DP1000 steel. The condition of heat dissipation during the welding has a significant effect on the temperature field as well as the shape and size of the laser weld. A series of welding experiments were performed, and good agreement was observed between the calculated weld dimensions and the experimental results. The microhardness values across the welded joint were measured to determine the range of the soft zone in the heat affected zone (HAZ) and simultaneously the temperature range experienced in this region. The results indicated that the soft zone significantly affects the mechanical performance of the welded joint. The width of the soft zone and its distance from the weld center increase with increasing laser power, while the width of the soft zone and its distance from the weld center decrease with increasing welding speed. 相似文献
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焊接时进行原位应变测量可以直接观测焊接过程中的力学现象,同时也可以用于验证焊接过程计算机模型。目前常见应变测量方法主要采用应变片,无法得到全场应变。使用数字图像相关(DIC)技术,测量了在不锈钢厚板表面进行激光堆焊时熔池周围的应变场分布,直接观测由于焊接过程中的非均匀热膨胀造成的焊接热影响区及其周围材料的变形。结果表明,在熔池侧面存在一定的负应变。在熔池后,随着材料逐步冷却,最终形成了正应变。 相似文献