【作者】 朱明；

【导师】 樊丁； 石玗；

【作者基本信息】 兰州理工大学 ， 材料加工工程， 2014， 博士

【摘要】 双丝旁路耦合电弧GMAW是旁路耦合电弧GMAW的高效化改进,通过特定的接法将两个GMAW焊枪相组合,使得熔化主路焊丝的焊接电流Im在电弧弧柱区分为两部分：一部分是熔化旁路焊丝的旁路电流Ibp,另一部是分熔化母材的电流Ibm,并且Ibm=Im-Ibp。双丝旁路耦合电弧高效GMAW过程中,用于熔化焊丝的电流较高,有利于提高焊丝的熔敷率；并通过旁路电弧的分流作用减小了流经母材的电流,有利于降低母材热输入与电弧压力。因此,双丝旁路耦合电弧高效GMAW可适用于高速、高熔敷率的焊接,薄板焊接或是耐磨、耐蚀材料的堆焊领域。文中针对双丝旁路耦合电弧焊的稳定性控制与熔滴过渡行为展开了三方面的研究：第一,焊接过程控制方面的研究针对双丝旁路耦合电弧高效GMAW过程中,焊接参数问耦合性干扰较强、稳定较差的问题,首先建立了描述焊接物理过程的动态数学控制模型；同时,提出了三种控制方案并进行了模拟仿真与焊接实验。结果表明：单路闭环控制可以通过调节旁路弧长有效地控制焊接过程的稳定性；双路闭环控制在保证焊接过程稳定性的同时,可以通过调节旁路电流有效地控制熔化母材的电流；解耦控制通过算法的改进,降低了双路闭环控制过程中旁路电流对旁路弧长的耦合影响,进一步提高了控制精度、响应速度与系统的稳定性。第二,熔滴过渡行为的控制研究针对双丝旁路耦合电弧高效GMAW过程中,由于主路、旁路电弧分别采用了直流反接(主路焊丝接正极)与直流正接(旁路焊丝接负极),并且两路电弧间相互作用,导致两路电弧熔滴过渡特性的行为并不相同。因此,通过建立的高速摄影采集系统,采用静力平衡理论分析了两路电弧熔滴过渡的特性,并对旁路熔滴过渡过程进行了控制：对于主路电弧,引入旁路电弧后会造成主路电弧弧根面积的扩展,产生“跳弧”的现象,此时促进旁路熔滴过渡的电磁收缩力随之显著增加,从而促进主路熔滴向熔池过渡,造成过渡过程中主路熔滴体积明显减小；对于旁路电弧,由于采用了正极性接法(焊丝接电源负极),旁路电弧会自动爬升到逸出功较低的旁路焊丝氧化膜上燃烧,此时电磁收缩力没有作用在旁路焊丝熔化区域,所以旁路熔滴只能依靠重力克服表面张力向熔池过渡,因此旁路熔滴尺寸较大且难以向熔池过渡；为了解决旁路熔滴过渡难的问题,提出向纯氩保护气体中添加氧元素来控制旁路熔滴过渡过程。当保护气体中含有氧元素后,由于焊接过程中旁路熔滴表面温度很高,氧元素会在旁路熔滴表面形成一层氧化膜,此时旁路电弧会在旁路熔滴表面的氧化膜燃烧,电磁收缩力会重新作用在旁路焊丝熔化区域,从而促进旁路熔滴向熔池过渡；同时,氧元素作为活性元素,会降低阻碍旁路熔滴过渡的表面张力。综上所述,当旁路保护气体中含有氧元素后,在选择正极性接法时,旁路熔滴由电磁收缩力与重力同时克服表面张力向熔池过渡,此时旁路熔滴尺寸明显减小。针对以上实验结果,采用“质量-弹簧”理论建立了双丝旁路耦合电弧高效GMAW熔滴过渡数学模型,通过数学计算验证了保护气体中氧元素对于旁路熔滴过渡行为的促进作用。第三,单电源双丝旁路耦合电弧高效GMAW过程控制研究提出采用单个平特性焊接电源实现双丝旁路耦合电弧高效GMAW的原理,并通过大量焊接工艺实验,获得了稳定焊接的工艺匹配范围；建立了相关控制数学模型并模拟了实际焊接过程；提出通过控制旁路送丝速度、调节旁路熔化速度、进而改变旁路电流、控制熔化母材电流的闭环控制方案并进行了仿真分析与焊接实验。结果表明,该方案可以实现母材电流的稳定控制。在此基础上,单电源双丝旁路耦合电弧高效GMAW方法进行了异种钢堆焊实验。通过对焊缝微观组织的分析,发现由于双丝旁路耦合电弧高效GMAW热输入较低,可以减缓碳元素的扩散行为,碳迁移层厚度明显降低；同时,由于较低的稀释率,焊缝中的合金元素稀释的问题得到了明显的缓解。更多还原

【Abstract】 Consumable DE-GMAW (double-electrode gas metal arc welding, DE-GMAW) is the efficient improvement of DE-GMAW. This modification utilizes a GMAW torch to bypass part of the melting current in a conventional GMAW process as illustrated. It can be seen that the main current Im(which melts the main wire) is decoupled into base metal current Ibm(which determines base metal heat input and arc pressure) and bypass current Ibp(which melts the bypass wire), also Ibm=Im-Ibp.As a result, the main current Im can be increased while the base metal current Ibm can be controlled at the desired level. Thus, consumable DE-GMAW would be widely used in efficient welding, low heat input welding or overlay welding.In this paper, due to stability controlling and metal transfer behavior, researches have been carried out in three aspects:1. The research on stability control in consumable DE-GMAW processDue to the instability of consumable DE-GMAW process, a mathematical control model was established at first to descripe the physical welding process. Then, a SISO, MIMO, decoupling control scheme were proposed, simulated and carried out. The results show that:the SISO control scheme can solve the instablity of bypass arc, which adjusts bypass wire feedspeed to stablize the bypass arc; MIMO control scheme can keep the welding process and base metal current stable, which adjusts bypass wire feedspeed to control the bypass arc and bypass current to control the base metal current together; based on the result of MIMO control, a better stability, faster response and higher accuracy can be gotten by decoupling control.2. The research on metal transfer behavior in consumable DE-GMAW processDue to the variety of coupled arc and metal transfer behaviors, this paper applies static force balance theory to analyze the changes in the forces acting on the main and bypass droplets separately. For main torch, the bypass arc changes the forces affecting on the main droplet, and the main metal transfer becomes more desirable. For bypass torch, with direct current electrode negative polarity, the volume of droplet is big and not easily transfers to the weld pool. In order to improve the bypass metal transfer, a method has been proposed which adds CO2to pure argon shielding gas to change the forces affecting on the bypass droplet. Then, with80%Ar+20%CO2shield, the welding experiment is carried out to test the effectiveness of this method. It is found that bypass droplet transfers easily and the diameter of bypass droplet is decreased significantly. At last, based on "mass-spring" theory, the abover results were simulated and proved by mathematical analysis. 3. The research on consumable DE-GMAW process with one power supplyTo decrease the welding costs, an innovation was put forward to realize a stable consumable DE-GMAW process with one power supply. With plenty of welding experimnets, the range of stable welding was fixed. Also the mathematical control model was established to descripe the welding process with one power supply. Then, a control scheme was proposed to control the base metal current stably, which adjusts bypass wire feedspeed to change the bypass current. Also the simulations and welding expriments were carried out to chech the control scheme. At last, to prove that the low heat input could improve tissues and quality in weld seam, expriments of overlay welding between stainless steel and low carbon steel was fullfilled.更多还原