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  • 中频点焊机与工频点焊机的区别
  • 本站编辑:杭州先创热熔设备厂发布日期:2019-10-18 19:02 浏览次数:
中频逆变点焊机与传统工频交流焊机相比的优势
 
      优势主要提示:与传统的工频交流点焊机相比,中频逆变点焊机运行的能源成本比工频交流点焊机节约近1/3,适合自动化运用,控制智能化程度高,适应材料范围广,尤其能够得到稳定、可靠的焊点质量。
 
与传统的工频交流点焊机相比,中频焊机运行的能源成本比工频焊机节约近1/3,适合自动线运用,控制智能化程度高,适应材料范围广,尤其能够得到稳定、可靠的焊点质量。
 
       随着汽车行业的快速发展,汽车车身结构的安全性及新材料的运用对车身的焊接工艺提出了新的挑战。对于带涂层的钢板、涂胶的钢板、多层板及不同材质板等条件下的焊接,传统的工频点焊机难以满足焊接要求,应运而生的是各种先进的焊接工艺及焊接设备,如中频逆变焊机、螺母输送机等。
      近年来,国外部分生产汽车批量大的企业将中频点焊机器人和伺服技术点焊机器人应用于轿车白车身焊装线。尤其在欧洲,中频点焊机器人使用量已占40%,并扩大到铝合金轿车车身的点焊作业。在国内中频点焊机在各大汽车厂中也得到了越来越广泛的应用,如一汽大众、奇瑞汽车、北京现代、东风日产等厂家都已将中频焊机运用于自动线焊接或人工点焊。
 
     与传统的工频焊机相比,中频焊机最大的优点在于直流极性好、焊接质量好。以RexrothPSQ6000的中频焊机在奇瑞汽车A5白车身生产线的运用为例,来说明中频点焊机良好的焊接质量性能。
 
      在A5白车身生产线的骨架总拼工位,由机器人使用工频焊机焊接。此工位的左右侧围门槛处,有10个焊点为四层板焊接,四层板总厚度达到5.5mm,此处焊点的焊接质量很不稳定。当焊接电流过大时,会引起焊点过烧或焊点烧穿;当焊接电流调小时,又会引起弱焊或虚焊。无论如何调整焊接参数,都无法得到稳定良好的焊点质量,因为此处不仅板厚、钢板层数多,而且装配时有一定的装配间隙,而工频焊机并不能根据实际的装配状态对焊接参数进行自动的调整来保证焊接质量。对此,中频逆变焊机正好能克服工频焊机的缺陷。
 
     在使用中频焊机之前,技术人员采用四层板试板分别用工频焊机和中频焊机进行焊接试验观察焊接质量。四层板的试验材料为:(1.8+1.5+1.5+0.8)mm组合的4块冷轧低碳钢板,焊钳电极直径16mm,焊接参数经过多次试验优化.
 
     从表1可见对于多层板的焊接,无论从操作环境,还是从焊点质量及其稳定性,中频焊机的焊接性能都明显优于工频焊机。由于中频焊机的电流非常接近直流电流,焊接时没有电流峰值,焊接过程中热量增加比较稳定无波动,因此焊接飞溅很少,甚至几乎没有。所以中频焊机的操作环境较工频焊机操作环境好很多,并且中频焊机的电流热效率高于交流电流,故中频焊机焊接的焊点熔核直径比工频焊机的大1~2mm。
      随后在A5车身侧围门槛处用工频焊机和中频焊机进行四层板焊点的焊接,试验结果与用试板做的试验结果基本吻合,具体车身焊点见图1。用中频焊机焊接的5个焊点熔核均在5~6mm之间,用工频焊机焊接的3个焊点的熔核在3~4mm之间。
 
      通过一段时间的现场验证,中频焊机焊接A5侧围门槛处四层板焊点焊接质量合格,且质量稳定,显著优于工频焊机的焊接质量。如此优良的焊接质量不仅与中频焊机的直流极性有关,还与它的控制系统有重要的关系。中频焊机拥有功能强大的监控软件,智能化程度高。它采用了恒功率控制技术和伺服运动控制器(气动元件),可以对焊接电流、焊接时间、焊接功率及焊接的压力等进行全闭环控制。
 
    恒功率控制技术是对次级电流和次级电压进行监控,通过调整焊接时间和焊接电流保证每一个焊接熔核的输入功率相等,因此它可以有效补偿焊接分流、焊接装配不良、焊接母材成分变化等非机器扰动因素。首先它根据焊接的条件,选取一个标准试板,建立一条电流和电阻的样本曲线,然后在实际的焊接工作中,根据实际的焊接电阻对实际的焊接电流和焊接时间进行补偿焊接板件之间有胶水干扰的一个焊接参数曲线图,红色曲线是实际的焊接电流-时间曲线,与它部分重合的黑色曲线是焊接样本的焊接电流-时间曲线,绿色曲线是实际的焊接电阻-时间曲线,与它部分重合的黑色曲线是焊接样本的焊接电阻-时间曲线。样本为没有胶水的同样钢板的焊接,当焊接板件之间有胶水时,板件电阻大大高于样本电阻,故焊接电流在开始段突然增大,使胶水层被击穿,同时损失的焊接电流以延长焊接时间得到补偿,保证了焊点的质量。图3为焊接板件之间有涂层干扰的一个焊接参数曲线图,曲线含义与图2相同,当焊接板件之间有涂层干扰时,控制系统通过增加焊接电流来进行补偿。
     由于中频焊机具备以上两方面的优点,故其焊接质量控制远远优于工频点焊机。但是它的缺点是价格比普通工频焊机高6~8倍,一次性投资大。然而,它的综合性能将决定它的应用程度,下面看一下它的综合性能,与普通的工频焊机相比,它有以下几个特点(其参数见表2):
 
1.中频焊机焊接电流接近完全直流,由于没有明显的峰值电流,熔核尺寸稳定扩大,几乎没有飞溅,焊接质量稳定、热效率高。与工频焊机相比,中频逆变焊机焊接电流可降低40%,电极使用寿命大大延长。
 
2.中频焊机变压器重量和体积小,输入功率低,便于采用连变压器式焊钳。当运用于机器人点焊操作时,可使机器人的负荷减轻,而工频焊机在自动线上运用时则需要负载能力更强的机器人。
 
3.中频点焊机的响应速度仅为工频焊机的1/20,电流能够更快地达到设定值,更准确地分析参数,焊接质量控制更精确。
 
4.中频点焊机三相负荷均衡,功率因数高(0.9左右),节能。而两相工频焊机,工作时很难保证相电压之间的均衡,功率因数低(0.6左右),三相工频焊机则很难实现恒流输出。
 
5.中频点焊机适用多种材料及异种金属的焊接,如铝合金、不锈钢、高强度钢板等材料。另外,对于镀锌板和普通多层板的焊接,其焊接质量也远高于工频焊机的焊接质量。而工频焊机只适应焊接性能好的材料,如低碳钢板。
Advantages of intermediate frequency inverter spot welder over traditional power frequency ac welder
 
 
 
Advantages main tips: compared with the traditional power-frequency ac spot welding machine, the energy cost of the operation of the medium-frequency inverter spot welding machine is nearly 1/3 less than that of the power-frequency ac spot welding machine. It is suitable for automation, highly intelligent control and wide range of materials, especially for stable and reliable welding spot quality.
 
 
 
Compared with the traditional power frequency ac spot welding machine, the energy cost of the operation of the intermediate frequency welding machine is nearly 1/3 less than that of the power frequency welding machine. It is suitable for the application of the automatic line, has a high degree of intelligent control and a wide range of materials. In particular, it can obtain stable and reliable welding spot quality.
 
 
 
With the rapid development of automobile industry, the safety of automobile body structure and the application of new materials pose new challenges to the welding process of automobile body. For the welding with coated steel plate, coated steel plate, multilayer plate and different materials, the traditional industrial frequency spot welding machine is difficult to meet the welding requirements, the emergence of a variety of advanced welding technology and welding equipment, such as intermediate frequency inverter welding machine, nut conveyor and so on.
 
In recent years, some foreign enterprises which produce large quantities of automobiles have applied intermediate frequency spot welding robot and servo spot welding robot to the welding line of car body in white. Especially in Europe, the use of intermediate frequency spot welding robot has accounted for 40%, and expanded to aluminum alloy car body spot welding operations. In the domestic medium frequency spot welding machine has been more and more widely used in the major automobile factories, such as faw-volkswagen, chery automobile, Beijing hyundai, dongfeng nissan and other manufacturers have used the medium frequency welding machine in automatic line welding or manual spot welding.
 
 
 
Compared with the traditional industrial frequency welder, the main advantages of the intermediate frequency welder are good polarity and welding quality. Take the application of RexrothPSQ6000 intermediate frequency welder in chery automobile A5 body in white production line as an example to illustrate the good welding quality performance of intermediate frequency welder.
 
 
 
The skeleton of A5 body in white assembly line is welded by a frequency welder. At the enclosed threshold on the left and right sides of this station, there are 10 welding spots for four-layer plate welding. The total thickness of the four-layer plate reaches 5.5mm, and the welding quality of the welding spots here is very unstable. When the welding current is too large, it will cause the solder burn or solder burn through; When the welding current is adjusted, weak welding or virtual welding will be caused. No matter how to adjust the welding parameters, it is impossible to obtain a stable and good welding spot quality, because here not only is the plate thickness and the number of steel plates are many, but also there is a certain gap in the assembly, and the power frequency welder cannot automatically adjust the welding parameters according to the actual assembly state to ensure the welding quality. In this regard, the intermediate frequency inverter welding machine can just overcome the defects of the industrial frequency welding machine.
 
 
 
Before using the intermediate frequency welder, the technician USES the four layer plate test plate to conduct the welding test with the frequency welder and the intermediate frequency welder respectively to observe the welding quality. The test materials of the four layers are :(1.8+1.5+1.5+0.8) mm cold rolled low carbon steel plates with electrode diameter of 16mm. The welding parameters have been optimized through multiple tests, and the final test results are shown in table 1.
 
 
 
As can be seen from table 1, the welding performance of the intermediate frequency welder is obviously better than that of the industrial frequency welder, no matter from the operating environment or the quality and stability of the welding spot. Since the current of the intermediate frequency welder is very close to the dc current, there is no peak current during welding, and the heat increase during welding is relatively stable without fluctuation, so there is little or even no spatter during welding. Therefore, the operating environment of the intermediate frequency welder is much better than that of the industrial frequency welder, and the current thermal efficiency of the intermediate frequency welder is higher than that of the ac current. Therefore, the diameter of the welding spot of the intermediate frequency welder is 1 ~ 2mm larger than that of the industrial frequency welder.
 
Then, the welding of the four-layer plate welding spot was carried out by the frequency welder and intermediate frequency welder at the threshold of the side wall of A5 body. The test results were basically consistent with the test results made by the test plate. The specific welding spot of the body was shown in figure 1. The core of 5 welding spots with intermediate frequency welder is 5 ~ 6mm, and the core of 3 welding spots with labor frequency welder is 3 ~ 4mm.
 
 
 
After on-site verification for a period of time, the welding quality of the four-layer plate welding spot at the girth threshold of side A5 welded by the intermediate frequency welder is qualified and stable, which is significantly better than the welding quality of the industrial frequency welder. Such excellent welding quality is not only related to the dc polarity of the intermediate frequency welder, but also to its control system. Intermediate frequency welding machine has powerful monitoring software, high intelligence. It adopts constant power control technology and servo motion controller (pneumatic components), which can control the welding current, welding time, welding power and welding pressure.
 
 
 
Constant power control technology is to monitor the secondary current and voltage, and ensure that the input power of each weld nugget is equal by adjusting the welding time and welding current. Therefore, it can effectively compensate for non-machine disturbance factors such as welding shunt, welding assembly failure, and change of welding base material composition. First it according to the welding conditions, the selection of a standard test plate, build a current and resistance of the sample curve, and then in the actual welding work, according to the actual resistance welding of actual welding current and welding time compensation have glue between the welding plate interference graph of a welding parameters, the red curve is the actual welding current - time curve, and it is the black curve parts overlap welding sample welding current - time curve, the green curve is the actual welding resistance - time curve, and it is the black curve parts overlap welding sample welding resistance - time curve. The sample is the welding of the same steel plate without glue. When there is glue between the welded plates, the resistance of the plate is much higher than that of the sample. Therefore, the welding current suddenly increases in the beginning section, which causes the glue layer to be broken down. Figure 3 is a graph of welding parameters with coating interference between welded plates. The meaning of the curve is the same as that in figure 2. When there is coating interference between welded plates, the control system compensates by increasing welding current.
 
Because the intermediate frequency welding machine has the advantages of the above two aspects, its welding quality control is far superior to the power frequency spot welding machine. But its disadvantage is that the price is 6 ~ 8 times higher than ordinary industrial frequency welder. However, its comprehensive performance will determine the degree of its application. The following is its comprehensive performance. Compared with ordinary industrial frequency welder, it has the following characteristics (see table 2 for its parameters) :
 
 
 
1. The welding current of intermediate frequency welder is close to full dc. Due to the absence of obvious peak current, the size of molten core expands steadily with almost no splash. Compared with power frequency welder, the welding current of intermediate frequency inverter welder can be reduced by 40%.
 
 
 
2. Medium frequency welding transformer weight and volume small, low input power, easy to use even transformer type welding tongs. When applied to the robot spot welding operation, can reduce the load of the robot, and the machine in the automatic line when the use of the need for a stronger load capacity of the robot.
 
 
 
3. The response speed of intermediate frequency spot welder is only 1/20 of that of industrial frequency welder. The current can reach the set value faster, analyze parameters more accurately and control welding quality more accurately.
 
 
 
4. Intermediate frequency spot welding machine three-phase load balance, high power factor (about 0.9), energy saving. While two-phase frequency welder, it is difficult to ensure the balance between phase voltage and power factor is low (about 0.6), and it is difficult to achieve constant current output of three-phase frequency welder.
 
 
 
5. Intermediate frequency spot welding machine is suitable for welding various materials and different metals, such as aluminum alloy, stainless steel, high strength steel plate and other materials. In addition, the welding quality of galvanized sheet and common multilayer sheet is much higher than that of power frequency welder. The frequency welder is only suitable for the material with good welding performance, such as low carbon steel plate.

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