中頻逆變點(diǎn)焊機(jī)與傳統(tǒng)工頻交流焊機(jī)相比的優(yōu)勢
優(yōu)勢主要提示：與傳統(tǒng)的工頻交流點(diǎn)焊機(jī)相比，中頻逆變點(diǎn)焊機(jī)運(yùn)行的能源成本比工頻交流點(diǎn)焊機(jī)節(jié)約近1/3，適合自動(dòng)化運(yùn)用，控制智能化程度高，適應(yīng)材料范圍廣，尤其能夠得到穩(wěn)定、可靠的焊點(diǎn)質(zhì)量。
與傳統(tǒng)的工頻交流點(diǎn)焊機(jī)相比，中頻焊機(jī)運(yùn)行的能源成本比工頻焊機(jī)節(jié)約近1/3，適合自動(dòng)線運(yùn)用，控制智能化程度高，適應(yīng)材料范圍廣，尤其能夠得到穩(wěn)定、可靠的焊點(diǎn)質(zhì)量。
隨著汽車行業(yè)的快速發(fā)展，汽車車身結(jié)構(gòu)的安全性及新材料的運(yùn)用對(duì)車身的焊接工藝提出了新的挑戰(zhàn)。對(duì)于帶涂層的鋼板、涂膠的鋼板、多層板及不同材質(zhì)板等條件下的焊接，傳統(tǒng)的工頻點(diǎn)焊機(jī)難以滿足焊接要求，應(yīng)運(yùn)而生的是各種先進(jìn)的焊接工藝及焊接設(shè)備，如中頻逆變焊機(jī)、螺母輸送機(jī)等。
近年來，國外部分生產(chǎn)汽車批量大的企業(yè)將中頻點(diǎn)焊機(jī)器人和伺服技術(shù)點(diǎn)焊機(jī)器人應(yīng)用于轎車白車身焊裝線。尤其在歐洲，中頻點(diǎn)焊機(jī)器人使用量已占40%，并擴(kuò)大到鋁合金轎車車身的點(diǎn)焊作業(yè)。在國內(nèi)中頻點(diǎn)焊機(jī)在各大汽車廠中也得到了越來越廣泛的應(yīng)用，如一汽大眾、奇瑞汽車、北京現(xiàn)代、東風(fēng)日產(chǎn)等廠家都已將中頻焊機(jī)運(yùn)用于自動(dòng)線焊接或人工點(diǎn)焊。
與傳統(tǒng)的工頻焊機(jī)相比，中頻焊機(jī)大的優(yōu)點(diǎn)在于直流極性好、焊接質(zhì)量好。以RexrothPSQ6000的中頻焊機(jī)在奇瑞汽車A5白車身生產(chǎn)線的運(yùn)用為例，來說明中頻點(diǎn)焊機(jī)良好的焊接質(zhì)量性能。
在A5白車身生產(chǎn)線的骨架總拼工位，由機(jī)器人使用工頻焊機(jī)焊接。此工位的左右側(cè)圍門檻處，有10個(gè)焊點(diǎn)為四層板焊接，四層板總厚度達(dá)到5.5mm，此處焊點(diǎn)的焊接質(zhì)量很不穩(wěn)定。當(dāng)焊接電流過大時(shí)，會(huì)引起焊點(diǎn)過燒或焊點(diǎn)燒穿；當(dāng)焊接電流調(diào)小時(shí)，又會(huì)引起弱焊或虛焊。無論如何調(diào)整焊接參數(shù)，都無法得到穩(wěn)定良好的焊點(diǎn)質(zhì)量，因?yàn)榇颂幉粌H板厚、鋼板層數(shù)多，而且裝配時(shí)有一定的裝配間隙，而工頻焊機(jī)并不能根據(jù)實(shí)際的裝配狀態(tài)對(duì)焊接參數(shù)進(jìn)行自動(dòng)的調(diào)整來保證焊接質(zhì)量。對(duì)此，中頻逆變焊機(jī)正好能克服工頻焊機(jī)的缺陷。
在使用中頻焊機(jī)之前，技術(shù)人員采用四層板試板分別用工頻焊機(jī)和中頻焊機(jī)進(jìn)行焊接試驗(yàn)觀察焊接質(zhì)量。四層板的試驗(yàn)材料為：（1.8+1.5+1.5+0.8）mm組合的4塊冷軋低碳鋼板，焊鉗電極直徑16mm，焊接參數(shù)經(jīng)過多次試驗(yàn)優(yōu)化.
從表1可見對(duì)于多層板的焊接，無論從操作環(huán)境，還是從焊點(diǎn)質(zhì)量及其穩(wěn)定性，中頻焊機(jī)的焊接性能都明顯優(yōu)于工頻焊機(jī)。由于中頻焊機(jī)的電流非常接近直流電流，焊接時(shí)沒有電流峰值，焊接過程中熱量增加比較穩(wěn)定無波動(dòng)，因此焊接飛濺很少，甚至幾乎沒有。所以中頻焊機(jī)的操作環(huán)境較工頻焊機(jī)操作環(huán)境好很多，并且中頻焊機(jī)的電流熱效率高于交流電流，故中頻焊機(jī)焊接的焊點(diǎn)熔核直徑比工頻焊機(jī)的大1～2mm。
隨后在A5車身側(cè)圍門檻處用工頻焊機(jī)和中頻焊機(jī)進(jìn)行四層板焊點(diǎn)的焊接，試驗(yàn)結(jié)果與用試板做的試驗(yàn)結(jié)果基本吻合，具體車身焊點(diǎn)見圖1。用中頻焊機(jī)焊接的5個(gè)焊點(diǎn)熔核均在5～6mm之間，用工頻焊機(jī)焊接的3個(gè)焊點(diǎn)的熔核在3～4mm之間。
通過一段時(shí)間的現(xiàn)場驗(yàn)證，中頻焊機(jī)焊接A5側(cè)圍門檻處四層板焊點(diǎn)焊接質(zhì)量合格，且質(zhì)量穩(wěn)定，顯著優(yōu)于工頻焊機(jī)的焊接質(zhì)量。如此優(yōu)良的焊接質(zhì)量不僅與中頻焊機(jī)的直流極性有關(guān)，還與它的控制系統(tǒng)有重要的關(guān)系。中頻焊機(jī)擁有功能強(qiáng)大的監(jiān)控軟件，智能化程度高。它采用了恒功率控制技術(shù)和伺服運(yùn)動(dòng)控制器(氣動(dòng)元件)，可以對(duì)焊接電流、焊接時(shí)間、焊接功率及焊接的壓力等進(jìn)行全閉環(huán)控制。
恒功率控制技術(shù)是對(duì)次級(jí)電流和次級(jí)電壓進(jìn)行監(jiān)控，通過調(diào)整焊接時(shí)間和焊接電流保證每一個(gè)焊接熔核的輸入功率相等，因此它可以有效補(bǔ)償焊接分流、焊接裝配不良、焊接母材成分變化等非機(jī)器擾動(dòng)因素。它根據(jù)焊接的條件，選取一個(gè)標(biāo)準(zhǔn)試板，建立一條電流和電阻的樣本曲線，然后在實(shí)際的焊接工作中，根據(jù)實(shí)際的焊接電阻對(duì)實(shí)際的焊接電流和焊接時(shí)間進(jìn)行補(bǔ)償焊接板件之間有膠水干擾的一個(gè)焊接參數(shù)曲線圖，紅色曲線是實(shí)際的焊接電流-時(shí)間曲線，與它部分重合的黑色曲線是焊接樣本的焊接電流-時(shí)間曲線，綠色曲線是實(shí)際的焊接電阻-時(shí)間曲線，與它部分重合的黑色曲線是焊接樣本的焊接電阻-時(shí)間曲線。樣本為沒有膠水的同樣鋼板的焊接，當(dāng)焊接板件之間有膠水時(shí)，板件電阻大大高于樣本電阻，故焊接電流在開始段突然增大，使膠水層被擊穿，同時(shí)損失的焊接電流以延長焊接時(shí)間得到補(bǔ)償，保證了焊點(diǎn)的質(zhì)量。圖3為焊接板件之間有涂層干擾的一個(gè)焊接參數(shù)曲線圖，曲線含義與圖2相同，當(dāng)焊接板件之間有涂層干擾時(shí)，控制系統(tǒng)通過增加焊接電流來進(jìn)行補(bǔ)償。
由于中頻焊機(jī)具備以上兩方面的優(yōu)點(diǎn)，故其焊接質(zhì)量控制遠(yuǎn)遠(yuǎn)優(yōu)于工頻點(diǎn)焊機(jī)。但是它的缺點(diǎn)是價(jià)格比普通工頻焊機(jī)高6～8倍，一次性投資大。然而，它的綜合性能將決定它的應(yīng)用程度，下面看一下它的綜合性能，與普通的工頻焊機(jī)相比，它有以下幾個(gè)特點(diǎn)（其參數(shù)見表2）：
1.中頻焊機(jī)焊接電流接近完全直流，由于沒有明顯的峰值電流，熔核尺寸穩(wěn)定擴(kuò)大，幾乎沒有飛濺，焊接質(zhì)量穩(wěn)定、熱效率高。與工頻焊機(jī)相比，中頻逆變焊機(jī)焊接電流可降低40%，電極使用壽命大大延長。
2.中頻焊機(jī)變壓器重量和體積小，輸入功率低，便于采用連變壓器式焊鉗。當(dāng)運(yùn)用于機(jī)器人點(diǎn)焊操作時(shí)，可使機(jī)器人的負(fù)荷減輕，而工頻焊機(jī)在自動(dòng)線上運(yùn)用時(shí)則需要負(fù)載能力更強(qiáng)的機(jī)器人。
3.中頻點(diǎn)焊機(jī)的響應(yīng)速度僅為工頻焊機(jī)的1/20，電流能夠更快地達(dá)到設(shè)定值，更準(zhǔn)確地分析參數(shù)，焊接質(zhì)量控制更準(zhǔn)確。
4.中頻點(diǎn)焊機(jī)三相負(fù)荷均衡，功率因數(shù)高(0.9左右)，節(jié)能。而兩相工頻焊機(jī)，工作時(shí)很難保證相電壓之間的均衡，功率因數(shù)低（0.6左右），三相工頻焊機(jī)則很難實(shí)現(xiàn)恒流輸出。
5.中頻點(diǎn)焊機(jī)適用多種材料及異種金屬的焊接，如鋁合金、不銹鋼、高強(qiáng)度鋼板等材料。另外，對(duì)于鍍鋅板和普通多層板的焊接，其焊接質(zhì)量也遠(yuǎn)高于工頻焊機(jī)的焊接質(zhì)量。而工頻焊機(jī)只適應(yīng)焊接性能好的材料，如低碳鋼板。
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.
