Modern body structure, about to complete more than 3,000 solder joints. In order to ensure the welding quality, the general inspection of the cutting means (supplemented by visual inspection), but this approach requires more time, and the resulting deformed parts must be re-shaping, the high cost of enterprise spend. After trying, ultrasonic technology for nondestructive testing of resistance spot welding efficient, almost able to identify a variety of defective solder joints.

Body spot welding quality control

Currently, resistance spot Welding Electrode to connect the body is still the most widely used process in a way, therefore, the major automobile manufacturers for resistance spot welding quality control very seriously. In general, the body spot welding quality control can be divided into three sections: prevention, control and inspection.

Prevention means is that during the resistance spot welding before, failed to take appropriate measures to prevent the formation of solder joints. Typically, the key measure is daily monitoring of the welding equipment. For example, periodically check the welding parameters to ensure that the settings meet the technical requirements; regular measurement of the actual welding pressure, the actual current and the power of time, to ensure that the output value and set value; regularly measure the resistance of the secondary circuit, especially sub- level without feeling the resistance of the cable (if using split transformer structure) to ensure the normal power capacity welding system. As the solder joint is accomplished by welding equipment, welding equipment only on the state of appropriate monitoring, in order to prevent the production of solder joint failure.

Control refers to, during resistance spot welding process, the application of appropriate technology for on-line monitoring to ensure the solder joint failure to be identified. Currently, the main method is to weld by welding controller monitors the output current of each size (may be the primary current, secondary current can be), once below the set range on the timely warning, to avoid the generation of solder joint failure. In addition, the technology is relatively new welding process monitoring of the dynamic resistance, and thus determine the solder joint eligibility. In this way, each weld is completed, we can detect failure of solder joints, in order to take measures.

Test means is that for the solder joints have been completed for destructive and non-destructive examination, to exclude the failed solder joint purpose. Destructive inspection of the entire body of the solder joints for each inspection, a more comprehensive, you can find all the failed solder joints. However, examination of the body can only be scrapped, and the sampling frequency is low, is not conducive to timely detection of problems. Non-destructive inspection is carried out daily inspection body joints, the traditional method of inspection is visual inspection and chisel, usually select some typical solder joints, and there are some limitations. Ultrasonic non-destructive testing technology can compensate for this limitation, and with the promotion and development of the technology, but also gradually replace the existing destructive inspection, thereby further reducing the cost of the vehicle plant.

Ultrasonic nondestructive testing

1 Background

Modern body structure, about to complete more than 3,000 solder joints. In order to ensure the welding quality, the general inspection of the cutting means (supplemented by visual inspection), so check the need for more time, and the resulting deformed parts must be re-shaping. In addition, there are some limitations chisel inspection, such as a chisel can not reach the solder joints, solder joints requiring high surface quality and some high-strength steel joints and so on. For the whole body or part of the sub-assembly of the destructive examination, takes a lot of cost.

After trying a number of other non-destructive inspection method for resistance spot welding does not apply, such as infrared, X-ray and eddy current testing. Resistance spot welding using ultrasonic technology for nondestructive testing of efficient, almost able to identify a variety of defective solder joints. Therefore, ultrasonic non-destructive testing for resistance spot welding, is an effective, reliable technology.

2 Principle

Ultrasonic testing of spot welded structure is the last interface from multiple reflections of the detection and middle parts of the echo reflected junction (Figure 1). For the correct and defective solder joints, the thickness of the reflected echo from the complete series of the length of the echo signal attenuation and the magnitude and location of the middle there is a difference between to identify the defective solder joints. Ultrasonic beam diameter should be equal to the effective melting point of the diameter of the nucleus.

3. Determine the quality

Obtained by ultrasonic detection of defects in solder joints echo graphics and has a certain relationship between (Figure 2).

4 Application conditions

Sometimes the application of ultrasonic testing by the state of the actual solder joints (Figure 3), resulting in reduced accuracy of test results.

5 Detection System

As a more complete system, the application of ultrasonic testing techniques can be divided into three steps: (1) using the database, the establishment of measurement programs; (2) the use of professional software testing; (3) statistical analysis, and output reports.

6. Testing equipment

Currently, for ultrasonic inspection equipment OEMs There are three main (Figure 4): notebook + portable measurement equipment; portable one; desktop + measurement equipment.

As an advanced non-destructive testing method, ultrasonic solder joint quality inspection by more and more attention. Chisel and break the traditional inspection methods of inspection with advanced ultrasound method organically combine to form the body's main method of Nickel Welding Rod. Shanghai Automotive Group Co., Ltd. in order to ensure the quality of its own brand of welding, including ultrasonic testing techniques to establish a more comprehensive, including the welding quality control system, destructive solder joint inspection pass rate of 99%.

First, the requirement

Solder joints should be good contact between the weldment can be guaranteed to be stable through a certain current.

The occurrence of sweating should be avoided. Weld is not formed or formed part of the heap with solder alloy of tin solder. Weld reasons: dirty surface of the welded parts, welded (Recommended Product: Ningbo welding), the gripping tool shaken, the tip temperature is too low, the flux does not meet the requirements of the solder joints too much or too little.

Solder joints have enough welders (Recommended Product: Ningbo welder) mechanical strength.

Solder joints to be beautiful, smooth solder joints to show the state should not have sharp edges or pull the phenomenon, the causes and tensile welding tip temperature; iron removed in the direction, speed and flux related.

Welded to the qualifications

1. Weldments must have been weldability
2. Welded surface should be kept clean
3 using the appropriate flux
4. Appropriate welding temperature.

5 in the Welding Electrode temperature is confirmed, the decision should be based on the wet state to weld the length of time. Time is too short, insufficient solder a wet, too long, there is the risk of damage to the circuit board, which controls between the 1.5-4s.

The basic method of welding

Wires and components on the tin. First with a knife or fine sandpaper remove wires, the surface of the metal oxide component leads, the roots of some components do not scratch, for the multi-strand, respectively, should scrape, more shares of twisted rope, then on the tin. Tin on the process, so that power to the electric iron electric iron contacts rosin, issued Zizi's voice and the white smoke, indicating the temperature is moderate. Then scrape a good weldment on the rosin on the soft reduction with iron wire, then repeated friction, side turn lead until the lead parts evenly coated with tin.

Soldering iron grip

Anti-grip, is grip, hold a pen method.

Anti-grip: Action stable, long-operator is not easy to feel tired, for high-power soldering iron and heat capacity of the welded pieces.

Positive grip: suitable for curved or straight tip tip operating in the rack (recommended: Shelves) on the operation of welding wire is connected.

Hold a pen method: long hand fatigue easily, suitable for low-power soldering iron and heat capacity of small welded pieces.

Second, the basic method of welding in the welding pieces guaranteed to be fixed, it is often left to take tin wire, right hand soldering iron, can be welded to the welded pieces.

Five-step welding:

1 preparation. Weldment will be fixed in place, the solder, soldering iron and other easy to use ready to put into place, into the welding state.

2 with the tip heated by weldment.

3 into the solder. After heating the welded parts, reaches a certain temperature, immediately into the left hand holding the solder to the tip welded parts and the connection point on the appropriate solder melts.

4 Remove the solder. When a certain amount of solder melts, quickly remove the solder.

5 Remove the soldering iron. When the flow of solder joints after covering the entire spread, quickly remove the soldering iron. Remove the soldering iron in the direction and quality of welding, is generally required to tip away a 45-degree angle direction, smooth solder joints at this time, taking only a small amount of solder tip.

Nickel Welding Rod

1 preparation.
2, while the solder and the tip is welded to the pieces, so that the solder and welded parts are heated simultaneously.
3 At the same time remove the soldering iron and solder.