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%.