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Spot Weld Testing

Application

Evaluating the integrity of spot weld joints in metal.

Background

Spot welding is a common technique for joining two pieces of metal, usually thin sheets or plates, by means of a series of small circular tack joints. The process is widely used in the automotive industry for body assembly and some chassis joints, and by other types of sheet metal fabricators as well. Spot welds are made by pressing electrodes against both sides of the parts to be joined and passing a high current through them, which momentarily creates a pool of molten metal that solidifies into a round joint known as a nugget.

Spot Weld Testing

If the weld is improperly formed, it is possible that the two parts may not fuse completely, or that the area of the nugget may be smaller than what is required for a strong joint. These problems are seldom visible to optical inspection, and destructive pull tests are inefficient and limited to a few samples. However, with proper equipment and technique, ultrasonic spot weld inspection can quickly and nondestructively provide valuable information about weld quality.

Equipment

The recommended instruments for spot weld inspection are the EPOCH 650 or EPOCH 1000 ultrasonic flaw detector. Spot weld testing requires coupling sound into a cup-shaped weld, typically 3 to 6 mm (0.125 to 0.250 in.) in diameter and generating multiple back wall echoes at high frequency. Olympus offers a wide variety of delay lines and captive water column transducers with a frequency range from 10 to 20 MHz for this purpose. Delay line transducers use a small plastic waveguide to couple sound energy from the transducer element to the test piece. Captive water column transducers incorporate a pliable rubber membrane enclosing a column of water that conforms to the topography of the spot weld to optimize coupling. In the case of delay line transducers, the delay line diameter and element diameter are normally matched to the nominal nugget diameter to within a few tenths of a millimeter. In the case of captive water column transducers, the element diameter is normally matched to the nominal nugget diameter. For further details on transducer selection, contact Olympus.

Spot Weld Testing

Theory of Operation

In a good weld, the spacing between echoes will be proportional to the thickness of the weld, and the decay rate (the rate at which successive echoes decrease in amplitude) will be related to the attenuation within the nugget. There will be a characteristic echo pattern associated with each weld condition; good, un-weld, undersized weld, and stick weld. It is encouraged to utilize the template storage software option which stores and recalls the outlines of the various echo patterns of each weld condition. Each echo pattern can be easily overlaid onto the live A-scan with a push of a button to facilitate comparison and enhance inspection. Multiple templates can be stored and an -A- denotes the active template selection.

Spot Weld Testing
Spot Weld Testing

If there is no fusion between the two pieces of metal (a "no weld" or "un-weld" condition), then the successive echoes will be much closer together and larger in amplitude.

Spot Weld Testing
Spot Weld Testing

In the case of an undersized weld, only a portion of the sound beam will reflect from the total thickness of the two metal sheets, while a portion reflects from a single thickness. This creates a pattern in which small peaks representing single-sheet thickness appear between the larger and more widely separated peaks representing the full weld thickness.

Spot Weld Testing
Spot Weld Testing

Finally, in a stick weld (or stuck weld) condition where the metal sheets are fused but because of insufficient heating the weld nugget is not fully formed, the echo decay rate will change, resulting in larger peaks appearing on screen with a longer ring-down time. This is because the grain scattering effect of a fully formed nugget is absent and the weld zone is more transmissive than in the case of a fully formed weld.

Spot Weld Testing
Spot Weld Testing

Olympus IMS

이 애플리케이션에 사용되는 제품
EPOCH 6LT 휴대용 초음파 결함 탐상기는 한 손 작업에 최적화되어 있으며 로프 접근 및 고소 작업이 필요한 고휴대성 응용 분야에서 탁월한 성능을 제공합니다. 가볍고 인체 공학적 디자인으로 사용자의 손에 단단히 고정시키나 로프 접근이 필요한 응용 분야에서는 다리에 묶을 수 있습니다.
초음파 탐촉자는 결함 감지, 두께 측정, 소재 연구 및 의료 진단과 같은 다양한 응용 분야에 사용됩니다. 5000개 이상의 초음파 탐촉자 유형은 다양한 스타일, 요소 직경, 주파수 및 커넥터 스타일로 제공됩니다.
EPOCH 650은 다양한 응용 분야에 대한 우수한 검사 성능과 유용성을 갖춘 재래식 초음파 결함 검출기입니다. 이 직관적이고 견고한 장비는 인기 있는 EPOCH 600 결함 탐상기 후속작이며 추가 기능을 갖추고 있습니다.
와전류 배열 시험 검사를 수행합니다. 테스트 구성은 브리지 또는 송수신 모드에서 작동하는 32개의 센서 코일(외부 멀티플렉서 사용 시 최대 64개)을 지원합니다. 동작 주파수는 20Hz에서 6MHz까지이며, 동일한 수집에서 여러 주파수를 사용할 수 있습니다.
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