Weld Evaluation Of Camshafts Using Ultrasonic Testing

Generally, ultrasonic testing (UT) is used to figure out the quality of brazed joints. With the help of this unique process, evaluating brazing quality becomes simple. It uses a focused transducer, and ultrasonic waves along the radius of the shaft are focused on the brazed joint. By monitoring the amplitude of the echoes returning from the joint position, one can evaluate the brazing quality easily.

When the echo becomes weak, it indicates a strong bond where most of the ultrasonic waves travel through the joint. On the other hand, a strong echo means that there is no mechanical bonding, causing the ultrasonic waves to bounce back at the interface. A reference sample with a known unbonded area can be used to set the ultrasonic machine sensitivity and evaluate the amount or percentage of any flaw in the part.

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Camshafts

Camshafts are typically manufactured by machining cast iron, forged steel or billets down to the desired shape. Some manufacturers have started to produce camshafts by joining cams to shafts with a brazed joint. Due to the force being potentially applied to the brazed joint, quality control is required to ensure brazing quality and that a sufficient percentage of cam is solidly brazed to the shaft. Ultrasonic testing must be conducted only through experts who provide certified non destructive testing in Melbourne.

Camshaft geometry

A camshaft is basically a shaft with cams distributed along its length. Cams can come in different shapes with one common characteristic: there is at least one protuberance found along the circumference, resulting in an irregular shape. A common model is a cam with a nose (lobe), where the brazed joint is not parallel to the outer surface. In such a situation, there is little to no probability of recording an echo from the joint; this is what will be referred to as the uninspectable area of a cam.

Brazed joint evaluation

It is not always necessary to inspect each individual part of the camshaft to control the quality of a production. A statistical analysis can be performed on sampled parts taken from the production line. The same logic applies to the uninspectable area of the cams; a statistical analysis can still be performed by monitoring the percentage of good brazing within the inspectable portion of the cams. When using ultrasounds to monitor the brazed joint quality, the evaluation must be normalized to ratio of inspectable area.

As ultrasonic testing is sensitive to both surface and sub-surface discontinuities, be sure to hire the certified personnel to figure out the flaws properly and end on a positive note.

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