It is well known that plating and other coatings processes can cause reduction of Fatigue Resistance in metal parts. Shot peening prior to coatings processes will restore most, or all, of the lost fatigue properties. To assure repeatable and reliable results from the shot peening process, the shot must be controlled. The most critical characteristics of peening media are size and shape. Improperly sized shot will give too little, too much or inconsistent layers of compressive stress. Improperly shaped shot may cause surface damage and fatigue properties lower than in the unpeened condition.
For the past forty years, the methods for measurement of shot size and shape have not changed. Shot size is measured by sieve analysis and shape is measured visually by an inspector. These inspection techniques lack speed, accuracy and repeatability and are subject to a significant amount of human error.
This report describes a new method of evaluation that gives improved accuracy, repeatability and speed. Shot peening media can be evaluated simultaneously for both size and shape by image analysis. The results of inspection using an image analyzer are superior to sieve analysis and visual methods. Image Analysis measurements provide much better control of peening media. The time saved in this faster technique can offset the cost of the image analysis system designed for shot evaluation.