Shot Peening – for longer component life
The strength and service life of components exposed to high dynamic stresses can be significantly improved by shot peening. In order to be able to quickly develop tailor made shot peening solutions for their customers, Rősler now have their own in house testing facility in Memmelsdorf.
Shot peening is a special shot blasting process during which spherical blast media is thrown at the surface of metallic work pieces at high speeds and under highly controlled operating conditions.
The impact energy of the round “pellets” “cold forms” the upper layers of the metal similar to hammering and forging processes. The surface of the metal is alternately stretched and compacted causing a compressive stress in the upper surface layers. This offsets any inherent tensile stress as well as external tensile or compressive loads acting on the work piece. It increases fatigue strength and significantly reduces the risk of stress cracks.
Depending on the components and the loads they are exposed to, shot peening has been measured to increase their fatigue life by up to 1300%.
X-ray diffractometry expedites the development of peening processes. Starting with the customer specifications, Rősler, with a wealth of experience and knowledge, develops the required process and equipment parameters through extensive test trials and their careful documentation.
Important process parameters are:
- Material, nature and shape of the work pieces
- Material and size of the peening media
- Throwing speed and impact angle projection of the blast peening media on the work piece surface
- Blast media quantity and coverage / surface saturation (number of “hits” within a certain time period)
To ensure that the peening process is perfectly adapted to the material and the shot peening objectives, the compressive stress values achieved during the processing trials must be carefully measured and documented.
X-ray diffractometry has proven to be a highly accurate and the reliable method to make such compressive stress measurements. The upper work piece layers are exposed to x-rays hitting the crystalline and partially crystalline structure of the metal at a pre-set angle. The majority of the x-rays pass through the crystals. However, a special detecting device registers the small portion of x-rays that are deflected or reflected by the crystals. Based on the known material characteristics this x-ray diffraction, in combination with the Bragg equation allows the measurement the compressive stress values.
Multiple measurements at different angle settings ensure that the compressive stress readings are highly accurate. Investing in advanced laboratory equipment with an x-ray diffractometer now gives Rősler the ability to make these measurements in-house without having to send the results of processing trials to external laboratories for evaluation. This helps significantly speed up the development of customer specific shot peening processes. In addition, it allows a faster reaction to the challenges posed by the development of new metal alloys.
Rősler can now also offer x-ray diffraction measurements for differing types of work pieces, as a service, thus allowing the review of complete shot peening processes, even those processes run in other manufacturers’ peening equipment.
Post published by
Shot Blasting Technical Manager