VOL. 14 November ISSUE YEAR 2013

MFN Trainer Column

in Vol. 14 - November Issue - Year 2013
Creating Competence in Shot Peening

Specific manufacturing processes aren't normally taught in depth in technical schools. The shot -peening process is one of them. This is not due to lack of consideration about the process, but due to the immense amount of knowledge about different processes that needs to be transferred and assimilated by the students, for example, in an undergraduate engineering course. It is common to find well-trained technicians who  have developed all their knowledge with special courses and many hours of practice in the workshop, but in such an unstructured study, done in practice, a question is plausible: Is the achieved competence good enough? This question should be answered without putting your customer products, and sometimes his life, at risk.
The shot-peening process, like welding, heat treating, and so on, has many variables related not only to the machine set-up, but also to the metallurgical quality of your product in process. Also, this process handles an invisible material characteristic, responsible for the enhanced product reliability: residual stress.
The process set up, diverse hidden variables, and advanced techniques of inspection, makes a long run to obtain the competence to control and optimize the peening process.

Process history
The shot-peening intensity control and its correlation with reliability was reported by JO Almen in 1943. And in 1945-46, the first works in residual stress measured in shot peened parts were published. Since than, we have had 70 years of process and machine development up to the current state of the art process. As a process technician, we can visualize many improvements that have occurred in the last few years. Coverage, Residual Stress, Surface Quality, and Reliability are process outcomes that have been developed immensely in the last years and are very difficult to demonstrate to workers with little technical formation.
And how did we improve our competence training in shot peening? What improvements were made in training through these years?

Technical knowledge and skills
Nowadays, we have best common practices that assure effective training in our companies, like the standard ISO 9000:2000, and others. If you have the shot-peening process in your company, there should be a periodic training program about this process and also for all the related activities to plan and control it.
The training should provide knowledge and train the skills in shot-peening activity. Competence is defined as the ability to apply the knowledge and skills in the process activity like measuring an Almen strip and correcting the hot spot.
More specific standards require records to attest that the worker shows enough competence to do his job, and such type of records would be written examinations and in some cases demonstrated execution of samples.  

Training needs and challenges
The challenge in the Peening training is to demonstrate all the surface product modifications and the bad and good impacts in reliability that could result. The peening objective to extend life in service is abstract. A good structured training program, considering all the process techniques, is recommended.
All this training needs to be done periodically and also the written examination. New company workers need to be trained in the same way as their coworkers, assuring the same level of competence.
In such a training program, we should plan how to create a shot-peening culture in your company. Owing to its impact in reliability and quality, shot peening needs different experts in all the process chain from purchase and manufacturing to sales.
Each area has a specific need, like engineering in planning the process and manufacturing in executing it, and for both, for example, it is very important that they have knowledge about residual stresses and the different ways to measure them. In purchasing, it is necessary to have the knowledge concerning the impact of the quality of the shot in the reliability of the manufactured product. Those responsible for training should consider these needs along the process chain to create the 'Peening Culture' inside the company.

Assessing competence
At the bottom line, the quality of your products in use will show if you have the domain of the process or not, but in this way, we are not assuring quality in a preventive way. We need to be proactive and assess our competence before we have any problem in our customers. This is also indicated to the companies that are acquiring a shot-peening machine for the first time.
A written exam, after training, could be part of the competence assessment. A complete assessment needs to be done in a matrix, considering the impact of each company area in the process, its key factors, and workers. There would be a set of competences for each worker or sector involved, with a minimum grade in the written exam.

Improving your competence
All systems needs to be challenged to evolve. A simple challenge would be to set higher levels of grades, or create a peening improvement program coordinated by the workers appointed in the competence matrix.

For questions contact: freddy@mfn.li

Author: Freddy Poetscher