Abstract: Work piece surfaces are peened by electromagetically controlled steel nees which are guided for back and forth sliding movement in a guide plate. Each needle has its own electrically controllable drive magnet. All the magnets are energized in a controlled sequence by a control unit which energizes the drive magnets in a given sequence or pattern and in accordance with adjustable parameters such as the stroke amplitude and frequency of each needle stroke. Thus, the work piece may be deformed into a particular shape and/or its surface may be work hardened or densified and areas of different surface stress may be produced in the work piece surface. Work pieces may be shaped into any desired three-dimensional curvature.