Components of today’s injection systems are exposed to pulsating pressures of up to 2500 bar. The realization of sufficient fatigue resistance is difficult to imagine without the introduction of high compressive stresses on the internal surfaces of the high pressure components. Autofrettage is an extremely effective method of production, both economically and technically, using excessive pressure pre-loading to generate maximum compressive stresses.
Essential pre-requisites for effective autofrettage are a powerful high-pressure pump, mechanically stable high-pressure lines, pressure controls and pressure measurement systems. The adjustment of optimal pressure level when unequal wall thicknesses and transverse holes prevail, require a mechanical understanding of the material dependent plastification processes during pressure built up and the development of residual compressive stresses during deloading.
A set of small and large autofrettage units established at FUCHS DIESEL COMPONENTS PRODUCTION in Henggart provides economic autofrettage starting from small adapters or valves to 3 m long accumulators (Figure left and right). For the measurement and storing of the pressure data an in-house developed pressure measurement system is utilized, which today is used for the diagnosis of pressure in the cylinders of large diesel engines (The Doctor). Optimization of the autofrettage pressure is based on a refined computational model. The development of compressive residual stresses in complex geometries as well as the verification of durability is carried out with the aid of technological material models and using FEM.