Comparative study of residual stress prediction methods in additive manufacturing processes

The additive manufacturing (AM) of products involves various processes, such as raising the temperature of a work-piece (part) and substrate to the melting point and subsequent solidification, using a movable source of heat. The work piece is subjected to repeated cycles of heating and cooling. The main objective of this work was to present an overview of the various methods used for prediction of the residual stresses and how their contributions can be used to improve current additive manufacturing methods. These novel methods of manufacturing have several merits, compared to conventional methods. Some of these merits include the lower costs, higher precision and accuracy of manufacturing, faster processing time and more eco-friendly approaches to processes involved.

Manufacture of Defined Residual Stress Distributions in the Friction-Spinning Process: Investigations and Run-to-Run Predictive Control

Friction-spinning as an innovative incremental forming process enables high degrees of deformation in the field of tube and sheet metal forming due to self-induced heat generation in the forming area. The complex thermomechanical conditions generate non-uniform residual stress distributions. In order to specifically adjust these residual stress distributions, the influence of different process parameters on residual stress distributions in flanges formed by the friction-spinning of tubes is investigated using the design of experiments (DoE) method. The feed rate with an effect of −156 MPa/mm is the dominating control parameter for residual stress depth distribution in steel flange forming, whereas the rotation speed of the workpiece with an effect of 18 MPa/mm dominates the gradient of residual stress generation in the aluminium flange-forming process. A run-to-run predictive control system for the specific adjustment of residual stress distributions is proposed and validated. The predictive model provides an initial solution in the form of a parameter set, and the controlled feedback iteratively approaches the target value with new parameter sets recalculated on the basis of the deviation of the previous run. Residual stress measurements are carried out using the hole-drilling method and X-ray diffraction by the cosα-method.

Effects of ultrasonic surface rolling process on tribological behavior of 4Cr13 stainless steel

Ultrasonic surface rolling (USR) process is a novel surface strengthening technique based on the tool head's high-frequency impact on the workpiece. USR can cause severe plastic deformation on the superficial surface of metal material, and greatly improving the mechanical properties of the material. This paper elucidates the effects of USR passes on the surface roughness, sample height, microstructure, microhardness, residual stress, and tribological properties of 4Cr13 stainless steel. The results revealed that multiple USR treatments refined the near-surface layer grain of the sample. Compared with untreated sample, USR treatments significantly improved the surface roughness and microhardness of the samples. Obvious compressive residual stress and plastic deformed with a maximum value of about -723 MPa and a depth of about 229 μm were also introduced into the sample surface. Under a dry friction environment, the samples that underwent the USR treatments exhibited significantly enhanced wear resistance, and six rolling passes were found to be the most suitable treatment.