Eric Moumi

Process Chains in Microforming Technology Using Scaling Effects

Cold formed micro parts with dimensions <1 mm show in some aspects characteristics due to scaling effects that can be positively used in process chains. Whereas aspect ratios in upsetting processes are limited to l0/d0<2 in the macro scale, a laser induced free‐forming process generates droplet shaped pre‐forms for consecutive calibrating processes, i.e. micro rotary swaging. Scale effects on establishing and shortening of process chains like free‐form heading/rotary swaging/heat treatment are discussed. On the other hand a geometric scale‐up approach in the macro range is described to overcome the specific handling problems of miniature parts. This is achieved by leaving the parts in a physical linkage during the processing steps. An effective application of linked micro parts requires intensive modeling and simulation work.

Investigation of Deformation Induced Martensitic Transformation during Incremental Forming of 304 Stainless Steel Wires

Wires with 1 mm initial diameter have been reduced between 10 and 64 percent at different temperatures and strain rates by infeed rotary swaging, which is an incremental cold forming process mainly used for rods and pipes. The volume fraction of martensite in the deformed wires has been determined by X-Ray diffraction and by magnetic induction for different processing parameters. Measurements show that for already small percentage of reduction, martensite is present in the wires and its amount changes with the strain rate and temperature. While for smaller strain rates at room temperature the formation of martensite is promoted, it is restrained for higher strain rates and higher temperatures. Results also reveal that the martensite distribution in the sample is inhomogeneous. Further investigations have been made to analyze the microstructure by optical microscopy and to determine mechanical properties by tensile testing.

Co-spray-formed graded steel for micro rotary swaging tools

Micro rotary swaging tools are required to have different material properties in different functional areas. These requirements can be fulfilled by applying different materials in the specific regions of the tools. The different materials can be combined with a gradient zone in between to reduce critical stresses at the interface during heat treatment and in swaging process. Such graded tool materials are supposed to be manufactured by means of a newly developed co-spray forming process. In this study, a flat deposit of graded tool steel (HS6-5-3C/HS6-5-2C) was produced via co-spray forming, followed by hot rolling and heat treatment. Micro infeed rotary swaging tools with fine geometrical structures were precisely machined from the graded steel. The tool performance during swaging of stainless steel wires was evaluated.