Fundamental studies on tube hydroforming and laser assistance in the manufacture of micro-parts

This PhD-Thesis focuses on initial investigations of tube hydroforming (THF) as a new technology in the field of micro-part manufacture. THF has been widely adopted in the automotive industry for approximately fifteen years and is now commonly used in many other industries. In the forming process the semi-finished part is formed with the aid of a forming liquid which acts inside the hole of the tube. Under the influence of hydrostatic pressure and additional mechanical loads the tubular blank is forced to conform to a given die cavity giving the part its final shape. In comparison to "conventional" procedures for the manufacturing of hollow-shaped constructional work pieces, as for instance the welding of deep-drawn metal sheets, THF offers many advantages by enabling the production of parts having: - Complex and variable cross sections in their longitudinal axis - High strength due to cold-work hardening and homogenous grain structure - High rigidity achieved by closed cross-sections - Narrow tolerances in their outer dimensions - Optimized transitions for fluid transport Further on, THF especially offers a considerable time saving potential for manufacturing hollow shaped components compared to currently used techniques based on the removal of material. However, current state-of-the-art manufacturing of hydro-formed parts is still restricted to conventional parts which well exceed micro-part dimensions. Micro-THF as a new technology would add all these advantages to the micro technology sector and can establish access to other new fields and application. Examples of micro-hydroformed components are all hollow straight as well as bent components with complex shapes which currently cannot be (mass-)produced with any other micro manufacturing technology; components such as elements for micro-fluidic chips, micro heat exchangers and fluidic sensors or tubular parts for endoscopes etc. The research performed aimed at carrying out the fundamentals of process design necessary for hydroforming micro-parts. Investigations were carried out on tubular parts having an outer diameter smaller than 1 mm and a length of ca. 10 mm. Extensive studies regarding material properties of micro-tubes especially its forming abilities were conducted and procedure limitations identified and analysed. In order to examine extended forming limits and to approach the so-called size effects which arise from scaling down a traditional forming process to micro-level, the process has further been investigated under the influence of laser energy. A diode Laser was used to increase the temperature of the tube material during forming, reducing the flow stress and increasing the ductility in the required area of the part. Additionally, numerous theoretical design studies had been performed which led to the development of the entire forming machine components. As a result of the intensive research and development work carried out, process specific fundamentals suitable for an industrial application were established as well as the world's first micro tube hydroforming prototype machine was constructed that successfully manufactured hollow shaped micro components.This PhD-Thesis focuses on initial investigations of tube hydroforming (THF) as a new technology in the field of micro-part manufacture. THF has been widely adopted in the automotive industry for approximately fifteen years and is now commonly used in many other industries. In the forming process the semi-finished part is formed with the aid of a forming liquid which acts inside the hole of the tube. Under the influence of hydrostatic pressure and additional mechanical loads the tubular blank is forced to conform to a given die cavity giving the part its final shape. In comparison to "conventional" procedures for the manufacturing of hollow-shaped constructional work pieces, as for instance the welding of deep-drawn metal sheets, THF offers many advantages by enabling the production of parts having: - Complex and variable cross sections in their longitudinal axis - High strength due to cold-work hardening and homogenous grain structure - High rigidity achieved by closed cross-sections - Narrow tolerances in their outer dimensions - Optimized transitions for fluid transport Further on, THF especially offers a considerable time saving potential for manufacturing hollow shaped components compared to currently used techniques based on the removal of material. However, current state-of-the-art manufacturing of hydro-formed parts is still restricted to conventional parts which well exceed micro-part dimensions. Micro-THF as a new technology would add all these advantages to the micro technology sector and can establish access to other new fields and application. Examples of micro-hydroformed components are all hollow straight as well as bent components with complex shapes which currently cannot be (mass-)produced with any other micro manufacturing technology; components such as elements for micro-fluidic chips, micro heat exchangers and fluidic sensors or tubular parts for endoscopes etc. The research performed aimed at carrying out the fundamentals of process design necessary for hydroforming micro-parts. Investigations were carried out on tubular parts having an outer diameter smaller than 1 mm and a length of ca. 10 mm. Extensive studies regarding material properties of micro-tubes especially its forming abilities were conducted and procedure limitations identified and analysed. In order to examine extended forming limits and to approach the so-called size effects which arise from scaling down a traditional forming process to micro-level, the process has further been investigated under the influence of laser energy. A diode Laser was used to increase the temperature of the tube material during forming, reducing the flow stress and increasing the ductility in the required area of the part. Additionally, numerous theoretical design studies had been performed which led to the development of the entire forming machine components. As a result of the intensive research and development work carried out, process specific fundamentals suitable for an industrial application were established as well as the world's first micro tube hydroforming prototype machine was constructed that successfully manufactured hollow shaped micro components