Lightweight design is one of the current key drivers to reduce the energy consumption of vehicles. Design methodologies for lightweight components, strategies utilizing materials with favorable specific properties and hybrid materials are used to increase the performance of parts for automotive applications. In this paper, various forming processes to produce light parts are described. Material lightweight design is discussed, covering the manufacturing processes to produce hybrid components like fiber–metal, polymer–metal and metal–metal composites, which can be used in subsequent deep drawing or combined forming processes. Approaches to increasing the specific strength and stiffness with thermomechanical forming processes as well as the in situ control of the microstructure of such components are presented. Structure lightweight design discusses possibilities to plastically form high-strength or high-performance materials like magnesium or titanium in sheet, profile and tube forming operations. To join those materials and/or dissimilar materials, new joining by forming technologies are shown. To economically produce lightweight parts with gears or functional elements, incremental sheet-bulk metal forming is presented. As an important part property, the damage evolution during the forming operations will be discussed to enable even lighter parts through a more reliable design. New methods for predicting and tailoring the mechanical properties like strength and residual stresses will be shown. The possibilities of system lightweight design with forming technologies are presented. A combination of additive manufacturing and forming to produce highly complex parts with integrated functions will be shown. The integration of functions by a hot extrusion process for the manufacturing of shape memory alloys is presented. An in-depth understanding of the newly developed processes, methodologies and effects allows for a more accurate dimensioning of components. This facilitates a reduction in the total mass and an increasing performance of vehicle components.

/pdf/lightweight-in-automotive-components-by-forming-technology-25fo91hysb.pdf

Lightweight in Automotive Components by Forming Technology

This work presents a comprehensive analysis of the effects of strain and strain rate on the adiabatic heating and the mechanical behavior of a CoCrFeMnNi high-entropy alloy (HEA). In this investigation, compression tests were carried out at quasi-static and dynamic strain rates. The temperature of the specimens was measured using high speed infrared thermography. The high strain rate tests were conducted with a Split Hopkinson Pressure Bar, and the tests at lower strain rates were performed using a universal testing machine. The material exhibited a positive strain rate sensitivity, as true stress–strain plots were shifted upwards with the increase in strain rate. With exception of the isothermal tests, temperature rise and the Taylor–Quinney coefficient (β) were noticeably similar for the investigated strain rates. This study shows that the common assumption that β can be considered 0.9 and constant is possibly not very accurate for the CoCrFeMnNi alloy. The β is influenced by at least strain and strain rate.

/pdf/effects-of-adiabatic-heating-and-strain-rate-on-the-dynamic-53eotm38j8.pdf

Effects of Adiabatic Heating and Strain Rate on the Dynamic Response of a CoCrFeMnNi High-Entropy Alloy

As a promising material for the new generation of high-speed railway contact wires, the comprehensive optimization of the electrical conductivity, strength, hardness and wear resistance of the Cu-Cr-Zr alloy has received extensive attention. In this paper, a high-performance Cu-1Cr-0.1Zr alloy with an ultimate tensile strength of 599.1 MPa, a uniform elongation of 8.6%, a microhardness of 195.7 HV0.2 and an electrical conductivity of 80.07%IACS was achieved by the continuous extrusion forming (CEF) and subsequent peak-aging treatment. The grain refinement strengthening, dislocation strengthening and precipitation strengthening are identified to be responsible for the excellent electrical and mechanical properties of Cu-Cr-Zr alloy. The wear behavior of Cu-Cr-Zr alloy was investigated by examining the evolution of worn surface morphology and subsurface microstructure. The microhardness (H) and reduced elastic modulus (Er) of the subsurface below the worn surface measured by nanoindentation were calculated to gage the tribological performance of Cu-Cr-Zr alloy. Results show that the continuously extruded and subsequently peak-aged specimen has the best wear resistance, which indicates that the tribological properties of Cu-Cr-Zr alloy strongly depend on its strength and hardness. It can be concluded that the CEF and subsequent aging treatment process provides a new and high-efficiency procedure for the continuous preparation of Cu-Cr-Zr alloys. 

Enhanced electrical, mechanical and tribological properties of Cu-Cr-Zr alloys by continuous extrusion forming and subsequent aging treatment

Tube forming technologies based on internal forming pressures, such as hydroforming or hot tube gas forming, are state of the art to manufacture complex closed profile geometries. However, materials with excellent specific strengths and chemical properties, such as titanium alloys, are often challenging to shape due to their limited formability. In this study, the titanium alloy Ti-3Al-2.5V was processed by superplastic hot tube gas forming to manufacture a helically shaped flex tube. The forming process was investigated in terms of process simulation, forming tool technology and process window for the manufacturing of good parts. Within a simulation study, a strain rate optimized forming pressure–time curve was defined. With the newly developed tool design, forming temperatures up to 900 °C and internal forming pressures up to 7 MPa were tested. A process window to manufacture good parts without necking or wrinkling has been successfully identified. The experiment data showed good agreement with the numerical simulations. The detailed study of the process contributes to an in-depth understanding of the superplastic forming of Ti-3Al-2.5V during hot tube gas forming. Furthermore, the study shows the high potential of superplastic hot tube gas forming of titanium alloys for the manufacturing of helical flex tubes and bellows.

https://www.mdpi.com/2075-4701/10/9/1150/pdf

Process Development for a Superplastic Hot Tube Gas Forming Process of Titanium (Ti-3Al-2.5V) Hollow Profiles

The high cycle fatigue (HCF) behavior is investigated for a 6082 aluminum alloy in an as-extruded peak-aged condition and after single-pass equal-channel angular pressing (ECAP). The focus of this study is on the effect, that ECAP processing exerts on the mean stress sensitivity of the fatigue strength. The fatigue strength at 107 cycles is compared for alternating tension-compression (R = −1), tension (R = 0) and tension-tension loading (R = 0.1) and related to the microstructural features examined by electron backscatter diffraction (EBSD) measurements and the mechanical properties determined by quasi-static tensile and compression tests. For the as-extruded peak-aged alloy, the fatigue strength depends on the stress ratio. An increase in mean stress due to a higher applied stress ratio leads to decreased fatigue strength. Single-pass ECAP enhances the fatigue strength for all stress ratios when compared to the as-extruded peak-aged alloy. Furthermore, the mean stress effect is diminished and the fatigue strength is almost the same for the tested stress ratios. The mean stress insensitive behavior of the ECAP processed condition is most likely a result of an increased sensitivity to compression loading, which is caused by the ECAP induced shear-deformation and expresses further in a minor yield strength under compression loading when compared to the as-extruded peak-aged alloy.

Equal-channel angular pressing influencing the mean stress sensitivity in the high cycle fatigue regime of the 6082 aluminum alloy

In conventional forming processes, quasi-static conditions are a good approximation and numerical process optimization is the state of the art in industrial practice. Nevertheless, there is still a substantial need for research in the field of identification of material parameters. In production technologies with high forming velocities, it is no longer acceptable to neglect the dependency of the hardening on the forming speed. Therefore, a method for determining material characteristics in processes with high forming speeds was developed by designing and implementing a test setup and an inverse parameter identification. Two acceleration concepts were realized: a pneumatically driven one and an electromagnetically driven one. The method was verified for a mild steel and an aluminum alloy proving that the identified material parameters allow numerical modeling of high-speed processes with good accuracy. The determined material parameters for steel show significant differences for different stress states. For specimen geometries with predominantly uniaxial tensile strain at forming speeds in the order of 104–105/s the determined yield stress was nearly twice as high compared to shear samples; an effect which does not occur under quasi-static loading. This trend suggests a triaxiality-dependent rate dependence, which might be attributed to shear band induced strain localization and adiabatic heating.

Sven Winter

Papers

Process Development for a Superplastic Hot Tube Gas Forming Process of Titanium (Ti-3Al-2.5V) Hollow Profiles

Equal-channel angular pressing influencing the mean stress sensitivity in the high cycle fatigue regime of the 6082 aluminum alloy

Determination of Material and Failure Characteristics for High-Speed Forming via High-Speed Testing and Inverse Numerical Simulation

Adiabatic blanking of advanced high-strength steels

Processing Q&P steels by hot-metal gas forming: Influence of local cooling rates on the properties and microstructure of a 3rd generation AHSS