NUMERCNAL ANALYSIS OF CONTACT INTERACTION OF BODIES WITH NEARLY FORM SURFACES

Contact interaction of structural elements has been studied in the case of nominally close (nearly matching) surfaces. A non uniform gap is present between the contacting parts. Contact pressure and contact spot depend on the shape of this gap. Correspondingly so does the stress-strain state of the contacting bodies too. Since the problem is essentially nonlinear, the contact pressure distribution and the contact zones change with the growing loads. The solution is qualitatively different to the case of perfectly matching bodies. For the latter case, the contact pressure is linearly proportional to the load and the contact zone is predefined. Hence for the real structures for which the deviation from the nominal shape is unavoidable the impact of these inaccuracies on the contact pressure distribution and the stress-strain state need to be taken into account. This problem is addressed in the paper by example of elements of stamping dies. Keywords: element of stamping dies, stress-strain state, contact pressure, contact interaction, variational inequalities, Kalker’s variational principle, finite element method, boundary element method

Mitigating Scatter in Mechanical Properties in AISI 410 Fabricated via Arc-Based Additive Manufacturing Process

Wire-based metal additive manufacturing utilizes the ability of additive manufacturing to fabricate complex geometries with high deposition rates (above 7 kg/h), thus finding applications in the fabrication of large-scale components, such as stamping dies. Traditionally, the workhorse materials for stamping dies have been martensitic steels. However, the complex thermal gyrations induced during additive manufacturing can cause the evolution of an inhomogeneous microstructure, which leads to a significant scatter in the mechanical properties, especially the toughness. Therefore, to understand these phenomena, arc-based additive AISI 410 samples were fabricated using robotic gas metal arc welding (GMAW) and were subjected to a detailed characterization campaign. The results show significant scatter in the tensile properties as well as Charpy V-notch impact toughness data, which was then correlated to the microstructural heterogeneity and delta (δ) ferrite formation. Post-processing (austenitizing and tempering) treatments were developed and an ~70% reduction in the scatter of tensile data and a four-times improvement in the toughness were obtained. The changes in mechanical properties were rationalized based on the microstructure evolution during additive manufacturing. Based on these, an outline to tailor the composition of “printable” steels for tooling with isotropic and uniform mechanical properties is presented and discussed.

Stamping Tools for Sheet Metal Forming: Current State and Future Research Directions

Sheet metal forming tools play an important role in the manufacturing of many products. With shorter product life cycles and demand for shorter time to market for new products, the process for design and manufacturing of stamping tools becomes a critical part. Stamping dies are often designed and manufactured by smaller, specialized companies. For a tooling company, knowledge and experience is an important competitive advantage. Traditionally the design process has been characterized by being based on few key individuals with much experience and craftsmanship. To stay competitive in this market there is a need for more efficient processes, systems, tools and supports in order to become more industrialized. This paper presents results from a study of the state of practice in industry within progressive stamping tool design as well as a review of relevant literature. The design and manufacturing processes for stamping dies in six companies have been investigated through semi-structured interviews, from which the main challenges in the current state for the companies are identified. The results from the interviews was analyzed and compared to the established concepts and frameworks of methods found in the literature review. The results and analysis points in the direction of efforts needed in supporting the formalization and reuse of information and knowledge from previous tool projects and production, especially during the critical steps of tool process planning and creating the tool layout.

Multi-Pass Stamping Forming a Concave Ring

To improve the production quality and efficiency of the concave ring, a multi-pass stamping technology is used to replace the spinning technology to form the concave ring. First, the multi-pass stamping dies are designed according to the structural characteristics of the concave ring. Then, the process parameters are determined based on the bending conditions and the dimensional requirements of the concave ring. Next, the rationality of the designed stamping dies is verified by analyzing the stress and strain field of the multi-pass stamping concave ring. Finally, the stamping experiments are carried out. Experimental results show that the dimensional error of the concave ring formed by multi-pass stamping is less than 0.5%. The multi-pass stamping technology is feasible to form the concave ring. The reasonable design of the mold is the key factor to prevent defects in the workpiece. The concave ring formed by multi-pass stamping meets the industrial requirements.

Analysis of the risk of galling in sheet metal stamping dies with drawbeads

Sheet metal stamping of complex geometries normally involves the use of drawbeads to control the metal flow in the forming die. Drawbeads are, however, often the most tribologically severe part of the stamping dies. Selection of a suitable tribosystem for this type of forming operation depends on parameters such as local contact pressures, sliding speed, tool/workpiece interface temperature, tool and workpiece materials, and surface topographies. Furthermore, it depends on the required tool life and acceptable maintenance costs. This study demonstrates a methodology for offline evaluation of tribosystem applicability for a specific production platform for stamping of a three-dimensional component using a forming die with drawbeads. Based on an industrial case study, this work combines experimental and numerical analyses of the risk of galling in the different regions of an industrial forming die.