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This post was last edited by Shaobin Fluid on 2026-3-27 09:46. It explains that in the industries of medicine, precision engineering, and electronic devices, the growing demand for thin metal components has driven the development of micro-molding technology. Tantalum biomaterials have attracted particular attention due to their unique properties, showing broad application potential especially in the manufacture of microcomponents. As the size of materials decreases, challenges arise such as reduced ductility and uneven deformation, which necessitates the development of materials and processes suitable for microfabrication. In industries such as medical technology and communications, the use of micro-components has become a key factor in adding value, enabling micro-molding technology to play a central role in the manufacturing of innovative products. The trend toward miniaturization has driven the development of new manufacturing technologies, especially when traditional silicon-based microelectromechanical systems (MEMS) reach their processing limits. Microforming technology offers a promising manufacturing method that enables the creation of precise microscopic details, provides near-net-shape properties, enhances the ability to produce complex geometries, and allows for the fabrication of miniature components with high stiffness and strength using various materials including tantalum. Furthermore, the molding process can meet the production needs of large quantities of micro-components; in key economic markets, these tiny parts play an important role in various industrial products. The current research focus is on investigating and analyzing the formability of tantalum biomaterials, particularly their performance at a material thickness of 80 µm. The study adopted the ASTM-2218-14 standard and conducted comparative analysis through simulation and numerical methods. Microstructural analysis was carried out using an optical microscope and a scanning electron microscope (SEM) to study the behavior of tantalum materials and explain their formability. Energy-dispersive X-ray spectroscopy (EDS) verified the elements in the material, showing good consistency. The ultimate goal of this research is to define and compare the formability of tantalum materials through experimental and simulation methods. Microstructural studies using scanning electron microscopy provide support for the behavior of materials. Formability and Forming Limit Curve The forming limit curve (FLC) describes the maximum formability of metal sheet materials, as expressed through two key combinations of surface strains. FLC provides excellent guidance on materials, tools, and lubrication conditions, and depends to a large extent on the parameters of the material. The concept of FLC was first proposed by Keeler, who observed that the maximum local elongation rate was insufficient to determine the possible deformation rate of the diaphragm. In the same diagram, the configuration of the main deformation at ε1 failure is represented by a curve: ε2 forms a limiting curve along two axes. This curve is first confined to the region where ε2 > 0, and was extended by Goodwin to ε2 < 0. This curve divides the plane into two regions: a successful region below the shape constraint curve and a failed region above it, which are used for drawing operations. Currently, the criterion for determining whether an elongated portion is qualified is the presence of local necking. Figure 1 is a schematic diagram of FLC, where the horizontal and vertical axes represent small strain and large strain, respectively. All regions are represented by different color combinations. The red area at the top indicates failure, while the green area represents the safe zone that needs to be shaped. The blue, purple, light green, and brown areas are actually defect areas; objects formed in these areas end up with one kind or another defect. This method is used to predict the formability of Ta. Tantalum: The discovery of tantalum is attributed to the Swedish chemist Anders Gustaf Ekenberg, who found this mineral in the Itterby mine in 1802. Although it was initially mistaken to be a form of niobium, Swiss chemist Jean Charles Galissard de Marignac confirmed in 1866 that tantalum and niobium are two distinct elements. This study deals with Ta materials, an alloy composed of tantalum, carbon, oxygen, niobium, and other elements, which are renowned for their excellent corrosion resistance and ability to bond with organic acids and bones, making them an ideal material for use in the biomedical field. Due to its excellent biocompatibility, Ta is widely used in medical applications, including orthopedic and dental implants, pacemakers, and aneurysm clips. This material not only exhibits excellent bone ingrowth and fixation capabilities, but also possesses good biocompatibility and osteointegration properties; coupled with its outstanding mechanical properties, it makes it an ideal material for medical devices that require long-term implantation. Through energy-dispersive X-ray spectroscopy (EDS) analysis, Table 1 shows the elements contained in the Ta material and their energy levels, while Figure 2 presents the specific results of the EDS analysis. The detailed mechanical property data of Ta are shown in Table 2. Table 1. Chemical composition of Ta. Figure 2. EDS analysis of Ta. Table 2. Mechanical properties of Ta. Sample preparation: First, circular grid markings were created using screen printing to prepare the samples. The mold used for circular grid markings consists of holes with a diameter of 1 millimeter, and the distance between two holes is 2 millimeters. Grid markings were applied, as shown in Figure 3. These circular grids of markers are stretched into ellipses during the experiment, thereby acquiring a major axis and a minor axis. Large and small strains are calculated using Equation 1, and ultimately the FLC of the material is plotted. Experiments and measurements were conducted on each sample in the group. Cutting is performed using the wire cutting electro-discharge machining process. The specified shapes required for the experiments are in accordance with ASTM 2218-14 standard, which is used to determine the FLC value of any material with specific sample shapes and sizes. This is a specific standard that is primarily used by researchers to predict and define the formability of any material with a particular test sample. The sample diameter considered in the experiment is 10 mm, and the samples used in the current research were prepared based on the Nakajima test, as shown in Figure 4. Various strain paths are predicted to be uniaxial, intermediate uniaxial, planar, intermediate biaxial, and biaxial. Figure 3. Samples with grid markings. Figure 4. Preparation of the Nakajima specimen. Tool setup development: To conduct in-depth research on the micro-forming properties of Ta materials, we designed and developed a specialized fixture. As shown in Figure 5, the fixture consists of two upper and lower parts, each with a mold, and two friction plates are used between these two molds to generate the necessary friction. This tool is equipped with a hemispherical punching head with a diameter of 4 millimeters to meet the requirements of micro-forming processes. The entire setup is installed on a Universal Testing Machine (UTM) with a maximum load capacity of 5 kN, in order to enable precise force and displacement testing. During the experiment, the crosshead movement speed of the UTM was set between 0.4 mm/min and 1.2 mm/min to ensure precise control over the material forming process and to obtain accurate test data. Figure 5. Design and development of micro-forming research tools. Experimental investigation: The experimental investigation was conducted in accordance with ASTM 2218-14 standards, and three sets of Nakajima tests were performed on six different samples. These tests involve using screen printing technology to print circular grids on the samples. Each sample underwent crack growth after being joined. Once cracks begin to form, the long and short axes of each sample are measured to improve measurement accuracy. These measurements were carried out using a visual measurement system, ensuring the accuracy of predictions for both large and small strains. This is achieved by measuring the primary and secondary axes that occur near the connection area. According to Equation 1, the strain rate is calculated, which is the ratio of the length change to the original length. This process ultimately ensures the accuracy of the FLC plot for the material, which depicts all six strain paths, as shown in Figure 6. Figure 6. Samples after the experiment. Using the M-K criterion for the theoretical prediction of FLC: To obtain the FLC (Forming Limit Diagram) of a material accurately and quickly, methods based on plastic deformation theory are commonly used. The Swift model is calculated based on the relationship between the root mean square value and the shear stress edge increment. Calculations are performed using the initial thickness and defect depth, and they are widely used due to their simplicity and accuracy. The M-K model has been improved by adding an angle between the groove and the principal direction to better correct it. The schematic diagram of the M-K model is shown in Figure 7. Figure 7. Schematic diagram of the M-K model structure. The purpose of conducting tensile tests is to record the mechanical properties of the material, particularly the ultimate tensile strength, elongation, and fracture angle. These specific data are required when conducting simulation tests on the M-K model. As shown in Figure 8. Figure 8. Standard tensile specimen for films. The specimen was prepared using wire-cut electrical discharge machining to reduce stress concentration. The testing was carried out on a 5KN UTM machine using specific fixtures. The test results yielded the mechanical properties of the material and its engineering stress-strain curves. Results and Discussion Experimental studies were conducted on six samples, and an FLC was constructed based on the strain measurement data. The principal and secondary strains of all samples were measured using a visual measurement system, and the results were plotted on an FLC diagram, as shown in Figure 9. Table 3 lists the measured strain paths. In addition, the ABAQUS software was used to conduct simulation analyses on all the measurement paths related to the M-K model; the simulation results are detailed in Table 4. Based on the experimental data, the FLC curve of Ta material was plotted and compared with the simulation results of the M-K model; the results showed good agreement between the two. Table 3. Strain measurement values in the 6 strain paths (experimental data). Figure 9. Comparison between the experimental model and the M-K model FLC. Study on the microstructure of tantalum: The microstructure of 80-micron Ta films was analyzed using an optical metallographic microscope. At 100X magnification, two phases were observed, accounting for 39% and 61% respectively, which have a significant impact on the properties of tantalum. Phase analysis was performed using image analyzer software. To determine the chemical composition, an 80-micron sample was analyzed using the EDS method, and the results showed that in addition to tantalum, it also contained Ni, Nb, O, and C elements. Figure 10 shows the microstructure of Ta. Figure 10. Microstructure of Ta. SEM and EDS analyses conducted using a FEI Nova NanoSEM 450 and a Brukerx Flash 6S30 showed that the surface of the unformed Ta sample was free of cracks (Figure 11), whereas the surface of the formed sample exhibited numerous cracks (Figure 12). The alpha phase and beta phase can be clearly seen in the unformed samples ； The formed sample experienced deformation of its grain structure due to stretching, resulting in nanoscale microcracks. Figure 11. SEM image of unformed Ta. Figure 12. SEM image of Ta. The unformed samples showed no voids or material stretching, whereas the formed samples exhibited distinct stretching patterns, indicating that failure was caused by material expansion rather than voids or irregularities. Small cracks can also be seen at the top of the figure, further confirming that the material failed due to expansion. Conclusion We conducted research on the microforming of tantalum films, with a particular focus on their applications in the biomedical field. A 80µm thick tantalum diaphragm was selected as the subject of study. The experimental method was carried out using the Nakajima test, and simulation analysis was performed with the M-K model of the ABAQUS software. The forming limit curves (FLC) obtained from experiments and simulations show good consistency, providing a fundamental benchmark for the design and simulation of tantalum materials in the field of microforming.