Stamping Tools Research Articles

Digitizing the Fitzgerald Family at the University of South Carolina

Digitizing the Fitzgerald Family at the University of South Carolina

Concept Validation for Selective Heating and Press Hardening of Automotive Safety Components with Tailored Properties

A new strategy termed selective heating and press hardening, for hot stamping of boron steel parts with tailored properties is proposed in this paper. Feasibility studies were carried out through a specially designed experimental programme. The main aim was to validate the strategy and demonstrate its potential for structural optimisation. In the work, a lab-scale demonstrator part was designed, and relevant manufacturing and property-assessment processes were defined. A heating technique and selective-heating rigs were designed to enable certain microstructural distributions in blanks to be obtained. A hot stamping tool set was designed for forming and quenching the parts. Demonstrator parts of full martensite phase, full initial phase, and differentially graded microstructures have been formed with high dimensional quality. Hardness testing and three point bending tests were conducted to assess the microstructure distribution and load bearing performance of the as-formed parts, respectively. The feasibility of the concept has been validated by the testing results.

An Evaluation of Primer Preseating in Small Caliber Cartridge Production

This work presents the findings of a study to quantify the relative effectiveness of the primer preseating operation in small caliber cartridge production. In theory, primer preseating would enable cartridge stamping tools to achieve deeper stamping penetration depths and subsequently, greater primer retention forces. This is because, with preseating incorporated in the existing small caliber cartridge production process, a cartridge stamping tool would be fully dedicated to performing the case stamping operation (rather than the simultaneous primer seating and case stamping operations it currently performs). The findings presented in this work include measured percentages of total stamping tool force dedicated to primer seating, stamping tool penetration depths with and without primer preseating and primer retention forces with and without primer preseating. These findings and their underlying principles were produced through a static force equilibrium analysis and finite element modeling and simulation studies.

Deformation analysis of hot stamping tools by thermal–fluid-mechanical coupled approach based on MpCCI

Hot stamping tools with cooling systems are key facilities for hot stamping processes in the automotive industry. In hot stamping, the tools are heated by workpieces and rapidly cooled by cooling water. The thermal deformation of the tools has a significant influence on the properties of the hot stamped parts and the useful life of the tools. In this paper, a multi-field simulation method is proposed for analysis of deformation in the tools. Based on a mesh based parallel code coupling interface, a thermal–fluid–mechanical coupled model is established to analyse the cooling effect and the deformation of the tools. The experimental set-up was built to verify the multi-field coupling model. It is shown that the cooling rate of the hot stamped part was 217°C s−1, higher than the critical cooling rate of 30°C s−1. The temperature history of the hot formed part was in good agreement with the experimental result. The cooling ducts were deformed because of the thermal expansion of the hot tools. This led to stress concentration at the rectangular corner of the ducts. The speed of cooling water flow increased by 112% through the bottom ducts, while at the corners of the ducts, the speed was very low and a ‘hot spot’ appeared.

Cooling Systems Design in Hot Stamping Tools by a Thermal-Fluid-Mechanical Coupled Approach

Hot stamping tools with cooling systems are the key facilities for hot stamping process of Ultrahigh strength steels (UHSS) in automotive industry. Hot stamping tools have significant influence on the final microstructure and properties of the hot stamped parts. In serials production, the tools should be rapidly cooled by cooling water. Hence, design of hot stamping tools with cooling systems is important not only for workpieces of good quality but also for the tools with good cooling performance and long life. In this paper, a new multifield simulation method was proposed for the design of hot stamping tools with cooling system. The deformation of the tools was also analyzed by this method. Based on MpCCI (Mesh-based parallel Code Coupling Interface), thermal-fluid simulation and thermal-fluid-mechanical coupled simulation were performed. Subsequently, the geometrical parameters of the cooling system are investigated for the design. The results show that, both the distance between the ducts and the distance between the ducts and the tools loaded contour have significant influence on the quenching effect. And better quenching effect can be achieved with the shorter distance from the tool surface and with smaller distance between ducts. It is also shown that, thermal expansion is the main reason for deformation of the hot forming tools, which causes the distortion of the cooling ducts, and the stress concentration at corner of the ducts.

Effect of a CNT based composite micromold on the replication fidelity during the microfabrication of polymeric microfluidic devices

In recent years, polymer based microfluidic devices have become more widespread with the driving force being the development of inexpensive disposable analytical devices. Hot embossing and injection moulding are the two promising techniques that are widely used for micro-fabrication of polymeric substrates because identical devices can be mass produced using a master/mold. However, the major problem with these techniques is the time and expense needed to produce a stamping tool (mold) which can withstand the temperature and stress of the fabrication process over multiple cycles. To overcome this problem, we have developed an epoxy toughened nanocomposite mold material, which is relatively inexpensive compared to the commonly used metallic glass mold material. Our molds can be produced with ease, and are sufficiently durable to withstand multiple embossing cycles. Moreover, compared to other mold materials, very high aspect ratio microchannels can be replicated. We have characterized the morphological, physical and thermomechanical properties of this new nanocomposite mold material including its surface morphology, roughness and friction coefficient. Finally, the performance of the nanocomposite mold to fabricate microdevices using a cyclic olefin copolymer (COC) by the hot embossing and injection molding techniques was assessed. This mold material was found to be suitable for fabricating polymeric microdevices with high channel integrity.

Measurement of 3D Displacement Fields and Deformation Using 3D Laser Scanner and CCD Camera (0-10 mm)

Many applications dealing with the mechanical behavior of materials require the measurement of displacement fields or deformation fields. For this type of measurement, optical methods have become unavoidable due to their non-intrusive approach, their high spatial resolution, their high sensitivity, the large size of their examinated field, and the increasing power of the computers that now allow the processing of huge quantities of data. In this context we have developed a system for measuring 3-D displacement fields using CCD (camera charge digital) and 3D laser scanner .This method allows the measure of the 3-D displacement field using at least two pairs of stereoscopic images of an object corresponding to two states of its deformation (or the processing of a sequence of pairs of images acquired during the deformation). The main topics developed in this study are: the calibration of a camera and a 3D laser scanner, and measuring 3D displacement fields from coupling of camera and 3D laser sensor. The potential application of our method is the characterization of structures, for example, to provide assistance in the development of tools for stamping.

Cooling channel design of hot stamping tools for uniform high-strength components in hot stamping process

Although high strengths up to 1,500 MPa can be obtained by means of hot stamping, the strength and uniformity of components cannot be guaranteed during mass production if the cooling channel is not properly designed. In this paper, we propose a method for designing the cooling channel by means of the energy balance principle and arrangement methods such as the triangular method, tool split, and the connection rule for 2D sections to improve the strength and uniformity of hot stamped components. Two separate approaches for designing the cooling channel are suggested. One is to reduce facility and maintenance costs, and the other is to reduce the cooling cycle time, which critically affects productivity. These approaches were applied to hot stamping tools for manufacturing a roof side that is used as part of the structure of an automobile. Cooling performance and cooling uniformity of the designed cooling channel were verified with finite element simulation. Finally, hot stamping tools for manufacturing a roof side were designed to reduce cooling cycle time and were then manufactured to verify the proposed design methods. A roof side was manufactured by means of the hot stamping tools with the designed cooling channel, and the strength and the uniformity of the component were evaluated by means of a tensile test, observation of the microstructure, and measurement of the micro-Vickers hardness.

Enhancement of dimple formability in sheet metals by 2-step forming

In this study, a 2-step stamping model with an additional 1st stamping tool is proposed to reduce stamping flaws in the curved parts of dimples in nuclear fuel spacer grids. First, the strains in the curved part of the dimple are analyzed and compared with strain solutions for pure bending. A reference 2D FE (finite element) model of the 1-step stamping is established, and the corresponding maximum strain is obtained. FE solutions are obtained for various process variable values for the 1st stamping tool used in the 2-step stamping model. Based on these solutions and applying the RSM (response surface method), strains are expressed as a function of process variables. This function then serves to evaluate optimum process variable values. Finally, by transferring these optimum values to a 3D FE model, we confirm the enhanced formability of the proposed 2-step stamping model.

Investigation into adhesive wear of PVD coated and uncoated hot stamping production tools

The tribological behaviour of two sets of industrial hot stamping tools, one tool made of uncoated hot work tool steel and another PVD coated hot work tool steel set, were analysed by means of a surface replication technique. This technique allows using laboratory equipment and methodology for the inspection of tools without removing them from production. By means of this procedure, on the one hand adhesive wear mechanism can be identified and properly described and, on the other hand, the morphology and thickness of adhered material on tool surface is measured. The tribological behaviour of different industrial tools can be compared objectively.

2중 성형에 의한 금속판재 딤플의 성형성 향상

In this study, a 2-step stamping model with an additional 1st stamping tool is proposed to reduce stamping flaws in the curved parts of a dimple in a nuclear fuel spacer grid. First, the strains of curved part of dimple are characterized via a comparison with strain solutions in pure bending. A reference 2D finite element (FE) model of 1-step stamping is then established, and the corresponding maximum strain is obtained. By varying the values of design variables of the 1st stamping tool in the 2-step stamping model, FE solutions are obtained to express the strain as a function of process variables, which provides the optimum values of process variables. Finally, applying these optimum values to a 3D FE model, we demonstrate the enhanced formability of the proposed 2-step stamping model.

Calculation of the compensation of a stamping tool after springback in the software package pam-stamp

Calculation of the compensation of a stamping tool after springback in the software package pam-stamp

Thermo-Mechanical Analysis of a Cooling System for Hot Stamping Tools

Several studies and design of cooling systems for hot stamping tools have already been made. The phase transformations which occur during the process are known, and numerical simulations are now very close to the reality [1]. However these studies are often related to a specific part and can hardly be extrapolated to other parts. This paper presents several results based on a thermo-mechanical analysis which can be used to make a first design of a cooling system for hot stamping tool. A theoretical study describes the heat transfer from the tools to the cooling pipes related to different flow parameters. Numerical simulation with the software COMSOL Multiphysics has been carried out to obtain results about cooling rate and maximum stress into the tool against geometry parameters. The heat transfer model used for simulation has been validated through experiment. To finish a data analysis describes the relationship between the different parameters, more specifically their impact on the cooling. With this study we can now determine which pipes’ location and size and flow properties are likely to provide the most efficient cooling system, and which parameter we must modify to optimize it.

Optimal design of multi-step stamping tools based on response surface method

This paper describes a new numerical method for the design of multi-step stamping tools, in which the optimization approach is based on the Response Surface Method (RSM) with Kriging interpolation as well as the Sequential Quadratic Programming (SQP) algorithm. The present work attempts to provide a reliable methodology for the optimum design of the forming tools in order to produce a desired part by multi-step stamping within a severe tolerance (0.1mm). The numerical method has been proposed to reduce the number of forming steps and therefore increasing the process productivity. To reach this goal, an integrated optimization approach, using the commercial finite element code ABAQUS© together with an optimization algorithm was developed. The optimization algorithm consists in constructing an explicit form of the objective function according to the design variables. To search the global optimum of the objective function, the SQP algorithm has been used. A thin metallic part formed by manual press and without blank-holder has been considered, to demonstrate the effectiveness of the optimization approach to get the optimal tools shape in a few iterations.

Experimental Primer Seating-Stamping Tool Study in Small Caliber Cartridge Production

In an effort to produce a more secure assembly fit between the primer and the cartridge case in 5.56 mm combat ammunition, variants of the conventional case stamping tool were developed and incorporated in the small caliber ammunition manufacturing process (or SCAMP). The challenge is to develop a tool that provides a secure cartridge case-primer assembly fit while maximizing tool life. Two concept tool designs were realized—a concept four-prong triangular stamping tool and a concept four-prong wave stamping tool. This work compares the results of SCAMP trials using a concept four-prong triangular stamping tool, a concept four-prong wave stamping tool and the conventional circular stamping tool. Comparison data include cartridge case material movement after stamping, stamping tool stress distribution, stamping tool life, and stamping forces required to achieve the objective primer seating depths. Although the SCAMP trials are still ongoing, the findings to date show that the wave stamping tool has consistently met the design challenges of improved cartridge case-primer assembly fit and maximized tool life and is currently the leading candidate for implementation in SCAMP.

Microcutting and Forming of Thin Aluminium Foils for MEMS

This paper presents a simple procedure for simultaneous cutting and forming of thin Al foils for use in MEMS components. The procedure makes use of scaled down macroscopic sheet forming and cutting techniques by using a hydraulic press, a soft counterpart, and a microfabricated stamp tool. The relation between applied pressure and forming and cutting features has been characterized for a specific set of stamp geometries and boundary conditions. The results show that 10 μm forming features can be transferred to 4 μm thick Al foils, which simultaneously can be cut into products by 25 μm wide cut lines. Using the procedure presented in this paper scaled to full 4–8 in. silicon wafer stamp tools, a fast and adequate method for high volume production of MEMS components is obtained.

Patterning pallet arrays for cell selection based on high-resolution measurements of fluorescent biosensors

Pallet arrays enable cells to be separated while they remain adherent to a surface and provide a much greater range of cell selection criteria relative to that of current technologies. However there remains a need to further broaden cell selection criteria to include dynamic intracellular signaling events. To demonstrate the feasibility of measuring cellular protein behavior on the arrays using high resolution microscopy, the surfaces of individual pallets were modified to minimize the impact of scattered light at the pallet edges. The surfaces of the three-dimensional pallets on an array were patterned with a coating such as fibronectin using a customized stamping tool. Micropatterns of varying shape and size were printed in designated regions on the pallets in single or multiple steps to demonstrate the reliability and precision of patterning molecules on the pallet surface. Use of a fibronectin matrix stamped at the center of each pallet permitted the localization of H1299 and mouse embryonic fibroblast (MEF) cells to the pallet centers and away from the edges. Compared to pallet arrays with fibronectin coating the entire top surface, arrays with a central fibronectin pattern increased the percentage of cells localized to the pallet center by 3–4-fold. Localization of cells to the pallet center also enabled the physical separation of cells from optical artifacts created by the rough pallet side walls. To demonstrate the measurement of dynamic intracellular signaling on the arrays, fluorescence measurements of high spatial resolution were performed using a RhoA GTPase biosensor. This biosensor utilized fluorescence resonance energy transfer (FRET) between cyan fluorescent protein (CFP) and yellow fluorescent protein (YFP) to measure localized RhoA activity in cellular ruffles at the cell periphery. These results demonstrated the ability to perform spatially resolved measurements of fluorescence-based sensors on the pallet arrays. Thus, the patterned pallet arrays should enable novel cell separations in which cell selection is based on complex cellular signaling properties.

Light Metal in High-Speed Stamping Tools

The required number of punched and blanked parts in the electronic industry, such as leadframes, contact pins or plugs often reach several million pieces. According to this, the production process has been sped up to frequencies up to 2000 parts per minute. At this production rate parts of thin steel or copper sheets are produced with high-speed stamping presses and blanking tools. Because of the high gating velocities in the blanking tool there is a recurring acceleration at the moment, when the blank holder contacts the sheet metal. A second shock in the blanking tool arises, when the sheet cracks. This is also known as the impact shock during the blanking process. Trough these two impulses and through the cycle of the plunger movement a periodic oscillation arises in the tool. Horizontal vibrations can lead to an undefined position between punches and die-plate, while vertical movement leads to increased wear because of friction forces between the blanked surface and the lateral area of the punches. The goal of this project was to minimize these oscillations in cutting tools by the usage of lightweight materials in the flux of forces. An experimental cutting tool was designed with alternative top and bottom plates for the comparison of the oscillation status in the cutting process when using plates of steel, aluminium or magnesium. The centre plate of the tool remains constant. Experiments were accomplished for several velocities and tool setups with different plate materials. To determine the influence of the materials with different density and elasticity acceleration, force and acoustic emission sensors were integrated in the tool. The set of problems was investigated by analyzing the measured data and by determining the wear in practical tests.

Experimental and theoretical study of thermal aspects of the hot stamping process

The objective of the present article is the thermal conductance estimation to improve the Usibor 1500P® blank cooling during the hot stamping process. An experimental device was designed and developed to estimate the thermal contact resistance at the part/tool interface. The designed stamping tool is composed of a die and a punch made in Z160CDV12 steel and presenting an omega shape. Samples and tools are thermally instrumented with thermocouples type K sheathed with silky glass, forming heat-flux meters in the most interesting locations in the tools. Reproducibility tests showed a good repeatability of recorded and estimated parameters with a mean dispersion less than 5%; it was noticed that a re-heating of the cooled part due to its microstructure transformation occurring systematically at 400 °C. At the surface boundary of the part, thermal conductances are calculated using convective/radiation modeling of both phases: approach and forming. At the contact interfaces, thermal contact resistances RC are estimated experimentally through a non-linear 1D inverse technique founded on sequential method of Beck. Results have been established as correlation of type: RC = f(P) to be used for numerical simulation.

Improving the wear resistance of tools for stamping

In the present investigation, the wear resistance of tools for the precision stamping of a mechanical part for the automotive industry is optimised. The investigation is divided into two stages. In the first one, the progression of damage in the punches and dies is assessed. Wear mechanisms are evaluated by means of observations and measurements in a scanning electron microscope (SEM). In the second stage, specific improvements are proposed based on the results of the first stage and are evaluated by specific field tests. The improvements include coating by physical vapour deposition with a AlCrN layer, production of the tools with hard metal and cryogenic treatment of the high-speed steel tools. The results show that all the proposed treatments help improve the performance of the tools, and the best improvements are displayed by the use of hard metals and coated tools.