Cold Stamping Research Articles

Development of a partition panel of an Al6061 sheet metal part for the improvement of formability and mechanical properties by hot forming quenching

In this study, the hot forming quenching process was investigated to improve the deficiencies that arise in materials subjected to conventional cold stamping, such as low formability and undesirable mechanical properties. The hot forming quenching process was mainly discussed in terms of formability and mechanical properties in this study and was first evaluated by preliminary tests. To examine formability, an evaluation was conducted using hot-tensile and hemispherical-dome stretching tests at temperatures of 350°C and 450°C, respectively. In addition, the mechanical properties of the formed part were predicted using quench factor analysis, which was based on the cooling temperature during the die quenching process. These preliminary test results were then used to predict the formability and hardness of the partition panel of an automotive part, where the analytical results indicated high performance of the hot forming quenching process, in contrast to conventional forming. Finally, the hot forming quenching experiment of the partition panel was carried out to validate the predicted results and the obtained formability and hardness values were compared with conventional forming at room temperature using T4 and T6 heat-treated sheets. The analytical and experimental results indicate that the hot forming quenching process is a very effective method for obtaining desirable formability and mechanical properties in the forming of aluminum sheets.

Hot stamping of high-strength aluminium alloy aircraft parts using quick heating

To improve the formability and productivity in conventional cold stamping of high-strength aluminium aircraft parts, a hot stamping process of heat-treatable aluminium alloy sheets using quick heating below the solution treatment temperature was developed. Quick heating just before forming has the function of producing sufficient strength increase in subsequent artificial ageing. This leads to the elimination of solution treatment and sizing processes for cold stamping. The effect of heating conditions was evaluated in hot hat-bending of A2024-T4 aluminium alloy sheets. In addition, an aluminium alloy aircraft part having high strength and dimensional accuracy was successfully produced by the present process.

Design of Stamping Processes of Pinless FSWed Thin Sheets in AA1050 Alloy for Motomotive Applications Using FEM

In the present paper, the cold stamping of friction stir welded AA1050-O thin sheets, obtained using a pinless tool, was studied. A preliminary investigation allowed to define the weldability window, in terms of the rotational and welding speed values, leading to joints with the desired mechanical properties. Then, the constitutive behavior of both the parent material and welded zone was characterized by means of uniaxial tensile tests. The constitutive equations obtained by analyzing the experimental results were implemented into the FEM code used to simulate the cold stamping process of FSWed blanks. The virtual prototypes were validated by performing stamping experiments of the FSWed blanks and comparing the predicted and measured results in terms of sheet thickness, and major strain vs. minor strain data.

Formability and lubrication of a B-pillar in hot stamping with 6061 and 7075 aluminum alloy sheets

Abstract Aluminum alloy sheets have drawn more and more attention in recent years in the automobile industry for the purpose of weight loss and energy saving. Hot forming-quenching (HFQ) integrated process (also called hot stamping) has been developed recently for heat-treatable aluminum alloy forming to improve the formability, overcome the springback of the part. In this paper, in order to investigate the formability and lubricationof a B-pillar in hot stamping with 6061 and 7075 aluminum alloy sheets, different solution heat treatment (SHT) temperatures, SHT time and lubricants were used in the stamping experiments.The forming precision detections were also carried out after trimming. The results showed that the B-pillar wrinkled badly and cracked or even broke into pieces in cold stamping with or without lubricants.The B-pillar also cracked in hot stamping without lubricants. With the help of properlubricants, B-pillars with no crackand better surface quality could be obtained. The failure mechanismswere also explained in the present work. Besides,forming precision of most regions ranged from -1mm to 1 mm and there are still large errors in the local regions of the both ends of the B-pillar.

Thermal Drilling with Force-Feed Tool

To reach the sufficient strength of threaded connection it is necessary to make 3 or more turns of the thread. In bars with the thickness of less than 2 mm the length of screwing is reached by sheet bending, connection pressing, cold stamping and other ways, which demand time requirements, additional operations, technical equipment, workforce. The article shows the way of making thread holes by rotating the punch in sheet blanks. There are five steps of the process being held. The following steps of forming holes are used these ways: with constant load and forced feed. The influence of bar thickness and forced feed on geometry of flanging: height and thickness of upper and lower extracting bases has been considered. The experimental data suggest that reducing the bar thickness, the height and thickness of upper and lower flanging bases. Herewith on bars with 5 mm thickness upper extracting is not being formed. Feed increasing causes reduction of height and increase in thickness of the upper and lower flanging. It can be seen on bars with all kinds of thickness (0,5...2,0 mm). The calculated and actual strength of the gained threaded connection on slice is submitted. Also it is clear that the actual strength of the gained threaded connection is higher than the calculated one, because of increasing micro hardness in the threading zone. The result of micro hardness measuring is assumed. To indentify the opportunity of using this method in industry the field of dissipation of the gained diameter was spotted in comparison with the limits by GOST 16093-2004. Also the gained hole corresponds to the 7th limit of accuracy of the inner thread diameter, what allows using this method in the industry [1-7].

Component simulation in problems of calculated model formation of automatic machine mechanisms

The paper deals with the problems of the component simulation method application in the problems of the automation of the mechanical system model formation with the further possibility of their CAD-realization. The purpose of the investigations mentioned consists in the automation of the CAD-model formation of high-speed mechanisms in automatic machines and in the analysis of dynamic processes occurred in their units taking into account their elasto-inertial properties, power dissipation, gaps in kinematic pairs, friction forces, design and technological loads. As an example in the paper there are considered a formalization of stages in the computer model formation of the cutting mechanism in cold stamping automatic machine AV1818 and methods of for the computation of their parameters on the basis of its solid-state model.

Integrated hot forming and heat treatment process on Al6061 tailor rolled blank

Using the cold stamping process, aluminum tailor rolled blanks (TRB) have been recently used to manufacture automotive parts to reduce the body weight of cars. However, when used to achieve uniform mechanical properties, the conventional method of aluminum TRB leads to low formability and excessive springback, and it also requires additional heat treatment because of thickness difference and work hardening during the rolling process. This study proposed an integrated hot forming and heat treatment process to improve the formability and dimensional accuracy of Al6061 TRB. In this process, the heated sheet was immediately formed after the solution heat treatment, and was then rapidly quenched within cold dies. The practicality of this process for sheet forming of Al6061 TRB was evaluated by performing the Erichsen and V-bending tests. Furthermore, hardness was measured to confirm the uniform mechanical properties of the Al6061 TRB achieved after artificial and natural aging. The integrated hot forming and heat treatment process was also compared with the conventional forming method in terms of formability, dimensional accuracy, and mechanical properties, which demonstrated the feasibility of this process for Al6061 TRB.

Sheet Forming Processes for AW-7xxx Alloys: Relevant Process Parameters

High strength AW-7xxx sheet alloys are promising candidates to manufacture crash relevant parts, but their limited formability at room temperature presents a major challenge. Formability is controlled through heating rate, heat treatment temperature and time, quenching rate, forming temperature and strain rate. In the literature retrogression forming, W-temper forming, warm forming and hot stamping processes have been proposed to improve the formability of AW-7xxx alloys. Of these the greatest improvement in formability comes from W-temper forming and hot stamping. Considering the similarity to the conventional forming processes of cold stamping for aluminium and hot stamping for steel, the W-temper forming and hot stamping of aluminium are promising for AW-7xxx alloys.

Inclusion of hot stamping operations in progressive-die plate forging of tailored high strength gear part

Hot stamping operations of a quenchable steel sheet were included in progressive-die plate forging to produce a tailored high strength gear part without additional heat treatments. As process design for the inclusion, the former stages in the progressive-die operations for punching and trimming were cold stamping, and subsequently, resistance heating, blanking, forging and die quenching were performed. The plate was partially resistance-heated with a pair of electrodes to produce a tailored gear part having high strength teeth and a ductile remainder. The tooth portion was uniformly heated around 1050 °C in the transversal current direction, and a gear part having teeth having 520 HV2 in hardness was produced. The quality of the teeth was improved by hot semi-blanking with local compression and cold scrap removing. It is found that the combined process of plate forging and hot stamping is useful to produce ultra-high strength steel parts.

Cold Stamping of 6061 Al Alloy Assisted by Arc Welding Pretreatment

Considering the poor plastic forming capacity of Al alloys at room temperature, this study proposed a stamping technique assisted by arc welding for partial material modification. The plastic forming capacity of the sheet pretreated by arc welding was confirmed with the V-shaped bending test. The microstructures and mechanical properties of the sheets were tested, and the cause of the increase in sheet deformability was analyzed. The Al alloy sheet pretreated by arc welding showed good plastic capacity at room temperature and under large deformations. The main advantage of arc welding is high speed, by which plastic working efficiency can be increased under certain conditions. In this technology, the difficult forming areas of structural parts are first located. Before plastic forming, sheets are pretreated by arc welding to convert the rolled grains in the softened heat-affected zones (HAZs) of the sheets into equiaxed grains and thereby regain grain deformability. Arc welding pretreatment is only used to soften difficult forming areas. Moreover, the local plasticity of sheets significantly increases in comparison with that of base metals, and the hardness of HAZs after plastic forming is improved.

Development of a cold stamping process for forming single-welded elbows

This paper presents a cold stamping process for single-welded elbows, which has advantages of no heating, no adjusting roundness and single weld. This process is particularly suitable for forming large diameter thin-walled deep-water pipeline elbows. The main procedure composes of blanking, machining groove, U-forming, O-forming, welding, and removing excess material. The initial blank is calculated inversely by Dynaform software, and then the finite element model of cold stamping process is developed to simulate the deformation process under different process parameters by ABAQUS software. The forming tools are designed and the experiments are carried out. Finally, the U-forming process and the O-forming process are analyzed and possible causes of the elbow wrinkling are studied. When the compression ratio is 0.75 % and the clearance between the U-punch and die is 1.05 times of blank thickness, the formed pipe elbow will be with good quality. The geometric parameters of formed elbows from FEM and the experiment are tested, the results show that the ovality is less than 0.6 %, the maximum thickening rate is less than 12 %, and the maximum thinning rate is less than 8 %. All of these verify the feasibility of the cold stamping process for forming the single-welded elbow.

Improving the plasticity of thin cold-rolled steel sheet for cold stamping

Two methods of surface treatment are proposed to improve the technological plasticity of thin cold-rolled carbon-steel sheet: ionic bombardment by low-energy titanium atoms; and epilam coating. Both methods markedly increase the extensibility of the sheet (by a factor of 1.2–1.3), as estimated by the maximum crater depth without cracking in Erichsen tests (from the VG group to values exceeding those for the VOSV group, which corresponds to extremely complex extension, in State Standard GOST 9045–93). This is associated with change in the behavior of the sheet on deformation (with change in the properties of the material) as a result of two processes: the healing of surface defects; and the creation of hybrid nanocrystalline and submicrocrystalline structure in the surface layer. In epilam coating, only the first process occurs; in ionic bombardment, both are observed.

Improved seizure resistance of ultra-high-strength steel ironed cups with a lubricant containing SiO2 nanoparticles

Good boundary lubrication is necessary during cold stamping of high-strength steel sheets to prevent die wear and seizure of the parts owing to the high contact pressure. This study is aimed to improve the seizure resistance in a 1-step combined process of deep drawing and ironing of ultra-high-strength steel cylindrical cups using a commercial lubricant containing SiO2 nanoparticles with an uncoated die. In this study, the extreme pressure performance of the lubricant containing 0.0, 0.5, 1.0, 1.5, 2.0 and 2.5 wt% of SiO2 was first evaluated using a deep drawing process under increased blank holding forces. The optimum concentration of SiO2 was determined, i.e. 2 wt%, based on successful drawing of cups having smooth surfaces under the highest holding force. Then, the ironing limits of the cups for the lubricants containing 0 and 2 wt% of SiO2 respectively were investigated with the 1-step combined process under increased ironing ratios. The experimental results showed that seizure was observed for the lubricant containing no nanoparticles at an ironing ratio of −16.7 %. However, no seizures were observed for ironing ratios up to 4.2 % using the lubricant containing 2 wt% of SiO2. The resistance to seizure of the cup was significantly increased, leading to the formation of cylindrical cups having smooth surfaces and uniform side wall thickness.

Influence of Deformation and Temperature on the Austenitic Stainless Steel Performance

Austenitic stainless steels widely used in cryogenic pressure vessel construction, and heads are formed by cold or warm spinning and stamping. Because of large deformation at excessive circular arc and at the straight parts of head during fabrication, the possibility of damage in these two positions during service is very high. In order to solve this problem, the commonly used S304408, S30403, S31608 steel plates processed under different temperature, different deflection and deformation rate were comparative studied. The evolution of the microstructure and mechanical properties were investigated to quantify the driving characteristics of the martensitic transformation by temperature and mechanical deformation. Consequently, the intergranular corrosion resistance of different microstructure was studied. The results of the research provide valuable reference for the selection and the processing technology of the head steel. Meanwhile, this study also provides a simple method for estimating the material properties after forming.

Thermo-Mechanical Coupled Stamping Simulation about the Forming Process of High-Strength Steel Sheet

The developing trend of Automotive Lightweight has brought about the application of High-Strength Steel sheet in the automotive body, but High-Strength Steel sheet has poor formability with cold stamping process, and the existing cold stamping process cannot fully meet the needs of high strength steel forming. The hot stamping technology of High-Strength Steel sheet is the effective method to solve the above-described problem. It can greatly shorten the tryout time of die, and can effectively solve some problems like discarding of die, unreasonable process, and poor forming quality etc. In this paper, mainly for the Thermo-Mechanical Coupling process of sheet metal, introduce the thermal field analysis of High-Strength Steel sheet, the interaction of deformation and temperature field, and the main steps of Thermo-Mechanical Coupling. And for the U Shaped part, built the Finite element model and set process parameters with software ‘Dynaform’. Simulated its forming process of Thermo-Mechanical Coupling with solver ‘LS-DYNA’. The changing temperature field, thickness, and thickness reduction rate were calculated. The results show that, Thermo-Mechanical Coupled Stamping Simulation is an effective method to forecast high temperature formability of High-Strength Steel Sheet.

Application of Magnetic Kinds of Nondestructive Inspection to Parts From Die Tool Steels

Possibilities of control of the level of accumulated damage in dies for cold and hot forming as a function of the coercivity are considered. The coercivity of the material of dies for hot forging and cold stamping is studied. Formulas are obtained for determining the coercivity in steels for hot die forging in the state as delivered.

SPRINGBACK EFFECT OF AUTOMOTIVE LOWER ARM COMPONENT PREPARED VIA BURRING PROCESSING

Complex components of the sheet metal forming process need to be designed with high precision and accuracy in order to prevent defects and misalignment of the end products. One of the sheet metal cool stamping process for these complex automotive components is burring which is the forming of a flange around a hole made in a piece of sheet metal. Springback is a common defect during the burring process. The aims of this paper are to investigate the springback effect and improve shape accuracy of hole burring by inner burring process of lower arm part for automotive lower arm part. The springback defects at hole burring usually happened on the inner burring process. Experimental stretch flanging for cold stamping process of inner burring process was used to investigate the reasons of springback effect around the burred hole for a lower arm part of high strength steel (HSS) sheets SPFH590. From the two designs of burring punch dies, the result shows the values of springback effect for clearance -0.15 which have a big gap at hole burring A arm and B arm diameters, are larger than clearance -0.34 which have small gap for inner burring process of lower arm part. The experimental analysis shows that springback is proportionally related to the punch-die clearance parameter of the tool profile where the springback increase as the clearance increases.

Heuristic optimisation of cooling channel design in the hot stamping die for hot stamping process

In hot stamping process, similar die is used as in cold stamping process but with additional cooling channels. The cooling channel systems are integrated into the die design to control the cooling rate for quenching process of hot blanks. During quenching process, the die is effectively cooled to achieve the optimum cooling rate and homogeneous temperature distribution on hot blanks. In this paper, heuristic method with finite element analysis (FEA) of static analysis and thermal analysis are applied to determine the cooling channel size, pitch size between channels and channel distance to the blanks surface. This static analysis identifies either the tool able to stand the pressure applied or not, while the thermal analysis is to ensure the die obtains the high cooling efficiency with homogenous temperature distribution. In this heuristic method, each parameter of the cooling channels inside the die are optimised and benchmarked with traditional Taguchi method. The results showed that the heuristic method coincides with Taguchi method even better and achieved the acceptance error between FEA in temperature distributions.

Research on Prediction Method of Plastic Deformation for Cold Stamping Formed Standard Elliptical Head Made of Austenitic Stainless Steel

It is the main purpose to acquire the method of predicting the plastic deformation of cold stamping standard elliptical heads. As the formulas are derived, the physical meaning of the two plastic deformation prediction methods, one is used in home and the other one is used in abroad, is realized. A finite element model of the head cold stamping process is developed and validated by comparing the simulation and the experimental results. Thus, heads with different nominal diameter Dn and nominal thickness δnhave been simulated and a plastic deformation prediction method of heads is proposed. The calculation results of two prediction methods are compared with those calculated by the new prediction method. The results of the two existing prediction methods reflect the average plastic deformation of heads in warp and loop direction respectively, but not the real one. However, the new prediction method is built, which can be used effectively to predict the plastic deformation of heads, is more accurate and reliable.

高温焼なまし処理された市販Mg合金板の冷間プレス成形

高温焼なまし処理された市販Mg合金板の冷間プレス成形