Circular Cups Research Articles

A study of the formability of stainless steel foils during micro deep drawing

Stainless steel foils are extensively used in the manufacture of micro-metallic products for their excellent corrosion resistance, high mechanical strength and superior ductility. In the present work, stainless steel foils with 50 μm thickness were annealed at temperatures ranging from 750 to 1150 °C for 5 min and then cupped at drawing speeds ranging from 0.1 to 2 mm/min. The formability of metal foils was systematically investigated and the quality of drawn cups via micro deep drawing (MDD) was discussed. The results show that the total elongation of metal foils appears a gradual increase when annealing temperature rises from 750 to 950 °C. With a further increase of annealing temperature from 950 to 1150 °C, both the ultimate tensile strength and the total elongation decline sharply, while the scatter of stress increases. The results of MDD tests show that wrinkling problem becomes increasingly significant on the drawn cups whilst thickness distribution on the drawn cup mouth become quite nonuniform with the increase of drawing speed from 0.1 to 2 mm/min. Overall, optimal annealing temperature and drawing speed are obtained with the purpose of manufacturing high quality micro circular cups.

Effects of annealing temperature on micro deep drawing of stainless steel-copper composite

With the advantages of high utilization of raw materials, high precision and low cost, micro metallic parts produced by micro deep drawing (MDD) have been tremendously used in a variety of fields such as micro-electromechanical systems (MEMS), vehicle engineering and chemical engineering. In order to study the deformation behavior of two-layer stainless steel-copper composite foils during MDD, a series of MDD tests were performed with specimens annealed at temperatures ranging from 600 to 1000 °C. The results show that complete circular cups cannot be formed using the as-received material due to its poor formability. For the specimens annealed at 600 and 700 °C, significant wrinkling is observed on the drawn cups. Differently, few wrinkles are characterized on the drawn cups when the composite foils are annealed at temperatures ranging from 800 to 1000 °C. An optimal annealing temperature of 800 °C is obtained for the MDD of stainless steel-copper composite cups with high surface quality.

Punch Motion Curve in the Extrusion–Drawing Process to Obtain Circular Cups

Servo press technology is gaining attention because its punch motion curve offers greater formability than that of a conventional stamping press. This study investigated the effect of punch motion curves on the circular cup extrusion–drawing process. Various punch motion curves were analyzed, and the optimal curve for application was determined. Both the extrusion–drawing process and spring back of U-shaped sheet metal were investigated. In the circular cup extrusion–drawing process, the punch motion curve of a conventional stamping press (Case A) and three punch motion curves of a servo press (Cases B–D, the strokes of which differed from that of Case A by 0.5, 1.5, and 2.5 mm, respectively) were compared, particularly regarding the effect of the coefficient of friction on the circular cup extrusion–drawing process. The simulation analysis was performed using the software program DEFORM. A set of simulated parameters were compared with experimental results. The formability, cup shape, cup height, cup thickness, extrusion force–displacement curve, stress distribution, and strain distribution were analyzed for the design of the die required. Additionally, experimental and simulation results were compared to determine the reliability and precision of the DEFORM simulations. The results indicated that the conventional punch motion curve resulted in a shorter cup, greater stress, greater strain, and the need for a greater extrusion force. By contrast, the servo punch motion curves resulted in taller cups, less stress, and less strain. The findings can serve as a reference for the development of servo presses.

Evolution of texture distribution in thickness direction of aluminum sheet in metal spinning

We evaluated the texture distribution in the thickness direction of the spun workpieces and clarified the mechanism of the change in the crystal orientation of the texture during metal spinning. Blank aluminum disks with a thickness of 1.44 mm were deformed into circular truncated cone cups by under-, true shear, and over-spinning and into cylindrical cups by 13 passes of conventional spinning. Crystal orientation analysis using electron backscatter diffraction revealed that the calculations of the orientation densities for small Miller indices could lead to a systematic evaluation of high intensity texture. The orientation density of Cu {121}<11¯1> decreased or that of B {110}<11¯2> increased on the roller side of the shear-spun part, of the workpieces formed by shear spinning, and on the roller side of the wall part and on the mandrel side of the open-edge part, of the workpieces formed by conventional spinning. The cosine similarity and Euclidean distance showed that the texture distributions obtained by shear spinning and that of the wall part obtained by conventional spinning were similar. Based on the stress state and preferred crystal orientation in deep drawing, the mechanism of the change in crystal orientation during spinning were described. The density of the texture with {110} (corresponding to B in this study) parallel to a disk plane increased when tensile stress was applied in the circumferential direction, contrarily, when compressive stress was applied in a similar fashion the density of the texture with {112} (corresponding to Cu) parallel to the disk plane increased.

The Effect of Elevated Temperature on the Drawability of a Circular Deep Drawn Metal Cup

Product quality is one of the important aspects in deep drawing practice and the variation in process temperature was claimed to improve the quality. Therefore, in this research, the effect of the heating temperature on the drawability of a circular metal cup has been investigated. Firstly, circular metal cups of aluminium, mild steel and stainless steel were drawn from the blank diameters of 60 mm, 65 mm, and 70 mm. The experiment was conducted at room temperature followed by at 100 °C, 150 °C and 200 °C. The Taguchi method was selected as the design of experiment approach, and L9 (34) array design methodology was adopted in this experimental research. The drawability was measured based on the punching force needed to deform the sheet metal blanks. The deep drawing process was conducted at room, and elevated temperature conditions and the response factor was analysed and compared through the analysis of variance (ANOVA) statistical approach. The results obtained from ANOVA indicate that the blank material has a significant influence on the deep drawing process followed by the blank size, heating temperature and heating technique. The optimal parameter combinations are blank diameter of 60 mm, heating temperature of 200 °C and the die and punch heating technique. Out of the three materials investigated, aluminium has a better drawability compared to mild steel and stainless steel.

Micro-Drawing of Circular Cups with Thin Stainless Steel Sheets

With the ongoing development of product process, there is a growing demand on micro products. Though the macro-drawing process has been well-developed, the design concepts may not be directly applicable to the micro-drawing due to the size effect occurred in the micro-forming processes. In the present study, experiments were conducted first to establish the stress-strain curves, r-values and work hardening exponents of 304 stainless steel sheets with different grain sizes. The experiment results reveal that the stress-strain and r-value become smaller and the work hardening exponent increases for larger grain sizes. The difference between stress-strain curves in various directions of 0°, 45° and 90°, respectively, is significant when the grain size increases. The stamping of a vibration motor shell of cell phone, which bears a circular cylindrical shape, was also examined in the present study. The finite element simulations were performed to evaluate the formability of the multi-stage drawing process with initial die design. The forming characteristics were identified and an optimum die design was then developed with the use of the finite element analysis. The stamping process with multi-stage tooling design based on the finite element analysis was implemented and the actual stamping experiments were conducted to verify finite element analysis. The experimental results confirm the validity of the modified tooling design and the efficiency of the finite element analysis.

Study of micro hydromechanical deep drawing of SUS304 circular cups by an ALE model

Abstract Accurate estimation of hydraulic pressure on the blank is important for micro hydromechanical deep drawing simulation. An Arbitrary Lagrange Eulerian (ALE) simulation model that considers strong fluid-solid interaction (FSI) was generated to accurately predict the hydraulic pressure on the blank. The changeable pressure significantly affects the drawn cup’s quality regarding wall thickness. Both the minimum and the maximum wall thicknesses in the ALE model are significantly different from that in a conventional model with a simple pressure load. The relationship between the maximum thickness and the hydraulic pressure in the ALE model is similar to that from the experimental results while reverse to that from the conventional simulation model. The ALE model provides more precise hydraulic pressure on the blank and accurate prediction of the drawn cups’ quality compared with the conventional model.

Analysis of the forming behaviour of in-situ drawn sandwich sheets

Abstract One way to produce metal fibre-reinforced plastic-metal sandwich parts is to inject the polymer between the sheets during deep drawing. A new process has been designed in which parts with an interlayer of glas fibres including a thermoplastic matrix and two metallic sheets can be produced by combining deep drawing and thermoplastic-resin transfer moulding (T-RTM). With the possibility of forming sandwich sheets with a wide range of states of the interlayers’ viscosity and due to the polymerisation of the monomers between the sheets, the process combines a lot of advantages but also faces challenges due to the viscous fluid interlayer being hindered from squeezing out. This contribution analyses the dependency of the interlayer on the forming behaviour of the sheets in this process. When forming circular cups with aluminium (AA5182) sheets and a viscous interlayer of different heights, the effect of bulging could be observed which affects a free formed shape during forming. The viscous interlayer does not remain at the same position during forming which leads to an inhomogeneous total blank thickness of the part. In experiments and FE simulations a shape with bulged zones could be observed. An analytical approach for the prediction of these bulge heights has been developed so that both bulge dome heights could be predicted analytically. This approach is verified by experiments and numerical simulations. The results serve to set the process window for the in-situ hybridisation method in which the starting point of injection, volume fraction of the thermoplastic matrix in the fibres, mechanical properties of the materials, and geometrical parameters can be adjusted so that this effect is reduced.

Effects of Hydraulic Pressure on Shape Accuracy of Drawn Circular Cups during Micro Hydro Deep Drawing

Micro hydro deep drawing is a promising technology to fabricate micro metal products with complex 3D shapes. However, the size effects in the micro hydro deep drawing become considerable and significantly influence shape accuracy of drawn cups. In this study, a Voronoi micro scale simulation model was developed to consider the size effects of SUS304 foils. A surface layer model was additionally applied in the simulation to further explain the size effects. The micro hydro deep drawing experiments were conducted with annealed SUS304 foils and the drawn cups were examined. The wrinkling phenomenon was generally aggravated with the hydraulic pressure. Simulation results also show that the high hydraulic pressure does not improve the shape accuracy of the drawn cups as that in the normal scale hydro deep dawning process does. The simulation results are in accordance with the experimental results.

Effects of hydraulic pressure on wrinkling and earing in micro hydro deep drawing of SUS304 circular cups

Influences of hydraulic pressure on forming features in micro hydro deep drawing are different from those in normal drawing due to the small size of specimens. In this study, micro hydro deep drawing of SUS304 sheets was carried out in order to study the impacts of the hydraulic pressure on the quality of the drawn cup. Experimental results indicate that there is a critical hydraulic pressure range from 3 to 6 % of the blank’s initial yield stress, where wrinkling and earing development trends change twice. The wrinkling and the earing of the drawn cup also reach their local extremes in the critical pressure range. The cup earing value moves in the opposite direction from the wrinkling value. Hydraulic pressure affects the wrinkling and the earing of the drawn cup through changes in the micro-frictional condition, the shape of the blank and its strain-stress state. Micro-finite element (FE) simulation which takes these factors as well as the material size effects into consideration showed similar results to the experimental ones, thus validating the experimental results and the suitability of the micro-simulation model for micro-forming FE simulation. The experimental and simulation results indicate that the critical hydraulic pressure based on the blank’s initial yield stress can restrict the wrinkling and the earing of the drawn cup. Ultra-high pressure has the potential to avoid the cup wrinkling and earing.

Investigations on dry sliding of laser cladded aluminum bronze

The aim of this study was to investigate the tribological behaviour of laser cladded aluminum bronze tool surfaces for dry metal forming. In a first part of this work a process window for cladding aluminum bronze on steel substrate was investigated to ensure a low dilution. Therefore, the cladding speed, the powder feed rate, the laser power and the distance between the process head and the substrate were varied. The target of the second part was to investigate the influence of different process parameters on the tribological behaviour of the cladded tracks. The laser claddings were carried out on both aluminum bronze and cold work tool steel as substrate materials. Two different particle sizes of the cladding powder material were used. The cladding speed was varied and a post-processing laser remelting treatment was applied. It is shown that the tribological behaviour of the surface in a dry oscillating ball-on-plate test is highly dependent on the substrate material. In the third part a deep drawing tool was additively manufactured by direct laser deposition. Furthermore, the tool was applied to form circular cups with and without lubrication.

Effects of surface roughness on micro deep drawing of circular cups with consideration of size effects

Surface roughness, compared with tiny sizes of micro products, can be relatively large and has significant influences on micro forming processes and products’ quality. In this study, a voronoi finite element model that considers size effects of material was developed. Next the surface roughness information was assigned to this voronoi model through different elemental thickness distributions. Furthermore, springback simulation was conducted for the micro deep drawn circular cups. Simulation results demonstrate that the surface roughness with consideration of size effects has significant influences on the overall springback, the drawability represented by the minimum thickness and products’ quality regarding thickness evenness and shape accuracy. This study also shows that the results from the new models are close to the experimental results concerning the diameter of cup mouth and the maximum drawing force. The developed model for the micro deep drawing is accurate and beneficial for the development of micro deep drawing process.

Development of servo-type micro-hydromechanical deep-drawing apparatus and micro deep-drawing experiments of circular cups

A micro-hydromechanical deep-drawing (MHDD) apparatus for manufacturing a micro-complex-shape components and increasing of drawn cup accuracy has been developed in this study. This apparatus with simple tooling structure and forming process can achieve high dimensional accuracy using servo press mechanics with a double-action type, one-stroke forming process without transferring and positioning, force control, and fine flow rate control of the pressure medium. The developed MHDD apparatus can prevent wrinkling by applying an appropriate constant gap and stably generate the counterpressure. Micro drawn cups of 0.8mm diameter are successfully fabricated. Also, the effects of counterpressure on drawability and dimensional accuracy at the bottom of the cup are investigated for phosphor bronze, stainless-steel, and pure titanium foils with a thickness of 50μm. The appropriate counterpressure applied in MHDD can eliminate wrinkling and reduce the frictional drawing force. It is concluded that the forming limit and dimensional accuracy can be improved by MHDD.

알루미늄 판재의 다단계 드로잉에 있어서 원통컵의 치수 정밀도 비교

Deep drawing of cylindrical cups is one of the most fundamental and important processes in sheet metal forming. Circular cups are widely used in industrial fields such as automobile and electronic appliances. Some of these cups are formed by a one-stage process, others such as battery cases and beverage cans are made by a multi-stage process. In the current study the multi-stage deep drawing of aluminum sheet metal is examined. The process consists of two deep drawing operations followed by two ironing operations. The press die, which can be used for the four-stage forming process, was manufactured allowing punch and die components to be easily changed for various experiments. The rolling direction of both the sheet and the drawn cups was always positioned toward the horizontal x-direction on the die face to minimize experimental errors during the progressive forming. The dimensional accuracy of the cylindrical cups formed at each stage and the earing defect due to the anisotropy of sheet were investigated. The influence of anisotropy on the thickness distribution was also examined. Both the thickness and the outer diameter of the cups were measured and compared for each set of experimental conditions. It was found that the dimensional accuracy of cups rapidly improves by employing the ironing process and also by increasing the amount of ironing.

Dry metal forming of high alloy steel using laser generated aluminum bronze tools

Regarding the optimization of forming technology in economic and environmental aspects, avoiding lubricants is an approach to realize the vision of a new green technology. The resulting direct contact between the tool and the sheet in non-lubricated deep drawing causes higher stress and depends mainly on the material combination. The tribological system in dry sliding has to be assessed by means on the one hand of the resulting friction coefficient and on the other hand of the wear of the tool and sheet material. The potential to generate tailored tribological systems for dry metal forming could be shown within the investigations by using different material combinations and by applying different laser cladding process parameters. Furthermore, the feasibility of additive manufacturing of a deep drawing tool was demonstrated. The tool was successfully applied to form circular cups in a dry metal forming process.

An experimental and numerical study of micro deep drawing of SUS304 circular cups

Micro deep drawing is a promising technology for mass production of complex 3D micro metal products. Significant size effects at a micro scale, however, obstruct application of this technology and block utilisation of traditional finite element method (FEM). Therefore, a micro tensile test system was developed to obtain accurate material properties considering size effects. Subsequently, a Voronoi blank model was developed for the micro scale simulation. Moreover, micro deep drawing experiments were conducted and their results were compared with the simulation results. The simulation results have a good agreement with the experimental data. Furthermore, the wrinkling at the cup mouth increases with the growth of grain sizes on the SUS304 sheets.

Marchantites huolinhensis sp. nov. (Marchantiales) – A new fossil liverwort with gemma cups from the Lower Cretaceous of Inner Mongolia, China

A new fossil liverwort species Marchantites huolinhensis R.Y. Li & B.N. Sun sp. nov., is founded based on twenty-seven fossil specimens collected from the Lower Cretaceous Huolinhe Formation in Huolinhe Basin of Inner Mongolia, China. The fossil liverwort is characterized by thalloid and prostrate gametophyte, and elliptical–circular gemma cups. Thallus is strap-like, dichotomously branched and with prominent costa. Imbricate ventral scales are in two rows and smooth and unicellular rhizoids are produced in considerable numbers around the costa. Cells on prominent costa are elongated and parallel to the long axis of the thallus. The relatively complete gametophyte, gemma cups, ventral scales and rhizoids indicate that they were likely to be autochthonously buried in dysoxic or anoxic silty deposits. Marchantites huolinhensis, along with other fossil records from other localities and age, indicates that the Marchantiales was already diverse in the Early Cretaceous and its morphological evolution is very slow.

Elliptical Redrawing from Circular and Elliptical Cups

Elliptical redrawing is an essential intermediate forming operation in producing flat-type case products. In this work, two forming schemes were investigated, namely direct elliptical redrawing from circular and elliptical cups. Cold-rolled steel sheet SPCE was used as the workpiece. Finite element software DYNAFORM was used in simulating the two forming schemes. The thickness distribution both along the major and minor axes was evaluated. The flange geometry of the redrawn cups was examined from the experiments. An analysis of eccentric redrawing was proposed to help explain the difference in the thickness distribution and the flange geometry along the major and minor axes of the two forming schemes. The results indicate that elliptical redrawing from elliptical cups can be adopted in the design of redrawing schemes to reduce the thinning and consequently the risk of fracture at the major axis—the most vulnerable part during elliptical redrawing.

Finite Element Method Based Simulation on Warm Deep Drawing of AISI 304 Steel Circular Cups

Warm deep drawing, one of the unconventional deep drawing processes, has attracted more attention of lot of researchers in the recent years. In this study, finite element method based simulation using a commercially available software package is carried out on deep drawing of circular cups of austenitic stainless steel at an operating temperature ranging from room temperature to 300°C. Experiments are also conducted at the same temperatures. Comparison between the experimental values and the finite element simulation results shows a good agreement between the two. Thus, finite element method simulation can be used effectively to analyze the deep drawing operation at any temperature within this range by modifying any input parameters without conducting the experiment and hence a lot of cost saving.

Investigation on Formability of AISI 304 Circular Cups by Warm Deep Drawing

Deep drawing is one of the sheet metal forming processes used widely in industries like automobile, aerospace etc. In drawing operation, the limiting draw ratio (LDR) is used as an index of drawability of a material. In this investigation, stainless steel AISI 304 grade blanks of 1.0 mm thickness with different diameters are drawn into a circular cups in single stage. The experiments were conducted at room temperature as well as at temperatures 100oC, 200oC, and 300oC. The LDR values obtained in each condition were analyzed. The experimental results show that there is a significant improvement in LDR values by warm working.