Blank Thickness Research Articles

Experimental Analysis and Prediction of Springback in V-bending Process of High-Tensile Strength Steels

Experimental setup has been designed, to study the effects of thickness, width, bend angle and machine tool parameters on the springback, in two high-tensile strength steel grades, namely JSC440 and JSC590, during the V-bending process. Relationship between the springback and the parameters are analyzed using plots. Optimal combination of parameters for the minimum springback is evaluated. Analysis of variance has been carried out to analyze the magnitude of influence of these parameters on the springback. Using the experimental results, analytical models for the prediction of springback for the combinations of blank thickness, width, bend angle and machine tool parameters have been developed. Results reveal that in V-bending of JSC440, thickness and width are the dominant factors influencing the springback, whereas in JSC590 steel, insignificant change in springback is observed with the change in width of blank and using the hydraulic press with holding. However, thickness of steel sheet and bend angle influence significantly the springback in JSC590 steels.

Mechanics of double-sheet die-less shear spinning: a novel potential method for wall thickness control in spinning process

Die-less spinning has high flexibility in aeronautics, aerospace vehicles and other manufacturing fields; however, the wall thickness of the workpiece is hard to control in die-less shear spinning. A flexible control method of wall thickness distributions on the truncated cone shape is attempted using double-sheet shear spinning. The fundamental approach entails the adjustment of original thickness during forming. In double-sheet die-less shear spinning, two aluminum disk blanks arranged concentrically are formed for truncated cone. The cover thicknesses of the spun workpieces are smaller than the value that conforms to the sine law using the same blank thickness. The wall thicknesses of base spun workpieces are bigger than the sine law value under the same circumstances. The theoretical mechanics analysis of the double-sheet shear spinning process is carried out through mechanics and finite element analysis.

Study on the influence of the blank thickness on the dynamic behavior of mechanic eccentric presses

This paper presents a method for studying the dynamic behavior of mechanical presses with eccentricity based on a mathematical model. The novelty elements of the proposed model are as follows: the essential non-linear evolution of the force in process; the frictional force in the slider guides is also considered to have a non-linear character; the friction moments in the kinematic chain structure are considered different at start-up compared to the nominal regime and the weight of the slider together with the elements attached to it is taken into account. The equations characterizing the movement of the system were deduced starting from Lagrange’s generalized equations. Finally, an interactive graphical interface was developed that allows the study of the influences of some constructive and adjusting parameters on the parameters that characterize the dynamic behavior of the working mechanism: the angular speed, the motor moment and the power consumed by the electric drive motor. The method was applied to the case of PAI 63 press. Based on the results obtained by changing the parameters mentioned above (around the existing values), a serie of conclusions were drawn that could lead to an improvement of the construction and the exploitation. of this machine.

A Comparative Study of Simulation Models on Incremental Forming Process by Using the Enhancement Tools

Incremental Forming IF is a suitable sheet metal forming technique for producing complex forms by local deformation. The forming tool movement follows the designed tool path controlled by the CNC machine programme. The main categories of the process are single point, SP and two points, TP "with enhancement tools". Additionally, the product design determines the enhancement tool type used and its obstacles. The enhancement tools are used for improvement of the product profile quality, while maintaining the simplicity of the process. The material formability is affected by mechanical properties and characteristics of the product profile. The limits are concerning the forming tools used and the blank thickness. On the other hand, due to the difficult environment of these process models, numerical methodologies controlled by Finite Element Method, FEM are currently in extensive use. The research offers the main data and results of a comparing study on the influence of using the enhancement tools in IF through FEM. The study purposes to identify the scientific differences of the IF processes, "with and without enhancement tools" by evaluating the thickness and strains distribution of the deformed blank section. In addition, the analysis and the evaluation of the final product profile have been studied.

Study on die-less spinning of cone–cylinder combined hollow parts

Die-less spinning can achieve the thin-walled parts with the regular shape of cone and cylinder or even some non-axisymmetric shapes. And it has advantages in forming some difficult demolding shapes. In this study, die-less spinning in a cone–cylinder combined hollow part and its forming mechanism were investigated. A ball-crown-shape roller was used to replace a conventional roller in the spinning process. The roller movement and spindle rotation were controlled by a computer numerical control spinning machine to achieve a planned roller path. The pass sets of tilted and horizontal lines were designed to form the cone and cylinder shape, respectively. Further, two methods were adopted to link the two forming pass sets and spin the cone–cylinder combined shape. One is to connect the cone and cylinder forming lines directly (Schemes A); the other is to connect the cone and cylinder forming lines by transition lines (Schemes B). The effects of two key parameters (roller path and feed ratio f) on the wrinkling and wall thickness distribution were analyzed. The product exhibited wrinkling on the wall using the roller path of Scheme A with f = 0.5 mm/r. f affected the occurrence of wrinkling considerably. Larger f made the flatness of the cylinder wall worse, no matter which roller path (in Scheme A or B) was used. When f was set to 0.25 mm/r (f was lower than LT1 in this study) with a blank thickness of 2.05 mm, wrinkling could be suppressed in the roller path of Scheme A. The product had an increasing thickness distribution on both the cone and the cylinder. The cylinder wall was even thicker than the disk blank with a blank thickness of 2.05 mm.

An Experimental and Numerical Study of Dieless Water Jet Incremental Microforming

Conventional single-point incremental forming (SPIF) is already in use for small batch prototyping and fabrication of customized parts from thin sheet metal blanks by inducing plastic deformation with a rigid round-tip tool. The major advantages of the SPIF process are its high flexibility and die-free nature. In lieu of employing a rigid tool to incrementally form the sheet metal, a high-speed water jet as an alternative was proposed as the forming tool. Since there is no tool-workpiece contact in this process, unlike in the traditional SPIF process, no lubricant and rotational motion of the tool are required to reduce friction. However, the geometry of the part formed by water jet incremental microforming (WJIMF) will no longer be controlled by the motion of the rigid tool. On the contrary, process parameters such as water jet pressure, stage motion speed, water jet diameter, blank thickness, and tool path design will determine the final shape of the workpiece. This paper experimentally studies the influence of the above-mentioned key process parameters on the geometry of a truncated cone shape and on the corresponding surface quality. A numerical model is proposed to predict the shape of the truncated cone part after WJIMF with given input process parameters. The results prove that the formed part's geometric properties predicted by the numerical model are in excellent agreement with the actually measured ones. Arrays of miniature dots, channels, two-level truncated cones, and letters were also successfully fabricated on stainless-steel foils to demonstrate WJIMF capabilities.

Experimental investigation of forming metallic bipolar plates by hot metal gas forming (HMGF)

In this study, the effects of various parameters in forming of aluminum alloy bipolar plates using hot metal gas forming (HMGF) were studied. The effect of applied gas pressure P, channel width w, and outer fillet radius of die R were investigated. For evaluation of the forming state, both thickness distribution and filling profile of formed plates were measured. The results showed that increase in the gas pressure led to decrease in the blank thickness and increase in the filling profile. Moreover, by increasing the outer fillet radius, the maximum thickness reduction at formed plates was decreased and filling percentage was increased. Different aspect ratios h/w of rigid die were applied. It was concluded that by increasing aspect ratio, the thickness reduction was increased and the filling percentage was decreased. Finally, high accurate plates were fabricated in experimental tests which confirmed the feasibility of forming the thin bipolar plate by HMGF.

Processing maps for wrinkle free and quality enhanced parts by shear spinning

An experimental investigation was conducted to study the effects of key processing parameters when shear spinning conical part geometries from both aluminium alloy and mild steel disc shaped blanks. It investigated the effects of feed ratio, spindle speed, initial blank thickness, and thickness reduction on the occurrence of the wrinkling failure, effectiveness of thickness reduction, part springback, surface finish, and strain hardening effects resulting from the process. A design of experiments approach was used to conduct the experimental tests and a multi-variate regression analysis method was applied to obtain processing maps of the key parameters which produced wrinkling free and quality enhanced spun parts. The results showed that the feed ratio was the most critical processing parameter, with higher feed ratios led to the onset of wrinkling failure, less effective thickness reduction, more part springback and rougher part surfaces. The process was shown to result in a significant strain hardening effect in the blank material, which was found to be enhanced when the amount of blank thickness reduction was increased.

Flexible rolling of rotational symmetric tailored blanks with a two-sided thickness profile

Abstract The application of bulk forming operations to sheet metals leads to an increase of the material efficiency due to the enhancement of the process limits compared to conventional forming processes. The main challenges within the process class of sheet-bulk metal forming are high resulting forming forces and a defined control of the material flow. Additionally, the initial blank thickness influences the resulting quality of the geometrical and mechanical properties of functional components, like synchronizer rings. Previous investigations have shown that the application of tailored blanks with a defined one-sided thickness profile can meet these challenges which lead to an increase of the sufficient die filling of functional elements in subsequent forming processes. Due to the further increase of the geometrical complexity with functional elements in- and outside of the frame like carriers or gear teeth, the layout of the tailored blank has to be adapted. Thus, a two-sided thickness profile is necessary, for achieving the sufficient die filling of the functional elements. One possibility for manufacturing these semi-finished parts is a flexible rolling process which is used within the presented work. Thereby, it is necessary to develop a new process strategy for achieving a material thickening on both sides, rolled- as well as die-sided. For enabling a homogeneous material flow, the deep drawing mild steel DC04 with an initial sheet thickness of t 0 = 3 mm is used, due to a high formability of this material. The tailored blanks are hereby analyzed regarding the resulting process forces, geometrical dimensions like the sheet thickness, mechanical properties such as the hardness distribution and the resulting surface roughness in important areas.

Determination of formability considering wrinkling defect in first-pass conventional spinning with linear roller path

Flange wrinkling is one of the common defects that occur in conventional spinning process, severely restricting the improvement of forming quality and formability. How to universally determine the formability dependent on flange wrinkling is a critical issue in conventional spinning process. For this end, such a determining method for the formability in the process is proposed to rationally design the forming parameters to prevent flange wrinkling. The method is as follows: firstly, the maximum circumferential stress during the process is calculated at the outer edge of the flange, where the circumferential stress is considered as the combining result of the shrinkage of flange diameter and the bending of flange; then, the formability is determined by comparing the maximum circumferential stress to critical circumferential stress for wrinkling defect. Based on the method, a formability analytical model considering wrinkling defect in the first-pass conventional spinning process with a linear roller path is established. The formability model is validated by experiments and FE simulations at different spinning conditions. Sequentially, the influences of forming parameters and their interaction on the formability considering wrinkling defect are systematically analyzed. Furthermore, the forming diagrams considering wrinkling defect for the first-pass conventional spinning are established. It is found that the feed ratio has the most significant effect on the formability, followed by the blank thickness, the hardening exponent, the feed ratio-hardening exponent interaction and the feed ratio-sheet blank thickness interaction. The smaller feed ratio and hardening exponent, thicker sheet blank and greater relative sheet blank radius are helpful to increase the formability. The research results could provide a theoretical basis and guidance for the selection of forming parameters in the actual production of the first-pass conventional spinning.

Investigating the Effects of Cold Bulge Forming Speed on Thickness Variation and Mechanical Properties of Aluminum Alloys: Experimental and Numerical

In this work, cold bulge forming of an Aluminium-Magnesium (Al-Mg) sheet with a solid bulging medium is performed experimentally and numerically. Mechanical properties and thickness variations of Al-Mg sheet are evaluated before and after the forming process. The results indicated that the Al-Mg sheet has taken the desired shape without necking using the cold bulge forming process. Also, the experimental results show significant improvements in mechanical properties of Al-Mg sheet after bulge forming. It is proved that the maximum thickness reduction of Al-Mg blank is less than 6% after cold bulge forming. Numerical simulations of cold bulge forming of Al-Mg sheet are conducted using Abaqus finite element software. For this purpose, many numerical models are created and analysed to investigate the effects of bulge forming speed on the blank thickness variation for different Aluminium alloys. In these simulations, four different speed of 1, 5, 15 and 25mm/min are used as forming speeds. Numerical results of bulge forming of Al-Mg sheet are compared with experimental measurements and good correlation is observed between the results. Moreover, obtained results from numerical simulations for different Aluminium alloys show that the thickness variations of formed Al-Mg sheet are more uniform by reducing the forming speed.

Efficient simulation of ironing process for deep drawn parts

In deep drawing of automotive components, the thickness distribution of the workpiece is a major concern regarding the feasibility of the process. A major geometrical parameter regarding the thickness distribution is the clearance between the punch and the die. The general industrial convention regarding this clearance is to use the initial blank thickness combined with a tolerance. This approach assures that the sheet is not compressed in the thickness direction which leads to undesired or undefined deformations and also high forces. Nevertheless, deformation in the thickness direction during stamping operations can be desired or advantageous in some cases. For instance, in flanging operations, ironing is used to reduce springback. There are already applications using solid elements for modelling such operations but these simulations are industrially not relevant due to high computation times. Currently, there is a need for an efficient simulation solution using shell elements. In order to address this problem, the shell element formulation was enhanced by taking the through-thickness deformation into account. In order to verify the new formulation, cup drawing experiments were performed using three different degrees of ironing. The material was a DC04- SUPERMOD with 1.75 mm thickness that was characterized by tensile tests in three directions, a bulge test and a layer compression test. Numerical and experimental results were compared in terms of the thickness distribution along the cross-section and the cup heights. Results show that the ironing process, which occurs in automotive stamping parts, can be simulated with enhanced shell elements without significant additional computational cost.

Influence of blank thickness fluctuation on flange state and final thickness distribution in the power spinning of thin-walled head

The initial blank exists unavoidable thickness fluctuation. In the spinning process of head parts, this fluctuation affects the flange state and final wall thickness distribution of the parts, which seriously deteriorates the forming quality. To research the blank thickness fluctuation on flange and spun head thickness distribution, three-dimensional (3D) finite element (FE) models considering blank fluctuation for the spinning process of 2219 aluminum head parts were established. The blank fluctuation was characterized using the Latin hypercube sampling method (LHS), and three fluctuation ranges and three fluctuation types were adopted (type 1, the average blank wall thickness is approximately equal to 1.0 mm, 1.0 mm is defined as the ideal standard blank thickness (ST); type 2, the average blank wall thickness is bigger than ST; type 3, the average blank wall thickness is smaller than ST). Then, flange fluctuations and the variations of wall thickness deviation were analyzed. The results showed that the maximum flange fluctuation appears within the 20% spinning process; the maximum flange fluctuation of type 1 is larger than those of type 2 and type 3. In the top zone of the spun head, the maximum wall thickness deviation of type 3 is the largest. While in the middle and edge zones, the maximum wall thickness deviation of type 2 is the largest. Simultaneously, a greater initial blank fluctuation leads to the bigger thickness frequency deviation. The research provides an in-depth understanding of the effects of blank wall thickness fluctuation on the forming quality in the head spinning process, and thus lays a basis for choosing the blank.

Experimental investigation of the mechanical performances of titanium cranial prostheses manufactured by super plastic forming and single-point incremental forming

In the present work, sheet-forming processes, i.e. super plastic forming and single-point incremental forming, have been adopted for the manufacturing of custom prostheses, instead of subtractive and additive techniques that are time- and cost-consuming for a single-piece production. Regarding concerns of the material, three different titanium alloys were used: pure titanium and two grades of the alloy Ti-6Al-4V (the standard one and the extra low interstitial one). Since no standard protocol exists to assess the mechanical performance of cranial implants, an experimental procedure has been designed and used in this work for producing polymethylmethacrylate supports, on which the cranial prostheses were firmly connected and subjected to impact puncture tests (drop tests). An experimental campaign could thus be conducted to investigate the effect on the mechanical response of (a) the titanium alloy, (b) the initial blank thickness and (c) the manufacturing process. Drop tests, carried out according to the proposed procedure, have shown no failure of the prostheses, neither in the area of the impact nor in the anchoring region and have revealed that, irrespective of the adopted manufacturing process, which does not alter the material, the amount of energy absorbed by the implants is always larger than 70%.

Orthodontic thermoformed retainers: a two-arm laboratory study into post-fabrication outcomes.

Retainers are commonly used to maintain post-orthodontic occlusion stability. We aimed to determine post-fabrication thickness and thinning rate of thermoformed retainers. Forty-eight retainers were fabricated from polyethylenterepthalat-glycol copolyester or polypropylene blanks, using vacuum- or pressure-thermoforming. Retainer thickness was measured at multiple locations. Thinning rate had a broad range: the mid-labial incisor region of 1 mm polyethylenterepthalat-glycol copolyester pressure-thermoformed mandibular retainers had the greatest thinning rate (68.25 ± 8.26%) and smallest mean post-fabrication thickness (0.32 ± 0.08 mm). Polyethylenterepthalat-glycol copolyester retainers were 0.11 mm thinner than polypropylene (P=0.0222), and polypropylene retainers were 0.21 mm thicker, when pressure-thermoformed (P<0.0001). The interaction of manufacturing method and material used, and tooth type, explained over a third of the variability in the post-fabrication thickness of these retainers. Maxillary retainers made from 1 mm blanks were 0.04 mm thicker in the incisor region compared with the molar region (P=0.0492). Thermoformed retainers do no thin uniformly against individual teeth and have variable intra- and inter-arch post-fabrication thicknesses. There is no clear benefit in using a specific type of thermoforming machine or material for increasing post-fabrication thickness or reducing thinning rate. Blank thickness and tooth morphology influence these outcomes.

Development of reversed deep drawing without blank-holder for producing brass elliptical cup

A new technique “Reverse Deep Drawing Process” without blank holder was adopted, for the single stage to produce an elliptical cup through an elliptical die. In this process an elliptical-cup is produced by pushing an elliptical blank using a hollow elliptical punch through an elliptical die in a single stroke. FEM via ANSYS is used to analyze this process. The clearance ratio was varied to study its effect on some parameters of this process like load, stress, strain, thickness distributions. A die with clearance =1mm and blank thickness=1mm gave the best drawability in this technique and no wrinkling observed on the product but it has minimum earring. Several attempted have been done to get the shape and dimensions of the blank, the major axis (a) =85mm &amp; the minor axis (b) =65 mm was the better blank for this process to produce elliptical cup of major axis is twice minor axis. Good agreements are evident between the experimental and finite element results; the discrepancy is 4.0797% for load-extension and 0.852% for the wall thickness in minor axis and 1.145% in major axis.

Research on Single Pass Deep Drawing Spinning Formability of Cup-Shaped Parts

The deep drawing spinning (DDS) formability of metal material refers to the ability to produce an opened hollow part with a circular blank through DDS without fracture or wrinkling defect. The cup-shaped parts of DP600 were selected as the research object, the coefficient m=d/D0was put forward as the evaluation index of DDS formability, and the minimum coefficient without the occurrences of wrinkle and fracture is defined as the limit DDS coefficient mlim. The single pass DDS formability of cup-shaped parts was investigated experimentally and the influences of blank thickness, roller feed rate and roller fillet radius on the DDS formability were discussed in detail. The results show that the DDS coefficient decreases with the increasing of blank thickness; fracture or wrinkling occurs easily when the roller feed rate is excessively large or excessively small; the large roller fillet radius is helpful to improve the DDS formability of metal material.

Kinetics of the melting front movement in process of centrifugal induction surfacing of powder material with nanoscale modificaters

For solving the problem of improving the powder coatings modified by nanostructure components obtained by induction surfacing method tribological characteristics it is necessary to study the kinetics of the powdered layer melting and define the minimum time of melting.For powdered layer predetermined temperature maintenance at sintering mode stage it is required to determine the temperature difference through blank thickness of the for one hundred-day of the define the warm-up swing on of the stocking up by solving the thermal conductivity stationary problem for quill (hollow) cylinder with internal heat source. Herewith, since in practice thickness of the cylinder wall is much less then its diameter and the temperature difference is comparatively small, the thermal conductivity dependence upon the temperature can be treated as negligible.As it was shown by our previous studies, in the induction heating process under powdered material centrifugal surfacing (i.e. before achieving the melting temperature) the temperature distribution in powdered layer thickness may be considered even. Hereinafter, considering the blank part induction heating process quasi-stationarity under Fo big values, it is possible to consider its internal surface heating as developing with constant velocity.As a result of development the melting front movement mathematical model in a powdered material with nanostructure modifiers the minimum surfacing time is defined. It allows to minimize negative impact of thermal influence on formation of applied coating structure, to raise productivity of the process, to lower power inputs and to ensure saving of nonferrous and high alloys by reducing the allowance for machining.The difference of developed mathematical model of melting front movement from previously known is that the surface temperature from which the heat transfer occures is a variable and varies with a time after the linear law.

Influence of process parameters on residual stresses in deep-drawing process with FEM and experimental evaluations

This paper presents experimental and simulation study to minimize residual stress in cylindrical deep-drawing process. Eight significant process parameters including initial blank thickness, punch and die shoulder radii, blank–holder force, punch velocity, and coefficients of friction between die–blank, holder–blank, and punch–blank are considered. According to number of parameters, the Taguchi’s method is employed to perform design of experiments. The die is designed and manufactured, and the experiments are carried out using AISI 1006 carbon steel sheet. Hole-drilling method based on ASTM E 837-99 standard is applied to measure the residual stresses in drawn cups. Moreover, the deep-drawing process is simulated wholly using ABAQUS/explicit software and the accuracy of finite-element model is verified using experimental results. Finally, the analysis of variance method is applied to define the most important parameters and obtain an optimum level to minimize the residual stress in cylindrical deep-drawing process.

Sheet Metal Forming Processes – Recent Technological Advances

The sheet metal industry has seen more technological advances than any other since the last century. Right from hand-forming processes to finite element based simulation, the transformation is very significant. They have prominent industrial applications especially in automotive industries. This may be attributed to the ease with which the final component with desired shape and appearance can be produced using simple tools. Due to wide range of applications, the process of forming the sheet metal into various shapes leads to classification of the forming processes based on specific operation. This classification involves bending, blanking, stretch forming and deep drawing. Each process has some parameters that define the quality of the work achieved. This paper aims at scattering light on the recent research and developments in the sheet metal forming processes over the last two decades. Most of the literature available on sheet metal forming focuses on the parameters that influence the quality and economic factor of the final product. The influence of process parameters based on geometry such as punch nose radius, blank temperature, and blank holding force, tooling dimensions, blank thickness and punch depth is significant. Similarly, the parameters based on the material properties like elastic strength, yield strength, plasticity and anisotropy have as much influence as the geometry based parameters. The literature raises the issue of defects in the formed parts. Defects such as wrinkling, tearing, springback, local necking and buckling in regions of compressive stresses have been analysed using both experimental and simulation techniques. Springback, the most predominant defect, has been researched thoroughly while considering sheet thickness, punch force, nose radius, binder force, die opening, punch velocity, punch height, sheet anisotropy, clearance, elastic limit and yield strength of the blank material as input parameters. Lastly, this paper also aims at reviewing the finite element based tool design, experimental and numerical investigations into sheet metal forming processes.