Die Profile Radius Research Articles

Parameter study of the axisymmetric hydromechanical deep drawing process

In this paper, hydromechanical deep drawing and the effect of process parameters on the process have been studied using the finite element (FE) method. In order to verify the results of FE simulations, a study has also been carried out using experimental tooling. Numerical results indicate a working zone with a maximum chamber pressure in which the maximum limit drawing ratio (LDR) can be achieved and where the effect of chamber pressure on the process can be shown. Also, the effect of parameters such as initial chamber pressure, die profile radius, blank thickness, and friction effect has been investigated. It is shown that initial chamber pressure has an optimum value in which the maximum LDR can be achieved. Increasing the die profile radius increases the LDR at lower chamber pressures but has no marked effect at higher pressures. The numerical result also shows that increasing the friction between blank and die or blank and blank-holder decreases the LDR value, while increasing the friction between blank and punch increases the LDR value.

両面しごき限界に及ぼす加工条件の影響

A both-sided ironing process can iron the inner and outer surfaces of a can at the same time using inner and outer dies. The limiting ironing ratio of the both-sided ironing process is lower than that of the one-sided ironing process. In the case of an ironing die profile radius of 10mm, the limiting ironing ratio of the both-sided ironing process is 27%, and that of the one-sided ironing process is 36%. This characteristic depends on the difference in the forming mechanism. The limiting ironing ratio of the both-sided ironed can is found to be influenced by the combination of different die profiles for inner and outer dies, the lubrication on both sides of the can. The limiting ironing ratio increases with increasing the profile radius of the inner die. The limiting ironing ratio is slightly affected more by the lubrication of the outer side rather than that of the inner side. The limiting ironing ratio decreases when the outer side is not lubricated.

Springback characteristics of tailor-welded strips in U-draw bending

The purpose of this study is to investigate the springback characteristics of tailor-welded strips in U-draw bending. Two different welded strips were adopted to compare the effects of weld-line locations on the springback. One was welded along the centerline of the strip-width and the other was welded along the centerline of the strip-length. To investigate the effect of different thickness combinations on the springback, the tailorwelded strips were joined by a laser welding process. Three sheet thickness combinations were assessed, SCP1 0.8 t* SCP1 1.2 t, SCP1 0.8 t* SCP1 1.6 t and SCP1 0.8 t* TRIP 1.0 t. Three punch profile radii of 3, 6, and 9 mm and three die profile radii of 5, 10, and 15 mm were prepared and three blank holding forces (BHF) of 125 kgf, 250 kgf, and 500 kgf were applied to investigate the effects of punch profile radius (Rp), die profile radius (Rd), and BHF on the springback of tailor-welded strips. With consideration for the thickness of the sheet and the material properties, the extent of the springback on the sidewall of unloaded sheet shapes increases as the thickness and the yield strength of the sheet increase in the U-draw bending process. For longitudinally welded strips, the amount of springback of the TRIP steel sheet in TWB could be reduced through a springback combination of the thinner side and weld-line. For the thinner side (0.8 t) of the centrally welded strips, the deformed shapes after the springback were almost the same regardless of the thickness com|bination, and the extent of the springback decreased compared with that of non-welded SCP1 0.8 t. Some experimental results are compared with analytical results obtained by using the finite element method.

Springback characteristics of steel sheets for warm U-draw bending

The purpose of this study is to investigate the characteristics of springback for various process conditions of the U-draw bending operation. The process variables are the forming temperature and the tool geometry, including punch profile radius (Rp) and die profile radius (Rd). In order to control springback, the use of a warm forming method is applied. For the warm draw-bending, five steps of temperature ranges, from room temperature to 200°C, were adopted. Two kinds of steel sheets, cold rolled carbon steel (SCP1, for general purposes in the automobile industries) and TRIP (transformation-induced plasticity) steel, were adopted. TRIP steel was the newly developed high-strength steel sheet. The results indicated that elevated temperature and the geometry of tools in the two kinds of steel sheet affected the springback.

Stretch-drawing of titanium sheets

Stretch-drawing is a type of the popular deep-drawing process, which utilizes a sharp die shoulder of less than three times the sheet thickness, whereas the conventional process adopts about eight times. When the sheet slides over the die shoulder it is subjected to a strong bending under tension and thus the sheet becomes thinner to yield a deeper cup. Titanium is paid much attention to for its lightness and property of anti-rust. Here, its ability and behavior in the stretch-drawing process is investigated in detail. Two kinds of pure titanium and one of its alloys are tested, of which the thickness is commonly 0.5 mm. It is evidenced that the merit of stretch-drawing or bending under tension is remarkable for titanium sheets as much as for other metals. The variation of the cup wall thickness with the die profile radius, and the relationship between the blank diameter and the depth of formed cups are clarified. The shape quality of the formed cups is also inspected, especially regarding the roundness and the three-dimensional radius distribution of the cup wall cross-section. The former indicates the level of deviation of any cup cross-section from an exact circle, and the latter the global distortion pattern of the cup. The shape quality of a stretch-drawn cup is confirmed to be better than that of a deep-drawn cup. Furthermore, the measurement of the shape implies that its feature depends on the planar anisotropy of the sheets tested.

A fundamental study of can forming by the stretch-drawing process

The double stretch-drawing process is studied experimentally within the scope of the best or better combination of first and second drawing ratios in which the second punch diameter is fixed, for a the sheet thickness of 1.0 mm. It is concluded that the largest total limiting drawing ratio (=initial blank diameter BD divided by the second punch diameter) is achieved when the smallest first drawing ratio and the largest second drawing ratio are adopted, both for the double stretch-drawing and the usual double deep-drawing processes, in which case the deepest cup can be formed for both processes, respectively. It is emphasized that the deepest cup can be formed by the double stretch-drawing from a smaller limiting BD, applying an appropriately small die profile radius. Stretch- and deep-drawing processes accompanied by ironing are also studied with respect to a thick sheet (=3.0 mm) experimentally. Numerical simulation of the stretch-drawing process is also performed by the use of the explicit dynamic FEM code, DYNA3D code, to confirm that a satisfactory prediction, especially of the depth of the drawn cup, can be done at least in a practical sense, although this kind of numerical analysis is very difficult because of the severity or localization of deformation around the die profile.

Finite element simulation of warm deep drawing of aluminium alloy sheet when accounting for heat conduction

The deformation behaviour and the temperature change in cylindrical deep drawing of an aluminium alloy sheet at elevated temperatures are simulated by the combination of the rigid-plastic and the heat conduction finite element methods. The comparison with the experimental results shows that the forming limits and the necking sites are successfully predicted by the simulation. It is clarified that the appropriate distribution of flow stress depending on temperature must exist in the sheet for the higher limiting drawing ratio. The numerical as well as the experimental results show that the limiting drawing ratio in the warm deep drawing increases with the die profile radius.

アルミニウム合金板材製自動車用オイルパンの温間成形

In this study, warm forming die and blank holder could be heated and punch could be cooled always. At first, relation between die profile radius and drawing ratio was experimented in cylindrical cup drawing. Next, oil pan that is one of difficult part to press forming at room temperature was experimented and foreword experimental result was applied to die profile radius of oil pan. At last, warm forming of oil pan was continually examined. The results were following, (1) LDR of cylindrical cup drawing of warm forming were great than that of room temperature forming, but showed a violent variation with die profile radius, and fractures were in cup wall near to die profile. (2) An indication of good performance of warm forming was given with oil pan 1 stroke press, so oil pan from aluminum alloy sheets by warm forming had no fracture, but that by room temperature forming had fracture and that from steel sheets too. (3) Warm forming of oil pan from aluminum alloy sheets could be continued without break and mass productivity should be improve with insulation of handling machines.

A Fundamental Study of Cup Forming by Stretch-Drawing Process. 2nd Report. Experimental Search for Advantageous Process in Two-Stages Operation.

Double stretch-drawing process is studied experimentally within the scope of the best or better combination of 1st and 2nd drawing ratios in which the 2nd punch diameter is fixed. It is concluded that the largest total limiting drawing ratio (= initial blank diameter BD divided by the 2nd punch diameter) is achieved when the smallest 1st drawing ratio and the largest 2nd drawing ratio are adopted, both for the double stretch-drawing and the usual double deep-drawing processes. Then the deepest cup can be formed as well. The deepest cup can be formed by double stretch-drawing from smaller limiting BD, applying an appropriately small die-profile radius. However, when we wish to form the deepest cup from a specified BD (not necessarily its limit), or do we to select the smallest BD for a specified cup depth (again not necessarily its limit), this rule is not valid. For the medium size of BD, the best choice of combination of 1st and 2nd drawing ratios exists other than the rule mentioned above. It is emphasized that the best profit of stretch-drawing can be obtained in this region from the view point of material conservation.

Deep drawing characteristics of automotive aluminum alloys

Abstract Limiting draw ratios (LDRs) and other axisymmetric deep drawing characteristics of AA5754-O and AA6111-T4 automotive aluminum sheet materials are investigated as a function of die profile radii by experiments and numerical predictions. A procedure for rapid determination of LDR based on a characteristic limit load of the material at fracture is developed and verified. Other deep drawing characteristics such as punch load versus displacement traces, flange draw-in, strain distribution along the cup profile, flange wrinkling, wall ironing and fracture characteristics are experimentally assessed for the two sheet materials as a function of the die profile radius. The results are compared with a recent analytical model by Schedin (Ph.D. Thesis, Royal Institute of Technology, Stockholm, Sweden, 1991). as well as axisymmetric FE models of cup draw, to analyse the sensitivity of various material and test parameters towards the maximum punch load and stresses and strains in various regions of the cup. The deep drawability of AA5754-O, as measured by cup depth at fracture and LDR, is superior to that of AA6111-T4. The differences in the deep drawing behaviour of the two materials can be explained in terms of the competition in work hardening between the material in the flange at the die profile region versus the material at the punch profile region, bendability of the two materials, and fracture characteristics. A decrease in LDR and flange draw-in is observed as a function of the die profile radius. This decrease is attributed to the increased work hardening in the die profile region resulting from additional bending, unbending, and stretching of the material as it enters the die cavity, as well as increased tendency towards fracture for AA6111-T4.

アルミニウム合金薄板のフランジ成形におけるスプリングバックとウェブの反り

The springback of bending at the die shoulder and the warp of web are discussed experimentally for the products formed by shrink, stretch and straight flanging of aluminum alloy sheets. The springback decreases with the decrease in die profile radius and this tendency is remarkable for larger flange height. When the die shoulder radius becomes large, the springback also becomes large. The springback angle correlates with the proof stress of sheet. The web of products warps downward for shrink flanging and upward for stretch flanging, though the web doesn't warp in case of straight flanging. The height of warp changes not monotonically but having a extreme value when the die profile radius decreases and finally the direction of warp turns to the opposite side. This phenomenon is explained by an analysis in which the warp is generated by both elastic recovery of flange and springback of die shoulder bending. The warp is decreased by reduction of flange height and it increases with increasing die shoulder radius in case of shrink flanging, while decreases in case of stretch flanging.The height of warp also correlates with the proof stress of sheet.

A New Apparatus for Estimating Die Profile Friction in Deep Drawing

A new deep-drawing apparatus is developed for examining the compatibility problem between the tool and the workpiece material in metal forming. The die consists of two parts divided coaxially, the radius part rotating at a desired speed and the flange part fixed. The division of the die makes it possible to control the meridian component of the frictional force on the die profile radius by changing the direction of frictional force with its rotation. The characterization of the apparatus is made by drawing tests of copper blanks with a sintered carbide die. The result shows that it is possible to estimate the absolute value of die profile friction in deep drawing by using the apparatus developed.

Research on the tool-workpiece compatibility in deep drawing. 2nd report. Assessment of compatibility from the standpoint of contact ratio and frictional shearing stress at die profile radius.

Experimental equipment used to assess the tool-workpiece compatibility in deep drawing is designed and built. In this construction, a die is divided into two coaxial parts and the one with die profile radius can be rotated so that the meridian component of frictional force reduces with increasing its peripheral velocity. A sophisticated procedure, which clarifies contact ratio and frictional shearing stress in the tool-workpiece interface using experimental results and theoretical relationships, is introduced. By means of experimental drawing of copper and stainless steel sheets with three kinds of die materials (carbide, die steel, and aluminum bronze), the response of the contact ratio and frictional shearing stress to changes in blank holding force, drawing ratio and ironing ratio, is evaluated. Consequently, a deeper understanding of the phenomenon acquired, and it is confirmed that the contact ratio and the frictional shearing stress behave independently to determine the tool-workpiece compatibility.

Research on the tool-workpiece compatibility in deep drawing. 1st report Construction and characterization of a new equipment with rotatable part of die.

An experimental equipment to assess the tool-workpiece compatibility in deep drawing was designed, built, and characterized. In this construction, a die is divided into two coaxial parts and the one with die profile radius can be rotated at a desired speed so that the meridian component of frictional force reduces to zero. In order to test the performance of this equipment, some trial draws of copper sheets were carried out, and it was proved that the all functioned as designed. While the forces carried by the flat part and the curved part of die gave a vivid description of the interaction between tool and workpiece, absolute value of frictional force on the die radius was estimated for the first time by subtracting punch load with rotation from one without rotation.

The effect of mechanical properties of sheet steels on the wrinkling behaviour during deep drawing of conical shells

Wrinkling is a common defect in press-formed parts, particularly in those with sloping walls. Its elimination often presents considerable technological problems. It is known that wrinkling can be prevented by stretching the material in the shell wall. This can be achieved by increasing the blankholder load but this is, of course, limited by the ductility of hte material in the cup wall. Only if the blankholder load is within a narrow range above that necessary to stretch out wrinkles on the one hand, and below that producing wall fracture on the other, will pressing be defect-free. The size of this workable range of blankholder loads determines the criticality of the pressing. The wider the range, the less critical the draw. It has been shown that for a given cup with sloping walls, the workable blankholder-load range cannot be significantly increased by modifying such forming conditions as blank size, die-profile radius and lubrication. A minor improvement can be achieved by increasing punch-profile radius, or by selected lubrication in the punch-nose area. In practice this means that, if the design or material thickness cannot be changed, the wrinkling problem can only be alleviated by using material with better mechanical properties. In the present investigation, the effect of mechanical properties on wall wrinkling in conical cups has been studied using cold-rolled and annealed stabilised steel, interstitial-free steel and high-strength low-alloy steel. The material with a higher n-value, higher r-value and a lower yield stress has generally been considered to be more wrinkle-resistant. The present investigation indicates that the effect of these properties is more complex. It has been found that the n-value influences the plastic-strain distribution during forming. In conical cups a high- n-value material develops higher compressive strains in the cup wall than a low- n-value material when pressed to the same depth, thus leading to earlier wrinkling. A high- r-value material has been found to be more wrinkle-resistant than a low- r-value material. Consequently, when selecting steel sheets for pressed parts where wrinkling is a problem, consideration has to be given to the effect of both r- and n-values. A material with high r m -and low Δr-values should be specified. A high- n value material will not however alleviate the wrinkling problem in those cases where wrinkling is caused by excessive draw-in of material into the die orifice, such as in simple tapered cups, unless other changes in forming conditions, e.g., increased blankholder load, are also made. In complex parts, the effect of n-value on strain distribution should be evaluated with the grid-strain technique.

Cup-drawing from a Flat Blank: Part I. Experimental Investigation

Part I gives an account of an experimental investigation of the forces, work and strains involved, and the conditions for successful drawing of a cylindrical shell from a flat circular blank. It is claimed that the results are sufficiently accurate to provide a basis of reference for theoretical treatments of cup-drawing, as well as an empirical basis of comparison between different drawing conditions. The work was carried out in an experimental crank-press of 50 tons nominal capacity, and was based on a cup diameter of 4 inches. Blank thicknesses from 0·025 to 0·060 inch were used, and although most of the work was carried out on a low-carbon rimming steel, comparative tests were made with aluminium, brass, and copper, of different tempers. The conditions examined included methods of blank-holding, drawing ratio, punch and die profile radii, punch-die clearance, and blank thickness. Although this part has no theoretical pretensions, it includes a descriptive account of stresses and strains in the deep-drawing process, based on plastic theory.