Deep Drawing Tool Design Pdf

Deep Drawing

Deep drawing is one of the most widely used processes in sheet metal forming, in which a sheet metal blank is radially drawn into a forming die by the mechanical action of a punch.

From: Microforming Technology , 2017

Fundamentals of Microforming

Zhengyi Jiang , ... Haibo Xie , in Microforming Technology, 2017

1.3.3 Micro Hydromechanical Deep Drawing

MHDD is a kind of sheet hydroforming method in which a counterpressure is applied to enhance material flow and achieve uniform deformation with the control of thickening and thinning behavior by deformation localization and strain allocation. MHDD is effective in the fabrication of long and complex-shaped micro products with high shape accuracy through enhancing the forming limit and improving the tribological behavior owing to the combination influences of friction holding effect, hydrodynamic lubrication effect and prebulging effect [35,36]. Fig. 1.12 shows a schematic illustration of MHDD processes and movement of forming tool [37]. As indicated in the figure, MHDD processes can be divided into four stages: ① The drawing die (blanking punch) is fixed, whereas the upper die including the drawing punch, the blank holder, the blanking die, and the bush moves downward. In this stage, the clearance between the drawing die and the bush becomes small, as a result, the die cavity is sealed and a counterpressure is generated. ② When the upper die moves further downward, the killer sheet integrated with the blank holder is fixed because of the killer pins, causing the blank holder to be simultaneously fixed. Thus, only the drawing punch, blanking die, and bush move downward during the blanking process. ③ During drawing, the drawing punch moves downward while maintaining a constant gap between the drawing die and the blank holder. By controlling the length of the killer pins, an arbitrary constant gap is maintained. ④ When the stroke reaches the bottom dead point, the upper die starts to move upward and the drawn cup is taken out knockout process.

Fig. 1.13 compares the appearance of cups drawn by MDD and MHDD. It can be seen that wrinkling occurs frequently at the cup edges for all the tested materials in MDD. In contract, wrinkling could be suppressed when an appropriate counterpressure is applied in MHDD. In MHDD, the value of counterpressure should be controlled to be within an optimal range in order to fabricate high-quality micro products. For example, when counterpressure is increased from 4, 15, and 2 MPa to 8, 20, and 4 MPa for phosphor bronze, stainless steel and pure titanium, respectively, the cups will be fractured at the punch shoulder, as indicated in Fig. 1.13. For achieving high formability and fabricating high-quality micro cups without failure, fine-grained metal foils are desirable in MHDD [38].

Tribological behavior in MHDD is an important factor that may have significant effect on the whole forming process and the subsequent micro product quality. In MHDD, the effect of fluid behavior, the ratio of the punch diameter to the minimum thickness, open lubricant pocket (OLP) and closed lubricant pocket (CLP) on the tribological behavior need to be characterized in order to clarify the tribological size effects in MHDD. The work of Sato et al. [39] has indicated that MHDD can induce hydrodynamic lubrication and lubrication in OLP, which can then improve the tribological behavior in microforming process when appropriate fluid pressure is applied. MHDD has the opposite tribological behavior compared with the conventional microforming, i.e., the friction force decreases with the scaling down in MHDD, whereas it increases in the conventional microforming process. The feature size effect has a significant impact on the deformation and fluid behavior and has to be considered in the determination of the forming conditions in MHDD. The forming limit achievable in MHDD is much higher than those obtained by the conventional micro sheet forming techniques, and is effective in the fabrication of quite long micro cups with high accuracy [40]. As a promising microforming method, the research on MHDD in future can be focused on the simplification of the tooling system and optimization of the processing conditions. In order to realize further miniaturization of micro products, punchless forming technology can be developed because there is a limitation of miniaturization of target size when a mechanical punch is applied, even though its size is tiny. Moreover, development of precise positioning and control systems for MHDD is essential in order to achieve a high microforming efficiency.

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Deep drawing of sheet metals using the friction-actuated blank-holding technique

Maziar Ramezani , Zaidi M. Ripin , in Rubber-Pad Forming Processes, 2012

6.1 Introduction

Deep drawing is a common process in industry for manufacturing products from sheet metals. Very complex parts can be achieved using deep drawing. The process is widely used for producing different products such as automotive parts, cans, sinks and housing, and the application areas are getting larger every day.

In the deep drawing process, the sheet metal is radially drawn into the die cavity by the mechanical action of a punch. In this process the workpiece is put onto the die and the blank-holder is then introduced on the top of the workpiece, which is not deformed by the punch. The role of the blank-holder is to control the sliding of the workpiece during the process. After closing the blank-holder, the punch moves down and deforms the workpiece to its final shape. The punch possesses the shape of the product to be drawn.

In general, a metal forming process is called deep drawing if the depth of the drawn part exceeds its diameter. The schematic drawing of the conventional deep drawing process is depicted in Figure 6.1. The stress in the flange region during the deep drawing process is a combination of radial tensile drawing stress and a tangential compressive stress (hoop stress). The main defects of deep drawn parts are wrinkling and/or necking. Wrinkling usually occurs at the flange region by excessive compressive stresses leading to local buckling of the sheet. On the other hand, necking is due to the excessive radial tensile stress. These two defects, i.e. wrinkling and necking define the limits of the deep drawing process.

The blank-holder at the top of the workpiece exerts a compressive force at the upper surface of the blank during the drawing process. By controlling the blank-holder force during the process, it is possible to control the flow of the metal into the die cavity. The blank-holding force is usually applied by the outer ram of a double-action hydraulic press or by a cushion in a single-action press. A proper blank-holder force can prevent wrinkling of the drawn cup and delay necking. A blank-holder force profile which starts from zero at the beginning of drawing and reaches a maximum, and then reduces to zero at the end of the process is desirable for minimizing frictional resistance at the flange area and eliminating wrinkling.

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Practice of Micro Hydromechanical Deep Drawing

Zhengyi Jiang , ... Haibo Xie , in Microforming Technology, 2017

18.2.2.7 Verification and Size Effects Prediction on Lubricated OLPs by Fluid Pressure in MHDD

In MHDD, not only the hydrodynamic lubrication, but also boundary and mixed lubrications exist during the MHDD process. In general, the lubricant cannot be kept in OLPs which connect to the edge of the blank in boundary and mixed lubrications in conventional microforming. On the other hand, if the fluid medium can be filled in the OLPs in MHDD as shown in Fig. 18.16, the lubricant can be kept in the OLPs and the COF can be reduced in microscale. To confirm this phenomenon, an evaluation test for OLPs utilizing liquid was carried out and the size effects of lubricated OLPs by fluid pressure is theoretically investigated.

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Practice of Micro Deep Drawing

Zhengyi Jiang , ... Haibo Xie , in Microforming Technology, 2017

17.1.3 Equipment of Micro Deep Drawing

The micro deep drawing (MDD) experiments have been conducted on a MDD system, as shown in Fig. 17.3. Fig. 17.4 shows (A) the overview/back and (B) the die set attached. Firstly, the blanking die and the blanking holder moved downwards at a speed of 0.1 mm/s and the die stayed still as a blanking punch. A raw blank for the following drawing process was cut at the first half stroke. Subsequently, the punch moved down continuously and contacted with the blank, whereas the die stayed still. Finally, a micro circular cup was drawn by the punch at the end of the second half stroke. Due to this design of the MDD system, the press machine performing one stroke can fulfill the blanking and the MDD processes subsequently. Table 17.3 lists parameters of MDD machine and process.

Table 17.3. Parameters of MDD Machine and Process

Punch Diameter	Die Diameter	Radius of Punch Fillet	Radius of Die Fillet	Drawing Speed	Blander Gap	Friction Condition	Initial Blank Diameter
0.8 mm	0.975 mm	0.3 mm	0.3 mm	0.1 mm/s	0.055 mm	Dry friction	1.6 mm

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Forming of Micro-sheet Metal Components

Yi Qin , ... Jie Zhao , in Micromanufacturing Engineering and Technology (Second Edition), 2015

Deep drawing of sheet metal parts

Deep drawing is a sheet metal forming process used industrially to produce cup-shaped, box-shaped, and other complex-curved hollow-shaped sheet parts. Micro-cups/micro-boxes may be produced with similar process configurations ( Figure 7) for micro-housing applications, such as for the packaging of micro-sensors and micro-actuators. As for conventional deep drawing, the major parameters which influence the process and product quality include the dimensions of the blank, the punch and die dimensions, especially the punch corner radii, the clearance between the punch and the die, as well as the blank-holder geometry, the interfacial conditions, and the holding pressures. Deep drawing is a more complex process than shearing/cutting and bending because it usually combines processes such as bending, unbending, stretching, compression, and shearing, depending on the part geometry to be produced. These processes become more complex when the micro-structure of the sheet metal becomes a dominant factor as the scale decreases [2].

The drawing ratio (DR = diameter of the blank/diameter of the punch) achievable is usually about 2.0 (the limiting drawing ratio (LDR)), depending on the sheet material thickness and micro-structure. With fine-grain sheet metals, controlled friction at the contact surface of the blank-holder with the sheet, the sheet with the die, the punch to sheet metal interfaces, and possibly providing counterpressures under the sheet, the LDR value could be increased. A major challenge faced in micro-deep-drawing is to achieve these DR values within a limited space, which usually limits the tooling arrangement. Control of the interfacial conditions is even more difficult. Ideally, no other media should be used, and enhanced complexity of the tool/material interface conditions should be avoided. For example, a great potential use of various coating on micro-deep-drawing tools has made it possible to have a lubrication-free micro-deep-drawing. This technique is desirable because the friction between the surfaces can be precisely controlled compared to the use of lubrication. This will also avoid the complication during cleaning and handling of the micro-product because of its small size [25–27].

The actual LDR achievable in micro-deep-drawing production also depends on how the blanks and the formed cups will be toggled with the sheet metal strips in the forming/stamping layout design, since the blanks and the finally formed cups are unlikely to be detached from the strip during forming/stamping due to the difficulties associated with handling these small objects, while a reasonable production rate may have to be maintained. This is a special issue to be addressed, compared to the laboratory-based prototype process development.

Common defects in drawn thin sheet parts include the formation of wrinkles (due to buckling), material fracturing (especially at the punch and die corners), and surface scratching (Figure 7). Wrinkles often occur when very thin sheet metals are to be drawn (the material most likely buckles), such as 20-μm thick sheets. Blank holding will be crucial, but it may not be easily arranged due to the limited space for tool components in micro-deep-drawing. Fine-grain materials and materials with superplastic flow characteristics will be helpful in overcoming the fractures which often occur at the punch corner (small radius) and the flange/cup–wall interface. Smaller cups with thin sheet metals may not be achievable, due either to excessive springback for shallow geometries or to the initiation of fractures arising from the use of small punches, similar to what can occur in a piercing process. Again, the avoidance of these features will also depend on how the blanks are to be toggled with the strip.

Redrawing is usually necessary, due to the limitation in the achievement of a feasible reduction value of a cup, in one stroke. Redrawing or reverse redrawing, even introducing an annealing process and ironing, is possible for miniature cups. These steps are unlikely to be introduced in the forming of a micro-cup, due to the difficulties occurring in the handling and alignment of the workpiece, etc. Ideal processes would be those without the need to reposition the workpiece while the tools are being changed.

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Manufacturing methods

Donald B. Richardson , ... (Section 16.5), in Mechanical Engineer's Reference Book (Twelfth Edition), 1994

16.2.8.6 Deep drawing

Deep drawing is normally associated with the manufacture of cups, cans and similar containers. The operation is usually divided into two main groups: first-stage drawing, in which a flat circular metal blank is made into a cup; and a redrawing stage (or stages) in which the cup reaches its final size. The latter operation is necessary because first-stage drawing cannot normally produce a higher degree of deformation than that defined by the ratio of the diameter of the blank and the die throat (drawing ratio) of about 2.2, or a cup height/diameter ratio of about 1.

The sequence of operation is as follows. Initially, the specimen held in position by a blank holder, is partly in contact with the die, partly with either the die or punch, and partly with the punch only. The downward movement of the punch initiates drawing. The outer rim of the blank is then subjected to pure radial drawing (i.e. drawing towards the vertical axis of the system) between the die and blank holder. A part of the material bends and slides over the die and is further stretched between the punch and the die, whereas the material initially in the vicinity of the punch head and actually in contact with it bends and slides over the radiused part of the punch and stretches over the punch head.

The redrawing systems often used are shown in Figure 16.56. Parts (a) and (b) in the figure show direct redrawing systems with and without blank holders, respectively, while a reverse system is shown in (c). In (a), the wall of the cup undergoes double bending and unbending, the severity of which is expected to be high because the respective directions of deformation are at right angles to each other. System (b) shows less severity because of the tapered wall support, although double bending is involved. This system can be used only for relatively low cup diameter/wall thickness ratios which do not require the use of a blank holder. In comparison with the direct methods, system (c), having a generously radiused die profile, tends to reduce the degree of (or with a semicircular profile to eliminate completely) one bending and unbending effect. Whether there is significant advantage to using any system depends on the balance between the reduction in redundancy and practical production considerations.

The definition of 'redundancy' in deep drawing is not easy since redundancy is not necessarily associated with the effects of macroshear. The nature of the processes is such that portions of the blank material undergo some phases of deformation which in themselves induce redundant effects and yet are physically unavoidable if the process is to be completed. It is therefore the degree of severity imposed rather than the avoidance of a certain phase of the operation that matters. In this respect, the process differs significantly from the bulk forming operations discussed previously.

The three main sources of unnecessary strain in and/or distortion of the blank or cup material are flange wrinkling, the already discussed bending and unbending, and, partly, ironing. The latter is used to eliminate the increase in cup wall thickness which can be as much as 30% in the first stage of drawing. If this is followed by a further substantial rise in successive processing stages and is accompanied by wrinkling, an additional drawing operation becomes necessary. As far as redundancy is concerned, ironing is the only operation that brings back the 'standard' features of shearing.

The formability of a material depends on the blank-holder pressure and, consequently, the deep drawing ratio R = D/d may be limited either by wrinkling of the flange, tearing of the cup bottom, or by galling.Figure 16.57 shows diagrammatically the boundaries of these conditions and indicates the presence of a 'safe window' within which deep drawing is likely to be successful.

In determining the drawability, the criterion to be adopted is that relating to the first incidence of any fault.

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Macroscopic ductile fracture phenomena

Kazutake Komori , in Ductile Fracture in Metal Forming, 2020

1.1 Introduction

Deep drawing ( Dieter, 1988), in which a cylindrical cup is produced from a circular sheet, is considered. Deep drawing is performed by placing the circular sheet over a die and pressing the circular sheet into the die using a punch. A blank holder is usually used to press the circular sheet, which is also called a blank, against the die. When the pressure to hold the circular sheet is appropriate, a sound defect-free cylindrical cup is obtained. However, when the pressure to hold the circular sheet is insufficient, the circular sheet buckles and wrinkles. Furthermore, when the pressure to hold the circular sheet is excessive, the circular sheet fractures and is occasionally broken into two parts.

Fig. 1.1 shows the forming limits for the deep drawing of a cylindrical cup. The vertical axis indicates the blank holder pressure, whereas the horizontal axis indicates the drawing ratio, which is defined as the diameter of the circular sheet divided by the punch diameter. The circular sheet buckles and wrinkles in the region below the wrinkling limit curve, that is, in the regions II and IV. The circular sheet fractures and is occasionally broken into two parts in the region above the fracturing limit curve, that is, in the regions III and IV. Hence, a sound defect-free cylindrical cup is obtained only in the region I. The horizontal coordinate of the point at which the wrinkling limit curve intersects the fracturing limit curve, is called the limiting drawing ratio, which is abbreviated to LDR and indicates the maximum drawing ratio in the case that the pressure to hold the circular sheet is optimized.

Buckle and fracture are the two representative shape defects in metal-forming processes. If productivity is required to increase in metal-forming processes, the possibility of the occurrence of either buckle or fracture increases. Because productivity will be required to increase limitlessly in future metal-forming processes, researches on the prevention of the occurrence of either buckle or fracture will be required endlessly in the future. However, the cause of the occurrence of buckle differs from the cause of the occurrence of fracture, as described in the following.

Representative shape defects due to buckle are center buckle and edge buckle in sheet rolling, wrinkle in deep drawing, and buckle in upsetting of a cylinder having large initial height/diameter ratio. Buckle generally occurs under compressive stress and has no relevance to voids. Hence, increasing the mean normal stress in the region at which buckle occurs is generally required to prevent the occurrence of buckle.

Representative shape defects due to fracture are edge crack in strip rolling, central burst and surface crack in drawing, central burst and surface crack in extrusion, crack in deep drawing, and surface crack in upsetting of a cylinder having small initial height/diameter ratio. Fracture generally occurs under tensile stress and has relation to voids. Hence, decreasing the mean normal stress in the region at which fracture occurs is generally required to prevent the occurrence of fracture. Therefore, the method for preventing and predicting the occurrence of buckle differs from the method for preventing and predicting the occurrence of fracture. Hence, buckle in metal-forming processes is not dealt with in this book.

Fracture is divided into following two types: brittle fracture and ductile fracture. Brittle fracture is a fracture in which the material fractures after little plastic deformation, whereas ductile fracture is a fracture in which the material fractures after large plastic deformation. Because this book deals with the fracture in metal-forming processes, ductile fracture is mainly dealt with in this book.

Working is divided into following two types: hot working and cold working. Hot working is a working in which metal forming is performed above the recrystallization temperature of the material, whereas cold working is a working in which metal forming is performed below the recrystallization temperature of the material. Because the workability of the material in hot working is much higher than the workability of the material in cold working, researches on the fracture of the material in hot working are less required than researches on the fracture of the material in cold working. Hence, fracture of the material in cold working is mainly discussed in this book.

In dynamic plastic deformation, an adiabatic shear band (Zener and Hollomon, 1944) occasionally appears. Although strain rate has only a slight effect upon the isothermal stress–strain relationship, an isothermal deformation is subjected to change to an adiabatic deformation with increasing the strain rate. When the material deforms plastically, the majority of the energy dissipated in the material is converted into heat. Hence, when the material is subjected to deform adiabatically, the heat generated in the material is hardly conducted to surrounding material and the temperature increases drastically in the material. Therefore, with increasing the strain, stress increases due to the strain hardening of the material, whereas stress decreases due to the increase of the temperature. If the magnitude of the stress increase is lower than the magnitude of the stress decrease, stress decreases with increasing the strain, that is, the strain softening of the material occurs and the region where the material deforms plastically is localized.

When the localization of the adiabatic deformation occurs in steels, a white band of martensite appears, which yields when the high-temperature face-centered cubic austenite is rapidly quenched. Hence, the adiabatic shear band is not a slip line, because in the slip-line field theory (Johnson et al., 1982), the material is assumed to be rigid, perfectly plastic. The adiabatic shear band in metal-forming processes is described in a few books (Bai and Dodd, 1992; Dodd and Bai, 1987). Hence, the adiabatic shear band in metal-forming processes is not dealt with in this book.

In Chapter 1, Macroscopic ductile fracture phenomena, macroscopic ductile fracture phenomena are observed experimentally using an optical microscope and are mainly described to utilize observed phenomena in Chapter 2, Macroscopic ductile fracture criteria.

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Advanced metal-forming technologies for automotive applications

N.J. Den Uijl , L.J. Carless , in Advanced Materials in Automotive Engineering, 2012

Bending

In deep drawing the stresses and strains are the same all over the thickness of the material. A gradient will only occur where the material is drawn over a die radius. This is a secondary effect. In bending operations it is the aim of the operation. Die bending refers to a bend where the sheet is in contact with both the punch and the die to precisely define the shape of the work piece. V-bending, or free air bending, is used to set the material in an edge. The sheet is supported on two sides whilst a punch deforms the material in the middle. The final shape is influenced by the material properties as well as the die shape, as springback will occur. Bending usually requires simpler tooling than deep drawing and stretching.

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Simulation of Micro Deep Drawing

Zhengyi Jiang , ... Haibo Xie , in Microforming Technology, 2017

10.2.5 Springback Models

After MDD simulation, only the drawn cup was employed for a following springback simulation. The material model, the elemental information, and the parts arrangements were the same as that in the deep drawing models while the solver was changed from explicit to implicit solver in LS-DYNA. The thickness and strain–stress information at the end of the drawing simulation was also included in this springback model. As seven integration points were employed, the thickness and strain–stress information were accurate and adequate for springback simulation. Furthermore, two points on the symmetrical edges were fixed according to the symmetrical boundary conditions to limit the rigid movement of the cup. Consequently, the residual stress can be released gradually in a few calculation steps. Dynamic step adjustment and artificial stability were added to improve the calculation. As Voronoi models were still used in the springback simulation, size effects on springback behavior can be presented. Furthermore, effects of surface roughness on the springback could be observed as well.

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Formability of auto components

E.H. Atzema , in Automotive Steels, 2017

3.6.3 Deep drawing

In deep drawing, essentially the same tools are used but now the flange is allowed to flow in, or draw-in, and is transformed to a cylindrical wall. This way much deeper products can be made. This is evident from Fig. 3.27 where three experimental cups can be seen, ranging from low blank holder force (left, drawn) to high blank holder force (right, stretched).

The process does have a lower limit on blank holder force though, because otherwise wrinkles will be formed, some examples of which are shown in Fig. 3.28. The formation of wrinkles is directly related to blank holder force. The final fracture is caused by the restraining force generated by blank holder through friction with the sheet. This implies that low friction is beneficial for drawability.

As most of the deformation is in the flange and this is useful deformation, i.e., the stress should be as low as possible, high hardening is not actually beneficial for stamping. Some hardening is needed, as early in the process some stretching occurs before the sheets starts "sliding" into the die opening. But high hardening (in the simplest view: high n-values) will be bad for deep drawability. The influence of hardening is not as strong as the yield locus so one should look for high r-value, or better still: good DDR first and limited hardening second.

In a typical stamping the complex geometry causes some parts to be stretched and other parts to be drawn. In areas that are (in mathematical terms) not developable, stretching will have to occur to enable the desired shape. Other areas may shift more to drawing depending on blank holder force. In Fig. 3.29 the yellow and magenta points indicate stretched parts of the geometry. The blue parts are deformed near plane strain mode. And finally, the gray points are the remainder but mainly represent the flange, which shows typical drawing behavior.

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