• Journal of the Korean Society for Precision Engineering
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• v.32 no.11
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• pp.945-952
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• 2015

In drawing sheet metal, the blank holding force is applied to prevent wrinkling of the product and to add a tensile stress to the material for the plastic deformation. Applying an inappropriate blank holding force can cause wrinkling or fracture. Therefore, it is important to determine the appropriate blank holding force. Recent developments of the servo cushion open up the possibility to reduce the possibility of fracture and wrinkling by controlling the blank holding force along the stroke. In this study, a method is presented to find the optimal variable blank holding force curve, which uses statistical analysis with consideration of the nonlinear deformation path. The optimal blank holding force curve was numerically and experimentally applied to door inner parts. Consequently, it was shown that the application of the variable blank holding force curve to door inner parts could effectively reduce the possibility of fracture and wrinkling.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.10a
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• pp.93-97
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• 1997

Since the modified membrane element has the same external appearance as the ordinary membrane element, it is not able to apply the thickness variation of sheet metal in the blank holder to the contact treatment and the equally distributed blank holding force should be inevitably imposed on sheet metal along the periphery regardless of the contact status. But sheet metal does not contact with the blank holder at the periphery, nor the blank holding force is distributed uniformly along the boundary. To impose the blank holding force properly, the scheme is improved so that the blank holding force at each node imposed on sheet metal is dependent on the calculated thickness derivation and a state of equilibrium with the total blank holding force. The validity of the improved scheme is demonstrated with the simulation of cylindrical and rectangular cup deep drawing.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.05a
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• pp.394-396
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• 2007

In this study, in order to see effect of the blank holding force on the friction behavior in the sheet metal forming, a sheet metal friction tester is designed and manufactured, which can measure friction forces in various forming conditions, such are lubrication, die roughness, drawing speed, radius of die corner, blank holding force, etc., and performed the friction test in which friction coefficients in various blank holding forces and pulling speeds are calculated using Coulomb's friction law. The friction test reveals that friction coefficient decreases maximum 30% as the blank holding force and the drawing speed are increased to 2.5kN and 1500mm/min, respectively.

• Transactions of Materials Processing
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• v.16 no.5 s.95
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• pp.381-385
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• 2007

In order to examine the effect of the blank holding force on the friction behavior in the sheet metal forming, a sheet metal friction tester is designed and manufactured, which can measure friction forces in various forming conditions such as lubrication, die roughness, drawing speed, radius of die corner, blank holding force, etc., and the friction tests are performed, in which friction coefficients in various blank holding forces and pulling speeds are calculated using Coulomb's friction law. The friction test reveals that friction coefficient decreases as the blank holding force, the drawing speed and lubricant viscosity increase together or individually.

• Transactions of Materials Processing
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• v.8 no.4
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• pp.347-355
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• 1999

The paper is concerned with an improved scheme for application of the blank holding force in order to take account of the thickness distribution in the sheet material of the flange region. The scheme incorporates with a modified membrane finite element method for planar anisotropic materials. The new scheme proposed two coefficients α and βto calculate the compressive stress in the sheet metal due to the blank holding force, which should be determined properly for accurate analysis. The effect of αand βon the blank holding force distribution and the deformed shape is investigated with simulation of rectangular cup deep drawing processes by changing parameter values.

• Transactions of Materials Processing
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• v.14 no.1 s.73
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• pp.21-28
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• 2005

This paper is concerned with the quantitative effect of design parameters on a stamped part of the auto-body. The considered parameters in this paper are the blank holding force, the draw-bead force, the blank size which greatly affect the metal flow during stamping. The indicators of formability selected in this paper are failures such as tearing, wrinkling and the amount of springback. The stamping process of the front side inner member is simulated using the finite element analysis changing the design parameters. The numerical results demonstrate that the blank holding force cannot control the local metal flow during forming although it controls the overall metal flow. The modification of the initial blank size considering the punch opening line ensures the local wrinkling and reduces the amount of springback after forming. The restraining force of draw-bead controls the metal flow in the local area and reduces the amount of excess metal. It is noted that the parametric study of design parameters such as blank holding force, the blank size and the draw-bead are very important in the process design of the complicated member.

• Transactions of Materials Processing
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• v.21 no.6
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• pp.348-353
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• 2012

Micro-drawn parts have received wider acceptance as products become smaller and more precise. The subject of this study was the deformation characteristics of ultra thin sheet metal in micro drawing of a rectangular shaped part. The influence of drawing speed and blank holding force on the product quality was investigated in micro-drawing of ultra thin sheet of beryllium copper (C1720) alloy. The specimen had a diameter of 4.8 mm and a thickness of $50{\mu}m$. Experiments were carried out in which, different blank holding force and drawing speed were considered. The product quality was evaluated by measuring the thickness and hardness along two specified directions, namely, the side and diagonal directions. The distribution of the thickness strain showed severe thinning especially around the punch radius in both directions. In the diagonal direction, thickening occurred in the flange area due to the axi-symmetric drawing mode. The increase of blank holding force and/or drawing speed was found to cause severe thinning around the punch radius. The blank holding force had a greater effect on thinning of the product than the drawing speed.

• Design & Manufacturing
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• v.10 no.1
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• pp.31-35
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• 2016

In sheet metal forming process, drawing is typical process. And the key factor of drawing is blank holding force (BHF) A low BHF can cause wrinkling, whereas a high BHF can cause fracture during a deep drawing process. Thus, formability can be influenced by application appropriate BHF. In this study, a variable blank holding force (VBHF) is applied to extend the forming limit by avoiding both wrinkling and fracture. To determine VBHF in drawing process, numerical simulations and statistical analysis are carried out using commercial FEM software.

• Transactions of Materials Processing
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• v.3 no.3
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• pp.335-346
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• 1994

The effect of sheet steel properties and lubrication on the optimal range of blank holding force (BHF) was investigated by means of the model die stamping of various sheet steels. The optimal range of blank holding force was expressed as the range between the lower BHF at flange wrinkling and the upper BHF at local necking. It showed that mechanical properties, thickness of sheet steel and lubrication condition were important factors affecting the optimal range of BHF in sheet steels. Especially, lubrication played an important role in the case of coasted sheet steels.

• Transactions of Materials Processing
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• v.14 no.7 s.79
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• pp.628-634
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• 2005

The drawability of AZ31B magnesium sheet is estimated at various temperatures (200, 250, 300, 350, $400^{\circ}C$), forming speeds (20, 50, 100mm/min), thicknesses (0.8, 1.4mm) and blank holding forces (2.0, 2.8, 3.4kN). The deep drawing process (DDP) of circular cup is used in forming experiments. The results of deep drawing experiments show that the drawability is well at the range from 250 to $300^{\circ}C$, 50mm/min forming speed and 2.0kN blank holding force. The 0.8mm magnesium sheets were deformed better than 1.4 mm. Blank holding force was controlled in order to improve drawability and prevent the change of cup thickness. When blank holding force was controlled, tearing and thickness change were decreased and limit drawing ratio was improved from 2.1 to 3.0.