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| Reference Notes on Die Design | Resource Information for Tool and Die | Tutorials and Technical Articles on Design Design Calculations | On-line Guide Book for Precision Metal Stamping | |
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| Educational Resource on Die Design and Metal Stamping | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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This section of the web site will contain reference notes, white papers
and technical articles specific to die design and metal stamping die maintenance.
Tool Design
Blanking Die Design
Bending and Forming Die Design
Draw Forming and Draw Die Design
Die Design for Performance
Tooling Enhancement for PerformanceSheet Metal Raw Material Specifications
Click on the pictures below for enlarged views. Bending Force CalculationV-Type and U-Type Bending without pressure pads below:  V-Type Bending with V-shaped pressure pad below (coining):  U-Type Bending with pressure pad below:  L-Type Bending or 90 degree bending:  Tutorial on Bending Force Calculation Calculate the bending force required for the above forming: First, calculate C1. From the L/C1 table in the reference notes above, as L=8t, then C1=1.33. Accordingly, applying the numbers into the equation: P1=C1* (B*t2*σB)/L = 1.33*(100*12*30)/8= 498.75 ≒ 500 kg Therefore, the required bending force is about 500 kgf. >> Back to Articles Menu Key Factors in Draw Forming
Blank Size Calculation for Draw Forming or Draw StampingMost textbooks teach that there are 2 ways of determining the blank size for a draw stamped part. They are namely, algebraic method through centerline of stock using either the surface area or weight of the part, and the graphical method of calculating blank size. The example below shows how to find the blank size for a deep drawn can using the surface area algebraic method:  Most draw forming design and simulation softwares come with modules to calculate the blank based on the stamped part data automatically. If further examples of different drawn components and the equations for calculating the blank sizes are useful as tutorial questions and answers purpose, email us at sales@suwaprecision.com. These equations have been extracted from various sources. >> Back to Articles Menu Metal Reduction RatesDraw forming a metal part is basically a series of reduction steps from the blank to the first draw, to the second draw, and so on. The reduction rate is calculated as follows: Ri=100(1-di/di-1) Ri: i-th reduction in percentage di: Diameter of the part after the i-th draw reduction d0: Diameter of the blank before the first draw reduction As the actual draw forming of the same part would differ based on the different quality of the raw materials, tooling coatings and lubricants, most die design experts agree that the metal reduction rates available today merely serve as a guide based on past experience. During the assembly and troubleshooting of the draw die, the toolmaker will still need to make finer adjustments. Blanks with equal surface dimensions but different metal thickness have different outcomes when subject to the same draw reduction rates. Thinner metal is more difficult to draw consistently when compared to thicker metal. It is recommended that metal thickness to blank diameter ratio (t/d) should be above 0.25. Recommended maximum rates of reduction for round deep drawn parts are as follows:
The general maximum cupping reduction rates for different metals are as follows: Aluminum alloys => 45% Copper => 45% Brass => 50% Bronze, Tin => 50% Low Carbon Steel => 45% Austenitic Stainless Steel => 50% Zinc => 40% >> Back to Articles Menu Component Design and Function# Design of Blank Holder and Blank Holding ForceThe design of the blank holder is important as it affects the rate of flow of the sheet metal during draw forming. The examples below shows the effect of insufficient blank holder force during the draw stamping of a can, causing either wrinkling of the flange or the side walls.  
The punch and die clearances are arranged so that the metal is lightly drawn between them. This removes any creases which tend to form during the drawing operation. However, if we were to draw cup-shaped components with larger depth to diameter ratio from thinner metal, then puckering or wrinkling of the flange as shown above is likely to occur round the edge of the blank rim outside the die. This puckering is caused by the local thickening of material round the edge setting off hoop stress forces in the material. This puckering may be sufficient to prevent the metal flowing smoothly through the die and the punch may tear the bottom out of the component. Even if the tensile strength of the metal allowed it to be forced through the die, it would be impossible to 'iron out' all the pucker marks. The solution to this problem is to add a blank-holder to the deep draw tools. The blank-holder basically presses the blank rim material outside the die, and provides a tensile force opposing the compressive hoop stress within the blank rim. This allows the metal under the blank-holder to thicken uniformly around its annular rim and progressively between the die mouth and the outside of the blank. When using double action presses that have mechanically operated blank holders, the setting of the blank-holder force is usually determined empirically. This is done by drawing the shell progressively deeper using blanks of the same diameter while progressively lowering the blank holder until the surface of the drawn shell is smooth and free from wrinkles. The pressure of the blank holder on the blank increase during the drawing operation as the edge thickness of the blank increases under the effect of the hoop compression forces set up. In cases when it is not possible to exert sufficient force on the blank-holder to prevent wrinkling, or there may be problems with lubrication of the blank itself, the tool may be designed with an entry bead to the die. 
The minimum blank holding force for the various stamping materials are listed below for your reference: Mild Steel t<0.5mm ==> 0.25~0.30 kg/mm2 Mild Steel t>0.5mm ==> 0.20~0.25 kg/mm2 Aluminum ==> 0.03~0.07 kg/mm2 Copper ==> 0.08~0.14 kg/mm2 Brass ==> 0.11~0.21 kg/mm2 Stainless Steel (18-8) => 0.40~0.45 kg/mm2 Bronze ==> 0.20~0.25 kg/mm2 Aluminum Alloy ==> 0.14~0.70 kg/mm2 >> Back to Articles Menu Warm Metal Forming of Thin Walled Magnesium Components
Magnesium is the lightest structural material offering very good damping characteristics, weldability and excellent shielding against electro-magnetic interferance, and is unlimited in
supply. It has been an excellent material for making portable electronic and telecommunication
devices, and automotive and aerospace equipment such as MD player casings, chassis for cell phones,
video cameras and notebook computers, automotive gear housings, car wheels and engine blocks.
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| Suwa Precision - competitive supplier of precision metal stamping, tool and die, miniature precision metal components fabrication, miniature precision balls, printed circuit boards and custom semiconductor chips. |
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