Metal Stamping Dies: Part One

概要:

Metal stamping is the practice of cutting and forming metal sheet into a required contour with the help of tool known as a stamping tool.
Sheet metal stamping is the most common method of producing metal parts in the automotive industry because of its high production rate and low cost. In basic sheet metal stamping, a flat metal sheet is pressed to the desired shape between a die and a punch.

Metal stamping is the practice of cutting and forming metal sheet into a required contour with the help of tool known as a stamping tool. Sheet metal components are used universally, from the regular clips to complex computer hard drive components, all are manufactured by a precision sheet metal stamping process. Stamping die design is the preliminary phase in stamping tool and die making and is carried out as soon as the component design is finished. The stamping die drawing stage is extremely critical as a good quality stamping die blueprint can generate accurate stamped components which can run for an extended time with less maintenance.

Stamping tool design calls for selecting the required metal stamping operations, basic strip layout, manufacturing processes, type of stamping presses to be used and so on. It is necessary for a tool designer to have thorough knowledge of these elements to construct a fine die design. Computer aided design techniques have progressively developed in the last decade to assist die designers.

There are various procedures involved in metal stamping tooling designs which are necessary for accurate tool production. The very first stage in die design is the process of evaluating the metallic part to be made, it’s properties, dimension and complexity of the contour. Next the designer will proceed with the strip layout design and then he will determine the cutting force and the die-set to be used and then begins making the assembly sketch. Once the assembly sketch is completed, part details, drawing of die parts, and the final step of preparation of the bill of materials can be undertaken.

2.1 Sheet metal stamping

Sheet metal stamping is the most common method of producing metal parts in the automotive industry because of its high production rate and low cost. In basic sheet metal stamping, a flat metal sheet is pressed to the desired shape between a die and a punch. The die is used to define the outside shape of the part. And the punch is applied to define the inside shape of the part. As well as the aforementioned parts, there is usually a third component of the tool called the blank holder, which is used to hold the blank against the die top and to control the blank during stamping.

Sheet metal stamping is essentially a position control process. During the stamping process, the punch moves to the predetermined position and stops. Then the part is positioned ready for shaping. In many practical operations, the blank holder would clamp the metal sheet flange before the punch moves. Since the punch movement can be controlled according its position, the press and the controls that are required for this forming operation can be quite simple. The most commonly used press machines are mechanical, which are relatively simple and inexpensive. There are also hydraulic presses, which are relatively expensive; however these can provide independent control of speed and position of the tooling during the forming process.



Figure 1: Metal stamping products

How Does Metal Stamping Work?

Metal Stamping includes many different types of sheet-metal forming manufacturing processes. Key parts of the process include punching (using a machine or stamping press), blanking, coining, embossing, and bending. Stamping is primarily carried out on sheet metal, but can also be used on other materials, such as aluminum, steel, plastic and foil.

Bending

Process that results in a V, U, or channel shape in any bendable material (most often sheet metal) without fracturing. An example would be the bottom of a drinks can.

Blanking

A shearing operation that uses a punch to create a blank from the sheet metal or a plate.

Progressive Die

Metal Stamping die that pushes a sheet of metal through a series of operations until a finished part is made. An example would be the lid of a soda can (separate operations for the lid and pull tab).

Compound Die

Metal Stamping Die that performs more than one operation in a single press.

Deep Draw

Process where a drawing press is used to form sheet metal through the mechanical action of a punch. An example would be a kitchen sink.

Tapping

Process of cutting the threads in a hole. An example of this would be a nut, where a bolt screws into.

Coining

A precision metal stamping form used most often where high relief or very fine features are needed. An example would be money (quarter, nickel, dime), badges, and medals.

Embossing

Metalworking process where soft malleable metals are shaped and designed by hammering on the reverse side.

Blanking

Metal stamping operation by which the sheet metal is punched to get the required outer profile of the sheet metal component. During the blanking process the blanking punch penetrates into the sheet metal and forces the material into the blanking die. The portion of the sheet Metal which comes out through the blanking die opening is the component with the required profile. Hence it is important that the dimension of the blanking die profile is equal to the dimension of the component profile. In blanking tools, the cutting clearance is given on the blanking punch.

Types of Blanking Dies

Blanking dies can be a single stage press tool where the component is produced in each stroke of the blanking press. In single stage blanking tools, there could be many stamping operations done prior to the blanking or those operations could also be done after blanking depending upon the complexity of the blanking profile of the part, sheet thickness, or dimensional importance of different stamping operations required to produce the final component. In progressive blanking press tools, stamping operations like piercing, bending and forming are done in various stages prior to the blanking stage. In the blanking stage the final component is punched through the blanking die.

Blanking Die Design

See the below drawing for a simple blanking die design. The portion of the sheet metal which is punched through the die is the blank or the component.



Figure 2: Schematic view of Blanking Die Process

Note The blanking die is designed with an angular relief after a straight sided area. This is to ensure that blanks which are punched through the blanking die do not get stacked up inside the die. Buildup of blanks can cause damage to the blanking tool. As a general rule the straight sided depth is 3 mm for sheet thickness lesser than 3mm and for sheet metals above 3mm thickness, the area should be equal to one sheet thickness. The amount of angular relief is normally from 0° 30' to 1° per side.

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