Process Spotlight: Stamping
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Stamping is a process that uses ‘dies’ to shape and cut sheet metal parts. This method allows the material to be punctured, shaped and cut along an automatic assembly line by numerous mechanical presses, and is ideal for high volumes of sheet metal parts.
What Are Dies?
As mentioned, stamping uses something known as a ‘die’. This is a generic term that describes the tooling used in this process and can be thought of a little like a stencil, or a cookie cutter attached to a press. Dies use designs that are normally developed through CAD software, allowing for a high level of precision. Those designs will then be recreated as stamping dies by professional engineers known as ‘diemakers’.
From there, the dies are then mounted into presses, and can be used to print the shapes needed. The press provides the necessary force to close the stamping dies onto the metal and cut/shape it as required, while the parts are passed from one point to the next.
Types of Dies
Compound dies are press cools that are only used for cutting operations. These are most often used for blanking and hole punching. Combination dies meanwhile, are press tools used for both cutting and shaping. Shaping, or forming, is a term used to describe a range of processes including: drawing, bending, flanging and hemming. In drawing for instance, a piece is forced deeply into the cavity of a die in order to shape it to the contours of the punch face and sides.
Normally there will be multiple stations with different dies, where each station performs a single step in the shaping and cutting of the required parts. Normally, each stroke of the press is able to perform multiple station operations at once. Alternatively, a piece can be moved around underneath a single, larger die in order to perform multiple operations sequentially.
Stamping processes can further be divided into progressive die processes and compound die processes. Progressive die operations parts are made from a continuous coil stock, and will remain connected while they are passed from one station to the next. In other words, the parts begin life as one long strip of metal, called a carrier strip, with the operations performed at various points. At the end, the piece will be broken off to create the finished part – like tickets attached to a ticket reel.
Transfer die operations use parts that are blanked from the start or at the very beginning of the operation. These pieces are then moved through the conveyor by mechanical transfer devices that can grip and move the pieces around a single press and a single die to complete all the necessary operations.
Pieces will finally need to be inspected and assessed, and this may result in further manual changes to meet the highest standards possible.
Materials and Limitations
Normally, printing will be used for sheet metal parts around .020’’ to .080’’. However, it can also be useful for much thinner pieces (like tin foil) and thicker pieces (like plate stock).
The materials used can be described in terms of ‘ductility’ and ‘formability’. Formability is the ‘primary attribute’ of the sheet metal and its ability to be bent, stretched or drawn as necessary. This is metallurgically known as ductility; the ability of a metal to deform and elongate without fracturing or becoming otherwise damaged. This is important because the formability of the metal will influence the design of the die, the press speed and the lubrication.
Dies must be lubricated in order to allow for successful sheet metal forming. This is because the amount of force required to form and puncture metal creates a lot of friction which can cause issues otherwise. Lubrication helps to minimize the contact between the tooling and the piece, and gives the dies a longer lifespan as well as improving the quality of the end product.
Lubricants used include light mineral oils and drawing compounds. They can be oil based, water soluble, or synthetic, and will be applied either manually with a brush or using sprays or machine rollers.
Is Stamping Right for You?
Whether or not stamping is right for you will largely depend on the nature of your product. This is a process that is suitable for sheet metals only, and that is particularly well suited to large production runs. Stamping dies are less expensive and last longer when compared with casting dies (which also need frequent replacing). Stamping is also much quicker than casting and allows for the use of stronger materials.
On the other hand, die casting potentially allows for more complex shapes with thinner walls and more detail. If you wanted to create something more intricate, then you might prefer die casting. Or maybe your product would be better served by another process altogether, or even a plastic construction. Ultimately, it’s always worth examining the different options available to you in order to make the most cost effective decision that will also lead to the best end product.
Stamping is a very efficient, affordable and quick way to create large runs of sheet metal parts. If that’s what your business needs, then certainly it’s worth examining further. Or perhaps you’re already using stamping or another similar process? Do let us know in the comments below if so, we’d love to hear about your experiences, and why you chose the processes you did. And for more product spotlights and other tips and advice for hardware startups, be sure to subscribe!