Precision Sheet Metal Contract Manufacturing Part I:
Sheet metal is metal formed by an industrial process into thin, flat pieces. Sheet metal can be cut in various ways, from hand tools to very large powered shears. With the advances in technology, sheet metal cutting has turned to computers for precise cutting.
Punching and stamping are two of the most common machining processes in a typical modern precision sheet metal contract manufacturing facility. Punching is selected to achieve a specific shape on a specific area of a certain workpiece, while stamping is used to machine an entire workpiece.
This blog addresses the punching process. Stamping and progressive dies will be discussed in the next blog.
Punching & CNC Turret Punch Press
Punching is performed by placing the sheet metal between a punch and a die mounted in a press. Typically, presses are electronically linked (via a computer controller) to an automatic feeder which feeds metal raw material through the die. The punches pass through the sheet metal while the dies, located on the other side of the metal piece, working as support and helping punches to put more force ensuring non-breaking of metal.
The press pushes the punch against and into the die with enough force to cut a hole in the workpiece. A simple shape (e.g. a square, circle, or hexagon) is then cut (punched out) directly from the sheet metal.
A typical computer-numeric-controlled (CNC) turret punch is an automated punching press that features a heavy-duty (30-ton or more) turret punch press equipped with a high capacity tool rack and an automatic tool changer. The CNC punch press is equipped with fully rotational punching heads and with various tools housed in a “turret” which permits most tooling to be rotated to the punching position. Some high-end presses are able to house a few hundred tools and dies — providing the optimal punching solution.
CNC turret provides precision and speed. For example, a typical component (such as the side of a computer case) can be cut to high precision from a blank sheet in under15 seconds by a CNC press. This manufacturing process provides you with a wide range of hole and forming possibilities with minimal lead time and usually with little tooling cost.
Standardized Punching Tools & Dies and Cost Advantage
The tools and dies for the punch presses for sheet metal works can be standardized punches and are usually readily available from various tool manufacturers. The standard punches can produce a standard shape (round or square holes and so on) or a special shape at each stroke of the punching machine. The standard punches clearly have lower costs than the special press tools.
A CNC punch, although efficient for cutting repetitive shapes, is not very effective in mass production with variable cutting and forming needs.
In Part 2 of the article, we will look at stamping operations and discuss how a modern-day precision sheet metal manufacturer implements progressive dies to solve complicated machining tasks on sheet metal products.