CNC Punching Of Sheet Metal Components

Computer numerically controlled (CNC) punching is a manufacturing process that is carried out by CNC punch presses. We currently run a multi-tool turret machine. The turret is capable of holding 15 different tools at once drastically reducing tool time change. The basic principle of a CNC punching machine is to move a sheet of metal in an x and y direction to accurately position the sheet under the machine’s punching ram whilst the turret simultaneously positions the correct tool ready to punch a hole. The limitations of our CNC punch press is 0.5mm to 6.0mm thick in a range of sheet materials including mild steel, zintec, galvanised steel, stainless steel and aluminium. The size of the hole is also important, the bigger the hole to be punched the greater the tonnage required. The size of sheet also plays a factor for suitability. If the sheet is longer than the machines working range the machine will automatically reposition the sheet and continue to process the punching sequence. If however the sheet of material is deeper than the working range of the machine, the work piece may require turning round manually by the operator.

The punched hole can be as simple as a circle or rectangle through to custom special shapes to suit a client’s specific design. Using the combination of single hits and overlapping tool geometries, complex sheet metal component shapes can be produced.

Our machine is also capable of producing 3D forms such as louvers, dimples, countersinks, screw threads, and electrical knockouts using specialist tooling. Such forms are often required to produce sheet metal enclosures. Some modern machines may have the ability to tap threads, fold small tabs, punch sheared edges thus eliminating further operations making the machine very productive within the component cycle time. The instruction to drive the machine to create the desired component geometry is known as the CNC program.

CNC Programming Of The Punching Machine

SAMS Fabrications utilises the latest Radan CNC sheet metal punch programming software. This part of the process is also known as computer aided manufacturing (CAM).

Sheet metal components can be produced in 2D format using this software or imported from DXF or DWG files. These drawings and information is converted to produce flat sheet metal components. The tooling geometry and punch routine is then applied to create the specified design.

The software can automatically generate a parts nest achieving the maximum yield from a given size of a sheet of metal. By nesting parts economically and reducing wastage ensures parts are produced as cost effective as possible

When designing components that will be CNC punched, it may be useful to take a look at the following design tips to assist you with your sheet metal parts.

Design Tips For CNC Punching Of Sheet Metal

Hole diameters should ideally be no smaller than the material thickness of sheet metal being punched.

When a hole is punched in piece of metal the diameter of the hole on the top side of the material is pierced by the punch and will be the same diameter as the punch tool diameter. The diameter of the hole on the underneath of the material is produced by the die which the punch passes through. The hole therefore is slightly larger than the punch due to a die clearance thus producing a partly tapered hole. The die clearance required to punch a hole depends on the type and the thickness of the metal sheet to be punched. SAMS stock a wide range of die clearances to cover sheet metal materials from 0.9mm thick up to 6.0mm thick. When a hole is punched the taper can vary due to the material type, tensile strength and thickness. When a hole is punched approximately the first 25% to 33% of the sheet material is sheared by the punch and is a parallel hole. The next 75% to 67% then “breaks” and tapers out to the die clearance diameter. For example a 5mm diameter punch with a die of 0.3mm clearance will produce a hole that is 5mm diameter on the punch side of the sheet and 5.3mm diameter on the underside of the metal sheet. Should your metal fabrication design require a constant diameter through the sheet metal then drilling and reaming operations are available but it is a much slower and a far more costly operation.

Protruding up forms produced in the parent sheet metal can be supplied unthreaded ready for self-tapping screws which can save money on the insertion of threaded inserts and taping holes. This is specifically useful if the component is to be painted saving masking up the threads. These features also enable a self-tapping screw to cut into more material than just the sheet metal gauge reducing the risk of stripping the thread if the screw is over tightened.

Cluster tools are available to reduce CNC punching time for multiple holes and save money on repeated batches of sheet metal work. The initial tool setup investment is greater but can save in the long run. The tool can have many individual punches enabling a number of holes to be punched in one hit. These CNC tools can be particularly effective when there are perforated areas of a component such as air ventilation areas, speaker grilles, LED panels or light fittings.

Stamping and engraving tools can be used to identify parts with part names, drawing numbers or item codes. Such identification is often required when manufacturing sheet metal fabrications. CNC tool stamping is mainly used on larger batch productions with repeat requirements. For smaller batches and for a range of different sheet metal parts then CNC engraving is the most efficient solution. A vibrating stylus is used that vibrates thousands of times per minute on the surface of the material. An additional advantage of using a CNC punch press to do this engraving is any changes to the information provided by the customer for their identification can simply be reprogrammed without any cost to re-tool.

Wheel tooling can be used to produce a shallow raised ridge in a sheet metal part to increase rigidity enabling the part to be produced from a thinner material saving costs.

Flat packing parts. Save on storage space and the need secondary manufacturing operations. A series of slots in a CNC punched sheet metal component can weaken the part at a given point so it’s easier to bend by hand in assembly. The same principle can be used for earth tags enabling them to be bent to the required angle on site install.

Tags can be used to aid the assembly of light weight small components instead of welds or screw fixings. These features are often used on reflectors for light fittings. Where strength is not of great importance in the finished item and the parent sheet metal can be easily bent over with your fingers.

We have a wide selection of case studies within our gallery which illustrate these design ideas and enable you to fully benefit from the versatility of CNC punching, please take a look at our gallery to learn more.

For more information on all our stock CNC punching tools please take a look in our tooling library.

Our Clients