Sheet Metal Fabrication
The technology behind sheet metal fabrication has grown by leaps and bounds over the last couple of decades. The process is the commonly used to manufacture enclosures, covers, brackets, shims and a myriad of other components. Sheet metal fabrication can be thought of as a combination of two different disciplines, cutting and forming.
In most shops the CNC turret press is the workhorse of the cutting department. Modular tools are mounted in a turret located above the work surface. The tools all perform a different function, some cut a straight line, and others punch radii, while some punch holes of a certain size. For some smaller stampings, special punches can be built to blank the part in one stroke. This approach can be very competitive when compared with short run stamping. The turret press uses a nibbling action to blank the desired configuration. Parts are laid out in such a manner as to make optimum use of the sheet of material. For parts with very complex curves or are too thick to use a turret press, laser cutting is used. Water jet cutting is used for parts where edge condition is a concern.
Bending and forming is usually handled by press brakes. A modern sheet metal shop will have numerous stock form dies available, and special tooling can be easily fabricated. Programmable backstops allow several operations to be performed on a single set up. Press brakes are available that can bend material up to fifteen feet wide. Most shops have several press brakes in order to form parts in the most efficient manner possible.
Turret press cut parts usually have nibble marks on the edges, making them poor datum points. It is better to dimension off of hole centers.
Feature tolerance in the flat can range between +/- .005” to +/- .015” depending upon part configuration and distance between features. Repeatability generally is within .002”
Holes formed during laser cutting generally are larger at the top than the bottom. The heat involved with laser cutting can also harden the edges of parts.
Hole diameters should be at least 20% greater than material thickness. In order to avoid warping, holes should be located at least twice the material thickness from edge to edge.
Minimum bend radii should be at least one material thickness. Holes located close to bends should be at least 3 material thicknesses plus the bend radius or else they may deform.
The techniques as described above are generally competitive from just a few pieces to thousands of parts. Blanking and forming operations can be automated further as volume dictates.
Common material thickness amongst several components provide the opportunity to nest parts more efficiently. For example if an enclosure has a large internal void, chances are several smaller parts could be cut from material which would ordinarily be scrapped.
Investigate some of the base metal clinching technologies which are available as opposed to spot welding when joining pieces together.
How We Can Help
Should this part be laser cut or formed on a turret press? When does water jet cutting make sense? What type of encapsulated hardware should I specify? We can answer these questions as well as advising you as to when it may be more appropriate to hard tool your component as a metal stamping. Send us your drawing for immediate analysis.