March 27, 2003
Gone are the days when engineers and draftsmen slaved for hours over drafting boards with a pencil and slide rule in hand (does anyone remember slide rules?). Today we've moved beyond slide rules and even beyond hand-held calculators to personal computers and mainframes to do much, if not all, of our design work. CAD and CAM software has made this possible.
Even with the advancements in computer design systems, parts layout still can still be a very difficult process, particularly when ease of forming is a major concern. But when is ease of forming not an issue at some time in almost every shop?
The majority of parts being manufactured are pretty straightforward--a square-corner notch here, a compound flange there. However, many times radius bends, features, or radius edges are required that can make parts extremely difficult to produce. For example, how would you develop a flat blank for a part that literally has no flat or square edges from which the press brake operator can gauge? And, just to make it interesting, let's say that the part has no uniform hole or feature patterns from which to pin gauge. The question then arises: Can this part be designed, manufactured, and still formed easily at the press brake?
Sure, this type of project could be done with elaborate side gauging, fixturing, or specialized tooling, but at what cost? Perhaps the $8,000, $10,000, or $20,000 for a custom tool, or perhaps running up huge labor bills while some press brake operator spends hours trying to solve the riddle just to produce a part like the one shown in Figure 1.
Believe it or not, even without a single straight edge or usable hole pattern, the part still can be formed easily. A square or straight edge for gauging can be accomplished by laser stitching, which is, in effect, adding extra material to the part.
Laser stitching usually is accomplished using a standard 2laser to produce all of the compound radii and angles a complex part might have. Of course, this does not mean that stitching can't be done on a turret press, but punching radius edges on a turret press produces an edge that won't look quite as nice as a laser-stitched edge.
The part in Figure 1 has no straight edge from which to square or gauge easily. Now look at the flat blank for the same part with additional material laser-stitched to the workpiece (see Figure 2). Notice the way in which the extra material has been stitched onto the radius edges. This extra material then is used to gauge the part.
To make the process even easier for setup personnel--not to mention general press brake operations--the additional material should be a standard size, for example, exactly 1 or 2 inches, a nice round number. This allows the setup person or operator simply to add an inch or two to the desired finished part dimension of the workpiece and to write that value to the controller. Once the forming process is completed, the extra stitched-on material (tab) is broken off by hand and discarded (see Figure 3).
The size of the stitched tab, or hanger, varies depending on material type and thickness. Type and thickness combined with the shape of the tab will determine if extra deburring or edge dressing is necessary to complete the part satisfactorily (See Figure 4).
The time required to add and remove the tab is minimal when compared to the time, effort, and costs incurred by attempting to produce the same part on a press brake minus the stitched-on additions. In fact, it is quite possible that the part might be too difficult to form on a standard press brake without first adding the laser stitched material.
By adding laser stitching to your bag of tricks, what once might have seemed an impossible workpiece or unprofitable venture can become a reasonably easy and profitable item to produce. Simply add the dimension of the actual workpiece (regardless of flange dimension) and the extra flange extension value from the part edge to the square or straight edge of the extension to set up the press brake.
Doing so validates the following quote: "The impossible will take only a moment longer." Just a moment longer than the average part would take!