Source: Amerimet. Cut to Length Line using some of my tips for blanking lines and cut to length lines
Cut to length or blanking lines for steel strip coil processing have seen increasingly tight tolerances imposed by the end product users. Even just a few decades ago loose tolerances were completely acceptable because the benefits of cut to length lines and the lack of precision in most manufacturing processes allowed for much wider tolerances.
With the advent of robotic assembly and more precise fitting across all forms of end products, the new tolerances are often +/-.005 of an inch or less. I will share several tips for maintaining these extremely tight tolerances while maximizing the productive capacity of your cut to length or blanking lines.
The ideal end product of a cut to length or blanking line is a precisely parallel and measured piece of steel that does not need further modification by the end product user. The bulk of the accuracy or lack of accuracy, for a cut to length and blanking line will come from the line feed systems.
This ultimately will determine whether or not the length and the precision of the blank meets quality control standards. There are a number of different feeding systems, but I will focus on the grip feet method as one of the more precise and controllable systems.
The first area for precise cut to length and blanking performance involves minimizing camber. Camber is essentially the deviation of an edge relative to what would be perfectly straight. Minimizing camber requires that the original coil that feeds the line has to be absolutely straight with both sides parallel.
As anyone who is experienced with cut to length lines and steel coil strip processing lines is fully aware, this is not always the case. After steel undergoes a cold rolling process, the resulting coil will usually have some level of camber.
Two forms of camber exist. The snake form is not quite as common and involves the deviation going from side to side on the coil. Narrow coils will tend to have snake rather than the other form of camber.
The other form of camber is known as sweep. This is the general form you will run into on most coil processing lines, and it means that the strip has a curvature that is continuous in the same direction.
Edge trimmers and slitters do not, contrary to popular misconception, cure sweep or snake. All edge trimmers and slitters do on a steel coil processing line is modify the existing snake or camber, and keep it in place.
Camber gets in the way of the ideal end product of a perfectly parallel and perfectly sized blank. The blank either comes out as a parallelogram, or as a part with camber. The only type of part really reproduced is one with camber that has been minimized to the greatest extent possible. Perfectly square parts do not exist.
Tip number one to eliminate the parallelogram is that you either have to position the shear relative to the material or position the material relative to the shear. This positioning can be accomplished through laser and servo integration on the CTL line.
Tip number two is to use the correct method for determining the squareness of your final blank. One method is to measure the diagonals and see that they are equal. This eliminates the parallelogram to a certain extent.
The other method of determining squareness is to measure all the sides and measure their deviation from straight edge. Combining both of these methods is the most precise form of determining the squareness of the blank or cut to length and product.
The grid feed measuring systems along with the control mechanism for achieving tolerances based on measurements have been around for many years. They are often known as either slide or hitch feed systems.
The grip feeders have to be accurate to within thousands of an inch or else there may be damage to the blanking die. The goal of a fully accurate and precision production cut to length or blanking line is to match the performance of an automatic press feeding system.
This means that the grip measuring system needs to be capable of measuring down to a thousandth of an inch. It then inputs that information into the gripper feeder system that can move the metal precisely enough to maintain dimensions less than five thousandths of an inch.
The challenge with grip feeders relative to automatic press feeders is that grip feeders use a mechanized system designed for high speed instead of a much slower and more precise hydraulically or pneumatically driven feed system strictly designed for precision. With speeds of around 250 feet per minute or even faster, achieving precision becomes a compromise.
The last tip for maintaining precision is to tie the grip feeder system with a movable sheer that adjusts to whether or not there is camber or a parallelogram forming with the cut to length line. By tying the adjustment of the sheer into the grip feeder system you can modify both the feed speeds and the cut angles to eliminate one aspect of out of tolerance cut to length or blanking lines.To return from this Tips for Blanking Lines page to the Strip Metal Coil Processing Home page, click here.
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