ACHIEVING GREATER PRODUCTIVITY WITH MODERN LASER CUTTING SYSTEMS
New laser cutting systems address the inefficiencies of older systems and offer much higher competitive value and throughput than the older systems on the market today. That’s not all. Adding full automation can enable you to take advantage of off shifts and weekend operations to meet the demands of your customers. Here’s how.
Modern laser systems offer vastly different options to work with than years ago. Higher laser powers are introduced almost every year, along with consistent and vastly improving machine dynamics and features.
Applications that were once punch-only are now equally, if not more, economical to be processed on a laser because it can process at high accelerations while using increased laser wattage for high cutting speeds. High-speed lasers now process many hundreds of round holes per minute, negating the advantage that punch technology once held in the past. However, the laser still cannot make forms such as louvers, so punching systems remain a viable tool where internal forming is necessary.
Automation has vastly increased the throughput efficiencies of laser cutting systems by achieving increased capacities with unattended shift operations.
Operating high-speed lasers efficiently requires careful programming considerations. For example, at the speeds now being achieved, programming techniques must consider possible collisions from cut pieces, such as cut outs and other parts. When traveling from feature to feature, most systems employ a Z-axis down condition where the X and Y are the only moving axes. In such cases it is imperative to ensure that programming completely avoids the features that were previously cut. Effectively, the end of cut from one feature needs to be in the shortest path to the subsequent feature to be cut. This technique is called feature avoidance and requires that the lead-ins are aligned in the direction of the next feature to be processed.
Lead-ins are not always necessary depending on the thickness of the material, but the orientation of the start location will be the location of your end point as well. As the cut feature is released from the part it will either fall through the support grates or tip up. With feature avoidance programming, you completely avoid the tip ups by moving away from the previous features and never crossing over these features while positioning.
Another programming consideration is the cut direction of the feature itself, combined with the travel direction of the next feature. If, for instance, we are cutting a series of holes and transitioning from the left-to-right direction, the most efficient way to ensure a smooth transition without making sudden changes of direction is to program so that the feature’s direction of processing is counter-clockwise. If we change the transitioning from right-to-left in the second row of holes, we would program the direction of the holes to be clockwise. The smooth transition occurs because the motion from feature to feature is in the same orientation as the cut feature itself.
Another technique for high speed processing is called scanning technology, which is only available on high-speed machines with a fast switching laser power supply and very accurate positioning at high speeds. Scanning allows the high speed processing of square holes or any feature that consists of straight line segments. Scanning is achieved by moving across a series of square holes. As you travel, the laser beam cuts all of the straight lines in one direction that are in line with each other. In the case of the square holes, as we travel in the X direction all of the bottoms and the tops of the squares would be cut and, likewise, the left and right sides of the squares would be cut while traveling in the Y axis direction.
HIGH SPEED LASER CUTTING
The term “high speed” as it is pertains to laser cutting can be associated with three main categories; feed rate, positioning speed and acceleration.
Feed rate is most influenced by the wattage and the assist gas properties that are in use. The higher the wattage, the faster the feed rate. Gas properties also play a large role in the achievable feed rate. For example, nitrogen (as compared to oxygen) assist can be faster by 100 percent in thinner material under 0.080 in, but air assist can be as much as 30 percent faster than nitrogen in this same thickness range. Most importantly, increasing the feed rate in small features or parts does not yield faster part times because the full feed rate is never reached in small line segments or small features. Only in large line segments is the feed rate fully achieved.
Positioning speed is a measure of the top end speed of a motion system. The positioning speed does not affect part times that much because this top end is seldom ever reached. Most practical positioning within a sheet involves short positions from feature to feature or from part to part that never reach the fully stated positioning capability of a machine.
Acceleration has the most impact on part times because it reduces the point to point and feature to feature times. Since most positioning within a sheet are short positions, how fast you get from point to point is dependent upon acceleration or distance traveled/time, expressed in m/sec2. The higher the rate of acceleration, the more distance traveled per time until the top end speed is finally reached. Each line segment requires an acceleration and deceleration point; each feature is an acceleration and deceleration point. The greater the quantity of features or line segments, the greater the impact acceleration has on the overall part time.
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