Bending boom profiles and large radius shells for markets such as yellow goods (construction and earth moving equipment), transportation and offshore is traditionally a highly labour-intensive process that involves multiple setups and multiple part handlings to achieve an accurately formed part.
CNC V-dies and other special tooling is frequently
required for production
As such, productivity suffers and the risk for error and operator injury is high. Today, adaptive forming technology addresses the challenges of large-profile bending, making it possible to bend these profiles with consistent accuracy, at high throughput and with minimal operator intervention.
Bending a four-metre part or larger in high-tensile steel to make a boom profile or large radius shell is no small task. Though bending technology has made significant strides in reducing press brake set up time and improving the accuracy and repeatability of forming, these jobs and others that involve the bending of large parts, remain a challenge fundamentally because of their very hefty size.
Bending Large Profiles
To produce one of the largest cranes in the world, a leading European crane manufacturer cut 24 construction modules which were bent and welded into seven crane sections measuring a total of 84 m long. To put that into perspective, Turkey’s largest flagpole stands 110 m high, weighs 65 tonnes and is made of 11 galvanised pieces. The bent undercarriage of a single section of the crane consisted of three construction modules in thicknesses of 8.6 mm, 9.5 mm, and 10 mm.
The process of bending such mammoth parts is as mammoth as the parts themselves. Here are some of the processes that are typically involved.
One of the world’s largest cranes has
seven crane sections measuring a total
of 84 m long
Workpiece handling: An overhead crane is used to transport the material and position it on the front support arms of the press brake. Most fabricators handling such extra-large parts use front supports on guide rails to help position the workpiece along the length of the machine. Positioning in this way is usually slow, inefficient and potentially dangerous.
Measuring and determining bend lines: The machine operators (typically two on each job) will take measurements of the workpiece. Often accomplished with a basic measuring tape and chalk, this process is a must to calculate the bend lines. Once the calculations are made, the bend lines are marked on the workpiece.
Material consideration: The workpiece is typically a high-tensile steel such as Strenx or Bisalloy. These structural steels have high yield, tensile and fatigue strengths for demanding load-bearing applications. Their special construction makes them costlier than alloy steels and their springback value is inherently high.
Springback is a variable of sheet metal forming. The bending angle is the angle to which the operator overbends so that the metal springs back to the desired bent angle. The stronger the material, the greater the springback.
Tooling setup: CNC V-dies and other special tooling is frequently required for production. Depending on the scope of the profile and the number of bend radiuses, tools may need to be changed during the production process. Considering a 12 or 14 m press brake, changing tooling can take upwards of half a day. Tooling is expensive and tooling setup is labour-intensive.
Bending and correction: Parts are then formed. The entire part isn’t always programmed because it’s necessary to progressively bend to achieve an accurate part. The only way to compensate for accumulated error is to bend in steps, making program adjustments as necessary along the way.
After a series of bends, the operators will stop to manually measure the radius. If the part is forming properly, bending continues; if the part is not forming correctly, corrections must be made. The operators must calculate how much correction they need for each bend.
If it is necessary to re-bend on the bend line, the operator will need to reposition the part (manually or using a crane) and re-bend. After more bends, operators will again check part accuracy. Before the part exits the machine, all radiuses will be checked using gauges. This highly manual work takes experienced operators and is a trial-and-error method fraught with potential for error.
New Adaptive Bending Technology
Given the nature of this process and considering the material, tooling, labour and production time, bending boom profiles or large radius parts can be quite costly.
Next-generation adaptive bending technology is now changing the process. By using an in-process quality management system such as LVD’s Synchro-Form to measure the accumulated angle and compensate for angle deviation in the bends that follow, this advanced technology can improve productivity of large profile bending up to 50 percent or more, depending on the specific profile.
Adaptive bending is a modern manufacturing technique that provides real-time part angle sensing and real-time error correction to ensure the accuracy of the formed part. The adaptive bending system automatically performs functions that are typically handled manually by the machine operator in order to ensure accurate bend angles.
The system automatically compensates for variations in material property (springback), thickness, machine/tool geometry and positioning.
21st Century Advantages
The evolution of this technology for large profile bending manipulates and positions the workpiece during the bending cycle, correcting in process for any variations.
The system uses a gauge/push device, sheet supports and magnetic grippers to automatically position and guide the workpiece. The accumulated angle is measured in process and any angle deviations are automatically compensated. The system checks the unfolded workpiece length, thickness and validates the part geometry. As a result, this solution:
- Reduces the direct cost of the part by reducing the manual operations.
- Increases throughput by automating the bending process and ensuring bent part accuracy.
- Makes for a safer production environment.
Offline programming software is used to program parts/profiles, eliminating manual programming at the machine. This saves time in preparing and editing part programs and can also help optimise cycle times and part quality. Programming offline increases press brake productivity, as there is no interruption in production.
Standard tooling can be employed for most applications, eliminating the need for costly CNC V-dies and reducing tooling setup time. This is possible because step bending is used to bend various radiuses, reducing the number of special tools needed for the job. Step bending is not practical with traditional large profile bending because of the difficulty in manually calculating the corrections and positions.
Market Segment Impact
As fabricators in Asia Pacific move to higher value-added manufacturing as the region continues its fast growth, next-generation adaptive bending technology for large profile bending applications holds much promise. Manufacturers in markets from transportation to offshore to yellow goods stand to benefit.
APMEN Sheet Metalworking, Mar 2017