Product category:
Robots and robotic systems
News Release from: Motoman Robotics (UK) | Subject: Linked robotic sheetmetalworking cells
Edited by the Manufacturingtalk Editorial
Team on 26 January 2004
Linked cells automate bending, welding
of lights
Two linked robotic cells provide a high degree of production automation to counteract local shortages of skilled sheet metal workers as well as reducing costs and improving production.
Two linked robotic cells provide a high degree of production automation at Designplan Lighting, Sutton, Surrey, part of a British-owned, worldwide group specialising in the manufacture of lighting systems and accessories One cell comprises a single Motoman robot that loads and unloads a press brake
This article was originally published on Manufacturingtalk on 14 Jul 2000 at 8.00am (UK)
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Once folded, the lighting component can be transferred by the robot directly into an adjacent cell where it is automatically welded.
Supplied by Bauromat UK, the latter cell uses two Motoman robots, one to carry the weld torch and the other to manipulate the component.
Each cell can also work independently, in which case the robot in the first cell stacks folded parts onto a pallet for later manual handling, and the second cell is fed by hand with components for welding.
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Said Designplan's production director, Alastair Johnson, "Unemployment in Sutton is very low and it is not an area where sheet metalworking skills are traditionally found, so it is difficult to recruit good staff.
We were therefore keen to start automating these functions as part of an on-going production improvement and cost reduction programme.
"We looked at dedicated CNC box folders, but they are really for large volumes and ours are not particularly high.
In any case, most of our products have down- and up-forms that would need to be accommodated in a special machine.
So we opted instead for a solution based on a robot-loaded press brake, which is a mature and proven technology.
The non-dedicated equipment means that there can be no system redundancy and it is an easy matter for us to automate the folding of new products as they are introduced." The press brake cell was integrated by Motoman in mid 2002, based on a new PPEB 1100kN machine from LVD, the fourth on site from this supplier, fed by a Motoman UP20 6-axis articulated-arm robot.
It picks up a sheet metal blank from a stack at one side of the cell and swivels through 90 degrees to present it to the press brake for bending.
Sometimes as many as four automatic repositionings are needed, performed with the help of an interchangeable, dedicated fixture on the floor in front of the machine.
The finished component is handled to the other side of the cell where it is either stacked on a pallet or transferred directly to a UP130 robot in the welding cell carrying an appropriate gripper.
It is exchanged manually, although this could be carried out automatically by the robot itself.
A second Motoman robot, this time a smaller UP6, performs the arc welding function while the first robot manipulates the component.
For the first six months after installation, the press brake cell was programmed using the teach-in method, after which Motoman's MotoPBM off-line programming software was introduced to increase productive time and to deskill further the whole process.
The software imports component drawings as DXF files from Designplan's computer-aided design system.
It then automatically generates an optimum handling program and downloads it to the robot's XRC controller, synchronising it with the computer-controlled movements of the press brake.
A simulation of the machining cycle may be viewed on-screen.
The press brake cell works largely unattended for 20 hours a day over two manned shifts plus up to four hours unmanned between shifts.
Based on this level of utilisation, the robot element of the cell paid for itself within nine months of purchase, as the operator is redeployed for much of his time onto other jobs.
As Mr Johnson points out, they would have bought the press brake anyway to cope with increased demand.
Taking everything into account including the cost of the machine and peripherals as well as of the robot, the whole cell was amortised in 15 months.
Continued Johnson, "Loading and unloading a press brake in our typical batches of between 20 and 600-off is a monotonous job for an operator.
In addition, some of our lighting products can be up to 6 metres long and weigh 8kg.
So handling the part end-on in the machine to form end features is very arduous when performed repetitively, especially as it involves following through to avoid bending the bottom of the material.
"It used to mean that the operator needed extra relaxation allowance during the shift to avoid the risk of strain injury, or else we had to produce the end feature separately and fit it in an additional operation.
Either way, the cost of production was increased.
Now the robot has eliminated the problem and raised productivity, as it operates continuously without any need for stoppage." Changeover between batches is as quick for the robotic press brake cell as it is for Designplan's manually loaded machines, according to Mr Johnson, which is just as well as hundreds of different varieties of component are folded.
The majority of work is in 0.9 mm coated mild steel, although some stainless steel and aluminium is used and thickness can go up to 1.2mm.
Cycle times vary from 1.5 to 3.5 minutes.
The welding cell is a more recent addition and is predicted to pay for itself within 18 months.
It was installed by specialist integrator, Bauromat, in May 2003 to complement six manual welding bays on the Sutton site.
Again, the rationale was deskilling and cost reduction, as well as improved cosmetic appearance of the weld seam and minimisation of subsequent hand dressing.
It is the first time the welding function has been automated by Designplan, except for a simple machine that has been used for many years for automatic MIG welding in straight lines.
A robot was chosen to manipulate the component rather than a servo-powered positioner.
A series of grippers is needed to accept different components from the press brake cell or from the manual loading gate, or both, depending on the product.
Two end effectors have been designed and installed on the UP130 by Bauromat, one for long components and the other for smaller, square parts.
It would not have been feasible to position components for welding using traditional manipulation techniques, as some products need to be held at unusual angles to the weld torch to achieve the correct attitude for laying down a neat weld pool that does not require extensive dressing afterwards.
Furthermore, positioning accuracy is crucial as it is only too easy to blow a hole in thin sheet material with the weld torch, and it was felt that twin-opposed robots could better provide the required degree of accuracy and control.
Already a wealth of data and experience has been gained, and the cell continues to be used both for research and as a production tool.
The need to retain two methods of loading the welding cell was driven by the disparity between the press brake cycles and the welding times, the latter being considerably shorter at between 0.5 and 1.5 minutes.
In practice, for most of the day shift a mix of jobs is manually loaded for welding, including some components that cannot be folded by the automated press brake anyway.
The turret punch press operator also runs the robot welder, so there is no additional labour cost involved.
During the ghost shift and at appropriate times during the manned evening shift, the press brake robot passes the folded part directly to the handling robot in the welding cell.
Currently, when the cells work in tandem, the welding system is idle for a proportion of the time waiting for components to arrive from the press brake.
However, the intention is to introduce grinding or linishing after welding to dress the components and balance the cycles, using the UP130 to present the weld seams to a static, abrasive machining station.
Weld cycle programming is currently by teach-in, but this too will be taken off-line in the near future.
Sixty to seventy product variants, mainly long, thin fittings but also end caps, are produced in the cell in batches of 200 to 6,000-off, although this will reduce as in-house jig design and manufacture progresses.
Johnson summarised: "For anyone thinking of automating production processes, it is noteworthy that articulated arm robots are very reliable these days.
The Motoman equipment has not failed once in either cell since their installation.
"Another, often-overlooked factor is that this type of automation is visually appealing and has proved to be a useful sales tool when customers visit us.
Rightly or wrongly, people do not expect a part that comes out of a robot cell to be inaccurate.
"Perhaps most importantly, the modern trend is towards manufacturing more product variants of greater complexity in smaller batches; certainly this is our experience.
Automated CNC cells are the best way to handle such production economically.".
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