When international automotive suppliers use production lines for manufacturing parts of the exhaust gas system, these are often tube production lines made in Müllheim. Cost pressure, quality requirements and flexible production conditions dictate developments within the automotive industry.
With the Ecostar 200/600, a highly flexible tube production line is leaving the main factory to produce tubes for catalytic converter housings in 10-second cycles. Before the tube leaves the machine, the laser-welded seam is annealed, strengthening it for higher loads. To be able to track the quality of every component, a DataMatrix Code is applied by a marking laser, which allows product seam tracking (Industry 4.0).
The machine is attended by an operator in the production process and adjusts automatically to the selected program after program selection. The program memory contains all the machine’s roll forming and welding parameters.
Innovative clamping technology for the fully automatic production of round, oval and polygonal tubes
Calls for flexibility in tube production in terms of length and diameter range and the minimization and elimination of retooling times were requirements on a machine concept that is successful in the material thickness range of 0.5 to 2.0 mm.
Program-controlled retooling and the automatic adaptation of diameters in the roll forming and welding area such as have already been successfully implemented in various machines are at the heart of the “Ecostar”. The roll-formed sheet is joined by radially movable clamping bars on the outside and continuously welded under a vertical laser optic.
Flexible clamping and welding up to 2.0 mm sheet thickness
The “Ecostar” has been designed for a diameter range of 60 - 200 mm, tube lengths between 50 - 600 mm and sheet thicknesses from 0.5 to 2.0 mm. For these reasons, this machine is ideal for the production of catalytic converter housings, small round/oval containers, pressure tanks and the like in the given dimensions.
Freedom of tube geometry
Alongside the benefits for modern short tube production without forming rework of the tubes already achieved, the machine provides a great freedom of choice in terms of tube geometry. Optimum roll-forming results are achieved by edge forming. Round or oval geometries – alternating if required – can be reproduced in stable process quality from batch sizes of just 1.
The use of a diode laser is efficient in terms of both investment and operating costs.
The United States automotive market place is undeniably unique. For 32 years, the best-selling vehicle in the US has been the Ford F-150, a 5500-lb., V8-powered pickup truck popular for farmers, small businesses, and suburban families alike. To an outsider, it might seem that the US is not concerned about fuel economy, but over the last decade that has finally started to change. Gas prices started to climb significantly about 10 years ago and for many years, the US government has been tightening mandated fuel economy regulations known as the Corporate Average Fuel Economy (CAFE) standards. Even the current glut of low-priced oil won’t make the government backtrack on these standards, which were implemented in an effort to protect the environment. Car designers have been looking for improvements in fuel economy in every aspect of their design.
The first wave of mileage improvements was substantial: changing from body-on frame to unit-body designs and downsizing engines from V8s to V6s and from V6s to 4 cylinders across the marketplace, without major impacts on performance. Also in the first revolution of changes were automatic transmissions with 6, 8, 9, or 10 gears. Who would have thought that an automatic transmission could ever offer better acceleration and fuel economy than a manual transmission? Even Ford’s best-selling truck—almost always sold with a V8—has changed to an aluminum body and is becoming popular with their Ecoboost V6 Turbo. US consumers and car manufacturers are paying attention to fuel economy and changing the automotive landscape.
Now, the big "low-hanging fruit" design changes are mostly done and engineers are looking to squeeze every gram of weight out of every passenger vehicle. If one compares the typical 3500-lb. weight of sedans designed by the American "Big 3" (Chrysler, Ford, and General Motors) to the 3223-lb. weight of Asian-designed sedans also built in America, you can quickly see the US has a way to go.
Laser welding of exhaust systems
It’s known that laser welding can play a big part in weight reduction, as it is already widespread in body and chassis applications to allow engineers to reduce the mass of metal required in each welded joint. They can utilize smaller overlaps and tabs for laser welding than that needed for spot welding. Plus, laser welding doesn’t require access to the back side of the weld. These same advantages are starting to be adopted in the exhaust system.
The last generation of silencers was typically made from stamped components with lock-seamed longitudinal seams, and end caps that were attached with either lock seams or overlap welds (FIGURE 1). A traditional lock seam has four layers of material overlapped and locked together for at least 3/8 or 1/2in. of overlap across the entire shell, wasting material and increasing mass. The stamped end caps had to be recessed into the end of the muffler to have a sufficient overlap for a seam lock or overlap weld, increasing mass and reducing tuning volume. Laser welding came to the rescue: in the exhaust system specifically, laser welding allows the elimination of lock seams and overlap welds while achieving lower emission leak rates.
New car designs raise exhaust system problems
Interestingly, as modern car designs evolve, exhaust system engineers are faced with a particular set of juxtaposed challenges:
- As with all other parts of the car, the weight of the exhaust system has to be reduced to improve fuel economy—make it lighter.
- Engine down-speeding through the use of taller gear ratios lowers the frequencies that need to be attenuated, resulting in the need for larger average tuning volumes. These larger silencers would traditionally require more packaging space—make it larger inside.
- Increased use of hybrid electric powertrains requires packaging space for the battery packs, reducing the packaging space available for the exhaust system—make it smaller outside.
- Increased adoptions of all-wheel drive systems also reduce the space available for the exhaust system, and complicate the pipe designs—keep it out of our way.
Laser welding in the exhaust system has been utilized for many years, primarily in the commercial truck field. There, lower volumes and larger-diameter components, compared to passenger car exhausts, make it difficult or uneconomical to get suitable round shells unless they are custom-made by roll formers and longitudinal seam welders. So, the technology is readily available to use butt-welded exhaust components, and the high volumes of the passenger car world are well served by the high speeds of laser welding. Roll-formed silencers offer more volume than stamped shells with their inset ribs. Butt-welded silencers weigh less than lock-seamed or overlap-welded units, and don’t have an obvious potential leak point where the can meets the end cap. Domed end caps welded to the silencer offer more tuning volume and less weight.
Additionally, laminated mufflers are in favor at some of the world’s largest automakers. Making the silencer shell from two thinner pieces of stainless steel can offer improved sound attenuation over a single-wall silencer, and allows selection of materials with different anti-corrosion properties for the inside and outside of the silencer. Laser welding fits right in, being able to butt-seam-weld both layers at the same time with a cosmetically attractive weld and no weld strength problems.
Modern silencers have shells, heads, and reduced baffle thicknesses (FIGURE 2), as well as:
- Welded seams to eliminate lock seams;
- Some muffler shells will be two layers of 0.5mm material;
- Some single-layer shells will have material as thin as 0.6mm;
- In the case of deep-drawn heads, starting thickness may be 1.2mm;
- Dimpled muffler shells will help suppress radiated noise;
- Baffles are already at 0.8mm and will likely go thinner; and
- Nonstructural passage tubes will be 0.6mm or thinner.
Catalytic converters, known as "hot ends," can also benefit from laser welding, and are perhaps a little ahead in adopting more modern manufacturing techniques. Clamshell converter shells with overlap weld joints seem to be losing ground to tubular butt-welded designs, whether done by TIG or laser. This reduces their mass and required packaging space while eliminating the need for hard tooling. A laser-welded converter shell can also have its ends spun down to the pipe diameter as long as it receives a little post-weld processing such as annealing or seam planishing.
Another place where laser welding offers advantages to exhaust system designers is in fabricating the internal pipes that connect the different chambers of the silencer. Traditionally, these will be made by placing solid tubes onto a purpose-built "punching" machine that will use die-less punching to put holes in the pipe. But the mechanical tooling can be difficult to maintain and will leave the punch burr on the inside of the tube, which can cause a whistling noise in operation.
Laser welding tubes out of pre-punched steel coils allows making any desired hole pattern while placing the burr on the outside of the tube.
Today, silencer manufacturers still use lock seams on their silencers in North America, while European manufacturers have been quicker to adopt laser welding. As the weight reduction, tuning volume, leak rates, and quality standards continue to push their design, laser welding offers a unique set of advantages to address the future demands on exhaust system design.
DAN ROBINSON vice president of sales for Weil Engineering North America
A gripper holding a component preformed in a press swivels into a clamping device, picks up a prepared cover sheet from the stack table and a laser beam joins the two parts. At the same time, a laser at the adjacent station cuts a series of metal sheet segments and a gripper places these segments one after the other in the previously welded component. After a dozen repeated cutting, transport and welding operations, a robot places the completed metal assembly onto a discharge belt, while the process has already started again in another place. An employee checks the stack tables as well as component feeding and removal, and the FLC 1002 continuously works through the prepared program. A brief glance at the control screen confirms: production is running, output up to four components per minute.
The FLC 1002 is a laser cell which can carry out laser cutting and welding processes (in one clamping = CutFusion process). Internal automation (transport axes, robot) takes over the transport between the individual working steps. Every component position required is adopted suitable for laser processing thanks to the interplay between processing optics, clamping devices and the automation axes.
The real strength of this type of system is that all components can be processed completely in one clamping, because the FLC 1002 has been designed in such a way that cutting and welding operations must be carried out in a fixed position. This results in maximum precision and reproducibility. The aim of this development is to improve manufacturing processes (transport times no longer required thanks to concentration of work sequences), increase component quality and make significant savings by using laser technology.
Clamping devices and programming are tailored to the respective components. The individual quick-release devices are retracted and the processing programs prepared in cooperation with the customer. In production, the customer is responsible for the fine tuning after the devices have been installed and the program opened. Then production can start. Further customer-related devices and programs can be realised in the FLC 1002.
With the intention of radically reducing projecting expense, processing times and assembly effort, weil technology has developed a flexible laser cell which opens up new perspectives for component design. Together with an integrated and additional adaptive handling system, entire 3D sheet metal assemblies can be constructed in one machine. The machine comprises two stations which can be configured depending on the manufacturing requirements.
The coil or board material is cut in 2D components on a precision clamping table and removed from the cutting process directly by robot handling before separation. This means they are 100% aligned to position and free of cutting splashes or other soiling such as occurs in conventional cutting solutions.
In this state, they are fed directly to the welding jig (station 2) and welded into an assembly. Unloading of the finished assembly and the magazined feeding of additional components for the assembly is also performed by a handling robot. This way, processes necessary for sequential manufacturing such as component sorting, logistics, component preparation for the welding process (cleaning) as well as measuring sensors for position detection and orientation are no longer required,
Changes or adaptations of the cutting contours are possible at all times through the CADCAM-based programming.
This laser cell offers the CutFusion process as a special highlight:
Here, components are machined completely in one clamping with the following process steps: Cutting – welding – cutting – automatic feeding of attachment components – welding.
This means that in just one clamping the following can be realised: trimming of two pressed half shells by the laser cutting process – welding to one another in the same clamping – cutting using a hole contour on the welded component – feeding of a threaded bushing via the integrated handling system – tacking and welding of the bushing by laser. The position of the components and/or the cut contours is known at all times in every process step for the feeding of components and the welding process. Detection of the 3D component by sensors for the jointing process and detection of the position of later cutting contours for the feeding of components is no longer necessary.
This leads to shorter machining times, significantly greater component precision compared to sequential manufacturing solutions as well as maximum flexibility for changes or adaptations to changed bushings through finished machining cycles.
The method was developed to increase the quality and precision of the components to the highest possible level. The cutting and welding operations are carried out without any intermediate storage in a forced position (jig).
Components can be supplied to the welding process or the clamping device through internal automation. Separate optics for welding and cutting create maximum precision and minimum process time. Non value-creating transport times are dispensed with by integrating working sequences. There is no buffering between working sequences either.
By combining both methods in one machine, expensive methods can be replaced by an economic and quality advantage for the client:
• Reduces logistics effort and makes material flow easier
• Product quality and component precision are improved
• New design freedom puts clients a step ahead of the competition
Fields of application
- Media-carrying systems
- Semi-finished product structures
- Substitution of cast components
- High-precision profile connection of tube and square