FABTECH365,

Lasers Tackle Automotive’s Toughest Joining Challenges

By Jennifer Dallos on on September 8, 2017

By David Havrilla, manager, product and project management, at TRUMPF Inc., Farmington, Conn. Reprinted with permission: The AWS Welding Journal The enhanced focus of today’s solid-state lasers offer the automotive sector creative solutions

Laser welding of a powertrain component.

Since its first industrial applications more than four decades ago, the laser has been undertaking joining challenges. One of the first was replacing electron beam welding in a variety of automotive powertrain components such as clutches, shafts, gears, and carriers. The joining difficulties posed by powertrains were numerous, one of which was the requirement of a high aspect ratio weld with low distortion and high throughput. Moving forward from those early days, literally tens of thousands of laser material processing applications have been implemented into automotive production facilities all over the globe. It is astonishing to consider the laser applications that have been incorporated in the manufacturing of a typical modern vehicle. Beginning with the steering wheel and column, applications such as the welding of the air bag inflator and assembly, steering column, and power steering unit are used in production. There is laser marking on the instrument panel of numerous displays, knobs, and panels. Peel back a layer and look at the instrument panel bar to find laser joining of all sorts of subassemblies and brackets. Penetrate even deeper, into the engine compartment, and panels are cut and welded. There is welding of battery tabs and the battery assembly. Also, numerous engine and powertrain components are heat treated and welded, including the fuel filter, fuel injectors, oxygen sensors, valve lifters, camshafts, and manifolds. Breaking through to the front of the vehicle, the radiator and radiator support structure are welded. In addition, the bumper is cut, and plastic headlights are laser welded. Upward, sideway, and rearward are dozens of laser welding, cutting, heat treating, cladding, drilling, and marking or ablating applications. However, some of the most challenging applications in the modern vehicle are in the area of joining. Welding Several Kinds of Steels Galvanized Welding of galvanized steel has always been a challenge for fusion joining processes. Even adapting lasers to successfully weld zinc-coated steel took many years due to the high volatility of the zinc coating, because the zinc vaporizes out of the molten zone, resulting in an extremely porous weld. It wasn’t until about ten years ago that the longstanding problem had a viable solution, and it was based on knowledge that had been acquired years earlier. If a small opening of about 200 microns between the parts to be welded exists, the zinc can vaporize laterally instead of through the molten pool. The challenge was always how to create that opening quickly and repeatedly. Remote welding on the fly, which uses ultrafast scanning mirrors, offered a resolution to the problem in a two-step process. During the first step, the laser and scanner are used to put down 200-micron-high dimples on one panel at a rate of about 10 ms per dimple. Then the second panel is placed in position, clamped, and welded. The result is excellent welds at a cycle time suitable for automotive production. Press Hardened The challenge with welding press-hardened steel components resides in the roughly 20-micron protective AlSi coating on them. If the coating wasn’t removed prior to joining, molten aluminum would mix into the weld zone, forming brittle FeAl intermetallic compounds, thus weakening the weld. Laser ablation can remove the AlSi coating millimeters away from each edge of a joint at up to 20 m/min. Tailor-Welded Blanks Though tailor-welded blanks have been around for a while now, the challenges and benefits are well worth recounting. The original idea is simply this: to tailor, or engineer, blanks specifically for the application by laser joining steels of different grades, thicknesses, or coatings. Typically, the objectives are to optimize the strength, weight, and corrosion performance of the blank. One of the initial implementation challenges was formability of the weld joint, especially when two different thickness blanks are joined. More challenges arose, however, as tailor-welded blanks gained worldwide acceptance, and automakers desired more complicated blanks. Suppliers needed to produce linear welds in multiple directions and were even asked to produce nonlinear welds. Today, the challenges continue with developing engineered welded blanks of lightweight materials such as press-hardened steel and aluminum. Laser joining was, and continues to be, an ideal way to meet the demands of the formability and material challenges facing tailor-welded blank manufacturers. Brazing for Enhanced Aesthetics Laser brazing is a useful and prevalent process tool in the hands of automotive product designers. Body-in-white joints, such as the roof to side panel and hang-on panels like deck lids and tailgates, take advantage of the enhanced aesthetics, process optimization, and cost savings that laser brazing offers. For example, the roof to side panel nonlaser brazed joint is a “ditch joint” where the joint is joined via resistance roll welding. After joining, a sealant is applied to the joint to ensure watertightness. Finally, the U-shaped joint is filled and made aesthetically pleasing with the help of a long plastic molding piece. Laser brazing eliminates the need for a sealant and molding and, thereby, saves time and money. Copper and Aluminum Characteristics Lasers are ideally suited for fusion joining of materials specifically used for automotive batteries, like copper and aluminum. The laser’s high focusability and power yield a narrow, deep-penetrating weld that minimizes the adverse effects of thermal conductivity, thermal expansion, and solidification shrinkage. Joining of aluminum components and panels for light-weighting applications are similarly aided by the laser welding process, while benefitting from the high throughput and enhanced flexibility of the laser. For example, a single laser can be switched from one weld station to another in less than 50 ms, allowing the laser to be a shared resource on the production floor. Recent advancements in laser welding show promise for autogenous welding of 6000 series aluminum. This technique involves relatively high frequency and low amplitude manipulation of a small focused spot, which directly influences residual stresses and grain geometry. Different Types of Joining Dissimilar Materials Laser welding offers attributes that are often beneficial to solving the problems that vex the joining of dissimilar materials. Issues such as differences in thermal conductivity, melting temperature, and coefficiency of thermal expansion, as well as the thickness of the intermetallic zone and amount of distortion or residual stress, are exacerbated by most other conventional fusion joining techniques. Lasers have demonstrated successful joining of aluminum to steel, but other challenges remain such as galvanic corrosion and differences in material elongation that can lead to wrinkling of visible panels. Plastic-to-metal joining is another unique and interesting application that lasers have taken on. The process is relatively straightforward. An ultrafast, short pulsed laser is used to texture the metal part at the region to be joined; the plastic component is heated and pressed into the textured area. The result is an extremely strong mechanical joint wherein failures occur in the plastic outside the joint region. Preparation for Carbon Fiber-Reinforced Plastic Lasers sometimes appear where you least expect them. In the case of carbon fiber-reinforced plastic, lasers have been used to cut this material in European automotive production facilities for several years. For laser joining of carbon fiber-reinforced plastic, however, the application is less obvious. In the end, it is similar to the plastic-to-metal joining mentioned previously. The carbon fiber-reinforced plastic is textured by a short pulsed laser in preparation for, and to optimize, adhesive bonding. Lightweight Design with Lasers For the automotive product designer, the laser represents a unique instrument for trimming the excess weight off of vehicles. Laser welding offers numerous joint designs that enable redesign of components with increased strength, reduced package size, minimal or no flanges, and reduction or elimination of additional add-on strengthening patches or moldings. Altogether, these features provide myriad avenues for both mass reduction and enhanced aesthetics. In the 1970s, automotive engineers first recognized the value of the laser in solving their most critical fusion challenges. Forty years later, the applications are growing like never before, and this can be attributed to several reasons beyond the fundamental benefits of laser joining itself. Some such advantages include low heat input, minimal distortion, superior strength, high throughput, elimination of secondary processes, reduction of component size and weight, and the like. Beyond those, lasers have decreased significantly in price, making them more affordable than ever to employ in high production manufacturing. As a point of reference, about a decade ago, a 4-kW, solid-state laser was around $600,000. Today’s prices are a quarter of that. Furthermore, lasers have gained significantly in power over the last ten years, especially solid-state lasers that did not exceed 4 kW back then. Nowadays, it’s not uncommon to have moderately powered 8-kW lasers on the production floor, allowing automakers to weld deeper and faster, plus enabling them to keep up with fast-paced production needs. Conclusion Today’s solid-state lasers have significantly better focusability than the lasers of 2007, making them a much faster and more flexible tool. This enhanced focusability, referred to as “brightness,” enables high-speed welding, on-the-fly remote welding, and high brightness beam oscillation welding — all of which provide the automotive sector with creative and cost-effective solutions to numerous joining challenges. These realities have caused the installed base and application know-how to grow exponentially over the past decade. Combine all of this with breakthroughs on the horizon in the areas of laser technology, processing sensors, 3D laser printing, and laser material applications, and the next decade promises to be even more exciting than the last.

Join Us in Orlando

Expo Hours

Venue

About the Expo

North America's Largest Metal Forming, Fabricating, Welding and Finishing Event

From the Blog

Lasers Tackle Automotive’s Toughest Joining Challenges

About the Expo

2024 Platinum Sponsors

2024 Sponsors

Tuesday Oct 15	9 AM — 5 PM
Wednesday Oct 16	9 AM — 5 PM
Thursday Oct 17	9 AM — 4 PM