Laser Processing Meets Induction Heating

No one wants to buy a laser in order to have a whizzy tool on the factory floor. That was once the case. But no more. In fact, during the past few years, lasers have become, well, nearly hum-drum so far as production equipment goes.

One of the real benefits of lasers is the ability to do things that can't otherwise be performed. And what has lots of potential for growth is the use of the tool to make things that hadn't been previously possible.

A prime example of something that (1) provides the ability to do things that can't otherwise be done—or at least not done well or consistently—and (2) the means to make things that weren't previously possible has emerged from the Fraunhofer-Institute fur Werkstoff- und Strahltechik (IWS) in Dresden, or, as it is rendered in English, the Fraunhofer Institute for Material and Beam Technology. For those familiar with the Fraunhofer organization, they may know that the center for lasers has been located in Aachen. But as Eckhard Beyer, executive director of IWS explains, whereas the Aachen operation tends to focus on the development of lasers, IWS concentrates more on metallurgy and application of laser technology.

The Fraunhofer Institute performs contract research programs. One such program was initiated at IWS by Ford of Europe. This led to the development of laser induction processes that are not only capable of hardening, but also performing cladding and welding in a manner heretofore impossible.

To be sure, lasers can be and are being used for hardening, cladding and welding applications. But there are some limitations, such as the generation of cracks in hardening, slow operating speeds in cladding, and the inability to weld steels with more than 0.25% carbon or low-alloy steels with more than 0.20% carbon.

What the researchers have done, in collaboration with industrial partners including laser-manufacturer Rofin-Sinar (in the U.S.: Plymouth, MI), and two German companies: induction heating equipment supplier EFD and Arnold Ravensburg, a special machine builder, is to create the process and the related system that eliminates these limitations.

According to Berndt Brenner, who heads the IWS Department of Material Science, the induction heating and the laser processing are arranged to work in a complementary manner, as the photon energy of the laser works primarily on the surface as the inductive energy works on the near-volume area of the materials being processed. The laser-to-induction power is on the order of 1:8 up to 1:20, depending on the specific application. In operation, the workpiece is first inductively heated, then the laser is brought into action. Brenner says that the result of the hardening operation on components—and applications can include camshafts, cam follower, and rocker arms—is a hard, wear-resistant surface and a crack-free, fine microstructure. Importantly, the process can be performed at a faster rate than is ordinarily attained when the two tools are used separately: as much as 10X faster. Cladding can also be performed with the laser induction process, such as applying hardfacing alloys on harden-able steels, tool steels, or alloyed cold working steels, at this 10X rate.

Laser induction welding also provides some important capabilities. Ford, at a plant in Dueren, Germany, is producing link shafts with a special laser induction machine. There are three components: a race tripod, that's either formed SAE 1038 or SAE 1046; a tube that's made with an alloy, 26Mn5; and an inboard joint that's also either SAE 1038 or SAE 1046. This part had been produced with magnetic arc press welding. However, this process led to some difficulties, such as distortion problems, the necessity to perform post-weld turning in order to get rid of excess material at the weld joints, and high capital and running costs. The laser induction system, built by Arnold Ravensburg, is a four-station, transfer-through unit with a 19.5 second cycle time. The Rofin-Sinar CO2 laser used is rated at 6 kW; the EFD induction unit is rated at 60 kW. The weld depth is 0.3 in. Brenner says that the advantages of this system as compared with the previous one is that not only are the capital and operating costs lower, but the welded parts require no post-weld machining, there is better concentricity, and there is better length consistency than was previously achieved.

Brenner notes that Mercedes-Benz will be putting a laser induction system on line in September 1997 for gear shaft welding. In this application, three case-hardened ring gears are welded to a shaft. The shaft is fixtured vertically and a gear is manually placed on it. A location is precision ground into the shaft to assure the proper positioning. The laser induction process welds the gear in place. Then the shaft goes back to grinding, and another location is ground in. The procedure is repeated. The third gear gets the same treatment. One of the advantages of laser induction processing is that the area heated is localized. There is no problem, for example, with distortion of the teeth on the ring gears because the heating is concentrated around the outer diameter of the shaft and the inner diameter of the gears.

IWS has built a five-axis CNC laser induction machine that it uses in its Dresden facility for process development. This unit includes a 80-kW induction unit that provides a selectable frequency range of 8 to 10 kHz. The coils are water-cooled. There is a quenching device with a high-pressure (109 psi) pump. The laser is a 6-kW RS 860 HF from Rofin-Sinar. A Fraunhofer-developed integrated seam tracking system is used to guide the beam. It is based on a diode laser and photo-diode sensors that capture the reflection of the diode laser; the seam tracking system is capable of detecting gaps and edges. The workpiece can move in three axes for processing: X, Y and A (rotary). The laser and in-duction coil move in the Z axis. The induction coil can also move in the W axis (which is parallel to Y). The work envelope is X= 28 in., Y= 13 in., Z= 16 in., and W= 12 in. The A axis range= n × 360°.

A second development machine is being built. This one will have double the work envelope and will be equipped with an 8-kW laser. It will be installed at Rofin-Sinar in Michigan at the end of 1997 or the start of 1998, as part of the collaborative arrangement between IWS and the laser manufacturer (see "Working Together").

Eckhard Beyer says laser induction processing can provide users with a variety of advantages, such as reliably hardening materials, the ability to weld components that are otherwise difficult to join, and the means to clad with high efficiency. He noted that not only can existing components be improved, but that it opens up the possibility of making parts that didn't seem possible.

Working Together

"This is the first formal partnership in North America between and industrial laser company and a research institute," says Richard Walker, general manager of Rofin-Sinar Inc. (Plymouth, MI), about the relationship the laser company has established with the Fraunhofer Institute for Material and Beam Technology of Dresden, Germany.

The significance of this is that the prestigious industrial research institute will base personnel and equipment in Rofin-Sinar's applications center and will help develop applications for customers. Rofin-Sinar will concentrate on the development of laser equipment (Walker says that customers are looking for simplicity in design and operation, lower operating costs, reduced maintenance, and high reliability).

"These relationships are encouraged in Europe," Walker notes, "but they are quite alien here."

As an example of what this means for a customer, Walker says that Rofin-Sinar had been working with a company on a potential welding application. The company had been doing the welding with conventional equipment; it wanted to switch to laser welding. However, there was a cracking problem associated with the laser welds. It seemed as though the program would die. But now the metallurgical expertise of the Fraunhofer people will be brought to bear on the situation.

"Practical solutions to problems—it's part of their pedigree," Walker says of the people at the Dresden research center. AD&P