In-die joining transforms press into assembly system, Part II

Laser welding

STAMPING JOURNAL® JANUARY/FEBRUARY 2009

February 24, 2009

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In-die joining systems help stamping shops to expand their operations to include sub-assemblies and full assemblies without additional downstream equipment and processes, so they can carve out a bigger share of the production work.

Automotive multipart contact diagram

An automotive multipart contact, consisting of a box-shaped outer housing and a segmented inner spring, is stamped, formed, and welded in the same die.

Editor's Note: In-die joining systems help stamping shops to expand their operations to include subassemblies and full assemblies without additional downstream equipment and processes, so they can carve out a bigger share of the production work. This is Part II of a two-part article. Part I focused on in-die fastener feeding systems.

Of the four major in-die joining processes—mechanical (interlock systems), riveting, resistance welding, and laser welding, the latter has the greatest potential and is likely to be used increasingly for more applications.

In-die laser welding can be used to close a single stamped part formed inside the die, such as circular sleeves, connector pins, and bearing bushings. Alternatively, these parts usually are seam welded in a poststamping process or closed with mechanical interlock systems (dovetails) which require complicated cutting and forming stations in the die.

A second, and perhaps even more important, application for in-die laser welding is the firm connection of separate parts assembled inside the die. Both parts can be stamped in the same die from the same strip or two separate strips, or just one part can be stamped while the second part is supplied already formed. In both cases, it is most important to position the second part with extreme accuracy and to fix it tentatively on the strip so that it doesn't move while the assembly and the strip are fed into the welding stations.

In addition, it is necessary to clamp the assembly in position at the welding station to minimize vibration to ensure high welding accuracy. When the assembly is in position, the press control system will trigger the laser to begin welding.

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Restrictions, Parameters

Both materials to be joined must be weldable. If they are, there are few limitations for the application of in-die laser welding. Because of the wavelength of the type of laser generally used for in-die applications (solid-state laser), pure or highly alloyed copper materials are the most demanding and difficult to weld. High-carbon steel is also difficult to weld because of the laser's thermal hardening effect.

On the other hand, the hardening effect can be relieved if the welding process is followed by a short annealing phase created with an extra laser pulse within the same press cycle.

Installation Requirements

To integrate the in-die laser welding process into a press, some special equipment is necessary. This includes a laser system cooling device, special laser safety press shielding, an adapted press control system, suitable strip lubrication system, welding fume extraction unit, special installation material for fiber-optic cables, and so forth. All of this equipment becomes part of the stamping line and can stay in place, even if standard dies without laser welding are installed.

In addition, all dies designated for in-die laser welding must be equipped with appropriate welding stations. They are characterized by mounting units for the laser focusing heads, provisions for welding fume extraction, and the previously mentioned clamping mechanism to hold the assembly in place.

Once this equipment is installed, the setup time for installing the die and adjusting all parameters for a new component are nearly the same as for dies without integrated laser welding.

Critical Developments

Although in-die welding is relatively new in the U.S., it is well-introduced in the European market.

Stamping companies are under increasing cost pressure. Outsourcing of stamping to low-cost countries is not cost-effective, since labor costs play a minor role in high-volume stamping. Therefore, it is key to consider the entire stamping process rationally.

Stamped parts usually are not stand-alone elements, but are pieces of subassemblies. One significant possibility for reducing manufacturing subassembly costs is to integrate several manufacturing steps into the stamping process. Some in-die combinations now available are:

  • Parallel stamping of different parts
  • Assembly
  • Threading
  • Joining
  • Cleaning
  • Online inspection using vision systems
  • Discarding of rejected parts
  • Separating
  • Stacking

In conclusion, the stand-alone stamping press is becoming obsolete. Instead, stamping systems will be more prevalent in the future. The more sophisticated systems are clearly trending toward customized turnkey lines. Wherever possible, they still will incorporate standard line components.

Ingomar J.K. Summerauer is project manager, new technologies, and Alois J. Rupp is vice president for Bruderer Machinery Inc., 1200 Hendricks Causeway, Ridgefield, NJ 07657, 201-941-2121, info@bruderer.com, www.bruderer.com.



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