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New Horizons in Process Capability

Wed, 06/23/2010 - 7:03am
SPI

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In comparison with conventional laser technologies, the primary benefits of fiber lasers are their ease of use, straightforward integration capability, high reliability, and maintenance free operation. However, as discussed in this article, SPI’s latest generation of R-4 CW-M High Power Fiber Lasers have many other features, which result in significant performance benefits across a wide range of different process applications.

Reliability, Size, and Simplicity

The most immediate differences between a fiber laser and a conventional laser arise from the physical construction. In some conventional lasers, a fiber optic cable may be used to deliver the beam; whereas, fiber lasers are the only truly monolithic technology in which the laser cavity and beam delivery is a single integrated system made entirely in optical fiber. This feature, together with the fact that fiber lasers are pumped with high reliability single emitter pump laser diodes, means that there is no regular user adjustment, maintenance, or servicing required. This leads to substantial benefits in terms of the lasers’ simplicity and ease of use.

Other significant benefits arise directly from the design and construction of the laser. Optical fibers can be coiled to make very compact modules that make the design for thermal management straightforward, and result in a significantly reduced system footprint compared to other lasers. In addition, the high wall-plug efficiencies of greater than ten times that of conventional lasers makes a compelling business case for the fiber laser based on total cost of ownership, even disregarding any productivity or process improvements, and considering only equivalent parametric performance.

Beam Quality

The single-mode beam quality of fiber lasers allows the beam to be focused down near diffraction limited spot sizes at the work piece, giving unparalleled levels of brightness in the focused beam. This leads to unrivalled performance in areas such as the fine cutting of stents in the medical industry (where kerf widths down <12um have been demonstrated).

In high precision welding applications, as required in medical device manufacturing, the same performance allows superior weld results to be produced at lower power levels. The focused beam consistently affects a very small area of metal, with the benefit that very little heat is generated around the weld point. This way, high quality precision welding can be performed close to the most complicated and intricate component parts.

In some processing applications, the near ideal Gaussian mode shape of the beam may not be the preferred solution. In these cases, the output mode profile can be tailored to the application requirement by careful design of the optical fiber guiding properties. SPI is developing a range of products in which the beam profile is optimized for specific welding applications.

Range and Versatility

SPI’s R4 CW-M high power lasers are designed for operation in either continuous wave (CW), or modulated operation in which the laser is turned on or off by a TTL drive signal from a signal generator. This mode of operation means the laser can be modulated at frequencies up to 100kHz, with pulse widths as low as ~2uS. This gives the user an extensive process window in which the operating conditions of the laser can be optimized for a wide range of processes. To illustrate this versatility in performance, take a 200W laser as an example. At one extreme, the laser is capable of continuous seam welding at 200W output power; however, when using SPI’s Extended Performance Range (XPR) feature, the laser is also capable of producing stable pulse energies down to 0.02mJ.

 A further example of this range and versatility is the proven ability to use the same 100W aircooled laser for diverse applications, including seam welding, fine cutting, machining, spot welding, and extremely high sensitivity operations, such as fine wire end balling, cutting or shaping. The laser can be seamlessly switched between the different operating conditions for all these processes, by simply changing the laser setpoint and modulation pattern.

This versatility arises from the fact that fiber lasers do not exhibit the shortcomings in output power variation and spot size and focal point variations caused by thermal effects on the glass rods of traditional YAG lasers. Fiber lasers offer true consistency at all power levels, across all pulse sequences, and during the entire lifetime of the laser, the laser parameters remain both predictable and consistent. The reason for this is that the generation and transport of the laser beam to the work-piece takes place entirely within the confines of a single-mode fiber. The beam shaping provided by this fiber neither degrades over time, nor changes with laser power.

The fiber laser can also be configured for use in applications where the pulse shape is continuously varying with time, for example in controlling the cooling of weld pools, or in optimization of cutting parameters. For irregular pulse sequences, or single shot pulses, the pulse energy difference between the first and subsequent pulses can be minimized using SPI’s Pulse Shape Equalization (PSE) feature.

Speed and Stability

The high speed modulation capability and exceptional control stability of the laser, even as the average power of the laser is varied, has enabled productivity gains by a factor of two to four times to be made. This is both in the process cycle time and yield improvement in diverse fine cutting processes.

Similar improvements have also been demonstrated in spot welding applications where the main requirement is reproducibility. In a pulse to pulse stability test for a medical devices customer using 5mJ pulse energy, the energy of over 99.7% of all pulses was within 0.5% of the mean. Having the laser as a stable tool allows greater tolerances within tooling and materials, leading to a lower spread in general weld characteristics and tensile strength.

The unique capability of SPI’s lasers to operate under closed loop control and provide high speed peak, or average power readback, during processing enables a level of reproducibility and long term process stability previously possible only with extensive process engineering effort. The effectiveness of the closed loop control system is demonstrated by the ability to keep the laser output power variation to less than +/- 1% over the full operating temperature range of the laser.

Industry Standards

SPI’s R4 CW-M High Power Fiber Lasers have been designed as robust manufacturing platforms for industrial environments. Third party approvals to internationally recognized standards have been carried out for electrical safety, laser safety, and EMC. The dual redundancy safety interlock circuit has been assessed to be compliant with the highest level of safety requirements. The system can be fully controlled and monitored by using either an external analog/digital port, or a high speed computer control interface with options to operate using RS232, USB, CANbus or Ethernet communications.

Summary

Over recent years, fiber lasers have proven themselves to be a reliable and enabling technology in highly diverse manufacturing environments. The R-4 products found in SPI’s portfolio have been designed to incorporate the latest technology improvements and customer feedback, to ensure that the product platform provides the best performance available from a highly versatile manufacturing laser tool in an industrial environment.

  

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