Integrated laser systems deliver solutions
Multi-axis laser technology has a reputation for pushing the envelope in tackling the most challenging fabrication problems.
LAI International is a strategic supplier of precision components and sub-assemblies for OEMs. For over 30 years chief technology officer Eric Nelson has used Laserdyne multi-axis laser technology for the most difficult aerospace and power generation applications. Along the way, he has literally done it all - from pioneering the use of factory rebuilt systems, to beta testing and offering suggestions for developing hardware and software features which have become standard offering, to routinely increasing productivity and quality with the laser systems he uses.
‘We operate seven multi-axis laser systems here in Maine’ he says; ‘five Laserdyne 780 BeamDirectors and two 890 BeamDirectors. All are refurbished systems which we regularly upgrade with Laserdyne’s new software and hardware, so that functionally they have the capabilities of new machines.’ Early use of the latest improvements, he says, underpins service to customers such as General Electric and Pratt & Whitney with the most productive and highest quality processes: ‘We produce the really difficult parts efficiently for them.’
LAI also operates three Laserdyne systems with 94W laser process controls at its Tucson factory. The workstations can handle rotary parts up to 48” diameter, pre-formed parts up to 24” high, and materials thicknesses from the thinnest gauges to 1”. ‘We employ percussion, trepanning and drill-on-the-fly laser drilling techniques for effusion cooling holes as well as full 5-axis laser cutting on the pre-formed parts our customers supply,’ says Mike Grantham, Technical Director, LAI Southwestern Laser. ‘This facility can drill holes as small as 0.005” in diameter at angles from 20o to 90o to the surface.’
High productivity and accuracy
Rich Technology International (RTI) is a diversified contract manufacturer and one of the five LAI sites dedicated to precision parts and assemblies for the aircraft, power generation and defence industries. With its laser systems, RTI specialises in high volume work in difficult materials such as Inconel, stainless steel, super-cobalt alloy, hybrid nickel, chrome steel and Hastelloy X. 50% of laser work is for aerospace; 50% for land-based turbines, and some of it cannot be done efficiently using processes such as EDM or waterjet machining. The laser work can call for drilling thousands of holes in a single part, everything from 0.003” diameter rounds, to percussion drilling and trepanning special shapes. Drilling angles range from 90 o to as low as 10 o to the surface.
A typical job - spacer bands for land-based turbines - requires laser cutting a series of accurately spaced complex profiles along the part contour. Part runs for this job average 40-50 sets a week using one of the refurbished Laserdyne BeamDirector systems equipped with a 3000 Watt CO2 laser. The material is 440 stainless steel with a chrome additive - a very hard material - processed efficiently on the system with consistently smooth, burr-free edges. Accuracies are 0.004” true position total tolerance for the special airfoil shape and speeds are relatively fast considering the geometry of the part features, reports Nelson.
‘Achieving this level of productivity and accuracies from one job to another is possible because of how Laserdyne designs and integrates its system features,’he says; ‘everything works perfectly together - the controller, software, motors, laser - because everything is Laserdyne’s design and manufacture.’ A good example is Automatic Focus Control (AFC). Nelson trusts the system; it’s one which his feedback has helped refine. AFC guides the motion system, maintaining critical focus position and following the contour of the part regardless of slight surface irregularities. With AFC, all machine axes react to sensing of the part surface, creating unlimited R-axis correction with high speed and unmatched sensitivity. AFC allows top machine speeds so productivity is maximized without downtime or scrapped parts.
LAI uses trepanning, percussion drilling, and drill-on-the-fly laser processing techniques in which the AFC feature is extremely important in the laser drilling processes. Trepanning is a process for creating holes where the part is held stationary and the laser beam is moved with simultaneous multiple action motion to create a round hole or any feature by cutting the periphery of the shape. Accurate and repeatable laser positioning systems allow tight tolerance trepanned features. In contrast, percussion drilling delivers one or more pulses from the laser to a part while the laser beam and part are stationary. More than one pulse may be required depending on the material type and thickness.
A variation of percussion drilling is ‘drill-on-the fly’ where pulses are delivered to the part by the stationary laser while the part is rotated. The hole placement is a function of rotational speed and laser pulse frequency. If multiple pulses are required, special software synchronises the movement of the part to the laser pulses, ensuring that multiple pulses are delivered to the exact location required. By changing the laser pulse energy, pulse count or lens focal length, the characteristics of the drilled hole size and taper can be controlled to meet the requirements of the part. The software also allows changes of the pulse shape during the process to improve hole geometry.
Modules work together
‘System repeatability (±0.0001”) really comes into play on our jobs’ says Eric Nelson. Our 890 and 780 BeamDirectors with their AFC features are designed so we maintain extremely good accuracy with consistency through the entire work envelope.’ He goes on to reflect on his penchant for Laserdyne, explaining that when multi-axis laser began in the 1980s, it was the only manufacturer which offered systems with fully integrated software and hardware components of its own exclusive design and manufacture. ‘All of the modules work together the way they should and if there’s a problem or an opportunity to improve the process, there is one point of responsibility to get it right. It’s key to doing the best work, the real reason we are able to push the technology edge and do multi-axis laser work where alternative processes and systems either have limitations or just won't do the job.’
Peter Thompson, Technical Director of Laserdyne, explains his company’s approach to integrating all system components: ‘We learned in the early days that the key to getting the most from multi-axis laser processing required integrating the laser, motion system and control, user interface, and process sensors. The only way to do that was to design, manufacture, and integrate all of these components ourselves in the system. Our goal has always been to provide systems that were capable of the finest precision laser processing. Designing and manufacturing all of the major components of the system also allows us to introduce technology as it becomes available and to more tightly integrate the various components. The end result is superior process capability and control.
‘Drilling with today’s systems integrates the optics of the laser with sensors in the machine tool structure and with the motion system; all are optimised for the work required of multi-axis laser processing. Remember, there are no significant tool forces with multi axis laser processing and especially laser drilling. Without precise control over key components, it would be difficult for users like LAI International to achieve the performance levels, the speeds and quality our systems deliver. The performance LAI is achieving is just too difficult to accomplish by ‘bolting together’ a collection of commercially off-the-shelf components. That is why we refer to our products as systems’ and not just lasers or machine tools.’
Smaller aircraft engine components
With equipment options that include waterjet and EDM, Nelson’s preference for laser drilling aircraft vane sector components is a Laserdyne system with a BeamDirector because it provides higher feed rates and is more accurate. In the job pictured, the Inconel part sets up quickly with minimal clamping pressure. Multi-axis laser machining is essentially a non-contact process so highly rigid part clamping is not required. Using an updated 780 BeamDirector equipped with a 1500 Watt CO2 laser, 1500 to 2000 of these parts are laser processed at LAI, week after week, with only minimal operator adjustments.
Repeatability like this with positioning accuracy is a cumulative result of many factors working together that affect the overall laser system’s accuracy and the quality of the parts produced. Even system frames have an important influence on the successful integration of system components. The bases of the 780 and 890 BeamDirector systems are carefully engineered foundations on which integrated accuracy features have been built. Most laser machining systems are not rigid enough to isolate and eliminate the vibrations induced by continuous back and forth movement of a few thousandths of an inch necessary in many of our projects, says Nelson.
‘The multi-axis laser stands out as a unique manufacturing system in today’s broad array of fabricating systems,’ says Eric Nelson. ‘Getting the most out of a machine is one thing. Getting the most out of an entire manufacturing technology is something else. And it is much more challenging today because part features, hole configuration and size, material difficulty, speed and quality required have exceeded anything thought possible even just a few years ago, let alone when this all began in the mid-1980’s.’
