Milestones in industrial laser materials processing
ILS recognizes the top ten industrial laser applications developed in the first 50 years of laser technology
David A. Belforte
ILS recognizes the top ten industrial laser applications developed in the first 50 years of laser technology
|FIGURE 1. Early miniature electrical relay can (Raytheon Company)|
The first two choices, and the earliest in market commercialization, were developed as commercial processes almost simultaneously in the very early 1970s, and both were driven by the U.S. government’s NASA space program. The need: miniaturize electronic components that were to be lifted into space.
Hermetic sealing of electronic relays, driven by an industry need for miniaturized electronic circuitry, was commercialized in the period 1973–75 by several U.S. laser companies: Raytheon, GTE Sylvania, Holobeam, and Korad (all no longer in the laser business) all competing for early equipment orders from defense and NASA subcontractors. These companies were commercializing their scientific pulsed Nd:YAG laser developments, and the use of a finely focused beam sequenced to produce overlapping spot welds on the edges of thin-walled relay packages (see FIGURE 1) to produce a hermetic seal in a controlled atmosphere system was a perfect application for the low total heat input of a laser weld.
|FIGURE 2. Laser drilling and scribing of ceramic substrates (Lumonics)|
The first commercial sales of these laser systems occurred in 1973, and laser sealing of hermetic packages became a major business leading to today’ solid-state laser sealing of implantable hermetically sealed medical devices. This application spawned: more reliable Nd:YAG lasers, precision motion systems, and computer process control. And, more to the point, whetted equipment suppliers’ thinking about producing equipment that could survive in an industrial setting
Not enough can be said about the role that laser hermetic sealing played in the initiation and growth of the industrial laser business. Prior to the establishment of this application, lasers had a reputation as being laboratory devices looking for a commercial market and equipment suppliers were simply placing these laboratory devices in industrial settings. This quickly changed as the suppliers developed industrialized units that could withstand the rigors of multi-shift manufacturing operations. Industrial laser hermetic sealing along with the next application provided the foundation for today’s multi-billion dollar industrial laser market.
Ceramic substrate scribing
|FIGURE 3. Laser cutting of stainless steel in a UK job shop (Ferranti Ltd.)|
The same demand for lightweight, miniaturized electronics created the need for smaller microelectronic substrate materials on which complex hybrid semiconductor circuitry could be deposited. The material of choice was a thin high-purity fired alumina in a size that could be easily handled in a production environment. After the circuits were deposited the ceramic was divided by scribing a series of small holes around the edges of the chip, using a pulsed CO2 laser. After scribing an operator snapped the parts apart for further assembly operations.
Western Electric in the U.S. advanced the technology of the process in 1968, and by 1970 Coherent Inc. was selling low-power CO2 lasers for these applications. In late 1970 Lasermation, a Philadelphia job shop, made its first sale of scribed ceramic hybrid circuits to Bell Telephone. Within a year Lasermation was selling these scribed substrates to more than 100 of the top electronic firms in the U.S. By 1974 it was estimated that two billion scribe holes per day were being drilled. Ceramic manufacturers like Coors (U.S.) became heavy users of the laser scribing process, and by the end of the decade numerous contract processing shops were filling massive orders for scribed substrates. In the late 1970s and early 1980s more than a dozen job shops in the U.S. were processing hundreds of thousands of substrates every year.
Millions of these substrates have been processed since then, mainly in contract processing shops. One of the leading shops in this industry Laserage Technology Corp., founded in 1979, developed a laser drilling process that allowed through holes for electrical leads to be processed in high volumes (see FIGURE 2). Equipment suppliers such as Photon Sources developed better control hardware and software so that users such as Laserage could employ multi-beam processing where beamsplitting into four processing beams improved production throughput. From the application, advancements in laser design, beam splitting to increase productivity, effluent control, and precision high-speed motion systems developed.
|FIGURE 4. Ruby laser drilling of a turbine blade (General Electric)|
A subset of this application scribing silicon wafers, using Nd:YAG lasers sprang up in 1970 with the introduction of a system by Quantronix that employed a concept developed in 1968 at Bell Laboratories. The difference in the two processes is that wafer cutting used a continuous fine line groove whereas the alumina process uses discreetly spaced drilled holes. Both processes rely on manual separation of the scribed product.
Sheet metal cutting
The British invention of the gas jet assist nozzle by Sullivan and Houldcroft in 1967, combined with the initial acceptance of the laser as a metal cutting tool in 1970 was precursor to the establishment of a laser application that has grown to be the largest revenue source for industrial laser systems manufacturers today. The nozzles developed at The Welding Institute (UK) were commercialized and introduced to potential industrial users on laser systems built by Messer Greisheim (Germany) and British Oxygen Company (UK) and powered by 400W semi-sealed CO2 lasers from Ferranti (UK). Subsequently the laser power was increased to 1kW and the first installation at a fabricating shop outside Birmingham, England, opened the door for this application’s growth in job shops (see FIGURE 3). Since the initial installations more than 75,000 of these sheet metal cutting systems have been installed globally with an estimated total current value of more than $45 billion. Laser sheet metal cutting is now the most widely used global application for high-power industrial lasers.
One of the major contributions from Japan resulted from developments at Amada in 1985 that led to a “Clean Cut” finish that produced a non-oxidized cut in 3mm stainless steel on a system shipped in 1986. Subsequently TRUMPF developed inert gas (fusion) cutting with its RF-excited CO2 laser in Germany later in that decade. These processes and others opened the door for high-quality metal cutting, without secondary operations, a major industry advance.
The laser metal cutting system suppliers are responsible for many technology advances used widely in other applications by other industries. Among these are coaxial gas jet nozzles, automatic height sensing and focus head breakaway devices, PC control of the laser and the cutting process, non-reactive gas assist cutting of non-ferrous metals, high-speed linear motion systems, higher power and more reliable CO2 lasers especially RF-excited and sealed-off units, tele-servicing field support, high-speed shuttle tables and storage towers for raw stock, automatic nozzle cleaning, quick change cutting heads, and a multitude of other system and processing advancements.
|FIGURE 5. Laser welded zinc coated automobile underbody (Rofin Sinar)|
Laser sheet metal cutting is the largest revenue producer for industrial laser systems with more than half of annual revenues generated by this application.
Drilling of turbine blades
The first practical, value-added industrial application for the ruby laser invented by Ted Maiman was the drilling of cooling holes in aircraft engine turbine blades. As the operating temperature of these engines increased it was necessary to find a way to cool the blades to prevent thermal damage. Drilling of a series of small holes to allow a film of cooling air to flow over the surface of the blade was accomplished at General Electric in 1970 by a pulsed ruby laser system from a U.S. company SpaceRays and in 1974 multiple ruby laser systems from Raytheon (see FIGURE 4). The ruby laser with its spiky energy output was a perfect small hole driller, its only drawback being a slow pulse repetition rate. This laser was subsequently replaced by Nd:YAG lasers from Raytheon, with higher peak power and faster repetition rates, which became the laser of choice for this application.
The equipment supplier industry developed new, more efficient solid-state lasers and multi-axis computer-controlled processing systems because the laser drilling process brought challenges to the development of pulsed solid-state lasers. Drilling of crack-sensitive materials calls for pulse shaping to control the heat input and the percussion drilling technique which produces narrow, smooth deep holes required well defined energy intensity distribution in round beams.
Since the first commercial installations in the early 1970s more than 600 automated laser systems have been installed in OEM locations and primarily in subcontractor plants.
This application provided the impetus for many laser technology spin-offs including brighter lasers, more reliable first-shot lasers, precision multi-axis positioning systems, fast and accurate exchange of fixtures, computer control of beam focus, percussion and trepan drilling processes, break-through detection to prevent back wall strike, shaped hole drilling procedures, and on-the-fly hole drilling
Tailored blank welding
|FIGURE 6. Close-up of laser cut stainless-steel tubular stent (Synova)|
High-power CO2 lasers with good beam quality and reliable output power were the laser of choice for the joining of sheets of steel that are used in automotive body manufacturing. Although the first laser blank weld was done experimentally for British Leyland in 1981 it was the 1983 application for German auto manufacturer Audi who had need for sheets of metal large enough to be stamped into a limousine underbody that lays rightful claim as the first production laser welded blank. No required sheet sizes were available from German steel mills so Thyssen Steel using a Rofin Sinar 1.5 kW CO2 laser welded two pieces of available size sheet to make the needed size for stamping (see FIGURE 5). Thus was born the laser tailored blank welding business, which today finds laser tailored blank components used by auto manufacturers worldwide.
In 1984 Toyota stunned the rest of the global auto industry with the introduction of a laser welded five-piece body side ring for the Camry, which allowed a choice of metal thicknesses to reduce weight and consequently improve fuel economy. As the auto industry’s annual demands for tailored blank components increased an increasing number of new blank supplying subcontractors appeared and they asked for and received units with higher power (to 8kW) CO2 lasers.
The contribution of laser welded blanks to the design and production of lighter weight and more energy efficient vehicles is immense. The ability to mix steel materials and thicknesses has allowed designers to greatly improve body design and to minimize the number of components needed to meet strict crash standards.
With the introduction of high-power (>4 kW) diode-pumped Nd:YAG and fiber lasers a new generation of welding systems is now being installed in developing markets. To date more than 400 units with a value of more than $2 billion have been installed in the world’s auto assembly plant locations. The tailored blank welding application led to the development of on-line weld monitors, beam quality devices, improved beam quality lasers, and robot/laser systems.
The use of laser welded blanks has grown every year since 1984. For example since 2000 an estimated 1.8 billion tailored blanks have been fabricated worldwide. One U.S. supplier had produced, through 2008, up to 90 million laser welded blanks for 50 vehicle platforms over a 17-year period.
The fine focusability of laser beams is attractive in microprocessing applications. An outstanding example—and one that revolutionized an industry so much so that it became the process of choice as world demand increased—is laser cutting of stents (see FIGURE 6), which started in 1992. In 1993–94 a Lumonics low divergence Nd:YAG laser produced limited success cutting stents and was later replaced by a Lasag unit, which became a commonly used laser for this application.
A stent is a machined structure that is inserted into the veins of a human after a clogged vein or artery is repaired by balloon angioplasty. Stents are laser cut from thin-walled tubing so that they retain strength while they are reduced in weight by having excess metal removed by laser cutting. The laser of choice to reduce residual heat affects and to cut with a burr-free edge in a convoluted pattern set by the designer is a pulsed solid-state device, most often a pulsed Nd:YAG.
Stent cutting, now a major application in the medical devices industry, has been a driver in the introduction of quality, reliable industrial lasers and motion control systems. Flashlamp pumped Nd:YAG lasers were succeeded by diode-pumped units, then disc and fiber lasers, the latter currently the choice for this application. Advanced laser technology in the form of picosecond and femtosecond lasers are being considered for use with the new bioabsorbable stents. Today tens of thousands of stents have been produced worldwide.
|FIGURE 7. Miscellaneous parts produced by rapid prototyping (DTM)|
This application led to the development of higher reliability, stable pulse-to-pulse, and better beam quality solid-state lasers, more sophisticated control of assist gases, simpler and more powerful process and control software, and automatic load/unload devices.
The technology of rapid prototyping or rapid manufacturing, now known as Additive Manufacturing (AM) can be traced back to 1987 when the first commercial StereoLithography Apparatus (SLA) was patented and introduced by 3D Systems in California. In this process the beam from an infrared laser is scanned by computer control across a field of powdered photo-curable resin melting then hardening the powder in a mass that represents a two-dimensional cut through a three-dimensional part. Successive layers are formed, eventually producing a three-dimensional part (see FIGURE 7).
|FIGURE 8. Drilling 25µ vias in MCMs (Lumonics)|
Several competing techniques evolved by 1990: selective laser sintering, laminated object manufacturing, etc., which competed in a developing service industry market. Eventually original equipment manufacturers accepted the technology especially when the material used in SLS and SLM improved to allow the production of prototype parts. As a consequence the technology evolved into Rapid Manufacturing where it enjoys its greatest acceptance by industry. Advances in the technology now enable users to produce parts made of plastics, metals, ceramics, and composites. Today laser sintering systems are available from two dozen international suppliers, and a number of Asian companies offer stereolithography systems. It is estimated that several thousand rapid prototyping and manufacturing units have been installed worldwide.
Terry Wohlers, an authority on the technology estimates that 2008 revenues for laser-based Additive Manufacturing products and services totaled more than $700 million.
Whereas service providers were the earliest implementers of the AM technology, today this work is mainly being done in-house at the large companies.
Wohlers estimates there are several countries with annual installations of 100 or more AM units with strong double-digit growth in China (now with more than 2400 units installed), France, Germany, and the UK. Countries just beginning to accept the technology such as Brazil, Mexico, and Thailand enjoyed 75–100% growth in units installed in 2008.
This application produced stable, reliable, low-cost solid-state and low-power CO2 lasers, powerful CAD systems compatible with beam and part motion systems, and spawned a new generation of laser processable polymers and powdered metals used to produce the parts.
A via is a hole drilled into a thick-film dielectric that has been deposited on a multi-level substrate such that electrical contact can be made between levels. In a 1971 paper by engineers at Western Electric in the U.S. a process was described using a Coherent CO2 laser to drill small holes in ceramics to produce a conducting path, an early via drilling application. By 1974 Western Electric had installed CO2 via drilling systems from Photon Sources in its Andover, MA, plant where vias were drilled in thin film, bi-level circuits.
From this pioneering installation an industry, micro-via drilling, was born that involved the installation of hundreds of CO2, solid-state, and excimer laser drilling systems in microelectronics plants located around the world, drilling millions of holes annually. FIGURE 8 shows 25 µ blind vias drilled in MCMs.
The success of this application contributed to technology advances such as CO2 laser beamsplitting (up to four beams from one laser), parallel processing systems, more stable and reliable pulsed CO2 lasers, gas assist nozzles to prevent lens contamination, and automated load/unload devices to improve productivity. This application was one of the first that required three shifts per day system utilization using low-level skill operators.
Laser marking/engraving is the largest application for industrial lasers, in terms of units installed, with tens of thousands of units installed around the world. In the mid 1960s laser manufacturers and their user customers were experimenting with block character engraving by moving the workpiece in the X and Y directions under a fixed laser beam. Laser marking, through the use of galvo scanned Nd:YAG laser beams, can be traced back to 1973 when Korad built a system to mark watt meter faceplates, using a CW 5 W tungsten-halogen laser, General Scanning galvo scan technology, a Carl Zeiss flat field lens and a PDP8 minicomputer. In 1974 Control Laser (Orlando, Florida) delivered a wafer marker with a 30W q-switched Nd:YAG laser and a Siemens S319 computer.
Several other pioneer laser suppliers had successes with serial number marking for anti-theft applications. One of the first notable applications was the use of an Nd:YAG laser marker to engrave a serial number on the inside of an electric typewriter chassis in a location inaccessible to a grinding tool that might have been used to remove the ID number. The user improved the quality and permanence of the mark, increased production rates, and eliminated a manual die stamping operation. These characteristics of laser marking were common to many of the succeeding laser marking applications, for example the metal hip joint (see FIGURE 9) that is custom marked for warranty and traceability procedures, and even today remain among the prime reasons for choosing this technology. The first market of consequence occurred in 1978 when Control Laser received an order for 150 lasers to mark carbide tool tips and saw blades. In 1982 Baasel Lasertech showed the first 50 W Nd:YAG laser engraving marker at the Hannover Fair.
|FIGURE 9. Laser engraved mode marking of artificial hip joint (Quantrad)|
Concurrent with the laser marking development was the beginnings of the laser engraving market, when in 1973 engineers at Optical Engineering in California created stencil masks that could be scanned by a CO2 laser beam to replicate the mask image on a piece of wood.
From this work a new market—wood engraving award plaques and giftware—developed, leading to the creation of an industry supplying low-cost engraving systems that can be used in start-up businesses. Today tens of thousands of these units are used in the world’s engraving industry.
Laser marking/engraving spun off as myriad laser and technology advances; improved, low maintenance lasers, low-power fiber lasers, user-friendly software for programming, high-speed galvos, and chemical additives for color marking. The process of 2D matrix code marking has revolutionized traceability applications, especially in the fields of ID card manufacture.
The marking/engraving applications were the driving force behind the development of the most reliable laser systems available in the last two decades. Setting a standard for long-lived production use created the first laser “commodity.” Today a $700 million annual market for laser marking systems continues to grow at 20% per year as the laser is now the choice for serialization and traceability to meet security regulations.
The first reported use of a laser to trim a microcircuit to meet electrical performance requirements was reported by Bell Laboratories in the U.S. in the late 1960s. In 1971 Motorola, using a Korad Nd:YAG and a Coherent CO2 laser, performed some of the early development work in circuit adjustment by laser trimming. And in 1972 Teledyne and in 1973 Quantronix both promoted laser trimming systems. An early automated trimming system from ESI is shown in FIGURE 10.
FIGURE 10. Nd:YAG laser trimming of resistive material (ESI)
The process uses a focused laser beam to remove by evaporation a section of a deposited circuit such that a redundant circuit can replace the one cut from the circuit to bring the electrical characteristics of the circuit into conformance with restrictive design requirements.
From this early work sprung an industry that created new technology in probe measurement, wafer and chip handling, and CNC control of the laser and the process. Since this early start thousands of sophisticated circuit trimmers have been installed and today several companies continue to ship equipment around the world.
From the early days of the market about 5000 laser trimmers have been installed worldwide with a market value approaching $600 million.
Among the significant materials processing applications that were also considered for this highlights selection were: welding aluminum window spacers, cutting wooden die boards, custom cutting of men’s suits, welding the Gillette razor blade, and laser welding and brazing of automobile bodies-in-white. Each of these broke new ground for the design of automated laser processing systems and by their use revolutionized the industries in which they were installed. They did not make the cut for highlights choice because of the smaller number of units sold. This does not diminish the contributions that these and other applications made to the technology of industrial laser materials processing but, as we prefaced this article, rigid criteria were established so that the choices could be narrowed to ten.
ILS estimates that more than 420,000 industrial lasers worth more than $18 billion have been installed in the world’s manufacturing industries. This is a formidable number whose roots can be traced back, in great part, to the pioneering applications cited in this article. And it would be remiss of us to not acknowledge the contributions of the process and equipment developers responsible for these successes and to those “risk takers” who purchased the early systems.