| Laser material processing and Intelligent Energy Field Manufacturing |
| Lasers play an increasingly important role in modern science and engineering. To better uncover lasers' potential, laser energy should be treated as a common energy field used in engineering. This paper will reflect on the process of liquid core fiber laser machining, followed by a brief introduction on the methodology of Intelligent Energy Field Manufacturing. Finally, future trends in laser material processing will be discussed. Lasers are an amazing tool, but marketwise, they have not reached our expectations.
2010 marked the 50th anniversary of the first functioning laser. Laser energy is amazing in many ways. It can be highly collimated; thus, one can send a signal to the moon and still measure the reflected signal. It is monochromatic, which allows it to be used in precision metrology. It can easily be focused down to sub-100 micron spot sizes or operated on the femtosecond (10-15 s) time scale, which enables an individual laser pulse to locally exceed the material damage threshold and be used for material processing. Multiple laser beams can be combined into a single beam so that the resultant beam can be used to study nuclear fusion in the national labs. Beyond these facts, the military has recently used lasers to test the missile defense system, and optical fiber-based communication has enabled a flatter world.
There are plenty of achievements one should feel proud of in laser technology. For laser material processing in particular, few other energy forms can compare with laser in its versatility, its flexibility, its quality, or its spatial resolution. Laser is a source for concentrated and coherent photon energy. As long as the laser energy can be absorbed by a target material, this target will be heated or ablated independent of how hard it is or how soft it is. To attain the required spatial resolution, one can use ultraviolet (UV) or infrared (IR) laser beam or femtosecond pulse durations to achieve millimeter to nanometer spot sizes. When processing speed is needed, one can use high power and/or high repetition rate systems. With this versatility, it is not surprising that laser processing has achieved widespread applications in cutting, welding, marking, drilling, and surface texturing. There are also other applications that have shown the laser to be a very competitive tool to accomplish improved speed and quality in three-dimensional (3D) manufacturing, surface treatment, and surface cleaning.
Given its flexibility, laser still has not penetrated into many adjacent arenas. While the world laser market is expected to reach 8 billion in 2012 according to a recent projection from Photonics West 2011, what is limiting the speed of market penetration?
One potential factor affecting the speed may be that the cost of implementing laser technology is high, both financially and in terms of the skills required to develop and insert laser solutions into production. In addition, the broader laser community has often been accused of not aligning either laser technology or laser processing solutions with customer needs.
The laser lab in GE Global Research serves all of the GE businesses, including GE Aviation, GE Energy, GE Oil & Gas, and GE Healthcare. Based on experience working with such a diverse customer base, lasers often compete against more mature, often less expensive processes. As a result, laser-based solutions are most successful when they accomplish a goal that cannot be reached another way. In the following, two illustrative examples of how lasers have fared against competing technologies – laser hole drilling of acoustic panels and laser dicing of cadmium zinc telluride (CZT) wafers – will be discussed.
Reflection on laser acoustic hole drilling
In 2005, the laser lab was approached to investigate the feasibility of high speed drilling of composite acoustic panels. These holes are used as damping structures in aircraft engines. In an acoustic panel, there can be as many as 500,000 holes that have to be drilled into the 0.09 inch thick polymer matrix composite (PMC) panels. With a special CNC machine, one can drill ~2 holes per second when multiple drill heads are used. The process that is used induces substantial tool wear and generates back side delamination. Additionally, the drill bits used to produce these holes have to be replaced approximately every 200 holes.
Using lasers, it was possible to demonstrate suitable hole drilling quality at a rate of 2.2 holes per second. So, lasers could drill at comparable speed to the conventional process and demonstrated negligible tool wear and heat affected zones. Unfortunately, the process also induced discoloration on the samples, which the customer disliked. In addition, the substantiation procedure to qualify the laser process for production was lengthy. Also, the customer was concerned about practically implanting the technology.
In short, laser processing was still viewed as a "high risk" given that there was already a process that could do the job. Also, they did not have people trained to operate high power lasers. Thus, while laser drilling of acoustic holes showed good promise, it was not adopted as a solution yet.
One thing this example teaches about impediments to introducing laser material processing solutions is that the final technology decision is never a simple capital issue or process issue. It is always an engineering system issue involving more than laser process considerations. It is the total solution that competes against or works with other energy forms. As a result, an engineering system won't be complete unless one considers all of the system elements: energy, materials, information, people, and planning.
Just making better lasers is not sufficient. Neither is proving the feasibility of the laser process. One must instead prove that the engineering system, which includes laser material processing, is more competitive than other engineering systems to win the assignment.
This deficiency in systems thinking is not unique to laser materials processing. In fact, this attitude holds back many new innovative solutions with regard to other processes or solutions. Whenever one focuses solely on the process or technology or equipment in isolation rather than the benefit the user will experience, the full promise of the innovation will not be fulfilled. By contrast, when one views energy fields in tandem, a useful system solution emerges. Laser dicing of CZT wafers illustrates this point.
Liquid fiber based laser dicing of CZT wafers
This is a good example of the teamwork of energy fields to solve a challenging engineering task. Cadmium zinc telluride (CZT) is used as a nuclear detector material. A GE Global Research team was formed to develop a cost-effective CZT dicing process [1]. Single crystal CZT wafers are very expensive to grow. CZT is also prone to defect generation during crystal growth. As shown in FIGURE 1, the wafer has some good areas and some defective areas, as revealed by ultrasonic imaging. The marked squares are free from defects and are potential zones from which to dice the detector material.
Reference: http://www.industrial-lasers.com/
laser processing;hole drilling |
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江阴德力激光有限公司
