Mechanical wire strippers use sharpened steel blades to cut through and remove insulation. Although most systems offer fine blade adjustment and positive stops, damage to conductors such as combed, pulled, scraped, cut, nicked or "bird-caged" strands is inevitable.

Thermal stripping devices are costly to operate due to the high electrical consumption of the heater element. Additionally, thermal stripping is plagued with issues such as excessive edge flash, irregular transitions, and burned, melted and charred insulation. It also can leave dielectric residue on the conductors, which can adversely affect electrical conductivity through the termination of the wire.

Chemical stripping is governed by strict regulations that control worker safety, air and water quality. The chemicals need to be handled carefully and disposed of as hazardous waste, all adding cost to the process.

The "new mousetrap" for wire stripping is the application of a precisely controlled laser beam, which vaporizes wire insulation with absolutely no chance of damaging the critical underlying electrical conductors. There are no blades to replace, no high electrical current requirements and no hazardous chemicals to dispose of. Laser wire stripping improves the quality and reliability of wire stripping by selectively removing the dielectric insulation and adhesives that envelope a wire. In fact, laser wire stripping is the most precise stripping method available.

The use of lasers for removing wire insulation was developed in 1976 by the National Aeronautics and Space Administration (NASA) to satisfy its requirements for precision wire stripping. While the advantages of this technology were significant, general industrial use was limited, primarily because traditional methods were adequate, at the time, for most wire stripping needs. As consumers became more reliant on smaller, more complex electrical devices, the standards for wire stripping became stricter. Engineers can no longer afford to design wire assemblies with oversized conductors to compensate for damage caused by inferior wire stripping processes, as this adds weight and cost to the product.

Spectrum Technologies introduced the first commercial infrared CO2 laser wire stripping machine in 1987. Since the introduction of this first machine, laser wire stripping has been increasingly embraced, and a wide range of standard systems has been developed to accommodate the various needs of the wire processing industry.

A laser wire stripper consists of a laser, optical system, controls, application tooling and safety devices to protect the operator and those working around the equipment.

Although there are laser options available for specialty stripping, such as Nd:YAG and excimer lasers, the CO2 laser produces the ideal wavelength of laser light for stripping most wire insulations. This wavelength (10.6 microns) is absorbed by the wire insulation, which vaporizes. However, the wavelength is reflected by the metal wire conductors, making the process self-terminating and eliminating the need for process controls to prevent conductor damage.

To precisely control the laser beam, and ensure maximum productivity and versatility, the optical system is usually mounted on a single- or double-axis positioning device. The optical system directs the laser beam, through two opposed focusing heads, across a wire or wires that are held stationary. Depending on the application, the system can also be designed to move the wire relative to a stationary laser beam, or it could rotate the beam around the circumference of the wire.

Depending on the type of laser, process parameters consist of laser power, beam pulsation and the speed at which the laser beam passes over the insulation. Through the system's microprocessor-based controls, or an optional PC interface, these process parameters can be adjusted to selectively cut through one layer of insulation while leaving an underlying, second layer, virtually untouched. Although the laser energy is absorbed into the wire insulations, it is reflected by the metal conductors, and causes no damage to either the metal conductors or their plating. After the laser cuts through the insulation, the remaining slug is easily removed. At this point the wire is ready for electrical termination.

All laser stripping machines are equipped with safety covers to keep laser radiation from escaping. Interlock switches prevent operation of the machine if the cover is not in place. An air filtration unit extracts the fumes from the vaporized insulation.

Applying the Laser

Many products are manufactured using laser wire stripping equipment, including pacemakers, cell phones, medical ultrasound devices, laptop computers, automotive components, server interconnections, medical guide wires, hard drives, satellites and aircraft.

Compared with other wire processing methods, lasers offer many advantages. One is flexibility. Laser wire stripping equipment can remove insulation from single-core wire; twin leads; twisted pairs; multiconductor cables; shielded and screened wire and cable; ribbon cable; coaxial cable; and complex 2D- and 3D-shaped conductors, such as coils. In addition, laser wire strippers can process a wide range of wire sizes with no tool changes. They can strip wire sizes from less than 0.001 inch OD (50 AWG) to 1 inch OD. They can also process ribbon and flat cable up to 11.4 inches wide.

Laser strippers can process 99 percent of all insulation materials, including Teflon, silicone, polyvinyl chloride, Kapton, Mylar, Kynar, fiberglass, nylon, polyurethane, Formvar, polyester, polyesterimide, epoxy, enameled coatings, ETFE, Milene, polyethylene, polyimide and polyvinylidene fluoride.

Because laser wire stripping is a noncontact process and the beam can be controlled very precisely, it is possible to produce a variety of stripping patterns, many of which are virtually impossible by other means. For example, removing sections of insulation in ribbon cable, called window stripping, is nearly impossible using traditional stripping technologies. However, it is easily accomplished with laser wire stripping. A dual-axis laser wire stripping system can produce end strips; center strips; crosscuts; crosscuts with slits; jumpers; mini windows; and angled cuts. Variable strip patterns can be programmed to remove the insulation at any location on the wire.

In a low-volume operation, wires are cut to length and either inserted into the machine one at a time, or loaded into a custom nest so that multiple wires can be processed simultaneously. A typical system can move the laser across a width of 2.7 inches. To put that in perspective, a 20 AWG wire has a diameter of approximately 0.06 inch. Thus, up to 45 of these wires can presented side-by-side and processed at the same time. Excluding loading an unloading time, the time to process all 45 wires simultaneously would be less than 10 seconds.

To further increase productivity, an automatic wire handling unit can be added to feed, measure and cut the wire, while the laser stripper cuts through the insulation. Combined, the two machines can process well over 100 wires per minute.

Perhaps the biggest advantage of laser wire stripping is quality. Lasers produce the highest achievable strip quality, which guarantees reproducible results, maximizes yields and reduces costs. For precision applications, stripping can be done to a tolerance of ±0.001 inch. The laser will not damage the metal conductor even if it is plated with another metal such as tin or silver. The technology satisfies the stringent requirements for conductor damage set by NASA and the Federal Aviation Administration.

Laser wire stripping is used to produce some of the world's highest quality and most reliable electrical devices. As industry continues to develop new insulations and new processes to apply these materials, laser wire stripping will continue to be a leading wire stripping process.

For more information about laser wire stripping, call Spectrum Technologies at 602-493-9343 or visit www.spectrumtech.com.