SAE AIR 6894-2016 Laser Wire Stripping Tools General Understanding.pdf

1、_ SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising there

2、from, is the sole responsibility of the user.” SAE reviews each technical report at least every five years at which time it may be revised, reaffirmed, stabilized, or cancelled. SAE invites your written comments and suggestions. Copyright 2016 SAE International All rights reserved. No part of this p

3、ublication may be reproduced, stored in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of SAE. TO PLACE A DOCUMENT ORDER: Tel: 877-606-7323 (inside USA and Canada) Tel: +1 724-776-497

4、0 (outside USA) Fax: 724-776-0790 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.org SAE values your input. To provide feedback on this Technical Report, please visit http:/www.sae.org/technical/standards/AIR6894 AEROSPACE INFORMATION REPORT AIR6894 Issued 2016-04 Laser Wire Stripping

5、Tools, General Understanding RATIONALE AS5768 specifies general wire stripping tools used to strip aerospace electric wire and cable. This SAE Aerospace Information Report (AIR) specifically deals with laser wire stripping tools and describes recommendations on their use and qualification. INTRODUCT

6、ION Laser wire stripping technology was introduced by NASA in 1976 to provide an alternative solution to mechanical wire strippers with no risk of nicking or scraping the conductor, therefore reducing quality-control constraints. This technique can be also advantageously applied to cut the outer jac

7、ket of shielded cables whose cross section is highly non circular. NASA has made use of Continuous-Wave (CW) CO2 and Nd: YAG lasers. The CO2 laser technology is now established in different application fields including aerospace. A new technology making use of semiconductor lasers is emerging. SAE I

8、NTERNATIONAL AIR6894 Page 2 of 13 TABLE OF CONTENTS 1. SCOPE 3 2. REFERENCES 3 2.1 Applicable Documents 3 2.1.1 SAE Publications . 3 2.2 Terms and Definitions . 3 3. LASER WIRE STRIPPING TOOLS AND TECHNOLOGIES 4 3.1 Introduction to Laser Wire Stripping 4 3.2 CO2 Laser Technology 4 3.3 Semiconductor

9、Lasers 4 3.4 Other . 4 4. PROCESS SAFETY 4 4.1 Integrity of the Metallic Conductor or Shield . 4 4.2 Shielded Cable - Integrity of the Inner Wire(s) Insulation . 5 4.2.1 Protection of Inner Wires - Extruded Insulation 5 4.2.2 Protection of Inner Wires Wrapped Insulations, Polyimide + PTFE Tapes . 5

10、5. AddITIONAL FUNCTIONALItIES 6 5.1 Single Conductor Wire Removing the Slug . 6 5.2 Shielded Cable Removing the Slug . 6 6. PROCESS QUALITY REQUIREMENTS 6 6.1 Heat Affected Zone on Insulation 6 6.2 Soot on Conductor or Shield . 7 7. SHIELD, CONDUCTOR, AND WIRE INSPECTIONS 7 7.1 Effect of the Laser B

11、eam on the Metallic Conductor or Shield . 7 7.2 Effect of the Laser Beam on the Inner Wire(s) of a Shielded Cable . 8 8. TOOL INSPECTION . 8 9. USER HEALTH AND SAFETY . 8 9.1 Laser Radiation Hazards. 8 9.2 Fumes . 8 10. NOTES 9 10.1 Revision Indicator 9 APPENDIX A 10 FIGURE 1 EXAMPLE OF HEAT AFFECTE

12、D AREA 6 FIGURE 2 HEAT AFFECTED ZONE 6 FIGURE 3 SOOT ON CONDUCTOR OR SHIELD . 7 FIGURE 4 WIRE CONDUCTOR INTEGRITY TEST 7 FIGURE 5 SHIELD INTEGRITY TEST . 7 FIGURE 6 OUTER JACKET STRIPPING OF SHIELDED CABLE (UNACCEPTABLE STRIP) 8 SAE INTERNATIONAL AIR6894 Page 3 of 13 1. SCOPE This document describes

13、 laser wire stripping technologies and recommendations to strip electrical single conductor and shielded cables intended for aerospace applications. These recommendations include: x Laser stripping safety guidelines x Laser stripping quality x Tool qualification x Tool inspection x User health and s

14、afety 2. REFERENCES 2.1 Applicable Documents The following publications form a part of this document to the extent specified herein. The latest issue of SAE publications shall apply. The applicable issue of other publications shall be the issue in effect on the date of the purchase order. In the eve

15、nt of conflict between the text of this document and references cited herein, the text of this document takes precedence. Nothing in this document, however, supersedes applicable laws and regulations unless a specific exemption has been obtained. 2.1.1 SAE Publications Available from SAE Internation

16、al, 400 Commonwealth Drive, Warrendale, PA 15096-0001, Tel: 877-606-7323 (inside USA and Canada) or +1 724-776-4970 (outside USA), www.sae.org. AS5768 Tool, Stripper, Electrical Insulation, General Specification For 2.2 Terms and Definitions LASER: LASER is an acronym for Light Amplification by Stim

17、ulated Emission of Radiation. Lasers are a source of intense monochromatic light in the ultraviolet, visible or infrared region of the spectrum. The “active” or lasing medium may be a solid, liquid, gas, or semiconductor. The laser beam is generated by energising the active medium using an external

18、power source, which is most commonly electrical or optical. CO2 LASER: The carbon dioxide (CO2) laser was one of the earliest gas lasers to be developed. The active laser medium is a gas mixture composed of carbon dioxide, nitrogen, hydrogen, and helium. The CO2 laser produces a beam of infrared lig

19、ht with the principal wavelength bands centering around 9.4 and 10.6 m. Nd:YAG LASER: Nd:YAG lasers are one of the most common solid-state lasers. The lasing medium is an yttrium aluminium garnet (YAG) crystal doped with neodymium. Nd:YAG lasers are optically pumped using flashlamps or laser diodes.

20、 They emit light with a wavelength of 1.064 m, in the near infrared spectrum. SEMICONDUCTOR LASER: Also called diode laser or laser diode, a semiconductor laser is a solid-state laser in which the active medium is formed by a p-n junction of a semiconductor diode similar to that found in a light-emi

21、tting diode. EXCIMER LASER: Excimer lasers are gas lasers emitting in the ultraviolet range. They use a combination of a noble gas (argon, krypton, or xenon) and a reactive gas (fluorine or chlorine) as the lasing medium. CW LASER: Continuous-Wave (CW) lasers emit a steady beam of light with a const

22、ant power. PULSED LASER: Pulsed lasers emit light in a series of pulses of short duration at a given repetition rate with a given peak power. SAE INTERNATIONAL AIR6894 Page 4 of 13 3. LASER WIRE STRIPPING TOOLS AND TECHNOLOGIES 3.1 Introduction to Laser Wire Stripping The principle of laser wire str

23、ipping is to focus a laser beam onto the surface of the wire or cable in a perpendicular manner and move it with a controlled speed. The insulation absorbs the light beam energy and is therefore vaporized and ablated. The laser beam is essentially reflected by the metallic conductor or shield. Non r

24、eflected energy transferred to the conductor or shield is evacuated thanks to the high thermal conductivity. Several device configurations are possible. A rotatable optical unit can be used to generate a circumferential cut: the beam (or beams if several) rotates around the wire. Alternatively the l

25、aser beam is fixed while the wire is rotated. A second approach directs two separate beams with opposite directions and focuses these to a point in the center of the wire. The beams are moved transversally to the wire to cut its insulation on both sides at the same time. Another option utilizes fixe

26、d beams and moves the wire instead. A longitudinal slit along the wire direction may be used to help the slug withdrawal. Whatever the device configuration the two main stripping parameters are the laser beam power and the displacement speed. 3.2 CO2 Laser Technology CO2 lasers emit in the infrared

27、at a wavelength around 10 m. Most of insulation materials absorb that particular wavelength range and exhibit a low damage threshold. They can be ablated at a low laser power density. Metals have a high reflectivity and a high damage threshold at this wavelength. The CO2 lasers used in laser wire st

28、ripping devices have a typical average power between 10 and 50 watts. They may work in a CW (Continuous Wave) or pulsed (RF-excited) regime. The latter allows the heat affected zone appearing on some types of wire to be reduced. The main advantages of the CO2 laser technology are its versatility (in

29、 terms of number of compatible insulation types) and productivity (higher power machines can process wires by batches, not one by one). 3.3 Semiconductor Lasers Violet and blue CW semiconductor lasers have been recently introduced in laser wire stripping devices. Many insulation types scatter visibl

30、e and near infrared light but offer significant absorption in the violet or blue region and can therefore be cut efficiently even with a low power laser beam. The main advantages of this technology are a maintenance free operation, a low power consumption and a very high compactness. 3.4 Other Fiber

31、 CW Nd:YAG lasers have been tested and used by NASA. They can be used on a limited range of insulation types because of typically high light scattering of insulation materials in the near infrared range, but have proven to be an efficient way to cut polyimide insulated wires. Excimer lasers emitting

32、 in the UV range can be used to cut wire insulation by disassociating the molecules rather than by vaporizing with heat. This is particularly desirable to process very fine wires. These laser sources are, however, extremely large and require frequent replacement of the toxic gas mixture. Particular

33、care must be taken with these short pulsed laser sources that can easily damage the metallic conductor or shield because of their extremely high peak power. 4. PROCESS SAFETY 4.1 Integrity of the Metallic Conductor or Shield The key-concept of laser wire stripping technology is to provide a non-cont

34、act solution to strip wires and cables with no risk of damaging the conductor or shield. The choice of the laser technology must therefore guarantee that no damage can be caused at any time to the metals used in aerospace wires and cables within a comfortable safety margin. NASA made investigations

35、using a CW CO2 laser (wavelength 10.6 m) and a CW YAG laser (wavelength 1.06 m) with power and beam parameters adjusted to cut wire insulations. They noticed no negative effects on the conductors or shields. The power density levels needed to cut the insulation are far lower than the damage threshol

36、d of metals. SAE INTERNATIONAL AIR6894 Page 5 of 13 Typical conductors or shields used in aerospace wires and cables are made of tinned copper, silver coated copper and copper alloy, nickel plated aluminum, and nickel plated copper and copper alloy. Several parameters are to be considered when choos

37、ing a laser technology: x CW or pulsed x Pulse width (if pulsed) x Power density at the wire surface (beam power and focal spot size) x Metallic material absorption at the corresponding wavelength Nanosecond pulsed YAG lasers are typically used to scribe and mark metals thanks to the tremendous peak

38、 power offered due to the very short pulse width (a few nanoseconds or tens of nanoseconds), despite the high reflectivity of metals at this wavelength. Of course they must not be used for the wire stripping application. Section 7.1 depicts a recommended protocol to carry out during the process qual

39、ification phase to ensure that the laser stripping process is riskless for both metallic conductors and shields. 4.2 Shielded Cable - Integrity of the Inner Wire(s) Insulation Laser wire strippers are particularly adept to cut the outer jacket of shielded cables whose cross section is highly non cir

40、cular and therefore very tricky to process by mechanical means. It is crucial that the laser beam not cause damage to the inner wire(s) underneath the metallic shielding. Different types of shielding are used in the construction of aerospace cables including braided shields and helicoidal (spiral) s

41、hields. The covered surface is typically comprised between 80 and 90% in the case of braided shielding. The shielding density is higher in spiral shielding but usually never 100% guaranteed. Up to 2 mm window (along the cable direction) are possible because of manufacturing tolerances. Metallic shie

42、lds are not opaque to the laser beam radiation and reliable measures must be taken to prevent the laser beam from damaging the insulation of the inner wires. Shielded cables are typically composed of two different types of jacket: an extruded jacket or a jacket made of wrapped tapes, such as polyimi

43、de + PTFE. Sections 4.2.1 and 4.2.2 describe recommended safe laser stripping solutions according to the jacket type. Section 7.1 depicts a recommended protocol to carry out for tool qualification. 4.2.1 Protection of Inner Wires - Extruded Insulation In the case of extruded insulation, the jacket t

44、hickness variations are small. The laser stripping parameters can therefore be adjusted to provide a sufficient cut and leave a thin layer of insulation above the shielding with a limited risk of damage to the inner wire(s). The cable then needs to be slightly bent to completely cut the jacket. 4.2.

45、2 Protection of Inner Wires Wrapped Insulations, Polyimide + PTFE Tapes In the case of jackets made of polyimide + PTFE wrapped tapes, insulation thickness variations may be large. It is much more complicated to find the right stripping parameters that allow complete cutting in the areas where the P

46、TFE tapes overlap (two PTFE layers) and process the single PTFE tape areas (no overlap) without impacting parts underneath. One solution is to implement in the stripping tool a real time process to monitor and automatically set the laser parameters based upon the wires being stripped. SAE INTERNATIO

47、NAL AIR6894 Page 6 of 13 5. ADDITIONAL FUNCTIONALITIES 5.1 Single Conductor Wire Removing the Slug Removing the insulation slug after having made an annular laser cut is not necessarily easy to perform manually. Mechanical grippers can be integrated inside the laser stripping tool design or used sep

48、arately. Whatever the means used to remove the slug, the integrity of the conductor and remaining insulation should not be affected. Refer to the acceptance criteria specified in AS5768. 5.2 Shielded Cable Removing the Slug Removing the jacket on a long distance (several inches typically) may be dif

49、ficult by hand. Several means can be utilized including mechanical assistance, carrying out of several successive annular cuts or carrying out of a longitudinal slit. 6. PROCESS QUALITY REQUIREMENTS AS5768 specifies the general wire insulation strip performance characteristics. Quality performance specific to the laser stripping technique are described herein. 6.1 Heat Affected Zone on Insulation When using a la