• JLA Vol:9 Iss:1 (On the formation of the keyhole and its temperatures)

    E. A. Metzbower
    US Naval Research Laboratory, Code 6320, Washington, DC 20375‐5000, U.S.A.

    A thermodynamically based model has been developed to calculate the size and temperature of the ‘keyhole’ through the thickness of the weldment. The model is based on calculating the power loss resulting from evaporation of an element in the chemistry of the plate and a minimum power density required to produce a keyhole. The evaporative power loss is set equal to the Gaussian power density, which is used to represent the laser beam. The result is a temperature distribution across the keyhole. Absorption of the laser power in the keyhole is calculated based on inverse...


  • JLA Vol:9 Iss:1 (The development of a laser machining curriculum: An interdisciplinary approach (the MAST program))

    Gary J. Masciadrelli
    Nicholas M. Massa

    The development of an industry‐driven interdisciplinary curriculum in laser machining is presented. The Machine tool Advance Skills Technology (MAST) program is a US Department of Education grant to develop and demonstrate a national training model for new technologies and manufacturing processes in precision manufacturing. Springfield Technical Community College (STCC) in partnership with six other community colleges nationwide, developed, tested, and disseminated industry‐specific skills standards and model curricula in laser machining and related technologies for the United States machine tool industry. STC...


  • JLA Vol:9 Iss:2 (Integration of real time quality control systems in a welding process)

    E. Nava‐Ru¨diger
    M. Houlot
    Ecole Nationale Supe´rieure d'Arts et Me´tiers, Laboratoire Proce´de´s et Techniques de Production Me´canique, Paris, France

    The automation of laser welding processes requires the control of the various process components as well as the control of the laser—material interaction. These systems are essential for ensuring the quality of the weld seam as they are able to react to dynamic fluctuations during the process. During the process various phenomena occur which are potential sources of diagnostic signals: these include thermal, electrical, optical, mechanical and acoustic events. This pa...


  • JLA Vol:9 Iss:2 (Kinematic compensation of repetitive errors for non‐circular laser shaping)

    P. Sheng
    K. Liu
    Department of Mechanical Engineering, University of California, Berkeley, CA, U.S.A.

    This paper presents an approach for kinematic compensation of the laser shaping process which is capable of achieving improved dimensional accuracy for non‐circular profiles. In this approach, a plug‐in repetitive controller is added into the existing position servo loop to improve tracking of the desired sinusoidal trajectory and subsequently reduce tracking errors. The effect of tracking errors on different dimensional error modes in the non‐circular shaping process is identified. Simulation models are developed for testing the performance o...


  • JLA Vol:9 Iss:2 (Laser cladding with a pulsed Nd:YAG laser and optical fibers)

    M. Brandt
    D. A. Scott
    S. B. Emms
    J. M. Yellup

    A new laser cladding technique for producing wear and corrosion resistant surfaces on engineering components is reported. The technique involves the combination of the pre‐placed and injected powder delivery methods for producing clad layers. The clad layers were formed with a pulsed Nd:YAG laser and optical fibers. The results using a nickel‐based alloy (Hastelloy C) indicate that uniform clad layers in excess of 1 mm in thickness can be achieved in a single pass with 240 W average power incident on the workpiece. The laser beam was delivered through a step‐index glass ...


  • JLA Vol:9 Iss:2 (Relationship between airborne acoustic and optical emissions during laser welding)

    D. Farson
    Y. Sang
    A. Ali
    Department of Industrial, Welding and Systems Engineering, Ohio State University, Columbus, OH, 43210 U.S.A.

    This paper describes experimental work directed at understanding the relationship between acoustic and optical emissions from the laser welding process. Laser welds were performed and the emissions were measured with a microphone and photodiode and recorded with a data acquisition system. A time‐domain correlation analysis of the acoustic and optical signals revealed them to be highly related at a phase shift corresponding to the delay time for sound to propagate from the weld area to the microphone. A moving av...


  • JLA Vol:9 Iss:2 (Temperature&hyphen;dependent absorptivity and cutting capability of CO<sub>2</sub>, Nd:YAG and chemical oxygen&ndash;iodine lasers)

    J. Xie
    A. Kar
    J. A. Rothenflue
    W. P. Latham

    The most widely used high power industrial lasers are the Nd:YAG and CO2 lasers. The chemical oxygen iodine laser (COIL), whose wavelength (1.315 μm) is between that of the Nd:YAG (1.06 μm) and CO2 (10.6 μm) lasers, is another high power laser for industrial applications. The cutting capability of these lasers is investigated in this paper. The cut depth strongly depends on the absorptivity of the cut material, kerf width and cutting speed. The absorptivity is an unknown parameter for which experimental data at high temperatures are currently unavailable. Theoret...


  • JLA Vol:9 Iss:3 (A power distribution model of industrial CO<sub>2</sub> lasers for system diagnosis)

    James G. Katter
    Jay F. Tu
    Mark Gartner

    Industrial lasers are high power pieces of equipment that occasionally function under undesirable operating conditions. For example, the performance of a transverse&hyphen;flow d.c.&hyphen;excited gas laser can be adversely affected by many factors such as electrode arcing, poor lens and mirror cleanliness, focusing problems, improper gas mixture composition, poor gas quality, poor beam stability, poor beam path cleanliness, operator error, poor maintenance, poor chiller water temperature and flow rate stability, and improper laser beam ramp&hyphen;in/ramp&hyphen;out rates. Many of these factors which occur in ...


  • JLA Vol:9 Iss:3 (Diode laser scribing of non&hyphen;oriented 3 wt&percnt; Si&hyphen;steel for core loss reduction)

    Ravisankar Gurusamy
    P. A. Molian
    Mechanical Engineering Department, Iowa State University, Ames, IA 50011, U.S.A.

    The electrical power industries are experiencing a considerable energy loss in transformers and motors because of inefficiencies caused by core loss. The objective of our research is to investigate any effect of laser scribing on the reduction of the core loss in the low cost, non&hyphen;oriented steels used in numerous utility applications. A 15 W diode laser transmitted through fiber optics was used to scribe 0.35 mm thick, non&hyphen;oriented 3 wt&percnt; Si steel. The magnetic properties including the core loss and permeability were evaluated both...


  • JLA Vol:9 Iss:3 (Effective laser ablation of enamel and dentine without thermal side effects)

    Peter Kohns
    Ping Zhou
    Reinhard Sto¨rmann
    Optikzentrum NRW, Universita¨tsstraß 142, D&hyphen;44799 Bochum, Germany

    We present a feasibility study into laser treating dental materials by using femtosecond pulses generated by a titanium:sapphire laser system which consisted of an oscillator and a regenerative amplifier. The pulse duration was varied between 200 fs and 2 ps. The observed energy thresholds for the ablation process of dentine and enamel were clearly smaller than those observed when longer pulse durations were used. The consequence of this observation is a lower thermal load within the vicinity of the radiated area. Thus no th...