Patent Publication Number: US-2007104243-A1

Title: Laser apparatus for treating workpiece

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application is related to commonly-assigned co-pending applications entitled, “LASER WELDING SYSTEM FOR WELDING WORKPIECE”, filed on Jun. 23, 2006 (U.S. application Ser. No. 11/473,965), “LASER SYSTEM AND METHOD FOR PATTERNING MOLD INSERTS”, filed on Jul. 28, 2006 (U.S. application Ser. No. 11/309,343), and “APPARATUS FOR PROCESSING WORK-PIECE”, filed on Jul. 31, 2006 (U.S. application Ser. No. 11/309,353), and “LASER TREATMENT APPARATUS”, filed xxxx (Atty. Docket No. US8617). Disclosures of the above identified applications are incorporated herein by reference.  
     TECHNICAL FIELD  
      The present invention relates generally to laser apparatuses, and more particularly, to a laser apparatus for treating a workpiece.  
      Since lasers were first introduced into welding technical field in 1970s, lasers have been found to be very versatile, having applications including surface treatment (including welding) of metals, metal alloys, glasses, ceramics, and even plastics. For example, laser welding, which joins two formerly separate workpieces, has been demonstrated capable of joining not only workpieces of similar material, but also workpieces of dissimilar materials.  
      Laser apparatuses, which utilizes a laser such as carbon dioxide (CO2) laser for generating a powerful laser beam. The CO2 laser beam has a wavelength about 10.6 microns, and has several important advantages, such as high efficiency of power output, and good laser beam stability. When, for example, being used for welding, the laser beam is focused on a joint between two workpieces, heat from the laser beam makes the joint area materials melt, thus forming a weld pool. The weld pool contains the melt materials, and may penetrate a certain distant depth into the workpieces. When the laser beam moves along the joint between the workpieces, the weld pool moves along therewith, and the melt materials contained in the weld pool are cooled down, thus the joint between the workpieces forms a welding seam.  
      However, during the welding process of the workpieces, the joint area may easily become local overheated due to the heat from the powerful laser beam, thus leading to the welding seam having a weak bonding strength, and an uneven welding surface.  
      What is needed, therefore, is a laser apparatus for treating a workpiece which overcomes the above-mentioned problems.  
     SUMMARY  
      In a preferred embodiment, an exemplary laser apparatus for treating a workpiece includes a worktable, a cooling device, a laser, and a lens assembly. The cooling device is disposed on the worktable, the workpiece is positioned on the cooling device, and the cooling device is configured for absorbing heat from the workpiece. The laser is configured for generating a laser beam. The lens assembly is configured for converging the laser beam onto the workpiece.  
      Other objects, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Many aspects of the laser apparatus can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present apparatus. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.  
       FIG. 1  is a schematic view of a laser apparatus according to a preferred embodiment;  
       FIG. 2  is a schematic view of a laser shown in  FIG. 1 ;  
       FIG. 3  is a schematic view of a cooling device shown in  FIG. 1 ; and  
       FIG. 4  is a schematic view of a cooling unit shown in  FIG. 3 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Embodiments of the present laser apparatus for treating a workpiece will now be described in detail below and with reference to the drawings.  
      Referring to  FIG. 1 , an exemplary laser apparatus is used for welding two workpieces  17 , the laser apparatus includes a laser  10 , a controller  11 , a lens assembly  12 , a worktable  13  and a cooling device  14 .  
      Referring also to  FIG. 2 , the laser  10  includes a discharge tube  20 , a cooler  22 , a gas chamber  23 , a first mirror  24  and a second mirror  25 . The discharge tube  20  includes a cathode  212  and an anode  214 . The discharge tube  20  is held within the cooler  22 . The discharge tube  20  and the cooler  22  are placed inside the gas chamber  23 . The first mirror  24  and the second mirror  25  each are positioned at one end of the gas chamber  23  respectively to seal the gas chamber  23 , thus form an oscillating chamber. The discharge tube  20  is connected to a power supply  21  via the cathode  212  and the anode  214 . The discharge tube  20  has an opening  216  defined at one end near the cathode  212  and a gas-returning tube  218  connected at other end near the anode  214 , thus the discharge tube  20  is in communication with the gas chamber  23  via the opening  216  and the gas-returning tube  218 . The cooler  22  is configured for cooling the discharge tube  20 , the cooler  22  can be a water jacket or other coolant jacket. Preferably, a temperature controller cooperates with the cooler  22  for controlling the cooler  22 . The gas chamber  23  contains a gas therein, the gas may be a mixture of carbon dioxide (CO2), nitrogen (N2), and helium (He). The mixed gas can flow into the discharge tube  20  via the opening  216 , and be returned to the gas chamber  23  through the gas-returning tube  218 . The nitrogen gas thereof can help to excite the carbon dioxide to produce laser light, and the helium gas thereof can assist the mixed gas heat transmission. The first mirror  24  is a totally reflecting mirror, and the second mirror  25  is partly transparent to laser light generated by the discharge tube  20 .  
      The controller  11  is configured (i.e. structured and arranged) for controlling the operation of the laser  10 , such as activation and deactivation of the power supply  21 , adjustment of the power supply  21 , and as well as control of processing parameters, such processing parameters may include pulse energy, pulse duration, and repetition rate. For example, in a process for welding glass workpieces, the pulse energy may be controlled in a range from 20 to 100 micro-joules, the pulse duration may be in a range from 20 to 200 microseconds, and the repetition rate may be in a range from 1000 to 10000 hertz (Hz).  
      The lens assembly  12  is a multiple lens assembly, which includes a collimating lens  121 , and a converging lens  122 . The collimating lens  121  is configured for collimating the laser beam from the laser  10  into a parallel and uniform laser beam, and the converging lens  122  is configured for converging the parallelized and uniformed laser beam to a focus point, thus forming a laser spot on a joint to be welded between the two workpieces  17 . A size of the laser spot is preferably adjusted to match with a gap between the joint, for example, in a process of welding glass workpieces, a diameter of the laser spot may preferably be selected in the range from 10 to 100 micrometers.  
      The worktable  13  supports the cooling device  14  thereon, and the two workpieces  17  are positioned on the cooling device  14 .  
      The worktable  13  is preferably seated on a movable stage movable in dimensions defined by the Cartesian co-ordinates X-Y-Z, or driven by a X direction motor, a Y direction motor, and a Z direction motor, thus a distance between surfaces of the two workpieces  17  and the focus point converged by the lens assembly  12  can be adjusted. The distance may influence a weld pool geometry shaped on the joint, and as well as weld penetration depth into the joint. When the focus point is situated above the upper surfaces of the two workpieces  17 , it is called “positive defocus”, and when the focus point is situated below the upper surfaces of the two workpieces  17 , it is called “negative defocus”. In practical use, in a process of welding thin-walled workpieces, it is practical to use the positive defocus, and in a process of welding thick-walled workpieces, or a deeper weld penetration is required, it is practical to use the negative defocus.  
      Referring to  FIGS. 3 and 4 , the cooling device  14  may be a thermal electric cooler. The thermal electric cooler includes a first substrate  31 , a second substrate  32 , and a number of cooling units  30  mounted therebetween. The first substrate  31  and the second substrate  32  are both electrically insulated, but have a good heat transfer capability. Both the first substrate  31  and the second substrate  32  can be made of ceramics. The cooling unit  30  includes a p-type semiconductor  301 , an n-type semiconductor  302 , a first electrode  331  connected to the p-type semiconductor  301 , a second electrode  332  connected to the n-type semiconductor  302 , and an electrical and thermal conductor  34  connected with both the p-type semiconductor  301  and the n-type semiconductor  302 . The p-type semiconductor  301  and the n-type semiconductor  302  may both be an alloy of bismuth (Bi) and tellurium (Te). The first electrode  331  and the second electrode  332  are both disposed on the second substrate  32 . The electrical and thermal conductor  34  is disposed opposite to the first electrode  331  and the second electrode  332 , and is in thermal contact with the first substrate  31 .  
      When the two workpieces  17  are placed on the first substrate  31 , and a current is supplied from the second electrode  332  to the first electrode  331 , the first substrate  31  becomes a cold side, and the second substrate  32  becomes a hot side. The first substrate  31  can absorb heat from the two workpieces  17  during the welding process, then the p-type semiconductor  301  and the n-type semiconductor  302  cooperate to conduct the heat to a second substrate  32 , and the second substrate  32  discharges the heat to outside environment. Therefore, during the welding process, heat generated in the joint between the two workpieces  17  can be transferred away quickly, thus avoiding local overheating, and a bonding strength between the two workpieces  17  is improved, and an even welding surface is obtained.  
      Preferably, the laser apparatus may further include a detector  15  and a signal processing unit  16  (See  FIG. 1 ). The detector  15  can be configured for detecting the weld pool geometry signals and the weld penetration depth signals, such signals may include audible signals, supersonic signals, ultraviolet radiation signals, visible light signals and infrared radiation signals produced by the two workpieces  17  and laser spot applied thereon during the welding process. The signal processing unit  16  receives and processes the signals from the detector  15 , and feeds a feedback signal back to the controller  11  Thereby, the controller  11  can adjust the process parameters of the laser  10  quickly, thus enabling a better operational control of the laser  10 .  
      It is understood that the laser apparatus is not limited to welding in application, and can be used for purposes including surface treatments such as etching, shaping, machining of one or more workpieces.  
      It is understood that the above-described embodiment are intended to illustrate rather than limit the invention. Variations may be made to the embodiments and methods without departing from the spirit of the invention. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.