Patent Publication Number: US-2006000810-A1

Title: Method of and system for dynamic laser welding

Description:
BACKGROUND OF THE INVENTION  
      The present invention generally relates to power profile control for welding and in one arrangement, more particularly, to power profile control for welding inkjet printheads.  
      Generally, laser welding attaches a generally optically transparent or translucent material to a generally energy absorbing material using the standard constant power profile  300  illustrated in  FIG. 11 . The process begins with the two materials being held together. In one arrangement, the generally optically transparent material is positioned over the generally energy absorbing material. Laser light is passed at constant power intensity through the transparent material and absorbed by the absorbing material. As shown in  FIG. 11 , the constant power is usually set at a percentage (e.g., 65%) of the maximum power intensity that the materials can receive.  
      In some arrangements, laser light is applied to the weld area in a contour welding method. Contour welding applies the beam of laser light on a single point of the weld area and welds the materials of the weld area point by point. For example, the laser beam can maneuver around the weld area, or the weld area can maneuver around the laser beam. In other arrangements, the laser light is applied to the weld area in a semi-simultaneous welding method or a simultaneous welding method. Semi-simultaneous welding method and simultaneous welding methods heat and weld multiple points of the weld area at the same time.  
      The laser energy is generally absorbed in a very thin portion of the absorbing material near the surface. Heat is conducted to the transparent material and also further conducted to the absorbing material from the surface in order to soften enough material to create a good joint. The laser power is normally ended by a preset timer or by the equipment sensing a preset collapse distance of the welded materials.  
     SUMMARY OF THE INVENTION  
      Various material combinations have been successfully attached using laser welding. However, one of the issues occurring when welding a semi-crystalline material is that the material has a very narrow sealing and softening temperature range. Accordingly, semi-crystalline materials are more prone to overheating and to developing imperfections (e.g., bubbles) in the weld joint.  
      Typically, the standard constant power profile being used during the simultaneous weld cycle for semi-crystalline materials produces bubbles in the weld area and effects the reliability of the weld joint. A dynamic power profile used during the weld cycle can, in some arrangements, allow the semi-crystalline material to quickly heat to a desired temperature and then maintain that temperature in a more controlled fashion to produce reliable weld joints.  
      In other arrangements, the dynamic power profile can reduce the welding time of non semi-crystalline materials.  
      In several embodiments, the invention provides a dynamic power profile for a laser weld cycle. The dynamic power profile can be used to weld a first portion to a second portion that includes a semi-crystalline material. For example, the dynamic power profile can be used to weld a printhead lid to a semi-crystalline printhead body.  
      In one embodiment, the invention provides a method of welding a first material of an apparatus to a second, semi-crystalline material of the apparatus. The method includes the acts of heating a weld area with a first power intensity for one time period and heating the weld area with a second power intensity (not equivalent to the first power intensity) for a second time period. The weld area is also not heated using a contour welding method.  
      In another embodiment, the invention provides a method of welding a first material of an apparatus to a second material of an apparatus. The method includes the acts of heating a weld area with a first power intensity for one time period, receiving feedback regarding the weld area during the one time period, and heating the weld area with a second power intensity for another time period based at least in part on the received feedback. The second power intensity is not equal to the first power intensity.  
      In still another embodiment, the invention provides a laser welding assembly for welding a first material of an apparatus to a second material of the apparatus during a weld cycle. The assembly includes a laser source for producing a light beam operable to heat at least a portion of the weld area. The light beam has a power intensity, and the laser source includes a source input terminal. The assembly also includes a controller having an input terminal operable to receive a first signal, and an output terminal coupled to the source input terminal and operable to transmit a second signal. The second signal includes a command to vary the power intensity of the light beam during a weld cycle, and the command is based at least in part on the first signal.  
      In still another embodiment, the invention provides a method of welding a first material of an apparatus to a second, semi-crystalline material of the apparatus. The method includes the acts of heating a weld area with a first power intensity for one time period and heating the weld area with a second power intensity (not equivalent to the first power intensity) for a second time period. The method also includes applying pressure to the weld area and producing a collapse distance within a portion of the weld area. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a perspective view of an inkjet printhead.  
       FIG. 2  is an exploded perspective view of a portion of an inkjet printhead, such as the inkjet printhead shown in  FIG. 1 .  
       FIG. 3  is a perspective view of a portion of an inkjet printhead, such as the inkjet printhead shown in  FIG. 1 .  
       FIG. 4  is a perspective view of a laser welding assembly.  
       FIG. 5  is a perspective view of another laser welding assembly.  
       FIG. 6  is a graph illustrating a first welding profile for use with a laser welding assembly, such as one of the laser welding assemblies shown in  FIGS. 4 and 5 .  
       FIG. 7  is a graph illustrating a welding profile for use with a laser welding assembly, such as one of the laser welding assemblies shown in  FIGS. 4 and 5 .  
       FIG. 8  is a graph illustrating another welding profile for use with a laser welding assembly, such as one of the laser welding assemblies shown in  FIGS. 4 and 5 .  
       FIG. 9  is a graph illustrating still another welding profile for use with a laser welding assembly, such as one of the laser welding assemblies shown in  FIGS. 4 and 5 .  
       FIG. 10  is a graph illustrating collapse of a material given over time during a welding profile.  
       FIG. 11  is a graph illustrating a prior art welding profile for use with a prior art laser welding assembly. 
    
    
     DETAILED DESCRIPTION  
      Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limited. The use of “including,” “comprising” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The terms “mounted,” “connected” and “coupled” are used broadly and encompass both direct and indirect mounting, connecting and coupling. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings.  
       FIGS. 1-3  illustrate at least a portion of an inkjet printhead  10  which is assembled using a dynamic power profile during laser welding. The printhead  10  includes a housing or body  15  that defines a nosepiece  20  and at least partially defines an ink reservoir  25 . The body  15  further defines an opening  28 , as shown in  FIG. 2 .  
      The body  15  can be constructed of a variety of materials including, without limitation, at least one of polymers, metals, ceramics, composites and the like. In the illustrated embodiments, the body  15  is constructed of at least one semi-crystalline material. For example, the body  15  can be constructed from glass-filled polybutylene terephthalate resin (available from G. E. Plastics of Huntersville, N.C. under the trade name VALOAX).  
      The printhead  10  further includes a lid  30  that is welded to the body  15  to cover the ink reservoir  25 . When the lid  30  is welded to the housing  12 , the lid  30  and housing  12  form a seal to prevent leakage of ink from the ink reservoir  25 .  
      In the illustrated embodiments of  FIGS. 2 and 3 , the lid  30  includes a first portion  40  configured have a perimeter  45  approximately the same size as the perimeter  48  (shown in  FIG. 2 ) of the printhead body  15 . At least a portion of the lid  30 , such as, for example, an area of the first portion  40 , is constructed of a generally optically transparent or translucent material. In the illustrated embodiment, the entire first portion  40  of the lid  30  is constructed of a generally optically transparent or translucent material.  
      In another embodiment, such as the embodiment illustrated in  FIG. 3 , the lid  30  can also include a second portion  35  that substantially fits within the opening  28  defined by the printhead body  15 . In this illustrated embodiment, the second portion  35  is coupled to the first portion  40 . As shown in  FIG. 2 , the lid  30  may not include the second portion  35 . In other embodiments, the second portion  35  of the lid  35  can also be constructed of a generally optically transparent or translucent material.  
       FIGS. 4 and 5  illustrate exemplary laser welding assemblies  60  for heating the weld joint or area  65  (shown in dashed lines) of a printhead  10 . The laser welding assembly  60  illustrated in  FIG. 4  includes a single laser source  70  producing a beam of light  75 . The laser welding assembly  60  illustrated in  FIG. 5  includes a plurality of laser sources  70 , each producing a laser beam  75 . In other embodiments, the laser welding assembly  60  can include more or fewer laser sources  70  than shown and described.  
      In some embodiments, such as the embodiment illustrated in  FIG. 4 , the assembly  60  may also include one or more manipulating elements  80  that can manipulate (e.g., control, focus, redirect, converge, diverge, split, scatter and the like, for example) the beam  75 . The manipulating elements  80  can include, for example, one or more lens, one or more fiber optic cables, one or more wave guides, one or more mirrors, one or more masks, and the like, or a combination of these and/or similar elements. In further embodiments, the manipulating elements  80  can further be used to apply pressure to the weld area  65  during the welding cycle. For example, a manipulating element  80 , such as a waveguide, can apply pressure to the weld area  65  to produce a certain collapse distance, as discussed below.  
      In the illustrated embodiment of  FIG. 4 , the manipulating elements  80  each include a lens. The assembly  60  illustrated in  FIG. 4  is a contour system as is known in the art. In another embodiment, the assembly  60  can include one or more manipulating elements  80 , such as, for example, a user-programmed mirror, to circle the beam  75  rapidly around the weld area  65 , thereby establishing a semi-simultaneous system. In a further embodiment, the assembly  60  can include one or more manipulating elements  80 , such as, for example, one or more fiber optic cables or a metal mask, that can heat the entire weld area  65  at the same time, thereby establishing a simultaneous system. In the illustrated embodiment of  FIG. 5 , the assembly  60  is also a simultaneous system through the use of multiple lasers  70  that heat the entire weld area  65  at the same time.  
      As shown in  FIGS. 4 and 5 , the assembly  60  also includes a controller  90  operable to control the power intensity, as well as the position, of the laser(s)  70  and any manipulating element(s)  80 , for example. In these illustrated embodiments, the controller  90  provides a signal to the laser(s)  70  to modify the power intensity of the light beam  75  of each laser  70  during the weld cycle. In the illustrated embodiment of  FIG. 4 , the controller includes at least one output terminal  105 . In the illustrated embodiment of  FIG. 5 , the controller  90  includes a plurality of output terminals  105 , one dedicated output terminal  105  for each corresponding laser  70 . As shown, the output terminal  105  is connected to the laser  70  via a laser input terminal  108 . The controller  90  can output a control signal or command to the laser  70  via the output terminal  105  (and the connection between the laser source  70  and the controller  90 ). In some embodiments, the controller  90  can transmit one command signal to the laser(s)  70  throughout the duration of the weld cycle, or can transmit a plurality of command signals to the laser(s)  70  throughout the duration of the weld cycle.  
      In some embodiments, the controller  90  can accompany the laser source  70  in a single apparatus, or can be an external controller  90  from the laser  70 , such as, for example, a personal computer. In the illustrated embodiment of  FIG. 5 , for example, the controller  90  can be external to the plurality of lasers  70  or can be included in a single apparatus with at least one laser  70 .  
      In some embodiments, the controller  90  can also include one or more input terminals  110  for receiving various inputs or signals. In some embodiments, such as the embodiment illustrated in  FIG. 4 , the controller  90  can include a first input terminal  115  for receiving feedback information during the weld cycle. For example, the controller  90  can receive feedback information regarding the weld area  65 , such as collapse distance (e.g., distance of one material or area that is collapsing) at any given point of the weld area  65 , maximum collapse distance of a portion or throughout the weld area  65 , average collapse distance of a portion or throughout the weld area  65 , collapse velocity (e.g., how fast the material or area is collapsing), maximum collapse velocity, average collapse velocity, temperature at any given point of the weld area  65 , maximum temperature of a portion of or throughout the weld area  65 , average temperature of a portion of or throughout the weld area  65 , rate of temperature change, maximum rate of temperature change, average rate of temperature change, uniformity of temperature throughout the weld area  65  and temperature deviation of a portion or throughout the weld area  65 . In some embodiments, the feedback information received from the input terminal(s)  110  can be used to modify the power intensity of the laser  70  during the weld cycle, as discussed below. In some embodiments, the controller  90  may or may not collect feedback information and may or may not include the input terminal(s)  110 .  
      Also, in some embodiments, such as the embodiment illustrated in  FIG. 4 , the controller  90  can include a second input terminal  120  for receiving secondary information  125  from outside the weld area  65  during that particular weld cycle. For example, the controller  90  can receive a program or pre-set power profile to be used throughout a weld cycle. In some embodiments, the pre-set power profile can be created by a user through a software program included in the controller  90  or included in an external device. In other embodiments, the secondary information  125  can include information about a different weld area (not shown) from a previous weld cycle, information averaged over various different weld areas from various weld cycles, estimated information about the weld area  65  generated from a weld area model, and the like.  
      In some embodiments, the feedback information and/or the secondary information  125  can be used during the weld cycle to vary the power intensity of the laser(s)  70 . In some embodiments, the feedback information and/or the secondary information  125  can also be used during the weld cycle to terminate welding or to modify time periods throughout the weld cycle, as discussed below.  
      In some embodiments, the controller  90  can implement a dynamic power profile for each laser  70  during a weld cycle. The dynamic power profile includes at least one change in power intensity during the weld cycle. That is, the dynamic power profile varies the power intensity of the laser(s)  70  at least once between a first power intensity and a different, second power intensity.  
      For example, in a first general embodiment, the power of the laser(s)  70  is varied in a preset manner (e.g., set power intensities for set time periods). In this embodiment, the profile is not modified due to feedback during the weld cycle.  
      In a second general embodiment, the power of the laser(s)  70  is pulse width modulated in a preset manner. In this embodiment, the profile is not modified due to feedback during the weld cycle.  
      In a third general embodiment, the power of the laser(s)  70  is varied in a present manner. Power is modified or turned off due to input during the weld cycle, such as collapse distance. The input can include feedback from the weld area  65 , stored information from previous weld cycles, an estimated or calculated value derived from other information, and the like.  
      In a fourth general embodiment, the power of the laser(s)  70  is partially or completely varied during the weld cycle due to a temperature input from the weld area  65 .  
      In a fifth general embodiment, the power of the laser(s)  70  is varied as in the fourth general embodiment and/or with inputs of collapse distance, collapse velocity, rate of temperature change, uniformity of temperature, or the like, during the weld cycle.  
      In a sixth general embodiment, the power of the laser(s)  70  is varied as in the fifth general embodiment with inputs not from feedback during the weld cycle.  
      In a seventh general embodiment, the power of the laser(s)  70  is varied differently for different sections of the weld area  65 .  
      In an exemplary implementation illustrated in  FIG. 6 , the controller  90  utilizes temperature-based feedback (e.g., temperature, maximum temperature, average temperature, rate of temperature change, maximum rate of temperature change, average rate of temperature change, uniformity of temperature, temperature deviation and the like) for implementing and controlling a first dynamic power profile  200  during a weld cycle of welding a printhead  10 . In this example, the dynamic power profile  200  includes a first portion  205  and a second portion  210 . The first portion  205  includes the laser beam  75  being set at a constant power intensity  215  (e.g., approximately 95% of the maximum power intensity the lid  30  and printhead body  15  can receive). The second portion  210  includes a feedback-controlled varied power intensity  220 . As illustrated, the varied power intensity  220  of the laser  70  is gradually reduced as the temperature of the weld area  65  approaches a set temperature point.  
      In this embodiment, the controller  70  receives temperature-based feedback (e.g., ) from the weld area  65  throughout the duration of the weld cycle, and compares the temperature data to certain thresholds. As illustrated in  FIG. 6 , the weld cycle begins with the controller  90  setting the laser beam  75  to a set or constant power intensity  215  (e.g., 95% intensity). Typically, the constant power intensity  215  of the laser(s)  70  is set to a high value near the full power inentsity, 100%, such as for example, approximately 85% to 100% intensity. In this embodiment, the high, constant power intensity  215  quickly raises the weld area temperature to a temperature within a desired temperature range, such as a softening temperature range (e.g., the range of temperatures in which the weld area  65  will soften), at a much faster rate than the standard, lower constant power intensity  300 .  
      The temperature of the weld area  65  is raised to a temperature (e.g., a starting temperature) over a first period of time T 1 . In some embodiments, the starting temperature includes a plurality of temperatures within a desired or set temperature range (e.g., the softening temperature range). In other embodiments, the starting temperature can include a specific temperature within the desired or set temperature range, such as, for example, the lower temperature limit or the higher temperature limit within the desired temperature range. In further embodiments, the starting temperature can include a desired or specific temperature point that may or may not be included in a desired temperature range. In this example, the starting temperature includes a plurality of temperatures within a desired or set temperature range, such as, for example, the softening temperature range. Also in this example, the temperature of the weld area  65  reaches the starting temperature (at point  230 ) at time t 1 .  
      As shown in  FIG. 6 , the first portion  205  of the profile  200  concludes at the end of timer period T 1  (e.g., time t 1 ). Once the temperature reaches the starting temperature (e.g., one of the temperatures included in the softening temperature range), the varied power intensity  220  of the laser  70  included in the second portion  210  is gradually reduced during a second time period T 2  in order to maintain the temperature at the starting temperature (e.g., maintain the temperature within the desired temperature range). During this second time period T 2 , the average power intensity  240  (shown in dashed lines) of the laser  70  supplied to the weld area  65  is less than the constant power intensity  215  delivered during the first time period T 1 .  
      While the temperature is maintained at the starting temperature (e.g., at a temperature within the desired temperature range) (at point  245 ), the varied power intensity  220  has reached approximately zero, causing the weld cycle to be terminated at time t 2 . In some embodiments, the varied power intensity  220  in the second portion  210  can inversely correlate to the weld area temperature. When implementing this exemplary power profile  200 , the temperature of the weld area  65  is less likely to exceed any thresholds (such as, for example, a melting or bubbling threshold, or a temperature that is greater than the desired temperature range) and overheat. The weld area  65  is less likely to overheat, because the rate of temperature change in the weld area  65  gradually lowers as the varied power intensity  220  is reduced (and the weld area temperature is maintained within the desired temperature range).  
      In some embodiments, the temperature of the weld area  65  can be raised to a starting temperature (i.e., a first set temperature point) over a first period of time T 1 . During the second time period, the temperature of the weld area  65  can be maintained at the starting temperature (i.e., the set temperature point) or can be gradually raised or lowered to an ending temperature (i.e., a second set temperature point). In one embodiment, for example, the second set temperature point can be greater than the first set temperature point, such that the weld area  65  is heated to a first temperature during the first time period T 1 , and then gradually heated to a higher second temperature during the second time period T 2 . In another embodiment, for example, the second set temperature point can be less than the first set temperature point, such that the weld area  65  is heated to a first temperature during the first time period T 1 , and then gradually reduces to a lower second temperature point during the second time period T 2 . In these embodiments, both the first set temperature point and the second set temperature point may be included within a softening temperature range.  
      As mentioned previously, in other embodiments, the weld area  65  can be heated to a starting temperature point (which may or may not include a range of temperatures) during the first time period T 1 , and then can be maintained within a desired range of temperatures during the second time period T 2 . In these embodiments, the temperature of the weld area  65  can be raised and/or lowered to one or more temperatures included in a range of temperatures during the second time period T 2 . In some embodiments, the starting temperature point can include a first range of temperatures, and the desired range of temperatures can include a second range of temperatures. The first range can differ from the second range or can include the same temperatures as the second range. Furthermore, the second range can differ from the first range or can include the same temperatures as the first range.  
      Also in the exemplary implementation, the controller  90  can also receive collapse-based feedback (e.g., collapse distance, maximum collapse distance, average collapse distance, collapse velocity, maximum collapse velocity, average collapse velocity, and the like) to control and modify the varied power intensity  220  of the second portion  205 . For example, a manipulating element  80  can apply pressure to the weld area  65  during the first time period T 1  and/or during the second time period T 2  to produce a desired collapse distance D. In one embodiment, the desired collapse distance D is at least approximately 0.1 mm. The controller  90  can terminate the welding cycle when the controller  90  determines that the desired collapse distance D between the two materials has been achieved.  
      In other variations of the dynamic power profile  200 , the first portion  205  can include a first varied power intensity having a first average power intensity. The second portion  210  can then include either a second constant power intensity that is less than the first average power intensity, or can include a second varied power intensity having a second average power intensity that is less than the first average power intensity.  
      Other examples of the dynamic power profiles (and multiple power settings) that the controller  90  can establish during a laser welding cycle are illustrated in  FIGS. 7-9 . For example, the controller  90  can implement a single-step power profile  250  (illustrated in  FIG. 7 ) with or without feedback control. The controller  90  can also implement a multi-step power profile  260  (illustrated in  FIG. 8 ) with or without feedback control. The controller  90  can further implement a tapered power profile  270  (illustrated in  FIG. 9 ) with or without feedback control, and the controller  90  can still further implement a ramped power profile (not shown) with or without feedback control, a combination of portions of the various dynamic profiles with or without feedback control, and the like.  
      An operator can determine which dynamic power profile (e.g., the power vs. time control) to implement during the weld cycle based on several factors. In one embodiment, when welding a printhead lid  30  to a printhead body  15 , a certain dynamic power profile is selected or is created in order to 1) raise the temperature of both materials (e.g., the lid  30  and the body  15 ) of the weld area  65  to a softening temperature as fast as possible, typically starting at full-power intensity (e.g., 100% intensity), 2) maintain the weld interface temperature in an allowing range (such as the softening temperature range), 3) maintain the weld area temperature so both materials (e.g., the lid  30  and the body  15 ) are not degraded by overheating, 4) maintain the weld area temperature so it is not overheated causing low viscosity melted material (e.g., the lid  30  or the body  15 ) to move out of the weld area  65 , and 5) maintain the weld area temperature for enough time so that adequate cohesion or adhesion can occur in the weld area  65 .  
      In this embodiment, the factors are dependent of the characteristics of the different material types being welded, such as, for example, the softening temperature threshold, the softening temperature range, an overheating threshold, the temperature at which the material heats to a low viscosity, and the like. When welding a translucent material to a semi-crystalline material, for example, temperature-based feedback control can aid in the dynamic power profile due to the fact that semi-crystalline materials have a narrow softening temperature range which can produce reliable weld joints in the material.  
      The various dynamic power profiles discussed above can also produce a more controlled collapse rate of the welded materials, as shown in  FIG. 10 . By controlling the power profile, the controller  90  can in turn control the rate at which the materials collapse, indicated by graph  280 .  
      The embodiments described above and illustrated in the figures are presented by way of example only and are not intended as a limitation upon the concepts and principles of the present invention. As such, it will be appreciated by one having ordinary skill in the art that various changes in the elements and their configuration and arrangement are possible without departing from the spirit and scope of the present invention as set forth in the appended claims.