Laser drilling and trepanning device

Laser drilling devices are disclosed which include a laser beam source and a laser drilling head. The laser drilling head includes a beam manipulator system in which the only dynamically moving optical element is a mirror. The mirror is dynamically and reciprocally translatable along the direction of the incoming laser beam and is also dynamically and reciprocally tiltable about an axis that is perpendicular to the nominal optical axis of the drilling head. The drilling head also includes a spinnable laser beam rotating system, a simplified compensation system, and a focusing system. The compensation system includes as its only laser beam path shifting optical elements one or two wedge plates which, if two, are fixably rotatable relative to one another in planes which are perpendicular to the nominal optical axis of the laser drilling device.

BACKGROUND

Field of the Invention

The present invention relates to devices and methods for laser drilling and trepanning holes in workpieces.

Background of the Invention

In laser machining, a laser beam generation device is used in conjunction with an optical system to direct the laser beam onto a workpiece that is to be machined. The impingement of the laser beam on the workpiece locally melts and/or vaporizes the workpiece material to produce or extend a hole or cut in the workpiece. The location of the laser beam impingement point on the workpiece may be controlled by moving one or both of the laser beam and the workpiece relative to one another to thereby control the geometry of the hole or cut.

In laser drilling, a hole, which can be through or blind, is formed in a workpiece by directing the laser beam at a preselected spot on the workpiece. The focus point of the beam may be adjusted during the drilling to correlate with the current depth of the hole. Three common techniques for laser drilling are single pulse drilling, which uses a single pulse of the laser beam to make the hole, percussion drilling, which uses multiple pulses of the laser beam delivered to the same spot, and helical drilling, which uses multiple pulses applied in a descending helical-like pattern to form a circular or non-circular hole. In laser trepanning, the point of incidence of the laser beam on the workpiece is manipulated so as to describe and cut a geometric or irregular figure, e.g., a circle or an irregular polygon, into or through the workpiece. In both laser drilling and laser trepanning, the profile of the cut in the through-thickness direction may be controlled by manipulating the incident angle of the laser beam to cut, for example, conical, funnel-shaped, or double-conical holes. (See, e.g., FIGS. 1-3 and 9 U.S. Pat. No. 5,043,553).

Laser drilling and trepanning have become inexpensive alternatives, in many cases, to mechanical machining methods. Laser drilling or laser trepanning may be used with almost any kind of workpiece material, e.g., ceramics, metals, glass, gemstones, rubber, polymers, and composite materials. These methods permit tight tolerance manufacturing specifications to be met in a wide variety of industries.

Undesired localized thermal deformation of the workpiece may be caused by the heat input due to the irradiating of the workpiece with the laser beam. Such deformation is especially a problem when the workpiece has poor thermal conductivity and a thin through thickness. It is also a problem when the laser drilling or trepanning is being used to do very accurate machining of small features. Various schemes have developed to avoid localized thermal deformation. One is to use short or ultra-short pulse lasers, i.e., in the femtosecond and picosecond pulse ranges, respectively, so that the amount of energy delivered by each laser pulse is small and has a chance to partially dissipate before the next pulse is delivered. Another scheme is to dynamically manipulate the shape and location of the laser beam impingement point upon the target so that the cutting or hole making is performed in a series of overlapping locations which eventually combine to make the overall cut or hole.

An example of a laser drilling and trepanning device (hereinafter and in the appended claims referred to as a “laser drilling device”) utilizing both of these schemes is described in U.S. Pat. No. 7,842,901 to Wawers et al. The laser drilling device described in that patent comprises a laser beam source, a laser beam manipulator system, an image rotator system, a compensating system, and a focusing system. The laser beam manipulator system has a mirror that is linearly translatable in the direction of the incoming laser beam and a wedge plate that is pivotable about an axis that is perpendicular to the nominal optical axis of the laser drilling device. The image rotator element of the image rotator system may be a radiation-transmitting prism, such as a Dove prism or an Abbe-Koenig prism, or a reflecting system, such as a K-mirror arrangement. The image rotator system is configured to spin about the nominal optical axis of the laser drilling device at rates up to about 500 revolutions per minute during operation (which causes the laser beam to rotate at twice this rate), and may optionally include half-wavelength plate to reduce polarization induced variations of the incoming the laser beam. The compensating system includes a parallel displacement unit, such as a plane-parallel plate, and a pair of wedge plates, all of which are mounted to be able to be tilted on respective axes which are perpendicular to the nominal optical axis of the laser drilling device. Additionally, the two wedge plates can be rotationally adjusted relative to one another about axes which are perpendicular to the nominal optical axis of the laser drilling device. The compensating unit is configured so as to spin about the nominal optical axis of the laser drilling device with the image rotator system. The focusing system may be composed of one or more focusing lenses which may be mounted to translate along the nominal beam axis of the laser drilling device so as to permit continuous adjustment of the laser beam focus during use. In operation, the laser beam emanates from the laser beam source and may pass through an optional stationary quarter-wavelength plate (to convert a linearly polarized laser beam into a circularly polarized laser beam) and then enters the beam manipulator system where it is reflected from the mirror to a direction which is substantially parallel to the optical axis of the laser drilling device and then through the wedge plate. The laser beam then passes through the half-wavelength plate (if present) and then through the image rotator system. The spinning of the image rotator system acts to spin the laser beam about the laser beam's optical axis so as to compensate for any asymmetry the incoming laser beam may have and also causes the laser beam to rotate a preselected distance around the rotation axis of the image rotator system (which coincides with the nominal optical axis of the laser drilling device). The laser beam then passes through the three elements of the compensating system. Prior to use, the positions of these three elements are adjusted and locked into place so as to compensate for any manufacturing defects in the image rotator which would cause the laser beam to vary from its intended position. After exiting the compensating system, the laser beam passes through the focusing system and then onto the workpiece. The impingement point of the laser beam upon the workpiece is adjusted during use by dynamically moving the two components of the beam manipulator, i.e., the mirror and the wedge plate. The mirror is dynamically translated along the direction of the incoming laser beam to adjust the angle at which the laser beam impacts the workpiece and the wedge plate is dynamically tilted about its mounting axis so as to adjust the distance of the laser beam from the optical axis of the laser drilling device. Through the use of these controls, the shape of the laser cut as well as its contour can be controlled.

Although the prior art laser drilling devices, e.g., those taught by U.S. Pat. No. 7,842,901, produce good results, improvements are still desirable. For example, it is believed that higher laser beam rotation speeds would lessen the chance of thermal deformation when cutting very small features in thin materials, e.g., holes with diameters in the range of about 100 microns to 1 millimeter. Additionally, it would be advantageous to simplify the alignment of the laser beam in the device prior to use. It would also be advantageous to reduce the number of optical elements that need to be moved in the device in order to manipulate the incident point of the laser beam on the workpiece.

SUMMARY OF THE INVENTION

The present invention provides laser drilling devices which are able to provide one or more of the foregoing desired improvements. In one aspect of the invention, there are provided laser drilling devices which include a laser beam source and a laser drilling head. The laser drilling head comprises a beam manipulator system in which the only dynamically moving optical element is a mirror. The mirror is dynamically and reciprocally translatable along the direction of the incoming laser beam and is also dynamically and reciprocally tiltable about an axis that is perpendicular to the nominal optical axis of the drilling head. The drilling head also includes a spinnable laser beam rotating system, a simplified compensation system, and a focusing system. The compensation system includes as its only laser beam path shifting optical elements one or two wedge plates which, if two, are fixably rotatable relative to one another in planes which are perpendicular to the nominal optical axis of the laser drilling device.

In another aspect, the present invention provides a laser drilling head that is usable with a laser source.

DESCRIPTION OF PREFERRED EMBODIMENTS

In this section, some preferred embodiments of the present invention are described in detail sufficient for one skilled in the art to practice the present invention. It is to be understood, however, that the fact that a limited number of preferred embodiments are described herein does not in any way limit the scope of the present invention as set forth in the appended claims. It is also to be understood that whenever a range of values is presented, the range is to be construed as disclosing its endpoints and every point therebetween as if each point was expressly described.

Referring toFIG. 1, there is shown a laser drilling device25according to an embodiment of the present invention. The laser drilling device25includes a laser source22, which produces a laser beam13, and a laser drilling head23. The laser drilling head23comprises a laser beam manipulator system26, a laser beam rotating system27, a compensation system28, and a focusing system29. During operation, a laser beam13is produced by the laser source22. The laser beam13passes through the laser beam manipulator system26, then the laser beam rotating system27, the compensation system28, and the focusing system29after which it impinges upon the surface of the workpiece16at a preselected location. Although in this embodiment the compensation system28is located on the optical exit side of the laser beam rotating system27, in other embodiments of the present invention the compensation system28may be located on the optical entrance side of the laser beam rotating system27.

The laser source25may be any type of laser system that is capable of producing a laser beam of sufficient power, coherency, pulse width, pulse repetition time, and wavelength to be compatible with performing the desired machining operations upon the selected workpiece. For example, the laser source26may be a 25 Watt picosecond green laser of 532 nanometer wavelength for drilling holes in the range of 0.1 to 1 millimeters in diameter. For drilling holes in the range of 1 to 5 millimeters in diameter, visible lasers and infrared lasers of wavelengths such as 1024 nanometers and 1550 nanometers with pulse width in the range from nanoseconds to milliseconds and power levels in the 25 to 4,000 Watt range may be used. As those skilled in the art would realize, the optical components used in the laser drilling head23must be selected to be compatible with the laser source so as to avoid damaging those components during operation.

The beam manipulator system26includes a mirror2. The mirror2is the only dynamically movable optical component of the laser beam manipulator system26. In the embodiment shown inFIG. 1, the mirror2is dynamically and reciprocally translatable along the direction of the incoming laser beam13as is indicated by the arrows8. The mirror2is also dynamically and reciprocally tiltable around a first physical or virtual axis30which is perpendicular to the nominal optical axis14of the laser drilling head23. For alignment purposes, the mirror2in this embodiment, may also be tilted and locked in place around a second axis that is perpendicular to the first axis30.

The mirror2is provided with support and deflection systems for moving the mirror2during the operation of the laser drilling device25. Such systems are known in the art and not described herein. The linear motion of the mirror2, e.g., from a location where its axis30intersects the nominal optical axis14to a second position a distance d away as shown by the solid and outlined depictions of the mirror2, moves the laser beam13from its initial path along the nominal optical axis14to a new position indicated by laser beam13A which is a distance d away from the nominal optical axis14. This has the effect of moving the laser beam13A after it exits the compensation device28a distance r away from the nominal optical axis14and consequently, after passing through the focusing system, of determining the angle of incidence θ of the laser beam13A upon the surface of workpiece16(assuming the surface of the workpiece16is essentially perpendicular to the nominal optical axis14) and, consequently, the contour of the hole that is cut into the workpiece16. The dynamic tilting of mirror2is indicated by arrows11. The amount of tilting of the mirror2determines the angle of incidence at which the laser beam13(or13A) strikes a first optical surface of the optical rotating system, e.g., surface9of Dove prism1. This, in turn, determines the distance ρ away (seeFIG. 2for clearer indication of distance ρ) from the intersection point on the surface of the workpiece16of the nominal optical axis14of the laser drilling head23that the laser beam13(or13A) strikes the surface of the workpiece16.

The present invention also includes embodiments wherein the mirror2is dynamically and reciprocally tiltable about a second physical or virtual axis that is perpendicular to the first axis30. In some embodiments, this tiltability about the second axis is provided instead of the tiltability around the first axis30as described above, while in other embodiments this tiltability is in addition to the tiltability around the first axis30. Dynamically tilting the mirror2around this second axis permits the cut profile to take the shape of a hyperbolic curve.

In some embodiments of the present invention multiple mirrors, some of which may be stationary and others of which are dynamically and reciprocally movable, may be used in place of the mirror2such that together they perform the translation and rotational functions described above for mirror2. However, the use of multiple mirrors adds complexity to the laser drilling head23and so is less desirable than the use of a single mirror, e.g., the mirror2.

The laser beam rotating system27comprises one or more image rotation elements, such as the Dove prism1. Each image rotation element is spinnably supported so that it has an axis of rotation that coincides with the nominal optical axis14of the laser drilling head23. One manner of providing such a support is by mounting the image rotation element within a hollow shaft motor that has its axis of rotation aligned with the nominal optical axis14. In some embodiments, as described below, spinning the image rotation element around the nominal optical axis14has the effect of rotating the laser beam13(or13A) about its own optical axis, as is indicated inFIG. 1by arrow12with regard to laser beam13. When the optical axis of the laser beam13does not coincide with the nominal optical axis14of the laser drilling head23, as is the case for laser beam13A, spinning the image rotation element (e.g., the Dove prism1) permits the laser beam13A to traverse around the nominal optical axis at radius ρ upon the surface of the workpiece16. The mounting of the image rotation element (or elements) also permits the image rotation element (or elements) to be adjusted and locked into place during a pre-operation alignment setup procedure.

The image rotation element (or elements) may chosen to make the angular speed of rotation7of the laser beam13(or13A) to be the same as the angular speed of rotation6of the image rotation element (or elements), as would be the case if a set of wedge plates were used as the image rotation elements. However, such choices have the disadvantage that the laser beam does not spin about its own optical axis. Preferably, the element (or elements) is chosen so that the angular speed of rotation7of the laser beam13(or13A) is higher than that of the angular speed of rotation6of the image rotation device itself. For example, when the image rotation element is a prism (e.g., a Dove prism1or an Abbe-Koenig prism) or a mirror arrangement (e.g., a K-mirror arrangement), the angular speed of rotation7of the laser beam13(or13A) is twice the angular speed of rotation6of the image rotation element itself.

The compensation system28has as its only laser beam path shifting optical elements two wedge plates3,4fixedly mounted to synchronously spin with the image rotation element, e.g., the Dove prism1. The synchronous spinning may be accomplished, for example, by operably connecting the laser beam rotating system27and the compensation system28either mechanically or by providing separate spin drives for the two systems which are driven at the same angular rotation speeds. The synchronous spinning may also be accomplished by any means known in the art.

Although the wedge plates3,4are fixed in place relative to each other and the laser beam rotating system27during the operation of the laser drilling head23, they are mounted so as to be adjustable with relation to one another during a pre-operation alignment setup procedure of the laser drilling head23. This adjustability allows the wedges3,4to be set so that, in combination, they substantially cancel out the manufacturing optical defects and the mounting irregularities of the optical element or elements of the laser beam rotating system27. The mounting of the wedge plates3,4may be configured to permit both wedge plates3,4to be adjusted and then locked into place. Alternatively, the mounting may be configured so that one of the wedge plates3,4is fixed and only the other one is fixably adjustable with its adjustability confined to enabling the wedge plate to turn around the nominal optical axis14of the laser drilling head23a sufficient amount to cancel out the aforementioned deficiencies before it is locked into place.

In some embodiments of the present invention, only a single wedge plate, e.g., wedge plate3, is used instead of a set of two wedge plates as the only laser beam shifting optical element of the compensation system, e.g., compensation system28. These embodiments are less preferred because it is necessary to select the single wedge plate carefully so that, by itself, the wedge plate, e.g., wedge plate3, can cancel out the manufacturing optical defects and mounting irregularities of the optical element or elements of the laser beam rotating system27.

The focusing system29comprises one or more focusing lenses, e.g., lens5. The lens or lenses are mounted so that they may be adjusted during a pre-operation alignment setup procedure both with regard to tilt about axes perpendicular to the nominal optical axis14of the laser drilling head23and with regard to position along the nominal optical axis14. In some embodiments of the present invention, the lens or lenses are mounted so that they are immovable during operation. More preferably, the lens or one or more of the lenses of the focusing system29are dynamically and reciprocally translatable along the nominal optical axis14, as indicated by arrows31, so as permit the depth of the focus point with respect to the surface of the workpiece16to be dynamically and reciprocally adjustable.

During the pre-operation alignment setup procedure, the non-dynamically controlled features of the components of the laser drilling device25(or laser drilling head23) are adjusted and then locked in place so that the laser beam output from the laser beam rotating system27is collinear with the nominal optical axis14(and mechanical rotation axis of the laser beam rotating system27) and the laser beam13is focused on the intersection point15of the nominal optical axis14with the surface of the workpiece16. As part of this alignment procedure, the mirror2is moved to the position in which is it depicted with solid lines inFIG. 1. When the mirror2is moved to the position in which it is depicted with dashed lines inFIG. 1, the angle of incidence of the laser beam13A with the surface of workpiece16(assuming the surface of the workpiece16is essentially perpendicular to the nominal optical axis14) is changed from zero (as it was for laser beam13) to θ, but the impingement point of the laser beam13A is unchanged from that of laser beam13.

During operation, the laser beam rotating system, e.g., laser beam rotating system27, is rotated at a predetermined angular velocity or over a range of predetermined angular velocities as the particular machining circumstances warrant. Higher angular velocities are desirable when the workpiece and cutting geometries make localized thermal deformation more likely. In embodiments of the present invention wherein the laser beam rotating system causes the laser beam angular velocity to be twice that of the mechanical angular speed of rotation of the laser beam rotating system, angular velocities of the laser beam about the nominal optical axis of the laser drilling head are typically between zero and 5,000 revolutions per minute. In some preferred embodiments of the present invention, the angular velocity of the laser beam about the nominal optical axis of the laser drilling head are in the range of between zero and 10,000 revolutions per minute. In this regard, the inventor of the present invention has found the surprising result that the present invention may be used at laser beam angular velocities much higher than the 1,000 revolutions per second described in aforementioned U.S. Pat. No. 7,842,901 and at the same time provide excellent controllability of the laser cut with fewer optical components and fewer dynamically controllable optical elements.

The laser drilling devices and laser drilling heads of the present invention may be used to make any desired cutting pattern in cases wherein the laser drilling device (or laser drilling head) and the workpiece are configured to be controllably movable in relation to one another. When this is the case, the devices that control the relative motion of the workpiece and the laser drilling device (or the laser drilling head) can be used alone or in conjunction with the dynamically controllable elements of the laser drilling device (or laser drilling head) to make the desired cutting pattern.

In cases wherein the cutting is done at selected locations on the workpiece while the workpiece and the laser drilling device (or laser drilling head) are maintained in fixed positions with regard to one another, the shape and contour of the cut are controlled by the dynamically controlled elements of the laser drilling device (or laser drilling head). In such cases, the desired geometry of the cut (which may be symmetrical or non-symmetrical) is controlled by moving the mirror of the laser beam manipulator, e.g. the mirror2ofFIG. 1, and by changing the depth of focus of the focusing system, e.g., the focusing system29ofFIG. 1, in the manners described above. For example, referring now toFIG. 2, there is shown a schematic of location on a workpiece surface32onto which a pair of coordinate axes x, y have been superimposed. The nominal optical axis of the laser drilling device (or laser drilling head) intersects the workpiece surface32at the intersection33of the axes x, y. By dynamically tilting the mirror, the distance ρ of each impingement point, e.g., impingement point36, of each laser pulse is controlled to produce the cut34as the laser beam is being planetarily rotated by the spinning of the image rotating system.

Referring again toFIG. 1, the laser source22, the laser beam manipulator system, the laser beam rotation system, and the focusing system are operably connected to the control system35. The control system35comprises one or more computers and/or microprocessors programmed to provide signals to control and/or coordinate the operations of the laser source22and the various components of the drilling head23during the laser cutting operation. The control system35may be included in whole or in part as a component of the laser drilling system25or of the laser drilling head23. Alternatively, all or part of the control system35may be an ancillary control system that is interfaced with one or more of the laser source22and the laser drilling head23.

In addition to the elements described with regard toFIG. 1, embodiments of the present invention may include additional elements. For example, in some embodiments of the present invention fractional wavelength plates are inserted into the laser beam path at one or more locations to adjust the polarity of the laser beam. For example, a half wavelength plate may be included on the laser beam entrance side of the image rotating system, e.g. half wavelength plate60as shown inFIG. 4. Another example is inserting a quarter wavelength plate in the laser beam path between the laser source and the mirror of the laser beam manipulator system. In some of embodiments of the present invention, elements such as structural supports for the laser source, laser drilling head, the control system, and/or the workpiece are provided. Referring toFIG. 3, there is shown a laser drilling system40in conjunction with an embodiment of the present invention. The laser drilling system40comprises a laser source42, a laser drilling head44, a control system46, a worktable for fixedly and/or movably supporting a workpiece, and a cabinet50for enclosing and supporting the other named components during the operation of the laser drilling system40.

While only a few embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that many changes and modifications may be made thereunto without departing from the spirit and scope of the present invention as described in the following claims. All patent applications and patents, both foreign and domestic, and all other publications referenced herein are incorporated herein in their entireties to the full extent permitted by law.