WO2018217930A1

WO2018217930A1 - Infrared through transmissive laser welding using complementary optical part

Info

Publication number: WO2018217930A1
Application number: PCT/US2018/034195
Authority: WO
Inventors: Scott Caldwell
Original assignee: Branson Ultrasonics Corporation
Priority date: 2017-05-26
Filing date: 2018-05-23
Publication date: 2018-11-29

Abstract

A complementary optical part is disposed so that it surrounds and abuts a transmissive plastic part in TTIr laser welding. The complementary optical part includes a complementary portion having an inner surface that has a negative complementary shape to a shape of a laser facing surface of the transmissive plastic part and an outer portion that has an outer surface. The complementary optical part is transmissive and has the same index of refraction as the transmissive plastic part. The complementary optical part is disposed so that the inner surface of the complementary portion abuts the laser facing surface of the transmissive plastic part. Since the complementary optical part and the transmissive plastic part have the same index of refraction, the infrared laser beam travels in a straight line through the complementary optical part and the transmissive plastic part.

Description

INFRARED THROUGH TRANSMISSIVE LASER WELDING USING

COMPLEMENTARY OPTICAL PART

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application

No. 62/51 1 ,431 filed on May 26, 2017. The entire disclosure of the above application is incorporated herein by reference.

FIELD

[0002] The present disclosure relates to infrared through transmissive laser welding.

BACKGROUND

[0003] This section provides background information related to the present disclosure which is not necessarily prior art.

[0004] Laser welding is commonly used to weld plastic parts together. One type of laser welding is through transmissive infrared laser welding, commonly referred to as TTIr. During TTIr welding, a transmissive plastic part and an absorptive plastic part are held together with a force with abutting surfaces at a weld interface in good contact with each other. Infrared laser radiation of a suitable wavelength is passed through the transmissive plastic part and impacts the absorptive plastic part at the weld interface and gets converted to heat by absorption by the absorptive plastic part. This heats the absorptive plastic part at the weld interface which is heated above a melting

temperature. As the absorptive plastic part melts, the heat is transferred across the weld interface to the transmissive plastic part melting the transmissive plastic part at the weld interface forming a molten weld at the weld interface. Once the infrared laser is turned off, the molten weld solidifies welding the parts together at the weld interface.

[0005] Known TTIr laser welding systems include trace laser welding systems and scanning laser welding systems. A spot laser tracks a weld path by movement of the laser device and/or infrared laser beam, work piece, or a combination thereof.

Trace laser welding systems use a movable frame to which the infrared laser light source is mounted, such as a gantry, to move the infrared laser beam and scanning laser welding systems welding systems use a galvo mirror to move the infrared laser beam. However, the term "trace laser welding" in the context of laser welding systems is sometimes broadly used for both types of laser welding system and as used herein has this broader meaning.

[0006] Fig. 1 is a diagrammatic view of a trace laser welding system 10. Trace laser welding system 10 includes a laser support unit 12 including a controller 14, an interface 16, a laser power supply 18 and a chiller 20. Trace laser welding system 10 also includes an infrared laser 22 coupled to support unit 12. Infrared laser 22 includes a source 24 of infrared laser light, such as a laser diode. Laser light source 24 generates an infrared laser beam 26 which is directed the parts 28, 30 being welded together. Infrared laser beam 26 tracks along weld path 32 to weld parts 28, 30 together at weld path 32.

[0007] As used herein, a laser facing surface of the transmissive plastic part is a surface of the transmissive plastic part that the infrared laser beam first hits when transmissive plastic part and the absorptive plastic part are being welded. The laser facing surface may have a uniform geometry, such as planar, or have a varying geometry, such as having different contours, different angles for example, at different portions of the laser facing surface.

[0008] If the infrared laser beam does not hit the laser facing surface of the transmissive plastic part perpendicular to the laser facing surface, the infrared laser beam is refracted and not pass through the laser facing surface in a straight line. In some cases, it would be desirable to have the infrared laser beam pass through the laser facing surface of the transmissive plastic part in a straight line, that is, without being refracted. It is therefore an object of the present disclosure provide a method of TTIr laser welding where the infrared laser beam passes through a laser facing surface of the transmissive plastic part in a straight line. In other cases, it would be desirable to have the infrared laser beam travel along a simple geometric path, such as a linear path.

SUMMARY

[0009] This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.

[0010] In accordance with an aspect of the present disclosure, a complementary optical part is disposed so that it surrounds and abuts a transmissive plastic part in TTIr laser welding. The complementary optical part includes a complementary portion having an inner surface that has a negative complementary shape to a shape of a laser facing surface of the transmissive plastic part and an outer portion that has an outer surface. The complementary optical part is transmissive and has the same index of refraction as the transmissive plastic part and is made of a material that doesn't melt when the infrared laser beam passes through the complementary optical part. The complementary optical part is disposed so that the inner surface of the complementary portion abuts the laser facing surface of the transmissive plastic part.

[0011] In an aspect, the infrared laser beam is directed at the outer surface of the complementary optical part so that as it traces around a weld path, it hits the outer surface perpendicular to the outer surface and travels through the outer surface in a straight line. Since the complementary optical part and the transmissive plastic part have the same index of refraction, the infrared laser beam will thus also travel in a straight line through the complementary optical part and the transmissive plastic part.

[0012] In an aspect, the infrared laser beam is directed to the outer surface of the complementary optical part includes with a galvo mirror so that as it traces around the weld path it hits the outer surface of the complementary optical part at an angle Θ determined by:

where A is a lateral distance between a vertical line through a fixed point of the galvo mirror fixed in X, Y and Z planes and a point on a laser facing surface of the absorptive plastic part where the infrared laser beam hits the laser facing surface of the absorptive plastic part, B1 is a vertical distance from the fixed point of the galvo mirror to the outer surface of the complementary optical part, and B2 is a depth between the outer surface of the complementary optical part and the point on the laser facing surface of the absorptive plastic part where the infrared laser beam hits the laser facing surface of the absorptive plastic part.

[0013] In an aspect, a complementary optical part for conveying an infrared infrared laser beam to a transmissive plastic part being welded to an absorptive plastic part has a complementary portion having an inner surface having a negative

complementary shape to a shape of a infrared laser facing surface of the transmissive plastic part and an outer portion having an outer surface. In an aspect, the outer surface of the complementary optical part is shaped so that it is perpendicular to the laser beam where the infrared laser beam hits the outer surface.

[0014] Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

DRAWINGS

[0015] The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.

[0016] Fig. 1 is a diagrammatic view of an example of a prior art trace laser welding system;

[0017] Fig. 2 is a diagrammatic view of a trace laser welding system that laser welds plastic parts in accordance with an aspect of the present disclosure using a complementary optical part;

[0018] Fig. 3 is a diagrammatic view of a trace laser welding system that is a variation of the trace laser welding system of Fig. 2;

[0019] Fig. 4 is a diagrammatic view of a trace laser welding system that is a variation of the trace laser welding system of Fig. 2; and

[0020] Fig. 5 is a diagrammatic view of a trace laser welding system that is a variation of the trace laser welding system of Fig. 2.

[0021] Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. DETAILED DESCRIPTION

[0022] Example embodiments will now be described more fully with reference to the accompanying drawings.

[0023] Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. [0024] The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms "a," "an," and "the" may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms "comprises," "comprising," "including," and "having," are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.

[0025] When an element or layer is referred to as being "on," "engaged to," "connected to," or "coupled to" another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being "directly on," "directly engaged to," "directly connected to," or "directly coupled to" another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., "between" versus "directly between," "adjacent" versus "directly adjacent," etc.). As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

[0026] Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as "first," "second," and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.

[0027] Spatially relative terms, such as "inner," "outer," "beneath," "below," "lower," "above," "upper," and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as "below" or "beneath" other elements or features would then be oriented "above" the other elements or features. Thus, the example term "below" can

encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

[0028] With reference to Fig. 2, in accordance with an aspect of the present disclosure a through transmissive infrared laser welding system that laser welds plastic parts 200, 202 is a trace laser welding system 204. Trace laser welding system 204 includes an infrared laser 206, one or more one or more galvonometer mirrors 208 shown representatively by galvonometer mirror 208 and that are individually and collectively referred to herein as galvo mirror 208, and a controller 210 configured to control infrared laser 206 and galvo mirror 208.

[0029] Plastic part 200 is a transmissive plastic part that is transmissive to an infrared laser beam 212 from infrared laser 206 and plastic part 202 is an absorptive plastic part that is at least partially absorptive to infrared laser beam 212. It should be understood that the partial absorptivity of absorptive plastic part 202 can be provided by an absorptive weld additive provided at a weld interface between parts 200, 202 in cases where plastic part 202 is made of a plastic that is transmissive to infrared laser beam 212. Plastic parts 200, 202 and a complementary optical part 214 are received in a fixture 216 of infrared laser welding system 204 and held together. A complementary portion 218 of the complementary optical part 214 surrounds a laser facing surface 220 of transmissive plastic part 200. The complementary portion 218 has an inner surface 222 having a negative complementary shape to a shape of laser facing surface 220 of transmissive plastic part 200. The complementary optical part 214 also has an outer portion 224 having an outer surface 226 that is shaped so that it is perpendicular to infrared laser beam 212 from infrared laser 206 as infrared laser beam 212 is traced around a weld path 228. As can be seen in Fig. 2, surface 226 is irregular in shape so that any particular point on the surface will be perpendicular to infrared laser beam 212 when infrared laser beam 212 hits that point.

[0030] Complementary optical part 214 is placed against transmissive plastic part 200 so that inner surface 222 of complementary portion 218 abuts laser facing surface 220 of transmissive plastic part 200. Complementary optical part 214 is transmissive and has the same index of refraction as transmissive plastic part 200. Complementary optical part 214 is also made of a material that does not melt as infrared laser beam 212 passes through it.

[0031] In operation, infrared laser beam 212 is directed to outer surface 226 of outer portion 224 of complementary optical part 214 so that as it traces around weld path 228 it hits outer surface 226 perpendicular to outer surface 226 - that is, at a ninety degree angle to outer surface 226 at each point where it hits outer surface 226 as it traces along the weld path 228. Infrared laser beam 212 will then pass through outer surface 226 in a straight line and transit through complementary optical part 214 and transmissive plastic part 200 in a straight line, impinging upon absorptive plastic part 202 as it exits transmissive plastic part 200. Since the shape of outer surface 226 of complementary optical part 214 need not match the shape of laser facing surface 220 of transmissive plastic part 200, the shape of outer surface 226 can be configured to simplify and optimize the path of infrared laser beam 212 as it is traces along the weld path 228.

[0032] While trace laser welding system 204 shown in Fig. 2 is shown with one infrared laser 206 and one galvo mirror 208, it should be understood that trace laser welding system 204 can have a plurality of infrared lasers 206 with associated galvo mirrors 208, shown illustratively by infrared laser 206 and galvo mirror 208 in phantom in Fig. 2.

[0033] With reference to Fig. 3, a trace laser welding system 300 that is a variation of laser welding system 204 is shown. Galvo mirror 208 (which may include a plurality of galvo mirrors 208 as discussed above) directs infrared laser beam 212 from a fixed point 209 of galvo mirror 208 fixed in the X, Y and Z planes to parts 200, 202, 214.As shown in Fig. 3, outer surface 226' of outer portion 224 of complimentary optical part 214' is a surface having a simple geometric shape, such as a flat, planar surface. A vertical distance, B1 , from fixed point 209 of galvo mirror 208 to outer surface 226' of complementary optical part is a fixed length but a depth, B2, between outer surface 226' and a point where the infrared laser beam hits a laser facing surface 302 of absorptive plastic part 202 can vary, and illustratively does vary. For a given depth, B2 and lateral distance A (a lateral distance between a vertical line through fixed point 209 of galvo mirror 208 and a point on laser facing surface 302 of absorptive plastic part 202 where infrared laser beam 212 hits laser facing surface 302), the angle Θ from the vertical at which infrared laser beam 212 is directed from galvo mirror 208 is determined by the following equation:

A = Bl * tan(0) + B2 * tan(arcsin(^¾ (1 )

It should be understood that that Equation (1 ) is transcendental and cannot be solved for Θ directly. However, Θ can be found by populating a two dimensional lookup table with Y2 and X as the variables.

[0034] The simple geometric shape of outer surface 226' of complementary optical part 214' greatly simplifies the geometric path for the infrared laser beam 212 as it traces along the weld path 228. In this example embodiment, this geometric path that infrared laser beam 212 takes is effectively a linear path. While infrared laser beam 212 is refracted when it hits outer surface 226' of complementary optical part 214', since it does so at an angle, it then travels in a straight path through complementary optical part 214' and transmissive plastic part 200 since complementary optical part 214' has the same index of refraction as transmissive plastic part 200.

[0035] With reference to Fig. 4, another variation 400 of a trace laser welding system in accordance with an aspect of the present disclosure is described. In trace laser welding system 400, infrared laser 206 is mounted to a movable frame 402.

Instead of galvo mirror 208 directing infrared laser beam 212 along a desired path, movable frame 402 moves infrared laser 206 which moves infrared laser beam 212 along the desired path. Outer surface 226" of complementary optical part 214" is a surface that has a simple geometric shape, such as a flat, planar surface. Outer surface 226" is also perpendicular to infrared laser beam 212 at each point along a path that infrared laser beam 212 hits outer surface 226." The simple geometric shape of outer surface 226" of complementary optical part 214" greatly simplifies the geometric path for the infrared laser beam 212 as it traces along the weld path 228. In this example embodiment, this geometric path that infrared laser beam 212 takes is effectively a linear path. Since complementary optical part 214" has the same index of refraction as transmissive plastic part 200, infrared laser beam 212 travels in a straight path through complementary optical part 214" and transmissive plastic part 200. Also, since infrared laser beam 212 is perpendicular to outer surface 226" when it hits outer surface 226", infrared laser beam 212 will travel through outer surface 226" in a straight line without being refracted. Infrared laser beam 212 will then transit through

complementary optical part 214" and transmissive plastic part 200 in a straight line, impinging upon absorptive plastic part 202 as it exits transmissive plastic part 200. [0036] With reference to Fig. 5, another variation 500 of a trace laser welding system in accordance with an aspect of the present disclosure is described. In trace laser welding system 500, infrared laser 206 is mounted to a movable frame 502.

Movable frame 502 moves infrared laser 206 which moves infrared laser beam 212 along the desired path. Outer surface 226"' of complementary optical part 214"' is a surface that has a simple geometric shape that is circular. Outer surface 226"' is also perpendicular to infrared laser beam 212 at each point along a path that infrared laser beam 212 hits outer surface 226."' The simple geometric shape of outer surface 226"' of complementary optical part 214"' greatly simplifies the geometric path for the infrared laser beam 212 as it traces along the weld path 228. In this example embodiment, this geometric path that infrared laser beam 212 takes is effectively a linear path. Since complementary optical part 214"' has the same index of refraction as transmissive plastic part 200, infrared laser beam 212 travels in a straight path through

complementary optical part 214"' and transmissive plastic part 200. Also, since infrared laser beam 212 is perpendicular to outer surface 226"' when it hits outer surface 226"', infrared laser beam 212 will travel through outer surface 226"' in a straight line without being refracted. Infrared laser beam 212 will then transit through complementary optical part 214"' and transmissive plastic part 200 in a straight line, impinging upon absorptive plastic part 202 as it exits transmissive plastic part 200.

[0037] The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.

Claims

CLAIMS What is claimed is:

1 . A method of through transmissive infrared laser welding a transmissive plastic part and an absorptive plastic part with trace laser welding, comprising:

holding the transmissive plastic part and the absorptive plastic part together in an infrared laser welding system that is a trace laser welding system with a complementary optical part surrounding the transmissive plastic part such that an inner surface of a complementary portion of the complementary optical part abuts a laser facing surface of the transmissive plastic part wherein the inner surface of the complementary portion has a negative complementary shape to a shape of the angled laser facing surface of the transmissive plastic part and an index of refraction that is the same as an index of refraction of the transmissive plastic part;

directing at least one infrared laser beam from at least one infrared laser to an outer surface of the complementary optical part; and

having the infrared laser beam trace around a weld path.

2. The method of claim 1 wherein directing the least one infrared laser beam to the outer surface of the complementary optical part includes directing it so that it hits the outer surface perpendicular to the outer surface and transits through the outer surface in a straight line and then transits through the complimentary optical part and the transmissive plastic part in a straight line.

3. The method of claim 1 wherein directing the least one infrared laser beam to the outer surface of the complementary optical part includes directing it with a galvo mirror so that as it traces around the weld path it hits the outer surface of the complementary optical part at an angle Θ determined by:

4. The method of claim 1 including directing a plurality of infrared laser beams from a plurality of infrared lasers to the outer surface of the complementary optical part and having each infrared laser beam trace around the weld path.

5. A through transmissive infrared laser welding system for laser welding together a transmissive plastic part and an absorptive plastic part that are received in the laser welding system, comprising:

a complimentary optical part surrounding the transmissive plastic part such that an inner surface of a complementary portion of the complementary optical part abuts a laser facing surface of the transmissive plastic part wherein the inner surface of the complementary portion has a negative complementary shape to a shape of the laser facing surface of the transmissive plastic part and an index of refraction that is the same as an index of refraction of the transmissive plastic part; and

an infrared laser that generates an infrared laser beam that is directed to an outer surface of the complimentary optical part and traced around a weld path.

6. The through transmissive infrared laser welding system of claim 5 wherein the outer surface of the complementary optical part is shaped so that the infrared laser beam hits the outer surface perpendicular to the outer surface as the infrared laser beam is traces around the weld path and transits through the outer surface in a straight line and then transits through the complimentary optical part and the transmissive plastic part in a straight line.

7. The through transmissive infrared laser welding system of claim 5 wherein the at least one infrared laser beam is directed to the outer surface of the complementary optical part with a galvo mirror so that as it traces around the weld path it hits the outer surface of the complementary optical part at an angle Θ determined by:

8. The through transmissive infrared laser welding system of claim 5 including a plurality of infrared lasers with each infrared laser generating an infrared laser beam that is directed to the outer surface of the complimentary optical part and traced around a weld path.

9. A complementary optical part (214) for conveying an infrared laser beam (212) to a transmissive plastic part (200) being welded to an absorptive plastic part, comprising:

a complementary portion having an inner surface having a negative complementary shape to a shape of a laser facing surface of the transmissive plastic part and an outer portion having an outer surface.

10. The complementary optical part of claim 9 wherein the outer surface is shaped so that it is perpendicular to the infrared laser beam where the infrared laser beam hits the outer surface.