TWI276448B - A surface-modified golf club head - Google Patents

Abstract

A surface-modified golf club head comprises a club head and a striking plate, and at least one high-energy modified area is provided on one surface of the club head and the striking plate. The modified area is processed by a high-energy beam generated from a high-energy-modifying device via an energy-uniforming device. The high-energy modified area possesses different mechanical characteristics than other areas. These mechanical characteristics effectively enhances a striking distance of the golf club head.

Description

1276448 Eight, invention description:

Beier's head and its modification method. The present invention utilizes a high-energy device to heat the parts of the golf club head to change the nature of the medicinal machinery, so that the mechanical properties of different regions of the same thickness on the golf club head are different to effectively increase the hitting distance. [Prior Art]

In the golf club _ design, in order to improve the anti-power capability of the golf club head, the usual practice is to reduce the thickness of the high-strength slamming panel, but this will also reduce the impact strength of the golf club head. Therefore, if the anti-counterfeiting ability of the golf club head meets the expected demand and maintains the golf club's tolerance, it becomes an important issue in the design. In response to this design problem of reducing the thickness of the ball striking panel and improving the impact strength, a number of different solutions have been proposed in several documents. For example, U.S. Patent No. 6,652,391, "Golf Club Head with Variable Thickness Fiont Wall," reveals that the wall of the high-going head has a change in thickness. In the geometry of the face shouting face, a lion-in-the-shouldered dog's starting area is opened, and in the embodiment, the raised area is opened, and there is a ring-opening body that is extended by the dog. Thereby, the strength of the front wall of the golf club head C:\Linda\PK Pftt\PKD88a doc

06/01/24/02:36 PX —5 — .1276448 and the ability to hit the ball can be improved at the same time. However, since the production of the variable thickness front wall must be formed by casting, powder metallurgy and other processes, it is no different. Increased process difficulty and production cost are not very suitable for practical manufacturing. - In addition, U.S. Patent Application Serial No. 20,060,0306, the disclosure of which is incorporated herein by reference in its entirety, the disclosure of the disclosure of the disclosure of the disclosure of the disclosure of The processing method refers to the golf head", and discloses a remelting mechanism using high energy, such as a laser remelting mechanism or a plasma remelting mechanism, for local remelting processing on the ball striking surface of the golf ball. For example, laser or plasma processing to obtain a better hardness hitting surface. In principle, the use of this laser plus refining process can change the mechanical properties of the ball striking face, such as

, 2, I and fatigue resistance, but such a laser device or remelting mechanism can easily make the energy beam shooter ^ on the surface of the thickness that is too large without improving the accessories with uneven distribution of energy 1 When the energy distribution is uneven, the processing accuracy of the golf ball head is reduced or defects are generated. Further, U.S. Patent No. 6,776,726, "G〇lf club Head" discloses a heat treatment method for a ball striking panel. The method mainly performs a aging heat treatment on a whole of a metal material hitting panel which is divided into a central area and a peripheral area, and then uses a laser beam for aging heat treatment. For the perimeter of the hitting panel, the 1276448 area has a precise local principle until the surface hardness of the surrounding area is reduced to between 4545 and 0.9 times the surface hardness of the central area. In this way, in addition to the elastic deformation ability of the surrounding area of the ping-pong and the ball hitting panel, the restitution c〇efficient is improved, and at the same time, the surface hardness and durability of the hitting-the central area of the panel are ensured. . "However, in such a heat treatment process, when the laser beam is used to accurately measure the local axis, it is still possible to see that the Lei Lei has not had the good energy. The uneven distribution of energy causes the surface of the heat-treated concrete in the surrounding area to partially melt or dent. Therefore, in order to avoid the occurrence of surface depression, the irradiation time and intensity of the laser must be limited, so that the heat treatment of the laser is large. In view of this, the present invention proposes a surface-finished golf club head, which can eliminate the above-mentioned shortcomings, and can make the heat treatment zone of the golf club head have a uniform energy distribution and heat treatment of the thin-walled portion. The quality, in turn, makes the golf club head have better hardness, tensile strength and wear resistance. [Summary of the Invention] The purpose of the present invention is to provide a surface-modified golf club head which is attached to the golf club head. - a predetermined portion, for example, a thin portion formed with a relatively thin thickness - a modified region - a modified region having a mechanical property different from other regions Ο a secondary object of the present invention Provide - the kind of golf club head of the table money upgrading process, C: \ Linda \ PK Pat \ PK988a doc

06/01/24/02:38 PM

—7 — .1276448 2 ΐ 读 读 读 —— —— —— —— —— —— —— —— —— —— —— —— —— —— —— —— —— —— —— —— —— —— —— —— —— —— —— —— —— —— —— —— —— —— —— —— —— —— —— —— —— —— —— —— —— —— The modified area of the surface of the Nanfu head of the surface modification can be formed in any area of the body of the high = head, such as the top, the bottom, the side surface and the neck, or can be formed in the golf club head The ball panel is, for example, a sweet and a poor area and its surroundings. On the other hand, the surface modification method of the present invention can modify the outer side surface and the inner side surface of the modified area. Preferably, the energy device of the above description is preferably a laser device, and the energy uniform device is preferably an integrating mirror.曰 ― Compared to the conventional golf club head, the surface modification of the golf club head of the present invention and the Qiansi are improved, and the hardness and tensile strength of the golf club head are simultaneously improved. [0] In order to make the above objects, features and advantages of the present invention more comprehensible, the following detailed description of the present invention will be described in detail with reference to the accompanying drawings. 2, the surface modified golf club head 1 of the first embodiment of the present invention comprises a head body U having a top (crown, unmarked), bottom, side, back and neck, a ball striking panel 12 and a The sleeve 13 is made in one piece. The head body u has at least a thin wall portion a of a metal substrate, and as shown in FIG. 2, the thin portion a is selectively formed on the top of the head body 11, and its thickness is compared with the head body u = other The thickness of the part is small, generally below L5mm, preferably in i C:\Linda\PK Pat\PK988& doc

06/01/24/02:36 PM .1276448 〃 Below, more preferably below 1.0mm, the best is below 811.8111111. In addition, the thin-walled portion a is formed with annular modified regions 111 and 112, and the mechanical properties of the modified regions 111 and 112 are different from those of other non-modified regions - in this embodiment, The golf club head 1 can be manufactured by means of integral molding or a combination of components, such as precision casting, forging, machining, machining, welding, insert pressing, adhesion, brazing, screwing, and the like. When manufactured in one piece, the golf club head 1 is made from a metal material (isotropic). When manufactured by component bonding, the golf club head 1 can also be made of a composite material of a metal material and a non-metallic material (anisotropic material). The above metal material may be selected from stainless steel (such as 17-4PH stainless steel), carbon steel, low carbon steel, alloy steel, low alloy steel, iron alloy, cast iron, nickel base alloy, structural steel, super alloy or titanium alloy. (such as 6 aluminum _4 vanadium titanium alloy) and other materials. The above non-metal material may be selected from various polymers and fiber composite materials (p〇lymer 〇r fiber _ reinforced C0mp0Site), such as carbon fiber (carbifn 沘 维拉 维拉 fiber (Kevlar 8 poly urethane fiber (4) henylene terephthalamide; PPTA)). In this embodiment, the modified regions ill and 112 are irradiated from a high-energy device 2 and are irradiated by an energy beam of an energy-integrating device 3 such as an integrating mirror, and the thin portion a of the club head 1 is partially The outer side surface of the region is formed by performing an energy heat treatment, and the high energy device 2 may be a plasma device or a YAG (yttrium-doped yttrium aluminum garnet) laser device or a carbon dioxide (C02) laser device. When the high-energy device 2 is a riding device, the energy is uniform C:\Linda\PK Pat\PK988a doc 9 — 06/01/24/02:36 PM 0 .12/6448 a laser on the outer side surface The beam (not shown) is in the thin-walled part a. In addition, when the focusing mode of the two 1 can be compared to the 2nd a_ heat treatment, the 'laser device' avoids heat treatment in the laser beam ^^, Γ, and defocusing '# The power density of the wall and the surface is too high, causing thin words to change and □, 曰. The position of the region where the high-energy heat treatment is performed is formed in the central portion of the rod Hr, and the main stress concentration region of the modified region 112 is P> Hey. In terms of the range of areas where high-energy heat treatment is performed, the lands of the landscaping i 2 are 30 mm and 10 mm, respectively, and the preferred internal and external differences are 8 mm and 4 mm, respectively. *1} Compared with the unheated area of the head body 11, the modified region 111 after high energy enthalpy and the high hardness, tensile strength and wear resistance are y, Therefore, the thin wall portion a having a thin thickness can be provided with sufficient hardness and friction to ensure the overall strength of the golf club head i. In the present implementation, the preferred hardness of the modified regions (1) and 112 is summarized as % ^ On the other hand, in the formation process of the aforementioned modified regions ln and 112, the device 2 is only applied to the head body η The thin wall portion a is single-sided modified, that is, only the outer surface of the two partial portions of the thin portion a is irradiated or referred to as a high-energy heat treatment. In this case, the modified regions U1 and 112 are preferably modified. The degree of eucalyptus or the depth of the beam is less than Umm. However, we can also use the high-energy device 2 on the thin-walled part of the head body u: C:\Linda\P&Pat\PX95S&doc ~ 10 —

06/01/24/02:38 PM 1276448 a double-sided modification, that is, simultaneous high-energy heat treatment of the outer and inner surfaces of the two partial portions of the thin-walled portion a, in which case the modified region The preferred modified depth of the inner side surface and the outer side surface of 111 and 112 is less than 1 mm 〇 _ _, ",, table () which reveals that the surface of the surface of the head is not high after the high-energy heat treatment modification (four) The result of the hitting performance test of the golf turn of the genius: the takeoff angle speed is faster than the unmodified head of the head after the upgrade (code), the flying height (foot), the rear spin [rpm]

Mu): 曰V;: Figure 4 'The surface modification of the second embodiment of the present invention ^ - the head body 11, the ball striking panel 12 and the neck 1: the body 1 body 11 and The ball striking panel 12 is formed by a square #= of a plurality of pieces combined and welded. The joint portion of the head core 11 rotor plate 12 belongs to 3. And the junction forms a boundary line b. Further, a modified region 113 is formed along the peripheral region of the side of the thin portion, and the modified region 11: (4) is a machine of other money fn. In the second modification, the 'modified zone 113 is the same as the first embodiment of the V-in-the-ground device 2 and the energy uniform device 3 and the same way, and the boundary line of the bonding portion of the ball striking panel 12 b ^ The field outside the field is formed by high-energy recording. The method of defocusing and the method of modifying the modified zone for single or double-sided modification are also the same as in the first embodiment. C:\Linda\PK Pat\PK988A d〇c

06/01/24/02: 3« P 11 1276448. Through such a modification, the joint welding portion of the club head body 11 and the ball striking panel 12 of the golf club head can be relatively improved. (4) Mechanical properties. Referring to FIG. 5 and FIG. 6, the surface modification of the third embodiment of the present invention is achieved. The golf club head 1 comprises a head body u, a ball striking panel 12 and a neck 13 which are integrally formed. Further, an annular modified region 121 is formed around the sweet spot of the central flat portion c of the ball striking panel 12. ^ ^ ^ ^ ^ ^ ^ ^ ^ ' In the present embodiment, the annular modified region 121 is the same as the high energy device 2 and the energy uniform device 3 described in the first embodiment and in the same manner. The outer surface of the area around the sweet spot of the flat portion C is formed by high energy heat treatment. Here, the defocusing mode of the high-energy device 2 and the method of performing single-sided modification or double-sided modification of the modified region selection are also the same as in the first embodiment, and will not be described again. In this way, the ball striking panel & preferred elastic deformation capability can be provided, and the high-slipping head of the squat can be provided, and the hitting performance can be improved. Referring to FIG. 7 and FIG. 8, the surface-modified golf ball according to the fourth embodiment of the present invention. The head 1 includes a head body u, a ball striking panel 12 and a set of necks 13, which are integrally formed. In addition, the two partial regions on the ball striking panel 12 respectively form modified regions 122 and 123 which are arranged in a concentric manner from the inside to the outside. In this embodiment, the modified regions 122 and 123 are used in marriage. The high energy recording 2 and the energy uniform device 3 described in the first embodiment and the same manner are applied to the flat panel. The sweet and depleted area of P C (SWeet Sp〇t) and the outer area of the C:\Linda\Plt Pat\PK9«8& ctoc 06/01/24/02:36 Ρ» 8 ~ 12 — 1276448 area around the sweet area The surface is formed by high energy heat treatment of different powers. Thereby, the sweetness zone and the mechanical properties such as hardness and 9 tensile strength in the outer region of the sweet zone are different. Herein, the method of using the defocusing mode of the high-energy device 2 and the method of performing single-sided modification or double-sided modification of the modified region selection are also the same as in the first embodiment, and will not be described again. The sweet zone of the hitting panel 12 of the embodiment of the ocean cr can have a small thickness and the surrounding area of the sweet zone can have a large thickness, and when the high energy=housekeeping is performed, the sweet zone can be more powerful. The high-energy heat treatment is performed to change the L and the high-energy high-energy treatment of the sweet zone is performed to form the modified region 123. Thereby, the sweet ginseng zone containing the modified zone 122 has better hardness and durability, and the modified f zone 123 ^ has better elastic deformation ability, thereby improving the performance of the golf club head. The positive body has been described in detail above for the surface modification of each embodiment of the present invention. It should be noted that the aforementioned thin wall portion a is not = the top of the head body ,, but may be located in the head body domain such as the bottom, the side, the back and the neck 13 and the aforementioned thin wall adjacent: the second is located on the hitting panel Any area on the 12th. . As described above, the present invention can be used to overcome the conventional remelting processing method by using the energy-dissipating device 2 to handle the golf ball in an appropriate defocusing manner. The resulting uneven distribution of energy and reduced reliability: the quality of the problem. Mechanical property of Yushuo 1: Linda\PK Pat\PK988&doc 〇6/〇1/24/〇2.36 p%—13—— 1276448 Although the present invention has been disclosed using the above preferred embodiments, it is not The scope of the present invention is defined by the scope of the appended claims, and the scope of the invention is defined by the scope of the appended claims. . 1276448 BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view showing a surface modified golf club head according to a first embodiment of the present invention and a surface modification method thereof. Figure 2 is a cross-sectional view showing the 2-2 section of the surface modified golf club head of Figure 1. ^ Fig. 3 is a perspective view showing the surface modification of the golf club head and its surface modification method according to the second embodiment of the present invention. Fig. 4 is a cross-sectional view showing the 4-4 section of the surface of the golf club head modified in Fig. 3. Fig. 5 is a perspective view showing a surface modified golf club head according to a third embodiment of the present invention and a surface modification method thereof. Figure 6 is a cross-sectional view showing the ό6 profile of the surface modified golf club head of Figure 5. Fig. 7 is a perspective view showing a surface modified golf club head according to a fourth embodiment of the present invention and a surface modification method thereof. Figure 8 is a cross-sectional view showing the 8-8 section of the surface modified golf club head of Figure 7. [Main component symbol description] 1 Golf club head 111 modified area 113 modified area 121 modified area 123 modified area 11 head body 112 to poor area 12 hitting panel 122 modified area 13 neck

C:\Linda\PK Pat\PIC9888. doc —15 — 06/01/24/02:36 PM 1276448 2 High-energy device a Thin wall c Flat plate 3 Integral mirror b Combined with boundary line

Claims (1)

1276^4&amp;i8^j, Shenmu Patent Fanyuan: 1 machine year 〇〇f豸日修(more) original | b- kinds of surface modified golf club head, including: hitting panel, with a flat change a mass region; and a + plate portion 'formed on the flat portion-first-the head portion combined with the ball striking panel, the top portion of the head body, the bottom portion, and a thin shell portion are located on the thin shell portion The second modification; the surface of the first modification zone, the second modification D, the outer surface of the device receives the white energy, and the energy irradiation of the product and the panel body junction homogenizing device == amount The device and the pass-energy, tensile strength, durability and welding = the hardness of the domain, a surface modified golf club head, including the mechanical properties of the gold. - Batting panel, with - flat section ;:3. A head body having a thin wall portion; wherein the outer surface formed on the flat portion receives the energy irradiation from the first; the second: the modified region homogenizing device, and has = == , as in the second paragraph of the patent application scope r = r_ in the head - two sides and in the job - and The upper part of the department = the shell area, the outer side of the second modified area is worn and the surface of the side receives the mechanical properties from the high energy coating and the energy of the energy homogenizing device is irradiated with other areas. , or not C:\Linda\PK Pat\PKa888. doc ηπ/ιη/ΐ8/ηι:3ΐ pm —17 — I276M8i8 Patent No. 95102656, the scope of the patent application is amended. a golf club head, wherein the second modified region is annular. 5. The surface of the golf club head modified according to the third aspect of the patent application, wherein the modified surface of the outer surface of the second modified region is modified A golf club head having a surface modification of the third modification of the patent application scope, wherein the inner surface of the second modified region is further irradiated with energy of the high energy device. &gt; 7. Patent application scope The surface-modified golf club head of item 6, wherein the outer surface of the second modified region and the inner surface have a modified depth of less than 1.0 mm 〇8, and the surface modified golf club of claim 2 Head, where the high energy The measuring device is selected from the group consisting of a laser device and a plasma device. 9. The surface modified golf club head according to claim 2, wherein the energy equalizing device is an integral mirror. 10. The golf club head modified according to the scope of claim 2, wherein the first modified zone is in a ring shape. 11. The golf club head modified according to the second aspect of the patent application scope, wherein The modified surface of the first modified region is less than 1.5 mm 〇12, and the surface modified golf club head according to claim 2, wherein the inner surface of the first modified region further receives the height Energy irradiation of the energy device. C:\Linda\PK Pat\PK9888. doc — 18 — OR/10/18/01:31 PM 1276 Iron 18 No. 95102656 Patent Application Revision This is a surface-modified golf course as claimed in item 12 of the patent application. a club head, wherein the outer surface of the first modified region and the inner surface have a modified depth of less than 1.0 mm 〇14, such as the surface modified golf club head of claim 2, wherein the head body and the The batting panels are combined and welded. 15. A surface modified golf club head comprising: a head body; and a ball striking panel; wherein the head body and the ball striking panel form at least one modified region, the outer surface of the modified region is received from a high energy device and is homogenized by an energy The energy of the device is irradiated with mechanical properties different from those of other regions, such as hardness, tensile strength, wear resistance, and weld bond strength. 16. The surface modified golf club head of claim 15 wherein the modified zone is formed in a region of the head body or a large amount of elastic deformation of the ball striking panel. 17. The golf club head of the surface modification of claim 15 of the patent scope, wherein the modified zone is formed in a main stress concentration area of the club head body or the ball striking panel. 18. A golf club head having a surface modification as claimed in claim 15 of the patent scope, wherein the modified zone is annular. 19. The golf club head modified according to the surface of claim 15 of the patent scope, wherein the modified zone is in a ring shape. 20. For example, if the golf club head of the surface modification of the scope of patent application is modified, C:\Linda\PK Pat\PK9888. doc —19 — 0fi/10/18/0I:3l PM 1276#18#95102656 In the patent range revision, the modified depth of the outer surface of the modified region is less than 1.5 mm. 21. The golf club head of the surface modification of claim 15 of the patent scope, wherein the inner side surface of the modified region receives the energy of the high energy device. 22. If the surface of the golf club head modified in the scope of patent application No. 21 is modified, the depth of the outer surface and the inner surface of the modified area is less than 1.0 mm 〇23, as in the scope of claim 15 The surface modified golf club head, wherein the high energy device is selected from the group consisting of a laser device and a plasma device. 24. The golf club head of the surface modification of claim 15 of the patent scope, wherein the energy equalization device is an integral mirror. 25. The golf club head of the surface modification of claim 15 of the patent application, wherein the club head body and the batting panel are integrally formed. 26, a surface modified golf club head, comprising: a head body; and φ a ball striking panel, which is coupled with the head body; wherein the hitting panel and the head body form a change The outer surface of the modified region receives the energy from a high-energy device and is irradiated by an energy homogenizing device, and has different hardness, tensile strength, wear resistance and weld bonding strength from other regions. - Mechanical properties. 27. The surface modified golf club head according to claim 26, wherein the modified surface of the modified region has a modified depth of less than 1.5 mm. C:\Linda\PK Pat\PK9888.doc —20 — 0Γ./10/18/0Ι:31 PM 12764^8.18^ 95102656 Application for Patent Scope Amendment 12764^8.18^ 95102656 interest 28. The surface modified golf club head of claim 26, wherein the inner side surface of the modified region receives the energy of the high energy device. 29. The golf club head modified according to the scope of claim 28, wherein the modified surface depth of the outer side surface and the inner side surface of the modified area is less than 1.0 mm 〇 30, as in the surface modification of claim 26 A golf club head, wherein the high energy device is selected from the group consisting of a laser device and a plasma device. 31. A surface modified golf club head according to claim 26, wherein the energy equalizing device is an integrating mirror. 32. A method for modifying a surface of a golf club head, the golf club head comprising a head body and a ball striking panel, the method comprising the steps of: providing a high energy device and an energy homogenizing device; and from the high energy The device outputs an energy beam and passes the energy beam through the energy homogenizing device in an out-of-focus manner to illuminate the head body and a partial area of the ball striking panel, wherein the local region has a hardness different from other regions, Mechanical properties of tensile strength, wear resistance and weld bond strength. 33. A method of surface modification of a golf club head according to claim 33, wherein the partial region is located in a thin wall portion. 34. The surface modification method of a golf club head according to claim 32, wherein only the outer surface of the partial area is irradiated by the energy beam C:\Linda\PK Pat\PKi) 888. doc — 21 — 0fi </ RTI> </ RTI> <RTIgt; </ RTI> <RTIgt; </ RTI> <RTIgt; </ RTI> <RTIgt; </ RTI> <RTIgt; </ RTI> <RTIgt; </ RTI> <RTIgt; The method for modifying the surface of a golf club head according to claim 32, wherein the outer side surface and the inner side surface of the partial region are irradiated by the energy beam. 37. The surface modification method of a golf club head according to claim 36, wherein the outer surface and the inner surface of the partial region have a modified depth of less than 1.0 mm. 38. The surface modification method of a golf club head according to claim 32, wherein the high energy device is selected from the group consisting of a laser device and a plasma device. 39. The surface modification method of a golf club head according to claim 32, wherein the energy homogenizing device is an integral mirror. 40. The method for modifying the surface of a golf club head according to claim 32, wherein the defocusing method is one of positive defocusing and negative defocusing. I 41. A surface modification method for a golf club head, the golf club head comprising a club head body and a ball striking panel, the method comprising the steps of: providing a high energy device and an energy uniform device; from the high energy device Outputting a first energy beam and passing the first energy beam through the energy uniform device in a defocusing manner to illuminate a first partial region of the ball striking panel; and outputting a second energy beam from the high energy device and The second energy beam is passed through the energy uniform device in a defocusing manner and then irradiated on the hitting panel C:\Linda\PK Pat\PK9888. doc — 22 — ΟΓ, /10/18/01:31 PM 1276M §18 Special fiber H倐 is a part of the brother of Zhengtai. For example, it is the surface of the golf club head of the 41st Wei Wei, and the first partial area is located in the sweet area and the 4 field is located around the sweet area. A part of the area 3, such as the surface of the golf club head of the 42nd item (4), the thickness of the sweet area is smaller than the thickness of the sweet area around the sweet area. Wherein the power of the first energy beam is higher than the surface of the golf club head of the fourth method of claim 4, wherein the high energy device is selected from the group consisting of: The group consisting of lasers is seven, 'hujin. 'And the turning device 46. The golf club according to claim 41, wherein the energy equalizing device is an integral mirror. Surface modification method 4 7. If the surface of the golf club head of the patent application scope is changed, the defocusing method is positive defocusing and negative defocusing, and the golf club head is in the 41st patent application scope. The surface is modified, wherein the first partial region and the second partial region are only gamuted by the energy beam. 1 Surface The surface modification of the golf club head according to item 41 of the Shenqing patent scope, wherein the first partial area and the second partial area have a modified depth of less than 1.5 mm. ~ Face, such as the surface modification method of the golf club head of the 41st patent application scope 42, 48 49 50 C:\Lincla\PK Pat\PK9888. doc 〇B/|〇/|8/ni;31 pm —23 </ RTI> </ RTI> <RTIgt; </ RTI> <RTIgt; </ RTI> <RTIgt; </ RTI> <RTIgt; </ RTI> <RTIgt; </ RTI> <RTIgt; </ RTI> <RTIgt; 51. The surface modification method of a golf club head according to claim 50, wherein the first partial region and the outer surface of the second partial region have a modified depth of less than 1.0 mm. surface C:\Linda\PK Pat\PK9888. doc —24 — nn/10/18/01:31 PM