CONTROLLING THE STIFFNESS OF A HOLLOW METAL BAT BY PROVIDING HELICAL INTERNAL RIBS

Abstract

A hollow metal bat comprising an elongated tubular structure having a barrel portion, a handle portion and a tapered portion connecting the barrel portion to the handle portion, and further comprising at least one helical internal rib formed along at least a portion of the elongated tubular structure.

Description

REFERENCE TO PENDING PRIOR PATENT APPLICATION

This patent application claims benefit of pending prior U.S. Provisional Patent Application Ser. No. 61/448,063, filed Mar. 1, 2011 by Matthew Fonte for CONTROLLING THE STIFFNESS OF A METAL BAT BY CREATING INTERNAL RIBS (Attorney's Docket No. FONTE-5 PROV), which patent application is hereby incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to baseball bats and softball bats in general, and more particularly to metal baseball bats and metal softball bats.

BACKGROUND OF THE INVENTION

Baseball bats and softball bats (hereinafter sometimes referred to simply as “bats”) are well known in the art. Originally, bats were made of wood. However, more recently, some bats (and particularly softball bats) have been made of metal. In general, metal bats are made with a hollow construction in order to reduce their weight. See FIG. 1, which shows an exemplary hollow metal bat.

Metal bats exhibit two types of vibrational modes, i.e., bending modes and hoop modes. Bending modes relate to vibrations which extend along the longitudinal axis of the bat. See FIG. 2, which shows exemplary bending modes for a hollow metal bat. Hoop modes are unique to hollow bats and involve only a radial vibration of the barrel of the bat. See FIG. 3, which shows exemplary hoop modes for a hollow metal bat. The lowest-frequency hoop mode is responsible for both the “ping” sound of a hollow metal bat and the so-called “trampoline effect” (i.e., the spring effect of the barrel of the bat when it encounters the ball).

Modal analysis is used to determine the mode shapes and frequencies for a wide variety of bats. In general, higher bat performance (with respect to batted ball speed) tends to be achieved with bats which have lower hoop frequencies.

Thus, a primary objective of the present invention is to provide a new hollow metal bat which is characterized by lower hoop frequencies and hence improved bat performance.

SUMMARY OF THE INVENTION

In accordance with the present invention, one or more helical internal ribs are formed on the interior of the hollow metal bat in order to control the stiffness of the bat and thereby lower hoop frequencies (and hence improve bat performance). The helical internal ribs also help to minimize bending failure modes and hoop failure modes. The one or more helical internal ribs may vary in frequency (i.e., number), pitch, height and width profile in order to provide the bat with the desired performance characteristics. Among other things, the goal of the invention is to coordinate the frequency (i.e., number) of the spiral ribs disposed about the inner circumference of the bat barrel, and the pitch, height and width profile of those ribs, so as to allow the creation of a thin wall, light weight bat barrel, while tuning (i.e., controlling) the stiffness of the barrel. Controlling the stiffness of the barrel consequently controls the “trampoline effect” of the barrel, whereby to ensure maximum bat performance while staying within bat regulations. Without helical internal ribs, the only other way to control the stiffness of the bat is to either (i) increase the thickness of the side wall of the bat (which is undesirable since it increases the weight of the bat), and/or (ii) form the bat out of a material which has a higher modulus of elasticity (which typically means using a denser, and hence heavier, material).

U.S. Pat. No. 5,931,405 discloses a metal bat having internal grooves which are circumferential in nature, and which are machined into the interior side wall of the bat. However, these grooves are cavities, i.e., recesses formed in the side wall of the bat, and their purpose is simply to reduce the weight of the metal bat. Thus, the grooves of U.S. Pat. No. 5,931,405 are the structural inverse of the positive ribs of the present invention (i.e., they are recesses rather than the projections of the present invention). Furthermore, the internal grooves of U.S. Pat. No. 5,931,405 have a different configuration than the ribs of the present invention (i.e., they are circumferential rather than helical). And, significantly, the purpose of the surface grooves of U.S. Pat. No. 5,931,405 is different than the purpose of the helical internal ribs of the present invention (i.e., the surface grooves are for weight-reduction rather than strength increase). Also, the method of making the internal grooves of U.S. Pat. No. 5,931,405 is different from the method of making the helical internal ribs of the present invention—specifically, the grooves of U.S. Pat. No. 5,931,405 are made by machining away wall thickness, whereas the spiral ribs of the present invention are formed on the interior wall of the bat during cold working (i.e., flowform, swaging, impact extruding, drawing, etc.). The cold work process used to form the helical internal ribs of the present invention provides a microstructure which is metallurgically-superior to the microstructure provided by the “machined-away” process used to form the internal grooves of U.S. Pat. No. 5,931,405. And, furthermore, the circumferential ribs of U.S. Pat. No. 5,931,405 have little effect on the bending modes of the bat.

U.S. Pat. No. 2,340,156 relates to “cast integral” longitudinal ribs. These longitudinal ribs have little effect on the hoop modes of the bat. In contrast, the helical internal ribs of the present invention improve both the hoop modes and the bending modes of the hollow metal bat. Furthermore, the “cast integral” casting of U.S. Pat. No. 2,340,156 is done hot, yielding cast grains which are large, often brittle and susceptible to fracture—all features which are undesirable in a bat. In contrast, the cold worked helical internal ribs of the present invention provide both dimensionally—and metallurgically—superior ribs.

In one preferred form of the invention, there is provided a hollow metal bat comprising an elongated tubular structure having a barrel portion, a handle portion and a tapered portion connecting the barrel portion to the handle portion, and further comprising at least one helical internal rib formed along at least a portion of the elongated tubular structure.

In another preferred form of the invention, there is provided a method for forming a hollow metal bat, the method comprising:

positioning a preform on a mandrel, wherein the mandrel comprises at least one helical groove; and

applying compression to the outside diameter of the preform so as to form an elongated tubular structure having a barrel portion, a handle portion and a tapered portion connecting the barrel portion to the handle portion, and further comprising at least one helical internal rib formed along at least a portion of the elongated tubular structure.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention will be more fully disclosed or rendered obvious by the following detailed description of the preferred embodiments of the invention, which is to be considered together with the accompanying drawings wherein like numbers refer to like parts, and further wherein:

FIG. 1 is a schematic view of an exemplary prior art hollow metal bat;

FIG. 2 is a schematic view showing exemplary bending modes of a hollow metal bat;

FIG. 3 is a schematic view showing exemplary hoop modes of a hollow metal bat;

FIG. 4 is a schematic view, partially broken away, showing a new and improved hollow metal bat formed in accordance with the present invention;

FIG. 5 is a side sectional view of the hollow metal bat shown in FIG. 4;

FIG. 5A is a schematic view showing a section of the barrel portion of a hollow metal bat having a plurality of helical internal ribs;

FIG. 6 is a schematic view showing that hollow metal bats with lower hoop frequency have increased performance;

FIG. 7 is a schematic view of a bat;

FIG. 8 is a schematic view showing the optimal hoop frequency of an aluminum bat;

FIG. 9 is a schematic view showing exemplary bending modes of a hollow metal bat;

FIG. 10 is a schematic view showing exemplary hoop modes of a hollow metal bat;

FIG. 11 is a schematic view showing a preferred rib design;

FIG. 12 is a schematic view showing exemplary buckling deformations of a tube;

FIG. 13 is a schematic view comparing the balance point of various bats;

FIG. 13A is a schematic sectional view showing a multi-wall bat formed in accordance with the present invention;

FIG. 14 is a schematic view showing a flowforming process;

FIG. 15 is a schematic view showing longitudinal ribs formed inside a hollow metal bat; and

FIG. 16 is a schematic view showing helical ribs formed inside a hollow metal bat.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a new and improved hollow metal bat which advantageously addresses various aspects of bat design, as discussed herein.

Looking first at FIGS. 4 and 5, there is shown a new and improved hollow metal bat 5 which generally comprises an elongated tubular structure 10 having a barrel portion 15, a handle portion 20 and a tapered portion 25 connecting barrel portion 15 to handle portion 20. An end cap 30 closes off the distal end of barrel portion 15, and a knob 35 closes off the proximal end of handle portion 20.

In accordance with the present invention, one or more helical internal ribs 40 is formed along at least a portion of elongated tubular structure 10. More particularly, one or more helical internal ribs 40 is formed along at least a portion of barrel portion 15 and, in one preferred form of the invention, the one or more helical internal ribs 40 is formed along substantially the entire barrel portion 15. In one particularly preferred form of the present invention, one or more helical internal ribs 40 extends along substantially the entire length of bat 5. Preferably a plurality of helical internal ribs 40 are formed on hollow metal bat 5. See, for example, FIG. 5A, which shows a section of the barrel portion 15 of a hollow metal bat 5 having a plurality of helical internal ribs 40. The one or more helical internal ribs 40 may vary in frequency (i.e., number), pitch, height and width profile in order to provide the bat with the desired performance characteristics.

Furthermore, if desired, the pitch, height and/or width profile of each helical internal rib 40 may vary along the length of the rib.

By providing bat 5 with one or more helical internal ribs 40, and by varying the frequency (i.e., number), pitch, height and width profile of those ribs, various aspects of bat design can be advantageously addressed, as will hereinafter be discussed.

Regulatory Constraints

Regulatory constraints on bat designs, and specifically non-wood bat designs, are making it increasingly difficult to engineer superior performance while remaining within regulatory standards.

One standard for testing baseball bat performance is the National Collegiate Athletic Association (NCAA) Bat-Ball Coefficient of Restitution (BBCOR) protocol which became effective on Jan. 1, 2011. This protocol has been adopted as an addendum to the NCAA standard ASTM F2219, Standard Test Methods for Measuring High-Speed Bat Performance. For a bat to adhere to the new BBCOR standard, it must meet the following criteria:

• • size and weight specifications;
  • length-weight ratio;
  • Moment of Inertia (MOI) requirement (based the bat's length class);
  • the bat ring must pass over the entire length of the bat before and after every hit; and
  • the BBCOR must not exceed 0.500.

The Bat-Ball Coefficient-of-Restitution (BBCOR) measures the combined elastic properties of the bat-ball system as a function of hoop frequency. The solid curve shown in FIG. 6 is a theoretical prediction from a simple mass-spring model of the “trampoline effect” of the bat-ball system, and the data points represent the measured BBCOR values (extracted from the original field study data by Alan Nathan) for the five metal bats used in the Grisco-Greenwald batting cage study. The plot in FIG. 6 shows that the higher performing bats have a lower hoop frequency, which indicates that the simple mass-spring model of the trampoline effect captures the essential physics of the bat-ball system.

There is a fine line between optimizing bat performance and not exceeding the new BBCOR standard. Significantly, the present invention provides one method for doing so, i.e., by providing a hollow metal bat that uses helical internal ribs in its wall thickness to improve or control bat stiffness. In this respect it should be appreciated that longitudinal ribs increase the bending stiffness of a bat, while circumferential ring ribs control its hoop stiffness. The new helical internal ribs of the present invention simultaneously control both stiffnesses (i.e., bending stiffness and hoop stiffness) of the bat. The tapered handle of the bat can also have internal helical ribs which can control stiffness in the non-barrel section of the bat. Without helical internal ribs, the thickness of the side wall of the bat would have to be increased in order to increase the bending and hoop stiffnesses, which would add undesirable weight to the bat. Adding helical internal ribs to the bat increases the Moment of Inertia, which increases the bending stiffness, i.e.,

Bending stiffness=E×I

where E=Young's Modulus and I=Moment of Inertia.

Preferably, the height of the helical internal ribs should be less than the wall thickness of the bat in order to keep sinking to a minimum. In one preferred form of the invention, the height of the ribs ranges from about 40% to about 60% of the thickness of the side wall of the bat. In addition, the helical internal ribs are preferably attached to the base (i.e., to the side wall of the bat) with generous radii at the corners where the helical internal ribs meet the side wall of the bat. The helical internal ribs of the present invention can be spiraled to the center line of the bat, and/or can vary in frequency (i.e., number) around the circumference of the inner barrel and/or inner tapered section of the bat, and/or can vary in pitch, height and width profile along the length of the bat. The helical internal ribs of the present invention can be engineered so as to (i) allow the bat to have a thinner barrel wall thickness, thereby making the bat lighter (and hence able to be swung faster), (ii) enhance bat strength for durability so as to prevent denting or plastic deformation during usage, (iii) increase the barrel's “sweetspot” by tailoring its stiffness along the barrel, and (iv) design/tune the barrel's stiffness so as to maximize its “trampoline effect” for optimal BBCOR performance without violating regulatory constraints.

Bat Speed

As discussed above, by providing helical internal ribs in hollow metal bats, the bats can be provided with increased durability and improved performance characteristics.

As seen in FIG. 7, bats typically include a handle portion, a barrel portion, and a tapered portion joining the handle portion to the barrel portion.

The barrel of these bats is generally formed from aluminum or another suitable metal, and/or one or more composite materials. Barrels having a single-wall construction, and more recently a multi-wall construction, have been developed. Modern metal bats typically include a hollow interior, such that the bats are relatively lightweight and allow a ball player to generate substantial “bat speed” or “swing speed”—the lighter the bat, the faster it can be swung, and hence the further the ball will go. In accordance with the present invention, helical internal ribs can be provided on the interior of single-wall bats and double-wall bats (with double-wall bats, the ribs may be formed on the inner and/or outer sleeves) so as to reduce bat weight and hence improve bat speed.

Durability

While it is generally desirable to have a light bat, it is also important that the bat be durable enough that it will not dent when hitting the ball. As such, barrel wall thicknesses are often designed to be heavier than desired so as to prevent denting or plastic deformation of the bat during usage. However, with the present invention, the helical internal ribs of the bat can be used to strengthen a very thin, light-weight bat wall. Such helical internal ribs can be used on single-wall bats and double-wall bats (with double-wall bats, the ribs may be formed on the inner and/or outer sleeves) so as to improve bat strength and durability while minimizing bat weight. Helical or spiral ribs provide reinforcement for the thin wall barrel in both the bending (longitudinal) and hoop (radial) directions.

Sweetspot

The “sweetspot” of a bat is the portion of the barrel which, when struck by the ball, provides maximum batting performance. It is the location on the barrel at which the collision between ball and bat occurs with maximum efficiency and with the transmission of minimum vibration through the bat to the hands of a user. While highly subjective, many players would accept the proposition that the sweetspot of the bat has a dimension of approximately 2 inches in length, and possibly up to 4 inches in length, and is located generally midway along the barrel portion of the bat. It will be appreciated that it is highly desirable to provide an improved bat with the largest possible sweetspot while remaining within bat regulations. By providing a hollow metal bat with the helical internal ribs of the present invention, and by varying the frequency (i.e., number), pitch, height and width profile of those ribs, the axial and radial stiffnesses of the bat can be varied along the barrel so as to increase the sweetspot of the bat. Additionally, by thickening the barrel wall in the area of the sweetspot, and by providing the helical internal ribs of the present invention, an optimal sweetspot configuration can be achieved. Furthermore, by providing helical internal ribs in the tapered handle of the bat, vibration can be dampened, whereby to provide a vibration-free, “soft” feel to the bat.

“Trampoline Effect”

Hollow metal bats typically exhibit a phenomenon known as the “trampoline effect”, which essentially refers to the rebound velocity of a ball leaving the barrel of the bat as a result of dynamic coupling between the bat and the ball. It is desirable to construct a bat having a high “trampoline effect” so that the bat may provide a high rebound velocity to a pitched ball upon contact. The “trampoline effect” is a direct result of matching the fundamental frequencies between the bat and the ball (dynamic coupling), and the resulting compression and strain recovery of the bat barrel. During this process of barrel compression and decompression, energy is transferred to the ball resulting in an effective Coefficient of Restitution (COR) of the ball, which is the ratio of the post impact ball velocity to the incident ball velocity, i.e.,

COR=Vpost impact/Vincident

In other words, in general, the COR of the ball improves as the “trampoline effect” increases.

There is a need to tailor the trampoline effect of the bat so as to maximize the ball's COR, while still engineering the bat to be within bat regulations. In accordance with the present invention, helical internal ribs can be provided on single-wall bats and double-wall bats (with double-wall bats, the ribs may be formed on the inner and/or outer sleeves) so as to control and/or maximize the “trampoline effect” of the bat, yet remain within bat regulations.

See FIG. 8, which shows the optimal hoop frequency of an aluminum barrel.

For the new NCAA regulations, the maximum allowable BBCOR is 0.500. Therefore, it is desirable to tailor the hoop frequency (i.e., barrel stiffness) of the bat so that its “trampoline effect” is consistently optimized for a BBCOR of between 0.465-0.500 (and still meet the other bat regulations). As a point of reference, wood bats typically have a 0.462 BBCOR. In accordance with the present invention, the BBCOR of the bat may be specified by providing helical internal ribs of the appropriate frequency (i.e., number), pitch, height and width profile.

Hoop Frequency

During the collision between the ball and the bat, a large amount of kinetic energy is lost when the ball deforms and compresses around the barrel of the bat. In a wood bat, the barrel of the bat is essentially rigid, such that all of the deformation associated with the bat-ball collision occurs in the ball. However, in hollow non-wood (e.g., metal) bats, the barrel can flex during the collision. Thus, the ball typically deforms less when impacting the relatively “flexible” barrel of a hollow metal bat than when impacting the relatively inflexible barrel of a wood bat. Significantly, with a hollow metal bat, less energy is dissipated by the ball due to the reduced ball deformation, and the energy used to compress the barrel of the bat can be returned to the ball as the barrel rebounds. This phenomenon of barrel flexing is known as the “trampoline effect”. The rate at which the trampoline effect occurs is related to the mass and stiffness of the barrel of the bat and, therefore, to one of the natural frequencies of the barrel of the bat. The natural frequency at which the bat trampoline effect occurs is the aforementioned hoop mode. As noted above, the frequency (i.e., number), pitch, height and width profile of the helical internal ribs can be designed to stiffen the bat so as to control the hoop frequencies. In addition, as also noted above, bending modes are also important to consider during hitting. Again, the frequency (i.e., number), pitch, height and width profile of the helical internal ribs can be designed to stiffen the bat so as to control the bending frequencies. In the preferred form of the invention, the frequency (i.e., number), pitch, height and width profile of the helical internal ribs are designed to stiffen the bat so as to control both the bending and hoop frequencies.

See FIGS. 9 and 10, which show exemplary bending modes and hoop modes, respectively, of a hollow metal bat.

Internal Ribs in the Barrel and Tapered Section

As noted above, a primary reason for adding helical internal ribs in a hollow metal bat design is to improve the stiffness of the barrel and tapered sections of the bat. Helical internal ribs do this by increasing stiffness in the different sections of the bat where required. Because stiffness is a function of Young's Modulus and the Moment of Inertia, stiffness can also be improved by increasing the modulus of the material. However, moving from a material having a lower modulus (e.g., an aluminum alloy) to a material having a higher modulus, stiffer material (e.g., steel, stainless steel and/or a Titanium alloy) adds undesirable weight to the bat. Significantly, by utilizing the spiraled stiffening ribs of the present invention, it is now possible to use a material heavier than aluminum without increasing the overall weight of the bat, because the helical internal ribs can be used to add strength and stiffness to a very thin bat, e.g., a non-aluminum bat.

The frequency (i.e., number), pitch, height and width profile of the helical internal ribs can be varied so as to adjust bat stiffness. See FIG. 11, which shows one preferred rib profile.

The height of the helical internal rib is preferably less than the thickness of the adjoining wall, with the relative dimensions depending on loads, the frequency (i.e., number) of the helical internal ribs around the circumference of the bat, the pitch of the helical internal ribs, the width profile of the helical internal ribs, etc. at barrels can buckle, collapse, dent and even break from the buckling loads during barrel-ball contact, and the helical internal ribs of the present invention can help support the loads without adding significant weight to the bat.

See FIG. 12, which provides a schematic illustration of exemplary buckling of a barrel of a bat.

Center of Mass

The center of mass (CM) is also known as the balance point. The closer the CM is to the handle of the bat, the easier it is to swing the bat. FIG. 13 compares the balance points of four 30″ youth bats: three wood bats of weights 26 oz, 23 oz, and 20 oz, and one aluminum bat of weight 27 oz. The balance point for all three of the wood bats is located at the same place, which is to be expected since the profile shapes of the three bats are the same and they are all made from solid wood, so the balance point should be the same for all three bats regardless of their respective weights. In contrast, the balance point of the aluminum bat is more than an inch closer to the handle than the balance point for the wood bats—as a result, even though the aluminum bat is heavier than the wood bats, it is actually easier to swing since its balance point is closer to the handle. Thus, the swing weight of a bat is a function of both bat weight and the center of mass, which is the reason that not all 28 oz softball bats swing the same. An end-loaded bat can have the same weight as a normal bat, but will feel heavier because more of the mass is distributed towards the barrel end of the bat.

Technically, this all relates to the Moment of Inertia of the bat. MOI is the product of mass and the square of a distance which, while not the same as the balance point, is strongly influenced by the balance point. The closer the balance point is to the handle, the lower the MOI will be. Several studies have shown that swing speed depends strongly on the Moment of Inertia of the bat—a player can swing a lower inertia bat faster. This affects performance because higher bat speed is directly related to higher batted ball speed. Lowering the inertia of the bat too much will result in a lower amount of momentum that the bat carries into the collision with the ball, reducing the batted ball speed. Ideally, a player should use a bat with a high Moment of Inertia and swing it very fast in order to achieve optimal results. By using a hollow metal bat comprising helical internal ribs, the wall thickness of the bat can be designed thinner and the weight savings can be redistributed to the handle of the bat for an improved CM. Alternatively, the weight can be shifted to the distal tip/cap for increased MOI.

Single-Wall Bats and Multi-Wall Bats

Today, baseball bats and softball bats are frequently made solely from aluminum alloys, or aluminum alloys in combination with composite materials (“hybrid bats”), or most recently solely from composite materials, with the exception being the solid wooden bats used for the Major Leagues. Such bats are tubular in construction (i.e., hollow inside) in order to meet the weight requirements of the end user, have a cylindrical handle portion for gripping, a cylindrical barrel portion for hitting, and a tapered mid-section for connecting the handle portion to the barrel portion. Traditionally, such hollow metal bats have had a constant radial stiffness along their barrel portion, measuring the radial stiffness along the barrel wall as independent annular segments of the barrel wall at any location along the length of the barrel wall.

When aluminum alloys initially replaced wooden bats in most bat categories, the original aluminum bats were formed as a single member, that is, they were made in a unitary manner as a single-walled aluminum tube for the handle, taper and barrel portions. Such bats are often called single-wall aluminum bats and were known to improve performance relative to wooden bats as defined by increased hit distance. More recently (in the mid 1990's), improvements in bat design largely concentrated on further improving bat performance. This was accomplished primarily by thinning the barrel wall of the single-wall bat, and adding inner or internal, and/or outer or external, secondary members extending along the entire length of the barrel. These members are often referred to, respectively, as inserts or sleeves, while the main member is often referred to as a body, shell or frame. Such bats are often called double-wall bats, or multi-walled bats in the case where two or more secondary members provide more than two walls. The use of the helical internal ribs of the present invention can lighten the inserts and/or sleeves while maintaining bat stiffness/strength.

Such double-walled and multi-walled tubular bats generally obtain improved performance (in terms of hitting distance) by reason of the improved elastic deflection that is characteristic of a multi-layer barrel wall. The efficient batting of a ball is maximized by minimizing plastic deformation, both within the bat and within the ball. Ideally, during the collision between bat and ball, the barrel wall of the bat should not deform beyond its elastic limit. Use of a multi-wall (i.e., two or more members) construction along the entire barrel length allows the barrel portion of the bat to elastically deflect (or flex more) upon ball impact, which propels the ball faster and further than single wall bats.

The scientific principle governing improved bat performance is bending theory. When a ball impacts a bat, it has kinetic energy that must be absorbed by the bat in order to stop the ball. The bat stores most of this kinetic energy by flexing. The ball deforms as well. After the ball is stopped, the bat returns the energy it has stored by rebounding and sending the ball back towards where it came from. The more the bat barrel deforms upon ball impact without failing (i.e., denting or breaking) or experiencing plastic deformation, the lower the kinetic energy loss and hence the greater the kinetic energy returned to the ball from the bat as the impacted tubular barrel portion of the bat returns to its original shape.

To allow the bat barrel portion to deform requires lowering the radial stiffness of the barrel portion. The prior art double-walled (and multi-walled) tubular bats have traditionally accomplished this by thinning the main member of the barrel portion and adding thin secondary member insert(s) and/or sleeve(s) which are not bonded to the main member, but which generally extend throughout the full length of the barrel portion. Such inserts and sleeves are not coupled to the barrel wall portion of the frame, and these two contacting components may slide with respect to each other in the same manner that leafs slide within a leaf spring. The resultant lowered radial stiffness along the barrel portion length permits the barrel wall to deflect elastically.

U.S. Pat. No. 5,415,398 is an example of a multi-walled bat that discloses the use of a frame and an internal insert of constant thickness running the full length of the barrel portion of the bat in a double-wall construction.

U.S. Pat. No. 5,303,917 discloses a two-member bat of thermoplastic and composite materials.

U.S. Pat. No. 5,364,095 discloses a two-member bat consisting of an external metal tube and an internal composite sleeve bonded to the inside of the external metal tube and running the full length of the barrel portion of the bat.

U.S. Pat. No. 6,251,034 discloses a polymer composite second tubular member running throughout the full length of the barrel portion of the bat, with the members joined only at the ends of the barrel portion, with the balance of the composite member freely movable relative to the primary member.

U.S. Pat. Nos. 6,440,017 and 6,612,945 also disclose two-member bats with an outer sleeve and inner shell of constant thickness running the full length of the barrel portion.

See also U.S. Pat. Nos. 6,063,828, 6,461,760, 6,425,836 and U.S. Patent Publication No. 2001/0094882.

In all of the foregoing prior art multi-walled tubular bats, the bat secondary members (or inserts) extend along the entire frame barrel length, and the bat secondary members have a constant diameter and thickness which results in a uniform cross-sectional geometry along the length of the secondary members. Also, the bat members are not joined, except at their ends, in order to reduce radial stiffness of the barrel portion and thereby improve bat performance. Also, in all cases, the radial stiffness of the barrel portion is uniform or constant along the full length of the barrel portion of the bat.

While prior art single member tubular bats and prior art double-walled (and multi-walled) tubular bats have demonstrated improved performance, various regulatory authorities have raised safety concerns regarding improved performance bats and thus, some have established maximum performance standards for various categories of bats under their jurisdiction. As a result, manufacturers of bats are required to pass various controlled laboratory tests, such as bbf (batted ball performance), bbs (batted ball speed), etc. Furthermore, for a given bat category (e.g., “Slowpitch Softball”), there may be two or more regulatory bodies, each of which may establish a different standard. Furthermore, any of the regulatory bodies may change their standard from time to time. Such new or changed or varying regulations are extremely problematic, costly, and disruptive for both bat manufacturers and players.

It is generally undesirable to lower the performance of a bat by simply increasing the thickness of the barrel wall of one or more of the barrel members along its full length. This is because lowering the performance of the bat by merely increasing the wall thickness can increase bat weight, which creates new problems with bat weight standards. On the other hand, it can be desirable to increase the wall thickness in the sweetspot, or mid-region, of the barrel portion of the bat without significantly increasing the weight.

Therefore, what is needed is a simple, low cost approach to vary (e.g., decrease or at least control) the performance of tubular bats, in order to meet lowered or changed bat performance standards without significantly increasing or departing from bat weight standards. Furthermore, in conjunction with causing a decrease in batting performance, it would be desirable to improve another bat characteristic such as “sweetspot” size.

In typical existing single-wall metal bats, material strength and isotropic behavior have limited the degree to which the bat stiffness can be altered along the longitudinal axis of the bat. Lowering the stiffness of a bat barrel near the end of the barrel, either at the cap or at the tapered section, has generally lowered the durability of the bat due to insufficient material strength. Significantly, the design of the present invention (i.e., incorporating helical ribs on the interior of the metal bat) allows a designer to independently alter the hoop and axial stiffnesses of a bat barrel along the bat's longitudinal axis.

A multi-wall composite bat with helical internal ribs may offer even larger decreases in the barrel stiffness than a single-wall design, and is therefore generally preferred. Again, the helical internal ribs may be formed on the inner and/or outer sleeves of the multi-wall bat and the helical ribs may vary in frequency (i.e., number), pitch, height and width profile in order to provide the desired performance characteristics for the bat. See, for example, FIG. 13A, which shows a multi-wall composite bat having an inner sleeve 15A disposed inside a barrel portion 15, wherein inner sleeve 15A comprises one or more helical internal ribs 40 (one helical internal rib 40 is shown in FIG. 13A). A single-wall barrel, however, can also be enhanced using the helical internal ribs of the present invention.

Cold-Forming in the Ribs

Flowforming is an advanced, net shape cold metal forming process used to manufacture precise, tubular components that have large length-to-diameter ratios. With flowforming, a cylindrical workpiece, sometimes referred to as a “preform”, is fitted over a rotating mandrel. Compression is applied by a set of three hydraulically driven, CNC-controlled rollers to the outside diameter of the preform. The desired geometry is achieved when the preform is compressed above its yield strength and plastically deformed and “made to flow”. As the preform's wall thickness is reduced by the set of three rollers, the material is lengthened and formed over the rotating mandrel. The flowforming is done cold. Although adiabatic heat is generated from the plastic deformation, the process is flooded with refrigerated coolant to dissipate the heat. This ensures that the material is always worked well below its recrystalization temperature. With “cold” flowforming, the material's strength and hardness are increased and dimensional accuracies are consistently achieved well beyond accuracies that can be realized through hot forming processes.

See FIG. 14, which shows a general setup for a flowforming process.

The present invention preferably uses flowforming to create the helical internal ribs of the bat.

Alternatively, the present invention may use flowforming to create longitudinal ribs on the interior of the bat.

When helical grooves are ground into the flowform mandrel, reciprocating splines or ribs can be flowformed into the bore of the flowformed tube, i.e. helical internal ribs can be flowformed onto the inner wall of the bat. In accordance with the present invention, the mandrel grooves can be longitudinal or helical, although helical grooves are preferred in order to create the helical internal ribs discussed above. The mandrel grooves can vary in frequency (i.e., number), pitch, depth and width profile along the length of the mandrel, in order to create counterpart helical internal ribs on the bat. FIGS. 15 and 16 are photographs showing flowformed internal splines, with FIG. 15 showing longitudinal splines and FIG. 16 showing spiraled splines (i.e., helical internal ribs).

In addition to “flowforming in” the splines (i.e., the helical internal ribs), there are other cold work processes that can be used to provide the same helical internal ribs in the bore of the barrel, e.g., swaging, impact extruding, drawing over a mandrel (DOM), or a combination thereof.

Thus, in one form of the present invention, there is provided a novel metal bat which comprises one or more helical internal ribs which are engineered (e.g., in number, pitch, depth, width profile, etc.) so as to provide the bat with its desired characteristics. Preferably these helical internal ribs are formed by flowforming.

In this respect it should be appreciated that flowforming can simultaneously vary the wall thickness of the bat and impart the desired helical internal ribs to the bat.

Significantly, the present invention provides a novel approach to shift and modify wall thickness/weight/modulus and geometry along the length of the bat.

As noted above, the present invention uses helical internal ribs to tune/control the stiffness of the barrel of the bat so as to maximize the trampoline effect for peak bat performance, yet still keep the bat compliant with BBCOR regulations and/or other regulations. The provision of helical internal ribs can strategically take weight out of the barrel in certain areas to allow for a redistribution of the weight in other areas, if desired. By way of example but not limitation, putting weight at the handle allows the bat to be swung faster, putting weight at the distal (cap) end helps with bat Moment of Inertia, etc.

Being able to make lighter barrels and shells (double wall bats) utilizing helical internal ribs is also advantageous because the ribbed barrel/shell composite may equal the weight of a heavier single-walled bat but with enhanced/tuned, engineered stiffness/trampoline effect.

Furthermore, it should be appreciated that when a bat bends during contact with a ball, the bat does not snap back perfectly uniformly. Rather, the bat will tend to collapse in hoop, bend and twist back in torsion, in a “shear” bending mode. If the spiral ribs are formed clockwise it could help to counteract the shear bending mode for righthand batters. If the spiral ribs are formed counter-clockwise, it would help the shear bending mode for lefthand batters. Thus, the intentional directionality of the helical ribs can be used to help counteract the forces of the bat's natural shear bending mode, and to help the “trampoline effect” of the bat to pop balls upward rather than driving balls into the ground. Alternatively, in some situations, it may be desirable to cause the bat to drive the ball into the ground. A barrel with a biased, torsional twist would be advantageous in hitting the ball into the ground. Thus, in this form of the invention, a “left handed” bat or a “right handed” bat may be produced.

The spiral internal ribs may be provided in the handle and taper section of the bat in addition to the barrel section of the bat, because the counter-opposing spiral ribbing could have benefits in the tapered transition bending area too.

And in another form of the invention, there is provided a novel hollow metal bat which comprises longitudinal inner ribs which are formed by flowforming. Flowforming the longitudinal ribs, rather than forming them by casting as with the prior art, is a significant advantage over the prior art.

EXAMPLE

By way of example but not limitation, in one preferred form of the invention, hollow metal bat 5 may be formed out of aluminum, may have a barrel wall thickness of 0.092″, and may have a single helical internal rib 40 having a pitch of one revolution over 12″ and a rib height of 0.050″ (off the floor of the barrel wall).

MODIFICATIONS

It will be understood that many changes in the details, materials, steps and arrangements of elements, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art without departing from the scope of the present invention.

Claims

1. A hollow metal bat comprising an elongated tubular structure having a barrel portion, a handle portion and a tapered portion connecting the barrel portion to the handle portion, and further comprising at least one helical internal rib formed along at least a portion of the elongated tubular structure.

2. A hollow metal bat according to claim 1 wherein the at least one helical internal rib is formed along at least a portion of the barrel portion.

3. A hollow metal bat according to claim 1 wherein the at least one helical internal rib is formed along the entire barrel portion.

4. A hollow metal bat according to claim 1 wherein the at least one helical internal rib is formed along the entire elongated tubular structure.

5. A hollow metal bat according to claim 1 wherein the at least one helical internal rib has a clockwise orientation as the helical internal rib extends distally down the bat.

6. A hollow metal bat according to claim 1 wherein the at least one helical internal rib has a counter-clockwise orientation as the helical internal rib extends distally down the bat.

7. A hollow metal bat according to claim 1 wherein the bat is formed by flowforming.

8. A hollow metal bat according to claim 1 wherein the bat is formed by at least one from the group consisting of swaging, impact extruding, drawing over a mandrel (DOM), machining, and casting.

9. A hollow metal bat according to claim 1 wherein the at least one helical internal rib has its pitch, height and width profile tailored to provide the desired characteristics for the bat.

10. A hollow metal bat according to claim 9 wherein the pitch, height and width of the at least one helical internal rib is selected so that the bat has a BBCOR of 0.500 or less.

11. A hollow metal bat according to claim 1 wherein the bat comprises a plurality of helical internal ribs.

12. A hollow metal bat according to claim 11 wherein the plurality of helical internal ribs have their number, pitch, height and width profile tailored so as to provide the desired characteristics for the bat.

13. A hollow metal bat according to claim 12 wherein the number, pitch, height and width of the plurality of helical internal ribs is selected so that the bat has a BBCOR of 0.500 or less.

14. A hollow metal bat according to claim 1 wherein the bat comprises a multi-wall construction.

15. A hollow metal bat according to claim 14 wherein the multi-wall construction comprises a sleeve disposed coaxial with the barrel portion, and further wherein the at least one helical internal rib is formed on the interior of the sleeve.

16. A hollow metal bat according to claim 14 wherein the multi-wall construction comprises a sleeve disposed coaxial with the barrel portion, and further wherein the at least one helical internal rib is formed on the exterior of the sleeve.

17. A method for forming a hollow metal bat, the method comprising:

positioning a preform on a mandrel, wherein the mandrel comprises at least one helical groove; and

applying compression to the outside diameter of the preform so as to form an elongated tubular structure having a barrel portion, a handle portion and a tapered portion connecting the barrel portion to the handle portion, and further comprising at least one helical internal rib formed along at least a portion of the elongated tubular structure.