US20060068931A1

US20060068931A1 - Mold for a golf ball

Info

Publication number: US20060068931A1
Application number: US11/273,175
Authority: US
Inventors: Steven Aoyama; Chirstopher Cavallaro; Robert Wilson
Original assignee: Acushnet Co
Current assignee: Acushnet Co
Priority date: 2004-03-10
Filing date: 2005-11-14
Publication date: 2006-03-30
Also published as: US20060193934A1; US20050201418A1; US7422529B2; US20080317892A1; US7387504B2

Abstract

A golf ball mold having a non-planar parting surface that is formed a computerized modeling system such as CAD or CAE in combination with a CNC machine tool. The mold is comprised of hemispherical upper and lower mold halves being removably mated along the non-planar parting line that is distinct from the position corresponding to an equator line of the spherical cavity. Each mold half having an interior cavity detail for creating a pattern of dimples on the cover of the golf ball, wherein at least one dimple lies across an equator of the ball and the parting line passes around and between interdigitated dimples without intersecting them, therein creating a “seamless” golf ball. The non-planar surface of the upper mold half comprising at least three true sprues for venting of air and excess material; and at least three false sprues for the placement of tabs on the cover for use in aligning the golf ball as it is spun in a buffing machine.

Description

FIELD OF THE INVENTION

The invention relates in general to an improved golf ball mold having a non-planar parting surface used to manufacture “seamless” golf balls, and more particularly, to a method of defining the non-planar surface using a computerized modeling system.

BACKGROUND OF THE INVENTION

The usual golf ball manufacturing techniques include several different steps, depending on the type of ball, such as one, two, three or even more than three piece balls. According to the traditional method, a solid or composite elastomeric core is made, and an outer dimpled cover is formed around the core.
The two standard methods for molding a cover over a core or a core and inner layers are compression molding and injection molding. The compression molding operation is accomplished by using a pair of hemispherical molds each of which has an array of protrusions machined or otherwise provided in its cavity, and those protrusions form the dimple pattern on the periphery of the golf ball during the cover molding operation. A pair of hemispherical cover blanks, are placed in a diametrically opposed position on the golf ball body, and the body with the cover blanks thereon are placed in the hemispherical molds, and then subjected to a compression molding operation. The combination of heat and pressure applied during the molding operation results in the cover blanks being fused to the golf ball body and to each other to form a unitary one-piece cover structure which encapsulates the golf ball body. In addition, the cover blanks are simultaneously molded into conformity with the interior configuration of the hemispherical molds which results in the formation of the dimple pattern on the periphery of the golf ball cover. When dimple projections are machined in the mold cavity they are typically positioned below the theoretical parting line of the resulting mold cavity. The parting line is typically machined after the dimple forming process. For ease of manufacturing the parting line on the cavity is machined flat and perpendicular to the dimpled surface as to provide a positive shut off preventing flowing cover material from leaking out of the mold. This dimple positioning and flat parting line results in a great circle path on the ball that is essentially void of dimples. This is commonly referred to as the equator, parting line, or seam of the ball. Over the years dimple patterns have been developed to compensate for cosmetics and/or flight performance issues due to the presence of the seam.
As in all molding operations, when the golf ball is removed from the hemispherical molds subsequent to the molding operation, it will have molding flash, and possibly other projecting surface imperfections thereon. The molding flash will be located at the fused circular junction of the cover blanks and the parting line of the hemispherical molds. The molding flash will therefore be on the “equator” of the golf ball.
The molding flash and possible other imperfections projecting from the surface need to be removed and this is normally accomplished by one or a combination of the following: cutting blades, sanding belts, or grinding stones, and the like. These types of processes tend to enhance the obviousness of the seam. Alternative finishing processes have been developed to minimize this effect. These processes include tumbling with media, stiff brushes, cryogenic de-flashing and the like. Regardless of the finishing process, the result has been a flat parting line in an area substantially void of dimple coverage.
When flashing is removed by grinding, it is desirable that the molding operation be accomplished in such a manner that the molding flash is located solely on the surface of the golf ball and does not extend into any of the dimples. In other words, a grinding operation may have difficulty reaching into the dimples of the golf ball to remove the molding flash without ruining the golf ball cover. Therefore, prior art hemispherical molds are primarily fabricated so that the dimple-forming protrusions formed therein are set back from the circular rims, or mouths of their cavities. The result is that the equator of a molded golf ball is devoid of dimples and the molding flash is located solely on the smooth surface provided at the equator of the golf ball.
It is well known that the dimple pattern of a golf ball is a critical factor insofar as the flight characteristics of the ball are concerned. The dimples influence the lift, drag and flight stability of the golf ball. When a golf ball is struck properly, it will spin about a horizontal axis and the interaction between the dimples and the oncoming air stream will produce the desired lift, drag, and flight stability characteristics.
In order for a golf ball to achieve optimum flight consistency, its dimples must be arranged with multiple axes of symmetry. Otherwise, it might fly differently depending upon orientation. Most prior art golf balls include a single dimple free equatorial parting line, which inherently limits the number of symmetry axes to one. In order to achieve good flight consistency, it is often necessary to compensate for this limitation by adjusting the positions and/or dimensions and/or shapes of certain dimples. Alternatively, additional symmetry axes can be created by incorporating additional dimple free “false” parting lines. However, this practice increases the amount of un-dimpled surface on the ball, which can result in reduced ball flight distance.
For maximum performance and consistency, it is preferable to use a dimple arrangement that requires no adjustment or addition of false parting lines. Therefore, if it is desirable to eliminate the equatorial parting line, it is best that it be done by including dimples that intersect the equator. Some U.S. patents that seek to place dimples upon the equator of the ball include U.S. Pat. No. 6,632,078 to Ogg et al., U.S. Pat. Nos. 6,200,232, 6,123,534 and 5,688,193 to Kasashima et al., U.S. Pat. No. 5,840,351 to Inoue et al., and U.S. Pat. No. 4,653,758 to Solheim. These patents introduced “stepped” and/or “zig zag” parting lines. While this could potentially improve compliance with the symmetry, they did not sufficiently improve dimple coverage, since the parting lines included straight segments that did not permit interdigitation of dimples from opposite sides of the equator. A stepped path often results in a greater loss of dimple coverage than a straight path because it discourages interdigitation for a larger number of dimples. U.S. Pat. No. 6,936,208 to Ogg teaches the formulation of a partial or continuous tab created by overlapping of adjacent concave and convex tabs to reduce the dimension of the seam about the ball.
Therefore, a need exists for a mold to create a new and improved golf ball, one that would have a parting line configuration that would minimize dimple damage during flash removal, improve symmetry performance, increase dimple coverage, minimize the visual impact of the equator, and create a reduced amount of flash and the effort of removing it.

SUMMARY

The present invention provides a mold for forming a castable cover on a golf ball (Example: urethane). The mold contains hemispherical mold cups removably mated along a non-planar parting line, an upper mold cup and a lower mold cup. Both cups have interior cavity details, and when assembled create a generally spherical cavity and also provide a dimple pattern on the golf ball. The upper and lower mold cups have non-planar mating surfaces, wherein each surface comprises a plurality of peaks and valleys which are created by a computerized modeling system. When assembled the parting line follows the dimple outline pattern and allows the dimple outline pattern of one mold cup to interdigitate with the dimple outline pattern of the mating mold cup, thereby forming a golf ball of substantially seamless appearance. The non-planar surface of the upper mold comprises at least three true sprues and three false sprues, and more preferably five true sprues and five false sprues. Another embodiment would include the lower mold having these sprues in the non-planar surface. The false sprues have a recess wherein tabs are added to the cover for use in aligning the golf as it is spun in a buffing machine. The tabs are subsequently removed by a knifing procedure.
The present invention provides for the tabs, which are subsequently removed and discarded, to occupy less than 15% of the non-planar surface. This will substantially reduce the amount of material waste that must be discarded.
The present invention provides a method for molding the non-planar golf ball parting surface comprising the steps of first, creating a 3-dimensional computer model representing the golf ball and then constructing a parting line profile represented as a 2-dimensional curve upon a positioned plane. Secondly, the parting line profile is projected onto a 3-dimensional surface of the golf ball model, which generates a radiated surface that contains the parting line which forms the parting surface of a model of the golf ball mold. Finally, the non-planar parting surface is manufactured on a golf ball mold by use of a CNC machine tool.
The preset invention creates the non-planar parting line profile by use of a computerized modeling system such as either a CAD (Computer Aided Design) or CAE (Computer Aided Engineering).
Another object of the invention is to provide a parting line profile constructed of arc segments that are continuous with one another and that weave a path around and between dimples without intersecting them.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged pictorial expanded view of the mold comprising both mold halves showing the vents on the upper mold half.
FIG. 2 is plan view of the upper mold half for a mold designed for a Urethane covered ball.
FIG. 2A is an enlarged view of A on FIG. 2.
FIG. 2B is an enlarged view of B on FIG. 2.
FIG. 3 is a pictorial view of an upper mold describing a vent designed for a Surlyn covered ball.
FIG. 3A is an enlarged view of A on FIG. 3.
FIG. 4 is a pictorial view of a completed mold showing a non-planar parting line.
FIG. 5 is a golf ball segment model based upon the method of defining a parting surface of the present invention.
FIG. 6 is a golf ball segment illustrating a parting line profile construction plane.
FIG. 7 is a view normal to the construction plane of FIG. 6.
FIG. 8 illustrates arc segments that are constrained to be concentric with the neighboring dimples.
FIG. 9 projects the 2-dimensional parting line profile upon the surface of the ball to create a 3-dimensional parting line path.
FIG. 10 utilizes the parting line path of FIG. 9 as a profile to generate a radiated geometry component to define the parting surface of the golf ball mold.
FIG. 11 is an exploded view to show how the radiated component of FIG. 10 is used to form the parting surface of a mold cavity model.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1 to 4, wherein an improved mold of the present invention is shown, with the mold being indicated by the reference numeral 30, the mold 30 having a spherical cavity 31 which is used to form a cover for a golf ball wherein the mold 30 comprises hemispherical mold halves, an upper mold half 32 and a lower mold half 33, both halves having interior dimple cavity details 34 a and 34 b respectively with the details of the upper mold half 34 a shown in FIGS. 2, 2A and 2B, for a mold designed to form a castable cover over a core, and in FIGS. 3 and 3A, for a mold designed to form a cover made from Surlyn, and when these halves are mated they define a dimple arrangement therein. Any dimple arrangement, such as icosahedral, octahedral, cube-octahedral, dipyramid, and the like could have the dimple pattern. Although the preferred dimple is circular when viewed from above, the dimples may be oval, triangular, square, pentagonal, hexagonal, heptagonal, octagonal, etc. Possible cross-sectional shapes include, but are not limited to, circular arc, truncated cone, flattened trapezoid, and profiles defined by a parabolic curve, ellipse, semi-spherical curve, saucer-shaped curve, or sine curve. Other possible dimple designs include dimples within dimples and constant depth dimples. In addition, more than one shape or type of dimple may be used on a single ball, if desired.
The upper and lower mold halves 32 and 33 have non-planar parting line surfaces 35 and 36 respectively, which are staggered as shown best in FIG. 4, each surface 35 and 36 comprising a plurality of peaks and valleys which are created by a method of defining, modeling, and manufacturing, by using a computerized modeling system as discussed below. When assembled the non-planar parting line 37 follows the dimple outline pattern and allows the dimples of one mold half to interdigitate with the dimples of the mating mold half, to form a golf ball of substantially seamless appearance.
The non-polar parting line 37 is machined to follow the profile of the equator dimples. Typically, the non-polar parting line 37, as it is machined, is offset from the equator dimples by at least 0.001 inch, as to not interfere with the dimple perimeter. This produces the wavy or corrugated formed parting line consisting of multiple peaks and valleys. Typically, the peaks (the highest point of the parting line) are located above the theoretical center of the cavity half and the valleys (the lowest point) are located below the theoretical center of the cavity half. This offset distance of the peaks and valleys can be as much as about half the dimple diameter or as little as 0.001 inch. Designs which incorporate as little as 0.001 inch offset, provide the benefit of interdigitating dimples, yet only producing a small amount of undercut in the cavity. This alternating geometry is consistent over the entire parting line surfaces of both mold halves 32 and 33.
The cavity design of the present invention can be applied for any golf ball molding process including injection molding, compression molding and casting. It will also work with the standard flat parting line as well as non-polar parting lines used to manufacture “seamless” golf balls.
The cavity design of the present invention incorporates the above method for creating the staggered rim definition necessary for the non-planar parting line 37 on the golf ball. The design principles as discussed below apply whether the ball has a Surlyn or a castable cover, such as urethane. However, as discussed above the molds have a differing construction depending upon the cover material.
Most “seamless” molding methods today define groups of dimples that traverse back and forth across the theoretical mid-plane of a non-planar parting line. The above described method of the present invention defines a method whereby the position of each dimple can be easily and individually defined (not as a group of dimples) thereby identifying the undulating surface of the cavity, regardless of the dimple pattern.
A primary inventive concept of the present invention is shown on FIGS. 2, 2A, and 2B, which illustrates the upper mold 32 having a mold surface 35 for mating with the lower mold 33 for creating castable covered balls. The non-planar parting line cavity design of the present invention incorporates the use of 3 or more equally spaced vents (sprues) and this depends on the dimple pattern. As shown, FIGS. 2, 2A, 2B depict five (5) true vents 40 and five (5) false vents 50. The design of the false vents 50 (FIG. 2B) is such that a small section of material (a “tab”) is intentionally molded onto the ball and stays attached to the ball until the knifing process wherein they are removed. This tab is a result of the land area 51 having a partially dammed-up section 52 allowing for a relatively small recess 53 to fill with cover material therein creating the “tab”. In addition to the false vents 50, this cavity design incorporates the use of five (5) true vents 40 which are depicted in detail in FIG. 2A. The true vents 40 function primarily to provide a vent for trapped air and/or excess material to pack around the core and flow out of the cavity as needed. As stated above, in the preferred embodiment only the upper mold 32 contains vents 40 and 50, however, it is to be appreciated that both molds 32 and 33 could contain vents 40 and 50 and still be within the scope of the invention.
FIGS. 3 and 3A depict an upper mold 32 a for molding Surlyn as a cover material. When molding Surlyn covers the mold does not contain false vents 50, but rather open vents 55 which extend across the entire mold surface 35 a.
Regardless of whether the cover material is Surlyn, and therein formed by either compression molding or retractable pin molding, or whether it has a castable cover, such as urethane or urea, the resulting golf ball can have a “seamless” appearance.
The combination of three factors, first, a non-planar parting line, secondly, tabs molded and left behind from the real vents, and thirdly, the tabs that are molded in from the false vents, allows for a seamless ball to be oriented as it enters the buffing machine. When golf balls are spun on the orienting stations of the buffing machine, the molded-in tabs provide location of the actual buffing line. If alignment is not complete in a pre-determined amount of time, the ball will not be buffed and will be rejected as an un-buffed ball, which will require another pass through the machine at a later time. One of the key concepts of the present invention is the creation of the tabs that will minimize the amount of excess flash that must be removed therein saving both time and wasted material. The maximum amount of tab material needed to be removed will be held to less than 15% of the circumference. Another inherent advantage of the tabs as created by the present invention is that their removal can be done by a cutting knife which is a time saver over buffing or grinding off the flash.
The non-planar parting line of the above mold 30 is a result of incorporating into a mold a cavity design having a staggered rim definition (non-planar parting surface) which is created by using a computerized modeling system such as CAD (Computer Aided Design), CAE (Computer Aided Engineering), or similar type of system, along with a CNC machine tool. Preferably, the modeling system incorporates parametric 3-dimensional solid modeling capabilities that are required to properly manufacture and process Surlyn or castable covered golf balls which are often referred to as “seamless” golf balls.
Most dimple patterns incorporate repeating segments that are used to define the overall dimple arrangement. In such cases, it is only necessary to model a portion or portions of the golf ball or mold that are sufficient to define the entire golf ball or mold.
Molds with non-planar parting surfaces can be used to manufacture so-called “seamless” golf balls, in which the parting line on the molded product is not a great circle. Rather, it typically incorporates waveforms, steps, or other features that permit it to pass around and between interdigitated dimples without intersecting them. Once the parting line artifacts are removed through buffing and other finishing processes, the ball has a seamless appearance.
The method of the present invention utilizes six basic steps to achieve a seamless appearance. The steps are:
(1) Creating a 3-dimensional computer model representing the golf ball. The model may be constructed in many different ways that will depend on the particular system being used and the preferences of the designer constructing the model. It is generally preferred to work with the smallest ball segment that is sufficient to fully define the dimple pattern. FIG. 5 shows an example of a golf ball segment model 100.
(2) Constructing a parting line profile plane as a 2-dimensional curve on a conveniently positioned plane. It is preferred to position the plane 102 parallel to the polar axis of the ball, at a distance that is greater than the radius of the ball. Such a plane is shown in FIG. 6. To construct a parting line profile 104, it is convenient to use a view direction that is normal to the plane, as shown in FIGS. 7 and 8, wherein the profile 104 can then be constructed of arc segments, line segments, or any other type of curve component that the particular system supports. Typically, the profile 104 will weave a path around and between dimples without intersecting them. It is very beneficial to define the profile geometry in a parametric fashion using references and constraints based on the dimple pattern geometry. For example, the profile 104 in FIG. 8 comprises arc segments that are constrained to be concentric with the neighboring dimples, with a radius parameter that is defined to be a particular value greater than the dimple radius. It is required that the curve segments be continuous with one another, and it is preferred that they be tangent as well wherever possible. In this example, because of mirror symmetry inherent in the dimple pattern, it is only necessary to create the parting line profile 104 for half of the ball segment shown.
(3) Creating the parting line 37 by projecting the parting line profile 104 onto the 3-dimensional surface of the golf ball model as shown in FIG. 9. The projection is performed along a direction chosen to properly position the parting line of the ball, which will typically be normal to the plane of the 2-dimensional parting line profile 104. In this case, the remaining half of the parting line is created as a mirror image.
(4) Generating a radiated surface 108 containing the parting line 37 and defining the mold parting surface 110. As shown in FIGS. 10-11, the parting line path is used as a profile to generate a radiated geometry component 112 that defines the parting surface of the golf ball mold. Depending on the particular system being used and the preferences of the designer, the geometry component could be a radiated surface component 112 (as shown), or a radial extrusion solid component, or another type of radiated component. The radiated component 112 may be created as part of the golf ball model or as part of the mold model. It is preferred that the origin of the radiation is located along the polar axis of the ball or the mold cavity, and the direction of the radiation is parallel to the equator plane of the ball or mold cavity.
(5) Using the radiated surface 108 to form the parting surface of the golf ball mold. An example of an exploded view is shown on FIG. 11, wherein a cut operation can be performed using the radiated surface 108. The radiated surface 108 trims away waste material 104 along the edge of the mold, leaving the desired non-planar mold parting surface 110.
(6) Using the results of at least one of the steps 3-5 to manufacture the parting surface 110 of a golf ball mold 106. The parting surface of the golf ball mold is machined using the geometry created in the above steps. This is preferably accomplished using a CNC machine tool controlled by a program that was created directly from the model.
This method will enable a non-planar surface of any cavity to be easily defined regardless of dimple pattern.
In the manufacture of a golf ball, it is important that the parting surfaces of the molds mate very precisely. This minimizes the amount of flash and other parting line artifacts, which benefits the cosmetic quality of the finished golf ball, and it also produces greater uniformity and control over the size, weight, and roundness of the ball. Most golf ball molds employ a planar parting surface to easily provide a very precise mate. However, as previously discussed, the resulting great circle parting line on the molded ball introduces restrictions on dimple placement, which can affect the aerodynamic performance. This may manifest itself as reduced distance, reduced accuracy, or variations in performance depending on the orientation of the ball. Also, to some golfers the appearance of a great circle parting line free of dimples is not appealing.
While it is apparent that the illustrative embodiments of the invention disclosed herein fulfill the objectives stated above, it is appreciated that numerous modifications and other embodiments may be devised by those skilled in the art. Therefore, it will be understood that the appended claims are intended to cover all modifications and embodiments, which would come within the spirit and scope of the present invention. The dimple patterns of the present invention can be used with any type of golf ball with any playing characteristics. For example, the dimple pattern can be used with conventional golf balls, solid or wound. These balls typically have at least one core layer and at least one cover layer. Wound balls typically have a spherical solid rubber or liquid filled center with a tensioned elastomeric thread wound thereon. Wound balls typically travel a shorter distance, however, when struck as compared to a two piece ball. The cores of solid balls are generally formed of a polybutadiene composition. In addition to one-piece cores, solid cores can also contain a number of layers, such as in a dual core golf ball. Covers, for solid or wound balls, are generally formed of ionomer resins, balata, or polyurethane, and can consist of a single layer or include a plurality of layers and, optionally, at least one intermediate layer disposed about the core.
All of the patents and patent applications mentioned herein by number are incorporated by reference in their entireties.
While the preferred embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not of limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. For example, while the preferred dimple sizes have been provided above, dimples of other sizes could also be used. Thus the present invention should not be limited by the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

Claims

1. A mold for forming a cover for a golf ball having a non-planar parting line, the mold comprising:

hemispherical upper and lower mold halves being removably mated along the non-planar parting line that is distinct from the position corresponding to an equator line of the spherical cavity,

each mold half having an interior cavity detail for creating a pattern of dimples on the cover of the golf ball, wherein at least one dimple lies across an equator of the ball and the parting line passes around and between interdigitated dimples without intersecting them;

each mold half having an interior cavity detail, each mold half having a non-planar parting surface formed by a computerized modeling system and a CNC machine tool;

the non-planar surface of the upper mold half comprising at least three true vents for venting of air and excess material; and

the non-planar surface of the upper mold half comprising of at least three false vents which allow for tabs to be added to the cover for use in aligning the golf ball as it is spun in a buffing machine.

2. The mold according to claim 1, wherein the cover is formed from a urethane or a urea material.

3. The mold according to claim 1, wherein the tabs occupy less than 15% of the non-planar surface.

4. The mold according to claim 1, wherein the non-planar parting surface is offset from the adjacent dimples by at least 0.001 inch.

5. The mold according to claim 4, wherein the non-planar parting line comprises arc segments that are constrained to be concentric with neighboring dimples and having a radius parameter that is greater than the dimple radius.

6. The mold according to claim 5, wherein the arc segments are continuous with one another.

7. The mold according to claim 1, wherein the tabs are removed by a knifing process.

8. The mold according to claim 1, wherein the dimples of the molded golf ball are of an icosahedral arrangement pattern.

9. The mold according to claim 1, wherein the dimples of the molded golf ball are of an octahedral arrangement pattern.

10. The mold according to claim 1, wherein the dimples of the molded golf ball are of a cube-octahedral arrangement pattern.

11. The mold according to claim 1, wherein the dimples of the molded golf ball are of a dipyramid arrangement pattern.

12. The mold according to claim 1, wherein the non-planar surface of the upper mold comprises five true vents and five false vents.

13. The mold according to claim 1, wherein the non-planar surface of the lower mold half further comprises having at least three true vents and three false vents.

14. The mold according to claim 13, wherein the non-planar surface of the lower mold half further comprises having five true vents and five false vents.

15. A method for manufacturing a non-planar golf ball mold parting surface comprising the steps of:

creating a 3-dimensional computer model representing the golf ball;

constructing a parting line profile as a 2-dimensional curve on a positioned plane;

projecting the parting line profile onto a 3-dimensional surface of the golf ball model;

generating upon the golf ball model a radiated surface containing the projected parting line profile to therein define the mold parting surface;

forming the parting surface of a model of the golf ball ball mold using the radiated surface; and

manufacturing the non-planar parting surface of the golf ball mold.

16. The method of claim 15, wherein the ball has a radius and the positioned plane is parallel to a polar axis of the ball, at a distance greater than the radius.

17. The method of claim 15, wherein the parting line profile is constructed of arc segments that weave a path around and between dimples without intersecting them.

18. The method of claim 17, wherein the arc segments are concentric with neighboring dimples and having a radius parameter that is greater than the dimple radius.

19. The method of claim 17, wherein the arc segments are continuous with one another.

20. The method of claim 15, wherein the construction of the non-planar parting line profile is by means of a Computer Aided Design or a Computer Aided Engineering system.

21. The method of claim 20, wherein manufacturing of the non-planar parting surface of the mold is by means of a CNC machine tool.