WO1995006501A1

WO1995006501A1 - Process for making metal wood club heads

Info

Publication number: WO1995006501A1
Application number: PCT/US1993/008212
Authority: WO
Inventors: Inc. Niemin Porter & Co.
Original assignee: Sheehan, John, Patrick
Priority date: 1993-08-31
Filing date: 1993-08-31
Publication date: 1995-03-09
Also published as: AU5159093A

Abstract

In the manufacture of large metal wood golf club head (10), there is added to all walls (15-18) of a designed head body (11) an additional amount (t) of wall thickness sufficient to enable the thinnest of the thickened walls to be cast reliably and efficiently. That further wall thickness is added equally to the inner and outer surfaces of the head body. That thickened wall head body is then cast (35) and preliminarily dressed (36, 37). The amount by which the weight of the designed body is determined by weighing (38) the dressed body, and from that weight is deducted such weight as can be expected to be removed by further grinding and polishing (40, 41) of the head body. The result is a defined amount of weight to be removed from the head. That defined weight of metal is removed from all, or substantially all, of the surfaces of the dressed casting by chemically milling (39) those surfaces to move the added thickness of metal from the surfaces to which it was added. A readily manufacturable golf club head of the correct weight and wall thickness is thereby produced.

Description

PROCESS FOR MAKING METAL WOOD CLUB HEADS ****************************************

Field of the Invention

This invention has preferred utility in the manufacture of metal heads for golf clubs of the type known as "woods." More particularly, it pertains to an improved process for manufacturing and finishing jumbo heads for metal wood golf clubs; it can have utility in the manufacture of golf club irons and putters.

Background of the Invention Golf clubs, other than putters, fall into one or the other of two broad types, namely, "woods" or "irons." Woods are characterized by bulbous heads, whereas the heads of irons more closely resemble a blade-like article. The terms "wood" and "iron" are used for historical reasons. Woods originally were made of a unitary piece of wood, such as persimmon, or from a lamination of multiple layers of woods, such as maple. Irons, on the other hand, historically have been made of metal, such as various kinds of steel or other metal alloys formed initially by forging processes and, more recently, by casting processes.

In the 1970's or so, an advance in the art and science of golf club manufacture resulted in the introduction of wood-type golf clubs having heads made of metal. Because of the longstanding habit and jargon of those who play golf and who make equipment for use in its pursuit, such clubs were called, and still are called, "metal woods." The difficulties encountered in the manufacture of heads for metal wood golf clubs provided the stimulus for the present invention, and it is in the manufacture of such metal wood heads where this invention has its presently preferred utility.

Review of Prior Art Metal wood golf clubs have substantially displaced their wooden ancestors in today's marketplace for golf clubs. The reason is due, in principal part, to the enhanced "payability" of metal woods over their wood counterparts in the hands of most golfers. Playability of a golf club is directly related to the effective size of the so-called "sweet spot" of a golf club. The sweet spot of a golf club is the area on the club's striking face where the kinetic energy possessed by a moving golf club head is efficiently transferred to a golf ball to cause die ball, the golfer fervently hopes, to fly far and straight along an intended path. Physicists use the term "center of percussion" as a more precise descriptor of that which golfers call "sweet spot."

A metal wood golf club has a larger effective sweet spot, and therefore a larger margin for error ("forgiveness" to the golfer) in positional relation of the club head to d e ball at the moment of head-to-ball impact, than does a wooden headed club of the same head size and weight and shaft length. The difference is due to the different ways weight is distributed in those different club heads. A wood club head is substantially homogeneous. A metal wood club head is not homogeneous. A metal wood is hollow (albeit the hollow head usually is filled with lightweight foam plastic material), and so the weight of the head is distributed in its striking face and in a sole plate, both of which are relatively thick, and in a relatively thin walled shell which forms the remainder of the club head. It is die distribution of substantial portions of the weight of the head at die surfaces of the head outwardly from the center of the striking face which produces an enlarged sweet spot. It is that principle which has led to the development and introduction of metal woods of ever increasing head size and, correspondingly, at least in theory, increasing sweet spot size. That trend is continuing, but at the expense of, and up to die limits of, current abilities of investment casting foundries to cast and to finish such heads by use of the practices and procedures which now exist and are common.

Metal woods now are made by a combination of investment casting procedures to obtain a raw cast head body and a raw cast sole plate and of grinding and polishing procedures performed on the head body before and after affixation, as by heliarc welding, of the sole plate to the body in a bottom aperture defined in the cast body. Those practices are both motivated by and limited by a requirement that the finished club head shall not exceed a specified weight. For example, because of a number of reasons, it is a golf industry standard that the finished weight for a man's driver head shall not significantly exceed 200 grams. When the weight of the foam plastic filling (12 to 16 grams) for a metal wood head, and the weight of a sole plate (about 30 to 40 grams) are deducted from the total head weight, and allowances for grinding and polishing the head components are considered, the weight allowed for the head body casting is in the range from about 150 to 160 grams to about 145 grams. Using known foundry practices, it can be very difficult or impossible to cast a large metal wood body with the thin walls required without encountering very high scrap rates in the castings or in the subsequent head finishing operations which normally are performed by the foundry. Current practice in the golf industry is for the foundry to deliver an assembled, finish polished head to a club manufacturer for foam filling, painting (optional), shafting and gripping by the manufacturer.

The extreme difficulties and high scrap rates now encountered by foundries in making large metal wood heads is due to an assortment of factors. First, the striking faces of metal wood heads must have a relatively high thickness to be able to withstand the impacts they experience in use. That requirement consumes a substantial portion of the metal available to form a head body of the desired size and weight. Therefore, the remaining amount of metal must be distributed throughout the remaining other surface of the head body. As heads increase in size, that remaining amount of metal must be distributed over larger and larger areas, which means that the walls defining those other surfaces become thinner and thinner. Those walls may become so thin that they either cannot withstand transferred impact loads from the striking face, or they dent or crack in routine handling, or they cannot be ground and polished without acceptance of high scrap rates, or a combination of some or all of those factors. For example, because of the way in which molten metal flows, shrinks and hardens in a mold, it may not be possible to reliably cast thin walls of large area unless the mold is defined with multiple gates or the mold is defined to provide runners on inside surfaces of the casting from relatively thick wall spaces to relatively thin wall spaces; such practices have disadvantages and limitations, including increased time and cost to assemble and disassemble molds, or to grind and polish the castings in each gate area. As a consequence, metal wood head bodies must be cast overweight in order to obtain sound castings with acceptable foundry scrap rates. Overweight body castings d en must be ground and polished manually to remove sufficient metal from the casting to cause the casting to have the correct weight in relation to the sole plate and to die foam material present in the finished head. The need for extensive grinding and polishing creates further problems and sources of scrap, i.e., unacceptable heads.

The striking face of a casting for a metal wood head body cannot be ground away to any significant degree in the finishing of such a casting. The striking face is cast to a carefully defined contour, and has grooves in it and so it cannot be ground for head weight reduction without weakening that face, or distorting the desired contour or causing the grooves to not conform to applicable golf rules. The inside surfaces of the body casting are inaccessible to grinding operations. Weight at the heel and toe of die head are desirable. As a consequence, there are limited areas on die exterior of a head body casting where grinding operations can be performed to remove excess weight from the casting. Grinding in those areas must be done very carefully else the casting wall thickness will be reduced too much. Also, because the grinding operations are performed manually, the skill and touch of diose who perform such operations become very important, and persons having the requisite skill may be unavailable. Even skilled grinders may not be able to remove enough excess metal from a body casting without making the casting unusable; i.e., without creating scrap castings. In view of the circumstances reviewed above, scrap rates as high as 60% or more have been encountered, at times, in the manufacture of large or jumbo heads for metal wood golf clubs. Scrap rates of 25% to 30% on a continuing basis are not uncommon; they vary depending on the head designs. Such scrap rates directly affect the economic health of the foundries occupied in die casting, grinding, polishing and assembly of metal wood golf club heads, and they severely limit the ability of such foundries to satisfy increasing requirements for such heads. Also, to the extent that the skills of individual grinders vary, and different grinders remove more or less metal from different places on a head of a given design, the performance characteristics of clubs having that head design will vary from club to club. Golfers can be very concerned about such variations.

It is seen, therefore, that a need exists for the development of improved procedures and methods for the manufacture of metal wood golf club heads. A need exists for procedures and methods which enable such heads to be cast efficiently, to encounter reduced scrap rates in their casting and finishing operations, and, when finished by the foundry in a state ready for delivery to customer golf club manufacturers, to be of the correct weight, to have uniform weight distribution, and to have adequate strength in all areas. Fulfillment of that need will beneficially affect the economics of foundries and of golf club manufacturers, and can result in better golf clubs becoming available to more golfers at prices which are acceptable to a larger number of golfers. Fulfillment of that need also may be beneficial in contexts and utilities odier than in the field of golf club head manufacture.

United States Patents 5,042,806, 5,067,715, 5,163,682 and 5,180,166 illustrate the prior art reviewed above. Patent 5,042,806 shows and describes a larger-than-usual metal wood head which has no hosel extending from the head, in contrast to golf club woods (metal or wood) of conventional appearance. The metal not used to define die hosel is available, in large part, for distribution throughout the remainder of the head. Patents, 5,067,715, 5,163,682 and 5,180,166 are later patents pertinent to hosel-less metal wood heads which implicitly make die point that elimination of the hosel of such a head does not solve all die problems presented in the manufacture of large metal wood heads. Thus, these three patent show the use of reinforcing ribs (also called dendrites) on the inside of the head top wall adjacent the striking face, and also on the inside surfaces of the head top and rear walls. While those ribs serve load distribution functions in the finished head, they are artifacts of foundry practices in which runners are defined in die casting mold to conduct molten metal from a nearby mold gate to portions of the mold defined for the casting of thin walls in the finished large metal wood head. Additional ribs are defined on the underside of the head top wall in die vicinity of the heel of die head adjacent the cast sleeve in the head into which the club shaft ultimately is fitted. All of tiiose rib systems have various gates associated widi them in the casting mold. Each of diose gates creates an appendage to die raw head casting as it is removed from die casting mold. Each of those appendages must be cut from the raw casting, as by a saw, and a resulting appendage stub on the exterior of the head casting must be ground away to merge with die exterior of the head before finish grinding and polishing of the head is performed to adjust the weight of die casting to die desired weight for the finished head casting. Those manual procedures are time consuming and costly and, if not performed by skilled workers, can result in the casting walls being ground too thin in one or more places; when that occurs, the head casting must be scrapped.

Moreover, the mold components used to define an internally ribbed large metal wood head casting must be assembled and removed from a casting precursor with great care and some difficulty in the lost wax casting technique which commonly is used in making cast metal wood head bodies, mereby further complicating the manufacture of such a head and increasing the cost of die finished product.

United States Patents, 4,429,879, 4,465,221, 4,472,092, and 4,511,145 further illustrate the general state of the art in which this invention has its presently preferred utility.

Summary of the Invention This invention addresses and meets the need identified above. It does so by providing improved procedures and me iods which enable bodies for the heads of metal wood golf clubs to be cast more easily and effectively in molds of more simple design and nature. Those improved procedures and methods enable metal wood heads to be manufactured more efficiently and reliably, and widi reduced scrap rates and waste, to the correct weights. Current needs for manual grinding of head castings to remove undesired weight are meaningfully reduced. Finished club heads of a given design have better uniformity of weight distribution.

Generally speaking, this invention provides a mediod for manufacture of a cast metal head of predetermined weight for a golf club. The club head has a front striking face, a heel at a shaft end of die striking face and a toe at an opposite end of the striking face, and odier surfaces of desired contour extending rearwardly from top, bottom and end edges of the striking face. The method includes die step of forming the head body in a mold cavity defined for efficient casting of the body face and odier surfaces to produce a raw body casting which is overweight relative to a desired finished weight after allowance for metal removal in the performance of gate and casting artifact removal and of any polishing operations. The method also includes die step of removing from substantially all surfaces of the body by chemical processes, after performance of the gate and casting artifact removal and of any initial polishing operations, a defined amount of metal. The defined amount of metal is essentially equal in weight to the amount by which die actual body weight exceeds die finished weight less die weight pertinent to the allowance for any final polishing operations.

Brief Description of the Drawings

The above-mentioned and odier features of this invention are more fully set forth in the following detailed description of the presently preferred and other embodiments of this invention, which description is presented widi reference to die accompanying drawings in which:

FIG. 1 is a perspective view of a cast large metal wood golf club head according to this invention;

FIG. 2 is a front elevation view of the head as-cast upon removal from a casting mold and before removal from the head of a gate plug which is an artifact of the casting process;

FIG. 3 is a bottom plan view of the club head shown in FIG. 1 and shows an aperture in the bottom of the as-cast and partially finished head; FIG. 4 is a bottom plan view of the finished head showing a sole plate affixed in the aperture shown in FIG. 2;

FIG. 5 is a cross-sectional view taken substantially along line 5-5 in FIG. 4;

FIG. 6 is an enlarged fragmentary elevation view of the club head shown in FIG. 5 which, for purposes of general example, shows in broken lines the as-cast structure of the head in die vicinity of the head striking face (front wall) and its top wall, and which shows in solid lines die interior and exterior surface of those same walls after metal removal from the casting by chemical processes according to this invention;

FIG. 7 is a sequential block diagram which illustrates the general sequence of operations pursued in manufacturing a golf club head shown in FIGs. 1, 4 and 5; and FIG. 8 is a sequential block diagram which illustrates a manufacturing process somewhat different from d e process represented in FIG. 7.

Detailed Description of the Invention

The invention is described first in a general overall manner, following which more detailed discussions of particular aspects of the invention are presented.

FIGs. 1, 4 and 5 depict a foundry-finished cast large metal wood golf club head 10 according to diis invention, and FIG. 2 and 3 depict a cast head body 11 in different stages of processing of the body into die finished assembled head. As shown best in FIGs. 3, 4 and 5, the finished head 10 is composed of body 11 and of a sole plate 12 which is affixed, as by heliarc welding, in fully sealed relation in an aperture 13 which is defined in the bottom of the as-cast body shown in FIG. 3. The body and the sole plate of head 10 preferably are separately fabricated by known metal casting processes. The metal casting process which presently is preferred in die manufacture of head 10 is an investment casting process which incorporates the very well-known lost-wax process for defining die actual mold cavities into which molten metal, such as molten stainless steel of desired metallurgical composition, is introduced for flow and hardening into the desired raw body and sole plate castings.

The lost-wax process involves the creation in wax, by use of suitable disassemblable mold devices, of a precursor casting for the desired metal casting. The wax precursor has a shape and dimensions which are essentially the same as those of the desired metal casting. The wax precursor is dipped a desired number of times into a bath of ceramic slip to build up on the precursor a ceramic shell of desired thickness. That ceramic shell is heated in an autoclave during which time d e wax precursor melts and die wax flows out of the shell leaving in the shell a cavity which is of the same shape and essentially the same size of the desired metal casting. The resulting shell is then fired in an oven and used as the mold into which the molten metal is poured to create the desired metal casting. The metal is introduced into the mold cavity of die ceramic mold through a desired number of openings (gates) located at one or more places in the cavity walls chosen by the casting foundry, preferably in cooperation with the designer of die part being cast, to assure complete filling of the mold cavity by molten metal and to assure a satisfactory pattern of solidification of die molten metal in the cavity. Although die lost-wax investment process is very old and well known, it has been described above because a general understanding of it is believed useful to an understanding of die descriptions which follow.

Club head 10 has a front wall 15, a bottom 16, a top wall 17 and a curved side wall 18 which interconnects the top and bottom walls and which extends from a heel end of the front wall around a rear end 19 of the head and back to the front wall at a toe end of the front wall. The head has a heel end portion 20 and a toe end portion 21. A tubular hosel 22 extends upwardly at a desired angle relative to the bottom and front walls of the head from the heel portion of the head at substantially the junction of the head front, top and side walls. The hosel 22 receives the lower end of a club shaft (not shown) when the head is assembled into a complete golf club. The bottom of the assembled head is formed by sole plate 12 (see FIG. 5). The outer surface of the head front wall forms a strike face 23 of the head, and diat face defines, for example, a desired pattern of grooves 25 in a manner which conforms to applicable golf rules. Striking face 23 is not flat in most instances; usually it is curved in both heel-to-toe and bottom-to-toe directions in very carefully designed and subtle ways to achieve desired kinds of performance in the finished golf club.

Head body 11 is hollow and forms a cavity 27 which is bounded by the inner surfaces of the several walls described above. Aperture 13 in head bottom 16 opens to cavity 27. The aperture is made as large as possible consistent widi die overall contours of the finished head and consistent with the usually desired criterion that the sole plate for head 10 preferably is flat, or substantially so, to facilitate its welding to the head body. The larger the sole plate aperture 13, the easier it is to remove the preferably multi-part core assembly from the wax preform of the head body in performing the mold making process described above. The head body has an inner surface 28 defined by the inner surfaces of the several body walls and it has an outer surface 29 defined by the outer surfaces of those same walls.

Hosel 22 has a straight bore 30 which communicates to cavity 27 as shown in FIG. 5. The procedures which comprise the method aspects of this invention can be used to advantage to manufacture hosel-less golf club heads; in such event, die head casting defines a shaft receiving sleeve which preferably has communication to a cavity in the head casting in d e manner shown, for example, in U.S. Patent 5,042,806 to enable the head cavity to be filled widi a foam material after the sole plate has been affixed to the head body.

A practical and preferred way to practice this invention is for the club head to be designed and defined to have die dimensions, contours and wall thicknesses desired in the finished club head 10, and dien, before the molds for defining the head body casting are designed and constructed, for the casting foundry, based upon its knowledge and experience in the casting of diin walled articles, to add uniformly to the inner and outer body surfaces 28 and 29 (and to the inner and outer surfaces of hosel 22) additional diickness which causes the thinnest designed wall to have an acquired thickness sufficiently great to be readily castable in a mold cavity having as few gates as possible. The mold for making that modified, diickened-wall head body is dien designed and made, and a head body casting is made using that mold. Upon removal of the raw casting from its preferably ceramic casting mold, such mold gate plugs 32 (see FIG. 2) as are present on the exterior of the raw casting, and such other external casting artifacts (such as flash, mold parting line ridges, and the like) as may extend from the outer surface of the raw casting, are removed by conventional grinding and polishing operations. Those grinding and polishing operations may be performed manually but, as will be apparent to those skilled in the art having an understanding of the overall nature of this invention from the descriptions which follow, they are minimal in extent and are readily and efficiently performed. Upon dressing of the casting by those preliminary grinding and polishing procedures, the body casting is weighed and die amount by which its weight at mat time exceeds the body design weight is determined. That weight difference is the amount of weight which must be removed from the body casting so that the fully finished club head will have the desired weight (say, 200 grams) after the sole plate has been affixed to the body, that weldment has been ground and polished, the hosel bore or shaft receiving sleeve of the head has been finished as by drilling or reaming, and after the closed head has been filled with foam and is ready for such painting or other finishing as may be done by a golf club manufacturer before mounting of the head by the club manufacturer to a club shaft. That measured amount of weight is men removed from me dressed body casting by chemical processes which are known as chemical milling. That measured amount of weight is removed by etching all surfaces, inner and outer, of the dressed body casting to remove from all places on those surfaces sufficient metal to cause the head, after chemical milling to have the correct weight consistent widi such further manufacturing processes as it may encounter. In the course of chemical milling, the wall thicknesses of the body casting are reduced so that, upon completion of chemical milling, the body wall diickness are essentially as designed and are of die correct contour.

It will be seen, from die foregoing general summary of the club head manufacturing process, that this invention enables an investment casting foundry to efficiently, reliably and economically cast articles, such as jumbo metal wood club heads, which because of thin wall sections in the as-designed article, heretofore presented high scrap rates to the foundry.

FIG. 6 is an enlarged fragmentary cross-sectional elevation view of an exemplary portion of body casting 11 in the vicinity of d e junction of the front wall 15 of the body with its top wall 17. The broken lines in FIG.6 denote die inner and outer surfaces of the head body as cast. The solid lines denote die inner and outer surfaces of the body after removal of a controlled amount of metal from tiiose surfaces of the as-cast body by chemical processes; the solid lines also denote essentially the inner and outer surfaces of the head body in its as-designed condition.

As diose skilled in die art of designing metal wood golf clubs will appreciate, die thickness of the front wall of a metal wood golf club head is most important. That wall is critical in the transfer of kinetic energy from a rapidly moving club head to a stationary golf ball in the brief interval of impact upon and contact widi the ball. That wall must be sufficiently rigid to maximally transmit head kinetic energy to the ball without appreciable energy-absorbing deflection. That wall cannot be so thin as to be dented or cracked by repeated such impacts. That wall usually is the diickest one of die several walls which comprise the club head. It is the wall in which the ratio of wall weight per unit surface area is highest, as a rule. Consequently, the larger the club head, die diinner the odier walls of the head must be to meet the stringent weight and weight distribution specifications of the head. Thus, head body 11, as represented in FIG. 6, has a design front wall diickness T and a substantially smaller top wall design thickness t rearwardly of the junction of the top wall with die front wall. Thickness t may be taken as typical of the design diickness of all head body walls odier dian die head front wall.

In the large metal wood heads, the difference between thicknesses T and t can easily be so great that the head body can be cast to design wall thicknesses only with great difficulty even when using many casting mold gates at strategically defined places on the club head. If too few gates are used to introduce molten metal into the casting mold cavity, the metal may not be able to fiilly fill the cavity in thin-wall areas, and to properly blend with itself in all locations in the cavity, before solidification of die metal commences in thin walled areas. Also, it will be realized that molten metal shrinks significantly as it cools and solidifies. Therefore, to avoid the presence of voids and other defects in metal castings, it is essential that metal solidification and shrinkage begin in the mold cavity farthest from the gates to die cavity and progress controllably toward die gates where the metal solidifies only after the metal in the cavity has solidifies. When diat solidification pattern is achieved, diere is always molten metal between the solid metal and die gate to fill die cavity as the metal shrinks and becomes sold. Failure to achieve diat solidification pattern leads to voids, too tiiin walls and odier casting defects, all of which produce unacceptable or unrepairable castings, i.e., scrap. Assume that wall diickness t is sufficiently less than wall diickness T that head body 11 can be cast only with great difficulty, and poor success rates, even when many gates to the casting mold cavity are provided at all the correct places in the cavity. That is the situation with which foundries are presented by golf club manufacturers who are designing ever larger metal wood heads. Current designs for metal wood heads are uncastable as designed, in may instances. They can be cast only if the diin walls are thickened to enable casting of a head which is too heavy and must undergo substantial grinding away of its outer surface (the inner surfaces are inaccessible for grinding) in only a few places on the cast body odier than the striking face and die hosel if present. The result is the increasing presence of the problems described above and increasing foundry scrap rates.

In that context, dien, FIG. 6 illustrates an important aspect of this invention. No attempt need be made to cast head body 11 to its as-designed wall thicknesses. Instead, the body design is analyzed for its casting difficulty assuming the use of only one gate, or a minimum number of gates, to the mold cavity. A determination is made as to what is the minimum reliably castable wall thickness t¹ for that head body configuration. Clearly, t¹ will be greater than t. The amount by which t¹ exceeds t is halved (divided by 2), and die amount a = (t¹ - 1)/2 is added to botii die inner and outer surfaces of the as-designed head. The casting mold is defined to cast that thicker walled article.

Such a casting can be made quite effectively and efficiently, preferably in a multi-cavity casting mold which can be made conveniently by die lost wax process described above. The step of casting such a thickened-wall head body is denoted at 35 in FIG. 7.

Upon removal of die casting from the casting mold, die desired castings are removed from the typical sprue and gate "tree" so that a short gate plug 32 is attached to each casting at one or a very few places on the casting. Each gate plug is cut from the casting, preferably as close to the casting's outer surface as possible without marring that surface. A short plug stub, about 1/32 inch long, typically remains. That plug stub, and such other casting artifacts like parting line flash and ridges, are ground away. Those steps are denoted collectively at 36 in FIG. 7. If desired, die body casting dien can be lightly polished as indicated at 37 in FIG. 7. The result is a dressed head body casting in which all wall diicknesses are the designed thickness plus the added thickness 2a which is distributed substantially equally between the inner and outer surfaces of each wall.

The head body casting is then weighed. The amount by which the casting is overweight relative to a desired finished weight is measured. That measured weight is decreased by the weight which experience indicates is to be allowed for metal removal in finishing of the sole plate weldment and in any desired final polishing processes, thereby to obtain a defined amount of metal (by weight) to be removed from the dressed casting by chemical processes. Because the inner and outer surface areas of the casting are known or are knowable, and because the density of the metal defining the casting is known, that defined weight can be readily converted to a diickness of metal to be removed from both the inner and outet surfaces of the dressed casting. The body casting can be placed widi other body castings in a group of castings requiring the same or essentially the same weight-reducing wall thickness reduction. Those operations are shown as step 38 in FIG. 7.

The weighed and sorted dressed head body casting is then subjected to known, carefully controllable chemical milling processes in which the casting is placed, preferably with others from its sort group, in an acid etching bath which acts on all surfaces of die dressed casting; see FIG. 7 at 39. In the course of chemical milling, the same thickness of metal is removed from the inner and outer faces of die dressed casting. The rate at which a particular acid removes metal from an article of specified metallurgical composition is known or is easily determinable. Hence, the specification for the chemical milling process can be defined in terms of diickness of metal to be removed from each exposed surface of the article. When the casting has been in die acid badi for the desired time, it is removed from that bath and any acid remaining on or in the body casting is neutralized in an alkali bath, after which the chemically milled casting is washed, rinsed and dried. It is dien ready for connection of its sole plate 12 to it.

Upon completion of the chemical milling processes which form a part of the procedural aspects of this invention, the head body has wall diicknesses which are the same as, or essentially the same as within acceptable tolerances, the design thicknesses of the several walls of the body. That is, the chemical milling operations remove from the inner and outer surfaces of the head the same amount, or essentially the same amount, of thickness as was added to those surfaces to enable die body to be cast reliably in a minimally gated mold. As shown in FIG. 5, sole plate 12 of head 10 can be of greater diickness, if desired, tiian the diickness of at least some of the body walls which define its mounting opening 13 in die body. The sole plate is suitably positioned in that opening and is welded to die body about die entire perimeter of the sole plate. The welding operation may produce a raised bead along die weld line; if so, mat bead is ground and polished away, and any final polishing operations as may be required are dien performed. Those operations are represented at step 40 in FIG. 7. The club head is tiien essentially finished save for filling with foam and for such surface finishing, such as painting or plating, as may be desired by die golf club manufacturer; see step 41 in FIG. 7.

In some instances, the surfaces 28 of cavity 27 produced by die chemical milling process may be too smooth to enable die foam material later introduced into diat cavity to mechanically bond to those surfaces. In such instances, the cavity surfaces can be sandblasted before the head sole plate is affixed to the head body; see step 42 in FIG. 7. In other instances, the chemically milled body surfaces may not require roughening, as by sandblasting, for adhesion of die foam to them; in such events, the sole plate welding step 43, and the grinding and light polishing operations 44 can be performed before performance of chemical milling step 39, as schematically shown in FIG. 8. It will be recalled that the shaft receiving sleeve provided eidier by hosel 22 or within the head body itself has communication to the interior of the head body. That communication can make it possible to chemically mill, neutralize and rinse die head after the sole plate has been affixed to the head body. If the sole plate is affixed to the body casting before the casting is chemically milled, the sole plate is made thicker than desired on each side by the same amount as the thickness of metal to be removed from each casting surface by the chemical milling step 39.

As noted briefly above, die contour of the striking face of a wood-type golf club head is very carefully designed, and the size and definition of the grooves and other recesses in that face must conform to exacting standards imposed by die rules of golf. Because the weight-reducing metal- removing chemical processes described above equally affect all locations on a head body casting, the use of such processes on the striking face of the metal wood head does not adversely affect the face contour. However, depending upon die diickness of metal to be removed from a metal striking face, diose processes may adversely affect the size and definition of the grooves and the like in the striking face and cause diem not to conform to applicable rules. In that event, the procedures of this invention can be applied to all areas of a head body casting other than its striking face. That is, the thickness of metal added to die casting's as-designed inner and outer faces to make castable a iin wall portion of die head body can be distributed over the entire extent of the body inner surface and over all of the outer surface except on the striking face. Then, after the weight of metal to be chemically removed from die dressed body casting has been determined by weighing die casting as described above, and before performance of the chemical milling processes, the as-cast striking face of the head body can be masked by covering it with a wax or other material which is not attacked by die etching acid bath. The chemical milling process then can be performed, without effect upon the striking face, to remove the desired metal thickness from all other surfaces inside and outside die body casting. Upon completion of the chemical milling operation, that masking coating can be removed in a known suitable way from the striking face. It will be appreciated that precision is not required in making die determination of how much the diicknesses of the as-designed walls of head body 11 are to be increased to make readily and reliably castable a head body which, as designed, may be virtually impossible to cast by even the most sophisticated foundry processes and techniques without encountering very high scrap rates. It is much better to add more thickness to the as-designed surfaces than to add too little thickness. The metal used in forming the head body casting is relatively inexpensive compared to the cost of manual grinding and polishing processes now used to remove excess weight from cast head bodies. Whatever wall thickness is added to make the body readily castable is easily, controllably and inexpensively removed from the cast body by the chemical milling operations.

Also, close conformance of body wall thicknesses after chemical milling to the as-designed wall diicknesses can be achieved by distributing the total added thickness between the inside and die outside of die head body in proportion to the ratio of die as-designed inside surface area to the as- designed area of those outside surfaces which will be subjected to chemical milling processes.

It is a simple matter to empirically determine, for each style and size of a line of metal wood heads, a table which correlates the depths of metal removed from each casting surface to the amount of weight removed from the entire casting. A series of, say, five or six body castings for the same style and size of head are weighed and die measurements are noted. The weighed castings are subjected to different extents of chemically milling to remove 0.0002" to 0.010", in 0.002" increments, from each of the inner and outer surfaces of the castings. The chemically milled heads are then reweighed and the weight change of each in grams is determined. A substantially linear relation of overall weight change versus thickness of metal removed from an exposed casting surface then can be established, from which it is a simple task to specify the thickness to be removed by chemical milling as the defined weight to be removed is found by weighing a dressed body casting.

By way of example, a metal wood head as designed may have a front wall thickness of 0.120 " , a rear, top and side wall diickness of 0.025" , and a design finished weight (widi allowance of 6 grams for sole plate weldment removal) of 150 grams; such a head body design may be based upon a 40 gram sole plate and 16 grams of foam filling, to produce a fully finished club head weighing 200 grams. The 0.025" wall thickness presents difficult casting problems. However, a wall thickness of 0.040" is readily castable very reliably and efficiently. Therefore, in the practice of this invention, to enable the head body to be efficiently cast, the as-designed wall having a thickness of 0.025" is increased in diickness by die foundry to 0.040", i.e., 0.0075" of thickness is added to each side of diat wall and to all odier surfaces of the body which will be exposed to die appropriate chemical milling process. That thickened-wall casting is made and dressed as needed. On weighing the dressed body casting, it is found to weigh 174 grams, i.e., is 24 grams overweight. The empirically developed weight/tiiickness table for that casting design indicates that the removal of 0.001" of metal from all available surfaces of that casting will reduce its weight by 3.3 grams. Since 24/3.3 = 7.3, it is apparent that removal of 0.0073 inches of metal from those surfaces of that casting will produce a casting weighing 150 grams. The wall designed to be 0.025" diick has an actual thickness of 0.0254" in the chemically milled casting of the desired weight.

A metal casting which has been subjected to chemical milling processes has crystal structure characteristics and properties at and adjacent its chemically milled surfaces which are discernibly different from diose encountered inwardly from such a surface. Accordingly, careful inspection and analysis of a metal wood golf club head can reveal whether it was subjected to chemical milling processes during its manufacture.

The procedures and metiiods described above can also be used to produce investment cast hollow and solid heads for iron-type and putter golf clubs of carefully controlled head weight, especially in instances where the club head geometry or configuration precludes d e use of mechanical grinding or polishing techniques on areas of the head from which it desired to remove metal to achieve particular overall head weights or head weight distribution characteristics.

The foregoing description of presently preferred and other aspects of this invention has been presented principally for purposes of explanation and example for the benefit of persons skilled in the art to which the invention pertains. That description is not an exhaustive catalog of all of the procedures which can be pursued in die practice of this invention. Variations upon the procedures and operational sequences described above can be adopted and pursued widiout departing from the fair scope of the invention.

Claims

HAT IS CLAIMED IS:

1. A metal golf club head having a striking face on a front surface of the head and other exterior surfaces surrounding and disposed rearwardly of the striking face, at least substantial portions of die exterior surfaces of the head having tiiereat and adjacent diereto properties and characteristics consistent with the performance of chemical milling processes upon such surface portions.

2. A golf club head according to claim 1 wherein die head is hollow.

3. A golf club head according to claim 2 wherein interior surfaces of the head have diereat and adjacent thereto properties and characteristics consistent widi die performance of chemical milling processes upon them.

4. A golf club head according to claim 2 wherein the head is a metal wood head comprised of a hollow body having a cavity therein and a sole plate affixed to the body in closure relation to the cavity, and at least interior surfaces of the body bounding die cavity have said properties and characteristics.

5. A golf club head according to claim 4 in which a surface of the sole plate bounding die cavity has said properties and characteristics.

6. A method for manufacture of a cast metal head of predetermined weight for a wood- type golf club, which head is comprised of a head body having a front striking face, a heel at a shaft end of die striking face and a toe at an opposite end of die striking face, and other surfaces of desired contour extending rearwardly from top, bottom and end edges of the striking face, die mediod comprising the steps of: forming the head body in a mold cavity defined for efficient casting of the body face and odier surfaces to produce a raw body casting which is overweight relative to a desired finished weight after allowance for metal removal in the performance of gate and casting artifact removal and of any polishing operations, and removing from substantially all surfaces of the body by chemical processes, after performance of the gate and casting artifact removal and of any initial polishing operations, a defined amount of metal essentially equal in weight to the amount by which actual body weight exceeds the finished weight less die weight pertinent to allowances for any final polishing operations.

7. The method according to claim 6 wherein die head is hollow and has a cavity dierein which has an opening within the head to an open-ended shaft receiving sleeve formed by the head, and die step of removing a defined amount of metal includes subjecting at least some of die surfaces of the cavity to said chemical milling.

8. The method according to claim 7 wherein the cavity is adapted to be filled via the opening by a selected weight of a foam material, and die finished weight of the head body is substantially die selected weight less dian the predetermined weight.

9. The method according to claim 8 wherein the head is comprised by die head body and by a sole plate of known weight affixed in a bottom opening to die cavity which is defined in die head body.

10. The method according to claim 9 wherein the desired finished weight is that of the body and does not include die known weight of the sole plate, and including die step of affixing the sole plate to the body after performance of the step of removing by chemical processes a defined amount of metal.

11. The method according to claim 9 wherein the desired finished weight is diat of die head body and includes die known weight of the sole plate, and including the step of affixing die sole plate to die body before performance of the step of removing by chemical processes a defined amount of metal.

12. The method according to any one of claims 7, 8, 9, 10 or 11 in which the head is a head for a large-head metal wood golf club.

13. The method according to claim 12 wherein the head has an as-designed configuration in which at least some of the exterior surfaces of the head body are defined by certain walls of specified thickness, and including the step of casting die head body in such manner to cause die certain walls of the head body casting to be thicker than die specified diickness.

14. The method according to claim 13 wherein the step of casting the head body includes defining a mold cavity for the casting of the body casting so that there is added to each surface of the as-designed configuration which corresponds to a body casting surface to be affected by said chemical processes a diickness of metal equal to substantially one-half the amount by which the certain walls are thicker than those walls in the as-designed configuration.

15. A method for manufacture of a cast metal head of predetermined weight for a wood- type golf club, which head is comprised of a sole plate of known prefinished weight affixed in a bottom opening in a hollow head body having a front striking face, a heel at a shaft end of the striking face and a toe at an opposite end of the striking face, a top crown surface extending rearwardly from a top edge of the striking face, wall surfaces depending from other edges of the crown surface substantially to the sole plate opening between the heel and toe via a rear extremity of the body, a shaft receiving sleeve in association with the heel, and an aperture into the interior of the body in association with die shaft receiving sleeve for introduction of a selected weight of a foam material into the body after affixation of the sole plate to die body, die head after surface finishing thereof with die sole plate affixed to the body having a finished weight which is substantially die selected weight less dian the predetermined weight, die mediod comprising: forming the head body in a mold cavity defined for efficient casting of the body face, crown and wall diicknesses to produce a raw body casting which is overweight relative to die finished weight after allowance for metal removal in the performance of gate and casting artifact removal, initial polishing, sole plate finishing, and final polishing operations, and removing from substantially all surfaces of the body by chemical processes, after performance of the gate and casting artifact removal and die initial polishing operations, a defined amount of metal essentially equal in weight to the amount by which actual body weight exceeds die finished weight less die weight pertinent to the allowances for the sole plate finishing and die final polishing operations.

16. A hollow cast metal golf club head having a shaft receiving sleeve the interior of which communicates with a cavity widiin die head, which cavity is filled widi a selected weight of foam material, the head exclusive of die foam material having been formed by casting the head to have an excess of weight relative to the sum of the finished weight and die weight of such amounts of metal as are removed from the casting by mechanical grinding and polishing processes, and by subjecting selected surfaces of the casting to chemical processes for removal of said excess weight from the casting.

17. A golf club head according to claim 16 wherein die selected surfaces include a major portion of the surface area of the cavity, the interior surfaces of the sleeve and major portions of the exterior surfaces of the head.

18. A golf club head according to claim 17 wherein die selected surfaces include a striking face of the club head.

19. A golf club head according to claim 17 wherein the club head includes a sole plate affixed to a body casting in closure relation to a bottom portion of the cavity, and the selected surface of the sole plate.