Method of making golf clubs of thermoplastic composite material

A method of making golf clubs of thermoplastic composite material is disclosed. The present method is characterized in that the composite material wound around a mandrel is consolidated by using a metal sheet. This method comprises the steps of: (a) providing a tapered mandrel, and wrapping the mandrel with at least a sheet of thermoplastic prepreg to form a laminated outer shell; (b) heating the thermoplastic prepreg to a molten state; (c) enclosing the laminated outer shell with at least a metal sheet, and heating the metal sheet and the laminated outer shell while constricting said metal sheet to thereby consolidate the molten prepreg to form a tubular body; and (d) releasing the metal sheet and withdrawing the mandrel from the tubular body.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates in general to the fabrication of golf clubs. 
More particularly, it relates to a method of making golf clubs of 
thermoplastic composite material. 
2. Description of the Related Arts 
Composite golf clubs are conventionally made of thermosetting composite 
material such as epoxy resin/carbon fiber prepreg. Two major methods are 
employed for making thermosetting golf clubs, which are: (a) the tape 
rolling method; and (b) the filament winding method. 
The tape rolling method for making a thermosetting golf club will now be 
described by referring to the flow chart of FIG. 1. Epoxy resin/carbon 
fiber prepreg 100 is wrapped around a mandrel 102 by assistance of a 
rolling machine (a1). After the wrapping, the mandrel is further wound 
with longitudinally and latitudinally oriented polypropylene (OPP) tapes 
(a2), and then heated to 80-150.degree. C. for about 1-3 hours (a3). While 
the OPP tapes shrinks during the heating, the wrapping prepreg is 
compressed and hardened to form a compact tubular body. After releasing 
the OPP tapes (a4), the tubular body is shaped into an appropriate size 
(a5), and finally, its outer peripheral surface is polished (a6) and 
painted (a7) to produce a golf club 104. 
As to the filament winding method, referring to FIG. 2, the procedures are 
largely the same except that the composite materials are wrapped around 
the mandrel in a different manner. The raw material of carbon fiber 200 is 
first wetted with liquid epoxy resin 202 (b1), and then the resin-covered 
fiber is wound around the mandrel in a spiral orientation (b2). 
Afterwards, the same procedures of the OPP winding, heating, OPP 
releasing, and so forth (b3-b8), are repeated to complete a golf club 
product 204. 
The thermosetting golf clubs thus produced, however, do not have excellent 
plasticity and, in view of the fact that the thermosetting materials such 
as epoxy resin cannot be easily recycled, are potential sources of 
environment pollution. On the other hand, thermoplastic materials are 
easy-recycle and have excellent shock-absorbing and elastic features. 
Therefore, the future trend is to make golf clubs of thermoplastic 
materials. In recent years, polyphenylene sulfide (PPS) and nylon have 
been considered the most preferable materials for making thermoplastic 
golf clubs. There have been numerous attempts to make golf clubs of 
thermoplastic materials; see for example, U.S. Pat. No. 5,198,058. 
Methods for making thermoplastic golf clubs can also be classified into the 
tape rolling method, and the filament winding method. The processes are 
basically the same as those for making thermosetting golf clubs, except 
that heat-resistant shrink tapes are used to replace the OPP tapes because 
the subsequent heating will take place at a much higher temperature 
(0-80.degree. C. above the crystalline point or softening point of the 
thermoplastic material.) The crystalline melting points (Tm) of nylon 6 
and PPS are 225.degree. C. and 278.degree. C., respectively, whereas that 
of OPP is only 160.degree. C. Apparently, OPP tapes cannot be processed at 
such high temperatures, and a substitute having better heat resistance is 
thus required for making thermoplastic golf clubs. A silicon rubber tape 
is satisfactory for this demand when making nylon 6 golf clubs. However, 
because the silicon rubber tape is bound to decompose at above 290.degree. 
C., it is not qualified for making PPS golf clubs. 
The golf clubs produced by using the silicon rubber tapes as shrink tapes 
generally have spiral mark defects, and as a result, the golf clubs suffer 
from insufficient strength and rigidity. Also, the silicon rubber tape is 
high-cost and is made of thermosetting materials which cannot be easily 
recycled. 
SUMMARY OF THE INVENTION 
It is therefore an object of the invention to provide a novel method of 
making golf clubs of thermoplastic composite material. In this method, the 
use of shrink tapes is not necessary, thus reducing the manufacturing cost 
and avoiding the defects produced by the shrink tapes. 
It is another object of the invention to provide a method of making 
thermoplastic golf clubs, by which either nylon 6 or PPS can be used as a 
material for making thermoplastic golf clubs. 
It is still another object of the invention to provide a method of making 
golf clubs of thermoplastic composite material. The golf clubs produced 
thereby have excellent shock-absorbing and elastic qualities and can be 
recycled easily. 
To accomplish the above objects, the present method is characterized in 
that the composite material wound around a mandrel is consolidated by 
using at least a metal sheet rather than shrink tapes. 
The method of the invention can be applied in either the tape rolling 
method or the filament winding method. In the tape rolling method, the 
process of the invention includes the steps of: (a) providing a tapered 
mandrel, and wrapping the mandrel with at least a sheet of thermoplastic 
prepreg to form a laminated outer shell; (b) heating the thermoplastic 
prepreg to a molten state; (c) enclosing the laminated outer shell with at 
least a metal sheet, and heating the metal sheet and the laminated outer 
shell while constricting said metal sheet to thereby consolidate the 
molten prepreg to form a tubular body; and (d) releasing the metal sheet 
and withdrawing the mandrel from the tubular body. Examples of 
thermoplastic prepreg as used herein include nylon/carbon fiber prepreg, 
polyphenylene sulfide/carbon fiber prepreg, polyphenylene sulfide/glass 
fiber prepreg, polyether ether ketone (PEEK)/carbon fiber prepreg, and 
nylon/glass fiber prepreg. 
In the filament winding method, the process of the invention includes the 
steps of: (a) providing a tapered mandrel, and winding the mandrel with a 
composite material composed of thermoplastic resins and fibers to form a 
tubular outer shell; (b) heating the composite material so that the 
thermoplastic resins thereof enter a molten state; (c) enclosing the 
tubular outer shell with at least a metal sheet, and heating the metal 
sheet and the tubular outer shell while constricting said metal sheet to 
thereby consolidate the composite material to form a tubular body; and (d) 
releasing the metal sheet, and withdrawing the mandrel from the tubular 
body. Composite materials of thermoplastic resins and fibers suitable for 
use herein include: commingle yarns, for example, by BASF Structure 
Material, Inc.; tow powder, for example, by Custom Composite Material, 
Inc.; tow flex, for example, tow flex II and G30-500 12 K/N6 ribbon by 
Custom Composite Material, Inc; and 2-6 mm-wide prepreg sheets, for 
example, nylon 6/carbon fiber prepreg by Quadrax Advanced Materials 
System, Inc. In either the tape rolling method or the filament winding 
method, the step (b) is preferably carried out at 0-80.degree. C. above 
the crystalline melting point (Tm) or softening point of the thermoplastic 
material. In step (c), the metal sheet can be constricted by a tensile 
force produced by a pressure cylinder, wherein the tensile force is 
preferably within the range of about 1-100 kg/cm.sup.2. The metal sheet 
suitable for use in the invention can be made of stainless steel, 
aluminum, or copper, and preferably has a thickness of about 0.03-0.05 mm. 
As already mentioned, the present method uses the metal sheet to 
consolidate the composite materials, thus obviating the need for using 
expensive silicon rubber tapes. It is also economically advantageous that 
the metal sheet can be reused. Furthermore, owing to the refractory 
feature of the metal sheets, this method can readily be used for making 
nylon clubs, or even PPS clubs that needs high-temperature processing. 
Other objects, features, and advantages of the present invention will 
become apparent from the following detailed description which makes 
reference to the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
First Embodiment 
In this embodiment, a process for making a thermoplastic golf club 
according to the tape rolling method is illustrated. 
Two nylon 6/carbon fiber prepreg sheets are cut so as to have fiber 
orientations of +45.degree. and -45.degree. with respect to the axis of a 
mandrel, respectively, and to have a length of 115 cm and an enough width 
to form three plies around the mandrel. Another prepreg sheet is cut so as 
to have a fiber orientation of 0.degree. with respect to the axis of the 
mandrel and to have a length of 115 cm and an enough width to form six 
plies around the mandrel. 
The two prepreg sheets having orientations of +45.degree. and -45.degree. 
are heated to 280.degree. C. and laminated together. The laminated prepreg 
is wrapped around a tapered mandrel over a rolling table set at 
280.degree. C., and the prepreg sheet having the orientation of 0.degree. 
is subsequently wrapped thereupon to form a laminated outer shell. 
In the next step, the prepreg-wrapped mandrel is affixed to a clamping 
device as depicted in FIG. 3. As shown in the figure, the outer periphery 
of prepreg-wrapped mandrel 300 is enclosed with a metal sheet 310 which is 
clasped by a clamp 320. The clamp 320 is coupled to a pressure cylinder 
360 via a steel wire 340 and an iron ring 330 coupled to the clamp. The 
tensile force exerted from the pressure cylinder can be measured by a load 
cell 350 set between the cylinder 360 and the iron ring 330. When the 
clamp 320 is pulled by the pressure cylinder 360, it constricts the metal 
sheet 310, and at the same time the clamping blocks 305 move towards each 
other to insure that the entire outer peripheral surface of the tube body 
can be enclosed and compressed by the metal sheet. This procedure is 
carried out at a kiln set at 280.degree. C., and the pulling is continued 
for 30 minutes to complete the consolidation of the composite material. 
After cooling, the metal sheet is released, and the mandrel is withdrawn to 
give a monolithic tubular body. The tubular body is shaped into a suitable 
size and its outer peripheral surface is polished. Finally, a plating 
layer is applied on the polished surface to complete a golf club. 
Second Embodiment 
In this embodiment, a process for making a thermoplastic golf club 
according to the filament winding method is illustrated. The procedure 
outlined in the first embodiment is repeated with the exception that the 
laminated outer shell is prepared by winding commingle yarns of nylon 
6/carbon fiber around a mandrel. The tubular body thus formed is subjected 
to same procedures of shaping, polishing, and plating as set forth in the 
first embodiment to give a golf club. 
While the invention has been particularly shown and described with the 
reference to the preferred embodiment thereof, it will be understood by 
those skilled in the art that various changes in form and details may be 
made without departing from the spirit and scope of the invention.