Patent Application
20070049418
The present invention is related to a method for making a golf club head from a titanium alloy, and in particular to a method for making a golf club head from a bismuth-containing titanium alloy.
Golf club heads made from titanium alloys are very common now, which involves casting a titanium alloy in a centrifugal manner by a vacuum induction melting (VIM) or vacuum arc re-melting (VAR) to form a crown of the golf club head. A shell mold made of zirconium oxide or yttrium oxide is used in the casting, which is prepared by forming a wax mold by injection molding, impregnating the wax mold in a slurry to form a coating, drying, de-waxing and sintering. The materials of zirconium oxide and yttrium oxide are inert to molten titanium alloy. Even though the flowability of molten titanium alloy in the shell mold can be improved by centrifugal force, the resulting casts of the crown of the golf club head frequently suffer casting defects such as pin holes, and incomplete filling, etc.
A primary objective of the present invention is to provide a method for making golf club head with less casting defects from a titanium alloy.
Another objective of the present invention is to provide a method for making golf club head with at least a portion thereof being made from a bismuth-containing titanium alloy by casting.
In order to accomplish the above-mentioned objectives, a method for making a golf club head from a titanium alloy disclosed in the present invention comprises casting a titanium alloy to form at least a portion of the golf club head, wherein the improvement comprises the titanium alloy comprises at least 0.01% of bismuth, based on the weight of the titanium alloy.
A golf club head constructed according to the present invention comprises at least a portion of the golf club head which is made of a titanium alloy comprising at least 0.01% of bismuth, based on the weight of the titanium alloy.
Preferably, the titanium alloy comprises 0.1-10% of bismuth, more preferably 0.5-5% of bismuth, and most preferably 1-3% of bismuth, based on the weight of the titanium alloy.
Preferably, the titanium alloy consists essentially of bismuth and titanium.
Preferably, the titanium alloy consists essentially of bismuth, titanium and at least one element selected from the group consisting of Mo, Al, V, Sn, Cr, Zr, Fe, Nb, Ta, Si, Hf, Cu and Pb.
Preferably, the method of the present invention further comprises polishing the resulting cast from said casting to obtain a polished cast having a surface with an average surface roughness less than 1 μm, and more preferably less than 0.1 μm.
Preferably, said at least a portion of the golf club head is crown.
Preferably, said at least a portion of the golf club head is face plate.
Since 1990 the material used in manufacturing golf club crowns and face plates has been shifted from 17-4PH steel and persimmon wood to Ti—6Al—4V in view of its high strength, low elastic modulus, low density and anti-corrosion properties. In order to increase the area of the sweet spot and MOI (moment of inertia) value with a limited total weight, the size of the golf club head has been increased from 200 cc to 450 cc and the thickness of the golf club crown has also been gradually decreased. Further, various designs of the balance of the golf club head complicate the shape thereof. U.S. patent publication No. 2003-0036442 Al discloses a golf club crown has a thickness less than 0.8 mnm. It is not easy to make such a golf club crown from Ti—6Al—4V by casting. According to the teaching in U.S. Pat. No. 4,830,823, the castability of pure titanium can be improved by doping 1.5-4 wt % of Al and 1-3 wt % of V, typically Ti—3Al—2.5V. However, the strength of Ti—3Al—2.5V is 621 MPa, which is only 60% of that of Ti—6Al—4V (100 MPa), so that the use of Ti—3Al—2.5V in making a golf club head is not satisfactory. Recently, the golf club heads made by the leading brands such as Callaway® and Taylormade® contain many portions made of β phase titanium alloys, such as Ti—4.5Al—3V—2Fe—2Mo, and Ti—1.5V—3Zr—3Al—3Sn. β phase alloys have a high strength and a low elastic modulus, which provide advantages such as a high coefficient of rebound and a wider window in optimizing the mechanic design. However, these β phase alloys have high dosages of alloying elements, which renders their casting difficult. Therefore, there is a need in searching a high strength titanium alloy with improved castability.
The inventors of the present application in U.S. Pat. No. 6,409,852 and US patent publication No. 2004-0136859 disclose a technique for improving castability of pure titanium metal and titanium alloys by doping bismuth, disclosures of which are incorporated herein by reference. The castability of pure titanium can be enhanced 34% by doping 1 wt % of bismuth according to this technique. Certain bismuth-doped titanium alloys such as Ti—6Al—7Nb—1Bi, Ti—6Al—4V—1Bi, Ti—7.5Mo—1Bi and Ti—15Mo—1Bi also show significant improvement in captability in comparison with the corresponding un-doped titanium alloys. These bismuth-doped titanium alloys all have a castability superior to that of the Ti—6Al—4V used in casting golf club heads. In another search of the inventors of the present application a titanium-molybdenum alloy (typically Ti—7.5Mo) having α″ phase as a major phase exhibits an excellent combination of strength, elastic modulus and ductility, the ratio of strength/elastic modulus (the key index of mechanical properties) of which is remarkably higher that of Ti—6Al—4V and most of the known titanium alloys. Please refer to U.S. Pat. No. 6,409,852 for details, the disclosure of which is incorporated herein by reference. In the pending U.S. patent application Ser. No. 11/107,833 (filed Apr. 18, 2005) the inventors of the present application disclose a method of making a titanium alloy article by plastically deforming at room temperature from typically a β phase Ti—15Mo—1Bi alloy which has high strength, low elastic modulus and good cold working ability.
The inventors of the present application attempt to develop a novel method for making a golf club head, which includes casting a bismuth-containing titanium alloy, and further evaluating the mechanical properties, coefficient of rebound, and durability of the golf club head, so that the golf club head can be made more easily with precision casting, and still has high strength and low elastic modulus.
The following Table 1 lists the improvement in castability (cast length) of Ti alloys due to the presence of Bi disclosed in US patent publication No. 2004-0136859 A1.
It can be seen from Table 1 that the castability titanium alloys can be improved by doping bismuth.
The effects of the dosage of 1, 3 and 5 wt % of bismuth on the structure and mechanical properties of pure titanium and several titanium alloys are shown in Table 2, wherein X-ray diffraction (XRD) for phase analysis and bending test were conducted. It can be seen from Table 2 that the phases of pure titanium and titanium alloys do not change after doping with 1, 3 and 5 wt % of bismuth, and the bending strength and elastic modulus (bending modulus) are both increased.
The data in Tables 1 and 2 prove that the inventors of the present application who are the first ones using bismuth-containing titanium alloy to make a golf club head by casting can solve the drawbacks of the prior art—the frequent occurrence of casting defects of titanium alloy golf club heads. Further, the golf club head made by the present invention from a bismuth-containing titanium alloy still retains high strength and low elastic modulus of the titanium alloy.
The inventors of the present application conducted a cold rolling test on Ti—Mo and Ti—15Mo—1Bi specimens, and a bending fatigue test on the cold-rolled Ti—15Mo—1Bi specimens. Ti—15Mo (15 wt % Mo) and Ti—15Mo—1Bi (15 wt % Mo and 1 wt % Bi) alloys were prepared from a commercially pure titanium (c.p. Ti) bar, molybdenum of 99.95% and bismuth of 99.5% in purity using a commercial arc-melting vacuum-pressure type casting system (Castrnatic, twatani Corp., Japan). The melting chamber was first evacuated and purged with argon. An argon pressure of 1.8 kgf/cm2 was maintained during melting. Appropriate amounts of the c.p. Ti bar, molybdenum and bismuth were melted in a U-shaped copper hearth with a tungsten electrode. The ingot was re-melted three times to improve chemical homogeneity.
Specimens having a thickness of 5.0 mm, a width of 13 mm and a length of 70 mm were prepared from the Ti—15Mo and i—15Mo—1Bi alloys using a graphite mold. The specimens removed from the mold were water-quenched, and surface-finished before being subjected to cold rolling. The cold rolling was carried our at room temperature using a 100-ton rolling machine (VF PCAK-P1, Toshiba Corp., Japan), wherein the specimen was rolled through a gap between two rollers several times with different deforming magnitudes by adjusting the gap.
When the cold rolling was conducted with reductions in thickness of 1.5 mm, 0.9 mm, 0.9 mm, 0.3 mm and 0.3 mm in sequence (with a total reduction in thickness of 78%), all the specimens of Ti—15Mo—1Bi could be cold-rolled to the final thickness (with a total reduction in thickness of 78%) without breaking down or showing any cracking on the surfaces or edges of the specimens. However, the specimens of Ti—15Mo either showed deformation bands on the surfaces or cracking on the edges of the specimens, or even broke down during rolling. It can be understood from this cold rolling test that the addition of 1 wt % Bi into Ti—15Mo alloy can significantly enhance the cold-rolling workability of the alloy.
The bending fatigue test was conducted on the cold-rolled Ti—15Mo—1Bi specimens (78% reduction in thickness) with a heat treatment of (900° C., 1 min). A servo-hydraulic type testing machine (EHF-EG, Shimadzu Co., Tokyo, Japan) was used for the fatigue test on smooth plate specimens with dimensions of 40 mm in length, 5 mm in width and 1.5 mm in thickness. The smooth plate specimens were subjected to fatigue loading with a sinusoidal waveform at room temperature in air at a frequency of 4 Hz with a stress ratio R=0.1. Four different levels of surface roughness were prepared: (1) surface roughness of Ra=0.9-1.1 μm (the Ra value is measured according to ISO 4287: 2000 method) obtained from #60 sand paper; (2) surface roughness of Ra=0.1-0.2 μm obtained from #1000 sand paper; (3) surface roughness of Ra<0.1 μm obtained from #1500 sand paper, followed by mechanical polishing using 1 μm, 0.3 μm and 0.05 μm alumina powder in sequence; and (4) surface roughness of Ra<0.1 μm obtained from #1500 sand paper, followed by chemical polishing for 5 seconds in a solution containing 5 vol % HF, 15 vol % HNO3 and 80 vol % water.
It is discovered from the fatigue test data that the fatigue life/fatigue resistance is critically dependent on the surface roughness of the specimen being tested. The fatigue lives (numbers of cycles to failure) of all the five specimens prepared from #60 sand paper (Ra=0.9-1.1 μm) (the above-mentioned (1)) are between about 4×103 and 104 cycles; and the fatigue lives of all the five specimens prepared from #1000 sand paper (Ra=0.1-0.2 μm) (the above-mentioned (2) are between about 104 and 6×104 cycles.
It is worth noting that the mechanically polished specimens and the chemically polished specimens (both with Ra<0.1 μm) in the above-mentioned (3) and (4) have dramatically increased fatigue lives. In each group, four out of six specimens tested demonstrate fatigue lives longer than 106 (specimens did not fail after 106 cycles). This result suggests that, for practical application, it is critical for the Ti—15Mo—1Bi alloy to be prepared with a surface roughness of Ra<0.1 μm. Any cyclic load-bearing device made from this kind of material with surface roughness larger than 0.1 μm can have a risk of premature fatigue failure.
Although the present invention has been described with reference to specific details of certain embodiments thereof, it is not intended that such details should be regarded as limitations upon the scope of the invention except as and to the extent that they are included in the accompanying claims. Many modifications and variations are possible in light of the above disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 94129409 | Aug 2005 | TW | national |
