There was a day, not that long ago, when the “woods” in your golf bag were actually made from wood – primarily persimmon and maple. At that time, your irons were mostly forged. Investment-cast irons and woods first came on the scene in the late 1960s and early 1970s but were slow to be accepted because casting technology was lacking. Technological developments have improved the ability to cast thin-wall clubs accurately and repeatably, resulting in 85% of all golf clubs now being cast.
The science and engineering involved in golf-club design has made numerous advances. The club must account for human physics and 100-mph swings in the design phase. The weight distribution of clubhead mass is crucial for ball trajectory. For this reason, forged-steel clubs are more difficult to hit because the weight cannot be distributed around the perimeter of the club. Forgings, therefore, are better for the advanced golfer because there is much less room for error.
In many cases, design advances involve high-temperature thermal processes. As already mentioned, the first is the investment-casting process. Because of the criticality of clubhead weight distribution, designers and their casting suppliers must pay close attention to the club’s center of gravity, thickness tolerance and weight. Other critical concerns are the angles of the lie and loft, both of which are typically within ±1°. Casting a wall thickness of 0.030 of an inch needing to withstand an impact of 100 mph is a challenge.
The investment-casting process begins with a prototyped and tested design. Production-quantity molds are then built and tooled. Liquid wax is injected into the mold and cooled to create replicas of the clubheads. These individual replicas are attached to a common “tree,” and a series of wet and dry ceramic dips are applied to produce an extremely precise mold that can withstand the heat of molten-metal pouring. The molds are then turned upside-down in a steam autoclave. After several minutes, the wax melts and drains and is collected for recycling.
The empty ceramic shells are then preheated to about 2000°F (1093°C) to prep them for the liquid stainless steel at 2500°F (1370°C). After pouring and solidification, the brittle ceramic shell is removed from the metal casting. Final removal of clinging material is via sandblasting. The resultant clubheads, which are perfect stainless steel copies of the wax tree, are separated from the tree by a bandsaw. Most of the gate will be ground from the clubhead prior to heat treatment.
Another thermal process playing an important part in club design is heat treatment. Material selection is key as well, and the heat treatment used depends on the material chosen. Many clubs are made from heat-treated 8620 mild steel. The heat treatment of this material improves the hardness while providing a soft, solid feel and feedback. Higher-end clubs use more exotic alloys in order to develop an optimum combination of properties. Stainless steels such as 17-4 and 431 are commonly used, particularly in investment castings. These alloys are also hardened and have higher hardness than the 8620 material. Higher hardness transmits the maximum energy from the club to the ball, making the ball go farther.
In some cases, a 17-4 stainless club body is used with a face of beta titanium. The titanium is often alloyed with elements such as vanadium, which contributes to the material strength. A heat treatment keeps these alloys elastic. In general, titanium is gaining attention due to its high strength and low density. This means that a club made of titanium has the strength of one made from steel but weighs half as much, allowing the size of the club to increase while maintaining its weight. This larger head gives golfers more confidence in striking the sweet spot.
Next time you drive one for distance, remember to credit the investment-casting foundry and the heat-treat shop that had a hand in its manufacture.