Traditional Investment Casting
In the construction of investment cast metal woods, hybrids and hollow-bodied irons, these have to be produced from two (or possibly more) separate pieces otherwise the club would become way too heavy. The metal forming the hollow shell of the head is very thin and created specifically from durable metals such as various grades of titanium and stainless steels to have it withstand all the rigors it will encounter on the course and rattling around in the bag to and fro the course.
To give you a better understanding let’s take a look at how most investment cast stainless steel metal woods and hybrids are produced. Traditionally the crown, face, skirt and hosel are made wholly of one piece and of the same material where as the sole plate is the secondary piece. The tooling consists of several components which parts from the sole. Once the wax is shot into the mold, it has an opening located at the sole so it can be pulled or extracted away from the mold. After several processes later the metallic pieces are welded, polished and finished into the final form you see them in.
When titanium heads first became available, those were investment cast using the same technique. But few of the foundries invested in the costly vacuum casting furnaces as titanium could not be cast in the open air like stainless steel due to oxidation. Secondly, casting titanium had extremely high reject rates where as forging titanium plates did not. So today, the body of titanium drivers are made from both investment casting and forging methods, with the latter being the less costly method because of reduced tooling costs. Neither method is superior to one another, but investment casting does allow for more intricate shapes and more variable wall thicknesses.
One advantage of casting a separate sole plate is one set of tooling could be produced as an open model to make many more models. The foundry can engrave a company’s name and/or logo on the sole plate for customization. For larger clubmaking operations it is one way for a shop or small equipment manufacturer to create their own brand / image without the normally huge tooling and minimum purchasing requirements of new head construction.
What is pull-face construction?
Pull-face construction is a fancy way of telling you where the wax was pulled or parted away from the mold. Unlike the traditional method with the sole plate being the separate piece, in pull-face construction the face is created separately. In other words the crown, skirt, hosel and sole are all one piece. Companies will usually tout this as one of the key benefits.
Why is this important? In almost all cases a head with a pull-face construction will indicate a higher performance face material is incorporated in the design such as specialty titanium material in drivers or maraging steel in fairway woods and hybrids.
Incorporating the high performance face plate allows for more efficient energy transfer at impact and a higher coefficient of restitution (COR) for greater ball speed translating into more distance. In addition, there is one other advantage to the pull-face construction and that is further re-distribution of weight because the specialty metals tend to be lighter (lower density).
The thin face plate might be milled to create a variable face thickness, the clubface can be milled perfectly flat or allow milling on the front and back of the clubface so grooves can be created to exacting specifications creating a lot of options for manufacturers. One example of pull-face construction in Hireko’s line is the Power Play Caiman hybrids.
Pull-face construction is not relegated just to drivers, fairways and hybrids, but irons too. To increase the spring like-effect of the ball coming off the face, titanium or super-hard maraging steel (like in our upcoming Caiman Raw Power iron pictured here) will substitute the heavier and less re-active stainless steel material. Different production techniques can be used to join the two dissimilar materials.
The road less travelled
There is one other method, which can be called crown-pull construction or where the crown parts from the tooling. To my knowledge, no manufacturer touts this in any of their write-ups – up until now. The direction most manufacturers strive for in clubhead design today is to reduce as much weight in the crown as possible and then re-distribute that weight elsewhere (usually as low and rearward).
One term you will here a lot from Hireko in the future is Variable Crown Technology or VCT for short. This is where the crowns are cast as little as 0.5mm thick or 44% thinner than normal. To give you an insight of just how thin that really is, ½ millimeter it is equivalent to 5 sheets of ordinary copy paper. No other manufacturer out their can make their stainless steel crowns any thinner. What this does is allow all the unwanted weight to be repositioned deeper within the head. While it may not sound like a lot of weight, squeezing every little gram does counts toward improving performance and we go to great stride to accomplish this feat.
This is one reason why we opted for crown-pull construction to ensure the walls were more uniform in the new Dynacraft XMOI fairways, Acer XK fairways and matching hybrids.
There is a lot more that goes into clubhead construction than meets the eyes. This is just a sampling of how innovative thinkers have developed new construction methods to improve upon the equipment we play, even if the changes aren’t monumental.
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