4. 0 Golf Club Casting

The manufacturing method of a golf club depends on what type of golf club is being manufactured. In this case for irons, fairway woods, wedges, hybrids and putters are generally produce using the casting process. Basically the casting process involves pouring molten metal into preformed cast or molds. The metal is made of stainless steel which is a combination iron, nickel and chromium and other trace of materials. As molten stainless steel is more liquid compared to carbon steel used in the forging process, this can avoid bumps or not filling a recess inside the mold. Some manufacturers will differentiate its cast iron golf club such as the use of cast 17-4 stainless steel and the 431 stainless steel. The 17-4 stainless steel golf club is made up from 17% chromium and 4% nickel which create a golf club that is strong, durable, and harder than forged carbon steel and does not corrode easily. For the 431 stainless steel, this cast iron is softer than 17-4 and claims to give a better feel to the user.

In the market itself, the vast majority of golf clubs sold are made by casting. Under the method of ceramic shell process, this technique is a precision casting process, uniquely developed and adapted to produce complex-shaped castings, to near-net-shape, and in numerous alloys whereas fit to produce a golf club. Figure 4.1 illustrates the basic steps in the process of investment casting.

Figure 4.1: Sequence of Basic Steps in Investment Casting Process

4.1 Golf Club Investment Casting Process

Every golf club maker uses a slightly different casting manufacturing process. The largest companies use highly automated machinery, while the smallest companies use hand tools. Some parts of the manufacturing process may be unique to one company and the use of material may differ from one product to another. In today’s modern era, companies such as Ping and Mizuno are fully enhancing their manufacturing capability to produce quality and sophisticated golf products, at a higher rate and more economical. A detailed explanation on the steps of casting a golf club head is as described inside table 4.1 as per reference from the current technology used by the golf manufacturers.

Process Description1. Produce of a master pattern and mold/die 1. The desired golf club is firstly designed on a computer

using sophisticated CAD software.2. The computer design is used as the basis for the

development of a proprietary mold3. The mold consists of two halves with a hollow cavity that

is the exact shape and size of the desired club head4. Once a mold has been produced it is used in the

production of each and every club head.

2. Produce wax pattern1. Investment cast iron manufacturing begins by injecting

wax into a mold.2. This process sets the wax pattern to the exact size and

shape of the required part once it solidifies.

3. Assemble wax patterns1. The wax patterns are removed from the mold.2. Wax patterns are attached to a central wax column, called

a sprue, to form a tree.3. The wax patterns are then transferred to the slurry

station.

4. Investment: First Dip1. The first dip involves dipping the wax patterns into slurry

of fine refractory material and then letting any excess drain off which allows a uniform surface to be produced.

2. This fine material is used first to give a smooth surface finish and reproduce fine details.

3. Zircon slurry are often used, takes beautiful image of wax pattern and wont react to molten metal

5. Investment: Second Dip1. The coated slurry patter is stuccoed with a coarse

ceramic particle, by dipping it into a bed full of fine granule sand.

2. This process provides structural support for the mold.3. Finally, the coating is allowed to harden at controlled

environment of temperature and humidity.

4. These first and second processes are repeated until the investment is the required thickness.

6. Dewax1. The hardened mold is heated or quick steam to about in

an oven/autoclave to melt the wax patterns.2. The melted wax runs out the bottom and any wax residue

is vaporized.3. The process is done fast at high temperatures (550-1,100°

C) to avoid the hardened coat to break due to swelling of wax.

4. A hollow ceramic shell is produced once all the wax is totally removed.

7. Burnout and Preheating1. The mold is then subjected to a burnout, which heats the

mold between 870 °C and 1095 °C before molten steel can poured into them.

2. The mold is heated to a temperature for the purpose of that it can withstand the temperature of the poured molten steel. This allows the molten metal to stay liquid longer to fill any details and to increase dimensional accuracy, because the mold and casting cool together.

8. Pouring of molten metal1. Once the desired composition of steel are melted, the

molten steel is gravity poured into the preheat mold.2. It requires efficient and careful handling between the

person handling the molten steel and the mold.

9. Cooling of filled mold 1. Mold filled with molten steel is set aside to cool down at ambient temperature.

2. The exterior walls of the mold cools down the quickest while the interior club heads will cool at a slower rate.

10. Divesting 1. Once the steel has cooled down to room temperature, the ceramic shell is removed.

2. Several techniques can be used to remove the shell either it be hammered, media blasted, vibrated, water jet, or chemically dissolved.

3. Additional grinding or sand blasting is done to remove any excess of shells.

11. Cutting and boring1. A cutting process is executed to remove the club heads

from the tree.2. Separate golf club heads are heat treated to normalize the

metal.3. Once treated, the golf club is bored for the assembly of

the golf shaft.

12. Finishing and polishing1. The cast irons are polished to create a smooth texture on

the surface.2. Certain manufacturers apply mirror and satin finishes for

the golf club heads.3. Additional markings or engravings are applied such as

the manufacturer logo, names and the number of the iron club.

13. Quality inspection1. Final head inspections on the weight, diameter and

variance measurements are tested to ensure they fall within the strict tolerances set by the manufacturer of the clubs.

2. Finally the manufacturer will apply shrink wrap protection on the heads and package the product for next assembly process of shaft or direct shipment to the customer.

Table 4.1: Golf Club Head Casting Process

4.2 Improvements to Golf Casting Process

Continued advancements in materials and techniques used in the golf club casting process, are driven and supported by research and development (R & D) on many fronts both in the casting manufacturer as well as the sport industry itself. From Table 4.1 itself, the description of steps towards the manufacturing of a golf club show a lot of improvements can be done from the development of the mold master pattern until the production of the ceramic molds which are the critical in the manufacturing process.

Nowadays the patterns for golf clubs can be produce in rapid prototyping processes throughout the use of advance techniques such as 3D printing or Additive- manufacturing. These techniques produce patterns after depositing fine layers of various materials as defined by CAD. These patterns have been found to have easy for dewaxing, resulting in substantially improved surface quality for investment cast prototypes in many alloys.

The selection of pattern material that is injected into the mold can be substitute to with material other than wax such as plastic or foamed polystyrene. Each of the materials has their own advantages such as for plastic which is widely used pattern material, next to wax. Plastic is economical, very stable, can be molded at high production rates on automatic equipment, and has high resistance to handling damage. Other than the use are limited, the downside is that plastics have tendency to cause shell mold cracking during pattern removal, and it requires more expensive tooling and injection equipment than for wax.

Silica and aluminum silicates are commonly used materials for both slurry and stucco in producing the ceramic shell molds. In the manufacturing of golf clubs, nowadays zircon slurry is mostly preferred as it takes beautiful image of wax pattern and would not react to the high temperature of the molten metal. Compared to other silicates such as alumina, even though having a high refractory and stable compound, the material is expensive hence suitable for the manufacture of super alloy casting.

The improvement in the selection of equipment used for dewaxing also plays an integral part in the casting process. Dewaxing which also knows as pattern removal is the operation that subjects the shell mold to the most stresses in order to melt the wax quickly without affecting the outer shell of the mold. In order to avoid the outer shell from cracking due to the expansion of the wax in the mold, two suitable methods have been developed to implement which is the autoclave dewaxing and high temperature flash dewaxing. The autoclave machine applies pressurized steam whereas as the flash dewaxing is simply a hot furnace where both works to remove the wax. Most advance manufacturing companies applies the autoclave machine as the wax recovery is good and does not easily deteriorate compared to the use of flash dewaxing.

The preheat and burnout of the model plays an essential role to remove moisture, to burn off residual pattern material and any organics used in the shell slurry, to sinter the ceramic, and also to ensure the mold is preheat to the temperature required for casting. Unwanted cracks can appear on the molds should the burning process exceeds the time limit and cooled down prematurely. In order to avoid such case, many molds are wrapped with a ceramic fiber blanket at this time to minimize the temperature drop that occurs between the preheat furnace and the casting operation.

Improvements at the casting process are always being made to ensure the molten metal is distributed smoothly inside all the spaces in the model. Most are gravity poured such the use of air casting and vacuum casting. However with the demand of high sophisticated design of golf clubs, improvements are needed on the casting of thin parts of the golf heads henceforth different casting methods are needed such as the vacuum assist casting and pressurized casting. For vacuum assist casting, a pressure differential environment will be introduced around the mold, forcing the molten metal to fill in the thin layers of the mold naturally. Pressurized casting is simply forcing compressed air or inert onto the molten metal to fill in the thin gaps of the mold.

The future of golf club manufacturing relies together with the advancement of technology used in the casting process itself. The use of advance materials and high end machineries will allow the product to be produce with more sophisticated features hence improving the performance of the user itself.