Many valve manufacturers ask a common question: should we use hot forging or pure machining to make valve bodies? The answer depends on your production volume and the quality you need. Both methods work, but they fit completely different factory setups.

How Pure Machining Works

In this process, you start with a solid metal bar. For example, you take a long hexagonal brass bar and feed it into a CNC lathe or a rotary transfer machine. The cutting tools carve out the outside shape of the valve and drill the inside holes. This method is great when you only need to make 500 or 1,000 valves. You do not need to pay for expensive forging molds. You just write the CNC program and start cutting.

But there is a big problem with pure machining. You waste a lot of metal. Sometimes, more than 40% of your expensive brass bar turns into small metal chips on the floor.

The Process of Hot Forging

Hot forging takes a different path. Instead of cutting metal away, you squeeze it into the shape you want. First, you cut a brass rod into small, short pieces called billets. You heat these billets in a furnace until they reach about 700°C to 800°C. They become very soft. Then, a heavy forging press pushes the hot metal into a custom steel die. The metal flows into every corner of the mold.

After the forging press does its job, you get a "blank." This blank looks very close to the final valve. You still need to machine the threads and precise seating areas later, but you only cut away a tiny amount of metal. You save a massive amount of money on raw brass.

Strength and Leak Prevention

The biggest difference between these two methods is the internal strength of the valve. When you machine a valve from a solid bar, the cutting tool breaks the natural grain structure of the metal. It is like cutting across the grain of a piece of wood. This creates weak spots. Also, solid metal bars sometimes have tiny air bubbles hidden inside them from the casting process. If your cutting tool exposes one of these hidden holes, the final valve will leak when you put it under pressure.

Hot forging fixes the leak problem. The heavy impact from the forging press completely crushes any tiny air holes inside the brass. More importantly, the metal grain flows along the shape of the valve body instead of being cut in half. This continuous grain flow makes a forged valve much stronger and completely pressure-tight.

Upfront Costs and Long-term Savings

You also need to look at upfront costs. Hot forging requires you to buy heavy machinery and pay for custom steel dies. This costs a lot of money at the start. If you are making a custom valve for a small project, forging is too expensive.

But if you make tens of thousands of standard ball valves or gate valves every month, hot forging is much cheaper. A forging press can stamp out a hot valve body in just two or three seconds. You can then feed these strong, shaped blanks directly into a rotary transfer machine to finish the threads very fast.