Cold Extrusion-A Brief Talk on the Technology and Process of Gear Cavity Cold Extrusion
What is cavity cold extrusion technology
Cold extrusion or cold forging means that the metal blank forging is at room temperatures. It is the opposite of hot forging, where the workpiece heats to molten form to enable forging. In cold forging, the metal blank is placed in the mold cavity in the cold state, and under the action of strong pressure and a certain speed, the metal is forced out of the mold cavity to obtain the required shape, size, and certain mechanics.
Cavity Cold Extrusion?
Cavity cold extrusion is a type of cold forging forming technology where a hardened extrusion head acts and the die. The extrusion head or the punch slowly squeezes the blank under the high pressure of a hydraulic press to produce plastic deformation properties at room temperature. The deformed and forged workpiece takes the shape of the extrusion head. This cold forging method is also referred to as a no-chip forming method.
The origin of cavity cold extrusion technology
The cavity cold extrusion has been around for decades. It originates in 1970s and 1980s. However, it has been evolving with technology. Today, cavity cold extrusion is still used in the metal manufacturing industry because it has more significant advantages and some manufacturing.
The principle of gear cavity cold extrusion process
There are two main principles of the gear cavity cold extrusion process. Choosing either is dependent on the requirement of the forgings. In all, the most efficient and economic principle prevails for a certain task.
(1) The principle of closed gear cavity cold extrusion molding:
As the name suggests, the closed molding gear cavity cold extrusion has forging blank forced into an enclosed space. In the typical forging process, there are two molds, and the billet forces into them to form the need shape. Under compression, the billet forces between the extrusion head and the enclosed die.
The pressurized metal blades achieve plastic deformation and flow into the cavity to get the desired shape and size. However, safety functions are necessary to protect the billet and extrusion head from cracking, splashing, or breaking. The closed mold extrusion has so many advantages over the open type, which is why this method is mainly popular with manufacturers.
(2) The principle of open gear cavity cold extrusion molding:
This method is not completely closed, unlike the closed die gear cavity cold extrusion where the billet is constrained inside the mod and the punch. To deformation of billets using this method involves multiple molds, and the material is altered using a series of movements. The shaping continues until finally obtained the desired shape and size.
The forging blank will also sag significantly, produce large distortions, and result in defects such as cracking. Therefore, reliable safety measures are crucial. The open mold cavity forming is good for simple shape, shallow extrusion depth, and low precision requirements. After billet extrusion, there will be a need to perform subsequent processes like mechanical cutting and heat treatment.
Advantages and disadvantages of gear cavity cold extrusion process
There are many pros and cons that come with gear cavity cold extrusion. However, we are going to look at just the major ones and they include:
Advantages:
- High production efficiency and high material utilization rate. There is less wastage of the materials as the cold forging process produces near-net shapes.
- Can save costs to a certain extent by using the punch repeatedly. This means you do mass production with the same set-up, which makes the production fast and more efficient.
- Nitriding treatment is necessary to ensure the accuracy of the cavity size, and the obtained cavity has higher accuracy.
- For small surface roughness, the process has greater advantages for a cavity with a complex shape.
- The cavity formed by cold extrusion has a denser structure and a more reasonable flow direction and distribution of metal grains. Therefore, this cavity has high hardness, strength, and durability.
Shortcomings:
- It requires careful design of the extrusion head or the punch for cavity cold extrusion molding and in advance. Therefore, the cost of the punch might be higher than hot forging.
- There is need for large-tonnage hydraulic press to complete the gear cavity cold extrusion. This is because the metal pressed at room temperature, it requires much more compression force to achieve plastic deformation.