Cars comprise four cylinders, and each of the cylinders have four valves. Thus, there is a high demand for valves. Engine valves are conventionally solid, and the manufacturing process is established. However, the solid valves produced for strengthening treatment are still unable to satisfy current demands due to the constant development of new high-speed and high-load engines.
Hollow valves can decrease weight to a great extent. Hollow valves are more effective than solid ones; therefore, hollow valves must be incorporated in new-generation vehicles. Usually, hollow valves are produced by two methods:
- Drilling into solid valves
- Reverse extrusion.
However, these methods have many shortcomings:
- Low material utilization ratio,
- Low production efficiency,
- High manufacturing costs,
- Complex manufacturing process.
Due to the above disadvantages, the requirements of modern manufacturing are difficult to meet. Therefore, there is a need of an advanced manufacturing technology for hollow valve production. A number of studies have been conducted on valve production.
The main process parameters that affect die wear during extrusion of exhaust valves were examined. Die wear is primarily influenced by temperatures, velocities, and pressures at the workpiece and die interface.
The valves formed via cross wedge rolling (CWR) do not cause unsatisfactory filling after forging. Simulation of the coupled problem of electrical upsetting in valves is based on a mixed formulation and provides a simulation of heat generation in combination with the coupled thermo-mechanical problem of non-steady state visco-plastic material flow.
Currently, countries have been establishing new technologies to develop hollow valve production in order to reduce costs and improve quality. In 2012, a process was proposed by Mitsubishi Heavy Industries in which a hollow valve rod and head is used to produce hollow cylindrical blanks through cold forging. Another method was invented by Morii and Yoshimura for manufacturing hollow valves. This involves drilling of differently shaped holes in the hollow shaft. Thereby, moulding the shaft into a specific shape.
CWR is a plastic forming process where cylindrical workpieces are deformed into axisymmetric stepped parts with the help of two or more wedge tools that move tangentially to the workpieces. The process is performed at an elevated temperature to generate low deformation forces.
Study reveals the macro-deformation laws of the roll forging of automotive front axle beams. Crankshafts were generated through CWR and the bidirectional forging of preforms. This process chain comprises of (a) CWR step, (b) a lateral extrusion step, (c) a bi-directional forging step, and (d) a final forming step.
CWR-forging is a new process for forming hollow valve blanks. CWR is mostly applied to low alloy steel with large diameters (d > 25 mm). CWR hollow valves are made of materials with poor plasticity and hollow workpiece stability. Such valves are difficult to control given their small diameter. However, these difficulties are easy to overcome.
Following are the advantages of CWR Forging over existing technology:
- High Production efficiency.
- High Precision is high with good consistency.
- Low cost
- Simple equipment
- Environment friendly
Hollow valves with a near net shape are generated by the CWR-forging process, improving the organization performance and fatigue life of these valves. CWR-Forging is an innovation of the CWR technology.