Forging has been oneof the most common methods for the manufacture of car pistons for many yearsdue to the ability to create a variety of different shapes from a number ofmaterials. The desired material is first heated up to around 75% of its meltingpoint which loosens the crystalline structure of the metal to reduce the flowstress and reduce the amount of energy that will be required to deform thematerial. The reason hot forging is used over cold is because temperatures arerequired in order avoid strain hardening during deformation.
The hot materialis then placed either manually or autonomously into the cavity before the press/hammercomes down and forces the material into the shape of the cavity. The press issometimes heated as well as the material at the same temperature to reducetemperature loss of the material while the pressing takes place. Some presses depending on the material andsize of the part you are producing are forced with pressures of up to andhigher than 2000 tonnes (made, 2013).Once the material has been pressed into shape the part is the removed and leftto coolTo be able to perform closed die forging there are manycosts involved. The initial tooling cost for this process is huge and is themost expensive. You must buy/manufacture your two dies in the shape of theproduct you want to produce. You Must also consider the cost of thehammer/press that is used to force the material into shape. This can be hugedepending on the materials used and the size of the part.
You must also consider material costs which will varycompletely depending on the properties you require the part to have asdifferent grades of metal come at different prices.The post forging processes that are required can greatlyincrease the overall cost o the process as heat treatment is typically requiredto achieve the material properties that you require. Also surface treatment andmachining maybe required afterwards which can be costly.