Cold Shuts in Forging
Forging is the process of shaping a metal by pressing, rolling,squeezing, hammering and other such operations in one or more forging machines or equipments.
There are many defects in forging but one of the most common defect in forging is cold shut.
Cold Shut :-
Cold shut is a defect in forging in which small cracks appears at corner of forging. This defect is mainly caused due to improper design of the dies.
In this defect there is an unfilled section which creates pressure at the corner of the metal or workpiece. Due to the pressure created by unfilled section and quick cooling of the metal, some cracks are formed at the corner of the workpiece which are called cold shuts.
Other than cold shuts there are other common defects in forging which are listed below :-
Unfilled Section :-
In this defect some section of the die cavity are not completely filled by flowing metal. The defect is caused due to improper forging die design or due to improper forging techniques.
In this defect dirt particles or oxide layers are already present in the dies due to improper cleaning. These dust particles can be present in the upper die or lower die or both and gets mixed with finished forging surface.This defect is mainly caused due to improper cleaning of the stock used for forging. As a result of this defect the finishing of the product gets affected and hence resulting in bad quality product .
This are the defects which can not be noticed from outside because these are internal defects. Flakes are internal raptures caused due to improper cooling of large forging. Flakes appears as bright silvery discontinuous in fracture surface.
Die shift :-
Die Shift is a defect which results in improper shape of forging product due to misalignment of two dies used in forging. Since the dies are misaligned so when they meet each other, the cavity between the become of non uniform shape and this shape is taken by the workpiece and hence the forging product become non uniform. This defect can be rectified by aligning the upper die and lower die correctly. In this defect the forging product which can be easily noticed unlike the flakes which are internal cracks.
Improper grain growth :-
This defect is mainly caused due to improper flow of metal in the casting which changes predefine grain structure of product. It can be rectified by maintaining proper flow of metal throughout the forging process.
Incomplete Forging Penetration :-
This type of defect arises due to incomplete forging due to low hammmer force . It can be rectified by using proper force in froging whic can be done by controlling hammer force properly. This type of defect can result in very bad quality product.
Surface cracking :-
This type of defect occur due to working on surface at low temperature. This defect can create a lots of cracks in the workpiece which results in very bad quality product. This defect can be controlled by keeping the working temperature appropriate.
Residual Stresees in forging :-
This defect occur due to improper cooling of the workpiece after workpiece. This type of defect can cause a large number of cracks in the forged part. It can be controlled by not cooling rapidly or cooling slowly.