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Why does slag inclusion occur on the surface of forgings?

Update:25-12-2020
Summary:

The slag inclusion on the surface of the forging is due […]

The slag inclusion on the surface of the forging is due to the fact that part of the coating or oxide scale is extruded into the surface of the workpiece during the liquid forging process, and it will appear wrinkled or oxide slag pitting during the stale fire.

Therefore, the reasons for the slag inclusion on the surface of the forging are: the coating is too much or not dry before pouring, so that the coating is carried into the liquid metal, and some of it also interacts with the molten metal to form compound inclusions. For example, the "hard spot" of high tin bronze is like this; when the punch is pressurized, the crystalline hard shell that has solidified freely undergoes large wrinkles and deformation, squeezing paint, oxide scale, etc. into the surface of the part.

Forging

There is also a countermeasure to prevent slag inclusion on the surface of the forging: appropriately increase the mold temperature, and the coating must be sprayed uniformly and dry; the residence time before pressure is as short as possible to ensure that the solidified layer is not too thick during pressure. The folds are deformed.
Therefore, knowing the causes of slag inclusion on the surface of the forging and the preventive measures, you can pay attention from the beginning to prevent slag inclusion on the surface of the forging.
The process diagram is used to indicate the shape and size of the blank during the blanking and die forging process. The process of determining these process steps is called process design. The blank and die forging groove are designed and manufactured according to the process diagram.
As mentioned earlier, the most commonly used deformation steps are upsetting, shoulder pressing, bending, extrusion, pre-forging and final forging.
Final forging step design: mainly to design hot forging drawings, determine the form of burr grooves and the shape and size of the punching joint. The design of the forging drawing is the same as the die forging on the hammer, but the shape and size of the burrs are different.

hot forging steel

The final forging of the press is mainly based on the rough deformation method. The height of the forging is ensured by adjusting the stroke of the forging press, rather than relying on the abutment of the upper and lower die surfaces. In order to prevent stuffiness, when the slider is down, there must be a certain gap between the upper and lower parting surfaces to adjust the closing height of the mold, reduce the elastic deformation of the frame, and ensure the dimensional accuracy of the height direction of the forging. Due to these two reasons, the crank press die forging is required to adopt a more complete blanking process. Therefore, when die forging on the press, the resistance of the burrs is also relatively reduced, mainly to drain and accommodate excess metal. Therefore, the height of the burr groove bridge part and the warehouse part is correspondingly larger than that of the hammer forging.

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