Common defects and prevention of hollow forgings

It is a common quality problem that the blank end face of hollow forging is uneven.

The causes of this problem are as follows:

• 1) The deformation of blank during upsetting is uneven, resulting in uneven wall thickness after punching. When the mandrel is drawn long, it deforms along the axial direction and has different sizes.
• 2) During mandrel drawing, the heating temperature of blank is uneven, resulting in drawing deformation and inconsistent feeding in the length direction.

Uneven wall thickness will lead to the increase of machining hours and serious scrap of blanks.

The causes are as follows:

• 1) When punching the blank, the punch is not placed in the center of the blank.
• 2) When punching, the punch is skewed, resulting in uneven wall thickness at one end of the blank.
• 3) When the mandrel is drawn, the heating temperature of the blank is uneven, the part with high temperature is easy to deform, and the wall thickness is thinned quickly.

End longitudinal cracking is easy to occur on thin-walled long cylindrical parts. The reason for cracking is that the temperature of the end blank decreases rapidly, which is easy to occur if the temperature decreases slightly.

Inner hole heavy skinning inner hole heavy skinning is due to the burr on the edge of the inner hole when the blank is upsetting and punching. If it is not removed in time, it is easy to bring the burr into the inner hole of the blank when the mandrel is drawn long, and finally form a double skinning defect.
Inner wall cracks occur occasionally on hollow forgings with relatively small size and quality. For blanks with relatively small inner hole size, solid punches are mostly used for double-sided punching, which may sometimes cause breakage at the connecting parts. When the mandrel is drawn, with the increasing deformation, the damage continues to extend and form cracks.
The outer surface is rough. The outer surface roughness mostly occurs on long hollow forgings with large drawing amount. Due to the large drawing amount, in order to complete the forging as soon as possible within the forging temperature range, the method of rapid forging with large reduction is usually adopted during mandrel drawing, resulting in rough blank surface due to large hammering. In this case, if the outer surface of the blank is polished with a small reduction, it is easy to bite the mandrel and the blank. Measures and precautions:

• 1) Strictly implement the heating specification, and the blank shall be heated evenly and thoroughly. The initial forging temperature and final forging temperature shall be controlled for each forging fire.
• 2) After the blank is elongated, the surfaces at both ends shall be flat. If the material is cut with a chopper, the end surface burr shall be removed wrongly, and it is best to cut the material with large section.
• 3) During upsetting, the blank shall be placed correctly, that is, the blank axis shall be perpendicular to the ground. Under the condition of meeting the forging ratio and punching, the upsetting amount shall be reduced as much as possible to reduce the drawing amount.
• 4) When punching, the punch shall be placed correctly without skew, and the punch axis shall be close to the blank axis as far as possible. Burr or flash generated during punching shall be cleaned.
• 5) The surface of the mandrel shall be smooth, and the working surface shall have a taper of 1 / 100-1 / 50 without bending. For the mandrel with diameter greater than 200mm, the inside must be cooled with circulating water.
• 6) When the mandrel is lengthened, the turning angle shall be uniform and the reduction shall be uniform.
• 7) During mandrel lengthening, both ends shall be forged at high temperature to prevent cracks at the ends.

Source:  China Flanges Manufacturer: www.epowermetals.com

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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