Countermeasures to ensure product quality in the forging process of copper forgings

1. Forging cracks in copper forgings

The causes of forging cracks in copper alloys are as follows :(1) defects in the blank or surface; (2) forging temperature is not suitable, low plastic material; (1) Excessive deformation or tensile stress. Ingot surface quality is poor and internal segregation is serious. Therefore, ingot needs to be homogenized and annealed before forging. The forging temperature has great influence on the plasticity of copper alloy. Due to the addition of a large number of alloying elements in copper alloy, the initial forging temperature is low, the forging temperature range is narrow, and there is a medium-temperature brittle zone. If the heating temperature is too high, it is easy to overheat and overburn, resulting in forging cracks or coarse crystals. When the forging temperature is too low, some copper alloys (such as iron bronze) will crack due to insufficient recrystallization and reduced plasticity. Figure 5-36 shows a brass nut forged on a high speed hammer. When the temperature of the forging is in the range of 250~650^C, cracks appear in the corners of the forging. After that, the forging temperature was raised to 750C, and no cracks appeared. Therefore, the forging temperature should not be too high or too low to avoid the occurrence of medium temperature brittleness zone. Some alloy steel forgings often produce forging cracks due to excessive deformation (significant thermal effect) or local stress concentration. In the free forging operation, it is necessary to turn frequently to avoid continuous pounding in the same direction to prevent the thermal effect caused by overheating and overburning.

3. Cutting edge tear of copper forging

The cutting edge of copper forgings occurs immediately after die forging and die forging, and the forging body is often torn at the cutting edge. This defect can be avoided when the forgings are cooled before cutting.

4. The folding

Copper forgings wrinkle easily when deformed. Therefore, folding can occur easily. For example, when drawing, such as the deformed step is sharper, it is easier to produce folds on the second hammer stroke. For example, when there is a tube on the large valve body forgings, such as the shoulder chamfering process, the tube will produce shrinkage hole due to uneven deformation; If the end face is flattened by upsetting, wrinkles will form at the junction of the tube body. Therefore, when forging copper alloy, the radius of the tool and die corners should be larger, and pay attention to lubrication; For some pipe joints with small height and diameter ratio, it is suitable for extrusion forming of drainage plate. For easily folded copper alloy forgings, late cleaning should be considered. When determining the machining allowance and calculating the material, the allowance should be larger than that of carbon steel.