The thermal conductivity of the titanium rod and titanium alloy rod blanks is low, which will cause a great temperature difference between the surface layer and the inner layer during hot extrusion. When the temperature of the extrusion barrel is 400 degrees, the temperature difference can reach 200~250 degrees. Under the combined influence of suction strengthening and the large temperature difference of the blank section, the metal on the surface and the center of the blank produce very different strength properties and plastic properties, which will cause very uneven deformation during the extrusion process. Large additional tensile stress is generated in the medium and becomes the source of cracks and cracks on the surface of the extruded product.
Its main can be divided into:
1) Extrusion method. The reverse extrusion has a more uniform metal flow than the forward extrusion, the cold extrusion has a more uniform flow than the hot extrusion metal, and the lubricating extrusion has more uniform flow than the non-lubricating extrusion metal. The impact of the extrusion method is achieved by changing the friction conditions.
2) Squeeze speed. As the extrusion speed increases, the unevenness of metal flow increases.
3) Extrusion temperature. As the extrusion temperature increases and the deformation resistance of the billet decreases, the uneven metal flow increases. During the extrusion process, if the heating temperature of the extrusion cylinder and the mold is too low, and the temperature difference between the outer layer and the center layer is large, the unevenness of the metal flow increases. The better the thermal conductivity of the metal, the more uniform the temperature distribution on the end surface of the ingot.
4) Metal strength. When other conditions are the same, the higher the metal strength, the more uniform the metal flow.
5) Mold angle. The larger the die angle (that is, the angle between the end face of the die and the central axis), the more uneven the fluidity of the metal. When the porous die is used for extrusion, the arrangement of die holes is reasonable, and the metal flow tends to be uniform.
6) Degree of deformation. If the degree of deformation is too large or too small, the metal flow is uneven.
Solution:
1: When the unit pressure is the same as forging hammer forging, when forging with a press. The heating temperature of the blank can be reduced by 50100℃. In this way, the interaction between the heated metal and the periodic gas and the temperature difference between the blank and the mold are correspondingly reduced, thereby improving the uniformity of the deformation, the uniformity of the structure of the die forging is greatly improved, and the consistency of the mechanical properties is also improved. .
2: Increase the forging slope and fillet radius and use lubricant: the height of the burr bridge on the forging die is larger than that of steel, and the deformation of the titanium rod is more difficult to flow into the deep and narrow die groove than steel.
3: Reduce the deformation speed, the most obvious increase in the surface shrinkage rate, the surface shrinkage rate is the most sensitive to tissue defects caused by overheating.
