Stress and deformation of metal titanium rod titanium tube during drawing

The cutting force of titanium alloy processing is only slightly higher than that of steel of the same hardness, but the physical phenomenon of processing titanium alloy is much more complicated than processing steel, which makes titanium alloy processing face huge difficulties. The thermal conductivity of most titanium alloys is very low, only 1/7 that of steel and 1/16 that of aluminum.

Therefore, the heat generated in the process of cutting titanium alloy will not be quickly transferred to the workpiece or taken away by the chips, but will be concentrated in the cutting area. The temperature generated can be as high as 1,000 ℃, causing the cutting edge of the tool to quickly wear, crack and Generate built-up edge, wear blades quickly appear, and generate more heat in the cutting area, further shortening the life of the tool.

The high temperature generated during the cutting process also destroys the surface integrity of the titanium alloy parts, resulting in a decrease in the geometric accuracy of the parts and a work hardening phenomenon that severely reduces its fatigue strength.

The elasticity of titanium alloy may be beneficial to the performance of parts, but in the cutting process, the elastic deformation of the workpiece is an important cause of vibration. The cutting pressure causes the "elastic" workpiece to leave the tool and rebound, so that the friction between the tool and the workpiece is greater than the cutting action. The friction process also generates heat, which aggravates the poor thermal conductivity of titanium alloys.

This problem is even more serious when processing thin-walled or ring-shaped parts that are easily deformed. It is not an easy task to process thin-walled titanium alloy parts to the expected dimensional accuracy. Because when the workpiece material is pushed away by the tool, the local deformation of the thin wall has exceeded the elastic range and plastic deformation occurs, and the material strength and hardness of the cutting point increase significantly. At this time, machining according to the originally determined cutting speed becomes too high, which further leads to sharp tool wear.

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Causes of cracks in titanium rod extrusion

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.

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