Preparation of Aluminum Extrusion Tooling
Extrusion tooling typically refers to the extrusion stem, extrusion container, and dummy block. The most critical task prior to production is aligning the centers of the extrusion stem, extrusion container, die, and feeding manipulator. The maximum allowable center deviation between the extrusion stem and the extrusion container is ≤0.2 mm, while the maximum allowable center deviation among the stem, container, die, and manipulator is <1.5 mm (generally required to be within 1.2 mm). Excessive precision in alignment makes equipment adjustment and control difficult; conversely, excessive deviation causes the die to shift off-center, resulting in uneven metal flow and defects in the product, such as uneven wall thickness, bending, or twisting.
The diameter of the extrusion stem is determined by the inner diameter of the extrusion container; generally, it should be 3–12 mm smaller than the container’s inner diameter, with the lower end of this range applied to smaller containers and the upper end to larger ones. The length of the stem shaft should exceed the length of the extrusion container by 15–25 mm. The non-perpendicularity of the stem’s end surface relative to its central axis must not exceed 0.1 mm.
Continuous friction during the extrusion process causes the working section of the extrusion container liner (inner sleeve) to gradually enlarge, creating a diameter discrepancy between the diameter of the working part and the non-working part. When this discrepancy becomes significant, the liner must be replaced. Table 1 lists the allowable diameter deviations between the working and non-working sections of the extrusion container.
| Extrusion capacity/MN | 5.0～7.0 | 7.5～12.0 | 16.3～20.0 | 35.0～50.0 | 50.0 up |
|---|---|---|---|---|---|
| Tolerance/mm | <0.3 | <0.5 | <0.7 | <1.0 | <1.5 |
Replacing the liner of the extrusion container requires hot installation. Generally, the outer sleeve of the extrusion container is heated to a certain temperature to cause thermal expansion, and then the inner sleeve with an outer diameter slightly larger than the inner diameter of the outer sleeve is inserted into it. After cooling, due to the contraction effect, a preload assembly compressive stress is generated on the inner sleeve, and its direction is opposite to the tensile stress generated during extrusion, thus greatly reducing the compressive stress of the extrusion container inner diameter during extrusion and improving the allowable strength of the extrusion container. When the interference fit is selected appropriately, the service life of the extrusion container can be increased by 2 to 4 times compared to the common. The interference value is larger, and the generated preload compressive stress is also larger. Sometimes it can even completely counteract the longitudinal tensile stress. However, if the interference is too large, it will make it difficult to replace the liner of the extrusion container, and it will be difficult to remove the old liner. Therefore, choosing an appropriate interference value is very important. Table 2 gives the selection range of some extrusion container interference values.
| Container structure | Container liner diameter/mm | Interference/mm |
|---|---|---|
| Double layer | 200～300 | 0.3～0.5 |
| Double layer | 310～700 | 0.5~0.6 |
| Double layer | 510~700 | 0.6~1.0 |
| 3 layer | 800～1130 | 1.05～1.35 |
| 3 layer | 1500~1810 | 1.4～2.35 |
Heating the extrusion container: After a new extrusion container is assembled, it must be heated from a cold state to the operating temperature. To avoid thermal stresses caused by uneven heating—which could lead to cracking or even structural failure—gradient heating is required; the heating schedule is provided in Table 3.
| Heating temperature/ ℃ | 200 | 250 | 300 | 350 | 400 | 420 |
|---|---|---|---|---|---|---|
| Holding time / h | 4 | 4～6 | 6～8 | 8～10 | 10～12 | 12～14 |
Heating of tooling and dies: Architectural aluminum profiles are primarily made from 6063 and 6061 alloys. During extrusion, to prevent the billet from cooling and causing jamming and tool damage, and to ensure the uniformity of the aluminum profile’s structure and properties, all tool and mold in contact with the aluminum billet need to be fully preheated. The heating and soaking temperature for the extrusion container is generally 400–460°C, while the die heating temperature is 420–480°C. To ensure thorough heating, the heating time should exceed 1.5 hours for flat dies and 2.5 hours for hollow dies. To prevent annealing caused by prolonged exposure to heat, the time any die spends in the heating furnace should not exceed 24 hours. Specific heating temperatures for extrusion containers and dies are listed in Table 4. Generally, the upper limit of the temperature range is selected for products with high extrusion ratios, while the lower limit is used for those with low extrusion ratios.
| Container | Solid profile 400～440 | Hollow profile 420～460 |
|---|---|---|
| Die mold | Solid profile 420~460 | Hollow profile 430~480 |