The large burrs produced by extrusion dies are generally caused by uneven die surfaces leading to incomplete shearing, and by aluminum gradually sticking outward. The following are several possible causes of large burrs in extrusion dies:
1. If the end face of the extrusion die is uneven or has damaged areas, gaps will form on the locking surface, causing aluminum to flow through. Damaged areas of the die should be promptly welded, and the die surface must be milled flat.
2. If the outer diameter of the feed chamber is too large (die distance too short), the clamping area of the die barrel decreases. The distance between the outer diameter of the feed chamber and the cylinder wall should normally leave a 10mm gap on one side, with a minimum of 5mm. For dies with a high extrusion ratio, do not simply use the method of enlarging the distribution chamber to relieve pressure. When producing with such extrusion dies, the centers of top, bottom, left, and right must be aligned to prevent further deviation in die distance.
3. If the extrusion die has no milled gate and the die closing surface is too large, the unit area pressure will be too low-less than the outlet pressure. After aluminum adheres to the die face and is sheared incompletely, it will cause uneven die surfaces. Large caps like this are difficult to clean properly. Ensure the cylinder surface is appropriately oiled to prevent aluminum from sticking. The aluminum on the die surface can be sheared off multiple times; apply oil to the stamped areas on the cylinder to prevent sticking, then shear it off. Occasional small burrs are considered acceptable.
4. If the gate diameter of the extrusion die is smaller than the working surface of the cylinder, the die closing area will be small, which can also damage the cylinder working surface. Pay attention to the diameter of the die gate when adapting small machine dies to a large press to match the cylinder working surface.
5. If the extrusion die thickness is insufficient, the extrusion barrel will bear the force on the die sleeve. The thickness of the die and die sleeve should follow the 3-to-1 rule for front-to-back, meaning the die's flow surface should protrude 1mm beyond the die sleeve. The die sleeve should never directly bear extrusion pressure; otherwise, it will easily be damaged or deformed.
6. If the fit clearance between the die sleeve and the die is too large, aluminum sticking within the gap will cause incomplete shearing and result in an uneven die surface. This situation is commonly seen in dies adapted from smaller machines.
7. If the extrusion ratio is too high, and the exit resistance is greater than the extrusion force, or if the locking surface is uneven, aluminum may flow out from the locking surface. This situation often results in extrusion jams. You can appropriately increase the billet temperature, mold temperature, and barrel temperature. If necessary, you can heat the mold sleeve or even the gasket before starting production. At the same time, you can slightly shorten the billet length to reduce the set length. If the aluminum billets are too short, they can be processed by stamping instead of simply increasing the billet temperature. High billet temperature can also easily cause defects and limits the speed increase.
