[China Aluminum Network] The mold plays an important role in the extrusion process of aluminum alloy profiles. Reasonable mold structure is an important guarantee for product forming and dimensional accuracy, especially in controlling the microstructure and mechanical properties of hollow aluminum profiles. The mold processing is an important part of achieving the mold designer's concept and ensuring the mold structure accuracy. However, due to the limitation of the performance and accuracy of processing equipment, and the uneven level of processing personnel, it is often the case that there are more or less defects in the manufactured molds, which will bring unnecessary problems to the subsequent extrusion production. It also delays the delivery date of some products. Our company has adopted a series of measures to control the quality of molds, and the precision of molds has been steadily improved. The following describes the quality problems encountered during the mold processing and the control measures taken.
2 Quality status of mold processing 2.1 Processing defects are likely to occur due to factors such as the performance and accuracy of the manufacturing equipment and the level of the operator. The molds that caused the processing were not completely consistent with the design drawings but were not scrapped. This resulted in the production of incompletely qualified molds that were both defective and defective. These molds can cause quality problems in profile products during extrusion production. For example, the precision of the machining of the die of the die has an impact on the quality of the profile products, such as the starting of the profile, the dragging of the aluminum, the offsetting of the wall, the line pattern, etc.; the angle of the working belt is not correct. Will affect the formation of profile products. Figure 2 shows the proportion of the company's statistical processing defects on the quality of the product. It can be seen from the figure that the proportion of work belt and air knife defects is larger, and the other defects are more balanced. 2.2 The causes of the defects and the impact on the quality 2.2.1 The work belt accuracy is not high The working belt is directly in contact with the metal aluminum and it is in contact with the profiles. Forming and dimensions play a key role. However, due to inaccurate segmentation of the working belt when machining personnel are milling the electrodes, no arc transition is used between the high and low working belts, which may cause surface bones or bone shadows on the molding material. In addition, the working belt angle is not correct, flatness is not enough, often due to the relatively thick line cutting pattern, the amount of polishing is too large, the level and habits of the polishing staff cause the work belt with a positive or negative angle, so that the mold in the use of the material becomes Blocking or speeding up, misdirecting mold designers or molders, and making profile forming difficult. The poor smoothness of the work belt and the chamfering of the inlet and outlet are not enough to cause the mechanical deformation of the profile surface to be large.
2.2.2 The size of the empty knife is too large or too small When milling multi-core hollow knife, because the rough milling core is integral, the wall thickness between the cores is not processed, and the processing personnel often pre-scheduled the size of the empty knife according to the drawings. Processing, it is easy to cause the empty knife at the small mold core is too large and the stability is poor, and the uneven wall thickness of the profile is formed. In the cantilever part where the size of the air knife is smaller, especially near the working belt part, the spark does not strike the plug mold, or the aluminum drag is coarse, or the electrode is off center when the knife is set, so that the empty knife of the cantilever part is not Uniform, that is, the side of the knife is large, the side of the knife is small, the cantilever is biased to one side or broken when squeezing, resulting in mold scrap.
2.2.3 Shunt hole, weld chamber, diversion finish, smoothness, and taper are not enough for diversion die machining. The triangular dead zone often appears at the split die core and the diverter bridge. This is mainly due to the milling cutter being in the pendulum. Insufficient or inconsistent angles are caused by too few times. During the extrusion production, the metal flow in the area is not smooth, and the welding performance is poor, which causes the profile to have a yin and yang surface or an increase in surface line lines at the place. The smoothness and flatness (some taper) of the diversion chamber are insufficient. Mainly when fine milling or grinding plane, the workpiece is uneven, or the milling processing speed is too slow. When the taper is not enough, the taper is not accurately ground when the milling cutter is used, and these defects will cause the thickening of the line of the profile to increase.
2.2.4 The shunt of the diversion bridge is not rounded, and the feeding hole (slot) is not smooth. The diversion bridge is especially the diverging bridge with oblique expansion. Because the oblique expansion of the bridge has a certain depth in the deep part to ensure the strength of the bridge, processing When the pendulum angle is often not drilled directly deep position, and the dripping water level of the bridge is not used to follow the arc, resulting in poor welding properties of the profile, forming a clear weld line and the split bridge brittle. The upper mold ribs and the depth of the feed trough of the screw position are not enough, and these parts are insufficiently supplied during molding, and the surface of the profile is likely to produce a concave surface, and a bright line (or bright zone) is produced by spraying.
2.2.5 Mold hardness is insufficient (or too hard), hardness is not uniform, oxide layer flaking and other mold steel raw material quality is not stable, and heat treatment process is not well controlled, resulting in uneven hardness of the mold, insufficient hardness or too hard, so that the mold in production Unstable formation and long life. During nitridation, the mold cleaning is not clean or the nitridation process is unstable, causing the nitrided layer to be too thick and peeling off the work belt.
In addition to the above-mentioned defects, there are assembly stoppers, elasticity of the assembly pins, over-predistortion of the wire cutting, and wire jumps. The broken wires cause wall thickness and dimensional errors.
3 Improvement and control of mold processing quality Based on the above analysis of the causes of processing defects, our company adopts a series of measures to adjust the processing technology and obtain good results. The specific methods are as follows:
(1) Ensure the stability of raw material quality. Each batch of steel was spot checked, and the defects caused by the raw materials were substantially eliminated through the analysis of metallographic structure and internal flaw detection.
(2) Rough turning: In order to reduce the crack caused by the stress concentration in the heat treatment of the mold, there is an R connection at the transition point of the outer circle of the car, which is generally R3~R5.
(3) The use of CNC to process the diversion hole, diversion, welding room, bridge position. Through CNC programming modeling, the three-dimensional shape after processing can be intuitively seen in advance, and can be modified in time to meet the requirements of design drawings.
(4) For the simple shape of the split mold, the working band of the core, and the empty blade are completely completed by the CNC. For the complex manifold of the multi-core, the CNC engraving electrode is used to make the empty knife and the working belt.
(5) Using CNC model. Positioning pins and screw holes are machined by CNC and the wall thickness is also allocated by the CNC to reduce the amount of machining.
(6) The upper mold feed trough is first positioned by the CNC and processed to form a shape. After the cores are machined out, the electric spark continues to be completed. A conical hollow knife is used at the small cantilever to ensure the strength of the cantilever without causing plug or drag.
(7) Electrode sparked electrodes are completed by a CNC engraving machine. The complex shape of the die hole and the pre-deformed die hole are cut by the slow walking thread, which reduces the amount of artificial polishing and ensures the accuracy and finish of the die hole working belt.
(8) Periodically submit a batch of test blocks to check the stability of the heat treatment and nitriding process, and adjust the heat treatment process in time according to the test results of the test blocks.
4 Effect By adopting the above measures, the processing defects of the mold are greatly reduced, the precision of the mold is greatly improved, and the qualification rate of the mold on the machine is also greatly improved than before.
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