The die processing technology is as follows:
1. Processing Route
Rough processing (0.2-0.5mm allowance on one side) quenching finishing, electrical processing polishing, assembly test nitriding.
2. Heat treatment
(1) Material: 4Cr5MoSiV1 (H13).
(2) Technical requirements: HRC 48-52.
(3) Heat treatment process and equipment:
It is heated at 1020 C, oil-cooled, tempered at 580 C and 550 C twice. The equipment is 75KW salt furnace, 90KW gas carburizing furnace protection heating, well tempering furnace tempering. After the die test, nitriding treatment is carried out in our factory or customer side by ordinary gas nitriding. The nitriding process is carried out at 570 C for 6 hours. The depth of nitriding layer is 0.06-0.08mm, and the hardness of nitriding layer is HV900.
Using the above method to deal with general section die, extrusion rod and backlog cylinder can ensure that they do not collapse and crack in use. Some hardness can also be relaxed to HRC < 46-53>. In this case, extrusion life mainly depends on the quality and number of nitriding.
However, in recent years, with the rapid development of industry, a large number of profiles such as radiators and motor shells for various complex cross-section electronic industry are needed, as shown in Figure 1. This kind of complex cross-section die accounts for about one fourth of the total.
Figure 1: Complex section aluminium profiles
The extrusion ratio of these profiles during extrusion is large, the flow forming resistance is large, and some working sections of the die bear great shear stress, as shown in Fig. 2 and Fig. 3. In the early stage of extrusion, the suspension bridge of the die collapsed, collapsed (HRC < 46 >) or broken teeth. Even if the hardness of the broken bridge (HRC53) is within the qualified range, the extrusion life is not high. How to solve this problem? Of course, the life of imported steel products, such as Sweden 8407 or Japan SKD61, may be improved, but the price of imported materials is 80 yuan/kg, which is several times higher than that of domestic materials 16 yuan/kg. As a result, the users are not willing to accept the price of moulds, so this is a subject. The material cost of extrusion die is relatively large in the cost of die.
Fig. 2: Flat die die for radiator
Figure 3: Punch die for motor housing
There is also such a situation: when nitriding or pre-heating before extrusion (temperature 490-520 C), there is occasional run-off temperature phenomenon. At this time, the hardness of the die decreases, it can not be used any more, and must be re-quenched. But at this time, the die has been formed with a gap of about 0.02 mm. If the re-quenching deformation is a difficult problem, if not re-quenching, it will lead to mass scrap and large losses.