{"id":3513,"date":"2023-10-24T16:46:20","date_gmt":"2023-10-24T14:46:20","guid":{"rendered":"https:\/\/mnwell.com\/?p=3513"},"modified":"2023-10-24T16:53:49","modified_gmt":"2023-10-24T14:53:49","slug":"aluminum-alloy-die-casting-shrinkage-analysis-and-countermeasures-exploration","status":"publish","type":"post","link":"https:\/\/mnwell.com\/tr\/aluminum-alloy-die-casting-shrinkage-analysis-and-countermeasures-exploration\/","title":{"rendered":"Al\u00fcminyum ala\u015f\u0131ml\u0131 d\u00f6k\u00fcm: b\u00fcz\u00fclme analizi ve kar\u015f\u0131 \u00f6nlemlerin ara\u015ft\u0131r\u0131lmas\u0131"},"content":{"rendered":"
Shrinkage hole is a common internal defect of aluminum alloy die casting, often appearing in the product wall thickness is large or easy to form hot spot position. Generally speaking, as long as the shrinkage holes do not affect the use of product performance, are determined in a qualified manner. However, for some important parts, such as automobile engine cylinder block cooling waterway holes or lubricating oilway holes, shrinkage is not allowed to determine qualified.<\/p>\n\n\n\n
One of our company’s engine crankcases made of aluminum alloy is cast in B\u00fchler’s 28 000kN cold chamber die casting machine, made of ADC12 alloy<\/a>. The gross mass of the casting was 6.3 kg, and when X-ray flaw detection was carried out in the post-process, it was found that there was a shrinkage hole in the oil passage of the second crankshaft bearing hole, which was about 8 mm away from the oil passage, and there was a large risk of oil leakage. According to statistics, the scrapping rate of shrinkage holes in this position was 5% in 2017, and after a series of exploration, the scrapping rate was successfully reduced to 0.2%.<\/p>\n\n\n\n Lead to aluminum alloy die casting shrinkage of more reasons, trace its origin, mainly from the liquid phase of aluminum alloy to the solid phase transition process of aluminum liquid shrinkage caused by insufficient. Common reasons for shrinkage are: Shrinkage hole is a kind of aluminum alloy die casting and even casting common internal defects, often appear in the product wall thickness is large, mold sharp corners and mold temperature temperature difference is large and other areas. Figure 2 for a certain engine crankcase shrinkage hole pattern, shrinkage hole is like an ellipse, about 10 mm from the bearing oil hole, the inner wall is rough, no luster. Shrinkage hole area casting wall thickness<\/a> is larger, about 22 mm; oilway hole pin front without cooling water, mold temperature is higher. The two main journals of the crankshaft of the automobile engine (main journal and connecting rod journal) have a large working load and serious wear, and must be pressure lubricated during work. In this case, the presence of shrinkage holes near the oilway holes of the journals will seriously affect the lubrication effect.<\/p>\n\n\n\n Aluminum alloy die casting casting defects<\/a> are caused by the product’s own structural characteristics, mold design pouring system and cooling system design is unreasonable, process parameters are not designed reason. According to the common reasons for casting defects and aluminum alloy casting defects treatment process, to explore the solution of aluminum alloy die casting thick parts of shrinkage hole corresponding countermeasures.<\/p>\n\n\n\n Pre-analysis of casting shrinkage from the easy to operate process parameters, through on-site measurement and observation, measured the mold gate thickness of 4 mm, the calculated inner gate speed of 40 m\/s, the product wall thickness of the thinnest place for the 4.6 mm; cake thickness of 25 mm; casting pressure of 60 MPa. From experience, mold design in line with the structural characteristics of the product, the mold casting system should not have a pressurization stage to make up the shrinkage of insufficient problems. However, the aluminum liquid in the pressurization stage is not enough to make up the shrinkage. However, the shrinkage of aluminum liquid in the boosting stage is directly related to the thickness of the cake and the boosting pressure, and the appropriate thickness of the cake and the casting pressure can form the casting with dense internal organization. Therefore, it can be suspected that the shrinkage holes are caused by the casting pressure is low and the cake is thin.<\/p>\n\n\n\n The countermeasures to eliminate shrinkage in castings in the first stage are divided into two:<\/p>\n\n\n\n Since the essential cause of casting shrinkage is the insufficient shrinkage of aluminum solidification, and the uneven distribution of mold temperature can easily lead to the unreasonable order of aluminum solidification, thus insufficient shrinkage, therefore, the medium-term countermeasures analysis mainly starts from ensuring a reasonable mold temperature. From the 3D model of the product, it can be seen that the wall thickness at the shrinkage hole of the casting is 22.6mm, and the wall thickness is larger, which is easy to cause a higher mold temperature. When the aluminum liquid solidifies, the aluminum liquid inside the casting with large wall thickness is still in the liquid phase or solid-liquid mixed phase due to the high temperature, while the channel for making up the shrinkage in the inner gate may have already solidified at this time. As a result, the casting is not able to make up for the aluminum liquid during the pressurization phase, which may lead to the formation of shrinkage holes. In order to ensure the appropriate mold temperature, the thermal imaging camera was used to measure the maximum temperature of the mold after the mold release agent spraying was 272 \u2103, which was higher than the normal temperature of the mold after spraying, and the temperature of the mold and its distribution was normal in other areas. Therefore, it is necessary to reduce the mold temperature at the shrinkage hole. In addition, it was measured that the distance between the bottom of the cooling water hole and the surface of the mold cavity is 20 mm, because a larger heat transfer distance will reduce the cooling effect of the mold, so the cooling water hole needs to be changed.<\/p>\n\n\n\n In order to reduce the temperature of the mold at the shrinkage hole, three main methods are adopted:<\/p>\n\n\n\nAluminum alloy die casting shrinkage hole formation mechanism and morphology<\/h2>\n\n\n\n
Shrinkage formation mechanism<\/h3>\n\n\n\n
\u2460 Mold temperature gradient is unreasonable, resulting in inconsistent local contraction of liquid aluminum.
\u2461 liquid aluminum pouring volume is small, resulting in thin cake, insufficient pressurization stage of pressurization.
\u2462There are hot knots or sharp areas in the mold.
\u2463 The inner gate of the mold is not wide enough and the area is small, which leads to premature solidification of the casting, and the pressure transfer is blocked in the boosting stage, and the aluminum liquid cannot make up the shrinkage.
\u2464 The casting pressure is set too low, and the effect of shrinkage is poor.<\/p>\n\n\n\n<\/figure>\n\n\n\n
Shrinkage hole pattern of casting<\/h3>\n\n\n\n
Shrinkage hole related countermeasures<\/h3>\n\n\n\n
Pre-analysis and countermeasures<\/h3>\n\n\n\n
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Mid-term analysis and countermeasures<\/h3>\n\n\n\n
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Post-analysis and countermeasures<\/h3>\n\n\n\n