Magnesium alloy die casting production management and experience

Magnesium alloy is one of the most important engineering materials. Magnesium is the lightest of the structural metals and has a high strength to weight ratio that can replace steel, cast iron, zinc alloys and even aluminum alloys where they have traditionally been used. In addition, magnesium alloy also has :(1) excellent thermal conductivity, shock absorption; (2) Anti-EMI electromagnetic wave; (3) High dimensional stability; (4) Can be 100% recycled, known as green engineering materials. The advantageous characteristics of magnesium alloy make it one of the preferred materials for manufacturing structural parts in industrial products, mainly used for manufacturing light and high strength objects. The application fields of magnesium alloy die casting are mainly notebook computers, cameras and camera products (collectively referred to as 3C products).

First, reasonable selection of magnesium alloy die casting machine for die casting production

Magnesium alloy die casting mainly includes three kinds of die casting technologies: hot chamber die casting, cold chamber die casting and semi-solid injection forming.

The selection of magnesium alloy die casting machine for production mainly depends on the wall thickness and weight of the casting. In the study of "optimization of magnesium alloy die casting process", German Frech company put forward that under normal conditions, small castings of about 1kg, thin wall uniformity and complex shape are suitable to be produced by hot chamber die casting machine. Cold chamber die casting machines are usually used for die-casting large parts, because high injection pressure can be used, under the injection ratio of up to 15Mpa, 10kg or more liquid metal can be injected within 100ms. For 1.35~2.25kg die castings, it can be produced in die casting machines with clamping force of 500~700 tons. Both types of die casting machines can be used.

Hot chamber die casting machine is widely used in south China. Compared with cold chamber die casting machine, hot chamber die casting machine has the following characteristics (take HISHINUMA as an example for specific data) :

1. The magnesium alloy material is in liquid state during casting, which meets the general casting conditions.

2. Good castability, casting pressure about 250KG/CM2, lower casting pressure can be cast large castings.

3. Due to high casting temperature, the production cycle is fast.

4. Fast production cycle

5. The equipment purchase cost is low and the technology patent fee is not required.

6. The gate is small. Taking mobile phone forming as an example, the hot chamber die-casting is 44.8g, and the cold chamber die-casting is 110g.

The hot chamber die casting machine is more suitable for magnesium alloy production by updating the following hot chamber die casting technical equipment:

1. High-speed injection servo hydraulic system.

2. High frequency nozzle heating device.

3. Broken hot plate of the mold.

4. Mold temperature regulating device.

5. Magnesium ingot preheating device.

6. The high-speed Sensor without contact is adopted in the injection meter measuring mechanism, which makes the reading accurate and fast, and makes the warranty of the part without mechanical contact simple and easy.

The advantages of semi-solid injection machine are: high surface quality of parts; It can cast thin and light parts with wall thickness up to 0.7~0.8mm, precise size; No need for melting furnace, not only high safety and good working environment; Casting shrinkage is small; The surface yield of castings is high, which can make the die-casting process without surface defect yield up to about 50%.

The disadvantages of semi-solid die casting technology include: expensive equipment; The maintenance is more difficult, the failure rate of machinery and control equipment is higher, and the maintenance cost is more, which is about 50% higher than the die-casting method, so the product cost is higher; Because of the use of raw materials for magnesium grains, compared with the use of magnesium ingot die casting method raw material price is 20% higher; The production cycle of casting is long, which is 2~3 times that of ordinary die casting, so the output is low.

Table 1 shows the comparison of the three types of die casting machines in the production process. Which type of die casting machine to use in actual production should be chosen according to the needs of product production. At present, hot chamber die casting machine is widely used in mainland China. This paper introduces the management and experience of hot chamber die casting technology in the process of die casting.

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Point comparison item Semi-solid injection machine hot chamber die casting machine cold chamber die casting machine

Casting temperature (℃) of AZ91D is lower than 590~600, 630~650 and higher than 680~700

Injection velocity (M ˙ S-1)1~41~41~8

Injection specific pressure (Mpa)50~12025~3540~70

Pressurization without without (thick wall advantage)

Casting projection area is small and large

Forming stability is sometimes unstable good good

Feeding mode feeder automatic feeding crucible direct feeding automatic pouring machine feeding

Safety very good good common (spilled material)

Slag is not much more common

Die casting cycle 1(datum)0.91.1

The use of protective gas SF6 is not available