Advantages and disadvantages of die casting, characteristics and failure forms

R-C (1)

The cost of casting equipment and molds is high, so the die casting process is generally only used to manufacture large quantities of products in bulk. It is relatively easy to manufacture parts for die casting, which typically requires only four major steps with a low incremental cost per item. Die casting is especially suitable for the manufacture of large quantities of small and medium-sized castings, so die casting is the most widely used of the various casting processes. Compared with other casting techniques, the surface of die casting is smoother and has higher dimensional consistency.

The advantages and disadvantages

Advantages

The advantages of die casting include excellent dimensional accuracy of the casting. Usually THIS DEPENDS ON THE CASTING MATERIAL, WITH A TYPICAL VALUE OF 0.1MM FOR THE FIRST 2.5CM SIZE AND 0.002MM FOR EACH ADDITIONAL 1CM. Compared with other casting processes, the surface of the casting is smooth, and the radius of the rounded corners is about 1-2.5 microns. In contrast to sandbox or permanent mold casting, it is possible to make castings with a wall thickness of approximately 0.75 mm. It can directly cast the internal structure, such as wire sleeve, heating element, high strength bearing surface. Other ADVANTAGES INCLUDE THE ABILITY TO REDUCE or AVOID SECONDARY MACHINING, FAST PRODUCTION, casting tensile strength up to 415 MPA, and the ability to CAST highly LIQUID metals.

Disadvantages

The biggest disadvantage of die casting is its high cost. The casting equipment as well as molds and die related components are expensive compared to other casting methods. Therefore, it is more economical to produce large quantities of products when making die castings. Other disadvantages include the fact that this process is only suitable for metals with high mobility and that the casting mass must be between 30g and 10kg [5]. In normal die casting, the last batch of castings will always have pores. Therefore, no heat treatment or welding can be performed, because the gas in the gap will expand under the heat, resulting in micro defects inside and peeling of the surface.

The characteristics of

Pressure casting, referred to as die casting, is a casting method in which molten alloy liquid is poured into the pressure chamber, the cavity of the steel mold is filled at high speed, and the alloy liquid is solidified under pressure to form a casting. Die casting is distinguished from other casting methods by high pressure and high speed.

① The liquid metal is filled with the cavity under pressure, and crystallizes and solidifies at higher pressure, the common pressure is 15-100mpa.

② Liquid metal filling cavity at high speed, usually in 10-50 m/s, some can be more than 80 m/s, (through the gate into the cavity linear velocity – gate speed), so the filling time of liquid metal is very short, about 0.01-0.2 seconds (depending on the size of the casting and different) can be filled cavity.

Die casting is a precision casting method. The size tolerance of the die cast is very small, and the surface accuracy is very high. In most cases, the die cast can be assembled without turning, and threaded parts can also be cast directly. From the general camera parts, typewriter parts, electronic computing devices and ornaments and other small parts, as well as cars, locomotives, airplanes and other vehicles of complex parts are mostly made by the use of die casting.

Failure modes

Damage to the

Die casting production, die again and again by the chilling effect of thermal forming surface and its internal deformation, with each other and appear repeatedly cyclic thermal stress, lead to structure damage and loss of resilience, cause the emergence of micro cracks, and continue to expand, once the crack expand, fluid diapir and molten metal, and repeated mechanical stress to accelerate the extension of crack. Therefore, on the one hand, the die must be fully preheated at the beginning of die casting. In addition, in the process of die casting production, the mold must be kept in a certain working temperature range to avoid early cracking failure. At the same time, to ensure that the mold before production and manufacturing internal causes do not occur problems. In actual production, most die failure is thermal fatigue cracking failure.

Fracture

Under the action of injection force, the mold will crack at the weakest point, especially the streaking trace or electrical processing trace on the molding surface has not been polished, or the forming Angle will be the first fine crack, when the grain boundary there is a brittle phase or coarse grain, that is, easy to fracture. The rapid crack propagation during brittle fracture is a very dangerous factor for the fracture failure of the die. For this reason, on the one hand, all scratches and electrical processing marks on the surface of the mold must be polished, even if it is in the pouring system, it must also be polished. In addition, the mold materials used are required to have high strength, good plasticity, impact toughness and fracture toughness.

Dissolution

Previously mentioned, commonly used die casting alloys are zinc alloy, aluminum alloy, magnesium alloy and copper alloy, but also pure aluminum die casting, Zn, Al, Mg are more active metal elements, they have a good affinity with mold materials, especially Al easy to bite the mold. When the mold hardness is higher, the corrosion resistance is better, and the forming surface if there are soft spots, the corrosion resistance is not good.

There are many factors that lead to mold failure. Both external (case whether pouring temperature, mould preheating, water-based paint spraying quantity of how many, size matches, high pressure die casting, die casting machine tonnage gate open not too fast, cooling water and die casting production synchronization Fe casting material, the type and composition of high and low, casting dimension shape, wall thickness, size, coating type, etc.). There are also internal factors (such as the metallurgical quality of the material of the die itself, the forging process of the blank, the rationality of the structure design of the die, the rationality of the pouring system design, the internal stress generated by the die machine (electrical machining), the heat treatment process of the die, including various matching accuracy and finish requirements, etc.).

If there is an early failure of the mold, it is necessary to find out what internal or external causes are for future improvement. However, in the actual production, the dissolution is only in the local part of the mold. For example, the parts directly washed by the inner gate (core and cavity) are prone to the dissolution phenomenon, and the aluminum alloy sticky mold is easy to appear in the soft hardness.