Sand casting – machine modeling

Machine modeling — the molding machine completes the main actions of sand filling, compaction and touching during the molding process. Compared with manual molding, it can greatly improve productivity, labor conditions, casting precision and surface quality.

The classification, advantages, disadvantages and application scope of machine modeling methods are as follows.

Jarring

Sand compaction method and sand mold characteristics:

By means of mechanical shock, the molding sand is endowed with kinetic energy and inertia for compact forming. The sand mold is loose on the top and tight on the bottom, and often needs supplementary pressure.

Scope of application:

It is used for mass production of small and medium castings with low precision.

Compaction

1) Simple compaction

Sand compaction method and sand mold characteristics:

Molding sand is compacted by the pressure transmitted by the head or pattern. According to the specific pressure, it can be divided into three types: low pressure (0.15-0.4mpa), medium pressure (0.4-0.7mpa) and high pressure (> 0.7MPa).

Scope of application:

Medium and low pressure are used for small and medium-sized batch production of simple castings with low precision requirements, and high pressure is used for large-scale production of castings with high precision requirements and more complex castings.

2) One way compaction

Sand compaction method and sand mold characteristics:

The compactness of the sand mold on the direct compression surface is high, but not uniform. If the specific pressure is insufficient, the compactness is low.

Scope of application:

It is used for small and medium-sized batch production of flat castings with low precision requirements.

3) Differential compaction

Sand compaction method and sand mold characteristics:

The compactness and uniformity of the sand mold are better than that of the one-way compaction.

Scope of application:

It is used for mass production of castings with high precision and complicated requirements.

Seismic pressure

1) Ordinary seismic pressure

Sand compaction method and sand mold characteristics:

The sand mold with high compactness can be obtained because of its small fluctuation range of apparent density.

Scope of application:

It is used for mass production of castings with high precision and complex.

2) Microseismic compaction

Sand compaction method and sand mold characteristics:

The vibration frequency is 400-300 Hz, and the amplitude is small. It can be compacted by microseism at the same time, or by microseism before compaction. Compared with simple compaction, it can obtain higher compactness and uniformity of sand mold.

Scope of application:

It can be used for mass production of complex castings with high precision.

Injection pressure

Sand compaction method and sand mold characteristics:

With the help of compressed air, the molding sand is preloaded with kinetic energy and then compacted with a pressure head. It has high compactness and uniformity, including top shot, bottom shot and side shot. The structure of top shot is simple.

Scope of application:

It is used for mass production of small and medium-sized parts with low precision.

Sand throwing

Sand compaction method and sand mold characteristics:

The sand mass is thrown out by the high-speed rotating blade and hit on the sand layer in the sand box to make the molding sand compact layer by layer. The higher the speed of the sand mass is, the higher the compactness of the sand mold is. If the sand supply and the moving speed of the throwing head are stable, the compactness of each part of the sand mold is relatively uniform.

Scope of application:

It can be used to compact sand mold or sand core, not only for medium and large sand box modeling, but also for pit modeling. Single piece, small batch and batch can be used, but the casting precision is low.

Airtight

1) static pressure

Sand compaction method and sand mold characteristics:

The process includes: (1) filling sand in the sand box (there is a vent plug on the formwork); (2) applying compressed air to the molding sand for air pressure (generally 0.3s), “passing through the molding sand and discharging through the vent plug, at this time, the closer the molding sand is to the formwork, the higher the apparent density is; (3) using the compaction plate to compact the upper part of the molding sand to make the upper and lower compactness of the sand mold uniform. In this method, the amount of sand taken in the sand box is small, and the inclination of mould starting is small.

Scope of application:

It can be used for mass production of various complex castings with high precision requirements.

2) Air impact and its types

Type 1

Sand compaction method and sand mold characteristics:

The shock wave released by the instantaneous expansion of gas with a certain pressure acts on the molding sand to make it compact, and the thixotropy (instantaneous liquefaction) of the molding sand caused by the rapid impact overcomes the resistance caused by the clay film and improves the mobility of the molding sand. Under the action of impact and thixotropy, the sand mold is characterized by uniform compactness and reasonable distribution, and the compactness at the pattern is higher than that at the back of the sand mold.

Scope of application:

It can be used for mass production of various complex castings with high precision requirements, and has greater adaptability than hydrostatic molding.

Type 2

Sand compaction method and sand mold characteristics:

Air impact: ordinary compressed air is used as power to adjust the compactness of sand mold by adjusting the pressure of compressed air.

Scope of application:

It is used for sand box with flat area ≤ 1.2-1.5 m2.

Type 3

Sand compaction method and sand mold characteristics:

Gas impact: mix natural gas, propane gas, methane and ethane with air in a certain proportion, ignite and detonate, and adjust the sand compactness by adjusting the fan speed.

Scope of application:

For sand box with flat area ≥ 1.5 m2.

Type 4

Sand compaction method and sand mold characteristics:

Explosion airflow impact: use the arc discharge of high-voltage current to ignite liquid or solid substances and make them explode to produce high-pressure gas compact molding sand.

Scope of application:

Not yet in use.

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