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Vacuum Heat Treatment of Engine Cylinder Block Die-casting Mold

Mold is the basic process equipment for industrial production. In electronics, automobiles, motors, electrical appliances, instruments, home appliances and communications, 60% to 80% of parts are formed by molds. The quality of molds determines the quality of products. High and low, therefore, the mold is called “the mother of all industries”. The mold is also a “benefit amplifier”. The value of the final product produced by the mold is often dozens or hundreds of times the value of the mold itself.

Die-casting is a precision casting method. The die-casting parts through die-casting have small dimensional tolerances and high surface precision. In most cases, die castings do not require turning for assembly applications. There are many methods of surface treatment to choose from, such as electroplating, electroplating sandblasting, etc. Threaded parts can also be cast directly. Small parts such as general camera parts, typewriter parts, electronic computing parts, satellite parts and decorations, as well as complex parts of automobiles, locomotives, and other vehicles are mostly manufactured by die-casting.

The engine cylinder of a motorcycle is an important part of the engine and is generally made of precision casting. The casting mold frame is usually a frame-type four-plate structure, and a box-type two-plate structure is also used. The latter has a relatively compact and reasonable structure, good integrity, and high mold base strength, but it brings greater difficulty to processing.

Mold Process Requirements

The dimensional accuracy of the mold cavity is required to be ±0.05mm, and the positional accuracy is required to be 0.03mm. There are 10 main parts of the cavity, and the surfaces are all three-dimensional special-shaped polygonal shapes. In order to facilitate the mold opening, the joint surfaces of the left and right sliding sleeve seats and the movable and fixed mold cores respectively adopt special-shaped tapered surfaces with 20° and 15° along the circumference of the mold, and the fit clearance shall not be greater than 0.05mm. The parts of the cavity are made of 4CrSMoVSi material. The hardness requirement is HRC44~48, and the surface is nitrocarburized. Each main core is cooled by point water, which can better control the thermal balance of the mold temperature during die-casting, which is beneficial to the improvement of the quality of the die-casting blank and prolongs its service life.

The specific process is as follows:

Vacuum heat treatment means:

Since the mold has high requirements for dimensional accuracy and strength, vacuum heat treatment is the best way. Generally, molds undergo three heat treatments: preheating, stress relief annealing, vacuum quenching and vacuum tempering.

Preheating can improve the internal structure of the cavity material, refine the grains, and lay a solid foundation for the final vacuum heat treatment. At the same time, the hardness required for the mold pressure test is guaranteed to prevent the mold from being damaged during the pressure test.

Stress relief annealing has a good effect on eliminating most of the stress generated by the main block or large block during machining. It can avoid stress deformation or cracks during the final heat treatment, and prevent the mold from cracking in the early stage of use.

Vacuum heat treatment is carried out after the mold has passed the test, which is convenient for trimming the mold during the pressure test and avoids the difficulty of mechanical cutting.

Vacuum heat treatment process:

In recent years, vacuum heat treatment technology has been widely used. The introduction of this technology in mold manufacturing makes the mold manufacturing process more advanced and more reasonable. It provides a reliable guarantee for improving the manufacturing quality and prolonging the service life of the mold.

After vacuum heat treatment, the mold retains the original surface quality, the deformation is extremely small, and the average deformation is basically controlled within ± 0.05mm. It not only ensures the internal comprehensive performance of the mold, but also meets the assembly requirements of the mold. Taking 4Cr5MoVSi material as an example, the vacuum heat treatment process is as follows:

1.Cleaning: Remove grease and aluminum slag.

2.Vacuum quenching: The vacuum degree of the vacuum quenching furnace is 1.33-0.13 Pa. Heat to 800±20°C, keep warm for 1.5~2h, continue heating to 1020±10°C, keep warm for 1~2h. Then fill with nitrogen (≥80kPa), cool to 200-300°C, and immediately temper in vacuum.

3.Vacuum tempering: heat to 600±10°C, hold for 4-6 hours, wait for the vacuum furnace to cool below 150°C, then heat to 610±10°C, hold for 4-6 hours, cool in the furnace to below 150°C.

4.Inspection: measure hardness HRC42～46.

Vacuum heat treatment equipment selection: RVGQ series vacuum heat treatment furnaces produced by SIMUWU are high-quality products for vacuum heat treatment of die-casting molds. Good temperature control accuracy and uniformity ensure the effective vacuum heat treatment process. SIMUWU company focuses on the manufacture of vacuum furnaces, has more than ten years of relevant experience, and has a good reputation in the field of vacuum furnace manufacturing. The product line includes vacuum air quenching furnace, vacuum oil quenching furnace, vacuum brazing furnace, etc., which are widely sold in developed and developing countries.