Aluminum mold casting process: reduce the hindrance of defective products

A brief introduction to cast aluminum molds

For the past 30 years, metal die casting technology has been the primary method for the production of structural aluminum castings. The permanent casting process is also known as gravity die casting, and its variations (semi-permanent molding, low pressure, VRC/PRC, PCPCTM, etc.) are a series of metal casting processes that have been widely used in commercial, defense, and automotive applications.

Most of the engine pistons are made of aluminum

The production of cast aluminum molds requires demanding requirements for a wide range of industry applications such as automotive wheels, steering knuckles and control arms, brake components, automotive beams and engine mounts, cylinder heads and engine blocks, and structural housings on airplanes and helicopters.

At present, die-casting aluminum alloy is developing rapidly, it has incomparable high strength, good corrosion resistance and good electrical and thermal conductivity, which is widely used in auto parts, aviation, ships, home appliances and other industries, aluminum alloy die-casting has become the most widely used process.

The picture above shows a cast aluminum mold

Whether automotive, aerospace, or commercial, castings for structural applications have a unique set of requirements:

  1. reliability
  2.  Good fatigue life, especially for castings for structural and repetitive load applications
  3.  High strength/high ductility
  4.  Medium strength/high ductility
  5.  Good impact resistance

Cast aluminium is used as the main raw material for production in these requirements, as the requirements and expectations for aluminium components are often higher. Key requirements for the process used to manufacture these components include:

  1.  Soundness
  2.  Raw material refining
  3.  Mold cleaning and maintenance are complete
  4.  Fast curing
  5.  Homogeneous microstructure
  6.  Oxide-free

Thermal conductivity of different materials

The combination of aluminum’s high thermal conductivity and the rapid heat rejection rate of the metal mold results in a refinement of the microstructure.

This allows for finer grain sizes, more advanced eutectic morphology, smaller harmful secondary components (e.g., embrittlement iron phase), smaller SDAS (secondary dendrite arm spacing), and the observed reduction in dispersed pore size at the same alloy addition and given hydrogen content.

Phase diagram of carbon alloys

This usually reflects an increase in ductility and sometimes even an increase in strength values. When these inherent advantages are combined with technology that improves the feed and stability of castings through the use of pressure feeding, castings that meet these demanding requirements can be consistently produced.

Metal mold permanent forming process

The casting process of metal molds uses molds (also known as molds) that are usually made of ferrous materials, such as gray cast iron or various grades of steel (high-quality tool steels such as 1020, 4340, and H13).

Unlike the sand casting process, these molds are constantly reused. When an internal channel or external feature is obtained using a sand core, it is called semi-permanent molding.

Cast aluminum mold

In static mode, the lower half or fixed mold does not move, only the upper half, the movable half or the side core can be moved.

When the whole mold is tilted and rotated, after the pouring cup accepts the metal, it is called “tilt pouring permanent molding”. The DCX NS minivan front cross member was one of the first large-volume, largest aluminium structural parts produced with this technology, which was produced on a large turntable using six casting machines.

In order to properly feed and orient the molds, temperature management, paint handling and cleaning, and regular maintenance of these molds are very important. The process of temperature and demoulding is achieved by combining air and water cooling lines, heating and mold coating.

Simple diagram of mold cooling channel

The permanent tooling process series uses a refractory coating that is applied first before the mold is put into use, and this coating can be transferred from one shift to several shifts.

Problems with cast aluminum molds

Success in the mold process depends on the successful application and control of the mold coating, as well as the thermal management of the mold through the cooling line. The correct procedures and work instructions should describe the tools required, the method of applying the material, the coating that should be used, the appropriate die temperature and the maintenance cleaning technology applied, the cleaning and maintenance cycle of the refractory coating, and the cleaning method chosen should meet the national environmental protection requirements, while achieving a certain cleaning efficiency.

Cast aluminum mold coating

Proper coating techniques require training and review of these procedures. Often, these paints are purchased in pre-blend or can be diluted to the proper consistency. They can be too thick or too thin, and this problem is exacerbated during the winter months when the material freezes.

The pigments in the paint also settle as they are held, so the material should be stirred and mixed before use, and the bohm should be checked. Many of these paints use sodium silicate as a binder and are applied to a heated mold.

Mold temperature change cycle

It is important to control the mold temperature, as too high a mold temperature can cause the coating to blister, become brittle, and peel off during operation. The coating can also be applied too thickly, contrary to the desired effect. A thickness gauge can be used to verify the desired coating thickness.

When starting to die-cast aluminum alloy products, it is usually completed by molding at high temperature, and long-term molding causes some oil, refractory coating, chemical composition and release agent residues in the alloy to adhere to the die-casting mold, forming a stubborn residue after high temperature coking.

If you want to clean these stubborn carbon deposits in the die-casting mold, the mold is often damaged if the treatment is not good, and the carbon deposits of the die-casting mold can not be completely cleaned.

According to the in-depth comparison of the above cleaning processes, the above table shows that the cleaning effect that can be achieved by the cleaning method of the dry ice cleaning machine is satisfactory.

Advantages of dry ice cleaning machines:

Dry ice cleaners offer a safe, effective, and more economical solution without the use of chemicals or moisture, and without the need to add carbon dioxide to the atmosphere. Dry ice cleaning uses solid carbon dioxide as the injection medium, which can be recovered from other industrial processes and therefore has no impact on the environment.

Dry ice cleaning process

When the dry ice comes into contact with the surface to be cleaned and sublimates back into the atmosphere, there is no secondary waste disposal cost, and only the radioactive contaminants to be cleaned are left at the end of the cleaning. Since it is not used in combination with other cleaning agents such as water, sand or sand grains, it is much smaller, which allows for significant savings in waste disposal costs and eliminates the need for large storage containers to store radioactive contaminated materials.

Advantages of using a dry ice cleaning machine in mold processing

  • Reduce the cost of waste disposal
  • No chemicals need to be used
  • No water is used, downtime is eliminated, and the equipment to be cleaned can be cleaned with minimal disassembly
  • The cleaning process is dry and the electrical components can be safely cleaned in-line
  • More efficient and faster cleaning

Dry ice to clean other molds

Write at the end

The use of dry ice cleaning machine reduces many costs in the aluminum casting industry and safely and effectively improves the ability of online mold cleaning. Internationally, dry ice mold cleaning has been widely used in many mold manufacturing industries as well as related other cleaning industries.

Dry ice cleaning has been proven to be a very effective tool for the aluminium mould cleaning process. Compared with traditional cleaning methods, dry ice cleaning technology can clean all kinds of surface dirt with minimal environmental pollution and can do not harm the substrate. At present, this method has become an important supplement and extension of traditional cleaning methods