Die Casting Mold

Die-casting mold is a tool for casting metal parts, a tool for completing the die-casting process on a dedicated die-casting die forging machine. The basic process of die-casting is: first low-speed or high-speed casting of molten metal into the cavity of the mold, the mold has a movable cavity surface, it is pressurized forging with the cooling process of the molten metal, which eliminates the shrinkage of the blank. Loose defects also make the internal structure of the blank reach broken grains in the forged state. The comprehensive mechanical properties of the blank have been significantly improved.

Die-casting materials, die-casting machines, and molds are the three major elements of die-casting production, all of which are indispensable. The so-called die-casting process is the organic and comprehensive application of these three elements to enable the stable, rhythmic and efficient production of qualified castings with good appearance, internal quality, and dimensions that meet the requirements of the drawing or agreement, or even high-quality castings. .

The Common Materials Of Die Casting Mold

The alloys used in die castings are mainly non-ferrous alloys. As for ferrous metals (steel, iron, etc.) due to mold materials and other issues, they are rarely used. Aluminum alloys are widely used in non-ferrous alloy die castings, followed by zinc alloys. The following briefly introduces the situation of die-casting non-ferrous metals.

(1) Classification of die-casting non-ferrous alloys

hindered shrinkage, mixed shrinkage, free shrinkage, lead alloy—–0.2-0.3% 0.3-0.4% 0.4-0.5%, low melting point alloy, tin alloy, zinc alloy——–0.3- 0.4% 0.4-0.6% 0.6-0.8% Aluminum-silicon series–0.3-0.5% 0.5-0.7% 0.7-0.9% Die-casting non-ferrous alloy aluminum alloy aluminum copper series aluminum-magnesium series—0.5-0.7% 0.7-0.9% 0.9 -1.1% refractory alloy aluminum-zinc magnesium alloy———-0.5-0.7% 0.7-0.9% 0.9-1.1% copper alloy

(2) Recommended casting temperature for various die-casting alloys Alloy type

Average casting wall thickness ≤ 3mm Average casting wall thickness> 3mm Simple structure and complex structure Simple structure and complex structure

• Aluminum alloy Aluminum silicon series 610-650℃ 640-680℃ 600-620℃ 610-650℃
• Aluminum copper series 630-660℃ 660-700℃ 600-640℃ 630-660℃
• Aluminum-magnesium series 640-680℃ 660-700℃ 640-670℃ 650-690℃
• Aluminum zinc series 590-620℃ 620-660℃ 580-620℃ 600-650℃
• Zinc alloy 420-440℃ 430-450℃ 400-420℃ 420-440℃
• Magnesium alloy 640-680℃ 660-700℃ 640-670℃ 650-690℃
• Copper alloy Ordinary brass 910-930℃ 940-980℃ 900-930℃ 900-950℃
• Silicon brass 900-920℃ 930-970℃ 910-940℃ 910-940℃

*Note:

①The casting temperature is generally measured by the temperature of the molten metal in the holding furnace.
②The casting temperature of zinc alloy should not exceed 450℃ to avoid coarse grains.

The Designing Process Of Die Casting Mold

• Analyze the process of the product according to the materials used in the product, the shape and accuracy of the product and other indicators, and set the process.
• Determine the position of the product in the mold cavity, analyze and design the parting surface, overflow system and pouring system.
• Design the core assembly and fixing methods of each activity.
• Design of core pulling distance and force.
• Design of ejector mechanism.
• Determine the die-casting machine, design the mold base and cooling system.
• Check the relevant dimensions of the mold and die-casting machine, and draw the process drawing of the mold and each part.
• The design is completed.

The Common Problem Of Die Casting Mold

The control of the surface temperature of the die-casting mold is very important for the production of high-quality die-casting parts. Uneven or inappropriate die-casting mold temperature will also cause the size of the casting to be unstable, and the casting will be deformed during the production process, resulting in defects such as thermal pressure, mold sticking, surface depression, internal shrinkage and hot bubbles. When the mold temperature difference is large, the variables in the production cycle, such as filling time, cooling time, and spraying time, will have varying degrees of impact.

1). Cold Pattern

Reason: The temperature at the front of the molten soup is too low, and there are traces when they overlap

Improve methods:

1. Check whether the wall thickness is too thin (designed or manufactured), and the thinner area should be directly filled
2. Check whether the shape is not easy to fill; it is not easy to fill if the distance is too far, enclosed areas (such as fins, bumps), blocked areas, and rounded corners are too small. And pay attention to whether there are ribs or cold spots
3. Shorten the filling time, the method of shortening the filling time
4. Change the filling mode
5. Ways to increase mold temperature
6. Increase melting temperature
7. Check the alloy composition
8. Enlarging the escape airway may be useful
9. Adding a vacuum device may be useful

2). Crack

the reason:

1. Shrinkage stress
2. Cracking under force during ejection or whole edge
   way of improvement:
3. Increase fillet
4. Check for hot spots
5. Pressurization time change (cold room machine)
6. Increase or shorten the clamping time
7. Increase draft angle
8. Increase ejector pin
9. Check whether the mold is misaligned or deformed
10. Check the alloy composition

3). Stoma

the reason:

1. The air is mixed in the molten soup
2. Source of gas: when melting, in the material tube, in the mold, release agent
   Improve methods:
3. Moderately slow
4. Check whether the turning of the runner is smooth and whether the cross-sectional area is gradually decreasing
5. Check whether the area of ​​the escape airway is large enough, whether it is blocked, and whether the location is in the last filling place
6. Check if the release agent is sprayed too much and the mold temperature is too low
7. Use vacuum

4). Cavitation:

Reason: Due to the sudden decrease in pressure, the gas in the molten soup suddenly expands, impacts the mold, and damages the mold.

Improve methods:
Do not change the cross-sectional area of ​​the runner rapidly

5). Shrinkage

Reason: When the metal solidifies from liquid to solid, the space occupied becomes smaller. If there is no metal supplement, shrinkage cavities will be formed, which usually occur at a slower solidification place.
Improve methods:

1. Increase stress
2. Change the mold temperature. Local cooling, spray release agent, lower mold temperature,. Sometimes just change the position of the shrinkage hole, not the shrinkage hole

6). Peeling

the reason:

• Poor filling mode, causing overlapping of molten soup
• The mold is deformed, causing the molten soup to overlap
• Inclusion oxide layer

Improve methods:

• Switch to high speed early
• Shorten filling time
• Change the filling mode, gate position, gate speed
• Check whether the mold strength is sufficient
• Check whether the pin die device is in good condition
• Check for inclusion of oxide layer

7). Ripple:

Reason: The first layer of molten broth cooled rapidly on the surface, and the second layer of molten broth failed to melt the first layer, but there was enough fusion, resulting in a different organization

Improve methods:

• Improve filling mode
• Shorten filling time

8). Holes caused by poor flow

Cause: The molten stock flows too slowly, or is too cold, or the filling mode is bad, so there are holes in the solidified metal joints

Improve methods:

• The same method to improve cold lines
• Check whether the molten soup temperature is stable
• Check whether the mold temperature charge is stable

9). Holes on the parting surface

Reason: It may be shrinkage or pores

Improve methods:

• If it is shrinkage, reduce the thickness of the gate or the inlet of the overflow well
• Cooling gate
• If it is a pore, pay attention to the problem of exhaust or entrainment

10). Raw edges

the reason:

• Insufficient clamping force
• Poor mold clamping
• Insufficient mold strength
• Molten soup temperature is too high

11). Shrinkage

Reason: Shrinkage occurs below the surface of the pressing part

Improve methods:

• The same method to improve shrinkage
• Local cooling
• Heat the other side

12). Carbon deposit

Reason: Release agent or other impurities accumulate on the mold.

Improve methods:

• Reduce the amount of release agent sprayed
• Increase mold temperature
• Choose the right release agent
• Use soft water to dilute the release agent

13). Bubble

Reason: The gas is trapped under the surface of the casting

way of improvement:

• Reduce entrainment (same as stomata)
• Cool down or prevent low mold temperature

14). Sticky Mold

the reason:

Zinc deposits on the surface of the mold

Molten soup impacts the mold, causing damage to the mold surface

Improve methods:

• Decrease mold temperature
• Reduce the roughness of the scratch
• Increase draft angle
• Coating
• Change the filling mode
• Reduce gate speed

The Latest Technology

A variety of new die-casting mold surface treatment technologies continue to emerge, but in general they can be divided into the following three categories:

1. Improved technology of traditional heat treatment process;
2. Surface modification technology, including surface thermal expansion treatment, surface phase change strengthening, electric spark strengthening technology, etc.;
3. Coating technology, including electroless plating, etc.

Die-casting molds are a big category of molds. With the rapid development of my country’s automobile and motorcycle industry, the die-casting industry has ushered in a new period of development. At the same time, higher requirements are put forward for the comprehensive mechanical properties and life of die-casting molds. Luo Baihui, Secretary-General of the International Mould Association, believes that it is still difficult to meet the ever-increasing performance requirements only by the application of new mold materials. Various surface treatment technologies must be applied to the surface treatment of die-casting molds to achieve high efficiency for die-casting molds. , High precision and long life requirements.

Among various molds, the working conditions of die-casting molds are relatively harsh. Die casting is to fill the mold cavity with molten metal under high pressure and high speed and die-casting. It repeatedly contacts the hot metal during the working process. Therefore, the die-casting mold is required to have high thermal fatigue, thermal conductivity, wear resistance, and corrosion resistance. , Impact toughness, red hardness, good mold release, etc. Therefore, the surface treatment technology requirements for die-casting molds are relatively high.

Improved technology of traditional heat treatment process

The traditional heat treatment process of die-casting molds is quenching-tempering, and later surface treatment technology has been developed. Due to the variety of materials that can be used as die-casting molds, the same surface treatment technology and process applied to different materials will produce different effects. Schoff proposed substrate pretreatment technology for mold substrate and surface treatment technology. On the basis of traditional technology, suitable processing technology for different mold materials was proposed to improve mold performance and increase mold life. Another development direction for the improvement of heat treatment technology is to combine traditional heat treatment technology with advanced surface treatment technology to increase the service life of die-casting molds. For example, the chemical heat treatment method carbonitriding, NQN combined with conventional quenching and tempering process (namely carbonitriding-quenching-carbonitriding composite strengthening, not only obtains higher surface hardness, but also effective hardening layer The depth increases, the hardness gradient distribution of the infiltrated layer is reasonable, the tempering stability and the corrosion resistance are improved, so that the die-casting mold obtains good core performance while greatly improving the surface quality and performance.

Surface modification technology

Surface thermal diffusion technology

This type includes carburizing, nitriding, boronizing, carbonitriding, sulfur carbonitriding and so on.
Carburizing and carbonitriding co-carburizing processes are used in cold, hot work and surface strengthening of plastic molds, which can improve mold life. For example, the die-casting mold made of 3Cr2W8V steel is first carburized, then quenched at 1140～1150℃ and tempered twice at 550℃. The surface hardness can reach HRC56～61, which increases the die life of die-casting non-ferrous metals and their alloys by 1.8～3.0 times. . When carburizing, the main process methods include solid powder carburizing, gas carburizing, vacuum carburizing, ion carburizing, and carbonitriding formed by adding nitrogen to the carburizing atmosphere. Among them, vacuum carburizing and ion carburizing are technologies developed in the past 20 years. This technology has the characteristics of fast carburizing, uniform carburizing, smooth carbon concentration gradient and small workpiece deformation. It will be used on the mold surface, especially precision molds. Play an increasingly important role in surface treatment.

Nitriding and related low-temperature thermal expansion technology

This type includes nitriding, ion nitriding, carbonitriding, oxygen nitriding, sulphur nitriding, and ternary sulphur carbonitriding, oxygen, nitrogen and sulphur. These methods have simple processing technology, strong adaptability, low diffusion temperature, generally 480～600℃, small deformation of the workpiece, especially suitable for surface strengthening of precision molds, and high hardness of the nitride layer, good wear resistance, and good Anti-sticking performance.

3Cr2W8V steel die-casting mold, after quenching and tempering and nitriding at 520～540℃, the service life is 2 to 3 times longer than that of non-nitriding moulds. Many die-casting molds made of H13 steel in the United States need to be nitrided, and nitriding is used instead of one-time tempering. The surface hardness is as high as HRC65～70, while the core of the mold has low hardness and good toughness, so as to obtain an excellent synthesis. Mechanical properties. The nitriding process is a commonly used process for the surface treatment of die-casting molds, but when a thin and brittle white layer appears in the nitrided layer, it cannot resist the effect of alternating thermal stress, and it is easy to produce micro-cracks and reduce thermal fatigue resistance. Therefore, during the nitriding process, the process must be strictly controlled to avoid the generation of brittle layers.

Foreign countries propose to use secondary and multiple nitriding processes. The method of repeated nitriding can decompose the white bright nitride layer that is prone to microcracks in the service process, increase the thickness of the nitriding layer, and at the same time make the mold surface have a thick residual stress layer, so that the life of the mold can be significantly improved. In addition, there are methods such as salt bath carbonitriding and salt bath sulphur nitrocarburizing. These processes are widely used in foreign countries and rarely seen in China. For example, the TFI+ABI process is immersed in an alkaline oxidizing salt bath after nitrocarburizing in a salt bath. The surface of the workpiece is oxidized and appears black, and its wear resistance, corrosion resistance and heat resistance have been improved.

The life of the aluminum alloy die-casting die treated by this method is increased by hundreds of hours. Another example is the oxynit process developed in France, where the nitrocarburizing process is followed by nitriding, which is more characteristic when applied to non-ferrous metal die-casting molds.

The Industry Status Of Die Casting Mold

Status Quo of Die Casting Moulds in China

China’s die-casting mold industry has developed rapidly, and the total output has increased significantly. The total output of domestically-made die-casting molds is second only to the United States, and has become the second largest in the world, becoming a veritable die-casting country. This achievement is mainly due to the fact that China, with its unique and vast market and relatively low resources and labor advantages, has a very obvious cost-effective advantage in the international die-casting trade market. According to the situation, the future Chinese die-casting industry The development prospects are very broad.

Although China’s die-casting mold has made a major breakthrough during the “Eleventh Five-Year Plan” period. However, its international reputation is still low, and its output is rising day by day. However, most of the die-casting molds are only for China’s needs. Due to technical constraints, it is difficult to break through the quality. At the same time, some large-scale demanding companies in China have frequently extended olive branches to foreign die-casting mold companies. The severe trade deficit has made it difficult for Chinese die-casting companies.

International Die Casting Mould Status

In the context of increasingly fierce competition in the international die-casting mold market, the Japanese die-casting mold industry is also working hard to reduce production costs. In terms of market size, the decline in Japan is the most obvious regardless of output value or Chinese demand. Japanese mold manufacturers pay more attention to the polishing and grinding process in technology, while German mold manufacturers start by improving the accuracy and efficiency of mechanical processing and electrical discharge processing to reduce the time of manual processing. Japan’s die-casting mold industry is gradually shifting molds with low technical content to regions with low labor costs, and only produce products with high technical content in the country. Japan’s trend of accelerating the transfer to foreign countries has led to the use of die-casting molds in Japan. cut back.

Analysis of Factors Affecting the Development of China’s Die Casting Mould Industry

The main reasons restricting the development of China’s die casting mold industry are:

• First, there are still many shortcomings in the use of raw materials in Chinese die-casting molds;
• Second, the backwardness of technology is a great hindrance to the development of China’s die-casting mold industry;
• Third, the supporting system of China’s die-casting mold industry is not perfect.

The Industrial Development Of Die Casting Mold

New alloy die-casting mold products are selling well in my country, but this phenomenon does not mean that they are selling well all over the world. The demand in foreign markets is often different from that in China. According to relevant experts, there are three main reasons that restrict the export of die-casting molds in my country.

• First, there are still many shortcomings in the use of raw materials in domestic die-casting molds;
• Second, the backwardness of technology is also one of the obstacles to the development of my country’s die-casting mold industry;
• Third, the supporting system of my country’s die-casting mold industry is not perfect. These are the bottlenecks that restrict the development of my country’s die-casting mold industry. my country’s die-casting mold industry can only break through these bottlenecks, and its share in the international market will greatly increase.

Die-casting and molds are both different and connected. The birth of the die-casting mold industry is the perfect combination of the two. In other words, die-casting, molds, and die-casting molds are three different industries, and their relationship mainly exists in several ways. : Die-casting and mold integration, all molds are made by themselves, and they rarely make molds for other companies; professional die-casting mold manufacturing, no die-casting; only die-casting, no mold manufacturing capabilities. With the intensification of industrial division of labor, the gradual blurring of industrial boundaries and the development of cross-industry, the three industries should strengthen ties, learn from each other, and integrate the three industries into an “integrated” form. I believe that in the later period, my country The die-casting mold industry will usher in more and greater development opportunities and space