Usually refers to a variety of molds for drawing metal wires, as well as wire drawing dies for drawing optical fibers. All drawing dies have a hole in the center of a certain shape, round, square, octagonal or other special shapes. When the metal is pulled through the die hole, the size becomes smaller and even the shape changes. When drawing soft metals (such as gold and silver), a steel mold is sufficient, and the steel mold can have multiple holes with different diameters. The drawn steel wire (steel wire) generally uses a cemented carbide die (Tungsten carbide nib). The typical structure of this die is a cylindrical (or slightly tapered) cemented carbide core that is tightly embedded in a circular steel sleeve. In (case), there are bell radius, entrance cone, approach angle, bearing and back relief in the inner hole of the mold core. For drawing non-ferrous metal wires, such as copper and aluminum, wire drawing dies similar to steel wire molds are often used, with some differences in the shape of the inner hole. For thinning wires, polycrystalline molds (man-made diamonds) can be used, and natural diamond drawing dies are also used.

Some soldiers in the Terracotta Warriors and Horses of Qin Shihuang can see metal wires on their stone armors, so it is estimated that some people have mastered the drawing technology at that time. In Tiangong Kaiwu's book of the Ming Dynasty, we can see the craftsmanship of needle making, among which is the use of drawing dies.

1. The definition of wire drawing die

Usually refers to a variety of molds for drawing metal wires, as well as wire drawing dies for drawing optical fibers. All drawing dies have a hole in the center of a certain shape, round, square, octagonal or other special shapes. When the metal is pulled through the die hole, the size becomes smaller and even the shape changes.

Second, the type of drawing die

1. Steel mold-the steel mold is sufficient when drawing soft metals (such as gold and silver), and the steel mold can have multiple holes with different diameters.

2. Tungsten carbide die-drawn steel wire (steel wire) generally uses a tungsten carbide die (Tungsten carbide nib), the typical structure of this type of die is a cylindrical (or slightly tapered) cemented carbide core tightly The ground is embedded in a circular steel case. The inner hole of the mold core has a bell radius, an entrance cone, an approach angle, a bearing, and Exit angle (back relief).

3. Steel wire dies-for drawing non-ferrous metal wires, such as copper and aluminum, wire drawing dies similar to steel wire dies are often used, and the shape of the inner hole is somewhat different.

4. Polycrystalline molds-Polycrystalline molds (man-made diamonds) can be used to draw thin wires, as well as wire drawing molds that use natural diamonds.

Third, the use of wire drawing die

Wire drawing dies have a wide range of uses, such as high-precision wires used in electronic devices, radars, televisions, instruments and aerospace, as well as commonly used tungsten wires, molybdenum wires, stainless steel wires, wire and cable wires and various alloy wires are all drawn with diamond wire drawing dies The manufactured diamond wire drawing die adopts natural diamond as raw material, so it has strong wear resistance and extremely long service life.

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The wire drawing die is a very important and consumable die used by various metal wire manufacturers (such as wire and cable factories, steel wire factories, electrode welding wire factories, etc.) to draw wires. The wire drawing die has a wide range of applications, mainly used for drawing straight and difficult-to-machine objects such as bars, wires, wires, pipes, etc. It is suitable for drawing processing of metal and alloy materials such as steel, copper, tungsten, and molybdenum. Since the cost of the wire drawing die accounts for more than 1/2 of the wire drawing cost, how to reduce the cost of the wire drawing die and increase its service life is an urgent problem that metal wire production units need to solve.

In order to improve production competitiveness, the foreign metal product industry is paying more and more attention to the quality of drawing dies and the improvement of manufacturing processes. Starting from the improvement of the life of the drawing dies, the material, structure, manufacturing process, manufacturing equipment and testing instruments of the drawing dies have been carried out. Systematic research, the development of composite wire drawing dies, new materials for wire drawing dies, new surface coating technologies, new pass design methods for wire drawing dies, etc. have promoted the development of wire drawing production in the world.

my country is a large wire rod producer, and its output ranks among the top in the world. my country's wire drawing die manufacturing industry has developed rapidly since the 1980s. With the continuous improvement of wire drawing die manufacturing level and the continuous improvement of production technology, my country’s wire drawing die manufacturing technology has further developed, especially in the material, Significant progress has been made in the structure and other aspects. But in general there is still a big gap with foreign countries. Although the types of wire drawing dies produced abroad are similar to those in China, the materials and processes used are more advanced, and the machining accuracy, durability, and wear resistance of the wire drawing dies are better than those of our country. Therefore, strengthening the management of mold making, improving the quality level of drawing dies, and promoting the advancement of mold making technology are important issues currently facing the mold making industry. ?

2. Material of drawing die

After decades of development, many new wire drawing die materials have emerged. According to the type of material, the wire drawing dies can be divided into alloy steel dies, cemented carbide dies, natural diamond dies, polycrystalline diamond dies, CVD diamond dies and ceramic dies. In recent years, the development of new materials has greatly enriched the application range of the wire drawing die and increased the service life of the wire drawing die.

(1) Alloy steel mold is the early manufacturing material of wire drawing dies. The materials used to make alloy steel molds are mainly carbon tool steel and alloy tool steel. However, due to the poor hardness and wear resistance of alloy steel molds and short service life, they cannot meet the needs of modern production. Therefore, alloy steel molds are quickly eliminated, and alloy steel molds are almost invisible in the current production and processing.

(2) The cemented carbide die is made of cemented carbide. Cemented carbide is a tungsten-cobalt alloy, and its main components are tungsten carbide and cobalt. Tungsten carbide is the "skeleton" of the alloy, which mainly plays a role of hard and wear-resistant; cobalt is the bonding metal and the source of the toughness of the alloy. Therefore, compared with alloy steel molds, cemented carbide molds have the following characteristics: high wear resistance, good polishing, low adhesion, low friction coefficient, low energy consumption, and high corrosion resistance. These characteristics make cemented carbide wire drawing The mold has a wide range of processing adaptability and has become the most widely used drawing die mold today.

(3) Natural diamond is an allotrope of carbon, and the mold made with it has the characteristics of high hardness and good wear resistance. However, natural diamond is more brittle and difficult to process. It is generally used to make wire drawing dies with a diameter of less than 1.2mm. In addition, natural diamonds are expensive and the supply is in short supply. Therefore, natural diamond molds are not the economical and practical wire drawing tools that people ultimately seek.

(4) Polycrystalline diamond is made of carefully selected high-quality synthetic diamond single crystals plus a small amount of bonding agents such as silicon and titanium, and polymerized under high temperature and high pressure conditions. Polycrystalline diamond has high hardness and good wear resistance. Compared with other materials, it has its own unique advantages: due to the anisotropy of natural diamond, during the drawing process, when the entire hole is around Under working conditions, natural diamond will be worn preferentially at a certain position of the hole; while polycrystalline diamond is polycrystalline and has the characteristics of isotropy, thus avoiding uneven wear of the die hole and out-of-round die hole. Compared with cemented carbide, the tensile strength of polycrystalline diamond is only 70% of that of commonly used cemented carbide, but it is 250% harder than cemented carbide. This makes polycrystalline diamond molds have more advantages than cemented carbide molds. . The wire drawing die made of polycrystalline diamond has good wear resistance, uniform inner hole wear, strong impact resistance, high wire drawing efficiency, and the price is much cheaper than natural diamond. Therefore, polycrystalline diamond molds are currently widely used in the wire drawing industry.

(5) CVD (Chemical Vapor Deposition) coating wire drawing die is a new technology developed recently, and its main method is to coat diamond film on the hard alloy wire drawing die. The diamond film is pure diamond polycrystalline. It not only has the smoothness and temperature resistance of single crystal diamond, but also has the advantages of polycrystalline diamond wear resistance and low price. It has achieved good results in replacing rare natural diamonds in the preparation of wire drawing die tools. Its wide use will bring new vitality to the wire drawing die industry.

(6) High-performance ceramic materials have the characteristics of high hardness, good wear resistance, strong chemical stability, excellent high-temperature mechanical properties and not easy to bond with metals, and can be widely used in the processing of difficult-to-process materials.

In the past 30 years, due to the effective control of raw material purity and grain size in the ceramic material manufacturing process, various carbide, nitride, boride, oxide, whisker or small amount of metal addition technologies have been developed. And the use of various toughening and strengthening mechanisms has greatly improved the strength, toughness, and impact resistance of ceramic materials.

From the results of foreign research, ceramic materials have been widely used in the field of molds, and there have been many patents in Japan, the United States, France and other countries. Although ceramic wire drawing dies have not been widely used in my country, with the continuous improvement of manufacturing technology, ceramics will be a good wire drawing die material suitable for the wire drawing industry.

The ceramic wire drawing die is not easy to adhere to the metal wire during the wire drawing process, which is beneficial to improve the surface performance of the metal wire, especially for drawing colored hard materials (such as W, Mo wire, etc.) at high temperature. Drawing non-ferrous metal materials with ceramic drawing dies can avoid the defects of cemented carbide drawing dies, and can extend the life of the drawing dies and improve the surface quality of the materials.

The materials of various drawing dies have their own characteristics. Among them, the natural diamond wire drawing die is the most expensive and the processing is extremely difficult. At the same time, because of the anisotropy of natural diamond, the hardness varies greatly in the radial range, and it is prone to severe wear in a certain direction, so the natural diamond die is only suitable It is suitable for processing wire with very small diameter. The hardness of the cemented carbide die is low, and the wire drawn with the cemented carbide die has a higher quality and low surface roughness, but the wear resistance of the cemented carbide die is poor and the service life of the die is short. The hardness of the polycrystalline diamond mold is second only to that of natural diamond. Because of its isotropic characteristics, it will not cause a single radial aggravation phenomenon, but its price is very expensive, processing is difficult, and the manufacturing cost is high. CVD coated wire drawing die has good wear resistance due to its diamond properties, and the surface roughness of the drawn wire is low, but the production process of CVD coated wire drawing die is complicated, processing is difficult, and the cost is high; when the coating wears The later mold will wear out quickly, which is not only difficult to ensure the processing quality, but also cannot be reused and can only be scrapped. Ceramic material has higher hardness and wear resistance than cemented carbide, and is low in cost. It is an excellent material for making wire drawing dies between diamond and cemented carbide. However, due to poor toughness, poor thermal shock and processing difficulties, ceramic materials have not yet been widely used. The comparison of the advantages and disadvantages of various drawing die materials is shown in Table 2.

Table 2 Comparison of advantages and disadvantages of several drawing die materials

Drawing die material-advantages-disadvantages-scope of application

Alloy steel mold-easy to make-poor wear resistance, short life span-basically eliminated

Natural diamond-high hardness, good wear resistance-brittleness, difficult to process-wire die with diameter below 1.2mm

Cemented carbide-good polishability, low energy consumption-poor wear resistance, difficult to process-wires of various diameters

Polycrystalline synthetic diamond-high hardness, good wear resistance-difficult to process, high cost-small wire, wire

CVD coating material-high smoothness, good temperature resistance-complex process, difficult to process-small wire, wire

Ceramic material-wear resistance, high temperature resistance, good corrosion resistance-thermal shock, poor toughness, difficult to process-no large-scale application

In the drawing process of small wire and wire, natural diamond, polycrystalline diamond and CVD coating die are commonly used wire drawing die materials. When drawing small diameter wires, the CVD coated diamond mold overcomes the anisotropy of the natural diamond mold, and at the same time has excellent strength and hardness, the highest drawing output, and the surface quality also meets the requirements. Tests have proved that the life of the CVD coated diamond wire drawing die is equivalent to that of the natural diamond die, the product qualification rate is high, and the surface quality is better than domestic polycrystalline diamond. Therefore, for small diameter wire drawing processing, CVD coated diamond wire drawing die is an ideal choice.

Although the wire drawing dies can be used to process various metals and alloys such as steel, copper, tungsten, molybdenum, etc., the wire drawing dies of different materials have their applicable processing ranges. When the wire drawing dies of different materials process the same wire, their wear patterns and use There is a big difference in lifespan, so a reasonable selection of the material of the drawing die is the key to ensuring successful application. Wire drawing dies of different materials have their relatively reasonable processing objects. The rationality of the drawing process mainly refers to the matching of the mechanical, physical and chemical properties of the drawing die and the wire to obtain the longest die life. For example, when drawing copper wires of the same diameter, the service life of the polycrystalline diamond die is 300 to 500 times longer than that of the cemented carbide die, and it is only 80 to 100 times when drawing nickel wires. When drawing molybdenum wires, the service life The service life is only 50 to 80 times that of the cemented carbide die, and when drawing carbon steel, the life of the polycrystalline diamond die is only 20 to 60 times that of the cemented carbide die. Due to the lack of systematic research on the matching theory of drawing dies and wires in China, it has led to blind selection and waste of resources. The friction and wear of the wire drawing die is very complex, generally divided into two categories: damage and friction and wear. The damage of the drawing die can be divided into ring damage, tensile damage, shear damage and support surface damage. Friction and wear can be divided into abrasion wear, friction wear, corrosion wear, abrasion and wear caused by fine particles. The different working conditions (wire material, drawing die material, lubricant, etc.) make the wear and damage of the drawing die have its own unique process. The relationship between the wear and tear of the drawing die is essentially interrelated. The situation inside the drawing die may be very subtle, and some factors may work at the same time, and their superimposed effects are very complicated and difficult to understand. It is possible that the effect of one factor will conceal the effect of other factors. The above-mentioned forms of damage and friction and wear may often be intertwined, which increases the difficulty of analyzing the damage and wear mechanism of the wire drawing die. But in general, the order of wear resistance of various material drawing dies from high to low is: diamond drawing die (without considering the anisotropy of natural diamond)-ceramic drawing die-cemented carbide die- Obsolete alloy steel molds.

Through the research on the material of the drawing die, the drawing die is developing towards high strength, high hardness and high wear resistance. Various new materials that meet the requirements are emerging in an endless stream. The wear resistance of the drawing die is greatly improved, and the time of wear and damage is obvious. Delay, the life of the wire drawing die continues to increase, and the processing accuracy has also been improved to a certain extent. The applicable range of drawing processing is gradually expanding. Wires of various specifications from thick to thin can be processed, and special-shaped dies for processing irregular wires have appeared. ?

3. Drawing die structure

In recent years, with the deepening of reform and opening up, wire drawing dies and corresponding die hole testing instruments made by industrialized countries have been introduced in China. Through the analysis of the hole pattern of foreign wire drawing dies, we can understand the design idea of modern wire drawing dies, which provides a reference for improving the design level of the wire drawing dies in our country.

3.1 Inner hole structure of drawing die

According to the nature of work, the structure of the wire drawing die core can be divided into five sections: "entrance zone, lubrication zone, working zone, sizing zone, and exit zone". The inner diameter profile of the drawing die is very important, it determines the tension required to compress the wire and affects the residual stress in the wire after drawing. The functions of each area of the mold core are: the entrance area, which facilitates threading and prevents the wire from scratching the drawing die from the entrance direction; the lubrication area, through which the steel wire is easy to bring lubricant; the working area is the main part of the die hole, and the deformation of the wire The process is here