In modern manufacturing, tungsten steel mold accessories play a key role in many fields such as automobile manufacturing, electronic equipment production, aerospace, etc. due to their high hardness, high wear resistance and good high temperature resistance. However, its unique material properties make the production process face many technical difficulties. In-depth exploration of these difficulties and seeking effective solutions are crucial to improving the production quality and efficiency of tungsten steel mold accessories.
1. Processing problems caused by material properties
(1) High hardness and low toughness
Tungsten steel mold accessories are mainly composed of tungsten carbide (WC) and binder (usually metals such as cobalt). This material structure gives it extremely high hardness, with Rockwell hardness of up to HRA 85-93, which is much higher than ordinary steel. However, its high hardness also leads to low toughness. During the processing, especially during mechanical processing such as cutting and grinding, the material is very prone to defects such as chipping and cracking. For example, when milling the complex contours of tungsten steel molds, if the cutting force of the tool is slightly uneven, it may cause the edge of the mold to collapse, seriously affecting the dimensional accuracy and surface quality of the mold, and increasing the scrap rate of the processing.
(2) Low ductility
Compared with traditional steel, the ductility of tungsten steel is significantly reduced. In stamping, forging and other forming processes, low ductility makes it difficult for tungsten steel to fill the mold cavity, especially for mold accessories with complex shapes, such as parts with thin walls, sharp corners and other structures, which are prone to cracks or even breakage during the forming process. This not only limits the freedom of shape design of mold accessories, but also places extremely high demands on the control of forming process parameters.
(3) Special thermal properties
Tungsten steel has a low thermal conductivity but a high thermal expansion coefficient. During the processing, such as heat treatment, due to uneven heat transfer during heating and cooling, large internal stress will be generated inside the mold, leading to deformation or even cracking. Moreover, during cutting, the cutting heat generated is difficult to dissipate quickly, which will increase tool wear and affect the quality and dimensional accuracy of the processed surface, making thermal management during the processing a major challenge.
2. Complexity and high requirements of processing technology
(1) Difficulty in cutting
Due to the high hardness of tungsten steel, ordinary tools wear very quickly during cutting, and the tool life is only 1/5 – 1/10 of that when processing ordinary steel, which greatly increases the processing cost and the frequency of tool replacement. At the same time, the broken chips generated during the cutting process rather than continuous strip chips are easy to scratch the processing surface, causing the surface roughness to exceed the standard, affecting the accuracy and service life of mold accessories. Choosing the right tool material and cutting parameters is the key, such as using PCD (polycrystalline diamond) tools, CBN (cubic boron nitride) tools, and accurately controlling the cutting speed (usually 10 – 50m/min), feed rate and back cutting amount, but even so, the difficulty of cutting is still relatively large.
(2) Problems with electrical discharge machining (EDM) and wire cutting
In EDM, the high hardness and high melting point of tungsten steel lead to slow processing speed and low processing efficiency. Moreover, heat-affected zones and recast layers will be formed on the surface of the mold during the processing, changing the material’s structure and performance, affecting the surface quality and dimensional accuracy of the mold, and subsequent fine processing is required to eliminate these effects. During wire cutting, the processing progress is often slow due to the characteristics of tungsten steel, and the processing surface is prone to cracking. This requires operators to strictly control processing parameters, such as pulse width, pulse interval, etc., and carefully check the processing surface for defects after processing.
(3) High requirements for precision grinding and polishing processes
In order to achieve the high precision and low surface roughness requirements required for tungsten steel mold accessories, grinding and polishing processes are essential. However, due to the hardness and brittleness of tungsten steel, grinding burns, cracks and other defects are easily generated during the grinding process. Strict requirements are placed on the selection of grinding wheels, the optimization of grinding parameters, and cooling and lubrication conditions. For example, select grinding wheels with fine grain size and high hardness, reasonably control the grinding depth and feed speed, and use efficient coolant for cooling and lubrication. The polishing process requires special polishing processes and tools, such as ultrasonic polishing, electrolytic polishing, etc., to achieve a mirror polishing effect. This process is not only time-consuming, but also requires a high level of skill from the operator.
3. Challenges of quality control and testing
(1) Difficulty in detecting internal defects
Tungsten steel mold accessories may have defects such as pores and inclusions inside, which will seriously reduce the mechanical properties and service life of the mold. However, due to the complexity of its internal structure, traditional detection methods are difficult to accurately detect these tiny defects. For example, it is impossible to find internal pores and inclusions by naked eye observation or simple measuring tools. Although non-destructive testing technologies such as ultrasonic testing and X-ray testing can detect internal defects, the detection sensitivity of some tiny defects still needs to be improved, and the detection cost is relatively high.
(2) Dimensional accuracy and geometric tolerance control
Due to the influence of various factors during the processing, such as cutting force, thermal deformation, etc., it is very difficult to accurately control the dimensional accuracy and geometric tolerance of tungsten steel mold accessories. For some high-precision mold accessories, the dimensional tolerance is required to reach ±0.001mm or even higher, and the geometric tolerances such as coaxiality and verticality are also extremely strict. This requires real-time monitoring of the processing status during the processing, using advanced measuring equipment such as CMM measuring instruments for precise measurement, and adjusting the processing parameters and process methods to ensure that the dimensional accuracy and geometric tolerance meet the requirements.
(3) Surface quality inspection and evaluation
The surface quality of mold accessories has an important impact on their performance and service life, including surface roughness, surface cracks, burn marks, etc., which need to be strictly inspected and evaluated. However, the current surface quality inspection and evaluation methods are not perfect enough, and some inspection methods are highly subjective and lack unified standards. For example, although there are corresponding measuring instruments for surface roughness detection, different results may be obtained under different measurement conditions; and the detection of surface cracks and burn marks often depends on the operator’s experience and judgment, which makes it difficult to achieve automated and precise detection.
The production and processing of tungsten steel mold accessories faces many technical difficulties in terms of material properties, processing technology, quality control and testing. To overcome these difficulties, it is necessary to continuously develop new processing technologies and process methods, optimize processing parameters, improve the accuracy and reliability of detection methods, and strengthen the skills training and quality awareness of operators to improve the production quality and efficiency of tungsten steel mold accessories and meet the growing high-precision and high-performance needs of modern manufacturing.
