Vida útil del molde
- 2024-10-29
La vida útil del molde se refiere a la cantidad de piezas que se pueden formar garantizando al mismo tiempo la calidad de las piezas. Incluye el afilado y reemplazo repetido de piezas vulnerables hasta que se reemplaza la parte principal del molde, lo que da como resultado un total de piezas calificadas.
5 Mantenimiento y conservación
El fallo de los moldes se divide en fallo anormal y fallo normal. El fallo anormal (fallo temprano) se refiere a la imposibilidad de que un molde se ponga en servicio antes de que alcance una vida útil reconocida en un determinado nivel industrial. Las primeras formas de falla incluyen deformación plástica, fractura y desgaste localizado severo. La falla normal se refiere a la incapacidad de los moldes para continuar en servicio debido a una deformación plástica lenta, desgaste uniforme o fractura por fatiga después de la producción y el uso a gran escala.
La cantidad de productos calificados producidos antes de la falla normal del molde se denomina vida normal del molde, abreviada como vida útil del molde. La cantidad de productos calificados producidos antes de la primera reparación del molde se denomina primera vida; La cantidad de productos calificados producidos desde una reparación de un molde hasta la siguiente reparación se denomina vida útil de reparación del molde. La vida útil de un molde es la suma de su vida útil inicial y la vida útil de cada reparación posterior.
La vida útil de un molde está relacionada con su forma y estructura, y se refiere a las propiedades del material, el diseño y el nivel de fabricación del molde durante un período de tiempo determinado. Un reflejo integral del nivel de tratamiento térmico, uso y mantenimiento de los moldes. La vida útil de los moldes refleja hasta cierto punto el nivel de las industrias de fabricación metalúrgica y mecánica de una región o país.
Existen muchos tipos de moldes con diferencias significativas en las condiciones de trabajo y piezas dañadas, pero los modos de falla se pueden resumir a grandes rasgos en tres tipos: desgaste, fractura y deformación plástica.
(1) Fallo por desgaste
Cuando el molde está en servicio, entra en contacto con el tocho formado y genera movimiento relativo. El fenómeno de pérdida gradual de material de una superficie de contacto debido al movimiento relativo de la superficie se llama desgaste.
(2) Fractura fallida
Cuando el molde tiene grandes grietas o se separa en dos o varias partes y pierde su capacidad de servicio, se convierte en una falla por fractura. La fractura se puede dividir en fractura plástica y fractura frágil. Los materiales del molde son en su mayoría acero de resistencia media a alta, y la forma de fractura es principalmente fractura frágil. La fractura frágil se puede dividir en fractura única y fractura por fatiga.
(3) Fallo por deformación plástica.
Los moldes de plástico experimentan tensiones significativas y desiguales durante el servicio. Cuando la tensión en una determinada parte del molde excede el límite elástico del material del molde a esa temperatura, se producirá deformación plástica por deslizamiento de la red, macla, deslizamiento de los límites de grano, etc., cambiando la forma geométrica o el tamaño, y no se puede reparar. antes del servicio, lo que se denomina falla por deformación plástica. Los modos de falla de la deformación plástica incluyen recalcado, flexión, expansión de la cavidad, colapso, etc.
La deformación plástica de un molde es el proceso de fluencia del material metálico utilizado en el molde. La deformación plástica está determinada principalmente por la carga mecánica y la resistencia del molde a temperatura ambiente. La aparición de deformación plástica en moldes que funcionan a altas temperaturas depende principalmente de la temperatura de trabajo del molde y de la resistencia a altas temperaturas del material del molde.
(1) La influencia de la estructura del molde.
La estructura del molde tiene un impacto significativo en el estado de tensión del molde. Una estructura de molde razonable puede garantizar que el molde esté uniformemente estresado durante la operación, menos propenso a cargas excéntricas y menos concentración de tensiones. Existen muchos tipos de moldes, con importantes diferencias en forma y entornos de trabajo,
(2) La influencia de las condiciones de trabajo del molde.
1) Material and temperature of formed parts
① The materials used for forming parts include metal and non-metal. Generally speaking, non-metallic materials have low strength, require less forming force, have less stress on the mold, and have a longer mold life. Therefore, the lifespan of metal forming molds is lower than that of non-metal forming molds.
② When forming high-temperature workpieces, the mold heats up due to the heat it receives. As the temperature increases, the strength of the mold decreases, making it prone to plastic deformation. At the same time, there is a significant temperature difference between the surface of the mold in contact with the workpiece and the non-contact surface, which causes temperature stress in the mold.
2) Equipment characteristics
① The precision and stiffness of the equipment are provided by the force of the mold forming the workpiece. During the forming process, the equipment will undergo elastic deformation due to the force applied.
② The force exerted by the speed equipment on the mold and workpiece gradually increases over a period of time, and the equipment speed affects the force application process. The higher the equipment speed, the greater the impact force on the mold per unit time (high impact); The shorter the time, the less time it takes for the impact energy to be transmitted and released, making it easier to concentrate locally, resulting in local stresses exceeding the yield stress or fracture strength of the mold material. Therefore, the higher the equipment speed, the more prone the mold is to fracture or plastic deformation failure.
3) Lubrication
Lubricating the relative motion surface between the mold and the billet can reduce direct contact between the mold and billet, decrease wear, and reduce forming force. At the same time, lubricants can also hinder heat transfer from the billet to the mold to a certain extent, reduce mold temperature, and be beneficial for improving mold life.
(3) The influence of mold material properties
The performance of mold materials has a significant impact on the lifespan of molds, including strength, impact toughness, wear resistance, corrosion resistance, hardness, thermal stability, and heat fatigue resistance.
(4) The impact of mold manufacturing process
1) During module forging, the temperature difference between the inside and outside caused by module heating and cooling will generate thermal stress; Improper selection of technical parameters during processes such as upsetting, punching, and expanding holes can easily lead to cracking of the forging blank. In addition, when the forging ratio exceeds a certain value, the transverse mechanical properties sharply decrease due to the formation of fibrous tissue, leading to anisotropy.
2) In the electrical machining of molds, varying degrees of deterioration layers may occur. In addition, due to local sudden heating and cooling, residual stress and cracking are easily formed.
3) Heat treatment of molds
Mold heat treatment is arranged after module forging and rough machining, and is almost the final process of mold processing. The selection of mold materials and the determination of heat treatment processes have a significant impact on the performance of molds.
(1) Purpose: To maintain optimal performance and prolong the service life of the equipment, ensuring normal production.
(2) Scope of application: Suitable for the repair and maintenance of molds.
(3) Regular inspection and maintenance: Regular maintenance and inspection should be carried out by mold repair and upper and lower mold personnel.
(4) The electrolytic ultrasonic cleaning method has better cleaning effect on the processed molds. While cleaning, it also plays a role in rust prevention
1. Daily routine inspection and maintenance:
Is the mold in operation in normal condition
a. Is there low-voltage locking protection; b. Whether the active parts such as guide posts, top rods, and rows are worn and lubricated properly. It is required to refuel at least once every 12 hours, and for special structures, the refueling frequency should be increased. c. Are the screws and locking clips of the fixed template of the mold loose;
1.2 Normal production conditions: Check whether the defects of the product are related to the mold;
1.3 When dismounting, a comprehensive inspection of the mold should be conducted and rust prevention treatment should be carried out: wipe dry the moisture in the mold cavity, core, ejection mechanism, and row position, and spray mold rust inhibitor or apply butter.
1.4 The mold after being removed from the machine should be placed in the designated location and recorded:
a. Mold condition: intact or in need of repair. b. The anti rust treatment method during mold making.
2. Quarterly routine inspections:
Mainly for cleaning and maintaining molds that have not been used for more than two months.
2.1 Open the mold and check the internal rust prevention effect. If there are any abnormal situations, rust prevention treatment must be carried out again. Molds that are not used for a long time should be coated with butter.
2.2 Return to its original position and make records.
Mold is the basic process equipment for mechanical industry production and an indispensable tool in the production of industrial products. The performance of molds made of mold steel requires strict production process supervision, and the raw materials for mold production must also be strictly controlled to prevent early failure, heat treatment cracking, and other defects caused by material problems.
The control of raw materials for molds is carried out from the following aspects:
1. Macro inspection
The chemical composition is decisive in ensuring the performance of steel, but qualified composition cannot fully explain the performance of steel. Due to the unevenness of the internal structure and composition of steel, macroscopic inspection largely supplements this deficiency. Macroscopic testing can observe the crystallization of steel, the failure of steel continuity, and the non-uniformity of certain components. Eight common macroscopic defects: segregation, porosity, inclusions, shrinkage, bubbles, white spots, cracks, and folds.
2. Evaluation of annealed tissue
The purpose of annealing is to reduce the hardness of steel, facilitate machining, and also prepare the structure for subsequent heat treatment.
3. Non-uniformity of carbides
Cr12 type martensitic steel contains a large amount of eutectic carbides in its microstructure, and the unevenness of carbides has a very important impact on its performance. Therefore, strict control must be exercised over the distribution of carbides.
In summary, due to the complexity of the production objects in mold factories and workshops, and the fact that they are mostly single pieces or small batches, it brings certain difficulties to the formulation and management of mold production quotas. In addition, the production methods, equipment, and technical qualities of each factory and workshop are not the same. Therefore, when formulating quotas, it is necessary to find appropriate methods to develop advanced and reasonable working hour quotas based on the actual situation of the factory and workshop, in order to improve labor productivity.
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