Mold lifespan

  • 2024-10-29

Mold life refers to the number of parts that can be formed while ensuring the quality of the parts. It includes repeated sharpening and replacement of vulnerable parts until the main part of the mold is replaced, resulting in a total of qualified parts formed.


1 Basic meaning

2 Normal lifespan of the mold

3 Forms and Mechanisms

4 Influencing factors

5 Maintenance and upkeep

6 Production and Inspection


Basic meaning

The failure of molds is divided into abnormal failure and normal failure. Abnormal failure (early failure) refers to the inability of a mold to be put into service before it reaches a recognized lifespan at a certain industrial level. The early forms of failure include plastic deformation, fracture, and severe localized wear. Normal failure refers to the inability of molds to continue service due to slow plastic deformation, uniform wear, or fatigue fracture after large-scale production and use.


Normal lifespan of the mold

The number of qualified products produced before the normal failure of the mold is called the normal life of the mold, abbreviated as mold life. The number of qualified products produced before the first repair of the mold is called the first life; The number of qualified products produced from one repair of a mold to the next repair is called the mold repair life. The lifespan of a mold is the sum of its initial lifespan and the lifespan of each subsequent repair.

The lifespan of a mold is related to its shape and structure, and it refers to the material properties, design, and manufacturing level of the mold during a certain period of time. A comprehensive reflection of the level of heat treatment, usage, and maintenance of molds. The lifespan of molds reflects to some extent the level of metallurgical and mechanical manufacturing industries in a region or country.


Form and mechanism

There are many types of molds with significant differences in working conditions and damaged parts, but the failure modes can be roughly summarized into three types: wear, fracture, and plastic deformation.

(1) Wear and tear failure

When the mold is in service, it comes into contact with the formed billet and generates relative motion. The phenomenon of gradually losing material from a contact surface due to relative motion of the surface is called wear.

(2) Fracture failure

When the mold has large cracks or separates into two or several parts and loses its service ability, it becomes a fracture failure. Fracture can be divided into plastic fracture and brittle fracture. Mold materials are mostly medium to high strength steel, and the form of fracture is mostly brittle fracture. Brittle fracture can be divided into one-time fracture and fatigue fracture.

(3) Plastic deformation failure

Plastic molds experience significant and uneven stress during service. When the stress in a certain part of the mold exceeds the yield limit of the mold material at that temperature, plastic deformation will occur through lattice slip, twinning, grain boundary slip, etc., changing the geometric shape or size, and cannot be repaired before service, which is called plastic deformation failure. The failure modes of plastic deformation include upsetting, bending, cavity expansion, collapse, etc.

The plastic deformation of a mold is the yielding process of the metal material used in the mold. Whether plastic deformation occurs is mainly determined by mechanical load and the room temperature strength of the mold. The occurrence of plastic deformation in molds serving at high temperatures mainly depends on the working temperature of the mold and the high-temperature strength of the mold material.


Influence factor

(1) The influence of mold structure

The mold structure has a significant impact on the stress state of the mold. A reasonable mold structure can ensure that the mold is uniformly stressed during operation, less prone to eccentric loading, and less stress concentration. There are many types of molds, with significant differences in form and working environments,

(2) The influence of mold working conditions

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.



Maintenance and upkeep

(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.


Production and inspection

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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