Normal service life of aluminum profiles mold
Before a mold fails under normal conditions, the number of qualified products it produces is called the mold's normal lifespan, or simply mold life. The number of qualified products produced before the mold's first repair is called the initial lifespan; the number of qualified products produced from one repair to the next is called the repair lifespan. Mold life is the sum of the initial lifespan and the lifespans from each repair.
The lifespan of a mold is related to the type and structure of the mold. It is a comprehensive reflection of the material properties of the mold, the level of mold design and manufacturing, the level of mold heat treatment, as well as the level of use and maintenance over a certain period. The length of the mold's lifespan, to some extent, reflects the metallurgical and mechanical manufacturing industry levels of a region or a country.
Mold Failure Modes and Mechanisms
However, the forms of failure can generally be summarized into three types: wear, fracture, and plastic deformation.
(1) Wear failure
During service, the mold comes into contact with the forming workpiece, generating relative motion. Due to the relative motion of the surfaces, the phenomenon of gradual material loss on the contact surface is called wear. Wear failure can be classified into the following types:
(2) Fracture failure
When a mold develops large cracks or splits into two or several parts, resulting in a loss of serviceability, it is considered a fracture failure. Fractures can be classified as ductile fractures or brittle fractures. Mold materials are mostly medium- to high-strength steel, and the form of fracture is often brittle fracture.
Brittle fracture can be further divided into instant fracture and fatigue fracture.
(3) Plastic deformation failure
The plastic deformation of a mold is the yielding process of the mold's metal material. Whether plastic deformation occurs is primarily influenced by the mechanical load and the mold's room temperature strength. For molds operating at high temperatures, whether plastic deformation occurs mainly depends on the mold's working temperature and the high-temperature strength of the mold material.
With the development of trends in the aluminum industry, in recent years everyone has been seeking better and more optimal development models to improve efficiency and save costs.
Cost and increased efficiency. For the production of aluminum profiles, extrusion dies are undoubtedly an important control point. Improving their lifespan is certainly a systematic issue. In actual production practice, efforts generally focus on several key aspects, including optimized design, die processing, and maintenance during use.
1. Optimized Design
For extrusion molds, the level of design directly affects the quality of the output and, to a certain extent, the service life of the mold. The design of an extrusion die should first select an appropriate extrusion ratio based on the profile, determine the machine tonnage and the number of holes, so that the designed distribution holes create a balanced material flow. Additionally, the design structure should avoid stress concentration as much as possible, ensuring that all parts of the mold bear forces evenly to guarantee its stability.
For tool heads with more complex and numerous screw holes, the empty knife is generally appropriately lengthened to strengthen the strength around the screw hole positions. Considering factors such as better quenching penetration of heat-treated molds, improved stress relief, and more thorough heating, some large square or rectangular tool heads will have additional drilling in the middle.
If the profile has a longer diagonal and is of the square tube type, the thickness of the upper die is generally increased to better ensure its strength, and the bridge position is also appropriately widened, thereby effectively preventing premature corner cracking and other issues.
2. Mold Processing
The manufacturing of extrusion molds is divided into mechanical processing and electrical processing. Generally, mechanical processing is used for rough machining to complete the main structure of the mold, while electrical processing is for fine machining, mainly reworking important parts such as the working area. To improve the lifespan of extrusion molds, paying attention to certain details during the processing is very effective. In particular, analyzing the situation after mold repair can help determine how to better process the mold during the next supplementation.
1. Regarding heat treatment, the general hardness of extrusion dies is HRC47-HRC51. However, for large dies with specifications above ￠560, the hardness is generally taken at the lower limit of around HRC47. This ensures both the hardness of the die and the necessary toughness it requires.
2. For the machining of distribution holes, especially in multi-hole dies, particular attention must be paid to the symmetry after machining. During the process, tool wear must also be monitored to maintain final dimensional accuracy. The polishing room's task is to polish the die to a smooth finish. During rough polishing, it is essential to properly handle tool marks, flow channels, and transition areas. All bridge positions and die neck connections must be rounded to facilitate better heat treatment. Following this, our company has significantly improved the surface finish of dies according to the process of rough polishing before heat treatment and fine polishing after heat treatment, which is more conducive to smooth material discharge and reduced friction.
3. Flow channels play a crucial role in balancing material supply in extrusion dies, making their machining a focal point. Generally, the machining of flow channels is carried out according to the design drawings. However, to improve first-pass qualification rates and leverage the experience of on-site operators, our company performs machining of general flow channels and perforations based on the operators' experience, which is derived from accumulated knowledge from regular die repairs.
4. The machining of die cavities is crucial for its strength, particularly at burr positions, endpoints, and cantilever areas. Typically, to ensure strength, the slope in special cavity areas is increased slightly, and the cavity value is set lower. To prevent premature wall thickness deviations, the final finished wall thickness of a die is generally taken with a negative allowance (0 to -0.03MM).
3. Subsequent Use and Maintenance of the Die
1. During die testing and extrusion, special attention should be paid to the following aspects: A. Determining the temperature of the die and thermometer before extrusion, whether it meets the required extrusion temperature, and whether the heating penetrates the core (the placement of dies in the heating furnace is very important; there should be a certain heating gap between dies). B. The extrusion die must be aligned to the center to avoid phenomena such as collapsing or jamming. C. For different profile dies, an appropriate extrusion speed should be selected to avoid difficulties in material flow caused by too fast or sudden speed. D. During the extrusion process, attention should also be paid to the quality of the aluminum rods to prevent die damage due to impurities in the aluminum rods, and so on.
2. Mold modification is a very important step, but the first thing to consider is its strength. Mold modification should be carried out on the premise of ensuring the mold's strength. Unless absolutely necessary, welding is generally not used, as it has a significant impact on the mold's lifespan. Especially welding on the working area, which can easily shorten its lifespan. For adjusting the speed of profiles, it is generally preferred to correct slow areas rather than slow down fast areas. In this way, reducing the load in mold construction can, to a certain extent, ensure its lifespan. Of course, improving mold modification skills and reducing trial mold times is also one of the ways to extend the mold's service life.
3. During the mold seasoning process, special attention must be paid to the punching step, particularly in screw holes or other more fragile parts, otherwise, the mold can be easily damaged.
4. The handling of molds must be done carefully to avoid bumping areas such as the working surface. Before storing the mold in the warehouse, it must be thoroughly cleaned and carefully inspected for any minor cracks or damage.
5. For molds that have completed production, it is essential to manage their process data effectively, such as mold modification plans, processing details, and extrusion processes. These can serve as references for supplementing molds or duplicating similar molds, which can effectively improve the yield rate of molds in production.
In short, the improvement of the service life of extrusion molds depends on the seamless integration of design, manufacturing, use, and subsequent maintenance processes. Relying on a single link cannot effectively achieve the goal; through effective integration of all links, it is believed that the service life of molds can be correspondingly improved.
