Mold lifespan has always been an essential factor in the profitability of industrial projects. If we can use reasonable methods to extend the service life of the mold beyond the design requirements, it will significantly improve the company’s profitability. We know that many factors affect the life of the mold. No matter what type of mold, the most critical factor that affects its life is inevitably the material.
The common material used for injection and die-casting molds is mold steel. In order to understand the life of a mold, let’s start with the material.
Steel requirements for industrial molds
The selection criteria for mold steel include the following:
Requirements of the injection material: Different plastics require different steel materials based on specific needs such as high polishability, corrosion resistance, etc.
Price considerations: The performance of the steel does not solely depend on its cost. It is essential to balance the cost factors of the mold. Choosing the appropriate mold steel in accordance with the expected mold lifespan can prevent unnecessary waste. For example:
General P20 steel has a lifespan of approximately 300,000 cycles.
2738 steel can handle around 500,000 cycles without issues.
Depending on the situation, H13/2344 steel typically lasts between 800,000 to 1,000,000 cycles or more.
SPI Mold Classification to explain the mold lifespan and steel requirement
The SPI mold classification categorizes molds into different classes based on complexity, quality requirements, and expected production volume.
|SPI Mold Classification||Mold Type||Description||Number of Uses|
|Class 101||High-Production||Designed for extended production runs with high part quality requirements||More than 1000000 cycles|
|Class 102||High-Production||Similar to Class 101 but with slightly lower requirements||500,000 to 1000000 cycles|
|Class 103||Moderate Production||Molds for moderate production runs with less demanding part quality||300,000 to 500,000 cycles|
|Class 104||Low-Volume/Prototyping||Molds for low-volume production or prototyping purposes||100,000 to 300,000 cycles|
|Class 105||Prototype/Experimental||Molds for short-run production, testing, or experimental purposes||500 cycles|
|Class A||Critical Surface Finish||Molds for producing parts with high aesthetic standards||—|
|Class B||Functional Surface Finish||Molds for producing parts where appearance is less critical||—|
|Class C||Non-Specific Surface Finish||Molds for producing non-visible parts or parts without surface concerns||—|
Class 101 and Class 102 molds often require heat treatment to achieve a hardness of HRC50 or higher. The selected steel should have good heat treatment performance and cutting performance at high hardness levels. While the statement mentions specific steel grades like Sweden’s 8407, S136, the United States’s 420, H13, Europe’s 2316, 2344, 083, or Japan’s SKD61, DC53, the actual selection depends on factors such as the type of plastic, corrosiveness, appearance requirements, and transparency.
Class 103 molds typically use pre-hardened materials with grades like S136H, 2316H, 718H, 083H, and hardness ranging from HB270-340.
Class 104 and 105 molds commonly utilize steels like P20, 718, 738, 618, 2311, 2711. S50C, 45# steel, or directly machining the mold cavities into the mold embryo may be used for low-demand molds.
Injection Mold Lifespan
Factors affect the lifespan of injection molds
Structure: A well-designed mold structure enhances its load-bearing capacity and reduces thermal and mechanical stress. Proper die-guiding mechanisms prevent abrasion, and specialized treatment of high-strength components minimizes stress concentration.
Material: The choice of mold materials is crucial. Higher production volumes impose greater loads on the mold, requiring materials with superior load-bearing capacity and prolonged service life.
Processing quality: Defects from processing and heat treatment can negatively impact mold life. Residual knife marks on the mold surface, microscopic cracks from electrical discharge machining (EDM), and surface defects caused by heat treatment can impair the mold’s bearing capacity and lifespan.
Working conditions: Injection molds undergo repeated cycles of mold closing, locking, injection, holding pressure, cooling, mold opening, and ejection. To ensure optimal performance, we should ensure that all work mechanisms function reliably, operate smoothly, and receive regular maintenance and lubrication.
Part conditions: The surface quality, hardness, elongation, dimensional accuracy, and other mechanical properties of the processed parts directly affect the mold’s lifespan. Issues like surface defects or material adhesion can disrupt the mold’s normal functioning.
Tips to extend the injection mold lifespan
The reasonable setting of clamping force
Correct clamping force setting is crucial to extend mold life. The correct setting of the clamping force of the injection molding machine is important to improve the life of the mold. Setting the clamping force too high or too low can negatively affect the mold. A low clamping force may cause the mold to open or be damaged due to the injection pressure exceeding the clamping force. Conversely, a high clamping force can exert excessive pressure on the mold, damaging the parting line, exhaust area, and mold parts.
To avoid these issues, we can calculate the ideal clamping force for each mold by using mold flow analysis or the formula:
Clamping force = projected area x material clamping force factor x safety factor
The projected area comprises the product and the runner, and we can obtain the clamping
force factor for the material from the material properties table or by consulting the material supplier. The safety factor, typically 1.5 to 2, is selected based on factors such as the injection molding machine’s stability and structure.
Reasonable mold opening and clamping settings
Clamping speed have an impact on the cycle time of the injection molding process. However, finding a balance is essential, not simply aiming for the fastest clamping speed possible. Excessive clamping speed can lead to increased wear and potential damage to the mold components. Please ensure a smooth transition from fast to slow clamping to avoid any abrupt movements that could cause misalignment or damage to the mold, this is very important. Slow clamping should occur before the pin and part fit together to ensure proper alignment and prevent interference during clamping. Similarly, the transition between fast and slow mold release should be smooth. Fast mold releases should occur only after all products and parts have been successfully released from the mold to avoid any potential damage or interference.
Finding the appropriate clamping speed involves considering various factors such as the mold design, material being used, part complexity, and machine capabilities. We recommend consulting the machine manufacturer’s guidelines and mold specifications and conductingproper testing to determine the optimal clamping speed for a specific injection molding process.
Proper ejector setting
Incorrect ejector mechanism settings can jeopardize mold life by either over-ejecting or improperly ejecting the product, which can damage the mold. It is important to ensure the molded part is ejected correctly from the mold, taking into account the required separation for the actual product.
Excessive ejected volume can exert extreme pressure on the ejector pin. Therefore, it is crucial to set the ejector pressure at an appropriate level that aligns with the actual product requirements, in addition to considering the ejected volume.
Proper hot runner setting
The method of starting and closing a hot runner can indeed impact mold life. Improper start-up procedures can lead to mold issues such as mold rise, which may require mold removal and repair. To prevent such problems, we recommend manually operating the valve gate and verifying that the settings are correct and functioning properly before starting full production.
Additionally, it is advisable to export the material in the hot runner through the material distribution plate and measure its temperature to verify that it aligns with the desired temperature. During hot runner closure, it is important to promptly reduce the hot runner temperature to minimize the risk of material degradation. These practices contribute to the optimal performance and extended life of the mold.
Reasonable mold cooling settings
Excessive mold temperatures can negatively affect mold life. Excessive mold temperatures can reduce mold life. Limiting mold temperatures to the minimum necessary for achieving an acceptable part appearance is beneficial, as this approach helps improve mold life. Additionally, it is important to maintain a balanced temperature distribution within the mold. We should ideally keep the temperature difference between the moving and fixed sides of the mold within a range of 6 ℃. Temperature variations beyond this range can cause significant differences in thermal deformation between the two sides of the mold, leading to poor opening and closing, ultimately resulting in mold wear or damage. We can enhance the overall lifespan of the mold by controlling and balancing the mold temperatures.
Mold cleaning and maintenance
Inspect, clean, and lubricate molds regularly in the production environment, preferably at least once per shift. During the process, pay attention to signs of mold wear, such as scuffing, parting line wear, and burrs. Establishing a preventive maintenance schedule and keeping records of mold maintenance is crucial. By reviewing recurring maintenance events, the frequency of preventative maintenance can be determined, which helps reduce unscheduled maintenance events. It is essential to check the lubrication of slides and ensure their proper functioning. Monitoring signs of brake failure and loose hooks is also important. After each cleaning and inspection, it is necessary to verify that the slide is in the correct position before leaving the mold. Additionally, when the mold remains unused for more than 6 hours, applying a rust inhibitor and thoroughly coating textured and polished areas can help prevent rust damage. By following these practices, mold maintenance can be effectively carried out, enhancing mold performance and lifespan.
Die Casting Mold Lifespan
How to tell when a die-casting mold has reached the end of its life
In general, if the die-casting mold is used in the process of the following phenomena, indicating that the mold is close to the “end of life.”
Mold aging and surface cracking: As the mold ages, it may develop surface cracks, which can affect the appearance of the castings. These cracks can also lead to strains or deformations in the castings.
Mold cavity cracking: If the mold cavity has large cracks, it will prevent the casting from correctly forming. This indicates significant damage to the mold and hampers the casting process.
Mold parting surface collapse: When the parting surface of the mold collapses, it results in various defects. This condition severely reduces die-casting efficiency and requires extensive post-processing of the castings, leading to increased workload.
Ways to extend the die-casting mold lifespan
There are various ways to extend the service life of die-casting moulds, which should be mainly from four aspects: mould material selection, mould design, mould manufacturing, mould use and maintenance.
We have already discussed the material selection above, so we will not repeat it here.
Die-casting mold design
The design of the die-casting mold plays a significant role in determining its lifespan. A well-designed mold can significantly enhance the longevity of the die-casting process. Therefore, it is better to aspects below during the mold design phase, considering the characteristics of the casting:
Increase mold strength: We need to ensure that the mold is designed with ample strength and rigidity to withstand the mechanical and thermal stresses it experiences throughout the die-casting process. This can involve using high-quality materials, optimizing the mold structure, and reinforcing critical areas prone to stress concentration.
Enhance cooling system design: Pay close attention to the mold cooling system design to effectively control the temperature during the casting process. Optimize the layout and size of cooling channels, ensure uniform cooling throughout the mold, and use advanced cooling techniques such as conformal cooling to improve cooling efficiency and extend mold life.
Incorporate wear-resistant materials: Consider using wear-resistant materials or coatings for mold components that are subjected to high wear, such as the cavity, core, and slides. These materials can improve the mold’s resistance to wear and extend its lifespan.
Optimize gating system design: The design of the gating system plays a crucial role in the quality of the casting and the life of the mold. Carefully design the sprue, runner, and gate to ensure a smooth and controlled flow of molten metal, minimize turbulence and air entrapment, and reduce the impact on the mold cavity.
Reduce stress concentration: Identify areas in the mold design where stress concentration may occur, such as sharp corners or sudden changes in cross-section. Modify the design by incorporating fillets, radii, or gradual transitions to distribute stresses more evenly and reduce the risk of failure.
Implement proper venting: Adequate venting is essential to release air and gases from the mold cavity during casting. Insufficient venting can lead to porosity, defects, and mold damage. Carefully design and place vents in appropriate locations to ensure proper venting without compromising the integrity of the mold.
Conduct mold flow analysis: Utilize mold flow simulation software to analyze and optimize the mold design before manufacturing. By conducting this process, we can identify potential issues such as flow imbalances, air entrapment, or excessive pressure, enabling us to make design adjustments that improve the service life and perfomance of the mold.
Regular maintenance and inspection: Establish a regular maintenance schedule for the die-casting mold, including cleaning, lubrication, and inspection. Regularly inspect the mold for signs of wear, damage, or fatigue and address any issues promptly to prevent further deterioration and extend the mold’s life.
The mold manufacturing process and the accuracy of mold manufacturing are crucial factors that impact the lifespan of molds. It is essential to prioritize and thoroughly address the different aspects that influence mold life during the manufacturing phase. By dedicating attention and efforts to these areas, we can enhance the durability of molds and extend their lifespan.
Improve mold manufacturing process, improve mold manufacturing precision
Improving the mold manufacturing process and enhancing mold manufacturing precision can positively impact mold life. The generation of internal stress during mold processing is a significant concern for die-casting molds. To improve mold life, it is necessary to minimize the occurrence of stress and promptly eliminate it. It’s possible to achieve this through careful planning of the process route, creating detailed process specifications, and adhering to precise processing procedures.
Strengthening quality management practices and raising the level of mold manufacturing is essential for improving mold life. Reducing the need for mold patch welding is particularly important, as the materials used for patch welding, the high temperatures involved, and the resulting internal stress can significantly influence mold durability. Die-casting mold manufacturers generally aim to avoid cavity patch welding, but if necessary, using hot welding methods and conducting stress-relieving tempering after welding can help enhance mold life.
Reducing the hard layer of electrical impulses on the mold surface
Reducing the hard layer of electrical impulses on the mold surface is an important consideration in mold manufacturing. When using electrical discharge machining (EDM) for mold cavity processing, a bright white layer and a metamorphic layer can form on the mold surface. This results in the mold surface being subjected to tensile stress. If the subsequent polishing process fails to remove the tension from the surface, the mold is likely to experience early cracking or failure once it enters production.
Research has shown that after EDM, the surface of the mold can have tensile stresses ranging from 700 to 1100 MPa. Additionally, there can be numerous micro-cracks on the mold surface when high electrical discharge machining currents are used. These factors contribute to the risk of early cracking or failure of the mold once it is put into production.
Mold assembly clearance is reasonable
Mold assembly clearance being reasonable is an important aspect of die-casting mold manufacturing. The die-casting process involves high temperatures, high speeds, and high pressures. If the die-casting mold assembly is not done correctly, it can lead to issues, which can cause mold damage and affect its lifespan.
In fact, assembling a die-casting mold is generally considered more challenging and critical than an injection mold. Due to the unique characteristics of the casting process, especially with large molds, the temperature field of the mold undergoes significant changes between die-casting production temperatures and room temperature. Therefore, a thorough understanding of the mold’s characteristics and the temperature field variations is necessary during the assembly process. This allows for targeted assembly adjustments to ensure a reasonable mold assembly gap.
The die-casting production can be carried out smoothly without issues like “water runout” or slider jamming by achieving a proper mold assembly clearance. This improves the reliability of the mold and extends its overall lifespan.
Mold use and maintenance
Clean up the scrap in the use of the mold in time to prevent the extrusion of the mold
We should clean up the scrap in the mold promptly to prevent damage. If the mold contains debris or scrap, particularly in the slider area, it can lead to the collapse or damage of the slider when the die-casting machine operates again. Therefore, please clean the mold and address the issue promptly to prevent further damage. Delaying repairs until after the mold is damaged can significantly impact its lifespan.
Minimize cooling and heating of the mold and try to produce continuously
Minimizing the cooling and heating cycles of the mold and aiming for continuous production is beneficial for extending the mold lifespan. The reciprocal thermal expansion and contraction experienced by the die-casting mold during the process, with temperature fluctuations ranging from 220°C to 450°C, can lead to fatigue damage. Starting production with a cold mold results in increased temperature differences, mold expansion and contraction, and corresponding fatigue, accelerating mold damage and shortening its lifespan. Therefore, it is advisable to strive for continuous production and minimize mold cooling and heating cycles to prolong its life.
Furthermore, when the mold is in a cold state and hasn’t reached the average production temperature, it is essential to avoid opening high-speed pressure injection and pressurization. Opening these processes with a large mold gap can cause waste or debris to enter critical areas of the mold, such as slider and top bar holes, leading to mold damage and negatively impacting its lifespan.
Regular mold maintenance
Regular mold maintenance and servicing are crucial for ensuring the longevity and performance of die-casting molds. Due to the demanding conditions of high pressure, high speed, and high temperature during continuous production, die-casting molds are prone to damage, failures, and hidden issues. Therefore, it is essential to strengthen mold maintenance practices, including regular inspections, maintenance routines, and replacement of damaged or worn-out parts. Cleaning the slide, ejector hole, and other critical areas is also necessary. By prioritizing mold maintenance, die-casting enterprises can ensure the reliability of the mold during production and extend its overall service life.
Furthermore, mold life control is of utmost importance. I look forward to discussing mold life control in detail and appreciate your support and motivation in this matter!