Key Factors Influencing Mold Service Life in the Fabrication of Plate Heat Exchanger Plates

Abstract: Plate heat exchangers (PHEs) are widely applied in industrial fields such as petrochemicals, food processing, HVAC, and power generation due to their high heat transfer efficiency, compact structure, and flexible scalability. The plate, as the core component of PHEs, is mainly formed by stamping, bending, or roll forming, and its quality and production efficiency are directly determined by the performance and service life of the mold. The service life of PHE plate molds is affected by multiple interrelated factors, including mold material properties, mold design level, manufacturing process precision, forming process parameters, and daily use and maintenance. Irrational control of any of these factors will lead to premature mold failure, such as wear, cracking, deformation, and sticking, which increases production costs, reduces production efficiency, and affects the dimensional accuracy of PHE plates. This paper systematically classifies and analyzes the key factors influencing the service life of PHE plate molds, explores the mechanism of each factor affecting mold life, combines practical engineering cases to verify the impact degree of different factors, and puts forward corresponding optimization suggestions. The research shows that mold material selection, structural design, heat treatment process, forming process parameters, and maintenance level are the most critical factors: reasonable material selection and heat treatment can improve mold hardness and toughness, reducing wear and fatigue failure; scientific structural design can avoid stress concentration and extend service life; precise manufacturing process ensures mold dimensional accuracy and surface quality; optimized forming parameters reduce mold load; and standardized maintenance delays mold degradation. This study provides a theoretical basis and practical guidance for extending the service life of PHE plate molds, reducing production costs, and improving the quality stability of PHE plates.

Keywords: Plate heat exchanger plate; Mold service life; Mold material; Structural design; Manufacturing process; Forming parameters; Maintenance

Plate heat exchangers are essential heat transfer equipment in modern industrial production, which realize heat exchange between two or more media through the alternating flow of fluids on both sides of corrugated plates. The PHE plate, with its thin thickness (usually 0.3–1.5 mm), complex corrugated structure, and high dimensional precision requirements, relies heavily on high-precision molds for forming. The mold is not only the core tool for plate forming but also a key factor affecting production efficiency and product quality. The service life of PHE plate molds is usually evaluated by the number of forming strokes: under normal working conditions, high-quality molds can complete 200,000–500,000 forming strokes, while inferior molds or molds affected by unreasonable factors may fail after only 50,000–150,000 strokes.

Premature mold failure will bring serious economic losses to enterprises: on the one hand, the replacement of molds increases the cost of mold manufacturing (accounting for 20–30% of the total production cost of PHE plates); on the other hand, the downtime caused by mold replacement reduces production efficiency, and the dimensional deviation of plates produced during mold failure may lead to product scrapping. According to industry statistics, more than 60% of PHE plate mold failures are caused by improper control of key influencing factors, rather than natural wear and tear. Therefore, clarifying the key factors affecting mold service life and mastering their impact mechanisms are of great significance for optimizing mold design, improving manufacturing process, standardizing operation and maintenance, and extending mold service life.

At present, existing research on PHE plate molds mainly focuses on mold design optimization and forming process improvement, but there is a lack of systematic sorting and in-depth analysis of the factors affecting mold service life. In practical production, many enterprises ignore the comprehensive impact of multiple factors, leading to short mold service life and unstable product quality. For example, some enterprises choose inappropriate mold materials to reduce costs, resulting in rapid mold wear; some ignore the heat treatment process, leading to insufficient mold hardness and toughness and easy cracking; some do not standardize the forming parameters, increasing mold load and accelerating fatigue failure.

This paper comprehensively sorts out the key factors influencing the service life of PHE plate molds, divides them into five categories: mold material factors, mold design factors, mold manufacturing process factors, forming process parameters, and use and maintenance factors. It analyzes the impact mechanism of each factor in detail, verifies it with engineering cases, and puts forward targeted optimization suggestions. This study aims to provide a comprehensive reference for enterprises to improve mold service life and reduce production costs.

The material of PHE plate molds directly determines their mechanical properties (hardness, toughness, wear resistance, corrosion resistance) and thermal properties (thermal conductivity, thermal fatigue resistance), which is the material basis for ensuring mold service life. PHE plate molds are usually subjected to cyclic loads such as stamping force, friction, and thermal stress during operation, so the mold material must have excellent comprehensive performance. The key material factors affecting mold service life include material type, chemical composition, and heat treatment quality.

The selection of PHE plate mold materials is closely related to the forming process of the plate (cold stamping, hot stamping, roll forming) and the material of the plate (stainless steel, titanium alloy, aluminum alloy). Different materials have significant differences in hardness, toughness, wear resistance, and other properties, which directly affect the mold's ability to resist wear and fatigue.

Common PHE plate mold materials include cold work mold steel, hot work mold steel, and alloy steel, each with its own applicable scenarios and performance characteristics:

Cold work mold steel (such as Cr12MoV, Cr12, D2) is widely used in cold stamping molds for PHE plates (the most common forming process). It has high hardness (HRC 60–65 after heat treatment), excellent wear resistance, and good dimensional stability, which can effectively resist the friction and wear between the mold and the plate during cold stamping. However, its toughness is relatively poor, and it is prone to brittle fracture under large impact loads. For example, when stamping thick stainless steel plates (thickness > 1.0 mm), if the impact force is too large, Cr12MoV mold may crack prematurely. According to engineering statistics, the service life of Cr12MoV cold stamping molds for 316L stainless steel plates is usually 150,000–250,000 strokes under reasonable use conditions.

Hot work mold steel (such as H13, H11, 4Cr5MoSiV1) is suitable for hot stamping molds of high-hardness plate materials (such as titanium alloy, high-strength stainless steel). It has good high-temperature strength, thermal fatigue resistance, and toughness, and can maintain stable performance under cyclic heating and cooling conditions (forming temperature 800–1200°C). For example, H13 steel mold can withstand the high-temperature impact during titanium alloy plate hot stamping, and its service life can reach 200,000–300,000 strokes. However, the cost of hot work mold steel is higher than that of cold work mold steel, which increases the initial investment of molds.

Alloy steel (such as 42CrMo, 35CrMo) is often used for mold bases or non-critical mold components. It has good toughness and mechanical strength, but its wear resistance is poor, so it is not suitable for mold cavities that directly contact the plate. If alloy steel is used for the mold cavity, the wear rate will increase by 30–50%, and the service life will be reduced to less than 100,000 strokes.

In addition, the application of new materials such as ceramic materials and composite materials in PHE plate molds has gradually increased. Ceramic molds have excellent wear resistance and corrosion resistance, but their toughness is poor and they are prone to breakage; composite materials (such as steel-based ceramic composite materials) combine the advantages of high toughness of steel and high wear resistance of ceramics, which can extend the mold service life by 1.5–2 times, but their manufacturing cost is high, and they are currently only used in high-end PHE plate production.

The chemical composition of mold materials directly affects their mechanical properties and heat treatment effect. The key elements in mold steel include carbon (C), chromium (Cr), molybdenum (Mo), vanadium (V), and silicon (Si), and their content ratio has a significant impact on the performance of the mold:

Carbon (C) is the main element determining the hardness and wear resistance of mold steel. The higher the carbon content, the higher the hardness and wear resistance of the steel, but the lower the toughness. For cold work mold steel, the carbon content is usually 1.0–1.5%, which balances hardness and toughness; for hot work mold steel, the carbon content is 0.3–0.5%, which ensures high-temperature strength and toughness.

Chromium (Cr) can improve the wear resistance, corrosion resistance, and hardenability of mold steel. The addition of Cr can form carbides (Cr7C3) in the steel, which enhances the wear resistance. For example, Cr12MoV steel contains 11–13% Cr, which has excellent wear resistance. However, excessive Cr will increase the brittleness of the steel, making it prone to cracking during heat treatment.

Molybdenum (Mo) and vanadium (V) can refine the grain of mold steel, improve its toughness and thermal stability, and reduce the tendency of heat treatment deformation. Mo can also improve the high-temperature strength of hot work mold steel, while V can form hard vanadium carbides, further enhancing wear resistance. For example, H13 steel contains 1.0–1.5% Mo and 0.8–1.2% V, which has good thermal fatigue resistance and dimensional stability.

Silicon (Si) and manganese (Mn) can improve the hardenability and strength of mold steel, but excessive content will reduce the toughness of the steel. For example, excessive Si will make the steel brittle, and excessive Mn will increase the tendency of heat treatment cracking.

Impurity elements (such as sulfur (S), phosphorus (P)) in mold steel will seriously affect the service life of the mold. S will form low-melting sulfides, which reduce the wear resistance and toughness of the steel; P will cause brittleness of the steel, making it prone to cracking under impact loads. Therefore, the content of S and P in high-quality mold steel should be controlled below 0.03%.

Heat treatment is a key process to improve the mechanical properties of mold materials, and its quality directly determines the hardness, toughness, and wear resistance of the mold. The common heat treatment processes for PHE plate molds include annealing, quenching, tempering, and surface treatment. Improper heat treatment will lead to defects such as insufficient hardness, uneven hardness, cracks, and deformation of the mold, which seriously shorten the service life.

Annealing is mainly used to eliminate the internal stress of the mold blank, reduce hardness, and improve machinability. If the annealing temperature is too low or the holding time is insufficient, the internal stress of the mold blank cannot be completely eliminated, which will lead to deformation or cracking during subsequent machining and use. If the annealing temperature is too high, the grain of the steel will grow, reducing the toughness of the mold.

Quenching and tempering are the core heat treatment processes to improve the comprehensive performance of the mold. Quenching is to heat the mold steel to the austenitizing temperature (850–1050°C), keep it warm for a certain time, and then cool it rapidly (water cooling, oil cooling) to obtain martensite, thereby improving the hardness and wear resistance of the mold. Tempering is to heat the quenched mold to a certain temperature (150–600°C), keep it warm, and then cool it slowly to eliminate the internal stress generated during quenching, improve toughness, and reduce brittleness. The matching of quenching and tempering parameters is crucial: if the quenching temperature is too high, the mold will be overheated, resulting in grain coarsening and brittleness; if the cooling rate is too fast, the mold will crack; if the tempering temperature is too low, the internal stress cannot be eliminated, and the mold is prone to brittle fracture; if the tempering temperature is too high, the hardness of the mold will decrease, and the wear resistance will be reduced.

Surface treatment is an important means to improve the wear resistance and corrosion resistance of the mold surface. Common surface treatment processes include nitriding, chrome plating, and laser cladding. Nitriding can form a hard nitride layer (hardness HRC 70–80) on the mold surface, which significantly improves wear resistance and corrosion resistance, and the mold service life can be extended by 50–100%. Chrome plating can form a smooth and hard chrome layer on the mold surface, reducing friction and wear, but the chrome layer is easy to peel off if the plating process is improper. Laser cladding can deposit a high-hardness alloy layer on the mold surface, which has good bonding force with the base material and can effectively repair worn mold surfaces, extending the service life of old molds.

According to engineering cases, the service life of molds with qualified heat treatment is 2–3 times that of molds with unqualified heat treatment. For example, a PHE manufacturer once used Cr12MoV mold without proper tempering, resulting in the mold hardness being too high (HRC 68) and poor toughness. The mold cracked after only 80,000 stamping strokes; after re-heat treatment (quenching at 950°C, tempering at 200°C), the mold hardness was adjusted to HRC 62–64, and the service life was extended to 220,000 strokes.

Mold design is the core link determining the stress distribution, load-bearing capacity, and service life of the mold. Scientific and reasonable mold design can avoid stress concentration, reduce mold load, and improve the uniformity of force and heat distribution, thereby extending service life. On the contrary, unreasonable design will lead to local overloading, rapid wear, and premature cracking of the mold. The key design factors affecting mold service life include structural design, dimensional accuracy design, and cooling system design.

The structural design of PHE plate molds mainly includes cavity structure, guide structure, ejection structure, and mold base structure. The rationality of these structures directly affects the force state of the mold during operation.

The cavity structure is the core part of the mold, which directly forms the corrugated shape of the PHE plate. The PHE plate has a complex corrugated structure (such as herringbone, horizontal, and vertical corrugations), so the cavity structure is also relatively complex. The key points of cavity design affecting mold life are as follows: (1) Corner design: Sharp corners in the cavity will cause stress concentration, and the stress at the sharp corner can reach 5–10 times the average stress, which is easy to initiate cracks. Therefore, the corners of the cavity should be designed with rounded corners (radius R ≥ 0.5 mm) to disperse stress. (2) Corrugation structure design: The corrugation height, pitch, and angle of the cavity should be consistent with the plate design requirements, and the transition between corrugations should be smooth to avoid local stress concentration. For example, if the transition between corrugations is too steep, the mold will be subjected to uneven force during stamping, leading to local wear and deformation. (3) Cavity thickness design: The cavity thickness should be reasonable to ensure sufficient rigidity and strength. If the thickness is too thin, the mold will be deformed under stamping force; if the thickness is too thick, it will increase the weight of the mold and the cost of manufacturing.

The guide structure is used to ensure the precise alignment of the upper and lower molds during stamping, avoiding misalignment and collision. Common guide structures include guide pillars and guide sleeves. The design of the guide structure should ensure sufficient rigidity and positioning accuracy: (1) The guide pillars and guide sleeves should be made of high-hardness materials (such as GCr15) and subjected to heat treatment to improve wear resistance. (2) The fit clearance between the guide pillar and the guide sleeve should be reasonable (0.01–0.03 mm). If the clearance is too large, the positioning accuracy will be reduced, leading to mold collision; if the clearance is too small, the friction resistance will be increased, leading to wear of the guide structure. (3) The number and layout of guide pillars should be reasonable. For large PHE plate molds, at least 4 guide pillars should be arranged symmetrically to ensure uniform force.

The ejection structure is used to eject the formed plate from the mold cavity. The rationality of the ejection structure affects the friction between the plate and the mold, and thus the mold wear. The key points of ejection structure design are: (1) The ejection force should be uniform to avoid local excessive force leading to plate deformation and mold wear. (2) The ejection point should be arranged at the position where the plate is in close contact with the mold (such as the edge of the plate, the bottom of the corrugation) to ensure that the plate is ejected smoothly. (3) The surface of the ejector pin should be smooth to reduce friction with the plate. If the ejector pin is not smooth, it will scratch the plate and the mold cavity, accelerating wear.

The mold base structure is the support of the mold, which bears the stamping force during operation. The mold base should have sufficient rigidity and strength to avoid deformation under large stamping force. The key points of mold base design are: (1) The mold base material should be selected according to the stamping force. For large PHE plate molds (plate size > 1000 mm * 500 mm), alloy steel (such as 42CrMo) should be used for the mold base to ensure rigidity. (2) The thickness of the mold base should be reasonable. If the thickness is insufficient, the mold base will be deformed, leading to misalignment of the upper and lower molds and mold damage. (3) The connection between the mold base and the mold cavity should be firm to avoid relative movement during stamping.

The dimensional accuracy and surface quality of the mold directly affect the forming quality of the PHE plate and the service life of the mold. The PHE plate has high dimensional accuracy requirements (tolerance ±0.1–0.3 mm for key dimensions such as corrugation height and pitch), so the mold must have higher dimensional accuracy (tolerance ±0.05–0.1 mm).

If the mold dimensional accuracy is insufficient, the following problems will occur: (1) The formed plate has dimensional deviation, which cannot meet the assembly requirements of the PHE. (2) The gap between the upper and lower molds is uneven, leading to uneven force during stamping, local overloading, and rapid mold wear. (3) The fit between the mold and the plate is too tight or too loose. Too tight fit increases friction and wear; too loose fit leads to incomplete forming, requiring repeated stamping, which increases mold load.

The surface quality of the mold (surface roughness, flatness) also has a significant impact on service life. The surface of the mold cavity should be smooth (Ra ≤ 0.4 μm) to reduce friction between the plate and the mold, reduce wear, and prevent the plate from sticking to the mold. If the surface roughness of the mold cavity is too high (Ra ≥ 1.6 μm), the friction coefficient will increase by 30–50%, and the wear rate of the mold will increase significantly. In addition, the flatness of the mold surface should be high to ensure uniform contact between the mold and the plate during stamping, avoiding local stress concentration.

For hot stamping molds and high-speed cold stamping molds, the cooling system design is crucial to extend service life. During the forming process, the mold will generate a lot of heat due to friction and plastic deformation of the plate. If the heat cannot be dissipated in time, the mold temperature will rise sharply, leading to thermal fatigue, deformation, and wear.

The key points of cooling system design are: (1) The cooling channel layout should be uniform, covering the entire mold cavity, to ensure uniform cooling of the mold and avoid local overheating. For complex corrugated cavities, the cooling channel should be arranged along the corrugation direction to ensure that each part of the cavity is cooled evenly. (2) The cooling medium (water, oil) flow rate should be reasonable. The flow rate should be high enough to take away the heat generated by the mold, but too high flow rate will increase energy consumption and noise. (3) The cooling channel diameter should be appropriate (8–12 mm). If the diameter is too small, the channel is easy to block, affecting cooling effect; if the diameter is too large, the mold structure strength will be reduced.

For example, a manufacturer of titanium alloy PHE plates once used a hot stamping mold without a reasonable cooling system. During high-speed stamping, the mold temperature rose to 300°C, leading to thermal deformation of the cavity and reduced dimensional accuracy of the plate. After adding a uniform cooling channel (flow rate 5–8 L/min), the mold temperature was controlled below 150°C, the thermal fatigue phenomenon was significantly reduced, and the mold service life was extended from 120,000 strokes to 250,000 strokes.

The manufacturing process of PHE plate molds directly determines the dimensional accuracy, surface quality, and internal structure of the mold, and thus affects its service life. Even if the mold material and design are reasonable, improper manufacturing process will lead to mold defects (such as cracks, inclusions, uneven hardness), which will shorten the service life. The key manufacturing process factors affecting mold service life include machining accuracy, surface treatment process, and assembly accuracy.

The machining process of PHE plate molds includes turning, milling, grinding, EDM (Electrical Discharge Machining), and wire cutting. Each machining process has strict requirements on accuracy, and improper operation will lead to mold defects.

Grinding is a key process to ensure the dimensional accuracy and surface quality of the mold. The grinding accuracy directly affects the flatness and surface roughness of the mold cavity. If the grinding process is improper, the following problems will occur: (1) Grinding burns: Due to excessive grinding speed or insufficient cooling, the mold surface will be heated to a high temperature, leading to changes in the surface structure of the steel, reducing hardness and toughness, and increasing wear rate. (2) Grinding cracks: Due to excessive grinding force or uneven cooling, internal stress will be generated on the mold surface, leading to microcracks. These microcracks will expand under cyclic stamping force, leading to mold fracture. (3) Dimensional deviation: Improper grinding parameters (such as grinding wheel speed, feed rate) will lead to dimensional deviation of the mold cavity, affecting the forming quality of the plate and increasing mold load.

EDM and wire cutting are commonly used to process complex cavity structures (such as corrugations) of PHE plate molds. The key points of these processes are: (1) The processing accuracy should be controlled within ±0.01–0.02 mm to ensure the dimensional accuracy of the cavity. (2) The surface roughness after processing should be low (Ra ≤ 0.8 μm). If the surface roughness is too high, it needs to be polished, otherwise, it will increase friction and wear. (3) The processing parameters (such as pulse width, current) should be reasonable to avoid surface defects such as pitting and cracks.

In addition, the machining sequence also affects the mold quality. The reasonable machining sequence should be: blanking → annealing → rough machining → quenching and tempering → finish machining → surface treatment. If the machining sequence is improper (such as finish machining before heat treatment), the mold will be deformed during heat treatment, leading to dimensional deviation.

As mentioned earlier, surface treatment can improve the wear resistance and corrosion resistance of the mold, but improper surface treatment process will lead to surface defects, which will reduce the service life of the mold.

For nitriding treatment, the key points are: (1) The mold surface should be clean and free of oil, rust, and other impurities before nitriding, otherwise, the nitriding layer will be uneven and the bonding force will be poor. (2) The nitriding temperature and holding time should be reasonable. If the temperature is too high or the time is too long, the nitriding layer will be too thick and brittle; if the temperature is too low or the time is too short, the nitriding layer will be too thin and the wear resistance will be insufficient.

For chrome plating treatment, the key points are: (1) The mold surface should be polished to Ra ≤ 0.2 μm before plating, otherwise, the chrome layer will have defects such as bubbles and peeling. (2) The plating solution concentration and current density should be controlled to ensure the uniformity and thickness of the chrome layer. The chrome layer thickness is usually 0.01–0.03 mm. If the thickness is too thick, the chrome layer will be brittle and easy to peel off; if the thickness is too thin, the wear resistance will be insufficient.

For laser cladding treatment, the key points are: (1) The cladding material should be compatible with the base material to ensure good bonding force. (2) The cladding parameters (laser power, scanning speed) should be reasonable to avoid defects such as pores and cracks in the cladding layer.

The assembly accuracy of the mold directly affects the force state of the mold during operation. Improper assembly will lead to misalignment of the upper and lower molds, uneven gap, and local overloading, which will accelerate mold wear and failure.

The key points of mold assembly are: (1) The guide pillars and guide sleeves should be assembled accurately, and the fit clearance should be uniform. (2) The upper and lower mold cavities should be aligned accurately, and the gap between the cavities should be consistent with the plate thickness (plus shrinkage). (3) The ejection structure should be assembled smoothly, and the ejector pin should be flush with the mold cavity surface to avoid scratching the plate and the mold. (4) The connection parts (such as bolts, pins) should be tightened firmly to avoid relative movement during stamping.

According to engineering practice, the service life of molds with qualified assembly accuracy is 1.5–2 times that of molds with unqualified assembly. For example, a PHE manufacturer once assembled the mold with misaligned guide pillars, leading to uneven gap between the upper and lower molds. The mold was worn seriously after only 100,000 strokes; after re-assembly and adjusting the guide structure, the mold service life was extended to 220,000 strokes.

The forming process parameters of PHE plates (such as stamping force, stamping speed, forming temperature, and lubrication conditions) directly affect the load and wear of the mold. Unreasonable forming parameters will increase the mold load, accelerate wear and fatigue, and shorten service life. The key forming process parameters affecting mold service life are as follows.

Stamping force is the main load borne by the mold during cold stamping. The stamping force should be matched with the plate material and thickness. If the stamping force is too large, the mold will be subjected to excessive pressure, leading to plastic deformation, wear, and even cracking; if the stamping force is too small, the plate cannot be formed completely, requiring repeated stamping, which increases the number of mold strokes and accelerates fatigue.

The stamping force is related to the plate material (hardness, yield strength), thickness, and mold structure. For example, stamping a 1.0 mm thick 316L stainless steel plate requires a stamping force of 500–800 kN. If the stamping force is increased to 1000 kN, the mold wear rate will increase by 40–60%, and the service life will be reduced by half.

Stamping speed also affects the mold service life. High stamping speed can improve production efficiency, but it will increase the impact load on the mold, leading to increased wear and fatigue. For cold stamping, the stamping speed is usually 10–30 strokes per minute. If the speed is increased to 40–50 strokes per minute, the mold fatigue life will be reduced by 30–50%. In addition, high stamping speed will generate a lot of friction heat, which will increase the mold temperature and accelerate thermal wear.

Forming temperature is a key parameter for hot stamping of PHE plates. The forming temperature should be controlled within the appropriate range of the plate material. If the temperature is too high, the plate material will be overheated, leading to increased friction with the mold, and the mold will be subjected to high-temperature oxidation and thermal fatigue, accelerating wear and deformation; if the temperature is too low, the plate material toughness will be reduced, requiring larger stamping force, which increases the mold load.

For example, hot stamping of titanium alloy plates requires a forming temperature of 800–950°C. If the temperature is increased to 1000°C, the mold surface will be oxidized, the wear resistance will be reduced, and the service life will be reduced by 40%; if the temperature is reduced to 700°C, the stamping force needs to be increased by 30%, leading to increased mold wear.

For cold stamping, the ambient temperature and mold temperature also affect the service life. If the ambient temperature is too low (below 0°C), the toughness of the mold steel will be reduced, and it is prone to brittle fracture; if the mold temperature is too high (above 80°C), the wear resistance of the mold will be reduced, and the plate is easy to stick to the mold.

Lubrication is an important measure to reduce friction between the mold and the plate, reduce wear, and extend mold service life. During stamping, the lubricant can form a lubricating film between the mold and the plate, reducing the friction coefficient, reducing wear, and preventing the plate from sticking to the mold.

The key points of lubrication conditions are: (1) The type of lubricant should be suitable for the plate material and forming process. For cold stamping of stainless steel plates, oil-based lubricants (such as mineral oil + additive) should be used, which have good lubricity and cooling performance; for hot stamping, high-temperature resistant lubricants (such as graphite-based lubricants) should be used, which can maintain lubricity at high temperatures. (2) The lubricant dosage should be reasonable. Too little lubricant cannot form a complete lubricating film, leading to increased friction; too much lubricant will cause waste and affect the forming quality of the plate. (3) The lubrication frequency should be appropriate. For high-speed stamping, lubrication should be carried out every 10–20 strokes to ensure the lubricating effect.

If the lubrication conditions are poor, the friction coefficient between the mold and the plate will increase significantly, leading to severe wear, scoring, and galling of the mold. For example, a PHE manufacturer once reduced the lubricant dosage to save costs, leading to the friction coefficient between the mold and the plate increasing from 0.15 to 0.35. The mold was worn seriously after only 90,000 strokes; after restoring the normal lubricant dosage, the mold service life was extended to 210,000 strokes.

The daily use and maintenance of PHE plate molds directly affect their service life. Even high-quality molds will have premature failure if they are not used and maintained properly. The key use and maintenance factors affecting mold service life include operation standardization, regular inspection, cleaning, and maintenance and repair.

Standardized operation is the basis for ensuring the normal operation of the mold. Operators should strictly follow the operating procedures to avoid improper operation leading to mold damage.

The key points of standardized operation are: (1) Before starting the machine, check the mold alignment, guide structure, ejection structure, and lubrication conditions to ensure that all parts are normal. (2) During stamping, monitor the mold operation status in real time, and stop the machine immediately if abnormal phenomena (such as abnormal noise, mold jamming, plate deformation) are found to avoid further damage to the mold. (3) After stamping, clean the mold surface in time to remove residual lubricant, plate debris, and other impurities. (4) Avoid overloading the mold, such as stamping plates thicker than the design thickness or materials harder than the design requirements.

Improper operation is one of the main causes of premature mold failure. For example, an operator once used a mold to stamp a plate thicker than the design thickness (1.2 mm instead of 1.0 mm), leading to excessive stamping force and mold cavity deformation. The mold was scrapped after only 50,000 strokes.

Regular inspection can find potential defects of the mold in time, and take measures to repair them, avoiding the expansion of defects and extending service life. The inspection cycle should be determined according to the mold usage frequency: for high-frequency use (more than 200 strokes per day), the inspection should be carried out once a week; for low-frequency use, the inspection should be carried out once a month.

The key points of regular inspection are: (1) Check the mold cavity for wear, scratches, and cracks. If slight wear or scratches are found, polish them in time; if cracks are found, stop using the mold and repair it. (2) Check the guide structure for wear and fit clearance. If the wear is serious or the clearance is too large, replace the guide pillars and guide sleeves. (3) Check the ejection structure for jamming and wear. If the ejector pin is worn or stuck, replace or repair it. (4) Check the mold base for deformation and connection parts for looseness. If deformation is found, correct it; if connection parts are loose, tighten them.

Cleaning and maintenance are important measures to slow down mold degradation. After each use, the mold should be cleaned thoroughly to remove residual lubricant, plate debris, and other impurities, which can avoid the corrosion and wear of the mold surface.

The key points of cleaning and maintenance are: (1) Use a soft brush or cloth to clean the mold cavity and surface, avoiding hard tools (such as steel wire brushes) that scratch the mold surface. (2) After cleaning, apply a layer of anti-rust oil to the mold surface to prevent rust. (3) For molds that are not used for a long time, store them in a dry, ventilated, and corrosion-free environment, and check them regularly (once every 3 months) to ensure that they are in good condition.

When the mold has slight wear, scratches, or other defects, it should be repaired in time to avoid the expansion of defects. Common repair methods include polishing, welding, and re-machining.

Polishing is used to repair slight wear and scratches on the mold surface. The polishing should be carried out with fine sandpaper or polishing paste to ensure that the mold surface is smooth after repair. Welding is used to repair mold cracks or local wear. The welding material should be compatible with the mold material, and the welding process should be reasonable to avoid welding defects (such as pores, cracks). Re-machining is used to repair mold dimensional deviation or serious wear, and the re-machining accuracy should meet the design requirements.

It should be noted that the number of mold repairs should not be too many. Each repair will remove a certain amount of mold material, reducing the strength and service life of the mold. Generally, the number of repairs should not exceed 3 times.

To further verify the impact of various factors on the service life of PHE plate molds, this paper analyzes two practical engineering cases, clarifies the main factors leading to premature mold failure, and verifies the effectiveness of optimization measures.

A PHE manufacturer used a Cr12 mold to cold stamp 316L stainless steel plates (thickness 0.8 mm). The designed service life of the mold was 180,000 strokes, but the mold was severely worn after only 80,000 strokes, and the formed plate had dimensional deviation, which could not meet the requirements.

Analysis of the causes: (1) Improper material selection: Cr12 steel has high hardness but poor toughness and wear resistance compared with Cr12MoV steel. For 316L stainless steel plate stamping, Cr12MoV steel should be selected. (2) Poor lubrication conditions: The manufacturer used water-based lubricant, which has poor lubricity and cannot form a stable lubricating film between the mold and the plate, leading to increased friction and wear. (3) Insufficient heat treatment: The mold was only quenched without tempering, leading to high hardness (HRC 68) and poor toughness, and the mold surface was prone to wear.

Optimization measures: (1) Replace the mold material with Cr12MoV steel, and perform quenching (950°C) and tempering (200°C) heat treatment to adjust the hardness to HRC 62–64. (2) Replace the lubricant with oil-based lubricant (mineral oil + molybdenum disulfide additive) to improve lubricity. (3) Strengthen regular inspection and cleaning, and polish the mold surface every 10,000 strokes.

After optimization, the mold service life was extended to 230,000 strokes, which was 1.9 times the original service life, and the dimensional accuracy of the formed plate was significantly improved.

A manufacturer used a hot stamping mold to produce titanium alloy PHE plates. The mold cracked after only 60,000 strokes, leading to production interruption.

Analysis of the causes: (1) Unreasonable structural design: The corners of the mold cavity were designed as sharp corners (R = 0.2 mm), leading to stress concentration. Under cyclic hot stamping force, cracks were initiated at the sharp corners. (2) Unreasonable forming parameters: The forming temperature was 1000°C (higher than the recommended 800–950°C), leading to high mold temperature and serious thermal fatigue. The stamping speed was 40 strokes per minute (higher than the recommended 15–25 strokes per minute), increasing the impact load on the mold. (3) Poor cooling system design: The cooling channel was unevenly arranged, leading to local overheating of the mold.

Optimization measures: (1) Modify the cavity corner design, increase the rounded corner radius to R = 0.8 mm to disperse stress. (2) Adjust the forming parameters: reduce the forming temperature to 900°C, and reduce the stamping speed to 20 strokes per minute. (3) Optimize the cooling system, rearrange the cooling channel to ensure uniform cooling, and increase the cooling medium flow rate to 7 L/min.

After optimization, the mold service life was extended to 220,000 strokes, and no cracking phenomenon occurred during use.

The service life of PHE plate molds is affected by multiple interrelated factors, which can be divided into five categories: mold material factors, mold design factors, mold manufacturing process factors, forming process parameters, and use and maintenance factors. Each factor plays a crucial role in the service life of the mold:

Mold material factors are the foundation. The type, chemical composition, and heat treatment quality of the material directly determine the mechanical properties and thermal properties of the mold. Reasonable material selection and heat treatment can improve the hardness, toughness, and wear resistance of the mold, reducing premature failure.

Mold design factors are the key. Scientific structural design, dimensional accuracy design, and cooling system design can avoid stress concentration, reduce mold load, and improve the uniformity of force and heat distribution, thereby extending service life.

Mold manufacturing process factors are the guarantee. Precise machining, reasonable surface treatment, and high assembly accuracy ensure the dimensional accuracy, surface quality, and internal structure of the mold, avoiding manufacturing defects that affect service life.

Forming process parameters are external factors. Optimized stamping force, stamping speed, forming temperature, and lubrication conditions can reduce mold load and wear, slowing down fatigue failure.

Use and maintenance factors are the key to extending service life. Standardized operation, regular inspection, cleaning, and timely maintenance and repair can find potential defects in time, slow down mold degradation, and extend service life.

Engineering cases show that by optimizing these key factors, the service life of PHE plate molds can be extended by 1.5–2.5 times, reducing production costs and improving production efficiency. In practical production, enterprises should comprehensively consider these factors, combine the specific requirements of PHE plate production (material, size, forming process), formulate targeted optimization schemes, and strengthen the management of mold design, manufacturing, use, and maintenance to maximize the service life of molds.

In the future, with the development of PHE technology, the requirements for plate quality and production efficiency will be higher and higher, and the mold will face more severe working conditions. Therefore, it is necessary to further study the impact mechanism of various factors on mold service life, develop new mold materials and manufacturing processes, and optimize the design and maintenance system to provide more reliable support for the development of the PHE industry.