A burr removal process and mold for cold forgings

Abstract

This invention relates to the field of cold forging die technology, and discloses a burr removal process and die for cold forgings. The process includes: machining an array of microgrooves on the sidewall of a metal cutter and coating it with a modified fluorinated polyimide coating to form a surface micro-groove structure with liquid storage capacity; using a micro-lubrication system to spray cutting fluid droplets into the microgrooves; and during the punching process, utilizing the physical extrusion force generated by the deformation of the aluminum material being processed to directionally release the cutting fluid to the cutting interface. The corresponding die consists of an upper die, a lower die, and a micro-lubrication system with a piezoelectric micro-pump, and the electromagnetic control valve and the limit switch are interlocked. This invention, through the synergistic effect of the surface micro-nano structure and the functional coating, achieves precise delivery and physical extrusion release of the lubricating medium in the enclosed cutting space, effectively suppressing the formation of built-up edge, improving the surface smoothness of the aluminum material cut, and extending the tool life.

Description

Technical Field

[0001] This invention relates to the field of cold forging die technology, specifically to a burr removal process and die for cold forgings. Background Technology

[0002] In existing aluminum cold forging production processes, burr removal is typically achieved through punching. Due to the significant adhesion properties of aluminum alloys, aluminum chips easily adhere to the tool surface during punching and rapidly accumulate, forming built-up edge. This phenomenon not only compromises the dimensional accuracy and surface finish of the workpiece cut, leading to tearing or burring, but also accelerates tool sidewall wear and shortens die life.

[0003] Existing lubrication methods mainly rely on external spraying or manual application of lubricating oil. However, during actual cutting operations, the closed cutting interface formed between the tool and the workpiece is under high pressure. Under this instantaneous high-pressure environment, the externally sprayed lubricating medium is difficult to effectively penetrate deep into the cutting edge interface due to the air resistance generated by cutting heat and the repulsion of the contact surface pressure, resulting in the tool sidewall being in a state of insufficient lubrication for a long time.

[0004] Furthermore, traditional fluid supply systems often fail to achieve precise time synchronization and spatial alignment with the movement of the stamping press. Due to the lack of effective linkage control methods, continuous spraying or high-flow-rate fluid supply is usually the only option. This results in a significant loss of lubricant during non-working hours, leading not only to material waste and increased production costs, but also to severe oil contamination of the workpiece surface and working environment, increasing the difficulty of subsequent workpiece cleaning. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a burr removal process and mold for cold forgings, which solves the problems of built-up edge caused by material adhesion during the punching process of aluminum cold forgings, difficulty in the penetration of lubricating medium into the closed cutting space, and resource waste and workpiece contamination caused by inaccurate supply of traditional lubrication methods.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a burr removal process for cold forgings, employing the following technical solution: A burr removal process for cold forgings includes the following steps: Mold preparation: Take a metal cutter and process an array of microgrooves on the retraction sidewall of the metal cutter. Apply a modified fluorinated polyimide precursor solution to the sidewall of the metal cutter with microgrooves and the surface of the contoured part. After gradient temperature curing, a fluorinated polyimide coating is formed on the sidewall of the metal cutter and the surface of the contoured part. The cured coating has a surface micro-groove structure on the sidewall of the metal cutter.

[0007] Deburring: Fix the metal cutter and the contoured part to the upper and lower dies respectively, and set the single-sided punching gap between the metal cutter and the contoured part; use a micro-lubrication system to atomize the water-based composite anti-sticking punching fluid into droplets and spray it onto the side wall of the metal cutter, controlling the droplet size to be smaller than the width of the micro-groove, and the droplets gather in the surface micro-groove structure; start the machine to press down and punch, the metal cutter cuts into the aluminum material being processed, squeezes the punching fluid in the surface micro-groove structure to the cutting interface, and performs alternating cutting in both longitudinal and transverse directions. After the cutting is completed, the slider returns to its original position.

[0008] By adopting the above technical solution, the present invention achieves the following physical process in terms of lubrication and anti-sticking: Construction of the surface liquid storage space: An array of microgrooves serves as a macroscopic liquid storage pool, while the fluorinated polyimide coating covering it undergoes physical shrinkage during curing due to solvent evaporation and molecular chain rearrangement. This results in depressions at the microgroove openings, creating a micron-scale surface micro-valve structure. This structure can capture atomized cutting droplets through capillary force, preventing the lubricating medium from being lost under stamping inertia.

[0009] Physical extrusion release mechanism: At the moment of punching, the metal cutter cuts into the aluminum material, and the aluminum material generates normal pressure towards the sidewall under violent deformation. This pressure acts directly on the elastic fluorinated polyimide coating, forcing the punching fluid hidden inside the micro-grooves to be released directionally to the high-temperature, high-pressure cutting front interface, just like being squeezed out of a sponge. This breaks the limitation of traditional spray lubrication, which is difficult to enter the closed cutting space.

[0010] Low surface energy anti-sticking synergy: The fluorinated polyimide coating itself has extremely low surface free energy, which forms a liquid film support with the water-based composite anti-sticking punching fluid. After physical extrusion, the residual liquid film can effectively prevent aluminum chips from chemically bonding or physically welding with the cutting substrate, thus inhibiting the generation of built-up edge from the root.

[0011] Preferably, the water-based composite anti-sticking die-cutting fluid is made from raw materials comprising the following mass percentages: polyethylene glycol 15.0%-30.0%; sulfurized fatty acid ester 2.0%-8.0%; surfactant 3.0%-10.0%; sodium silicate 0.5%-3.0%; and the balance being deionized water; the surfactant is a compound of fatty alcohol polyoxyethylene ether and alkyl glycoside in a mass ratio of 1:1.

[0012] By employing the above technical solution, polyethylene glycol provides the basic film-forming properties, while the sulfurized fatty acid esters undergo thermal decomposition under the high temperatures generated by instantaneous punching, releasing active sulfur atoms that react with the metal surface to form a low-shear-strength sulfurized metal film. The composite surfactant reduces the interfacial tension of the system, enabling the punching fluid to possess excellent wetting and spreading properties in micron-level trenches.

[0013] Preferably, the preparation method of the water-based composite anti-sticking punching fluid includes the following steps: Based on a total mass of 100%, polyethylene glycol, sulfurized fatty acid esters, and surfactants are added to a preparation vessel and stirred at 300-400 rpm. The system temperature is controlled to rise to 45.0-55.0℃ and held at a constant temperature for 15 minutes to obtain a transparent oil phase. Sodium silicate is completely dissolved in deionized water to form a homogeneous aqueous phase; Maintain the temperature of the oil phase and the stirring speed in the preparation vessel, and use a metering pump to uniformly add the aqueous phase to the transparent oil phase at a flow rate of 1.0-2.0 L / min; After the aqueous phase is added, heating is stopped, the original stirring speed is maintained, and the mixture is allowed to cool naturally to 25.0℃ to obtain a microemulsion system with droplet size distribution of 100-500nm.

[0014] By employing the above technical solution, the preparation process follows the phase inversion emulsification mechanism. Under specific temperature and low-speed stirring, as the aqueous phase is added at a uniform rate, the system transforms from an oil-in-water type to a water-in-oil type. Due to the spontaneous emulsification at the interface near the phase transition temperature, the final microemulsion particle size reaches the nanometer scale. This ensures that the cutting fluid, after atomization, can accurately penetrate the micrometer-scale surface micro-grooves without being blocked by the air cushion at the groove opening.

[0015] Preferably, the method for preparing the modified fluorinated polyimide precursor solution includes the following steps: Under nitrogen protection, N,N-dimethylacetamide was added to the reactor as a solvent, the system temperature was controlled at -5.0 to 5.0℃, and 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane monomer was added and stirred until completely dissolved. Under conditions maintained at -5.0 to 5.0℃, pyromellitic dianhydride solid powder with a molar ratio of 1:1 to the monomer was divided into 4 equal parts and added to the reaction system at a uniform rate according to a set time interval. After the feeding is complete, allow the reaction system to heat up naturally to 15.0-25.0℃, and maintain mechanical stirring for 12-24 hours to carry out the polymerization reaction, so as to obtain a polyamic acid precursor solution with a solid content of 10.0%-18.0% and a dynamic viscosity of 800-1200 cP.

[0016] By adopting the above technical solution, the reaction mechanism is the polycondensation reaction of diamine monomer and dianhydride monomer.

[0017] First, the fluorinated diamine monomer (hexafluoropropane structure) is fully dissolved in a polar solvent, providing hydrophobic groups for subsequent cyclization; Secondly, pyromellitic dianhydride is added in steps to control the local reactant concentration, preventing uneven molecular weight distribution or gelation caused by excessively rapid reaction, and ensuring the steady growth of polyamic acid segments. Finally, polymerization was completed at room temperature, and the resulting polyamic acid precursor had a moderate viscosity, which ensured both adhesion in the dip coating process and precise preservation of the microgroove morphology during subsequent curing and shrinkage.

[0018] Preferably, the extension direction of the array-type microgrooves forms an angle of 30°-45° with the die pressing and punching direction, and the width of the microgrooves is 15-30μm and the depth is 10-20μm.

[0019] By adopting the above technical solution, a specific tilt angle can be set to utilize the principles of fluid dynamics. When the cutter moves downward, the cutting fluid is not only subjected to vertical compression, but also generates a lateral force along the groove direction. This combined force state helps the lubricating film to spread more evenly throughout the entire length of the cut.

[0020] Preferably, in the deburring step, the machine slide moves the upper die equipped with a metal cutter downward at a speed of 15.0-45.0 mm / s. When the slide moves down to a distance of 5.0-8.0 mm from the product contact surface, the limit switch is triggered to start the micro-lubrication system to spray liquid.

[0021] By adopting the above technical solution, precise time and space linkage was established. Pre-spraying ensures that the surface micro-grooves are pre-filled with cutting fluid before physical contact occurs between the metal and the surface, avoiding initial damage caused by dry friction.

[0022] Secondly, the present invention provides a burr removal die for cold forgings, which adopts the following technical solution: A burr removal die for cold forgings, used to implement the aforementioned burr removal process for cold forgings, comprising: The upper mold is equipped with a metal cutter. The retraction sidewall of the metal cutter has an array of microgrooves, and the surface of the metal cutter is covered with a fluorinated polyimide coating with a surface microgroove structure. The lower mold is provided with a contouring part for fixing the workpiece to be processed, and the surface of the contouring part is covered with a fluorinated polyimide coating; A micro-lubrication system is installed on the side of the machine. The micro-lubrication system is equipped with a piezoelectric micro-pump. The atomizing nozzle of the micro-lubrication system is aligned with the retraction sidewall of the metal cutter. The electromagnetic control valve of the micro-lubrication system is electrically interlocked with the downward stroke switch of the machine slide.

[0023] By adopting the above technical solution, this invention achieves precise delivery and efficient utilization of the lubricating medium through the integration of mechanical structure and control system. The specific principle is as follows: The integrated storage and supply structure features a synergistic physical design: the retraction sidewall of the metal cutter is not a traditional smooth surface, but rather a microscopic liquid storage space constructed through an array of microgrooves and a fluorinated polyimide coating. The piezoelectric micro-pump, acting as the power core, overcomes the surface tension of the water-based composite anti-stick cutting fluid, converting the liquid into micron-sized droplets. The directional positioning of the atomizing nozzles ensures that the droplets accurately penetrate the micro-groove structure on the surface. This design alters the previous state of lubricant overflowing across the cutter surface, confining it to a tiny area closest to the cutting edge.

[0024] The dynamic lubrication mechanism achieved through signal interlocking: Mechanical motion is converted into a fluid supply trigger command through electrical signal interlocking between the electromagnetic control valve and the downward limit switch. When the slider reaches a specific height, the signal path is activated, triggering a piezoelectric pulse. This instantaneous fluid supply mechanism ensures that the formation of the lubricating film and the cutting action are highly coincident in time, preventing premature loss or delayed replenishment of lubricating fluid.

[0025] Contouring support and low-friction interface construction: The contouring parts on the lower die are also covered with a fluorinated polyimide coating. During the cutting process, there is high-pressure contact between the workpiece and the contouring parts. The high modulus and low coefficient of friction of the coating work together to reduce secondary scratches on the bottom and sides of the workpiece, and together with the sidewall lubrication of the metal cutter, a complete protective barrier is formed on the upper and lower surfaces of the workpiece.

[0026] This invention provides a burr removal process and mold for cold forgings. It has the following beneficial effects: 1. This invention constructs a micro-groove structure with liquid storage capacity on the surface of a metal cutter by machining an array of micro-grooves on the sidewall and coating it with a modified fluorinated polyimide coating. During the punching process, the punching fluid stored in the micro-grooves is directionally squeezed out to the cutting front interface by utilizing the physical extrusion force generated by the deformation of the aluminum material being processed. This achieves precise release of the lubricating medium in the closed cutting space, reducing interfacial friction resistance and cutting heat.

[0027] 2. The modified fluorinated polyimide coating used in this invention has low surface energy characteristics. Combined with a water-based cutting fluid containing sulfurized fatty acid esters and polyethylene glycol, a composite physical and chemical protective film is formed at the interface between the metal cutting tool and the aluminum material. This inhibits the physical welding and chemical adhesion of aluminum chips on the tool surface, thereby reducing the generation of built-up edge from the source, improving the surface smoothness of the cut of cold forgings, and extending the tool life.

[0028] 3. By setting the atomized droplet size to be smaller than the width of the microgroove and coordinating the signal interlock between the machine tool slider limit switch and the piezoelectric micro pump, the present invention achieves precise matching between the amount of lubricating medium dispensed and the dispensing time. Through the convergence of micro-droplets in the micro-groove structure on the surface, the lubrication state of the cutting interface can be maintained under low circulating liquid supply, reducing lubricant waste, lowering production costs, and reducing the burden of subsequent workpiece surface cleaning. Attached Figure Description

[0029] Figure 1 This is a top view of the mold of the present invention; Figure 2 This is a side view of the mold of the present invention; Figure 3 A bar chart comparing test data on the percentage of coating peeling area according to the present invention; Figure 4 A bar chart comparing test data for the maximum thickness of the edge buildup of the present invention; Figure 5 A line graph comparing test data on the occurrence rate of secondary tearing at the cut surface of the present invention; Figure 6 This is a line graph comparing the test data of the surface roughness Ra value of the cut surface in this invention.

[0030] Among them, 1. Upper mold; 11. Metal cutter; 111. Retracting sidewall; 2. Lower mold; 21. Contouring part. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the preparation examples, examples, comparative examples, test examples, and accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] Preparation Examples 1-6: Preparation Example 1: This preparation example provides a method for preparing a water-based composite anti-sticking cutting fluid, including the following steps: Based on a total mass of 100%, in a preparation vessel equipped with a heating jacket and mechanical stirrer, add 15.0% polyethylene glycol, 2.0% sulfurized fatty acid ester, and 3.0% surfactant (composed of fatty alcohol polyoxyethylene ether and alkyl glycoside in a mass ratio of 1:1). Turn on the mechanical stirrer, set the speed to 300 rpm, control the system temperature to 45.0℃, maintain the temperature for 15 minutes, and obtain a transparent oil phase. 0.5% sodium silicate was completely dissolved in 79.5% deionized water to form a homogeneous aqueous phase. The temperature of the oil phase in the preparation vessel was maintained at 45.0℃ and the stirring speed was 300 rpm. The aqueous phase was added dropwise to the oil phase at a flow rate of 1.0 L / min using a metering pump. After the aqueous phase is added, heating is stopped, stirring is maintained at the original speed, and the temperature is allowed to drop naturally to 25.0℃. The system undergoes a phase transition from water-in-oil to oil-in-water, and finally a microemulsion system with droplet size distribution of 100 to 500 nm is obtained.

[0033] Preparation Example 2: This preparation example provides a method for preparing a water-based composite anti-sticking cutting fluid, including the following steps: Based on a total mass of 100%, in a preparation vessel equipped with a heating jacket and mechanical stirrer, add 22.5% polyethylene glycol, 5.0% sulfurized fatty acid ester, and 6.5% surfactant (composed of fatty alcohol polyoxyethylene ether and alkyl glycoside in a mass ratio of 1:1). Turn on the mechanical stirrer, set the speed to 350 rpm, control the system temperature to 50.0℃, maintain the temperature for 15 minutes, and obtain a transparent oil phase. 1.75% sodium silicate was completely dissolved in 64.25% deionized water to form a homogeneous aqueous phase. The oil phase temperature in the preparation vessel was maintained at 50.0℃ and the stirring speed was 350 rpm. The aqueous phase was added dropwise to the oil phase at a flow rate of 1.5 L / min using a metering pump. After the aqueous phase is added, heating is stopped, stirring is maintained at the original speed, and the temperature is allowed to drop naturally to 25.0℃. The system undergoes a phase transition from water-in-oil to oil-in-water, and finally a microemulsion system with droplet size distribution of 100 to 500 nm is obtained.

[0034] Preparation Example 3: This preparation example provides a method for preparing a water-based composite anti-sticking cutting fluid, including the following steps: Based on a total mass of 100%, in a preparation vessel equipped with a heating jacket and mechanical stirrer, add 30.0% polyethylene glycol, 8.0% sulfurized fatty acid ester, and 10.0% surfactant (composed of fatty alcohol polyoxyethylene ether and alkyl glycoside in a mass ratio of 1:1). Turn on the mechanical stirrer, set the speed to 400 rpm, control the system temperature to 55.0℃, maintain the temperature for 15 minutes, and obtain a transparent oil phase. 3.0% sodium silicate was completely dissolved in 49.0% deionized water to form a homogeneous aqueous phase; the oil phase temperature in the preparation vessel was maintained at 55.0℃ and the stirring speed was 400 rpm, and the above aqueous phase was added dropwise to the oil phase at a flow rate of 2.0 L / min using a metering pump. After the aqueous phase is added, heating is stopped, stirring is maintained at the original speed, and the temperature is allowed to drop naturally to 25.0℃. The system undergoes a phase transition from water-in-oil to oil-in-water, and finally a microemulsion system with droplet size distribution of 100 to 500 nm is obtained.

[0035] Preparation Example 4: This preparation example provides a method for preparing a modified fluorinated polyimide precursor solution, including the following steps: In a clean reactor equipped with a mechanical stirrer, thermometer, and nitrogen gas inlet pipe, high-purity nitrogen gas is introduced to replace the environment. N,N-dimethylacetamide is added as a solvent, the refrigerant circulation is started, and the system temperature is controlled at -5.0℃. 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane monomer is added to the system and stirred until completely dissolved. Under the condition of maintaining -5.0℃, the pyromellitic dianhydride solid powder with a molar ratio of 1:1 to the above monomer was divided into 4 equal parts and added to the reaction system at a uniform rate of one part every 15 minutes. After the feeding is complete, turn off the coolant and allow the reaction system to heat up naturally to 15.0℃. Maintain mechanical stirring for 12 hours to carry out the polymerization reaction. After the reaction was completed, a polyamic acid precursor solution with a solid content of 10.0% was obtained, and its dynamic viscosity was measured to be 800 cP.

[0036] Preparation Example 5: This preparation example provides a method for preparing a modified fluorinated polyimide precursor solution, including the following steps: In a clean reactor equipped with a mechanical stirrer, thermometer, and nitrogen gas inlet pipe, high-purity nitrogen gas is introduced to replace the environment. N,N-dimethylacetamide is added as a solvent, the refrigerant circulation is started, and the system temperature is controlled at 0.0℃. 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane monomer is added to the system and stirred until completely dissolved. Under the condition of maintaining 0.0℃, the pyromellitic dianhydride solid powder with a molar ratio of 1:1 to the above monomer was divided into 4 equal parts and added to the reaction system at a uniform rate of one part every 15 minutes. After the feeding is complete, turn off the coolant and allow the reaction system to heat up naturally to 20.0℃. Maintain mechanical stirring for 18 hours to carry out the polymerization reaction. After the reaction was completed, a polyamic acid precursor solution with a solid content of 14.0% was obtained, and its dynamic viscosity was measured to be 1000 cP.

[0037] Preparation Example 6: This preparation example provides a method for preparing a modified fluorinated polyimide precursor solution, including the following steps: In a clean reactor equipped with a mechanical stirrer, thermometer, and nitrogen gas inlet pipe, high-purity nitrogen gas is introduced to replace the environment. N,N-dimethylacetamide is added as a solvent, the refrigerant circulation is started, and the system temperature is controlled at 5.0℃. 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane monomer is added to the system and stirred until completely dissolved. Under the condition of maintaining 5.0℃, the pyromellitic dianhydride solid powder with a molar ratio of 1:1 to the above monomer was divided into 4 equal parts and added to the reaction system at a uniform rate of one part every 15 minutes. After the feeding is complete, turn off the coolant and allow the reaction system to heat up naturally to 25.0℃. Maintain mechanical stirring for 24 hours to carry out the polymerization reaction. After the reaction was completed, a polyamic acid precursor solution with a solid content of 18.0% was obtained, and its dynamic viscosity was measured to be 1200 cP.

[0038] Examples 1-3: Example 1: This embodiment provides a burr removal process for cold forgings, including the following steps: Mold preparation: Take four metal cutting blades 11 from the upper mold 1, and use a laser marking device to process an array of microgrooves on the retraction sidewall 111 of each cutting blade. The extension direction of the microgrooves forms a 30° angle with the downward pressing and cutting direction of the mold. The width of the microgrooves is 15 μm and the depth is 10 μm. After ultrasonic degreasing, the cutting blades with microtextures are fixed on a lifting machine and vertically immersed in the modified fluorinated polyimide precursor solution prepared in Preparation Example 4. After staying for 30 seconds, the solution is moved at a speed of 2.0 mm / s. The cutter is pulled upwards at a constant speed to form a wet film coating with a thickness of 10.0 μm on the side wall of the cutter. The coated cutter is then placed in an oven for gradient temperature curing: the first stage is at 80°C for 30 minutes, the second stage is at 150°C for 60 minutes, and the third stage is at 250°C for 60 minutes. After curing, the coating retains a surface micro-groove structure with an effective depth of 5 μm on the side wall of the cutter. The same coating process is applied to the surface of the blade-shaped contoured part 21 of the lower mold 2. Deburring: Fix the four processed cutters to the workpiece clamping plate of the upper die 1, and fix the contour part 21 to the lower die 2. Set the single-sided punching gap between the cutters and the contour part 21 of the lower die 2 to 1.5% of the thickness of the aluminum material being processed, with an absolute value of 0.015mm. Install a micro-lubrication system with a piezoelectric micro-pump on the side of the machine, align the atomizing nozzle with the micro-textured area of ​​the four cutters, and interlock the electromagnetic control valve of the system with the downward stroke switch of the machine slide. Use a quick clamp to fix the cold-forged aluminum extrusion product with burrs to the lower die 2. On the contour part 21 of mold 2; start the machine, the slider drives the upper mold 1 pressure block to descend at a speed of 15.0 mm / s. When the slider descends to 5.0 mm away from the product contact surface, the limit switch is triggered. The piezoelectric pump uses 0.4 MPa air pressure to atomize the punching fluid prepared in Preparation Example 1 into droplets with a particle size of 5 μm and spray them onto the side wall of the cutter. The liquid supply volume for a single cycle is controlled to be 0.01 mL. The mold continues to press down and performs a total of 2 alternating cuts in the longitudinal and transverse directions. The time difference between the two cutting actions is limited to 0.05 s. After the cutting is completed, the slider is reset.

[0039] Example 2: This embodiment provides a burr removal process for cold forgings, including the following steps: Mold preparation: Take four metal cutting blades 11 from the upper mold 1, and use a laser marking device to process an array of microgrooves on the retraction sidewall 111 of each cutting blade. The extension direction of the microgrooves forms a 37.5° angle with the downward pressing and punching direction of the mold. The width of the microgrooves is 22.5 μm and the depth is 15 μm. After ultrasonic degreasing, the cutting blades with microtextures are fixed on a lifting machine and vertically immersed in the modified fluorinated polyimide precursor solution prepared in Preparation Example 5. After staying for 30 seconds, the solution is then applied at a speed of 3.5 mm / s. The cutter is pulled upwards at a constant speed (s) to form a wet film coating with a thickness of 20.0 μm on the sidewall of the cutter. The coated cutter is then placed in an oven for gradient temperature curing: the first stage is at 90°C for 45 minutes, the second stage is at 165°C for 75 minutes, and the third stage is at 285°C for 90 minutes. After curing, the coating retains a surface micro-groove structure with an effective depth of 7.5 μm on the sidewall of the cutter. The same coating process is applied to the surface of the blade-shaped contoured part 21 of the lower mold 2. Deburring: Fix the four processed cutters to the workpiece clamping plate of the upper die 1, and fix the contour part 21 to the lower die 2. Set the single-sided punching gap between the cutters and the contour part 21 of the lower die 2 to 2.5% of the thickness of the aluminum material being processed, with an absolute value of 0.0475mm. Install a micro-lubrication system with a piezoelectric micro-pump on the side of the machine, align the atomizing nozzle with the micro-textured area of ​​the four cutters, and interlock the electromagnetic control valve of the system with the downward stroke switch of the machine slide. Use a quick clamp to fix the cold-forged aluminum extrusion product with burrs to the lower die. On the contoured part 21 of 2; start the machine, the slider drives the upper die 1 pressure block to descend at a speed of 30.0 mm / s. When the slider descends to a distance of 6.5 mm from the product contact surface, the limit switch is triggered. The piezoelectric pump uses 0.5 MPa air pressure to atomize the punching fluid prepared in Preparation Example 2 into droplets with a particle size of 10 μm and spray them onto the side wall of the cutter. The liquid supply volume for a single cycle is controlled to be 0.025 mL. The die continues to press down and performs a total of 2 alternating cuts in both longitudinal and transverse directions. The time difference between the two cutting actions is limited to 0.125 s. After the cutting is completed, the slider is reset.

[0040] Example 3: This embodiment provides a burr removal process for cold forgings, including the following steps: Mold preparation: Take four metal cutting blades 11 from the upper mold 1, and use a laser marking device to process an array of microgrooves on the retraction sidewall 111 of each cutting blade. The extension direction of the microgrooves forms a 45° angle with the downward pressing and cutting direction of the mold. The width of the microgrooves is 30 μm and the depth is 20 μm. After ultrasonic degreasing, the cutting blades with microtextures are fixed on a lifting machine and vertically immersed in the modified fluorinated polyimide precursor solution prepared in Preparation Example 6. After staying for 30 seconds, the solution is then applied at a speed of 5.0 mm / s. The cutter is pulled upwards at a constant speed to form a wet film coating with a thickness of 30.0 μm on the side wall of the cutter. The coated cutter is then placed in an oven for gradient temperature curing: the first stage is at 100°C for 60 minutes, the second stage is at 180°C for 90 minutes, and the third stage is at 320°C for 120 minutes. After curing, the coating retains a surface micro-groove structure with an effective depth of 10 μm on the side wall of the cutter. The same coating process is applied to the surface of the blade-shaped contoured part 21 of the lower mold 2. Deburring: Fix the four processed cutters to the workpiece clamping plate of the upper die 1, and fix the contour part 21 to the lower die 2. Set the single-sided punching clearance between the cutters and the contour part 21 of the lower die 2 to 3.5% of the thickness of the aluminum material being processed, with an absolute value of 0.080 mm. Install a micro-lubrication system with a piezoelectric micro-pump on the side of the machine. Aim the atomizing nozzle at the micro-textured area of ​​the four cutters, and interlock the electromagnetic control valve of the system with the downward stroke switch of the machine slide. Use a quick clamp to fix the cold-forged aluminum extrusion product with burrs to the lower die. On the contoured part 21 of 2; start the machine, the slider drives the upper die 1 pressure block to descend at a speed of 45.0 mm / s. When the slider descends to 8.0 mm away from the product contact surface, the limit switch is triggered. The piezoelectric pump uses 0.6 MPa air pressure to atomize the punching fluid prepared in Preparation Example 3 into droplets with a particle size of 15 μm and spray them onto the side wall of the cutter. The liquid supply volume for a single cycle is controlled to be 0.05 mL. The die continues to press down and performs a total of 2 alternating cuts in the longitudinal and transverse directions. The time difference between the two cutting actions is limited to 0.20 s. After the cutting is completed, the slider is reset.

[0041] Comparative Examples 1-5: Comparative Example 1: Compared with Example 2, the difference is that the surface of the cutter and the contouring part 21 is not coated with a modified fluorinated polyimide coating, but is a normal bare steel surface; otherwise, they are the same.

[0042] The design of this proportionate effect is based on the following mechanism: the hexafluoroisopropyl groups in the F-PI coating molecular chain impart extremely low surface free energy to the flat regions. This causes minute amounts of cutting fluid droplets, upon contact with the cutting tool, to spontaneously converge and be stored within the microgrooves due to the repulsive guidance of the low surface energy. The absence of this coating would prevent droplets from being effectively repelled into the microgrooves and would also prevent the microemulsion phase change from confining the instantaneous surface temperature within the heat resistance threshold, thus affecting the interfacial thermodynamic anti-sticking synergistic effect.

[0043] Comparative Example 2: Compared with Example 2, the difference is that the cutter retraction sidewall 111 is not laser microtextured, but a modified fluorinated polyimide coating is directly applied to the smooth sidewall; otherwise, they are the same.

[0044] The design of this proportionally highlighted effect satisfies the following mechanism: Traditional cutting fluid pouring easily leads to fluid splashing and waste, and it is difficult to enter the cutting zone where the tool and workpiece are in close contact. In this invention, the droplet size of the pulsed atomization (5-15μm) is smaller than the width of the microgroove (15-30μm). This causes extremely small amounts (0.01-0.05mL) of cutting fluid droplets to come into contact with the tool, and under the guidance of capillary force, spontaneously converge and store in the microgroove valleys with a depth of 5-10μm, forming a micro reservoir. When the cutter moves down at a set speed to cut into the aluminum alloy burr, the deformed aluminum chips act as micro-pistons at the moment of contact with the sidewall. The compression of the aluminum chips causes the cutting fluid sealed in the microgroove to be squeezed out instantaneously by hydrodynamic pressure, targeting and delivering extreme pressure anti-wear agents such as sulfurized fatty acid esters in the microemulsion to the highest temperature and high pressure cutting front interface, where a tribochemical reaction occurs to generate a boundary adsorption film.

[0045] Comparative Example 3: Compared with Example 2, the difference is that in the deburring step, the pulse atomization of the micro-lubrication system is turned off, and the conventional high-flow-rate cutting fluid continuous pouring method (50mL / min) is used for fluid supply. All other aspects are the same.

[0046] The effect highlighted by this design follows a mechanism: at the high temperature during cutting, the microemulsion system undergoes reverse demulsification, releasing the base lubricating oil phase and extreme pressure agent encapsulated by surfactants. This phase change synergistic mechanism not only reduces the interfacial friction coefficient but also limits the instantaneous temperature of the F-PI coating surface within its heat resistance threshold, preventing thermomechanical fatigue of the polymer material. Excessive liquid volume would disrupt the microscopic confined thermodynamic equilibrium of instantaneous vaporization carrying away latent heat from cutting, and could even trigger severe thermal shock peeling of the polymer coating.

[0047] Comparative Example 4: Compared with Example 2, the difference is that the cutting fluid is not prepared by the phase transition temperature method, but is directly prepared by mechanical stirring at room temperature to produce a common macroscopic milky liquid with a particle size greater than 2 μm. All other aspects are the same.

[0048] The design of this comparative effect is based on the following mechanism: the microemulsion prepared by the PIT method has a dispersed phase particle size in the nanometer range of 100-500 nm. Compared with conventional coarse emulsions, it has extremely low steric hindrance, enabling rapid penetration and spreading along capillary grooves within a very short contact time (0.02-0.05 s). Excessively large coarse emulsion particle size would prevent the fluid from penetrating into the 5-10 μm coating grooves in such a short time.

[0049] Comparative Example 5: Compared with Example 2, the difference is that the single-sided punching gap between the cutter and the lower die 2 contour part 21 is set to 10.0% of the thickness of the aluminum material being processed (absolute value is 0.19mm), while all other aspects are the same.

[0050] The design of this proportionate effect is based on the following mechanism: aluminum alloy is relatively soft and prone to ductile tearing, resulting in secondary burrs. This process strictly defines the die's single-sided punching clearance within 1.5% to 3.5% of the material thickness. At this critical clearance, the micro-cracks generated at the moment of contact between the upper die 1 cutting edge and the lower die 2 contouring edge can propagate along the same coplanar plane within the aluminum material and precisely overlap. At this point, the shear stress on the material exceeds its ultimate shear strength at an extremely rapid speed, causing the excess burr waste to peel off through macroscopic brittle fracture (rather than plastic drawing), ultimately resulting in a smooth, crack-free cut surface in both the transverse and longitudinal directions.

[0051] Test Example 1-2: Test Example 1: Durability and Coating Anti-adhesion Performance Test in Mold Industry This test example is used to determine the durability and anti-adhesion effect of the dies prepared in each embodiment and comparative example under continuous punching conditions. The specific experimental steps are as follows: The molds prepared in each embodiment and comparative example were installed on a stamping test machine, and cold-forged aluminum extrusions of the same batch and grade were used as test substrates.

[0052] The upper and lower dies prepared in Examples 1 to 3 and Comparative Examples 1 to 5 were respectively mounted on a high-speed precision punch press with a nominal pressure of 1000 kN.

[0053] The workpiece is set to be a 5.0mm thick 6061-O state aluminum alloy sheet, and the sheet is fed into the punching station by a feeder.

[0054] Set the operating frequency of the punch press to 60 times / minute, start the punch press and the corresponding liquid supply system, and continuously perform 10,000 burr removal punching cycles.

[0055] After the stamping cycle is completed, the metal cutters of each set of upper dies are disassembled and vertically immersed in an ultrasonic cleaning tank containing anhydrous ethanol. They are ultrasonically cleaned for 5 minutes at room temperature to remove residual stamping fluid and unconsolidated free aluminum chips from the sidewalls.

[0056] After cleaning and drying, the metal cutter was placed under a white light interferometer and the microstructure of the retracted sidewall and cutting edge was observed using a scanning electron microscope. The maximum thickness of the built-up edge was measured in the normal direction of the cutting edge.

[0057] Obtain images of the sidewall morphology under a scanning electron microscope, extract the pixel boundaries of the coating peeling area using image processing software, and calculate the percentage of the coating peeling area to the total area of ​​the set observation area.

[0058] Table 1. Test results of durability and anti-adhesion performance of the die after 10,000 consecutive stamping cycles.

[0059] Note: "-" in the table indicates that the experiment was conducted without a coating, i.e., using a raw metal cutter without any surface treatment.

[0060] In summary, based on the data in Table 1, the maximum thickness of the edge build-up and the percentage of coating peeling area in the example group were significantly lower than those in the comparative group, with Example 2 showing the best overall performance.

[0061] Comparing Example 2 with Comparative Example 1, it can be seen that a conventional uncoated and microtextured bare tool undergoes severe physical metal bonding during continuous cutting of aluminum alloy, with a built-up edge thickness reaching 128.45 μm, indicating that this process has the fundamental necessity for anti-adhesion.

[0062] Compared with Comparative Example 2, Comparative Example 2, which only has a coating without the arrayed microgrooves, showed an increase in the percentage of peeling area and the thickness of built-up edge to 14.62% and 54.38 μm, respectively. This indicates that a coating with a smooth surface alone cannot retain cutting fluid in the high-pressure cutting zone. The failure of hydrodynamic lubrication leads to the damage of the coating due to direct dry friction, verifying the core fluid storage role of the microgroove structure constructed by the microgrooves in the passive extrusion release mechanism.

[0063] Compared with Comparative Example 2 and Comparative Example 3, after replacing the fluorinated polyimide with a conventional polyurethane coating, the peeling rate increased significantly to 38.71%. Due to the high surface free energy of polyurethane, it cannot work synergistically with water-based cutting fluid to form a low-shear protective film. The adhesion between aluminum chips and the substrate is greater than the coating adhesion, causing the coating to tear in pieces by the adhered aluminum chips.

[0064] Comparing Example 2 and Comparative Example 4, Comparative Example 4 used conventional high-flow-rate cutting fluid casting and turned off the micro-lubrication linkage, resulting in a built-up edge thickness of 73.19 μm. Due to the hydrodynamic repulsion effect of the enclosed space during punching, the macroscopically cast liquid could not penetrate into the cutting front. At the same time, the continuous high-flow-rate liquid cooling during the non-punching stage caused thermal shock to the coating, accelerating the fatigue peeling of the coating.

[0065] Comparing Example 2 and Comparative Example 5, Comparative Example 5 used a conventional large-particle-size emulsion, resulting in an increased built-up edge thickness of 39.64 μm. Large-particle-size droplets, hindered by surface tension and the air cushion within the microgrooves, could not effectively penetrate the micro-groove space, and insufficient filling of the reservoir directly weakened the compression lubrication effect during cutting. The microemulsion system of the examples, combined with pulsed atomization, achieved efficient penetration of nano-sized droplets into micron-sized spaces.

[0066] Test Example 2: Burr Removal Quality and Process Yield Test of Cold Forgings This test example is used to determine the edge deburring quality of cold-forged aluminum alloy products produced after continuous stamping operations in each embodiment and comparative example. The specific experimental steps are as follows: During the continuous punching operation of Test Example 1, from the 5000th to the 8000th punching cycle, 150 cold-forged aluminum alloy workpieces that had completed the burr removal process were randomly selected from each experimental group as test samples.

[0067] The extracted test samples were placed in an ultrasonic cleaning tank containing anhydrous ethanol for 5 minutes of ultrasonic cleaning. After cleaning, compressed air was used to dry the surface of the workpiece to remove residual trace amounts of cutting fluid and free metal dust adhering to the cut surface.

[0068] The shear profile of all cleaned test samples was observed one by one using an industrial-grade high-magnification stereomicroscope. The number of workpieces with secondary tearing burrs or visible microcracks at the punching edge was recorded, and the percentage of secondary tearing occurrence was calculated.

[0069] The flatness of the cut surface of the sample was measured using a contact surface roughness measuring instrument. Three measurement points were randomly selected on the cut surface of each workpiece, and probe scanning was performed along the direction perpendicular to the die pressing and punching. The roughness Ra value was recorded, and the arithmetic mean of all sample test points was calculated as the average roughness of the cross surface of the group.

[0070] Table 2. Test results of burr removal quality of cold forgings in each embodiment and comparative example.

[0071] In summary, based on the data in Table 2, the incidence of secondary tearing and the surface roughness Ra of the cut surface in the Example group were both lower than those in the Comparative Group. Example 2 demonstrated the best processing quality.

[0072] Comparing Example 2 with Comparative Example 1, Comparative Example 1, which used a common uncoated mold and traditional scraping process, showed a secondary tearing rate of up to 17.62% and an Ra value of 5.34 μm on the cut surface. This indicates that when processing highly adhesive aluminum materials, the intense friction and material adhesion at the cutting interface directly lead to microscopic tearing of the cut surface using traditional processes.

[0073] Compared with Comparative Example 2, Comparative Example 2 lacked an array-type microgroove liquid storage structure on the mold surface, resulting in a secondary tearing rate of 8.93%. The failure of hydrodynamic lubrication led to direct contact between the metal cutting edge and the aluminum material, increasing friction and causing uneven shear stress distribution, which in turn triggered local material tearing, resulting in a deterioration of the cut surface roughness to 3.28 μm.

[0074] Compared with Comparative Example 2, Comparative Example 3, which uses a conventional polyurethane coating, produced built-up edge due to insufficient anti-adhesion ability. The build-up edge fell off during the stamping process and caused secondary scratches on the aluminum material, resulting in a secondary tearing rate of 12.45% and a surface roughness of 4.15 μm.

[0075] Compared with Comparative Example 4, Comparative Example 4 used high-flow casting with the micro-lubrication linkage system turned off, resulting in a cut surface Ra value of 2.56 μm. The macroscopic cutting fluid could not break through the fluid boundary layer of the closed cutting zone to enter the shear interface, and the high temperature and high pressure state at the cutting tip was not effectively alleviated, affecting the smoothness of the cut surface.

[0076] Compared with Comparative Example 5, Comparative Example 5, which uses a macromechanical emulsion, had a secondary tearing rate of 5.07%. Large droplets, limited by the geometry of the microgrooves and the internal cavitation effect, could not fully fill the micro-grooves on the mold sidewalls, resulting in a reduction in the volume of the lubricating medium extruded to the cutting interface by deformation pressure.

[0077] The microemulsion in Example 2, combined with the nanoscale surface micro-groove structure, achieves dense coverage of the lubricating film during stamping, inhibiting interfacial welding and tearing, and ensuring the punching yield and surface quality of cold forgings.

[0078] This invention provides a burr removal die for cold forgings, with the following structure: The upper mold 1 is equipped with a metal cutter 11. The retraction sidewall 111 of the metal cutter 11 is machined with an array of microgrooves. The surface of the metal cutter 11 is covered with a fluorinated polyimide coating. Due to the volume shrinkage of the fluorinated polyimide coating during curing, depressions are formed in the fluorinated polyimide coating at the locations of the array of microgrooves, and these depressions constitute liquid storage spaces with a surface microgroove structure. The effective depth of the surface microgroove structure is 5-10 μm.

[0079] The lower die 2 is provided with a contouring part 21, which is used to support the cold-forged aluminum extrusion product to be processed. The surface of the contouring part 21 is covered with the fluorinated polyimide coating. A pre-defined single-sided punching gap is maintained between the metal cutter 11 and the contouring part 21.

[0080] The micro-lubrication system is installed on the side of the machine tool. The micro-lubrication system is powered by a piezoelectric micro-pump. The atomizing nozzle of the micro-lubrication system is aligned with the retraction sidewall 111 of the metal cutter 11. To synchronize the cutting and lubrication actions, the electromagnetic control valve of the micro-lubrication system is connected to the limit switch of the machine tool slider via a signal line.

[0081] During operation, the machine tool slider drives the upper die 1 downward. When the machine tool slider touches the limit switch, the limit switch generates an electrical signal and transmits it to the electromagnetic control valve. The electromagnetic control valve opens instantaneously, and the piezoelectric micro-pump drives the water-based composite anti-sticking cutting fluid to be sprayed out through the atomizing nozzle. The droplets formed by the water-based composite anti-sticking cutting fluid enter the surface micro-groove structure according to a set path. When the metal cutter 11 contacts and cuts into the aluminum material being processed, the physical pressure generated at the cutting interface forces the cutting fluid in the surface micro-groove structure to overflow, forming a lubricating film at the interface between the cutter and the workpiece.

Claims

1. A burr removal process for cold forgings, characterized in that, Includes the following steps: Mold preparation: Take a metal cutter (11), process an array of microgrooves on the retraction sidewall (111) of the metal cutter (11), and apply a modified fluorinated polyimide precursor solution to the sidewall of the metal cutter (11) with microgrooves and the surface of the contoured part (21). After gradient heating and curing, a fluorinated polyimide coating is formed on the sidewall of the metal cutter (11) and the surface of the contoured part (21), and the cured coating has a surface microgroove structure on the sidewall of the metal cutter (11). Deburring: Fix the metal cutter (11) and the contour part (21) to the upper mold (1) and the lower mold (2) respectively. Set the single-sided punching gap between the metal cutter (11) and the contour part (21). Use a micro-lubrication system to atomize the water-based composite anti-stick punching fluid into droplets and spray it onto the side wall of the metal cutter (11). Control the droplet size to be smaller than the width of the micro-groove. The droplets gather in the surface micro-groove structure. Start the machine to press down and punch. The metal cutter (11) cuts into the aluminum material to be processed, squeezes the punching fluid in the surface micro-groove structure to the cutting interface, and performs alternating cutting in both longitudinal and transverse directions. After the cutting is completed, the slider is reset.

2. The burr removal process for cold forgings according to claim 1, characterized in that, The water-based composite anti-sticking cutting fluid is made from raw materials comprising the following mass percentages: Polyethylene glycol 15.0%-30.0%; Sulfated fatty acid esters: 2.0%-8.0%; Surfactants 3.0%-10.0%; Sodium silicate 0.5%-3.0%; The remainder is deionized water; The surfactant is a compound of fatty alcohol polyoxyethylene ether and alkyl glycoside in a mass ratio of 1:

1.

3. The burr removal process for cold forgings according to claim 2, characterized in that, The preparation method of the water-based composite anti-sticking cutting fluid includes the following steps: Based on a total mass of 100%, the polyethylene glycol, sulfurized fatty acid ester, and surfactant are added to a preparation vessel and stirred at a speed of 300-400 rpm. The system temperature is controlled to rise to 45.0-55.0℃ and maintained at a constant temperature for 15 minutes to obtain a transparent oil phase. The sodium silicate is completely dissolved in the deionized water to form a homogeneous aqueous phase; Maintain the temperature of the oil phase and the stirring speed in the preparation vessel, and use a metering pump to uniformly add the aqueous phase to the transparent oil phase at a flow rate of 1.0-2.0 L / min; After the aqueous phase is added, heating is stopped, the original stirring speed is maintained, and the mixture is allowed to cool naturally to 25.0℃ to obtain a microemulsion system with droplet size distribution of 100-500nm.

4. The burr removal process for cold forgings according to claim 2, characterized in that, The preparation method of the modified fluorinated polyimide precursor solution includes the following steps: Under nitrogen protection, N,N-dimethylacetamide was added to the reactor as a solvent, the system temperature was controlled at -5.0 to 5.0℃, and 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane monomer was added and stirred until completely dissolved. Under conditions maintained at -5.0 to 5.0°C, pyromellitic dianhydride solid powder with a molar ratio of 1:1 to the monomer was divided into 4 equal parts and added to the reaction system at a uniform rate according to a set time interval. After the feeding is complete, allow the reaction system to heat up naturally to 15.0-25.0℃, and maintain mechanical stirring for 12-24 hours to carry out the polymerization reaction, so as to obtain a polyamic acid precursor solution with a solid content of 10.0%-18.0% and a dynamic viscosity of 800-1200 cP.

5. The burr removal process for cold forgings according to claim 1, characterized in that, In the mold preparation step, the extension direction of the array-type microgrooves forms an angle of 30°-45° with the mold pressing and punching direction, and the width of the microgrooves is 15-30μm and the depth is 10-20μm.

6. The burr removal process for cold forgings according to claim 1, characterized in that, The specific implementation method of the mold preparation step is as follows: After being degreased by ultrasonication, the metal cutter with microgrooves is vertically immersed in the modified fluorinated polyimide precursor solution. After remaining for 30 seconds, it is pulled upwards at a speed of 2.0-5.0 mm / s to form a wet film coating with a thickness of 10.0-30.0 μm. The parameters for coating curing are controlled as follows: first stage: 80-100℃ for 30-60 minutes; second stage: 150-180℃ for 60-90 minutes; third stage: 250-320℃ for 60-120 minutes. After curing, a surface micro-groove structure with an effective depth of 5-10μm is retained on the sidewall of the metal cutter.

7. The burr removal process for cold forgings according to claim 1, characterized in that, In the deburring step, the atomizing pressure of the micro-lubrication system is 0.4-0.6 MPa, the atomized droplet size is 5-15 μm, and the liquid supply volume per cycle is controlled to be 0.01-0.05 mL.

8. The burr removal process for cold forgings according to claim 1, characterized in that, In the deburring step, the single-sided punching gap is 1.5%-3.5% of the thickness of the aluminum material being processed.

9. The burr removal process for cold forgings according to claim 1, characterized in that, In the deburring step, the machine slide moves the upper die equipped with the metal cutter downward at a speed of 15.0-45.0 mm / s. When the slide moves to a distance of 5.0-8.0 mm from the product contact surface, the limit switch is triggered to start the micro-lubrication system to spray liquid. The alternating cutting is performed twice, and the time difference between the two cutting actions is limited to 0.05-0.20 s.

10. A burr removal die for cold forgings, characterized in that, A burr removal process for a cold forging as described in any one of claims 1-9 includes: The upper mold (1) is equipped with a metal cutter (11), the retraction sidewall (111) of the metal cutter (11) has an array of microgrooves, and the surface of the metal cutter (11) is covered with a fluorinated polyimide coating with a surface microgroove structure. The lower mold (2) is provided with a contour part (21) for fixing the workpiece to be processed, and the surface of the contour part (21) is covered with a fluorinated polyimide coating. A micro-lubrication system is installed on the side of the machine tool. The micro-lubrication system is equipped with a piezoelectric micro-pump. The atomizing nozzle of the micro-lubrication system is aligned with the retraction sidewall (111) of the metal cutter (11). The electromagnetic control valve of the micro-lubrication system is electrically interlocked with the downward stroke switch of the machine tool slider.

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