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In the cold heading forming process system, hexagonal punches, as key tooling, play a decisive role in the forming accuracy, production efficiency, and die life of the hexagonal features of fasteners. This article professionally analyzes its technical points from the dimensions of material science, application scenarios, and operation and maintenance specifications, providing theoretical and practical support for precision cold heading production.
I. Material Selection and Heat Treatment: The Cornerstone of Precision and Service Life
(I) Adaptation of Matrix Materials
Hexagonal punches need to withstand high contact stress (≥1000MPa), metal flow friction, and periodic impact loads. The mainstream choice is W6Mo5Cr4V2 high - speed steel (containing 0.8 - 0.9% carbon, 6% tungsten, and 5% molybdenum). Its red hardness can reach 600°C, and its hardness (HRC62 - 65) and wear resistance are suitable for cold heading of M8 - M24 specification bolts. For high - strength bolts (grade 12.9 and above), Cr12MoV cold - working die steel (containing 1.45 - 1.70% carbon and 11.0 - 12.5% chromium) becomes the first choice for punches with complex cavities due to its good compressive strength (≥2500MPa) and hardenability.
(II) Optimization of Heat Treatment Processes
- Quenching: Use a salt - bath furnace for preheating at 820 - 850°C and quenching at 1210 - 1230°C, and control the cooling rate by oil cooling (or graded quenching) to make the martensitic structure uniformly refined and improve the hardness uniformity.
- Tempering: Perform tempering three times at 550 - 570°C, 1 - 2 hours each time, to eliminate quenching stress, stabilize the structure. After tempering, the hardness drops back to HRC60 - 63, taking into account both toughness and wear resistance.
- Surface Strengthening: Nitriding treatment (at 500 - 550°C for 3 - 5 hours of heat preservation) forms a 0.02 - 0.05mm nitrided layer with a hardness of HV1000 - 1200, reducing metal adhesion. Or use PVD coating (TiAlN coating with a thickness of 2 - 4μm) with a friction coefficient of ≤0.3, significantly improving anti - adhesion and wear resistance.
II. Application Scenarios and Adaptation Logic: Accurately Matching Production Requirements
(I) Standard Fastener Production Lines
In the cold heading line of GB/T 5782 hexagon head bolts, the punch must strictly follow the mechanical performance requirements of GB/T 3098.1, and control the hexagon opposite - side dimension tolerance (±0.02mm) and diagonal deviation (≤0.03mm). For M10 bolts, the depth of the punch cavity needs to match the blank upsetting ratio (usually ≤2.5) to ensure sufficient metal flow and avoid folding defects. In multi - station cold heading machines, it needs to cooperate with the preceding cutting die and upsetting die. By simulating the metal flow line with CAD/CAM, optimize the cavity transition fillet (R0.2 - R0.5mm) to reduce stress concentration.
(II) Customization of Special - shaped Hexagonal Parts
For titanium alloy hexagonal fasteners in the aerospace field (such as HB 1 bolts with safety holes), due to the high material strength (σb≥900MPa) and low plasticity, the punch needs to adopt a variable - cross - section cavity design. The entrance cone angle is 15 - 20° to guide metal flow, and the cavity surface roughness is ≤Ra0.4μm to reduce friction. For large - size hexagonal nuts (opposite - side S≥30mm) used in new energy vehicle battery packs, it is necessary to customize multi - piece combined punches. By controlling the metal flow rate through segmented forming, solve the problem of die cracking caused by excessive forming force (≥5000kN) of a single punch.
III. Operation and Maintenance Specifications: The Key to Ensuring Precision and Service Life
(I) Cleaning and Lubrication Control
- Cleaning: Use ultrasonic cleaning (frequency 40kHz, cleaning fluid is a neutral water - based cleaning agent) to remove residual metal debris in the cavity (especially the adhesion after cold heading of titanium alloys and stainless steels). After cleaning, blow dry with compressed air (pressure 0.4 - 0.6MPa) to avoid rust.
- Lubrication：Select forming oil according to the material. For carbon steel cold heading, use oil products with sulfur - containing extreme pressure agents (sulfur content 1.5 - 2.5%), and for stainless steel, use chlorine - free type (chlorine content ≤0.1%). The lubricating film thickness is controlled at 5 - 10μm, and it is accurately applied through an online spraying system (spraying pressure 0.2 - 0.3MPa).
(II) Parameter Monitoring and Adjustment
- Pressure Monitoring: Use a pressure sensor (accuracy ±1%FS) to collect the cold heading force in real - time. When the load fluctuation exceeds 10%, check the blank diameter tolerance (±0.05mm) and die clearance (≤0.03mm).
- Temperature Control: Use an infrared thermometer (response time ≤50ms) to monitor the surface temperature of the punch. When it exceeds 250°C, adjust the equipment cooling system (flow rate ≥10L/min) or reduce the production beat (≤60 pieces/min) to avoid temper softening.
(III) Preventive Maintenance Strategies
- Accuracy Detection: Every 50,000 pieces produced, use a coordinate measuring machine (accuracy ±0.002mm) to detect the hexagon opposite - side dimension and cavity wear (depth direction ≤0.1mm).
- Repair Process: For local wear, use laser cladding (power 800 - 1200W, cladding layer thickness 0.2 - 0.5mm). After repair, perform grinding and polishing (Ra≤0.4μm) to restore accuracy. After the overall service life expires, through die remanufacturing (re - quenching and nitriding), the reuse rate can reach more than 70%.
As the core tooling in the cold heading process, the technological iteration of hexagonal punches is deeply related to the precision and high - efficiency development of the fastener industry. From the scientific combination of material selection, to the accurate adaptation of application scenarios, and then to the digital management and control of the operation and maintenance system, each link requires professional technical support. Mastering its core technical logic can achieve a dual breakthrough in die life and product quality in high - strength and high - precision cold heading production, providing reliable basic component guarantees for high - end manufacturing.
In the cold heading forming process system, hexagonal punches, as key tooling, play a decisive role in the forming accuracy, production efficiency, and die life of the hexagonal features of fasteners. This article professionally analyzes its technical points from the dimensions of material science, application scenarios, and operation and maintenance specifications, providing theoretical and practical support for precision cold heading production.
I. Material Selection and Heat Treatment: The Cornerstone of Precision and Service Life
(I) Adaptation of Matrix Materials
Hexagonal punches need to withstand high contact stress (≥1000MPa), metal flow friction, and periodic impact loads. The mainstream choice is W6Mo5Cr4V2 high - speed steel (containing 0.8 - 0.9% carbon, 6% tungsten, and 5% molybdenum). Its red hardness can reach 600°C, and its hardness (HRC62 - 65) and wear resistance are suitable for cold heading of M8 - M24 specification bolts. For high - strength bolts (grade 12.9 and above), Cr12MoV cold - working die steel (containing 1.45 - 1.70% carbon and 11.0 - 12.5% chromium) becomes the first choice for punches with complex cavities due to its good compressive strength (≥2500MPa) and hardenability.
(II) Optimization of Heat Treatment Processes
- Quenching: Use a salt - bath furnace for preheating at 820 - 850°C and quenching at 1210 - 1230°C, and control the cooling rate by oil cooling (or graded quenching) to make the martensitic structure uniformly refined and improve the hardness uniformity.
- Tempering: Perform tempering three times at 550 - 570°C, 1 - 2 hours each time, to eliminate quenching stress, stabilize the structure. After tempering, the hardness drops back to HRC60 - 63, taking into account both toughness and wear resistance.
- Surface Strengthening: Nitriding treatment (at 500 - 550°C for 3 - 5 hours of heat preservation) forms a 0.02 - 0.05mm nitrided layer with a hardness of HV1000 - 1200, reducing metal adhesion. Or use PVD coating (TiAlN coating with a thickness of 2 - 4μm) with a friction coefficient of ≤0.3, significantly improving anti - adhesion and wear resistance.
II. Application Scenarios and Adaptation Logic: Accurately Matching Production Requirements
(I) Standard Fastener Production Lines
In the cold heading line of GB/T 5782 hexagon head bolts, the punch must strictly follow the mechanical performance requirements of GB/T 3098.1, and control the hexagon opposite - side dimension tolerance (±0.02mm) and diagonal deviation (≤0.03mm). For M10 bolts, the depth of the punch cavity needs to match the blank upsetting ratio (usually ≤2.5) to ensure sufficient metal flow and avoid folding defects. In multi - station cold heading machines, it needs to cooperate with the preceding cutting die and upsetting die. By simulating the metal flow line with CAD/CAM, optimize the cavity transition fillet (R0.2 - R0.5mm) to reduce stress concentration.
(II) Customization of Special - shaped Hexagonal Parts
For titanium alloy hexagonal fasteners in the aerospace field (such as HB 1 bolts with safety holes), due to the high material strength (σb≥900MPa) and low plasticity, the punch needs to adopt a variable - cross - section cavity design. The entrance cone angle is 15 - 20° to guide metal flow, and the cavity surface roughness is ≤Ra0.4μm to reduce friction. For large - size hexagonal nuts (opposite - side S≥30mm) used in new energy vehicle battery packs, it is necessary to customize multi - piece combined punches. By controlling the metal flow rate through segmented forming, solve the problem of die cracking caused by excessive forming force (≥5000kN) of a single punch.
III. Operation and Maintenance Specifications: The Key to Ensuring Precision and Service Life
(I) Cleaning and Lubrication Control
- Cleaning: Use ultrasonic cleaning (frequency 40kHz, cleaning fluid is a neutral water - based cleaning agent) to remove residual metal debris in the cavity (especially the adhesion after cold heading of titanium alloys and stainless steels). After cleaning, blow dry with compressed air (pressure 0.4 - 0.6MPa) to avoid rust.
- Lubrication：Select forming oil according to the material. For carbon steel cold heading, use oil products with sulfur - containing extreme pressure agents (sulfur content 1.5 - 2.5%), and for stainless steel, use chlorine - free type (chlorine content ≤0.1%). The lubricating film thickness is controlled at 5 - 10μm, and it is accurately applied through an online spraying system (spraying pressure 0.2 - 0.3MPa).
(II) Parameter Monitoring and Adjustment
- Pressure Monitoring: Use a pressure sensor (accuracy ±1%FS) to collect the cold heading force in real - time. When the load fluctuation exceeds 10%, check the blank diameter tolerance (±0.05mm) and die clearance (≤0.03mm).
- Temperature Control: Use an infrared thermometer (response time ≤50ms) to monitor the surface temperature of the punch. When it exceeds 250°C, adjust the equipment cooling system (flow rate ≥10L/min) or reduce the production beat (≤60 pieces/min) to avoid temper softening.
(III) Preventive Maintenance Strategies
- Accuracy Detection: Every 50,000 pieces produced, use a coordinate measuring machine (accuracy ±0.002mm) to detect the hexagon opposite - side dimension and cavity wear (depth direction ≤0.1mm).
- Repair Process: For local wear, use laser cladding (power 800 - 1200W, cladding layer thickness 0.2 - 0.5mm). After repair, perform grinding and polishing (Ra≤0.4μm) to restore accuracy. After the overall service life expires, through die remanufacturing (re - quenching and nitriding), the reuse rate can reach more than 70%.
As the core tooling in the cold heading process, the technological iteration of hexagonal punches is deeply related to the precision and high - efficiency development of the fastener industry. From the scientific combination of material selection, to the accurate adaptation of application scenarios, and then to the digital management and control of the operation and maintenance system, each link requires professional technical support. Mastering its core technical logic can achieve a dual breakthrough in die life and product quality in high - strength and high - precision cold heading production, providing reliable basic component guarantees for high - end manufacturing.
