The core of machining external threads with a thread rolling machine is to use the rotation and compression of a pair (or three sets) of thread rolling wheels to cause plastic deformation of the metal surface of the workpiece, ultimately forming an external thread that meets specifications. The entire process must follow a closed-loop flow of preparation, debugging, machining, inspection, and maintenance. The core of machining external threads with a thread rolling machine is to use the rotation and compression of a pair (or three sets) of thread rolling wheels to cause plastic deformation of the metal surface of the workpiece, ultimately forming an external thread that meets specifications. The entire process must follow a closed-loop flow of "preparation, debugging, machining, inspection, and maintenance." The specific steps can be broken down into the following six major stages, each with clear operational points and quality control requirements:
1. Pre-machining preparation: Confirmation of basic conditions (a prerequisite for machining quality)
Before starting the equipment, the workpiece, tools, and equipment must be pre-checked and processed to avoid thread scrap or equipment failure due to insufficient pre-machining.
2. Workpiece pre-treatment
Thread rolling machines rely on the plastic deformation of metal to machine threads. The initial state of the workpiece directly affects the final accuracy and must meet three requirements:
Dimensional calibration is based on the thread specification. The workpiece's "original diameter" (the diameter of the cylinder before crimping) is typically 0.1-0.3mm smaller than the nominal thread diameter (e.g., for machining an M10x1.5 thread, the original diameter needs to be controlled at 9.7-9.8mm). Excessive deviation will result in an overly full or shallow thread profile. Surface treatment: Remove burrs, scale, and rust from the workpiece surface (sanding or pickling can be used) to prevent impurities from damaging the thread rolling wheel or causing scratches on the thread surface during extrusion; Material confirmation: Ensure the workpiece material is a ductile metal (such as carbon steel, stainless steel, aluminum alloy). Brittle materials (cast iron, ceramics) or steel with a hardness > HRC40 after quenching are prohibited (as they are prone to cracking or chipping of the thread rolling wheel).
1. Thread Rolling Wheel Selection and Installation The thread rolling wheel is the "core mold" for machining threads and must be perfectly matched to the target thread: 8. Specification matching: Select the corresponding thread rolling wheel according to the thread profile (metric, imperial, trapezoidal), pitch (such as 1.5mm, 2mm), and nominal diameter (e.g., machining...). For M8x1.25 threads, use M8-1.25° thread rolling wheels. During installation and calibration, install the thread rolling wheels on the "drive shaft" and "driven shaft" of the equipment respectively. Use a feeler gauge or calibration tool to adjust the parallelism (deviation 50.02mm) and radial clearance (adjusted to 0.1-0.2mm depending on the workpiece diameter) of the two wheels to ensure synchronous and smooth rotation.
Wear Inspection: Check the thread rolling wheel teeth for chipping or wear (can be observed with a magnifying glass). If the tooth tips are blunt or have gaps, replace the wheel (otherwise, it will result in a rough thread surface or incomplete tooth profile).
1. Equipment Parameters Parameter Settings
Based on the workpiece material, diameter, and thread specifications, set the key machining parameters:
Spindle speed: 200-300 r/min for soft materials (e.g., aluminum alloy), 100-150 r/min for hard materials (e.g., stainless steel) (excessive speed can easily lead to workpiece overheating and deformation);
Feed speed: Control the radial feed of the thread rolling wheel to the workpiece, typically 0.5-1 mm/s (too fast a feed can easily crack the workpiece, too slow a feed will reduce efficiency);
Extrusion stroke: Set the total feed stroke of the thread rolling wheel according to the thread length (e.g., for machining a 20mm long thread, the extrusion stroke should be set to 20-22mm, with a margin). 2mm "overtravel" ensures thread end integrity: Cooling and Lubrication: Turn on the cooling system to ensure that the cutting fluid (extreme pressure emulsion suitable for metal extrusion processing) is evenly sprayed on the contact area between the thread rolling wheel and the workpiece (cooling + lubrication, reducing wear and improving thread finish).
1. Trial Processing: Verifying Parameters and Quality (Critical Step Before Mass Production) Before formal mass production, 1-2 pieces need to be "trial processed" to verify whether the parameters are reasonable and avoid batch scrap.
1. Trial Material Loading and Positioning: For manual thread rolling machines, place the pre-treated workpiece into a "workpiece fixture" such as a V-block or three-jaw chuck, adjust the fixture position with the handwheel to ensure that the workpiece axis is completely parallel to the thread rolling wheel axis (deviation ≤ 0.03mm), and tighten the workpiece (to prevent shaking during processing);
Automatic Thread Rolling Machine: Place the workpiece into the feeding mechanism (such as a vibratory feeder or feed channel), start the feeding button, and the equipment automatically transports the workpiece to the fixture and completes positioning.
1. Single Trial Extrusion: Start the equipment in "single run" mode and observe the processing process:
The thread rolling wheel first moves radially towards the workpiece at a set feed speed while rotating at high speed, pressing the metal on the workpiece surface through its tooth surface to gradually form a thread profile.
When the thread rolling wheel reaches the set "pressing stroke," the equipment automatically stops feeding, maintaining rotation for 1-2 seconds (to ensure a full thread profile), and then the thread rolling wheel retracts in the reverse direction, separating from the workpiece.
1. Sample Quality Inspection: Remove the sample-processed workpiece and inspect it using the following tools and standards:
Visual inspection: Check if the thread surface is smooth, free of cracks and burrs, and if the tooth profile is complete (no missing or collapsed teeth). Dimensional inspection: Measure the thread's "pitch diameter" (core dimension, must meet tolerance requirements, e.g., M10 thread pitch diameter tolerance is 9.026-9.276mm) using a thread ring gauge (go gauge, no-go gauge): the go gauge must screw in smoothly, and the no-go gauge should not screw in more than 2 teeth.
Problem adjustment: If the thread pitch diameter is too small (and the no-go gauge can screw in), increase the original workpiece diameter or reduce the radial spacing of the thread rolling wheels; if the surface is rough, reduce the speed, increase the cutting fluid flow, or replace the thread rolling wheels.
1. Batch processing: Standardized operation (ensuring efficiency and consistency) After successful trial processing, batch production can begin, strictly following the set parameters and operating procedures:
1. Continuous feeding. Manual Equipment: Operators must continuously place and tighten workpieces in the fixture. After processing each workpiece, manually remove it before placing the next one (be careful to keep your hands away from the rotating area of the thread rolling wheel to prevent accidents). Automatic Equipment: In "Continuous Operation" mode, the feeding mechanism automatically feeds in batches. After processing, the workpieces enter the receiving box through the unloading channel, requiring no manual intervention (only periodic replenishment of workpiece materials is needed).
1. Real-time Monitoring: During processing, workpieces should be randomly inspected every 10-20 pieces, with key monitoring of:
Thread size drift (e.g., if the pitch diameter gradually increases, it may indicate wear on the thread rolling wheel, requiring timely replacement);
Workpiece bending or deformation (if present, check if the fixture positioning is loose or if the feed pressure is excessive);
Thread rolling wheel temperature (detected with an infrared thermometer; if the temperature > 80°C, processing must be paused, and the cooling system checked for blockages).
2. Abnormal Handling: If the following problems occur, stop the machine immediately for troubleshooting. Workpiece jamming: This may be due to excessive feed speed or workpiece diameter being too large. The machine needs to be stopped, the thread rolling wheel manually removed, the workpiece inspected, and parameters adjusted. Thread cracking: This is often caused by excessive material hardness or insufficient cooling. A qualified workpiece needs to be replaced, or the cooling channels cleaned. Abnormal noise from the thread rolling wheel: This may be due to excessive installation clearance of the thread rolling wheel or bearing wear. The machine needs to be stopped, inspected, and recalibrated.
1. Sample Quality Inspection: Remove the sample-processed workpiece and inspect it using the following tools and standards:
Visual inspection: Check if the thread surface is smooth, free of cracks and burrs, and if the tooth profile is complete (no missing or collapsed teeth). Dimensional inspection: Measure the thread's "pitch diameter" (core dimension, must meet tolerance requirements, e.g., M10 thread pitch diameter tolerance is 9.026-9.276mm) using a thread ring gauge (go gauge, no-go gauge): the go gauge must screw in smoothly, and the no-go gauge should not screw in more than 2 teeth.
Problem adjustment: If the thread pitch diameter is too small (and the no-go gauge can screw in), increase the original workpiece diameter or reduce the radial spacing of the thread rolling wheels; if the surface is rough, reduce the speed, increase the cutting fluid flow, or replace the thread rolling wheels.
1. Batch processing: Standardized operation (ensuring efficiency and consistency) After successful trial processing, batch production can begin, strictly following the set parameters and operating procedures:
1. Continuous feeding. Manual Equipment: Operators must continuously place and tighten workpieces in the fixture. After processing each workpiece, manually remove it before placing the next one (be careful to keep your hands away from the rotating area of the thread rolling wheel to prevent accidents). Automatic Equipment: In "Continuous Operation" mode, the feeding mechanism automatically feeds in batches. After processing, the workpieces enter the receiving box through the unloading channel, requiring no manual intervention (only periodic replenishment of workpiece materials is needed).
1. Real-time Monitoring: During processing, workpieces should be randomly inspected every 10-20 pieces, with key monitoring of:
Thread size drift (e.g., if the pitch diameter gradually increases, it may indicate wear on the thread rolling wheel, requiring timely replacement);
Workpiece bending or deformation (if present, check if the fixture positioning is loose or if the feed pressure is excessive);
Thread rolling wheel temperature (detected with an infrared thermometer; if the temperature > 80°C, processing must be paused, and the cooling system checked for blockages).
2. Abnormal Handling: If the following problems occur, stop the machine immediately for troubleshooting. Workpiece jamming: This may be due to excessive feed speed or workpiece diameter being too large. The machine must be stopped, the thread rolling wheel manually withdrawn, the workpiece inspected, and parameters adjusted. Thread cracking: This is often caused by excessive material hardness or insufficient cooling. A qualified workpiece must be replaced, or the cooling channels cleaned. Abnormal noise from the thread rolling wheel: This may be due to excessive installation clearance of the thread rolling wheel or bearing wear. The machine must be stopped, inspected, and recalibrated.
