AYANK Straight Bevel Gear Precision Forging Production Line Introduction
2026-07-21
Straight bevel gears are widely used in mechanical fields such as automotive differentials, agriculture, and industrial transmissions. In the past, the cutting processing method had low material utilization and cut off the metal flow line, thus leading to a decrease in the strength of straight bevel gears.
The straight bevel gear precision forging production line can improve the bending fatigue life of gears and save costs, and is a choice for modern investment plans.
The forging plan for straight bevel gears is: raw material preparation → heating → pre-forging → final forging → heat treatment → inspection and other remaining links.
I. Raw Material Selection and Cutting
The first step of precision forging is to select high-quality alloy structural steel. Common grades for reference include:
20CrMnTi (excellent carburizing performance)
8620 / 4320 (good hardenability)
Cutting requirements:
Use band saw or high-speed shear to cut round steel into fixed-length billets
Single piece weight tolerance is controlled within ±1% to ensure full die filling during final forging
Billet surface must undergo flaw detection to eliminate defects such as cracks, folds, and decarburized layers
II. Induction Heating
The billet is placed into a medium-frequency induction heating furnace for rapid heating:
Heating temperature: 1050°C–1200°C (adjusted according to steel grade)
Temperature control accuracy: ±10°C to avoid overheating or underheating
Low oxidation and decarburization: fast heating speed, surface oxide scale thickness controlled within 0.2mm
Modern production lines are usually equipped with multi-station induction heating systems. After the billet exits the furnace, it is directly sent to the forging press by a manipulator, enabling continuous automated production.
III. Pre-Forging (Preforming and Pre-Shaping)
The heated billet first enters the pre-forging stage, typically performed on a 300–1600 ton hydraulic press, pneumatic hammer, or electric screw press:
Upsetting: Vertically compress the cylindrical billet to increase diameter, reserving sufficient metal volume for subsequent forming.
Pre-forging: Use a pre-forging die to initially extrude the gear profile. The key here is to reasonably distribute metal flow to avoid incomplete filling or folding defects during final forging.
After pre-forging, the billet shape is close to the rough blank of the bevel gear, but still retains a larger machining allowance.
IV. Final Forging (Precision Die Forging)
The pre-forged part is transferred to the final forging die and completed on a large-tonnage press of 1000–10000 tons.
Features:
Closed-die forging: After the die closes, a closed cavity is formed, with minimal flash (usually controlled within 2mm), and material utilization can reach 75%–90%.
Complete metal flow line: During forging, metal fibers are continuously distributed along the tooth profile direction, and the root bending strength is increased by 15%–35% compared to cut gears.
Accuracy grade: Precision forged straight bevel gears can directly achieve AGMA 7–8 grade accuracy.
After final forging, the workpiece enters a trimming press to remove flash.
V. Normalizing and Shot Blasting
To eliminate forging stress, refine grains, and prepare for subsequent heat treatment:
Normalizing: Heat the workpiece to 880–920°C, then air cool. Obtain uniform pearlite + ferrite structure to improve machinability.
Shot blasting: Remove surface oxide scale while introducing certain compressive stress on the surface, which helps improve fatigue life.
VI. Carburizing and Quenching
Straight bevel gears require hard surfaces and tough cores, so carburizing and quenching is the core process:
Carburizing: Performed in a gas carburizing furnace at 920–950°C, holding time determined by required case depth (typically 0.8–1.5mm).
Low-temperature tempering: Tempering at 180–200°C to eliminate quenching stress and stabilize structure.
For gears requiring extremely high precision, press quenching technology can be used, applying pressure during the quenching process to maximize deformation control.
VII. Strengthening and Finishing
To further extend service life:
Shot peening strengthening: Perform shot peening on the tooth root transition area to introduce residual compressive stress, which can increase bending fatigue life by 2–3 times.
Gear grinding/honing (optional): Only for cases requiring AGMA grade 8 or above or strict noise requirements. Most precision forged gears can be used directly after shot peening.
VIII. Strengthening and Finishing
To further extend service life:
Shot peening strengthening: Perform shot peening on the tooth root transition area to introduce residual compressive stress, which can increase bending fatigue life by 2–3 times.
Gear grinding/honing (optional): Only for cases requiring AGMA grade 8 or above or strict noise requirements. Most precision forged gears can be used directly after shot peening.
IX. Quality Inspection
Inspection Item
Inspection Method
Acceptance Standard
Metallographic structure
Microscope observation
Grain size ≥ grade 7, no Widmanstätten structure
Carburized case depth
Microhardness tester
0.8–1.5mm (as per drawing requirements)
Surface/core hardness
Rockwell hardness tester
Surface HRC 58–62, core HRC 30–42
Tooth profile and lead
Gear measuring center
AGMA grade 7 or above
Magnetic particle inspection
Fluorescent magnetic powder
No cracks or hairline cracks
X. Summary
A complete straight bevel gear precision forging production line has the following core advantages:
✅ High material utilization: saves 30%–50% compared to cutting processing
✅ Superior mechanical properties: complete metal flow line, greatly improved tooth root strength
✅ High production efficiency: cycle time can reach 18–32 seconds per piece, suitable for mass production
✅ Low overall cost: reduces processing steps, shortens production cycles
If you have a need for a new forging production line or wish to upgrade existing processes to forging processes, it is recommended to choose a manufacturer with full-process control capabilities.
XI. About Us
AYANK focuses on the overall design and delivery of straight bevel gear precision forging production lines, covering gear outer diameters from 80mm to 800mm. We can provide you with one-stop services from equipment selection, die design to installation and commissioning.
Welcome to visit our official website (https://www.ayankforging.com/) and contact the technical team for more case materials!
