Gears after Precision Forging Process – Wenlio Gear
Form the gear teeth directly by pressing or forging with dies.
Features:
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No cutting or minimal machining
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High material utilization
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Suitable for mass production
Equipment:
Precision forging presses; cold-extrusion machines.
Applications:
High-volume gear manufacturing such as automotive transmissions.
Better Forging Makes Better Gears
In gear making, forging the gear blank is a key step. Forging gives the blank high strength and tight, even density, which means better performance and longer life. It also improves the metal’s grain flow and microstructure, boosting mechanical properties.
At Wenlio, we focus on quality and cost when forging gear blanks. With advanced equipment and skilled staff, we forge complex shapes to strict tolerances and check every step for accuracy and consistency.
Forging is central to our process. By improving our methods, we cut waste in later cutting operations and deliver reliable, high-performance gears that fit your exact needs.
- Why forging: higher strength, uniform density, better grain flow → longer life.
- What we do: complex shapes, tight tolerances, step-by-step QC.
- Value: less machining waste, lower total cost, reliable performance.
Hot vs Warm vs Cold Forging Comparison Table (Temperature, Pressure, Accuracy, Strength, Cost, Applications)
Forging Process Differences: Hot Forging, Warm Forging, and Cold Forging
| Attribute |
Hot Forging |
Warm Forging |
Cold Forging |
| Temperature |
Above the recrystallization temperature |
Below the recrystallization temperature and above room temperature |
Room temperature |
| Required Pressure |
Low (material is soft) |
Moderate |
Very high (material is hard) |
| Dimensional Accuracy |
Lower (thermal shrinkage) |
High |
Very high |
| Strength Improvement |
Improves overall properties via grain refinement |
Between the two |
Significantly increases strength (work hardening) |
| Cost |
Medium (includes heating cost) |
Medium |
High die cost |
| Typical Applications |
Automotive crankshafts, connecting rods, gear blanks, aircraft landing gear |
Parts requiring a balance of precision and strength |
Screws, rivets, precision parts |
Hot Forging vs. Warm Forging vs. Cold Forging
Forging can be classified by deformation temperature into hot forging (forging temperature above the billet metal’s recrystallization temperature), warm forging (forging temperature below the metal’s recrystallization temperature), and cold forging (at room temperature). The recrystallization temperature of steel is about 460 °C, but 800 °C is commonly used as a practical boundary: above 800 °C is considered hot forging, while 300–800 °C is referred to as warm or semi-hot forging.
Cold vs. Warm vs. Hot Forging: Which Delivers the Highest Accuracy?
Cold forging outperforms warm and hot forging when tight tolerances and premium finishes matter. Formed at room temperature in closed dies, it avoids scale, decarburization, and thermal distortion—delivering near-net shapes with higher dimensional accuracy and Ra as low as sub-micron levels.
Work hardening increases strength and fatigue life while preserving continuous grain flow. Material yield is high and secondary machining is minimized, cutting cycle time and cost. Warm and hot forging excel for large or complex parts requiring lower forming loads, but typically need more finishing.
For small-to-medium shafts, gears, cups, and fasteners, cold forging offers the best balance of precision, strength, and surface quality.
How Gear Cold Forging Works？
There are various types of shaft components in the automotive transmission system, each with distinct structural characteristics and production requirements. With the continuous development and upgrading of new energy vehicles (NEVs), higher production standards have been set for gear shafts, which are key components in the automotive transmission system.
The rotational speed of gear shafts in NEVs generally ranges from 12,000 to 16,000 rpm, generating significant noise. Since NEVs lack engine noise to mask other sounds, the NVH (Noise, Vibration, and Harshness) requirements for transmissions have become more prominent. Consequently, the precision requirements for gear shafts in NEVs are higher than those in fuel-powered vehicles.
When gear shafts operate in the transmission system, they are subjected to complex forces. Therefore, gear shafts must possess excellent mechanical properties—such as impact resistance, wear resistance, high strength, and hardness—as well as good internal structural performance to ensure normal operation under high-load and high-speed conditions.
Currently, hot die forging is generally used for disc gear components. The main reason is that these components require a large forging ratio, and hot die forging is more technically feasible from a process perspective.
The forging process for shaft components needs to be selected from hot die forging, cold forging, or warm forging based on the component size and production cost. Their specific characteristics are as follows:
During hot die forging, the metal flow is relatively complex, which may lead to defects such as folding and insufficient filling during forming. Correspondingly, the dies are prone to severe wear, cracking, and other issues.
When cold forging is applied to the production of shaft components, its main advantages include longer die life, high productivity, excellent product consistency, effective reduction of machining allowances, shortened machining time, and lower costs. However, cold forging also has inherent drawbacks:
- Hardness Achievement Issue: Before cold forging, the blank typically undergoes an annealing process to improve plasticity. However, the spheroidal pearlite structure formed by annealing cannot reach the quenching hardness achievable by the lamellar pearlite structure (after normalizing) or the tempered sorbite structure (after quenching and tempering) when high-frequency quenching is required in subsequent processing. Thus, additional normalizing or quenching-tempering treatments are necessary.
- Heat Treatment Deformation Control Issue: Controlling heat treatment deformation is relatively difficult. After the blank undergoes normalizing or quenching-tempering, its structure undergoes recrystallization. Except for macro-stresses caused by machining (e.g., stresses at machining fillets, generally referred to as macro-stresses), there are no intergranular internal stresses (generally referred to as micro-stresses). Therefore, stress release during subsequent heat treatment is limited, resulting in relatively small deformation. While cold-forged blanks are chosen primarily for their economic benefits (high forging precision), when subsequent heat treatments (such as carburizing and quenching, or carbonitriding) are directly applied, the release of micro-stresses formed by grain deformation during forging can sometimes cause significant heat treatment deformation. Additionally, due to the grain shape, phenomena like “swallowing deformation” (a phenomenon currently lacking strong theoretical support and without consensus in the academic community) and coarse grains may occur, affecting the mechanical strength of the product.
After producing blanks via warm forging or hot forging, residual heat normalizing is generally adopted. This method is low-cost and energy-efficient but results in a certain gap in structural uniformity compared to the independent normalizing process.
If cost permits, isothermal normalizing is recommended. The application of isothermal normalizing effectively controls the quality of gear blanks for transmission gears and shaft components, thereby improving machinability and heat treatment deformation stability.
The key to formulating the isothermal normalizing process lies in reasonably controlling the rapid cooling rate, slow cooling rate, and corresponding time during the intermediate cooling stage, as well as the temperature and time of the isothermal treatment, based on the austenite isothermal transformation curve.
Compared with conventional normalizing, isothermal normalizing produces more uniform and consistent microstructures and hardness. Components pre-treated with isothermal processes can reliably achieve good machinability and stable quenching deformation.
