How to Ensure Phase Accuracy and Symmetry of Two Sets of Tooth Profiles in Double Gear
Publish Time: 2026-02-12
In high-precision transmission systems, double gears are widely used in automotive transmissions, construction machinery, and aerospace due to their compact layout and efficient power transmission capabilities. However, manufacturing such parts faces two core challenges: first, internal splines are prone to elliptical deformation or tooth distortion after heat treatment; second, double-tooth external splines not only have a large number of teeth and a small module, but also require strict assurance of the phase relationship and geometric symmetry between the two sets of external teeth. If the phase deviation exceeds the allowable tolerance, it will lead to meshing impact, increased noise, or even transmission failure. Our company has successfully achieved high consistency of internal and external tooth profiles and assembly reliability by optimizing the process route, introducing high-precision positioning datums, and using composite machining strategies.
1. Unified Datum Design: "Zero-Conversion" Positioning from Blank to Finished Product
The core of phase accuracy lies in the consistency of the datum during the machining process. Traditional processes often involve frequent changes in clamping datums during roughing, heat treatment, and finishing stages, leading to accumulated errors. Our company adopts an integrated datum strategy of "using the hole to determine the shaft and the internal spline to determine the external spline": using the internal spline hole as the main positioning datum throughout the entire process. Even before heat treatment, the inner hole is pre-bored and a process boss is machined to ensure that the alignment and finishing after quenching are based on the inner hole. In this way, the indexing of the double-tooth external spline and the internal spline always maintain a fixed angular relationship, fundamentally avoiding phase drift.
2. Heat Treatment Deformation Control: A Preliminary Guarantee for Internal Spline Accuracy
Internal spline deformation is a key factor affecting the overall phase. To suppress quenching deformation, our company optimizes the material pretreatment process, selects low residual stress forgings, and implements isothermal quenching + tempering during the tempering stage to refine the grains and homogenize the microstructure. After heat treatment, a dedicated hydraulic straightening machine combined with a high-precision inner diameter measurement feedback system is used to perform micron-level straightening of the internal spline hole, controlling the ellipticity within 0.01mm. Subsequently, the internal spline is precision drawn or inserted based on the inner hole to ensure that its geometric accuracy meets the requirements of AGMA or DIN standards, providing a stable reference for external gear machining.
3. High-Precision Indexing and Synchronous Machining: Achieving Phase Consistency of Double External Teeth
The phase accuracy of double-tooth external splines depends on the machine tool's indexing system and toolpath planning. Our company uses a five-axis linkage CNC hobbing machine or a high-rigidity CNC gear shaper, equipped with a high-resolution encoder and a closed-loop feedback system. During the programming stage, the starting angle positions of the two sets of external teeth are precisely set using CAD/CAM software, and the double-tooth machining is completed using a "one-time clamping, continuous indexing" method, eliminating angular errors caused by secondary clamping. For high-precision applications, online tool setting and laser angle calibration technology are also introduced to compensate for machine tool indexing errors in real time.
4. Composite Detection and Data Closed-Loop: Ensuring Process Stability
To verify phase accuracy and symmetry, our company has configured a high-precision gear measurement center, which can simultaneously detect the internal spline tooth profile, external spline tooth direction, cumulative tooth pitch error, and phase difference between the two external teeth. All key parameters are incorporated into SPC statistical process control. Once a trend deviation is detected, it is immediately fed back to the previous process to adjust cutting parameters or fixture status. In addition, some batches of products undergo blue light scanning and 3D comparison to comprehensively assess geometric consistency.
5. Process Integration and Experience Accumulation: From "Can Do It" to "Stable Production"
Ultimately, achieving high phase accuracy relies not only on equipment but also on a deep understanding of material properties, cutting force distribution, and thermal deformation patterns. Through years of process testing, our company has established a dedicated processing database for different materials and sizes, covering optimal parameter combinations for cutting speed, feed rate, and cooling methods. This "process package" model ensures that even in mass production, we can consistently output high-quality double gear products with phase errors ≤ ±3′ and symmetry better than 0.02mm.
In summary, through five major initiatives—unified benchmarks, deformation control, high-precision division, closed-loop testing, and process standardization—our company has effectively overcome the technical bottleneck of co-manufacturing of internal and external gears in double gears. While meeting the requirements for preventing deformation of the internal spline and machining the complex external spline, we ensure strict phase accuracy and symmetry between the two sets of external teeth, providing key component guarantees for the smooth, quiet, and long-life operation of high-end transmission systems.
