Nidec Launches New Mass-Production Internal Gear Grinding Machine

Manufacturing high-torque industrial robotic speed reducers, electric vehicle planetary transmissions, and automotive drive gearboxes requires internal ring gears that balance tooth contact stiffness with minimal transmission error. As gear diameters expand, gear cutting processes such as broaching and shaping frequently leave residual thermal stresses and surface deviations that compromise acoustic and mechanical performance. Grinding large internal gears to micron tolerances at mass-production cycle times introduces severe engineering hurdles, including spindle interference within internal bores, complex dressed-wheel geometry, structural deflection from shifting workpiece inertia, and thermal drift over extended machining cycles. Resolving these dimensional challenges requires high-rigidity machine kinematics, continuous generating grinding, and automated adaptive servo tuning.

Expanded Envelope and Generating Grinding Kinematics
Building upon the architecture of its ZI25A platform, Nidec Machine Tool Corporation developed the ZI35A mass-production internal gear grinder to extend processing capacity by 100 mm, accommodating internal ring gears with maximum outer diameters up to 350 mm and normal modules from 1 to 4.

The machine utilizes a continuous generating grinding process that synchronizes the rotation of the workpiece table axis with the grinding wheel spindle. To overcome internal clearance constraints, the system deploys a patented barrel-shaped threaded grinding wheel that tapers continuously in diameter from its midpoint toward both ends. Positioning the grinding spindle at an axis crossing angle between 20 and 35 degrees relative to the workpiece axis generates elevated sliding velocity along the contact line, accelerating stock removal rates without inducing subsurface thermal damage or grinding burns.

High-Load Rigidity and Adaptive Servo Tuning
The machine incorporates a high-rigidity direct-drive table axis rated for a maximum payload mass of 200 kg, supporting workpieces up to 20 kg under automated parts-handling regimes. Kinematic performance maintains dynamic rigidity at maximum table speeds of 3,500 min⁻¹ and grinding spindle velocities up to 15,000 min⁻¹.

To address variations in mass moment of inertia caused by swapping workholding fixtures or transitioning between different gear blanks, the ZI35A integrates a standard Table Axis Tuning Function. This algorithmic control system calculates and optimizes table servo control loop gains automatically. By adjusting gain coefficients to match real-time inertia profiles, the system dampens torsional vibration, prevents table axis oscillation, and preserves dimensional pitch accuracy without requiring manual retuning by specialized automation engineers.

Integrated Dressing, Metrology, and Shop-Floor Interfacing
Grinding wheel re-profiling is executed without unchucking the tool assembly from the machine spindle. In addition to a standard dressing gear approach, the system supports an optional dedicated rotary dressing device operating at spindle speeds up to 6,000 min⁻¹—double the speed of previous generations. For extended unattended shifts, an optional touch-probe thermal displacement compensation device measures reference fixture outer diameters before each grinding cycle, actively adjusting the radial center distance between the wheel and workpiece to counteract thermal bed expansion and stabilize Between Balls Diameter (BBD) dimensions.

Operator interaction is handled through a redesigned 21.5-inch LCD terminal running interactive machine software with softkey navigation, real-time dressing cycle progression, coolant tank level diagnostics, and spindle bearing thermal readouts. Automated gear meshing is verified prior to grinding via acoustic emission (AE) sensors. At the JIMTOF 2026 trade show, Nidec will showcase the platform's automation capabilities by demonstrating an automated grinding wheel arbor exchange using an articulated collaborative robot.

Additional Context
This section details technical specifications and competitive benchmarking not included in the original product announcement.

In precision gear manufacturing, internal ring gears applied in robotic strain wave and cycloidal reducers, as well as automotive planetary ring assemblies, are evaluated under DIN 3962 and ISO 1328-1 accuracy standards, targeting quality grades of DIN 4 to DIN 6. Because internal gears feature concave tooth flanks, mechanical envelope constraints make conventional cylindrical generating wheels impossible to clear within internal cavities. Nidec's specialized barrel-shaped threaded grinding wheel solves this geometrical interference by allowing continuous threaded generating grinding along the internal concave tooth space, mirroring the productivity of external gear hobbing and threaded grinding.

Within the high-precision internal gear finishing landscape, the ZI35A benchmarks against gear shaping, internal gear honing platforms (such as those from Gleason or DVS Group), and single-flank profile grinding machines (such as the Kapp Niles ZE series). While single-index profile grinding delivers extreme contour precision, its non-continuous feed cycles extend cycle times on high-tooth-count ring gears. Conversely, while power skiving and gear honing offer high throughput, they depend heavily on pre-heat-treat blanks or tool wear life in hardened alloys exceeding 58 to 62 HRC. By combining continuous generating grinding kinematics with an integrated 6,000 min⁻¹ rotary dresser, the ZI35A provides an alternative manufacturing route that meets production cycle constraints and achieves sub-micron pitch and profile deviations on large, hardened internal ring gears.

Edited by Romila DSilva, Induportals Editor, with AI assistance.