Views: 0 Author: Site Editor Publish Time: 2025-08-26 Origin: Site
Gear shaping is one of the common generating methods in gear machining. It cuts gears with involute tooth profiles by simulating the meshing motion between a gear shaper cutter and the workpiece. The core principle is to utilize the strict transmission ratio between the gear shaper cutter (a gear with cutting edges) and the workpiece (the gear to be machined). Through reciprocating cutting and generating motion, the gear tooth profile is gradually formed. Below, we will introduce it from aspects such as working principle, process characteristics, equipment and tools, and application scope.
1. Basic Concepts and Principles
The essence of gear shaping is to directly use the meshing principle of a pair of gears for generating gear machining. The gear shaper cutter is equivalent to a driving gear, with cutting edges (rake angle and relief angle) on its tooth surface; the workpiece is equivalent to a driven gear, maintaining a transmission ratio of i = z₁/z₂ with the gear shaper cutter (where z₁ is the number of teeth of the workpiece and z₂ is the number of teeth of the gear shaper cutter). The gear shaper cutter performs an up-and-down reciprocating linear motion (main motion), while rotating relatively with the workpiece (generating motion). The cutting edges gradually cut off the metal in the tooth space of the workpiece, and finally form an involute tooth profile conjugate to the tooth profile of the gear shaper cutter.
Gear shaping mainly involves four coordinated motions to ensure tooth profile accuracy and machining efficiency:
Main Motion: The up-and-down reciprocating linear motion of the gear shaper cutter along its axis (the cutting stroke is downward, and the return stroke is upward). It is the main motion for cutting metal, and its speed is expressed by the number of strokes per minute (e.g., 100-1000 strokes/minute).
Generating Motion: The relative rotational motion between the gear shaper cutter and the workpiece, maintaining a strict transmission ratio (i = z₁/z₂), which is used to generate the involute tooth profile. As the core motion of gear shaping, it directly determines the tooth profile accuracy.
Radial Feeding Motion: The slow radial movement of the gear shaper cutter along the workpiece until it cuts into the workpiece to the specified tooth depth (full tooth height). The radial feed rate is usually expressed by the radial movement per stroke (e.g., 0.01-0.1 mm/stroke).
Tool Retracting Motion: When the gear shaper cutter moves upward during the return stroke, the workpiece makes a slight radial movement (e.g., 0.1-0.2 mm) to prevent the flank of the gear shaper cutter from scratching the machined tooth surface and ensure the tooth surface quality.
(Note: The gear shaping principle diagram mentioned in the original text is not provided here due to format limitations. For reference, please refer to the relevant diagrams in the original WeChat article.)
2. Process Characteristics of Gear Shaping
Small Tool Retracting Clearance
The gear shaper cutter only requires a small tool retracting clearance at the end of cutting or the stroke, making it suitable for machining tooth profiles close to the shaft shoulder.
Suitable for Complex Gear Machining
It can machine gear sets that hobbing cannot handle due to insufficient tool retracting clearance.
It can machine double-helical gears with extremely narrow gaps between the helices, and can even produce "continuous" double-helical tooth profiles.
Requirements for Design and Clamping
Tool Retracting Groove Design
A tool retracting groove with the same depth as the tooth depth needs to be machined at the end of the tooth width. The specific width values are referred to the following table:
Module (mm) Spur Gear (mm) Helical Gear 15° (mm) Helical Gear 23° (mm)
1.0 5.0 6.0 6.5
1.8 5.0 6.5 7.0
2.5 5.5 7.2 8.0
4.0 6.5 7.2 8.0
6.0 7.2 9.0 9.5
Clamping Method
Parts are difficult to be clamped and machined between centers, so at least one end must be fixed by a fixture or chuck. Gear parts with a long shaft extension can be supported by an upper center or a follower rest, and the long shaft at the lower end can be accommodated through the machine base hole or the foundation groove.
Comparison of Advantages and Disadvantages between Gear Shaping and Hobbing
Comparison Item Gear Shaping Hobbing
Cutting In/Out Impact Has impact No impact
Number of Tooth Profile Envelopes The number of envelope lines of the tooth profile can be adjusted (by adjusting the number of strokes per minute and circumferential feed rate), resulting in better tooth profile accuracy. The number of envelope lines is limited, and the tooth profile accuracy is slightly worse.
Inertial Force of Tool Spindle Motion Part Affected by inertial force because the tool spindle performs reciprocating motion. Not affected by inertial force
Idle Time There is one idle time for each reciprocating motion of the gear shaper cutter. No idle time
Types of Machined Gears In addition to external cylindrical gears, it can also machine internal gears, herringbone gears, and double or multiple gears with adjacent teeth close to each other. Cannot machine internal gears and multiple gears with adjacent teeth close to each other.
Special Tools and Guides for Helical Cylindrical Gear Machining Special gear shaper cutters and corresponding gear shaping spindle guides need to be designed for machining helical gears. No special tools and accessories are required for machining helical gears.
Accuracy Better tooth profile accuracy, slightly worse tooth orientation accuracy Better pitch accuracy, slightly worse tooth profile accuracy
3. Equipment and Tools
Equipment
Ordinary Gear Shaping Machines: Such as the Y5120 gear shaping machine, which can machine gears with a diameter of ≤200 mm. It is suitable for the production of internal and external cylindrical gears in single-piece, small-batch, and mass production, and the applicable gear accuracy is grade 6-7.
CNC Gear Shaping Machines: Derived from ordinary models equipped with a CNC system. Their main motions are equipped with a computer numerical control system, which can realize multi-axis linkage and independent motions of each axis.
Tools
Classification by Tool Shape
Disc-type Gear Shaper Cutters: The most commonly used type, used for machining internal and external spur and helical cylindrical gears.
Bowl-type Gear Shaper Cutters: The clamping part is bowl-shaped, mainly used for machining multiple gears and gears with shoulders.
Taper-shank Gear Shaper Cutters: Mainly used for machining internal gears, with a small arbor diameter.
(Note: The images of disc-type, bowl-type, and taper-shank gear shaper cutters mentioned in the original text are not provided here due to format limitations. For reference, please refer to the relevant images in the original WeChat article.)
Classification by Material
They are usually made of high-speed steel (W18Cr4V) or cemented carbide (YG8, YT15). Cemented carbide gear shaper cutters are suitable for high-speed machining and can improve efficiency.
4. Application Scenarios
Gear shaping is mainly used for the machining of medium and high-precision gears, especially in the following cases:
Internal Gears: Such as the internal gear ring in planetary gear reducers.
Multiple Gears: Such as double and triple gears in gearboxes.
Small Module Gears (m ≤ 5 mm): Such as instrument gears and clock gears.
Gears with High Tooth Profile Accuracy Requirements (IT7-IT8 Grade): Such as machine tool spindle gears and servo motor gears.
Spline Teeth with Back Taper: For example, the back taper teeth of synchronizers or shift sleeves in automobile gearboxes.