Conical Hob Geometry for Parallel Gear Roots
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Solution Overview
Problem
Existing gear cutting methods using hobs result in tooth gaps with bases inclined to the workpiece spindle axis, leading to a weakened gear wheel due to varying base circle distances on opposite end faces, and the production of teeth with angled tooth roots.
Innovation Solution
A hob with milling teeth arranged on a helical path around its axis, where the root line is inclined at an acute angle α to the head line, allowing for a combined axial and radial feed that maintains constant maximum tooth engagement depth, resulting in teeth with parallel root lines and inclined flanks, and the use of a machine tool with synchronized spindle drives and adaptive feed control to achieve these geometries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If the hob is advanced with both axial and radial feed components to produce teeth with inclined flanks, then the tooth flank geometry is improved, but the tooth root line becomes inclined relative to the workpiece axis, weakening the gear wheel
Solution Approach 1:
The patent applies parameter changes by modifying the hob geometry itself - specifically, the milling tooth roots are positioned on a head line that is inclined relative to the hob axis, while the tooth gaps remain on a cylindrical surface. This geometric parameter modification allows the hob to cut teeth with inclined flanks while maintaining parallel root lines on the workpiece, resolving the contradiction between improved flank geometry and gear strength
Solution Approach 2:
The patent introduces a dimensional change by inclining the head line of the milling teeth relative to the hob axis in the longitudinal section. This creates a three-dimensional tooth configuration where the cutting edges follow a skewed path, enabling simultaneous achievement of inclined tooth flanks and parallel root lines through spatial geometry rather than simple axial-radial feed motion
2Shape
If the hobbing process uses conventional axial and radial feed to create inclined tooth flanks, then the tooth profile is improved, but the base circle distance varies on opposite end faces, weakening the structure
Solution Approach 1:
The patent changes the geometric parameters of the hob by positioning milling tooth roots on an inclined head line rather than on a line perpendicular to the hob axis. This parameter modification ensures that during conventional axial and radial feeding, the cutting action produces uniform base circle distances on both end faces of the workpiece while simultaneously creating the desired inclined tooth profile
3Ease of manufacture
If the hobbing cutter uses standard tooth arrangement to simplify manufacturing, then the production process is easier, but the tooth roots run at an angle to the workpiece axis causing structural weakness
Solution Approach 1:
The patent modifies the hob manufacturing parameters by arranging milling teeth with roots on an inclined head line relative to the hob axis. This controlled geometric parameter change enables the production of hobs that generate parallel root lines on the workpiece, improving tooth root strength while maintaining manufacturability through standardized hobbing processes
Data Source
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AI summary
The invention relates to a device for forming working gears (1) using a hob (10), wherein the working gear (1) can be driven rotationally by a workpiece spindle about a workpiece spindle axis (7), wherein the hob (10) can be driven rotationally by a tool spindle about a tool spindle axis (18) in a predetermined speed ratio relative to the working gear (1) and wherein the hob comprises cutting teeth (11, 21) whose cutting tooth bases (14, 24) run along a base line (15) in a longitudinal section through the hob (10) at the tool spindle axis (18), and whose cutting tooth heads (13, 23) run along a head line (16) in the longitudinal section, wherein advancing means are provided for moving the hob (10) relative to the working gear (1), wherein an axial component of the advancement runs in the direction of the workpiece spindle axis (7) and a radial component of the advancement runs substantially perpendicular to the axial component in the direction of the workpiece spindle axis (7). In order to form gears having tooth flanks with acute angles relative to one another, it is proposed that the head line (16) run at an acute angle (a) relative to the base line (15).