Flexible Collet Coupling for Draw Bar Concentricity
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Solution Overview
Problem
The existing connection between a collet and a draw bar in machine tools often results in inadequate concentricity, leading to run-out issues during rotation, due to gaps and variations in friction, clamping force, and external influences, which affect the accuracy of swarf removal and the quality of the finished workpiece.
Innovation Solution
A flexible coupling with threaded surfaces on the draw bar and collet, featuring a buttress thread configuration, is used to securely attach the collet to the draw bar, ensuring coaxial alignment through a method that involves a pulling device to apply an axial force, eliminating gaps and enhancing concentricity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a traditional fastener connection is used between collet and draw bar, then the结构简单 (structure is simple), but the concentricity varies due to gaps and external influences
Solution Approach 1:
The coupling structure is divided into multiple segments including a draw bar portion, a collet portion, and an intermediate portion with radial slots. This segmentation allows each part to perform its specific function while maintaining overall concentricity, resolving the contradiction between structural simplicity and precision requirements.
Solution Approach 2:
An intermediate portion is introduced between the draw bar and collet, featuring radial slots that act as an intermediary mechanism. This intermediate structure mediates the connection, eliminating gaps and ensuring consistent concentricity while transmitting the drawing force effectively.
2Manufacturing precision
If mechanical clamping is used to hold collet in adapter, then the clamping force is sufficient, but the concentricity is compromised during rotation causing run-out
Solution Approach 1:
The coupling structure incorporates dynamic elements including radial slots and flexible portions that allow the structure to adapt during rotation. The intermediate portion can dynamically adjust to maintain concentric alignment while the clamping force is maintained, preventing run-out during operational rotation.
Solution Approach 2:
The structure utilizes parameter changes in the form of radial slots that allow controlled movement and adjustment. These slots enable the coupling to change its physical state slightly during operation, maintaining optimal concentricity parameters while preserving sufficient clamping force through the drawing mechanism.
3Manufacturing precision
If there is a gap between collet and draw bar, then the assembly is easier to manufacture, but the contact point and draw-in force direction vary causing run-out
Solution Approach 1:
The coupling structure is designed with pre-formed radial slots and an intermediate portion that preliminarily establishes the correct geometric relationship between draw bar and collet. This preliminary structural arrangement ensures consistent contact points and draw-in force directions are built-in during manufacturing, eliminating the need for tight assembly tolerances while maintaining high concentricity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The flexible coupling improves concentricity between the collet and draw bar, reducing run-out tolerance and ensuring consistent alignment, thereby enhancing the rotational accuracy and quality of the workpiece.
Implementation Method 1
the first coupling surface has a first threaded area formed thereon and the second coupling surface has a second threaded area formed thereon... the first threaded area and the second threaded area are of a buttress thread configuration
Implementation Method 2
An axial pulling force is applied, via the pulling device, to the draw bar to concentrically seat the collet in the collet adapter such that the first longitudinal axis and the second longitudinal axis are coaxial
Data Source
Figure 1
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AI summary
A flexible coupling (50) for attaching a collet (30) to a draw bar (20) includes a draw bar (20) having a first longitudinal axis (L1) and a first coupling portion (22). The first coupling portion (22) includes two or more legs (22A, 22B) spaced apart from one another with each of the legs (22A, 22B) having first coupling surface (25) formed thereon. The flexible coupling (50) includes a collet (30) having a second longitudinal axis (L2) and a clamping portion (36) proximate one end of the collet (30). The collet (30) includes a second coupling portion (38) proximate a second end of the collet (30). The second coupling portion (38) has a second coupling surface (39) formed thereon and configured in a shape complementary to the first coupling surface (25) so that the first coupling surface (25), moveably engage the second coupling surface (39) such that the first longitudinal axis (L1) and the second longitudinal axis (L2) are coaxial when an axial force is applied to the draw bar (20) and the collet (30).