Hydrostatic Spindle Bearing Fluid Distribution for Milling Precision
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Solution Overview
Problem
Current milling and boring machine tools face issues with precision due to wear and corrosion of plain bearings, limited dynamic balancing, and high power dissipation in hydrostatically supported bearings, which restrict the use of large and heavy tools.
Innovation Solution
A machine tool design featuring a spindle with hydrostatically supported bearings and a fluid distribution system that reduces fluid drag and power dissipation, using rolling bearings for high stiffness and allowing larger tool diameters, with a spirally wound tubular element for fluid transmission and a rotary manifold for efficient fluid delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If plain bearings are used to support the boring bar in the spindle, then the coupling precision can be high initially, but the precision degrades over time due to wear and corrosion
Solution Approach 1:
The patent replaces the mechanical contact system of plain bearings with a hydrostatic bearing system that uses a fluid film to support the boring bar. This substitution eliminates direct metal-to-metal contact, preventing wear and corrosion while maintaining high coupling precision throughout the machine's operational life.
Solution Approach 2:
The patent implements hydrostatic bearings that use pressurized fluid (typically oil or water) to create a bearing film between the boring bar and spindle. This hydraulic system provides non-contact support, ensuring stable coupling precision by eliminating the wear mechanisms inherent in plain bearings.
2Manufacturing precision
If hydrostatically supported bearings are used to support the boring bar-spindle element, then the coupling precision is maintained, but high power dissipation occurs due to fluid drag
Solution Approach 1:
The patent divides the fluid supply system into multiple independent channels, each feeding specific bearing zones. This segmentation allows optimized fluid distribution, reducing overall fluid drag and power dissipation while maintaining the hydrostatic support necessary for precision coupling.
Solution Approach 2:
The patent optimizes parameters such as fluid viscosity, pressure, and film thickness to minimize power dissipation. By carefully controlling these parameters, the system maintains adequate bearing clearance and precision while reducing the energy lost to fluid drag during rotation.
3Loss of energy
If the spindle diameter is reduced to contain fluid losses in hydrostatic bearings, then fluid losses decrease, but the stiffness and torsional strength are insufficient for large and heavy tools
Solution Approach 1:
The patent features a nested structure where the boring bar is accommodated within the spindle, and the hydrostatic bearing system is integrated within this nested arrangement. This allows the spindle to maintain adequate diameter for tool support strength while the hydrostatic bearings minimize fluid losses through efficient fluid management in the nested configuration.
Solution Approach 2:
The patent incorporates preliminary fluid supply channels and distribution systems that are pre-configured to deliver fluid efficiently to the bearing zones. This preliminary arrangement optimizes fluid flow paths, minimizing losses before the fluid reaches the bearing interface, while allowing the spindle to maintain the diameter necessary for supporting heavy tools.
4Ease of operation
If thermal variations occur during operation, then the coupling play changes, but this affects the centering and balancing stability of the boring bar
Solution Approach 1:
The patent replaces mechanical contact bearings with hydrostatic bearings that use a fluid film to support the boring bar. This substitution eliminates the thermal expansion and contraction issues that affect mechanical contact systems, as the fluid film accommodates thermal variations without compromising centering stability or coupling play consistency.
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 solution provides a simple, cost-effective coupling with high stiffness, enabling precise machining of large tools with reduced fluid losses and power dissipation, improving machining reliability and precision.
Implementation Method 1
the boring bar is supported in the spindle by means of hydrostatically supported bearings, such that the boring bar rotates in the spindle spaced from it by a film of fluid that is injected between them
Implementation Method 2
it does not require extreme precisions in coupling between the boring bar-spindle element and its support, but it causes high power dissipation due to the fluid drag opposed by the film of oil that is interposed between the bearings and the boring bar-spindle element
Data Source
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Figure 3
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AI summary
A machine tool (10), particularly of the milling and boring type, comprising: - a support (1 1) for a spindle (12) that accommodates coaxially a boring bar (13) that is connected thereto by means of hydrostatically supported bearings ( 14), - means for the joint rotation of the spindle (12) and of the boring bar (13) about a main machining axis (X), - means for the translational motion of the boring bar (13) with respect to the spindle (12) along the main axis (X). First ducts (18) for feeding fluid to the hydrostatically supported bearings (14) are provided through the spindle (12). The boring bar (13) has means ( 19) for transmitting the fluid from a provided distribution unit (20), which is substantially fixed to the support (1 1 ), to the first ducts ( 18), which rotate with the spindle (12).