Spool Assembly Layout for Brazing-Stable Expansion Valves
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Solution Overview
Problem
The manufacturing process of known two-stage proportional control valves, such as MSEVs, is complex and costly due to the need for final machining steps after brazing operations, which can distort spool bores and result in tolerance issues, necessitating complex and costly fixtures and prolonged manufacturing times.
Innovation Solution
The improved two-stage proportional control valve design allows for the spool assembly to be machined and assembled before brazing, with a spool and sleeve configuration that maintains dimensional tolerance and facilitates easier assembly and testing, independent of the valve body machining and brazing steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If components are brazed to the valve body prior to final machining steps, then manufacturing time is reduced, but spool bore dimensional tolerance deteriorates due to heat-induced distortion
Solution Approach 1:
The valve body is divided into two separate components: a body portion and a spool assembly portion. The spool bore is machined in the spool assembly portion separately from the valve body, allowing independent processing. This segmentation enables the spool bore to be precision-machined before brazing without suffering from heat-induced distortion, while the overall manufacturing time is reduced by allowing parallel processing of different components.
Solution Approach 2:
The spool bore is machined to final dimensions in the spool assembly portion before the brazing operation. By performing the precision machining operation beforehand (preliminary action), the critical dimensional tolerance is established before the thermal distortion of brazing occurs. The spool assembly is then brazed to the valve body with the precision-bored component already in place, eliminating the need for post-brazing machining.
2Manufacturing precision
If final machining steps are performed after brazing operations, then spool bore dimensional tolerance is maintained, but manufacturing time increases and fixture complexity increases
Solution Approach 1:
By segmenting the valve into separate body and spool assembly components, the precision spool bore machining is performed on the spool assembly portion independently. This allows the critical tolerance to be achieved without requiring complex fixtures to hold the entire assembled valve during machining, and eliminates the need for time-consuming post-brazing machining operations.
3Manufacturing precision
If final machining steps are performed after brazing operations, then spool bore dimensional tolerance is maintained, but device complexity increases due to required fixtures and tools
Solution Approach 1:
The valve is segmented into a body portion and a spool assembly portion that can be processed separately. The spool assembly portion containing the precision spool bore can be machined using simple, standard fixtures rather than complex custom fixtures required for machining the complete assembled valve. This segmentation dramatically reduces fixture and tool complexity while maintaining precision.
Solution Approach 2:
The spool assembly is prepared with the precision-bored spool bore before brazing to the valve body. By performing the precision machining operation on the discrete spool assembly component beforehand, simple standard machining fixtures can be used instead of complex fixtures required to hold and machine the complete assembled valve, thereby reducing device complexity.
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
This design simplifies the manufacturing process, reduces costs, and maintains precise dimensional tolerances, avoiding the distortion issues associated with post-brazing machining and enabling more efficient production of the valve body and spool assembly.
Implementation Method 1
bores machined into the valve body may become distorted by as much as about 30 μm by the heat used in the brazing operation
Data Source
AI summary
A spool assembly configured for use in a two-stage proportional control valve in a fluid system includes a substantially cylindrical sleeve having an axially extending sleeve bore extending from an open first end to an open second end. A spool includes a spool bore that extends from an open first axial end to a closed second axial end and is slidably mounted within the sleeve bore. The spool further includes a first circumferentially extending groove defining a fluid flow path, a second circumferentially extending groove formed near a first end thereof, a third circumferentially extending groove formed near the second axial end thereof, a circumferentially extending pressure groove formed therein between the second axial end and the third circumferentially extending groove, and first, second, and third transverse fluid passageways formed through a side wall of the spool.