Control Analysis of a Novel Bearing Steel Pipe Cutting Machine

Literature Overview

This paper, authored by Lv Yuanjun, Chen Qiong, and Wang Wenkui from Zhejiang Vocational and Technical Institute of Industry and Shaoxing University respectively, published in Bearing (2009, No. 10, pp. 25-28), presents the structural design and hydraulic control analysis of a novel cutting machine specifically designed for cutting small-diameter steel tubes used in rolling bearing manufacturing. The project was supported by the Shaoxing Science and Technology Bureau. The paper addresses the limitations of manual cutting methods in bearing tube production and proposes an automated, high-precision alternative.

Industry Background and Requirements

Rolling bearing manufacturing requires precise cutting of steel tubes into rings that serve as bearing races or cage components. The cutting quality directly affects bearing performance, with dimensional accuracy, cut surface quality, and tube squashing (ovality) being critical parameters. Traditional manual cutting methods suffer from:

Inconsistent cut quality due to operator skill variation
Low production efficiency
Difficulty maintaining dimensional accuracy for small-diameter tubes
High labor costs and ergonomic concerns

Technical Requirements for Bearing Tube Cutting

Parameter	Typical Requirement	Significance
Cut length tolerance	±0.05-0.1 mm	Assembly fit and bearing performance
Cut surface perpendicularity	≤0.02 mm TIR	Raceway geometry accuracy
Tube ovality after cutting	≤0.01 mm	Bearing running accuracy
Surface roughness at cut	Ra ≤ 3.2 μm	Elimination of grinding allowance
Production rate	High (batch processing)	Economic viability

Machine Structure and Design Features

The novel cutting machine is designed primarily for small-diameter steel tubes (typically in the range of 10-50 mm outer diameter) used in precision bearing manufacturing. Key structural features include:

Tube clamping mechanism: Precision clamping that holds the tube without causing deformation, using adjustable jaws that accommodate different tube diameters.
Cutting head assembly: A rotating cutting tool with hydraulic actuation for feed and retraction, designed for clean cross-sectional cutting without excessive squashing.
Positioning and measurement system: Automatic detection of cut position with feedback control to ensure length accuracy.
Hydraulic power system: Provides controlled force for clamping and cutting operations.

Hydraulic System and Control Analysis

Hydraulic Circuit Design

The hydraulic system serves three primary functions:

Clamping force control: Applies consistent clamping force to secure the tube without excessive deformation. The system uses a pressure-relief valve to limit maximum clamping pressure and a check valve to maintain pressure during the cutting operation.
Cutting feed control: Provides controlled advance of the cutting tool with adjustable speed. The system incorporates a flow control valve to regulate cutting speed and a sequence valve to coordinate tool advance with clamping.
Tool retraction: Rapid retraction of the cutting tool after each cut to minimize cycle time, utilizing a separate high-flow circuit.

Control Process

The automated control sequence follows a logical cycle:

Tube loading and positioning
Clamping force application and verification
Cutting tool positioning
Cutting operation with controlled feed
Tool retraction
Clamping release
Tube unloading and cycle repetition

The control system ensures that each operation is completed before the next begins, preventing damage to the tube or tool. Pressure and position sensors provide feedback for closed-loop control of critical parameters.

Engineering Practice Considerations

From a manufacturing engineering perspective, several aspects of this machine design are particularly noteworthy:

Small diameter tube challenges: Cutting small-diameter tubes presents unique challenges because the tube wall is thin relative to its diameter, making it susceptible to ovality and deformation during clamping and cutting. The machine design must carefully balance clamping force against deformation risk.
Surface quality: For bearing applications, the cut surface quality is critical because it affects subsequent grinding operations. A clean, burr-free cut reduces grinding allowance and improves dimensional accuracy. The hydraulic feed control is essential for achieving consistent cut quality.
Tool life and replacement: The cutting tool experiences significant wear during continuous operation. The machine design should facilitate quick tool replacement and provide indicators for tool condition monitoring.
Production integration: For full automation, the cutting machine should interface with upstream tube straightening and downstream inspection stations. The control system architecture should support integration with production management systems.

Study Insights

This paper represents a practical engineering solution to a specific manufacturing problem in the bearing industry. The approach of developing dedicated equipment for a specific application, rather than adapting general-purpose machines, is often the most effective strategy for achieving optimal performance. The hydraulic control analysis provides valuable reference for similar automation projects in tube processing.

For engineers involved in bearing manufacturing or precision tube cutting, this work highlights the importance of process-specific equipment design. The systematic approach to hydraulic system design—matching circuit functions to process requirements—serves as a useful template for similar automation projects. The emphasis on precision control for small-diameter tubes addresses a real industrial need where general-purpose cutting machines often fail to meet the stringent quality requirements of bearing manufacturing.