Experiment Comparative Analysis of Feed Rate with Velocity Control in Cutting Mono Crystalline Silicon Using a Diamond Wire Saw

At a Glance

Metadata	Details
Publication Date	2024-03-29
Journal	Micromachines
Authors	Jiabin Wang, Shujuan Li, Lie Liang
Institutions	Xi’an University of Technology
Citations	4
Analysis	Full AI Review Included

Executive Summary

This research investigates the optimization of fixed-diamond abrasive wire sawing for monocrystalline silicon by implementing adaptive force control. The core objective was to stabilize the normal cutting force ($F_n$) to simultaneously improve cutting efficiency and surface quality.

Adaptive Control Implementation: A Proportional-Integral (PI) controller was successfully designed and implemented to maintain a constant reference normal force ($F_r$) during the slicing process.
Control Object Comparison: Two primary process parameters were tested as control objects: Workpiece Feed Rate ($V_x$) and Wire Saw Velocity ($V_s$).
Superior Performance (Feed Rate Control): Controlling the Workpiece Feed Rate ($V_x$) proved significantly more effective. It achieved an average 40.6% reduction in total cutting time.
Surface Quality Improvement: $V_x$ control resulted in the best surface finish, reducing the average surface roughness ($S_a$) by 63.3% compared to constant feed rate experiments.
Velocity Control Results: Controlling the Wire Saw Velocity ($V_s$) provided moderate improvements, yielding an average 11.7% reduction in cutting time and a 54.2% reduction in $S_a$.
Conclusion: Feed rate control is the preferred method for optimizing diamond wire sawing, offering a substantial increase in productivity and quality under stable force conditions.

Technical Specifications

Parameter	Value	Unit	Context
Workpiece Material	Mono-crystal Silicon	N/A	Specimen size: 220 x 20 x 26 mm
Workpiece Hardness	~6.5	Mohs	Polysilicon
Wire Saw Diameter	0.24	mm	Fixed-diamond abrasive wire
Abrasive Grain Size	30-50	µm	JR2-type diamond abrasive
Wire Saw Velocity ($V_s$) Range	0-4	m/s	Maximum operational range
Part Feed Rate ($V_x$) Range	0-3	mm/min	Maximum operational range
Wire Tension Range	0-0.6	MPa	Adjustable via movable wheel
Normal Force ($F_n$) Range	32	N	ATI Gamma SI-32-2.5 dynamometer
Feed Rate System Time Constant ($\tau_x$)	0.016	s	Determined by step response
Wire Velocity System Time Constant ($\tau_s$)	0.4	s	Determined by step response
Optimal $F_r$ (Feed Rate Control)	2.5	N	Reference force yielding best results
$V_x$ Control $S_a$ Reduction (Max)	65.2	%	Achieved at $F_r$ = 2.5 N
$V_s$ Control $S_a$ Reduction (Max)	64.6	%	Achieved at $F_r$ = 2.0 N
$V_x$ Control Time Reduction (Max)	42.0	%	Achieved at $F_r$ = 2.0 N

Key Methodologies

Experimental Platform Construction: A custom hardware system was built utilizing a reciprocating wire saw machine, integrating a DC motor for wire velocity and a stepping motor for workpiece feed rate.
Force Measurement: A six-component ATI dynamometer (Gamma SI-32-2.5) was used to measure the normal cutting force ($F_n$) acting on the silicon specimen, sampled at 10 Hz.
Static Force Modeling: An empirical static model relating normal force to feed rate and wire velocity was established using least squares fitting: $F_n(t) = K V_x(t)^\alpha V_s(t)^\beta$.
Controller Design: The static model was linearized, and a Proportional-Integral (PI) controller was designed to regulate the incremental command velocity ($\Delta V_c$) based on the incremental force error ($\Delta E_n$).
System Dynamics Characterization: Time constants ($\tau$) for the feed rate execution unit (0.016 s) and the wire saw velocity execution unit (0.4 s) were determined via step response measurements to tune the PI controller gains ($K_p$, $K_i$).
Feed Rate Control Experiment: The PI controller adjusted the Workpiece Feed Rate ($V_x$) dynamically to maintain reference forces ($F_r$) of 2.0, 2.5, and 3.0 N, while $V_s$ was held constant at 1 m/s.
Wire Velocity Control Experiment: The PI controller adjusted the Wire Saw Velocity ($V_s$) dynamically to maintain reference forces ($F_r$) of 2.3, 2.0, and 1.7 N, while $V_x$ was held constant at 0.75 mm/min.
Performance Evaluation: Cutting time and surface roughness ($S_a$) were measured and compared against baseline experiments conducted using constant, non-controlled parameters.

Commercial Applications

Semiconductor Wafering: High-yield, high-precision slicing of large monocrystalline silicon ingots for integrated circuit (IC) fabrication, minimizing subsurface damage (SSD) and maximizing wafer quality.
Photovoltaic Industry: Efficient production of silicon wafers for solar cells, where minimizing kerf loss and increasing throughput (40.6% time reduction) directly impacts manufacturing cost.
Advanced Materials Processing: Precision cutting of other hard and brittle materials, including sapphire, silicon carbide (SiC), and rare-earth permanent magnets, where maintaining low, stable cutting forces is essential to prevent cracking or chipping.
Precision Equipment Manufacturing: Integration of adaptive force control systems into next-generation wire saw machinery to automate parameter adjustment and ensure consistent processing quality regardless of wire wear or material variations.

View Original Abstract

Fixed-diamond abrasive wire saw cutting is one of the most common methods for cutting hard and brittle materials. This process has unique advantages including a narrow kerf and the ability to use a relatively small cutting force. In the cutting process, controlling the main process parameters can improve the processing efficiency, obtaining a better processing surface roughness. This work designs the PI controller (Proportional-Integral controller) based on the reciprocating wire saw cutting process. The control objects are the workpiece feed rate and wire saw velocity, and the control objective is the normal cutting force. For the control trials, several reference values of various normal cutting forces were chosen. The effects of feed rate and saw velocity on the cutting surface finish and cutting time were investigated in this work using wire saw cutting analysis on a square monocrystalline silicon specimen. The results of this study showed that under a constant applied force of 2.5 N, the optimal feed rate of the diamond wire through the specimen could reduce cutting time by 42% while achieving a 60% improvement in the measured surface finish. Likewise, optimal control of the wire saw velocity could reduce cycle time by 18% with a 45% improvement in the surface finish. Consequently, the feed speed control is more effective than the wire saw velocity.

Tech Support

Original Source

DOI: https://doi.org/10.3390/mi15040473

References

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