Ultra-strong diamond wire made from tungsten filaments

Amid the photovoltaic industry’s drive to reduce costs and boost efficiency, a thin wire less than 40 microns in diameter is emerging as a key enabler of transformation: tungsten-wire diamond wire. This cutting tool, which uses a tungsten wire as its base and incorporates fine diamond powder, is gradually replacing traditional high-carbon steel wire diamond wire thanks to its ultra-fine diameter, exceptional tensile strength, and minimal silicon-wafer loss, thereby becoming the “new favorite” in the field of photovoltaic silicon-wafer slicing.

From Rough to Refined: The Evolutionary Journey of Diamond Wire

The emergence of diamond wire sawing stems from an relentless pursuit of cutting efficiency. In the early days, the photovoltaic industry relied on slurry-based wire sawing, which involved mixing large quantities of silicon carbide abrasive with a cutting fluid and using a steel wire to drive the abrasive against the silicon ingots for cutting. This process was not only slow and costly in terms of consumables but also imposed significant environmental challenges due to the complex recycling and treatment of the cutting fluid. Around 2010, diamond wire sawing technology made a breakthrough: by electroplating fine diamond powder onto the surface of high-carbon steel wire, the cutting speed increased by two to three times, while the need for cutting fluid was reduced to water-based coolants, fundamentally transforming the traditional cutting paradigm.

However, technological advancement never ceases. As photovoltaic silicon wafers move toward larger sizes and thinner gauges, reducing the wire diameter has become central to cost reduction. The diameter of diamond wire has been progressively reduced from 120 microns in 2011 to 35–40 microns in 2022; yet the physical limits of high-carbon steel wire are becoming increasingly apparent: when the diameter falls below 35 microns, its tensile strength and flexibility decline sharply, leading to a dramatic increase in wire breakage rates. It is at this juncture that tungsten wire, owing to its unique material properties, has come into the industry’s focus.

Tungsten Wire: The “Super-Power Mother Wire” for Diamond Wire

Tungsten (W) has a melting point as high as 3,410°C, making it one of the metals with the highest melting point in nature. By doping it with elements such as rhenium (Re) and lanthanum (La) and subjecting it to a 36-pass diamond-die drawing process, tungsten wire can be drawn down to a diameter of less than 40 micrometers while retaining its remarkable physical properties:

1. Tensile strength exceeds 6,000 MPa: 1.5 times that of high-carbon steel wire of the same specification, enabling it to withstand higher cutting tension and reducing the risk of wire breakage;

2. Significant potential for finer wire: Tungsten wire mother rods have achieved mass production at 28–38 microns, further reducing the limit diameter compared with carbon steel wire (35 microns) and enabling smaller kerf widths.

3. Excellent fatigue resistance: Under high-frequency reciprocating cutting, the service life of tungsten wire is more than 30% longer than that of carbon steel wire, thereby reducing the per-unit consumable cost of slicing.

4. Excellent thermal stability: The heat generated during the cutting process has a minimal impact on the performance of the tungsten wire, ensuring stable cutting accuracy.

Take Xiamen Tungsten Co., Ltd. as an example: its doped tungsten wire, produced via a process that includes tungsten powder compaction, rotary forging to form billets, and 36 drawing passes, not only achieves line-diameter uniformity within ±0.5 microns but also boasts a surface roughness of Ra 0.2, providing an ideal substrate for the uniform embedding of diamond micro-powder. This high-precision manufacturing capability enables tungsten-wire diamond wire saws to reduce silicon-wafer loss by 0.1 gram per wafer during the cutting of monocrystalline silicon wafers; based on current silicon-material prices, this translates into a cost reduction of RMB 0.26 per wafer.

Technological Breakthroughs: Bridging the Gap from the Lab to Mass Production

The industrialization of tungsten-wire diamond wire has not been smooth sailing. In the early stages, tungsten-wire mother wire faced two major technical bottlenecks:

1. Low drawing process yield: Tungsten has significantly lower ductility than steel, making it prone to breakage during the drawing process; the industry average finished-product yield is only 50%–60%, a substantial gap compared with carbon steel wire (70%–90%).

2. Insufficient electroplating adhesion: The atomic bonding strength between tungsten and nickel is weaker than that between steel, resulting in easy delamination of the plating layer and compromising the bond strength of the diamond micro-powder.

In response to these challenges, leading companies are undertaking targeted technological research and development:

- Zhongtung Online employs a “two-stage hydrogen reduction followed by acid leaching for impurity removal” process to increase tungsten powder purity to 99.99%, thereby minimizing the interference of impurities during wire drawing.

- Meichang Co., Ltd. has pioneered a dual-layer electroplating technology combining “impact plating” and “sand-bonded plating,” which forms a gradient nickel layer on the surface of tungsten filaments, increasing coating adhesion by 40%;

- Gaoce Shares has developed “ultrasonic-assisted drawing” equipment that reduces the deformation resistance of metals through high-frequency vibration, increasing the yield rate of 38-micron tungsten wire from 52% to 68%.

In 2025, China’s domestic production capacity for tungsten-wire diamond wire is expected to exceed 137 million kilometers, with companies such as Meichang Shares, Xiamen Tungsten, and Dailer New Materials accounting for 80% of the global market share. Although the current cost of tungsten wire remains two to three times that of carbon steel wire, under the backdrop of persistently high silicon wafer prices—around RMB 260 per kilogram—using tungsten-wire diamond wire can reduce silicon material costs by RMB 1.2 million per gigawatt of silicon wafers, gradually highlighting its economic advantages.

The Future: The Ultimate Race for Fine-Grained Precision

The photovoltaic industry’s drive to reduce costs is relentless. Currently, 32-micron tungsten-wire diamond wire has entered mass production, while the 28-micron version is undergoing pilot-scale testing. According to estimates, if the wire diameter is further reduced to 25 microns, the number of wafers that can be cut from a single kilogram of silicon ingot could increase by 12%, translating into a module power boost of more than 5 watts. Meanwhile, tungsten-wire master-wire technology continues to evolve:

- Nanocrystallization treatment: By controlling the tungsten filament grain size to below 50 nanometers, material toughness is enhanced;

- Composite plating technology: Incorporating carbon nanotubes into the nickel layer to enhance the wear resistance of the coating;

- Intelligent manufacturing: An AI-powered visual inspection system is deployed to monitor diameter fluctuations in real time during the drawing process, maintaining wire diameter deviation within ±0.3 microns.

From high-carbon steel wire to tungsten wire, the evolution of diamond wire is a microcosm of technology-driven innovation in the photovoltaic industry.

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