What is Transformer Silicon Steel Sheet Shearing? The Critical Step for Core Efficiency

Introduction

When a transformer hums too loudly or runs too hot, the issue often begins long before electricity ever flows — it starts with how the silicon steel sheets are sheared. Poorly cut transformer laminations create microscopic air gaps and magnetic stress, increasing core loss, noise, and long-term energy consumption.
Precise silicon steel shearing, however, keeps every lamination perfectly aligned with the grain-oriented electrical steel (GOES)¹ direction, protecting the insulation coating and ensuring a cooler, quieter, and more efficient transformer core — engineered to perform reliably for decades.

Fundamentals: The Science and Purpose of Silicon Steel Shearing

When cutting is sloppy, the losses go up and the hum increases louder. Exact shearing turns coils into lamination sets that keep the grain orientation, cut down on air gaps, and protect the insulation, which keeps the core’s efficiency.

Definition: From Coil to Core Laminations

Example: Silicon Steel Coil to Core Lamination Process

Watch how CHBEB transforms GOES coils into precision-cut laminations — including shearing, punching, and stacking for step-lap transformer cores.

Shearing is the precise cutting of grain-oriented electrical steel (GOES/GOSS) from mill coils into laminations for E-I, C-core, wound-core, or mitered core stacks. Main goals:

• The length, width, window, and miter angles are all exactly right.
• Keep the inorganic insulation intact to avoid inter-lamination eddy currents that can damage the coating.
• Grain alignment: The flux follows the direction of rolling to lower the magnetizing VA.
• High stacking factor: flat, even laminations fit firmly together with very little air trapped inside.

Typical flow: uncoil, cut, shear/miter punch, notch/holes, deburr/clean, and sort and stack (step-lap plan). For wound cores, strip slitting and winding take the role of discrete cutting, but the standards for edge integrity stay the same.

The “Why”: How Cutting Quality Directly Impacts Core Losses and Noise

Cutting can harm the edge microstructure by making burrs, work-hardening, and microcracks. These make local flux detours and hidden air gaps, which makes:

• Loss at no load (P₀): extra core loss from hysteresis and eddy currents caused by poor silicon steel shearing at stressed edges.
• Exciting current: more VA is required to magnetize the transformer core.
• Magnetostriction noise: mechanical stress increases the 100/120 Hz transformer hum.

The Manufacturing Precision: Techniques, Technology, and Quality Control

Pressure to produce leads to flaws. Every lamination is exact, flat, and low-stress thanks to disciplined tools, steady procedures, and verifiable quality assurance.

The 45-Degree Secret: Step-Lap Joints and How to Cut Down on Air Gaps

In transformer silicon steel shearing, the 45° mitered joint is not just a design detail—it’s a performance secret.
By combining mitered 45° joints with step-lap stacking², the air gap at the core joints is distributed across several overlapping steps, allowing magnetic flux to flow more smoothly through the transformer core.

This precision design delivers multiple advantages:

• Lower no-load loss (P₀) and fewer hot spots due to reduced local flux density at the joints.
• Quieter operation, as stress-driven magnetostriction at the corners is minimized.
• Easier assembly, since the gradual overlap reduces mechanical stress and improves core alignment.

👉 The result: tighter magnetic circuits, lower energy loss, and longer-lasting, quieter transformers.

Checklist for good practice:

• Angle accuracy: 45.0° ± 0.1–0.2° (for premium low-loss cores, it should be closer).
• Step pitch control: the length of each step stays the same (for example, 6–20 mm vs. the width of the lamination).
• Overlap sequencing: set lap order (like ABC/ABC) to stop flux gaps from happening.
• Grain direction: line up the direction of the rolling; never flip a piece at the joint.
• Flatness and planarity: tight stacks keep air gaps and buzzing from happening.

Fine-blanking/miter punching (high throughput), CNC miter shear (flexible, precise), and laser (excellent geometry—manage heat-affected zone and think about stress-relief anneal for premium grades) are all ways to cut miters.

Quality Checks: Avoiding Burrs, Damage, and Mechanical Stress

In transformer silicon steel shearing, precision quality control ensures every lamination meets performance standards.
From burr height to surface coating and stack flatness, each metric directly affects core loss, magnetizing current, and noise level in the final transformer core.

1️⃣ Burr Height (Edge Quality)
For distribution transformer cores, burr height should be ≤ 0.02–0.05 mm.
Excessive burrs may bridge laminations and cause inter-lamination shorts, leading to higher eddy current losses and heating.

2️⃣ Tooling and Clearance
Maintain punch/die clearance at 5 – 10 % of material thickness.
Use SPC to monitor the rollover, shear, and fracture zones to detect die wear before it affects edge quality.

3️⃣ Coating Integrity (Surface Resistivity)
Check surface resistivity to confirm that the inorganic insulation coating remains intact.
Never stack laminations that are scratched, oily, or dirty — this can cause partial shorts and higher losses.

4️⃣ Dimensional Accuracy & Miter Angle
Apply vision gauging to verify length/width tolerances (±0.10–0.20 mm) and miter angle accuracy.
Hole and notch alignment keeps assembly stress evenly distributed and prevents frame distortion.

5️⃣ Residual Stress Control
Use low-stress shear parameters, sharp dies, and stress-relief annealing when needed.
Apply controlled torque when clamping frames to prevent additional mechanical strain.

6️⃣ Stacking Factor & Flatness
Compare the actual stack height with the theoretical value to calculate the stacking factor.
Use insulated clamps to compact the stack evenly and minimize trapped air.

7️⃣ Cleanliness Management
Treat the stacking area like a clean zone.
Use vacuum or ionized air to remove chips, dust, and oil film between laminations to avoid micro-air gaps.

8️⃣ Process Data Tracking
Record burr height, angle, dimensions, resistivity, and stacking factor for every lot.
Correlate QA data with no-load loss (P₀) and noise test results of finished cores to trace cause and effect.

👉 Precise quality control during silicon steel shearing is what guarantees long-term transformer efficiency, quiet operation, and minimal power loss.

CHBEB — Reliable Partner for Distribution Transformers

With over 60 years of transformer manufacturing expertise, CHBEB has become one of China’s most trusted distribution transformer suppliers. The company operates two factories in Wenzhou, one in Nanjing, and an office in Beijing, ensuring both strong production capacity and responsive customer support.

What makes CHBEB stand out:

• Strict Quality Commitment: All raw materials are 100% new and high-grade — no recycled or downgraded components.
• Proven Reliability: A qualified supplier for the State Grid Corporation of China, with a spotless record of zero major accidents.
• 100% Product Testing: Every unit is fully tested before delivery to guarantee safety, efficiency, and long service life.
• Fast-Track Orders: Ability to fulfill urgent orders in as little as one week, helping customers meet tight project deadlines.
• Custom Inventory Planning: Flexible stocking and supply strategies designed to align with customer procurement schedules.
• Global Outlook: Rooted in China and expanding worldwide, CHBEB actively supports local agents and partners, including assistance with market-specific certifications.
• Flexible Customization: Tailored transformer designs for utilities, contractors, and industrial clients, with reliable quality and fast delivery.

👉 Looking for a distribution transformer manufacturer that combines Chinese manufacturing strength with international standards?Contact CHBEB for a tailored solution or Download our full transformer catalog here.

Conclusion

Precise silicon steel shearing isn’t just a workshop detail—it’s the foundation of low core loss, quiet operation, and long transformer life. When burrs are controlled, coatings preserved, and 45° step-laps aligned, magnetic flux flows smoothly with minimal energy loss.

For global transformer buyers, shearing quality is a direct indicator of supplier capability. Every 0.01 mm of burr height or misaligned grain direction can raise no-load loss and noise by several percent—affecting both energy bills and reliability.

At CHBEB, precision CNC miter shearing and step-lap core assembly ensure every lamination meets IEC core loss standards before stacking. That’s why CHBEB’s cores stay efficient, quiet, and consistent in projects across the Middle East, Africa, and Southeast Asia.

👉 Learn more: Oil-Immersed Transformer Guide · Dry vs Oil Transformer Comparison · Transformer Maintenance Checklist

1. Grain-oriented electrical steel ↩︎
2. Step-lap core construction in transformers ↩︎