How To Minimize HAZ in Silicon Steel Laser Cutting: Ultimate Guide for Motor Core Prototyping

In the previous blog, we addressed the issue of burrs during the processing of motor cores. However, another critical factor determining motor core performance—the Heat Affected Zone (HAZ)—has yet to be thoroughly explained. This blog will delve deeper into the prototyping of silicon steel motor cores, providing a detailed analysis of HAZ and practical control methods.

Scientific Definition and Formation Mechanism of HAZ

Physical Essence of HAZ

The Heat Affected Zone (HAZ) refers to the area in metal materials where localized heating occurs during laser processing, without reaching the melting point. Microstructural changes, such as phase transformation, grain coarsening, or element segregation, occur due to temperature gradients, leading to significant alterations in mechanical properties, magnetic performance, and corrosion resistance.

Special Characteristics of Silicon Steel: As the core material for motor cores, silicon steel contains 3%–5% silicon to enhance magnetic permeability. However, silicon reduces thermal conductivity, exacerbating heat accumulation in the HAZ.

Three Primary Causes of HAZ Formation

1. Laser Operating Modes

Continuous vs. Pulsed Lasers:

Continuous lasers (e.g., standard cutting machines) expand the HAZ due to prolonged heat exposure；Pulsed lasers (e.g., nanosecond/picosecond lasers) minimize heat diffusion through ultra-short pulses (on the order of 10^-8 seconds).

Energy Concentration:
High power density (>10^6 W/cm²) enables near-instantaneous processing, reducing peripheral heating and HAZ width.

2. Material Properties

Thermal Dissipation: Silicon steel’s poor thermal conductivity leads to heat accumulation at cut edges, unlike ordinary steel with better heat dissipation.

Thermal Resistance: Silicon steel softens at ~1500°C (lower than ordinary steel), requiring precise temperature control to avoid oxidation and burrs.

3. Process Optimization

Cutting Speed: Too slow → edge carbonization；Too fast → irregular cuts.
Optimal speed ensures smooth cuts and minimal heating.

Assist Gas: Nitrogen suppresses oxidation but requires pressure adjustment based on material thickness to avoid deformation.

By combining these factors (appropriate laser type + material-specific parameters + precise operation), HAZ can be minimized effectively.

Visual Characterization of HAZ

(Source: Wikipedia)

Color Changes: Oxidation bands (yellow → purple → blue) reflect temperature gradients (300°C–600°C).

Metallographic Analysis: SEM reveals grain boundary migration and carbide precipitation.

Hardness Changes: Vickers hardness testing shows HAZ hardness increases by 15%–30%, with reduced toughness.

Technical Advantages and Industrial Applications of Laser Prototyping for Silicon Steel

Laser Cutting vs. Traditional Processes

Four Core Advantages of Laser Prototyping

1. Narrow Kerf & Low Heat Input: Fiber lasers (1064nm wavelength) with <30μm spot size reduce HAZ width (e.g., 0.15mm for 0.5mm silicon steel).

2. Non-Contact Processing: Eliminates mechanical stress, ensuring lamination flatness (≤0.02mm/m²).

3. High Flexibility: Supports rapid small-batch prototyping (72-hour delivery).

4. Green Manufacturing: No mold wear, intelligent nesting reduces scrap by 50%.

Industry Applications

EV Motors: Stator core skew slots (laser precision ensures magnetic symmetry).

Servo Motors: Ultra-thin (0.2mm) cuts reduce eddy current losses.

Appliance Motors: Complex cooling holes and insulation slots improve efficiency.

HAZ Impact on Motor Core Performance and Risks

Three Core Performance Requirements for Motor Cores

1. Magnetic Properties: Low iron loss (W/kg), high permeability (B/H slope).

2. Mechanical Strength: Shear resistance ≥200MPa to prevent delamination.

3. Dimensional Consistency: Total thickness tolerance ≤0.1mm post-stacking.

Four Failure Modes Induced by HAZ

1. Magnetic Degradation:

HAZ lattice distortion hinders domain wall movement → iron loss increases 10%–20%.

Case: HAZ caused motor efficiency drop from IE4 to IE3 due to overheating.

2. Hydrogen Embrittlement:

Hydrogen from moisture/oil penetrates HAZ grain boundaries → delayed cracking.

3. Stacking Inaccuracy:

Uneven HAZ oxidation (0.005–0.02mm) → cumulative gaps → motor vibration.

4. Corrosion Susceptibility:

Chromium depletion in stainless-clad HAZ → rust → insulation coating failure.

CH Laser’s HAZ Control Solutions

Laser Cutting Control

Methods:

Optimize power, speed, focus.

Use nitrogen assist gas for heat dissipation.

Results:

Increasing speed from 7m/min to 15m/min reduces HAZ by 50%.

Nitrogen reduces HAZ width by 90% vs. air.

Laser Welding Control

Methods:

Adjust power, speed, pulse mode, spot size.

Use argon/helium shielding gas.

Results:

Reduced HAZ temperature/width and crack risk.

Summary: Laser systems minimize HAZ via parameter optimization, gas selection, cooling, and pre-/post-heating.

FAQ: Top 9 Questions on Silicon Steel Laser Prototyping

Q1: Can HAZ be eliminated entirely?
A: Theoretically impossible, but CH Laser’s pulse modulation limits HAZ to <0.1mm.

Q2: Is laser prototyping costlier than stamping?
A: For small batches (<1000 units), laser saves 30%–50% by eliminating molds.

Q3: How to test HAZ’s magnetic impact?
A: CH Laser provides iron loss and permeability testing.

Q4: HAZ differences by silicon steel thickness?
A: Thicker sheets → wider HAZ (0.2mm→0.08mm, 1mm→0.15mm, 2mm→0.25mm).

Q5: Can coated silicon steel be cut?
A: Yes, via negative defocusing (post-cut insulation resistance >100MΩ).

Q6: Does laser prototyping create burrs?
A: Picosecond lasers achieve "cold cuts" with <5μm burrs, no polishing needed.

Q7: Turnaround time?
A: Standard 3–5 days; expedited 72-hour service (requires material specs).

Q8: Support for complex shapes?
A: Yes (e.g.sector, skew slots), ±0.01mm precision.

Q9: Ensuring stacking consistency?
A: CH Laser provides tooling design + <10μm burr control (stacking tolerance ≤0.01mm).

Why Choose CH Laser Prototyping Service- Four Core Values Explained

1. High precision and complex shape machining capability

1.1 Micron-level precision: the positioning accuracy of laser cutting can reach ±0.01mm, which is suitable for fine cutting of high magnetic permeability materials such as silicon steel sheet, ensuring even air gap after motor core laminations and reducing magnetic loss;

1.2 Complex contour realization: it can easily process complex structures such as shaped grooves, teeth, curved edges, etc., to meet the special needs of high-performance motors or transformers on the shape of iron cores;

1.3 No mechanical stress: non-contact machining avoids material deformation or burrs caused by traditional stamping, and reduces subsequent grinding processes.

2. Rapid response and moldless production

2.1 No need to make molds: traditional stamping requires customized molds (long cycle time and high cost), while laser cutting is directly programmed and processed according to CAD drawings, which is suitable for small-lot and multi-variety sampling;

2.2 Shorten the R&D cycle: from design to sample delivery takes only a few hours to a few days, accelerating product iteration verification;

3. High material utilization

3.1 Flexible Adjustment: Only program parameters need to be modified when the design changes, no need to re-mold, reducing the cost of trial and error.

Optimized nesting cutting: maximize the utilization rate of silicon steel sheet through intelligent nesting software, reduce the edge waste, and lower the material cost (especially significant for the higher price of high grade silicon steel sheet);

3.2 High-efficiency processing of thin plates: the cutting efficiency of laser cutting on 0.1~3mm thick silicon steel wafers is much higher than that of traditional processes, and the heat-affected zone is small to avoid degradation of magnetic properties of materials.

4. Strict quality control

100% full inspection: dimensions (CMM), surface (white light interferometer), magnetic properties (B-H analyzer)

If you are worried about motor core lamination burrs or are interested in CH Laser's innovative solutions, please feel free to leave your request and our professional team will be happy to serve you.

Conclusion

HAZ control in silicon steel sheets laser prototyping is the core challenge of balancing efficiency, cost and performance. CH Laser provides customers with “near-zero HAZ” motor core prototyping services by virtue of its pulse modulation technology, closed-loop dynamic control, and process innovation along the whole chain, helping new energy, industrial automation and other fields to realize high-efficiency motor design. energy-efficient motor design in the fields of new energy and industrial automation.