In the coated abrasives industry, laser cutting is increasingly used for sanding disc perforation and shape cutting. However, when it comes to coarse-grit materials such as P40 sandpaper, users often encounter a common problem:

The laser burns through the backing, but the abrasive grains remain intact. Small holes cannot be opened cleanly because the grains get stuck and do not fall off.

To understand why this happens, we need to look at both the structure of sandpaper and the working principle of laser processing.

1. Structure of P40 Sandpaper: The Abrasive Grains Are Too Hard

Sandpaper generally consists of:

1. Backing (paper, cloth, or composite)

2. Bonding resin

3. Abrasive grains

For P40 sandpaper, the abrasive particles are very coarse, typically 425–500 μm in size. These grains are made of extremely hard ceramic materials such as aluminum oxide, silicon carbide, or zirconia alumina, which have extremely high melting points.

High-power lasers can cut the backing easily, but cannot melt or vaporize the ceramic grains.

2. What the Laser Actually Does on Sandpaper

Laser cutting is based on a thermal ablation process:

• The backing burns or melts through easily

• The bonding resin softens or vaporizes

• But the abrasive grains remain solid and untouched

This means the laser only separates the backing layer, while the coarse grains remain in their original position.

3. Why the Grains Block the Hole: The Core Problem

When creating small holes (e.g., 2–6 mm), the following occurs:

① The laser burns the backing, but the abrasive grains do not break

Even after the backing is fully opened,
the grains stay intact because the laser cannot cut them.

② Grains interlock and cannot fall off

Because P40 grains are:

• large

• tightly packed

• bonded by a thick resin layer

they form a mechanically interlocked structure.

Even if the backing is removed,

the grains remain suspended inside the hole and clog it.

4. Why Small Holes Are Especially Difficult

The smaller the hole:

• the smaller the thermal area

• the less the resin can be vaporized

• the more tightly the grains bridge together

This leads to poor grain detachment, making clean perforation almost impossible.

Small-diameter laser holes on P40 sandpaper are structurally infeasible.

5. Why Finer Grits (P80, P120, P180…) Work Well

Fine sandpapers have:

• smaller abrasive grains

• thinner bonding layers

• weaker mechanical interlocking

• easier grain detachment during laser ablation

Therefore, the finer the grit, the better the laser processing performance.

6. Practical Recommendations for P40 Sandpaper

Laser-friendly operations:

• Outer-shape contour cutting

• Large-size holes (≥15–20 mm)

• Cutting from the backing side rather than the abrasive side

Not recommended for laser:

• Small holes (≤8 mm)

• High-precision perforation

• Fine slotting or surface micro-features

In these cases, mechanical die-punching is preferred.

Conclusion

Laser processing of P40 sandpaper is limited due to its material properties:

• The abrasive grains are ceramic and cannot be cut by laser.

• The laser only penetrates the backing.

• Large grains remain stuck and block small holes.

This is why coarse-grit sandpapers (like P40) are not suitable for small-hole laser perforation, even with high-power laser systems.