What Is Double-Sided Lapping? | IRD Glass

The term “lapping” stems from the acronym Loose Abrasive Process. Quite simply, the lapping process involves mixing water or oil with abrasive particles, which results in a slurry that acts as a liquid cutting tool. The liquid between the plate and workpiece creates an exact grinding and cutting action, leaving a rough, yet flat surface. 

Single-sided lapping involves one lapping plate, while double-sided lapping has an upper plate that floats, a lower plate, a gear ring, and a sun wheel. Efficiency doubles with double-sided lapping as two surfaces are machined simultaneously. Clamping stress is also avoided when using double-sided vs. single-sided lapping. 

What Is the Double-Sided Lapping Process?

The double-sided lapping process is as follows:

1. The lap wheel is fixed to the upper and lower lapping disc.
2. The workpiece is put in the differential gear (sun gear and ring gear).
3. The cylinder pressurizes the upper lapping disc, which causes lapping pressure. 
4. The upper and lower lapping wheels are typically rotated at equal angles of opposite magnitudes.
5. This rotation causes force to be applied to the workpiece.

Double-sided lapping can use either fixed abrasive or loose abrasive, depending on what is needed. Often, the components will also require double-sided polishing, but for other applications, only lapping is needed for completion. 

What Is Double-Sided Lapping Used For?

Double-sided lapping can be used for a variety of components. However, double-sided lapping is ideal when:

• The design requires a high level of flatness and parallelism
• The sides have certain requirements for flatness
• Both sides of the component must be exactly equal and parallel in finish

Our specifications for double-sided lapping include:

Typical:

• Max size 13.3″ / 340 mm
• Flatness +/- 50 μm / 1.25 micrometer μm
• Parallel (same as flatness above)
• Roughness Ra <10 μm / <0.25 micrometer μm

Best:

• Same max size
• Flatness +/- 10 / 0.25 μm
• Parallel same as flatness
• Roughness <5 / <0.12 μm

Other applications for double-sided lapping include gears, robotics, and electronics. Double-sided lapping used in electronics applications can achieve tolerances to the next level of zero.

What Are the Pros and Cons of Using Double-Sided Lapping?

There are certain advantages when it comes to double-sided lapping. The better the lapping quality, the less time it takes to polish, which is a much slower process. When comparing double-sided lapping (and polishing) to the single-side process, it has these advantages:

• Faster processing (lapping both sides at once)
• Flatness
• Parallelism

Disadvantages of double-sided lapping vs. single-sided include:

• There is a size limitation
• Extreme aspect ratios
• Not optimal for small volumes
• Two sides can’t have different surface requirements 

Double-sided lapping is a wise choice for larger pieces and larger volumes. 

To learn more about polishing and our other capabilities, contact IRD Glass today to speak with a team member or receive a quote.