Lesson 7 – Contact Mechanics and Removal Physics

What You Will Learn

Explain why contact between the tool and optic is important.
Describe how polishing pressure affects removal.
Understand the role of compliant polishing tools.
Recognize factors that influence material removal.
Learn how stable polishing conditions improve accuracy.

Understanding Contact Mechanics

During polishing, the tool must maintain smooth and consistent contact with the optical surface. This contact allows the abrasive particles in the polishing slurry to remove material evenly across the workpiece. If contact pressure changes unexpectedly, the removal function also changes. This can produce figure errors, uneven polishing, or poor surface quality. Even slight variations in pressure can create measurable differences in material removal across the optic. Engineers carefully design polishing tools and machine settings to create stable contact throughout the polishing process. Maintaining consistent contact is one of the keys to successful deterministic polishing because it allows the machine to repeatedly produce the same removal behavior.

Compliant Polishing Tools

Most UFF systems use compliant polishing tools rather than rigid laps. These tools are slightly flexible, allowing them to conform to changing surface shapes while maintaining consistent polishing pressure.

The flexibility of the tool makes it possible to polish steep curves, aspheric surfaces, and freeform geometries without damaging the optic. It also helps distribute polishing forces more evenly across the contact area.

Different polishing pads may be selected depending on the material being polished, the desired removal rate, and the required surface finish. Choosing the correct pad helps balance polishing speed with surface quality while extending tool life.

Factors That Affect Material Removal

Several variables influence how quickly material is removed from the optical surface. Pressure and relative velocity are the primary factors described by Preston’s Law, but other conditions also play important roles. Tool wear, slurry condition, abrasive size, polishing pad material, temperature, and machine stability all affect polishing performance. Even small changes in one of these variables can alter the removal function. A polishing pad that has become worn or contaminated may remove material differently than a new pad, even when all machine settings remain the same. For this reason, technicians monitor process conditions carefully throughout production to maintain consistent polishing results.

Maintaining Process Stability

Successful deterministic polishing depends on consistency. Operators routinely inspect polishing tools, clean machine components, replace worn polishing pads, and verify machine calibration. Stable polishing conditions allow the removal function to remain predictable from one polishing cycle to the next. This reduces rework, shortens production time, and improves manufacturing efficiency. Careful process control also helps ensure that every optical component meets its required specifications while producing repeatable, high-quality results.

Interactive Contact Pressure Simulator

The Contact Pressure Simulator allows you to adjust polishing force and observe how the contact area changes. You can compare light, moderate, and heavy polishing pressure while viewing the predicted removal pattern. As you change the pressure, notice how the contact area and expected removal profile respond. This exercise demonstrates why maintaining consistent polishing conditions is essential for achieving accurate optical surfaces.
Interactive Contact Pressure Simulator

Interactive Contact Pressure Simulator

Adjust polishing force to see how contact area, pressure distribution, and the predicted removal pattern respond.

Adjust Polishing Conditions

Polishing Force

28 N

Pressure Level

Moderate

Contact Diameter

14.2 mm

Peak Pressure

0.88 MPa

Relative Removal

1.00×

Tool Contact and Pressure Distribution

Predicted Removal Pattern

Compare Light, Moderate, and Heavy Pressure

Light Pressure

Small contact patch and lower removal.

Moderate Pressure

Balanced contact area and removal.

Heavy Pressure

Wider, deeper removal with more risk.

Contact Stability

The tool is operating near a balanced pressure range.

Process Meaning

Moderate pressure creates a predictable contact area and stable removal function.

Moderate force produces a balanced contact patch and predictable removal pattern.

Stable contact between the polishing tool and the optic provides the foundation for accurate material removal. Once the removal function is predictable, the polishing machine can precisely control where and how long the tool contacts the surface. In the next lesson, you’ll explore CNC toolpaths and discover how machine motion controls polishing accuracy, efficiency, and surface quality.

Introduction to Subaperture Polishing

Curriculum

Lesson 7 – Contact Mechanics and Removal Physics

What You Will Learn

Understanding Contact Mechanics

Compliant Polishing Tools

Factors That Affect Material Removal

Maintaining Process Stability

Interactive Contact Pressure Simulator

Interactive Contact Pressure Simulator

Adjust Polishing Conditions

Light Pressure

Moderate Pressure

Heavy Pressure

Modal title