CRACK DETECTION in ZrO2 CERAMICS

Resonance Ultrasonic Vibrations (RUV) Technology

• High accuracy: up to 99%
• High throughput: <5seconds/cycle
• Non destructive
• In-line & Off-line configuration

RUV TECHNOLOGY

The Resonance Ultrasonic Vibrations (RUV) technique was developed for off-line and in-line non-destructive crack and stress detection in ceramic materials such as pre-sintered dental ZrO2. The RUV method relies on deviation of the resonance frequency response curve measured on a sample with millimeter length crack compared to identical non-cracked samples.

The RUV technology allows to (1) reject mechanically unstable ceramic objects before they are introduced into further processing, (2) identify objects with cracks and high stress in real time to avoid parts breakage during milling or final sintering, and (3) to save production expenses by eliminating labor cost on cracked ceramic discs. RUV system also serves as a process control tool to increase yield by eliminating production flaws caused by mechanical defects.

Zirconia ceramics is a primary material for state-of-the-art dental industry. Its primary benefits are superior strength (x5 better than porcelain), durability, biocompatibility, natural color and translucency to match a natural teeth. However, as any other ceramics, ZrO2 discs are prone to invisible cracking which lead to dentures breakage during milling or initial wear. RUV technology is adapted to 100% cracks inspection of ZrO2 dental discs before processing in a dental lab.

FREQUENCY CURVE

Through a resonance frequency curve selected from a broad range (20 - 250 kHz) the RUV method enables screen out materials with hidden invisible cracks. A crack introduced into ceramics alters the RUV peak parameters: amplitude, bandwidth and peak position. The inspection approach is illustrated in Figure 1. Specifically, the crack in the disc measured at different angles in the rotation mode shows the following RUV feature: large individual peak variation between three scans (right plot) compared to high coincidence for a good sample (left plot). Therefore, the RUV approach is based on a fast measurement and analyses (below 5 seconds per scan) of a specific resonance peak and automatic part rejection if peak characteristics deviate from the normal non-cracked samples. Additional RUV feature is stress inspection caused by voids and components delamination.

The sensitivity of the system, which refers to the length of the cracks, is adjustable to the needs of the user. The rejecting method is based on a statistical approach. In production the accuracy of this method to find cracked material approaches 99%. RUV system is used in production of ZrO2 dental discs, Zr-based solid oxide fuel cells and metallized ceramic rings.

IN LINE & OFFLINE CONFIGURATIONS

Fully automatic In-line, Off-line and Quality Control RUV Tools are currently available for ceramic products. For technical information and RUV system availability, please contact Ultrasonic Technologies at support@ultrasonictech.com

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