How Is Sampling Conducted Using An Ultrasonic Plastic Welding Machine?
Apr 30, 2025
I. Pre-Sampling Preparation
1. Material Compatibility Verification
Conduct DSC (Differential Scanning Calorimetry) analysis to determine plastic melting points and crystallinity.
Example: ABS (melting point ~220°C) requires 20kHz equipment, while PP (melting point 165°C) necessitates 30kHz high-frequency devices to minimise thermal degradation.
For dual-component welding (e.g., PC+ABS), perform Melt Flow Index (MFI) testing (ASTM D1238) to confirm a flow rate difference ≤5g/10min, preventing interlayer separation.
2. Horn and Tooling Design
Adjust horn amplitude based on material thickness:
Use 5μm micro-amplitude horns for thin sections (<0.5mm).
Standard 15-20μm amplitude is recommended for thick sections (>2mm).
Energy Director design must comply with ASME standards:
Triangular profile height = 0.6 × material thickness.
Apex width ≤0.3mm improves welding efficiency by 30%.
3. Parameter Presets
Set welding pressure according to material hardness:
Semi-crystalline plastics (e.g., PA): 8-10 bar.
Amorphous plastics (e.g., PS): 5-7 bar.
Calculate welding time using:
T (ms)=Material Thickness (mm)×1.2Frequency (kHz)T(ms)=Frequency(kHz)Material Thickness(mm)×1.2
Example: 2mm PP at 30kHz requires ~80ms.
II. Sampling Procedure
1. Equipment Calibration
Validate horn amplitude with laser interferometry (tolerance ≤±5%).
Ensure frequency accuracy within ±0.1kHz.
Calibrate pressure sensors to ISO 7500-1 standards (repeatability error ≤0.5% FS).
2. Specimen Fixturing
Use three-point positioning fixtures (alignment accuracy ±0.02mm) to maintain weld interface gaps ≤0.05mm.
For complex geometries, employ vacuum adsorption fixtures (holding force ≥5kg/cm²) to prevent displacement.
3. Process Parameter Optimisation
Stepwise Testing:
Test pressure variables (6/8/10 bar) with 5 specimens per setting.
Determine optimal pressure via tensile testing (ASTM D638).
Response Surface Methodology (RSM):
Develop a three-factor model (time, pressure, amplitude).
Generate optimal parameters (e.g., 120ms, 8.5 bar, 18μm) using Design-Expert software.
