ultrasonic-welding

name	ultrasonic-welding
description	Ultrasonic welding — energy director design, joint types, frequency (20-40 kHz), amplitude, weld force, energy/time/distance modes, thermoplastic selection, amorphous vs. semi-crystalline, AWS/AWS standards.
metadata	{"priority":7,"promptSignals":{"phrases":["ultrasonic welding","ultrasonic plastic welding","energy director","ultrasonic weld","sonotrode","horn welding","thermoplastic ultrasonic"],"minScore":3}}

Ultrasonic Welding — Complete Skill

Process Overview

Ultrasonic welding joins thermoplastics using high-frequency mechanical vibration (20–40 kHz) Vibration → frictional and viscoelastic heating at interface → melting → solidification under pressure

Components:

• Power supply: converts 50/60 Hz to high-frequency electrical signal
• Converter/transducer: piezoelectric ceramics → electrical to mechanical vibration
• Booster: amplifies or attenuates amplitude (step-up/down ratios)
• Horn/sonotrode: amplifies and transmits vibration to part
• Fixture: supports and locates lower part; transfers welding force

Frequencies: 20 kHz: most common; larger parts; higher power; more robust 30 kHz: medium parts 40 kHz: delicate/thin parts; higher frequency → lower amplitude → less marking

Energy Director (ED) Design

Purpose: concentrate vibration energy at joint interface → initiates and controls melt front

Standard energy director (triangular cross-section): Height h: 0.2–0.5 mm (rule: h ≈ 0.25–0.30 × wall thickness) Apex angle: 60–90°; sharper → more energy concentration; more aggressive Width at base b: 2h (for 90° angle); h (for 60°)

Location: on one mating surface; vibrating horn presses onto flat mating surface

Multiple EDs: Longer joints → multiple parallel EDs; spacing ≈ 2–4 mm Hermetic sealing: serpentine or dual ED configuration

Shear Joint (Alternate to ED)

Telescoping fit; tight clearance (0.2–0.4 mm) Vibration → part moves laterally → melt forms at shear interface → locks when cooled Advantages: stronger; hermetic easier; lower residual stress Requires: better fixturing; tight tolerances

Scarf and Other Joints

Tongue-and-groove (butt joint): contains melt flash; cleaner appearance Stepped joint (lap): for thin film/sheet; requires intimate contact

Weld Process Parameters

Frequency (f)

20 kHz standard; horn length = λ/2 = c/f = 6350/(2×20,000) = 0.159 m for aluminum Higher frequency → shorter horn → smaller parts → less amplitude

Amplitude (A)

Peak-to-peak displacement at horn face Range: 15–120 μm peak-to-peak (0.5× to 2× base amplitude from converter + booster gain) Semi-crystalline polymers: higher amplitude required (50–120 μm) Amorphous: lower amplitude (15–60 μm)

Gain (amplitude ratio) = Booster ratio × Horn ratio Horn ratio from node-to-antinode design; stepped horn: gain = (D₁/D₂)²

Weld Force (Pressure)

Pneumatic actuator delivers constant force during welding Trigger pressure (initial squeeze): 20–100% of weld pressure Weld pressure: depends on material and joint area; typical: 0.2–2.0 MPa Hold pressure: same or lower than weld; maintains joint during solidification

Weld Time/Energy/Distance Control Modes

Time mode: fixed weld time → variable joint quality (less preferred) Energy mode: weld until set energy [J] delivered → more consistent Distance mode (collapse): weld until part collapses specified distance → most consistent Collapse = ED height × 0.5–0.9 (partial to full ED collapse)

Material Selection

Amorphous Thermoplastics (Most Weldable)

ABS, PC, PS, SAN, PMMA, PVC, PEI (Ultem): No discrete melting point; broad melt range → slower heat buildup → easier to control Low amplitude (15–50 μm); lower energy input required Excellent ultrasonic weldability

Semi-Crystalline Thermoplastics (More Difficult)

PP, PE, PA (nylon), POM (Delrin), PET, PBT: Sharp melting point; energy must raise T quickly above T_m Higher amplitude required (50–120 μm) PP: lowest weldability in class; high amplitude, short distance, near-field only PA (nylon): hygroscopic; must be DRY before welding (< 0.2% moisture); moisture → voids

Compatible Material Pairs

Both materials must be chemically compatible (similar structure) + compatible T_melt ABS + PC: compatible; PC/ABS alloys ABS + PMMA: compatible PP + PP: good; PP + PE: marginal PA6 + PA66: compatible; PA + POM: NOT compatible

Weldability Index

Product of acoustic impedance Z = ρ × c_sound and loss tangent (viscoelastic damping) High Z, high damping → weld energy generated close to surface ("near field" region > 6 mm from horn) Low Z, low damping → energy penetrates to joint without much absorption ("far field"; most favorable)

Far field weldable (excellent): ABS, PS, PC Near field only: PA, PP, PE, POM

Joint Strength Factors

Joint efficiency: S_weld / S_parent_material × 100% Excellent: ABS joints = 80–100% tensile parent strength Good: PC = 70–90%; Nylon = 50–75%

Weld failure modes: Cohesive failure (within weld): desired; shows good fusion Adhesive failure (at interface): poor fusion; increase amplitude or collapse Parent material failure: weld stronger than parent; over-welded

Fixturing

Nest/fixture material: Aluminum: standard; easy to machine; reflects ultrasound Delrin/nylon: absorbs vibration → reduces marking; used for delicate cosmetic surfaces Teflon-coated: release of part; for adhesive materials

Fixture design: Support as close to weld plane as possible Contact area: maximize to prevent part deformation Locate from features away from weld zone

Inspection and Quality Control

Destructive: peel test, tensile shear, burst test Non-destructive: vision inspection (surface quality); dimensional (collapse distance) Process monitoring: energy, time, distance, force logged by machine → SPC control charts Advanced: in-line ultrasonic inspection; thermal imaging during weld

Applications

Electronic enclosures (ABS); automotive lighting (PC/PMMA); medical devices (PS/ABS/PP); IV bags; toy assemblies; fluid filters; automotive fuel systems (PA)

Output

Provide: material weldability assessment (amorphous/semi-crystalline), energy director geometry (height h [mm], apex angle [°], spacing [mm] for multiple EDs), amplitude A [μm], weld force F [N], weld energy E [J] or collapse distance d [mm], frequency [kHz], material compatibility check, expected joint efficiency [%], hold time [s], critical process parameter recommendation (energy or distance mode), and failure mode prediction (cohesive/adhesive).