Ultrasonic Welding

Ultrasonic Welding

• Ultrasonic welding is a welding technique uses ultrasonic vibrations(10KHz to 20KHz) locally applied on the workpieces being held together under pressure to create a solid state weld.

• The two components are subjected to a static normal force and a oscillating shearing stress.

• The shearing stress is applied at the tip of a transducer.

Set Up

a. USW schematic for lap joint, b. Close up of joint

Schematic of USW

Major Parts1. Pneumatic Piston or Mass2. Ultrasonic Transducer3. Booster4. Sonotrode & Tip

Ultrasonic Transducer

• Converts electrical Signals to ultrasonic signals or vice versa.

• Types– Piezoelectric type– Magnetostrictive Type

Piezoelectric Type• Vibrations are produced by piezocrystal by “Reverse peizo

electric effect.• PZT – Lead Zicronate Titanate Crystals are used

Magneto Strictive TypeMagnetostriction is a property of ferromagnetic materials that causes them to change their shape or dimensions during the process of magnetization.

Sonotrode

Booster• The booster is a one-half-wavelength long

resonant section made of aluminum or titanium.

• It is mounted between the converter and the horn, and modifies the amplitude of vibration applied to the horn.

Sonotrodes

• Sonotrodes are ultrasonic welding tools that are caused to resonate when high-frequency mechanical oscillations are introduced.

Shape of tip depends upon profile to be welded

USW of Metals

USW of Plastics

Process Variations• Spot Welding• Ring Welding• Line Welding - Linear Sonotrode• Continuous Seam Welding - Roller Sonotrode• Microminiature Welding

Ultrasonic Spot Welding

• Ultrasonic spot welding is an assembly technique for joining two similar thermoplastic or soft metal(Like aluminum) components at localized points with no preformed hole or energy director.

Ring Ultrasonic Welding• Sonotrode vibrates with a

torsional motion rather than an axial motion.

• Suitable parts include those with square, rectangular, circular or annular welding areas—the latter two being unique for the torsional technique. Metal parts must be relatively thin (1.5 to 2 millimeters) and welded on the sonotrode side.

Seam Welding

• Ultrasonic roll seam welding is suitable for continuous welding of large films, width fabric, non-woven or textile fabrics. The result is continuous welds without interruption.

Ultrasonic Welding Variables

• Ultrasonic power• Clamping force• Welding time • Frequency • Linear Vibration Amplitude

• Frequency is transformed to vibration energy through the transducer.

• Energy requirement established through the following empirical relationship.– E = K (HT)3/2

– E = electrical energy– H = Vickers hardness number– T = thickness of the sheet

Electrical energy

Frequency Converter

Vibratory transducer

Ultrasonic Welding Power Generation

2/3)HT(KE

Where:E = electrical energy, W*s (J)k = a constant for a given welding systemH = Vickers hardness number of the sheet T = thickness of the sheet in contact with the sonotrode tip, in. (mm)

Power Requirements

The constant “K” is a complex function that appears to involve primarily the electromechanical conversion efficiency of the transducer, the impedance match into the weld, and other characteristics of the welding system. Different types of transducer systems have substantially different K values.

Peizo type or magnetorstrictive type

AWS Welding Handbook

<- Aluminum

Aluminum

AWS Welding HandbookHolding Pressure

Joints in USW

• Design of joints finds its utmost importance in Ultrasonic welding; a good understanding of the joint design will ensure the good quality of weld. To ensure that plastic assemblies are adequately joined

Three Major Joint Design Characteristics:• The initial contact area between the mating surfaces should

be small - to concentrate and decrease the total energy (and thus the time) needed to start and complete melting. Minimizing the time the vibrating horn remains in contact with the part also reduces the potential for scuffing, and since less material is moved, there is less flash.

• A means for aligning - the mating parts should be provided. Features such as pins and sockets, steps, or tongues and grooves, should be used for alignment rather than the vibrating horn and/or fixture, to ensure proper, repeatable alignment and to avoid marking.

• Horn contact and placement - must be considered to provide proper bearing over the joint area, to direct the mechanical energy and force to prevent marking of the contact surface.

Types of Joint Design

• The energy director joint – Butt Joint– Step Joint– Tongue And Groove Join

• The shear joint.

Butt JointThe peak of the energy director should be as sharp as possibleSimple and cheap

Step Joint

The step joint is used for alignment and for applications where excess melt or flash on one exposed surface is objectionable.

This joint is usually much stronger than a butt joint, since material flows into the clearance necessary for a slip fit, establishing a seal that provides strength in shear as well as tension.

Tongue And Groove Join

The major benefits of using this joint design are that it prevents flash, both internally and externally, and provides alignment. Containment of the material enhances the attainment of hermetic seals. The need to maintain clearance on both sides of the tongue, however, makes this more difficult to mold.

Flash

Shear Joint

• With a shear joint design, welding is accomplished by first melting the small, initial contact area and then continuing to melt with a controlled interference along the vertical walls as the parts telescope together. This allows a strong structural or hermetic seal to be obtained as the molten area of the interface is never allowed to come in contact with the surrounding air.

Shear Joint

Advantages

• It requires very little heat application during joining without melting of metal.

• No nuggets or brittle intermetallic are formed in ultrasonic welded parts

Nugget in Spot welding

No nugget in USW

Process is capable of joining variety of dissimilar metals.

Plastic

Advantages

• The process permits welding of thin to thick sections as well as joining a wide variety of dissimilar metals.

• Since, the temperatures used are low and no arching or current flow is involved, the process can be applied to heat sensitive electronic components with better efficiency for many electronic components.

Advantages

• Intermediate compounds very rarely form as there is no contamination of the weld under surrounding areas.

• The required penetration is less than most competing processes for example, resistance welding and correspondingly lesser energy is needed to produce the welds.

Disadvantage

• Ultrasonic welding is restricted to the lap joint welding of; thin sheets, foil and wires and the attaching of thin sheets to heavier structural members. The maximum thickness of weld is about 2.5 millimeter for aluminum and about 1 millimeter for harder materials.

Applications of USW

• Aerospace and automotive industries• Medical industry• Packaging industry• Electrical and electronics industry• Toy’s

Automotive Industry

Backlight module for buses

Door Parts

Hand brake and Gear cover seals fixing on plastic cover

Medical Industry

Masks

Blood Checking Straps

Respiratory filter assembly

Diaphragm on Plastic part

Packaging industry

Electrical & Electronics

Micro USB

Battery Cap

Fast cable connector on ceramic substrate