Flexible Manufacturing and Industry 4.0, Introducing Automated Ultrasonic Welding (pt. 1)
AAE (Grauel) pushes technical boundaries. We provide high tech printing & assembly solutions. We support smart printing and manufacturing with Industry 4.0 technologies and solutions. This series of articles provide background information on how these developments are supported.
This is the third article in our series, introducing flexible manufacturing and printing supporting industry 4.0.
In the previous articles a flexible manufacturing system (FMS) was introduced using two (2) operators for product placement. This was the first step in the automation process. In this article we will look at the automation of the ultrasonic welding process.
Ultrasonic welding is a manufacturing technique used to create a weld. It is frequently used for medical devices. This sounds easy enough, but a lot of factors come into play to create a good and solid weld. An additional challenge is the automation of this process.
Since so many factors are to be taken into consideration for ultrasonic welding, the process and techniques as well as the main components used will be discussed in this article.
This article focusses on the welding process and its components, in the next article we will focus more on critical factors for ultrasonic welding and dedicated part design requirements. An overview of the integrated ultrasonic welding system on the FMS (Flexible Manufacturing System) will be provide at the end of the second article.
The image above shows a typical (manual) ultrasonic welding unit where multiple parts are inserted that need to be welded. The welded parts (sub assembly) are taken from the us welding system by the operator and “dropped” in the storage bin for further processing (see previous article for the product flow).
What is Ultrasonic Welding, history and principle
Ultrasonic welding uses high frequency sounds to bond materials together. Introduced in the 1940’s, ultrasonic welding was originally used for metal bonding (as an alternative to gluing, screws, threads, etc). Ultrasonic metal welding was further developed during the 1950s through the 1990s as the electronics used in the equipment became more sophisticated and computers could control the process. Since this time, the technique has been applied to plastics, where it has really become popular. It is now used to assemble products from many industries ranging from medical devices to athletic shoes to automobiles.
Frictional heat is used to raise the temperature significantly in a very short time. Basically, high-frequency sound (ultrasound) causes rapid vibrations within the materials to be welded. The vibrations cause the materials to rub against each other and the friction raises the temperature at the surfaces in contact. This rapid frictional heat is what sets the conditions for the materials to bind together.
Different Welding Techniques
Especially when looking at automating the ultrasonic welding process, it is important to know which welding technique is used. A wide range of welding techniques is available each suitable for various applications. The methods include ultrasonic welding (near field and far field), ultrasonic heat staking, hot plate welding, spin welding, vibration welding, laser welding, electro-magnetic welding, etc. In some case these techniques are combined such as in the “cut and seal” technique where a material is cut (e.g. a mesh) first and then welded to the base material. This is commonly used to create e.g. filter application.
There are various techniques available, but we focus on the ultrasonic welding process in this article. The automation of the other techniques may require a different technical approach (but not discussed in this article).
Ultrasonic Welding Components
Having a basic understanding of ultrasonic welding processes, let’s look at the basics of the ultrasonic welding process by reviewing the main components that are used.
The six main parts that make up an ultrasonic welding system include:
1) Power supply: converts low-frequency electricity (50-60 Hz) to high-frequency electricity (20 – 40 kHz; 1 kHz = 1000 Hz).
2) Transducer or converter: changes the high-frequency electricity into high-frequency sound (ultrasound).
3) Booster: makes the ultrasound vibrations bigger.
4) Horn or ‘sonotrode’: focuses the ultrasound vibrations and delivers them to the materials to be welded.
5) Anvil: workpiece upon which the welded materials are stacked and held.
6) Force / Movement, usually a pneumatic system (air pressure) to hold the materials together during welding.
A lot of factors come into play to ensure good and high quality welds. The make and quality of the components listed above are important but also the different phases that make up the ultrasonic welding process itself.
The Welding Process
With a basic understanding of ultrasonic welding processes and the main components used we take a look at the process. Especially when automating this process, the various aspects of ultrasonic welding are to be considered carefully.
The welding process consists of various steps or different phases. The parts to be welded are held into place and pressure is applied during the welding process. Only when enough time is applied, can a good weld be achieved.
Four different stages can be distinguished in the US Welding process, respectively
• Solid friction phase
• Transient phase
• Steady-state phase
• Cooling phase
Solid / Friction Phase
In the solid friction phase, heat is generated due to the friction energy between the two surfaces. This causes the polymer material to heat up until the melting point is reached. The heat generated is dependent on the frictional properties of the polymer and the processing parameters frequency, amplitude and pressure.
In the transient phase the molten polymer layer increases due to shear heating in the viscous (melt) phase. Heating decreases as the thickness of the viscous layer increases.
In the steady-state melt flow phase, the melting rate equals the outward flow rate (steady state). As soon as this phase has been reached, the thickness of the molten layer becomes constant. The steady-state is maintained until a certain “melt down depth” has been reached at which the vibration is stopped
After stopping the vibration, the polymer melt cools and solidification starts. It is important that the parts (and weld) are held in position under constant pressure to allow for a uniform weld.
An overview of the various stages is shown below
The four stages determine the total welding time and pressure required for a good and solid weld. But also aspects such as ultrasonic welding systems settings, material used and the design of the parts play an important role. These are very important for the automation of the process and will be reviewed in the next article.
‘Manufacturing and Industry 4.0, supported by augmented & virtual reality’
By Ivo Brouwer – Business Developer Production Automation at AAE b.v.