Flexible Manufacturing and Industry 4.0, Introducing Automated Ultrasonic Welding (pt. 2)
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 second article looking at the automation of ultrasonic welding. The basic operation and welding components were introduced in the previous article. But there are more aspects to be taken into consideration to create a good and high–quality weld. These aspects are very important to understand and consider when automating the welding process. We will look at these aspects in this article. An overview of the integration onto the Flexible Manufacturing System (FMS) is included at the end of the article.
For reference purposes we include an image of a typical Ultrasonic welding integration onto a production line.
Critical factors for of US welding (automation)
A lot of factors determine a good and high-quality weld. Especially when the welding process is automated, these factors become over more important as they cannot be influenced by the staff operating the equipment. Incorrect settings may result in poor quality weld, misalignment of parts, reduced strength of the weld, cracks, etc.
Let’s take a look at the most important aspects (listed below):
Welding frequency and amplitude
One of the most important aspects for a consistent high-quality weld are wavelength and amplitude (welding frequencies). Depending on the material and the type of ultrasonic process used, different amplitudes are required. Amplitude is the peak-to-peak movement, or expansion/contraction.
Different materials require a different amplitude. Generally speaking, amorphous plastics require less amplitude than semi-crystalline materials. Depending on the material uses, different amplitudes may be required.
This image shows a close up of a Manual Ultrasonic Welding System
To make things a bit more complicated, different frequencies are used for different parts. For small, delicate assemblies (printed circuit boards, microelectronic components, etc.) with close tolerances, a higher frequency (for example, 40kHz) is better suited as applied pressure and ultrasonic vibrations can be minimized. Low frequency (for instance, 15kHz) is well suited for medium- to large-size parts and also permits the welding of many softer plastics with greater far-field distances.
Base materials used for the parts
Material (base material) selection also plays an important role in the ultrasonic welding process. In general, rigid plastics exhibit excellent far-field welding properties because they readily transmit vibratory energy. Soft plastics, having a low modulus of elasticity, weaken the ultrasonic vibrations and, as such, are more difficult to weld. For forming or spot welding, the opposite is true. Generally, the softer the plastic, the easier it is to stake, form or spot weld.
Also factors such as moisture content, mold release agents, lubricants, plasticizers, fillers reinforcing agents, pigments, flame retardants and other additives, along with actual resin grade (amorphous or crystalline resins require different welding settings). The compatibility between the material welded together is also important to evaluate and consider.
Design and Shape of the parts
The shape of the parts that are to be welded together is important as some shapes have better welding properties. This may make automation (feeding and transport) of the part more difficult. In some cases, the automation company is involved during the design phase of the part to support smooth and correct handling once the part has been fully designed (critical factors are identified early in the process, taking automation in consideration during design).
Common shapes used for ultrasonic welding are shown below (for reference purposes).
US Welding System with the individual components
Tooling, fixtures and automation quality
This relates to correctly designed, manufactured and selected parts used for the US welding application. Especially when automating the US welding process, the alignment of the parts becomes more critical when running at higher speeds. Also, vibrations are to be avoided as these may influence the part alignment or correct positioning of the US welding parts. Good quality automation machine design plays an important role for correct and high-quality welds (e.g. a poorly designed automation system may have a great influence on the quality of the US weld). Poor selection of US welding equipment installed on high quality automation solution may still result in a poor-quality weld.
Welding parameters settings
The US welding unit itself provides a lot of parameters that have an influence on the weld quality. These include amplitude/pressure, trigger force and tolerance limits, depending upon whether the welding is done by time, energy or distance. Likewise, some systems will allow the user to specify energy settings – with limits and a calibration pulse, for instance – while some also will allow distance settings – such as incremental, pre-trigger, absolute and limits.
Manipulation of these parameters can mean the difference between a successful weld and an ineffective weld or a cracked horn. To select the best processes, equipment and techniques for a particular application or assembly, consult directly with the automation partner that can integrate the ultrasonic welding equipment.
US welding and process automation
Once the correct US welding equipment has been selected, it needs to be integrated onto the production line.
It is important that the parts that are to be held are held accurately in place. This already requires high accuracy in positioning. Especially for medical devices, a constant process, even down to a batch size of one, is extremely important. With smaller batch sizes the need for flexible & programmable us welding settings (parameters) becomes very important.
With a fully automated us welding process, operators should no longer intervene. This can be achieved by loading the parameters and quality data from a central control unit.
Parameters and setting can be adjusted automatically when changing an anvil (or shuttle) on the production system. The control system registers the change and loads in the correct parameters. Especially when several us welding units each with different parameter & settings are present on a manufacturing line this contributes to a high-quality welding process supporting industry 4.0.
An overview of the integration onto a production line is shown below:
Stay tuned for the next article, coming up next month! In the meantime, consider following Grauel, a brand of AAE, on LinkedIn for weekly updates on Industry 4.0 and Flexible Manufacturing (and more extra content).