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1. Fracture and damage are common phenomena
Ultrasonic plastic welding is one of the most popular fastening processes for plastic parts.
However, during ultrasonic plastic welding, the internal ribs and pillars of the plastic parts often break, or the internal electronic components, crystals and chips fixed on the plastic parts are damaged by vibration. This is a very common phenomenon, and it is also one of the questions that people often ask.
Why do these ribs, pillars, electronic components, crystals and chips break when they are not in contact with ultrasonic sonotrodes or fixtures?
This leaves many engineers new to ultrasonic welding perplexed, leading them to hasty conclusions that the product is not suitable for ultrasonic welding and that a more appropriate fastening process should be chosen.
This article will combine experience and knowledge of ultrasonic welding to provide a systematic approach to addressing breakage and damage associated with the process.
2. Root causes of breakage and damage
To understand why breakage and damage occur, it is essential to grasp the basic principles of ultrasonic welding.
Ultrasonic welding essentially involves high-frequency, low-amplitude vibrations, with amplitudes typically ranging from 30 µm to 120 µm, which is equivalent to 0.03 mm to 0.12 mm. These vibrations are so subtle that they are virtually imperceptible to the naked eye.
However, the vibration frequency in ultrasonic welding is quite high, typically reaching 15, 20, 30 or 40 kilohertz, which corresponds to 15,000, 20,000, 30,000 and 40,000 vibrations per second respectively.
Therefore, the vibration energy of ultrasonic welding is very large, and at the same time, the vibration energy is transmitted to weak positions of plastic parts, such as ribs and pillars, as well as electronic components, crystals and chips fixed on the plastic parts, thus causing breakage and damage.
3. Overall direction of solving breakage and damage
Once we understand the root causes of breakage and damage in ultrasonic welding, we can begin to address the issues accordingly.
The approach to solving these issues can be divided into the following three main directions:
(1) Reduce energy in ultrasonic welding process
(2) Increase the strength of plastic parts
(3) Keep fragile components away from welding parts
Various solutions to address issues of breakage and damage, both from the design and production perspectives, are developed based on these three main directions.
4. Prevent breakage and damage from product design
Specific measures include:
(1) Change the welding interface design from basic type to shear type.
Under the same ultrasonic equipment, fixture and process parameter settings, the shear-type interface design makes the welding process easier and welding strength higher.
In other words, the shear-type interface design reduces the energy requirements during ultrasonic welding, effectively preventing breakage and damage.
(2) Correct energy director design
Correct energy director design helps to reduce the energy requirements during welding.
(3) Material selection: amorphous plastics that are easier to weld shall be selected
Compared with semi-crystalline plastics, amorphous plastics are easier to ultrasonically weld, require less welding energy, and are less susceptible to defects such as breakage and damage.
However, if semi-crystalline plastics are used for other reasons and the product includes vulnerable components, ultrasonic welding should be carefully selected.
(4) Thicken the weak areas of plastic parts and add rounded corners. If the wall thickness of the weak areas in plastic parts is too thin, the strength will be low. Additionally, the presence of sharp corners can easily create internal stresses, so it is necessary to replace sharp corners with rounded corners to prevent breakage during ultrasonic welding.
(5) Avoid internal stress of plastic parts
During the injection molding process of plastic parts, internal stresses are easily generated; these areas of internal stress are particularly prone to breakage during ultrasonic welding.
(6) Use near-field welding. Near-field welding shortens the distance between the sonotrode and the welding surface, reducing energy loss and thereby lowering the energy requirements during ultrasonic welding.
(7) Increase the contact area between the welding surface of plastic parts and the sonotrode
This measure facilitates energy transmission during ultrasonic welding and also helps to reduce the energy requirements during the process.
(8) Keep vulnerable components away from ultrasonic welding area
When assembling a circuit board that contains vulnerable components such as electronic elements, crystals and chips into plastic parts, it is essential to keep these components away from the ultrasonic welding area. Alternatively, the circuit board can be assembled after the ultrasonic welding process.
5. Prevent breakage and damage from product production
After mold opening of plastic parts, if breakage and damage occur during the ultrasonic welding commissioning, the issues can be addressed from the following two aspects.
(1) Ensure the correctness of ultrasonic sonotrodes and fixtures, which often require complex three-dimensional curved surface shapes and machining accuracy to ensure accurate positioning of plastic parts during welding.
If the shape or radian of sonotrodes and fixtures does not match the plastic parts, it is easy to make the plastic parts bear additional force, resulting in breakage during welding.
(2) Adjust the process parameters and reduce the ultrasonic welding energy
(3) Others
The following are various methods collected and organized on the network, provided for reference only:
Set the ultrasonic time appropriately to avoid activating the ultrasonic wave before the product is properly pressed; reduce the expansion rate of ultrasonic fixtures; use rubber pads for bottom fixtures;
Ensure that the bottom fixture and the product do not float and there is no gap between them;
After the upper fixture is hollowed out, paste silicon-rich elastic materials such as silica gel; add auxiliary pads to easily damaged components to reduce direct energy transmission.
Shenzhen Blsonic ultrasonic Automation Machinery Co., Ltd. was established in 2004 and is located in Shenzhen, China. It is a technical cooperation enterprise specializing in research and development, design, production and sales of ultrasonic industrial equipment. Due to the accumulation and continuous innovation of ultrasonic technology over the years, the company has developed into a one-stop service provider of ultrasonic industrial application technology solutions. We provide one-stop solutions including R&D, design, manufacturing and sales of ultrasonic welding machines, ultrasonic fusion splicers, ultrasonic metal welding machines, ultrasonic plastic welding machines, ultrasonic torsional welding machines, ultrasonic circumferential and radial welding machines, ultrasonic generators, ultrasonic converters, ultrasonic boosters, ultrasonic cutters, ultrasonic sonotrodes, among others. The product range encompasses plastic welding series, metal welding series, cutting and sealing series, and screening series, along with customized ultrasonic application technical solutions.
Products and technologies are applied in the fields of automobiles, household appliances, health care, packaging, textiles, electronics, consumer goods, food, etc.Uphold the "spirit of craftsmanship and commitment to excellence"; adhere to a quality policy of "meticulous design and stringent manufacturing".The product quality and service attitude have gained widespread recognition and support from our customers.
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