Reason analysis and solution for poor welding of ultrasonic plastic welding machine---Nansha ultrasonic spot melting machine

Reason analysis and solution for poor welding of ultrasonic plastic welding machine---Nansha ultrasonic spot melting machine

Ultrasonic plastic welding machine welding products often encounter some bad problems, which affect the production process and product surface damage of plastic products! ---Nansha ultrasonic spot melting machine

Plastic products produce flash or burrs! The tensile force of plastic products after welding is not up to the standard!

What are the reasons for the occurrence of various defects in the ultrasonic welding process? The editor will take you to discuss how to obtain high-quality plastic ultrasonic welding?

Influencing factors of ultrasonic welding----fishbone diagram:

1 Requirements for raw materials for ultrasonic welding

When it comes to ultrasonic welding, we have to mention its requirements for various resins. The most important factors include polymer structure, melting temperature, flexibility (hardness), and chemical structure. ---Nansha ultrasonic spot melting machine

Polymer Structure:

The process of bringing monomers together is called "polymerization," and polymers can basically be divided into two broad categories: thermoplastic and thermoset.

Thermoplastic materials can be softened and reshaped again after being heated and formed, and all the base experiences are only a change of state - this characteristic determines the adaptability of ultrasonic pressing of thermoplastic materials. According to the molecular structure, it can be divided into: amorphous polymer, semi-crystalline polymer. ⊙ The molecular arrangement of amorphous polymer is disordered, and there is an obvious temperature (Tg glass transition temperature) that makes the material gradually soften, melt and flow. These resins generally transmit ultrasonic vibrations efficiently and achieve good welds over a fairly wide range of pressure/amplitude. ⊙ Semi-crystalline polymer molecules are arranged in an orderly manner, with obvious melting point (Tm melting temperature) and re-freezing point. Solid crystalline polymers are elastic and can absorb part of high frequency mechanical vibrations. Therefore, such polymers are not easy to transmit ultrasonic vibration energy to the pressing surface and are difficult to weld.

Thermosetting materials are formed by irreversible chemical reactions, and reheating or pressing cannot soften the formed thermosetting products, so it has traditionally been considered that thermosetting materials are not suitable for the use of ultrasonic waves.

material compatibility

Other Factors Affecting Welding Results

Materials with water-absorbing properties, such as polycarbonate, polysulfone, nylon. After the plastic is added to the mixed material, attention should be paid to the proportion of the mold release agent in question: silicone grease, Teflon, internal lubricant, toner, recycled material, fire retardant, etc. ---Nansha ultrasonic spot melting machine

2 Influence of ultrasonic equipment and fixture design on welding effect

The main components of the ultrasonic machine: transducer, amplitude modulator, welding head.

The main material of the amplitude modulator and welding head is: titanium alloy or aluminum alloy.

Select the welding machine with appropriate frequency according to the size of the product. The following table shows the maximum welding head size matching the welding function of different frequencies.

Welding head surface amplitude design

Welding head surface amplitude =

Transducer Surface Amplitude x Modulator Gain x Weld Tip Gain

Ultrasonic used in plastic processing, the existing operating frequencies are 15KHZ, 20KHZ, 30KHZ, 40KHZ. The table below shows the amplitude requirements of plastics in welding machines with different frequencies. The surface amplitude of the welding head design should be within the amplitude range of the welding substrate. ---Nansha ultrasonic spot melting machine

3 Structure of plastic parts

In order to obtain a perfect product appearance, strong and reliable solder joints, three main design directions must be followed:

The two surfaces that are initially in contact must be small in order to concentrate the required energy and minimize the total energy required (ie, welding time) to complete the fusion. Find a suitable fixation and alignment method, such as sockets, steps, or tongue and groove for plastic parts. The welding head needs to be in direct contact and cover the entire welding area to meet the energy transfer required by the welding point.

Structure of integral plastic parts

Plastic parts must have a certain rigidity and sufficient wall thickness. Too thin wall thickness has certain dangers. Pressure is required during ultrasonic welding, and the general air pressure is 2-6kgf/cm2. Therefore, plastic parts must be guaranteed to be basically not deformed under pressure. In case of can-shaped or box-shaped plastics, etc., in the design, the top of the can can be thickened with plastic parts, stiffeners can be added, and the middle of the welding head can be avoided to avoid burns and perforations on the surface of the welding head.

The protruding or small parts attached to the inner or outer surface of the injection molded parts will be broken or fall off due to the influence of ultrasonic vibration. It is necessary to add a large R angle or strengthen the rib or increase the thickness of the appendage and the main body where the appendage intersects with the main body. Diameter etc. to reduce or eliminate this problem as much as possible. ---Nansha ultrasonic spot melting machine

In order to prevent interference and attenuation during ultrasonic transmission, holes and gaps should be avoided in the plastic parts at the contact point between the welding area and the welding head.

Short-distance welding means that the welding position is within 6mm of the contact position of the welding head, and long-distance welding is greater than 6mm. The energy in ultrasonic welding will be transmitted attenuated when the plastic parts are transmitted. Attenuation is also greater in low-rigid bottom plastics, so special care must be taken in the design to allow sufficient energy to be delivered to the processing area. For long-distance welding, it is more suitable for hard glue (such as PS, ABS, AS, PMMA), etc. Some semi-crystalline plastics (such as POM, PETP, PBTB, PA) can also be used for long-distance welding through suitable shape design.

Design of the contact surface of the plastic parts welding head The injection molding parts can be designed into any shape, but the ultrasonic welding head cannot be made arbitrarily. The shape and length may affect parameters such as the frequency and amplitude of the welding head. The design of the welding head needs to have a reference plane, that is, the reference frequency plane determined according to its operating frequency. The reference frequency surface generally occupies more than 70% of the surface of the welding head, so the shape of the protrusion on the surface of the injection molded part is preferably less than 30% of the entire plastic surface. The contact surface of the welding head of the plastic part is at least larger than the welding surface, and it should be aligned with the welding position as much as possible. If the contact surface of the welding head is too small, it will cause greater damage and deformation, as well as an unsatisfactory welding effect.

4 Welding line design

The welding line is the part that is melted by the direct action of ultrasonic waves. There are two basic design methods: energy-directed and shearing design.

Energy-directed Energy-directed is a typical injection-molded protruding triangular column on one surface of the quilt welded. The basic function of energy-directed is to concentrate energy to rapidly soften and melt the contact surface. Energy steering allows fast welding with maximum force. In this type of steering, the material flows mostly toward the contact surface. Energy steering is the most common method used in amorphous materials. ---Nansha ultrasonic spot melting machine

The design method and size of the energy guide column are as follows: Generally, in the ultrasonic welding operation, the best ultrasonic welding line height is 0.3~0.4mm according to the experience value. For example: this type Δ, the sharp angle is about 60° or 90° ;In general water and airtight requirements, the height of the fuse line should be in the range of 0.5~0.8mm (depending on the thickness of the product), if it is less than 0.5mm, the function of water and airtightness is to be achieved, unless the positioning is set It should be very standard, and the meat thickness is more than 5 mm, otherwise it will not work well.

Design of Alignment Mode of Upper and Lower Shells by Ultrasonic Welding

The upper and lower plastic parts must be accurately aligned during the welding process. The limit height is generally not less than 1mm, and the parallel detection position of the upper and lower plastic parts must be small, generally less than 0.05mm.

The positioning methods are generally: pin positioning and step positioning.

cut-out design

In the welding of semi-crystalline plastics such as nylon, acetal, polypropylene, polyethylene, and thermoplastic polyesters, a shear joint design is generally used, first melting the small and initially touching area to complete the weld, and then when The part continues to melt along its vertical wall with a controlled contact surface as it is embedded in the bottom. As shown in the image below, it is possible to obtain a strong structure or a good seal, since the melted area of the interface does not let in the surrounding air. For this reason, shear connections are especially useful for semi-crystalline resins.

The welding depth of the shear connection can be adjusted. The strength obtained by different depths is different. The welding depth is generally recommended to be 0.8-1.5mm. When the wall thickness of the plastic part is thick and the strength requirements are high, the welding depth is recommended to be 1.25X wall. thick. Shear connection requires a plastic wall with sufficient strength to support and prevent deviation in welding. When necessary, the support of the bottom mold is higher than the welding position to provide auxiliary support.---Nansha Ultrasonic Spot Melting Machine

5 Ultrasonic welding process control

In the ultrasonic welding operation, if there are scars on the surface of the product, fractures or cracks at the joints, flashes or burrs, and the size cannot be controlled within the tolerance after welding, the first thing to check the equipment parameter control, and through reasonable experiments. Optimize the execution parameters (pre-pressure, drop speed, delay time, welding time, reference medium coverage (such as PE bags), mold fixture surface treatment (hardening or chrome plating), reducing the number of machine segments or reducing the upper mold enlargement ratio, etc.) to Get good quality.

Ultrasonic waves propagate in plastic parts, and plastic parts more or less absorb and attenuate ultrasonic energy, which has a certain impact on the effect of ultrasonic processing. Plastics are generally divided into amorphous materials, and there are hard glue and soft glue according to hardness. , There is also the distinction of modulus. Generally speaking, the ultrasonic processing performance of plastics with high hardness and low melting point is better than that of plastics with low hardness and high melting point. Therefore, this involves the distance of ultrasonic processing distance, --- Nansha ultrasonic spot melting machine