If ultrasonic plastic welding is to be welded well, it is necessary to design the welding surface in this way---Chaoyang ultrasonic spot melting machine

19
If ultrasonic plastic welding is to be welded well, it is necessary to design the welding surface in this way---Chaoyang ultrasonic spot melting machine

When we want the product to achieve the functions of water, air tightness, firm welding and beautiful appearance, positioning and ultrasonic fusion wire are important keys to success or failure. Therefore, in product design, considerations such as positioning, material, meat thickness, and ultrasonic fusion are considered. There is an absolute relationship between the corresponding proportions of the lines. ---Chaoyang ultrasonic spot melting machine

The ultrasonic welding line is designed to facilitate the ultrasonic welding of plastic parts, and a sharp and thin linear structure pre-installed on the plastic, also known as ultrasonic welding line or ultrasonic welding line. Its shape is mostly designed as an isosceles triangle or a semicircular arc, but the semicircular arc ultrasonic line with the same cross-sectional area as the isosceles triangle has a lower height than the isosceles triangle ultrasonic line. When the ultrasonic energy is low, it is not easy to appear ultrasonic virtual. Welding, and the semi-circular arc-shaped ultrasonic wire can evenly distribute the ultrasonic energy in all parts of the welding area, maximize the use of the pressure generated by the ultrasonic welding machine and the released energy, not only save energy, but also make the ultrasonic wire fully welded to ensure All parts of the welding area in the narrow space of plastic parts are firmly connected and beautiful; at the same time, on the premise of sufficient filler material, the welding space can be saved, which is very suitable for narrow welding space, and can also save the space of ultrasonic line design, improve the unit Effective utilization of area design space.

In order to obtain a perfect and stable welding effect, the structural design of the ultrasonic plastic welding weldment must first consider the following points: 1. Whether watertightness and airtightness are required. 2. Whether a perfect look is required. 3. Whether it is suitable for welding head processing requirements. 4. The size of the weld (that is, to consider the required strength). 5. Avoid melting plastics or spills of composites.

There are three basic design criteria for the welding surface of ultrasonic welding machine weldments: 1. The initial contact area of the two welding surfaces must be reduced to reduce the total energy required for the initial and final complete melting, so that the contact time between the welding head and the workpiece is reduced to At the very least, the chance of causing scars is reduced, and the glue overflow is also reduced; 2. Provide a way to make the two welding surfaces align with each other. In the design of matching plastic parts, pins and sockets, steps or grooves can be used. It should not be fixed in the welding head or the bottom mold, which can ensure accurate and stable alignment and avoid scars; 3. The entire welding surface must be uniform and in close contact, and be kept on the same plane as possible. Such a shape can conduct energy evenly, which is conducive to achieving a consistent and controllable welding effect, and can reduce the possibility of overflowing glue; --- Chaoyang ultrasonic spot melting machine

The welding surface has two main design types: fuse wire and shear.

Fusible wire: The fusible wire actually forms a triangular protruding material on one of the two welding surfaces. The basic function of the fusible wire is to gather energy and quickly melt the other side to be welded. The highest welding strength is achieved because the material of the fuse wire itself melts and flows to the entire welding area. The fuse wire design is the most widely used welding surface design for amorphous materials. Of course, semi-crystalline materials can also use this design. 2. The size and position of the fuse wire depends on the following factors: 1. Material; 2. Welding requirements; 3. The size of the workpiece; the fuse wire must be as sharp as possible, and a dome or flat fuse wire will reduce the melt flow When welding plastics that are relatively easy to weld (such as PS with high hardness and low melting temperature), it is recommended that the height of the fuse wire should not be less than 0.25mm. If welding semi-crystalline or high melting temperature amorphous plastics (such as PC), the height of the fuse wire should not be less than 0.5mm; for semi-crystalline plastics (such as PA) with a fuse wire design, the welding strength is the width of the bottom line from the triangle of the fuse wire. The top angle changes with the wall thickness ;In principle, there is no difference on the welding surface of the plastic part on which side the fuse wire is set. However, in the special case of welding two different materials, the fuse wire is generally set at the melting temperature and the hardness is higher. The welding surface of the workpiece on the other side; the design of the fuse wire should have functions that can be aligned with each other, such as pins and sockets, rib-shaped alignment pieces, groove design, or require good support. The welding area cannot be placed thimble;

The following are the structural designs of several typical fuse wires:

1. Step welding surface

The one-step welding surface design is mainly used for high-quality requirements that require precise alignment and completely unacceptable over-melting or glue overflow on exposed surfaces; design attention (Figure 1.) An additional 0.25 to 0.64 mm of clearance around the entire workpiece interface , This new "shadow line (art line)" design feature makes a gap of 0.25 to 0.64 mm around the interface after the welding is completed. This will produce an aesthetic effect, because the deformation between the workpiece and the workpiece is not easy to be found. If Completely tight, it is very likely that there will be glue overflow in some places, but micro gaps will appear in other places; the setting of the art line makes the slight deformation difficult to detect. This fuse design adopts the same design as the flat head plus fuse The same basic concept (that is: material, welding requirements, workpiece size). Note that the minimum size of the wall thickness of this design is 2mm. 2. Grooved welding surface design

—The main advantage of this design is that it can prevent glue from overflowing from the outside of the package, and can provide a positioning function. Since the melt is sealed, it improves the chance of achieving water tightness. Also due to the design of the grooves, a certain tolerance is required It also increases the difficulty of forming. At the same time, due to the reduction of the welding area, its welding strength is often not as good as that of the flat head joint design. This fuse wire design adopts the same basic concept as the flat head plus fuse wire design. (That is: material, welding processing requirements, workpiece size). Note that the minimum size of the wall thickness required for this design is 2mm---Chaoyang ultrasonic spot melting machine

3. Bitten flower design

--This design is specially designed for use with fuse conductors. The welded surface has an embossed shape to improve the overall welding quality and strength. The reason is that the rough surface can improve friction and control melting (Figure 3.). Generally, the embossing depth is 0.076 to 0.152mm, the change depends on the height of the fuse wire. The advantages often obtained include the improvement of strength, the reduction of glue overflow or particles, the reduction of welding time and the reduction of amplitude; 4. Design of crisscross welding surface

- Design fuse lines on both welding surfaces of the plastic parts and make them cross each other perpendicularly, so as to minimize the initial contact surface and weld a large amount of plastic to increase the welding strength (Figure 4). The size of each section can be about 60% of the size of the standard fuse wire. If you want to achieve a water-tight welding effect, it is recommended that one side of the fuse wire should be designed with continuous hook teeth as shown in Figure 5. At the same time, it is recommended that the fuse wire be designed The apex angle of the horn is 600 instead of the standard 900, and it is also recommended to set the fuse wire with a hook-shaped design on the plastic part that contacts the welding head. It should be noted that this design will produce a large number of Glue overflow, so the problem of glue overflow must be considered or the welding surface with overflow groove design such as grooved welding surface design must be used. 5. Design of fuse wire perpendicular to the wall

- Used to increase tear resistance and reduce glue spillage (Figure 6), this design is only suitable for structural welding only;

6. Intermittent Fuse Design—

It can reduce the welding area and thus reduce the energy or required power level. This design can only be used for structural welding that is not watertight (Figure 7); 7. Chisel type fuse wire

-Used for workpieces with a wall thickness less than 1.524mm (Fig. 10.) If a standard fuse wire is used on such thin-walled plastic parts, the welding strength will be weakened. The height of the sharp knife can be 0.381 to 0.508mm and 450mm can be used. Angle. Since the welding strength depends on the width of the fuse wire, when using this type of fuse wire design, the bite surface must be used together;

8. Chisel Type Fuses

-Used for workpieces with a wall thickness less than 1.524mm (Figure 8) If a standard fuse wire is used on such thin-walled plastic parts, the welding strength will be weakened. The height of the sharp knife can be 0.381 to 0.508mm and a 450 angle can be used. .Because the welding strength depends on the width of the fuse wire, when using this type of fuse wire design, it is necessary to use an embossed surface; 9. Special welding surface design - in order to make the plastic that is more difficult to weld or the plastic part with irregular shape To achieve a water-tight weld, it may be necessary to use an elastic oil seal and a spiral bypass to block the flow of the melt. Figure 9. shows a welding surface design with an "O" ring. It should be noted that the "O" ring is welded After that, it is only compressed by 10% to 15%. The cylindrical plastic part and the socket (the big head column are welded) can also be successfully matched with the "O" ring to achieve water tightness; --- Chaoyang Ultrasonic Spot Melting Machine

1. Design attention points for cutting:

Shear Weld Face Designs—When welding semi-crystalline plastics such as nylon, acetal, polyethylene, polypropylene, and thermoplastic polyester, fuse wire designs are sometimes not as effective as expected. This is because these types of Semi-crystalline plastic quickly changes from solid state to solid state within a relatively narrow temperature range. When the fuse wire melts, it will start to solidify before it can fuse with the opposite plastic part, so the welding strength is only provided by the width of the triangle. Therefore, when welding the above plastics, if the appearance permits, it is recommended to use a shear welding surface design, which can achieve the ideal welding effect. The welding process of the shear welding surface is to first melt the small area of material that starts to contact, and then follow the The wall surface continues to be vertically downward and controlled to guide the lower workpiece to wrap the head (see Figure 10). This welding method will never let the surrounding air contact the melting area, so high-strength structural or water can be obtained. Airtight welding. For the above reasons, the shear welding design is particularly suitable for semi-crystalline plastic materials; the welding strength is directly related to the welding area vertically downwards on the welding surface. The strength can be changed by changing the welding depth to meet the welding requirements of individual applications .Note: If the welding strength is required to exceed the strength of the wall, it is recommended that the welding depth be 1.25 times the wall thickness; shear welding needs to be supported by solid side walls to avoid deformation during welding. The height of the surrounding walls of the lower workpiece must be as high as For the interface position, the inner wall must be completely consistent with the outer shape of the workpiece. The overall structure of the upper workpiece should also be very strong to prevent inward deformation. For the welding part in the center of the wall, the variant groove design shown in Figure 11. can be used. This design is also suitable for welding of large plastic parts. It is recommended to use unilateral interference as shown in Figure 12. It should be noted that if the maximum size of the workpiece is 89mm or larger and complex or right-angled corners are not suitable for shearing Welding design, because this will cause problems with the forming tolerances that must be maintained between the upper and lower workpieces. That is, it is difficult to maintain a stable welding effect. In this case, only the fuse wire design can be recommended. When only structural welding is required (that is, strength and water tightness are not required), the intermittent vertical fuse wire design shown in Figure 13. This can reduce the overall welding area and thus reduce the energy or power required. The appearance of scars Opportunities can also be greatly reduced to provide interference dimensions and workpiece size tolerances corresponding to the largest workpiece dimensions. Other considerations for welding surface design: 1. Right-angle corners will accumulate stress. If there are several stress accumulation points on the plastic part, after the After ultrasonic mechanical vibration, high stress areas such as corners, edges and junctions of plastic parts may appear fractures or other scars. The remedy is to increase the arc of the corner as much as possible (0.508mm). Please refer to Figure 152. Plastic Parts Holes or nicks like blowhole-like openings will block the ultrasonic energy transmitted by the welding head (Figure 16). Its effect on welding depends on the type of plastic material (especially semi-crystalline plastic) and the size of the opening , There is almost no way to weld directly below the gap. When there is a gap or a curved shape on the plastic part, the plastic will hinder the conduction of energy, making it more difficult for the energy to reach In the process of designing plastic parts, special attention should be paid to avoid the occurrence of such problems. Due to improper design of steel molds, there are pores in the plastic parts, which will also block energy conduction or cause problems. Perforation of plastic parts; 3. Comparison of near-field and far-field welding - Near-field welding means that the distance between the welding surface and the contact position of the welding head is within 6.35mm; the distance greater than 6.35mm is far-field welding (Figure 17), as shown above As mentioned above, because semi-crystalline molecular structure plastics will hinder the conduction of vibrational energy, it is difficult to weld them in the far field. As for amorphous plastics, due to the random arrangement of molecules, vibrational energy is easily conducted between them and the attenuation is also small. At low The vibration energy attenuation phenomenon also occurs in the rigid plastic wrapping head. Therefore, in the process of designing plastic products, it should be considered whether there is enough energy to transmit the welding surface;

4. Parts, shanks, or other details of plastic parts - Mechanical vibration can affect various protrusions on the inner and outer surfaces of the plastic part, which may cause fracture (Figure 18.) The following measures can reduce or eliminate this effect: ? Design the connection between the protrusion and the main body into the largest arc shape. Use external means to reduce the kink of the connection. Increase the thickness of the material. Evaluate ultrasonic waves with other frequencies

5. Thin film effect - an energy accumulation effect that causes burn-through in plastic parts. It is most common in flat, circular, and thin-walled locations. This phenomenon can be overcome by taking one or a combination of the following measures (Fig. 19) Reduce welding time Change amplitude Use amplitude analysis to design nodes on the welding head Pistons Increase wall thickness Use internal support ribs to evaluate other frequencies 6. Ultrasonic mold contact and placement can play a pivotal role in plastic parts welding. The size of the horn should be large enough to cover the entire job, so press directly on the weld area from the top, (Fig. 20.) This facilitates the conduction of mechanical vibration energy and avoids scarring of the contact surface. The horn or plastic part The surface of the welding head can also be raised in the welding area to improve the contact efficiency; this will improve the stability of the welding effect. Note: the contact surface between the welding head and the workpiece must be larger than the total area of the welding area, otherwise it may lead to surface scars. Another: 1. The plastic material with the same melting point has stronger welding strength. 2. The larger the melting point difference of plastic materials, the smaller the welding strength. 3. The higher the density of the plastic material (hardness), the higher the welding strength than the lower density (higher toughness). ---Chaoyang ultrasonic spot melting machine

The structure of ultrasonic integral plastic parts 1.1 The structure of plastic parts Plastic parts must have a certain rigidity and sufficient wall thickness, too thin wall thickness has a certain risk, ultrasonic welding needs to be pressurized, and the general air pressure is 2-6kgf /cm2. Therefore, plastic parts must be guaranteed to be basically not deformed under pressure. 1.2 Pot-shaped or box-shaped plastics, etc., will cause resonance on the surface that contacts the welding head to form some concentrated energy gathering points, resulting in burns and perforations (as shown in Figure 1). Consider the following

○1 Thicken plastic parts ○2 Add reinforcing ribs ○3 Avoid the middle of the welding head 1.3 Sharp corners If an injection-molded part has very concentrated stress, such as sharp corners, it will crack under the action of ultrasonic waves, melt. In this case, consider adding an R angle to the sharp corner. as shown in picture 2. 1.4 Attachment of plastic parts The protruding or small parts attached to the inner or outer surface of the injection part will be broken or fallen off due to the influence of ultrasonic vibration, such as fixed pins, etc. (as shown in Figure 3). This problem can be minimized or eliminated by the following designs:

○1 Add a large R angle to the place where the appendage meets the main body, or add a stiffener. ○2 Increase the thickness or diameter of the appendages. 1.5 Holes and gaps of plastic parts If the parts contacted by the welding head have holes or other openings, interference and attenuation will occur during the ultrasonic transmission process (as shown in Figure 4), depending on the type of material (especially semi-crystalline materials) and holes size, there will be a small amount of welding or no melting at the lower end of the opening directly, so it should be avoided as much as possible. 1.6 Thin and curved transmission structure in plastic parts In the shape of the plastic parts contacted by the welding head, if there is a thin and curved structure, and it needs to be used to transmit ultrasonic energy, especially for semi-crystalline materials, ultrasonic vibration is very high. Difficult to transfer to the machined surface (as shown in Figure 5), this design should be avoided as much as possible.

1.7 Short-distance and long-distance welding 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. 1.8 Design of the contact surface of the plastic parts welding head The injection molded parts can be designed in 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 surface of a plastic part with a smooth and arc transition can be appropriately relaxed than the standard, and the protruding position should be located in the middle of the plastic part as much as possible or symmetrically designed. 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 (as shown in Figure 6), it will cause greater damage and deformation, as well as an unsatisfactory welding effect.

If there are damage lines on the surface of the welding head, or its shape is slightly different from that of the plastic parts, scars will be left on the surface of the plastic parts during welding. The way to avoid it is: pad a film (such as PE film, etc.) between the welding head and the surface of the plastic part. Design of welding line 2 Design of ultrasonic welding line Ultrasonic welding line is the part melted by the direct action of ultrasonic waves, and its basic two design methods: ○1 energy guide ○2 shear design 2.1 energy guide Energy guide is a typical One surface of the quilt welding is injection-molded with a protruding triangular column, and the basic function of energy guidance is to concentrate the energy to quickly 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. The size and position of the energy guide column depends on the following points: ○1 material ○2 plastic part structure ○3 requirements for use For materials with high hardness and low melting point, a minimum height of 0.25mm is recommended. When the material is semi-crystalline material or high temperature mixed resin (such as polyethylene carbon), the height should be at least 0.5mm. When using energy guide to weld semi-crystalline resin (such as acetone, nylon), the maximum connection force is mainly Obtained from the wide width of the chassis of the energy column. ---Chaoyang ultrasonic spot melting machine

There is no rule stating which side of the plastic part should be used for the energy guide. In special cases, it should be determined through experiments. When two plastic parts have different materials and strengths, the energy guide is generally set on the side with high melting point and low strength. According to the requirements of plastic parts (such as watertightness, airtightness, strength, etc.), the energy-directed design can be combined and segmented. For example, when only a certain strength is required, segmented energy-direction is often used (such as mobile phone batteries, etc.), As shown in Figure 8.

2.2 Design of the alignment method in the energy-guided design. The upper and lower plastic parts must be accurately aligned during the welding process. The limit height is generally not less than 1mm. The parallel detection position of the upper and lower plastics must be small, generally less than 0.05mm. The basic Energy steering can be incorporated into a connection design instead of a simple butt joint, including alignment methods. Examples of different connection designs using energy steering include the following: Pin positioning: Figure 9 shows the basic pin positioning method. The strength of the plug should be guaranteed to prevent the ultrasonic shock from breaking.

Step positioning: Figure 10 shows the basic step positioning method. If h is greater than the height of the welding wire, a decorative line will be formed outside the plastic part. Generally, the size of the decorative line is about 0.25mm, creating a more attractive appearance. , and the difference between the two parts is not easy to find.

If the step is positioned as shown in Figure 11, there may be overflow. If the step is positioned as shown in Figure 12, internal flash may occur. The steps shown in Figure 13 are positioned on both sides to prevent internal and external flashing.

○1 Groove positioning: As shown in Figure 14, the advantage of using this design is to prevent internal and external spillage and provide alignment, and the material is easy to obtain enhanced sealing, but this method requires ensuring the oblique gap of the protruding parts , so the parts are more valuable than injection molding, and at the same time, the strength is not as good as direct and complete butt joints. ---Chaoyang ultrasonic spot melting machine

○2 The bottom mold is fixed: As shown in Figure 15, with this design, the design of the plastic parts becomes simple, but the requirements for the bottom mold are high, which usually leads to the parallel displacement of the plastic parts. At the same time, the bottom mold is fixed too tightly. affect the production effect.

○3 Welding head plus bottom mold positioning: As shown in Figure 16, this design is generally used in special cases, and is not practical and commonly used. ○4 Other cases: A: As shown in Figure 17, it is a method available for large plastic parts. It should be noted that the lower supporting mold must support the flange, the flange of the upper plastic part must contact the welding head, and the The upper surface should not be too far from the flange. If necessary, a multi-welding head structure can be used.

B: If energy guidance is used in the connection, and the two welding surfaces are injected into a frosted surface, the friction can be increased, the melting can be controlled, and the quality and strength of the whole welding can be improved. Generally, the frosting depth is 0.07mm-0.15mm. C: When welding resins that are not easily welded or irregular shapes, in order to obtain a sealing effect, it is necessary to insert a sealing ring, as shown in Figure 18, it should be noted that the sealing ring is only pressed against the welding end. Figure 19 shows the welding of thin-walled parts, such as thermoformed cardboard (with plastic coating), to a plastic cover. 2.3 Shear Design In the fusion of semi-crystalline plastics (such as nylon, acetal, polypropylene, polyethylene, and thermoplastic polyester), energy-directed joint design may not achieve the desired effect, because the semi-crystalline Crystalline resins quickly transition from solid to molten, or from molten to solid. Moreover, after passing through a relatively narrow temperature range, the melt flowing out of the energy-directing column will quickly resolidify before it fuses with the interface. Therefore, in this case, we recommend the use of shear-connected structures as long as the geometry allows. With a shear-joint design, the weld is accomplished by first melting the small and initially touching area, and then continuing along its vertical wall with a controlled contact surface as the part sinks down. As shown in Figure 20, it is possible to obtain a strong structure or a good seal because the melted area of the interface does not let ambient air in. 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. Figure 21 shows several basic shear structures: --- Chaoyang ultrasonic spot melting machine

Shear connection requires a plastic wall with sufficient strength to support and prevent deflection during welding. When necessary, the support of the bottom mold is higher than the welding position to provide auxiliary support. The following table shows the size of the part, the contact surface, and the approximate size of the error of the part: The maximum size of the part, the size of the contact surface, the allowable error of the size of the part <18mm 0.2mm-0.3mm ±0.025mm18mm-35mm 0.3mm-0.4mm ±0.05mm>35mm 0.4mm-0.6mm

±0.075mm When the size of the part is greater than 90mm, or the part has an irregular shape, it is recommended not to use shear connection. At this time, it is difficult to control the error and deformation during injection molding to keep it consistent. If this is the case, an energy-directed form is recommended. Figure 22 shows a double-sided shear design

Figure 23 shows the design of the button-type welding wire, which is used for high strength, but the upper and lower plastic parts are not in contact. In special cases, it can be used to increase the sealing ring. ---Chaoyang ultrasonic spot melting machine

Contact Us

Contact Us