Plastic part design
Generation of the injection molding method can effectively provide perfect welding plastic parts.We decided to use the ultrasonic welding technology to complete fusion, plastic parts of the structure design must consider the following points:
1 weld size (i.e., to consider the strength required)
2 whether watertight, airtight
3 whether it needs to perfect the appearance
4 avoid molten plastic or composite overflow
5 are suitable for welding processing requirements
The welding quality is possible through the next few points of control for:
Material 1
2 pieces of plastic structure
3 welding wire location and design
4 welding surface size
The 5 upper and lower surfaces of the location and degree of tightness
6 head and the plastic piece makeup contact surface
7 smooth welding path
8 bottom formwork support
In order to get perfect, repeatable welding methods, must follow the three main design direction:
1 first contact with a two surface must be small, so that the required energy concentration, and minimizing the need for total energy (i.e., welding time) to finish welding.
2 to find suitable for fastening and alignment methods, such as plastic socket, step or tongue-and-groove.
In 3 around a connecting interface bonding surface must be uniform and linked to each other in close contact.If possible, as far as possible contact surface in the same plane, so that the energy conversion consistency.
Below on the plastic design of essentials of classification example:
Overall plastic parts of the structure
1.1 pieces of plastic structure
Plastic parts must be rigid and of sufficient thickness, too thin wall thickness has certain dangerous sex, ultrasonic welding is needed when pressurized, general 2-6kgf/cm2 gas pressure.So the plastic pieces must be guaranteed in the pressure case basic deformation.
The 1.2 tank or box plastic, the contact head surface will cause the resonance and the formation of a number of concentrated energy accumulation point, resulting in burns, perforation of the situation (as shown in Figure 1), the design time can do the following considerations can-type top
1 thick plastic parts
2 stiffener enhancing
3 bonding intermediate position vacancy
1.3 corners
If an injection molded parts produced by stress concentration situation, such as corners, under the action of the ultrasonic wave will produce, melt fracture.This situation can be considered in the corners plus R angle.As shown in figure 2.
1.4 pieces of plastic.
Injection molding internal or external surface with prominent or fine small due to the ultrasonic vibration is generated due to the influence of fracture or exfoliation, such as fixed tip (as shown in Figure 3.).The following design can reduce or eliminate this problem:
1 in the accessory and main intersect with a large R angle, or with stiffener.
2 increase the appendage of the thickness or diameter.
1.5 plastic piece hole and gap
As the contact of the bonding tool parts with holes or other openings, in an ultrasonic transmission process will produce interference and decay (as shown in Figure 4), according to type of material (especially semi crystalline material) and pore size, openings in the end will appear a small amount of welding or completely fused to the situation, thus to try to avoid.
1.6 pieces of plastic in a thin, curved transfer structure
Be the contact of the bonding tool of plastic parts of the shape, if there is thin and bent structure, but also need to lodge pass ultrasonic energy, especially for semi crystalline material, ultrasonic vibration is difficult to transfer to the machined surface (as shown in Figure 5), the design should be avoided.
1.7 short and long distance welding
Close welding by means of welding position distance contact of the bonding tool position within 6mm is greater than 6mm, remote welding, ultrasonic welding in the energy in the plastic parts can be attenuated to transfer transfer.Attenuation at low hard bottom plastic are serious, therefore, the design should pay special attention to let enough energy to the processing area.
Remote welding, the hard plastic (such as PS, ABS, AS, PMMA) is suitable for, some half crystal plastic (such as POM, PETP, PBTB, PA) through the appropriate shape design can also be used for remote welding.
1.8 pieces of plastic welding head contact surface design
Injection molded parts can be designed into any shape, but the ultrasonic welding head and can not be produced.The shape, length can affect the frequency, amplitude and other parameters of welding head.Welding head design needs a reference surface, namely according to its working frequency determined by a reference frequency surface.Reference frequency surface generally accounted for more than 70% of the surface of the welding head area, therefore, the process of injection molding surface shape is preferably less than the plastic surface of super 30%.A circular arc transition surface, the plastic parts, than the standard can be relaxed, and prominent position as soon as possible in the middle or the symmetrical design of plastic parts.
Plastic welding head contact surface at least more than welding surface, and try to welding, small head contact surface (as shown in Figure 6), can cause great damage and deformation, and the less than ideal welding effect.
On the welding head can damage the surface texture, or its shape and plastic parts with a little difference, welding, the plastic parts surface scar.Avoid methods are: in the welding head and plastic parts surface between the pad film (such as PE film).
Design of the welding line
2 welding line design
Welding line ultrasonic direct melting section, the two basic design:
1 energy oriented
2 Shear Design
The 2.1 energy oriented
Energy oriented is a kind of typical in the quilt to weld a surface molding a bulge of triangular column, the energy directing the basic functions are: to concentrate energy, make its rapid softening and melting contact surface.Energy oriented allows fast welding, while the maximum strength, in this guide, which most of the material flow to the contact surface, the energy oriented amorphous materials is the most commonly used method in.
Energy guiding column size and position depends on the following points:
1 materials
2 plastic part structure
3 requirements for the use of
Figure 7 shows a typical energy guide column size, when using a hard welding material, such as polystyrene, high hardness, low melting point materials, recommendations for 0.25mm lowest height.When the material is a crystalline material or high-temperature mixed resin (such as polyethylene carbon), then the height of at least 0.5mm, when using the energy guide to welding semi crystal resin (such as ethylene acetal, nylon), the maximum connection force mainly from the energy pole chassis broadband degree to obtain.
No rules of energy oriented should do in plastic parts of which side, special circumstances to be determined through the test, when the two pieces of plastic material, strength at the same time, energy oriented generally arranged in the high melting point and low strength.
According to the plastic parts requirements (e.g. watertight, airtight, strength etc.), energy oriented design can be combined, sectional design, for example: just needs a certain strength, often using piecewise energy oriented (such as mobile phone batteries), as shown in figure 8.
2.2 energy oriented design of contrapuntal mode design
Upper and lower plastic parts in the welding process to ensure accurate contraposition, the limiting height of not less than 1mm, the upper and the lower plastic parallel test dynamic bit must be very small, generally less than 0.05mm, the basic energy guide can be combined to connection design, rather than a simple butt, including contrapuntal mode, using the energy guiding different connection design examples include the following:
Bolt positioning: Figure 9 shows the basic bolt positioning way, bolt positioning should be ensured in the latch member strength, prevent the ultrasonic seismic fault.
Stepped positioning: Figure 10 shows the basic steps of positioning mode, such as h than welding line height, will be in the plastic part to form a decorative line, general decorative line size is about 0.25mm, create more attractive appearance, while the two part is not easy to find the difference between.
Figure 11 shows the steps positioning, is likely to produce overflow material.Figure 12 shows the steps positioning, is likely to produce internal flash.Figure 13 step positioning for double-sided positioning, can prevent the external flash.
In 1 enterprises and export orientation: as shown in Figure 14, using the advantage of this design is prevented overflowing, and providing a calibration, materials easily increasing the sealing property is obtained, but this approach requires that protruding parts of the oblique slot, so the part more praiseworthy for one's excellent conduct in injection molding, at the same time, less than the welded surface, strength not directly complete butt joint.
In 2 the bottom die set forth: as shown in Figure 15, using this design, plastic parts of the design is simple, but the bottom die high requirements, usually causing plastic parallel shift, at the same time the bottom die is fixed tightly will affect the production effect.
3 head and bottom die positioning: as shown in Figure 16, this kind of design is generally used for special circumstances, is not practical and common.
In 4 other cases:
A: as shown in Figure 17, for large plastic parts are available as a way of, should pay attention to is the supporting mold must hold the flange, flange must be in contact with the head on plastic parts, plastic parts on the upper surface of the flange is not too far away, if necessary, can adopt a plurality of head structure.
B: such as connection using energy oriented, and the two welding surface injection into a matte surface, increases the friction and the control of melting, improve the welding quality and strength, usually matte depth is 0.07mm-0.15mm.
C: in welding without welding resin or irregular shape, in order to achieve the sealing effect, it is necessary for the insertion of a sealing ring, as shown in Figure 18, note that only pressure sealing ring in the welding end.Figure 19 shows the thin-walled parts of the welding, such as hot forming cardboard (with plastic coating), and a plastic cover welding.
2.3 shearing type design
In a crystal plastic (such as nylon, polypropylene, polyethylene, ethylene acetal and thermoplastic polyester) welding, using energy oriented design of connection may fail to achieve the desired result, this is because half crystal resin will soon from the solid state into the molten state, or from the molten state into solid.But after a relatively narrow temperature range, from the energy guiding column elution melt before and phase interface integration, and will soon no longer be cured.Therefore, in this case, as long as the geometric principle allows, we recommend the use of shear connection structure.
Using the shear connection design, first is small and the initial melting contact area to complete welding, then when the parts are embedded into the case, continue along its vertical wall, with a controlled contact surface to melt.As shown in Figure 20, the possibility of obtaining robust structure and good sealing effect, because the interface of melting zone will not let the surrounding air.For this reason, shear connection especially on crystal resin is very useful.
Shear connection weld depth is adjustable, different depth of the intensity of different, weld depth is generally recommended for 0.8-1.5mm, when the wall thickness of plastic parts and thicker and strength requirement is high, the welding depth is recommended for 1.25X wall thickness.
Figure 21 shows several basic shear type structure:
Shear connection requires a plastic wall has enough strength to support and prevent the welding of deviation, when needed, the bottom die support above the welding position, provide auxiliary support.
The following table shows the part size and contact surface, part of the general size error:
The maximum size of the size of the contact face parts parts size allowable error
< 18mm 0.2mm-0.3mm ± 0.025mm
18mm-35mm 0.3mm-0.4mm ± 0.05mm
> 35mm 0.4mm-0.6mm ± 0.075mm
When the part size is greater than 90mm, or parts with irregular shape, does not recommend using shear connection.This is because when injection is difficult to control the error and the consistent deformation.If the above, recommended the use of energy oriented form.
Figure 22 shows the double shear type design
Figure 23 shows the buckle type welding line design, used for high strength, but the lower plastic part does not contact the case, in special circumstances, can be used to increase the sealing ring.