Ultrasonic energy has been ud to join ther-moplastics for over 35 years. Ultrasonic weld-ing of thermoplastic materials is by far the most common form of ultrasonic asmbly, and is ud extensively in all major industries including automotive, appliance, electronic, toy, packaging, textile, and medical. I t offers advantages in speed, economy, and efficiency, and is frequently chon when parts are too complex or expensive to be molded in one piece.
This bulletin provides guidelines to aid the designer during the initial concept stage of a new product design, ensuring optimum pro-duction results. The dimensions given in the designs should be ud as guidelines only,since the specifics of your application may require variations. If you have questions or need assis-tance in designing your parts, contact your local Branson reprentative, regional technical center, or Branson headquarters in Danbury, Connecticut.
P r i m a r y F a c t o r s I n f l u e n c i n g J o i n t
D e s i g n
All of the following basic questions must be answered prior to the design stage to gain a total understanding of what the weld joint must do:
•What type of material(s) is to be ud?•What is the overall part size and configura-tion?
•What are the final requirements of the part?
-Is a structural bond desired and, if so, what load forces does it need to resist?
-I s a hermetic al required? I f so, to what pressure?
-Does the asmbly require a visually attractive appearance?
-s flash or particulate objectionable inside and/or outside?
-Any other requirements?T h r e e M a j o r J o i n t D e s i g n
C h a r a c t e r i s t i c s
In order to obtain acceptable, repeatable weld-ed joints, three general design guidelines must be followed:
1.The initial contact area between the mat-
新生儿需要补钙吗ing surfaces should be small to concen-trate and decrea the total energy (and thus the time) needed to start and complete melting. Minimizing the time the vibrating horn remains in contact with the part also reduces the potential for scuffing, and since less material is moved, there is less flash.
2.A means for aligning the mating parts
should be provided. Features such as pins and sockets, steps, or tongues and grooves, should be ud for alignment rather than the vibrating horn and/or fixture, to ensure proper, repeatable alignment and to avoid marking.
3.Horn con ac and placemen must be
considered to provide proper bearing over the joint area, to direct the mechanical energy and force to prevent marking of the contact surface.
T w o M a j o r T y p e s o f J o i n t D e s i g n There are two major types of joint design: the energy director and the shear joint.All other joint variations can be classified under the general categories or as hybrids combining aspects of both.
E n e r g y D i r e c t o r
会计会The energy director is typically a raid trian-gular bead of material molded on one of the joint surfaces. The primary function of the energy director is to concentrate the energy to rapidly initiate the softening and melting of the joining surface.
The diagrams in Figure 1 (next page) show time-temperature curves for a common butt joint and the more ideal joint incorporating an energy director. The energy director permits
Part Design for Ultrasonic Welding
Technical Information
PW-3
Branson
41 Eagle Road
Danbury, CT
06813-1961 (203) 796-0400 fax (203) 796-9838 email: info@bran-
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rapid welding while achieving maximum strength; material within the director generally flows throughout the joint area. The energy director is the most commonly-ud design for amorphous materials, although it is also ud for mi-crystalline materials.
B u t t J o i n t w i t h E n e r g y D i r e c t o r
The basic design formula for the energy direc-tor design is illustrated in Figure 2. It is very important to remember that the size and loca-tion of the energy director on the joint inter-face are dependent upon:
•Material(s)
•Requirements of the application
•Part size.
The peak of the energy director should be as sharp as possible; energy directors that are round or flat at their peak will not flow as effi-ciently.
When using a relatively easy-to-weld resin (e.g., polystyrene which has high modulus [stiffness] and low melt temperature), a mini-mum height of 0.010 inch (0.25 mm) is sug-gested, whereas a mi-crystalline or high-tem-perature amorphous , polycarbonate)would require a minimum height of 0.015 inch (0.4 mm).
In the ca of mi-crystalline resins (e.g., acetal, nylon) with an energy director, the maximum joint strength is generally obtained only from the width of the ba of the energy director. As a rule, it doesn’t make any difference which half of the part contains the energy director. In special situations (as in combinations of differ-ent materials), the general practice is to place the energy director on the part with the mate-rial that has the highest melt temperature and stiffness.
The energy director design requires a means of alignment such as pins and sockets, aligning ribs, tongue and groove designs, or fixturing. Knockout pins should not be placed in the weld area.
V a r i a t i o n s o f t h e E n e r g y D i r e c t o r J o i n t
The basic energy director design can be incor-porated into joint configurations other than the butt joint to gain additional benefits. Examples of joint design variations utilizing an energy director include the following alternatives: Step Joint—The step joint is ud for align-ment and for applications where excess melt or flash on one expod surface is objectionable. (Figure 3.) Note that 0.010 to 0.025 inch (0.25 to 0.64 mm) has been added to the gap sur-rounding the perimeter of the part. This adds a feature called a “shadow line” to the design. When welding is completed, a 0.010 to 0.025 inch (0.25 to 0.64 mm) gap will be formed around the periphery of the part, creating a more appealing appearance, since part-to-part variations will be less noticeable. I f the gap were completely clod, it is likely that flash would be formed in some outside areas, with
slight gaps in others; whereas with the shadow
诸葛亮黄月英*NOTE: Typically a 90o included angle is ud for amor-
phous resins, while a 60o included angle is ud for mi-
crystalline resins. The included angle may vary depending
on materials, fillers, part geometry, or requirements. For
your specific application, plea contact your local sales
engineer or regional office for recommendations.
line, minor variations in the parts are less like-ly to be noticed.
The design of the energy director us the same basic design thought process ud in the butt joint energy director (i.e., material, require-ments, part size). Note that a minimum wall thickness of 0.080 inch (2 mm) is recom-mended for this design.
Tongue and Groove —The major benefits of
using this joint design are that it prevents flash,both internally and externally, and provides alignment. Containment of the material enhances the attainment of hermetic als. The need to mai
ntain clearance on both sides of the tongue, however, makes this more difficult to mold. Also, becau of the reduced weld area, it is generally not as strong as a step joint. (Figure 4.)
The design of the energy director us the same basic design thought process ud in the butt joint 黄牙
energy director (i.e., material, require-ments, part size).
Textured Surface**—This feature is exclu-
sively ud in conjunction with an energy director. Molding a textured surface on the
mating part tends to improve the overall weld quality and strength by enhancing frictional characteristics and melt control. (Figure 5.) Usually the texture is 0.003 to 0.006 inch deep (0.076 to 0.152 mm), and is varied bad on the height of the energy director. In most cas,
the advantages include incread weld strength,reduced flash or particulate, reduced weld times, or lower amplitude requirements.(Branson T echnoLog TL-4 provides details on this concept.)
Criss-Cross —This design incorporates energy
directors on both mating ctions that are per-pendicular to each other, and provides mini-mum initial contact at the interface while allowing a potentially larger volume of materi-al involvement. This can result in incread strength in the weld. (Figure 6.) Each energy director should be dimensioned at approxi-mately 60% of the size that would be ud in a standard single energy director design, with an included angle of 60o versus the standard 90o .
I f an air- or liquid-tight al is required, it is recommended that the corresponding energy directors be continuous, like a saw tooth.(Figure 7.) The corresponding saw-tooth ener-gy directors must be located on the part that will be contacted by the horn. Note that this design generates a very high material flow;therefore, containing flash should be addresd in part design (e.g., u a tongue and
groove or step design).
Energy Director P erpendicular to the Wall —
Ud to gain resistance to peeling forces and to reduce flash. (Figure 8.) This design should be ud when only a structural al is required.
Interrupted —Ud to reduce the overall area
and subquent energy or power level required,or to minimize part marking. U only where
**This design is covered by Branson Patent No. 4,618,516. Licen to utilize this design is granted via the purcha of Branson equipment.
structural (non-hermetic) als are needed.(Figure 9.)
Chil Energy Director —Typically ud when
皇家美术学院nominal wall thickness is 0.060 inch (1.524mm) or less. (Figure 10.) If a standard energy director is ud, it will be too small (less than 0.010 inch/0.254 mm tall), thus resulting in lower weld strengths. The knife edge can be 0.015 inch to 0.020 inch (0.381 to 0.508 mm)tall and should utilize a 45o angle. As weld strength will be limited to weld width, a tex-tured surface should always be added when using this design.
Specialized Joints —In order to achieve a her-
metic al in less easily welded resins or irregu-lar shapes, it may be necessary to u a com-pressible al or a convoluted path for melt flow. Figure 11 shows a joint design incorpo-rating an O-ring. It is important to note that the O-ring should be compresd a maximum of 10 to 15%, only at the end of the weld. Pins and sockets (stud welding) can also be ud successfully with an O-ring design. (See data sheet PW-5.)
S h e a r J o i n t
An energy director type of joint design in some cas may not produce the desired results with mi-crystalline resins such as nylon, acetal,polypropylene, polyethylene, and thermoplas-tic polyester. This is due to the fact that mi-crystalline resins change rapidly from a solid to a molten state, and b
ack again, over a relative-ly narrow temperature range. The molten material flowing from an energy director,therefore, could re-solidify before fusing with the adjoining interface. The weld strength in a mi-crystalline resin could be limited to the ba width of the energy director. A shear joint configuration is recommended for the resins where geometry permits.
With a shear joint design, welding is accom-plished by first melting the small, initial con-tact area and then continuing to melt with a controlled interference along the vertical walls as the parts telescope together. (Refer to Figure 12.) This allows a strong structural or hermet-ic al to be obtained as the molten area of the interface is never allowed to come in contact with the surrounding air. For this reason, the shear joint is especially uful for mi-crys-talline resins.
The strength of the welded joint is a function of the vertical dimension of meltdown of the joint (depth of weld), which can be adjusted to meet the requirements of the application. Note: For joint strength meeting or exceeding that of the wall, a depth of 1.25X the wall thickness is recommended.
IMPORTANT: The shear joint requires rigid side
wall support to prevent deflection during weld-ing. The walls of the bottom ction must be supported at the joint by the holding fixture,which conforms cloly to the outside configu-ration of th贵州千户苗寨
e part. The top part should be of sufficient structural integrity to withstand
internal deflection.
For a midwall joint, the tongue and groove vari-ation shown in
Figure 13 is pre-
ferred. I t is also
麻辣豆
uful for large
parts. Interference
on one side only
is recommended.
Figure 14 shows variations of the basic shear joint design.
I t should be
noted that a
shear joint is
not recom-
mended for
parts with a
m a x i m u m
dimension of
3.5 inch or
greater, sharp
corners, or irregular shapes. This is due to difficulty in holding the molding tolerances necessary to obtain consistent results. An energy director type joint would be suggested for parts falling outside of the parameters (i.e., 3.5 inch, sharp corners, irregular shapes).
婆媳关系经典语录When welding parts that need a structural weld only (strength or air-tight als are not required), u the shear joint design with inter-rupted vertical energy directors shown in Figure 15. This design reduces the overall area and subquent energy or power required to weld the parts. The potential for part marking is also minimized.S h e a r J o i n t I n t e r f e r e n c e G u i d e l i n e s
The following table gives general guidelines for interference and part tolerance in relation to maximum part dimension.
O t h e r D e s i g n C o n s i d e r a t i o n s f o r A n y J o i n t
D e s i g n
Sharp corners localize stress. When a molded part with stress concentration is subjected to ultrasonic mechanical vibrations, damage (fracturing, melting) may occur in the high stress areas. This can be remedied by having a generous radius (0.020 inch/0.508 mm) on corners, edges, and junctions. At a minimum, all corners or edges should be broken. (Refer to Figure 16.)
Holes or voids like ports or other openings in the part being contacted by the horn can create an interruption in the transmission of the ultrasonic energy (Figure 17). Depending on the type of material (especially mi-crystalline resins) and the size of the hole, little or no welding will occur directly beneath the open-ing. When a hole or bend exists in the part,
Maximum Part Interference per Part Dimension Dimension Side (Range)Tolerance Less than 0.75"0.008" to 0.012"±0.001"
(18 mm)(0.2 to 0.3 mm)(±0.025 mm) 0.75" to 1.50"0.012" to 0.016"±0.002" (18 to 35 mm)(0.3 to 0.4 mm)(±0.050 mm) 1.50"to 3.50"0.016" to 0.020"±0.003" (38 to 90 mm)(0.4 to 0.5 mm)(±0.075 mm)
