In addition to Tables 3.2 and 3.3, it is also possible to predict the weldability of two different materials using the following guidelines:

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1 26 Ultrasonic Welding Table 3.4 contains recommended amplitudes for ultrasonic assembly. These values are starting points only during equipment setup, and often fine-tuning of the values is needed. Table 3.4 Range of Vibration Amplitudes at 20 khz for Various Materials and Applications Material Welding (µm) Insertion (µm) Staking (µm) PS PC ABS PP PE PA PPO PEI PVC SAN/ NAS Acetal PEEK PPS PI PBT In addition to Tables 3.2 and 3.3, it is also possible to predict the weldability of two different materials using the following guidelines:

2 Ultrasonic Welding 27 Similar melt temperatures. The T g or T m, depending if the application is an amorphous or crystalline material, should be within 22 C (40 F) of each other. Similar melt flows. The melt flow index for the two materials should be within 10% of each other. Similar surface energies. The relative surface energies should be within 10% of each other. 3.4 Part and Joint Design For any application, there are two major factors regarding design: part design and joint design. There are many variations on joint design, but most fall under two major categories: energy director and shear joint. Both promote stress at the bond line (faying surface) in order to assure that the energy is concentrated at the bond line. Figure 3.4 Details of a generic energy director

3 28 Ultrasonic Welding Upper Part With Internal Centering; Weld Covered on the Inside, Flash can Emerge Outside Upper Part With External Centering; Weld Covered on the Outside, Flash can Emerge Inside Upper Part With Double- Sided Centering; Because of the Need for Higher Dimensional Accuracy, this Should Preferably be Used for Small Parts Only Weld Shape for Lager Parts to be Joined Figure 3.5 Examples of variation of energy director Figure 3.6 Details of a generic shear joint

4 Ultrasonic Welding 29 Combination With Double Centering in the Lower Part Double Shear Joint Weld With And Without Energy Director on the Lower Part Figure 3.7 Examples of shear joints with part alignment and flash containment features. Table 3.5 details some of the advantages and limitations to each of these joint designs. Table 3.5 Advantages and Disadvantages of Energy Directors and Shear Joint Design Energy Director Advantages Low energy dissipation Minimal part marking Limited flash Minimal cycle time Disadvantages Marginal with crystalline materials Limited weld strength with some materials Some weld flash Shear Joint High weld strength Tight dimensional Hermetic seal Work well with all materials tolerance Relatively high power dissipation Complex fixtures are usually required

5 30 Ultrasonic Welding One of the limitations of shear joints is the need for tight tolerances on the molded parts in order to assure proper consistency from part to part. Table 3.6 contains general guidelines for the required tolerances for different part sizes. Table 3.6 General Dimensional Guidelines for Shear Joints with Parts of Different Sizes Maximum part Interference per side Part dimension dimension < 18 mm (0.75 in) 18 to 35 mm (0.75 to 1.5 in) > 35 mm (1.50 in) (range) 0.2 to 0.3 mm (0.008 to in) 0.3 to 0.4 mm (0.012 to in) 0.4 to 0.5 mm (0.016 to in) tolerance ± 0.025mm (± in) ± mm (± in) ± mm (± in) There are three major functions of a part design: Small initial contact. A small initial contact area is required to assure that all the deformation (strain) occurs at the joint interface (faying surface) and that the entire surface heats uniformly and quickly to the melt temperature of the thermoplastic. Assure proper alignment. The joint design should have built-in alignment to assure that the parts are positioned properly. Alignment is achieved through locating pins or through the joint design such as with tongue and groove joints. Part alignment can be achieved by relying on the horn and fixture but this is not the preferred method.

6 Ultrasonic Welding 31 Energy transfer. The part should be designed to maximize the horn contact area so as to minimize the induced stresses by the ultra-sonic energy and minimize the possibility of part marking. This distance should also remain constant throughout the part. There should not be any voids preventing the energy from traveling directly to the weld area. 3.5 Troubleshooting Table 3.7 provides general guidelines for selected problems related to application setup and equipment as well as possible solutions. Table 3.8 Welding Problem Overweldng Underwelding Possible Problems and Solutions for Ultrasonic Joining Probable Causes - Too much energy input for welding - Insufficient energy in put for welding - Energy loss to fixture (if fixture is made of Urethane) Recommendations - Reduce weld pressure, weld time, energy, welding distance - Reduce amplitude of vibration by using lower power setup and/or lower gain booster - Reduce down speed - Do the counter actions described for overwelding problem - Use a more rigid material

7 32 Ultrasonic Welding Table 3.8 Welding Problem Inconsistent welding from part-to-part Marking Flash (cont.) Possible Problems and Solutions for Ultrasonic Joining Probable Causes - Part dimension variation - Mold release - Variation in material characteristics - Variation in utility - Horn heats up - Weld cycle is too long - Improper fit of part to fixture - Energy director is too large - Overwelding - Shear interference is too great - Insufficient flash trap Recommendations - Run statistical study if a pattern develops with certain cavity combinations - Check part tolerances / dimensions, molding conditions, and cavity dimension variation - Clean mating surface or replace mold release - Check regrind and/or filler content variation - Check molding condition variation - Check moisture content - Check line voltage and air pressure fluctuations - Decrease amplitude - Check for cracked horn, booster, or converter - Check for loosened stud and horn - Utilize air nozzles for cooling - Increase amplitude and/or pressure - Adjust dynamic air pres sure - Check for proper fixture support - Redesign fixture - Reduce size of energy director, weld time, pres sure - Refer to recommendation in overwelding - Reduce amount of interference - Add flash trap - Increase flash trap