Characteristics of Thermoplastics for Ultrasonic Assembly Applications Basic Principles Near-Field / Far-Field Welding The basic principle of ultrasonic assembly involves conversion Before discussing welding characteristics, the difference be - of high-frequency electrical energy to high-frequency me - tween near-field and far-field welding must be understood. chanical energy in the form of reciprocating vertical motion, Near-field welding refers to welding a joint located 1/4 inch which, when applied to a thermoplastic, can generate frictional (6 mm) or less from the area of horn contact; while far-field heat at the plastic/plastic or plastic/metal interface. In ultra - welding refers to welding a joint located more that 1/4 inch sonic welding, this frictional heat melts the plastic, allowing (6 mm) from the horn contact area. The greater the distance the two surfaces to fuse together; in ultrasonic staking, form - from the point of horn contact to the joint, the more difficult it ing or insertion, the controlled flow of the molten plastic is used will be for the vibration to travel through the material, and for to capture or retain another component in place (staking/form - the welding process to take place. ing) or encapsulate a metal insert (insertion). The differential, if any, in the melt temperature of the materials Thermoplastics can be ultrasonically assembled because they being welded should not exceed 30 degrees F (17 degrees C), melt within a specific temperature range, whereas thermoset - and the materials’ molecular structure should be compatible; ting materials, which degrade when heated are unsuitable for i.e.: blends, alloys, copolymers, and terpolymers. Moisture ultrasonic assembly. content, mold release agents, lubricants, plasticizers, fillers, reinforcing agents, regrinds, pigments, flame retardants, and Weldability of any thermoplastic depends on its stiffness or resin grade are all variables that can influence weldability. modulus of elasticity, density, coefficient of friction, thermal conductivity, specific heat and T or T . m g Variables Influencing Weldability Rigid plastics exhibit excellent welding properties because they readily transmit vibratory energy. Soft plastics, having a The moisture content of parts molded from resins that are hy - low modulus of elasticity, attenuate the ultrasonic vibrations, groscopic (moisture absorbent) can be problematical. Nylon and as such are more difficult to weld. In staking, forming or (and to a lesser degree polycarbonate and polysulfone) pres - spot welding, the opposite is true. Generally, the softer the ent most of the problem, and parts molded in these resins plastic, the easier it is to stake, form or spot weld. should be stored in sealed polyethylene bags with an appro - priate dessicant immediately after molding. If moist parts are Resins welded, the escaping vapors may cause voids and fissures in the molten material resulting in a weld of poor integrity. Resins are classified as amorphous or crystalline. Mold release agents such as zinc stearate, aluminum stearate, Ultrasonic energy is easily transmitted through amorphous fluorocarbons and silicones are not compatible with ultrasonic resins and as such, these resins lend themselves readily to ul - welding. If it is necessary to use a mold release agent, the trasonic welding. Amorphous resins are characterized by ran - paintable/printable grades that permit painting and silk screen - dom molecular arrangements, and a broad melting ing should be considered. Other release agents should be re - temperature range that allows the material to soften gradually moved with either TF Freon for crystalline resins or a 50/50 before melting and flow without prematurely solidifying. solution of water and liquid detergent. Because the molecular structure in the crystalline resins at - Lubricants, whether waxes, stearates or fatty esters, reduce tenuate a great amount of energy, crystalline resins do not intermolecular friction within the polymer and inhibit the ultra - readily transmit ultrasonic energy, and they require higher en - sonic assembly process. However, since they are generally dis - ergy levels than amorphous resins. These resins are charac - persed internally, their effect is usually negligible. terized by a high, sharply defined melting point that causes Plasticizers, which usually impart flexibility and softness to a melting and resolidification to occur rapidly. For these reasons, resin can interfere with a resin’s ability to transmit vibratory when welding crystalline resins, higher amplitude and energy energy. FDA-approved plasticizers do not present as much of levels should be used, and special consideration should be a problem as metallic plasticizers, but experimentation is given to joint design. recommended. 1 Although fillers and reinforcing agents such as glass and talc tic has not been degraded. Regrind limitations suggested by can increase the ultrasonic weldability of soft thermoplastics the resin suppliers should be observed. considerably, they should be judiciously used. When additive Although most pigments do not interfere with the ultrasonic content exceeds 10%, premature horn wear may result, and process, some oil-based colorants can adversely influence specially treated steel or carbide-faced titanium horns might weldability. Non-oil based pigments should be used. be required. When filler content approaches 35%, there may be insufficient resin at the surface to attain hermetic seals; and Flame retardants greatly affect the weldability of thermoplas - when filler content exceeds 40%, insufficient plastic is present tics and the effects of these various additives should be in - at the interface to form a positive bond. Reinforcement com - vestigated experimentally prior to resin selection. The grade of posed of long glass fibers are always more problematical than resin can have a significant influence on weldability. There is a reinforcement composed of short glass fibers. great difference between injection/extrusion grades and cast grades. Their molecular weight, melt temperature and modu - Ultrasonic assembly is one of the few methods that permits lus of elasticity are quite different. Injection/extrusion grades regrinding of parts, since no foreign substance is introduced should only be used with injection/extrusion grades, and cast into the resin. Ultrasonically assembling parts which have been grades should only be used with cast grades. manufactured from regrind parts presents no problem provided that the percentage of regrind is not excessive, and the plas - . 2 Chart I Characteristics of Thermoplastics FIELD OF WELDING SPOT STAKING MATERIAL WELDING SWAGING INSERTING NEAR FAR AMORPHOUS: ABS EEEEG ABS/POLYCARBONATE GGGGF ABS/PVC GGFGF ACRYLIC GFGGF ACRYLIC MULTI-POLYMER-XT POLYMER GGGGF ACRYLIC/PVC GGFGF ACRYLIC – IMPACT MODIFIED FFPFP BUTADIENE – STYRENE (BDS) GGGGF CELLULOSICS – CA, CAB, CAP PGEP – MODIFIED PHENYLENE OXIDE EEEEG POLYARYLATE FFGGF POLYCARBONATE GFGGF POLYETHERIMIDE GGE EG POLYSTYRENE, G.P. FFGEE POLYSTYRENE, IMPACT MODIFIED FFGGP PVC – RIGID FGEPP PVC – FLEXIBLE P––P– SAN – NAS – ASA FFGEE STYRENE-MALEIC-ANHYDRIDE EEEEG SULFONE POLYMERS FFGGF CRYSTALLINE: ACETAL COPOLYMER FFGGF ACETAL HOMOPOLYMERS FFGGF FLUOROPOLYMERS –––P– NYLON FFGGF PC-PET GGE EG POLYESTER – PBT FFGGF POLYESTER – PET FFGGF POLYETHERETHERKETONE GGE EG POLYETHYLENE (LDPE, HDPE) GFGPP POLYETHYLENE (UHMW) ––––– POLYMETHYLPENTENE GFEFP POLYPHENYLENE SULFIDE FPGGF POLYPROPYLENE EEGF-P P E - Excellent G - Good F - Fair P - Poor – Not Suitable for Ultrasonic Assembly . 3 Chart II Compatibility of Thermoplastics E D I R R E D E Y N H E M O T T Y N L A E A - N O K E E E C P R O I T T T I D N E E E B I A B E T E E L H N R S L E P P N M L I T A N - - E A T C U Y O I L E R R R R A C M S P B S M E E Y - R L E E S Y E R O E T T O Y Y L H H H C C C N A I I L R T L S S T T T N R T O V N L L O C E E E E E P S A E U A E P P O Y Y T / / O F L Y Y Y Y Y Y Y Y Y R P P L L L L L L L L L S R E R L / L L S S S N C Y P E Y D B C C C B B C O O O O O O O O O V A U T A A A A C A A B M N P P P P P P P P P P P S A S ABS I G I GGG GI ACRYLIC MULTI POLYMER G I GGG G ACETAL I ACRYLICS I G I GG GI CELLULOSICS I ABS/POLYCARBONATE GG G I GG G ABS/PVC GG G GI GG BDS G I GG MPPO I G NYLON I PC/PET I GG POLYARYLATE I POLYCARBONATE GGI G POLYESTER-PBT I POLYESTER-PET G I POLYETHERTHERKETONE I POLYETHERIMIDE I POLYETHYLENE I POLYPROPYLENE I POLYSTYRENE GG I GG PVC G I SAN GG G G I G ATYRENE-MALEIC-ANHYDRIDE IIGGG G G GI SULFONES I I Denotes compatibility G Denotes some compatibility, but not all grades and compositions are compatible. © 2016 Sonics & Materials, Inc. Specifications subject to change without notice. Not responsible for 10000819 ISO 9001 Corporate Headquarters 53 Church Hill Road, Newtown, CT 06470 USA typographical errors. 203.270.4600 800.745.1105 203.270.4610 fax [email protected] Printed in U.S.A. 1C/06/16 Sonics & Materials, Inc..