The Vibration and Hot-Tool Welding of Polyamides.
Polyamides, commonly known as nylons, are a versatile class of widely used semicrystalline, engineering thermoplastics. Short glass-fiber filled grades are the materials of choice in under- hood automotive, lawn and garden, and power tool applications. One noteworthy application is the replacement of cast aluminum air inlet manifolds in automotive engines by monolithic, injection-molded 33 wt% chopped-glass filled parts. Because of the hollow geometry, the molding of these parts required fusible metal cores. Now such air inlet manifolds are being manufactured by vibration welding of conventionally molded parts, thereby reducing cycle time and cost (1, 2).
While most polyamides are semicrystalline, amorphous polyamides are also available. This paper examines the vibration welding of several commercial polyamides (PA): a polyamide 6 that will be referred to as PA-6, and polyamide 6,6 that will be referred to as PA-6,6. The hot-tool welding of this material is also assessed. A 33 wt% glass reinforced polyamide 6,6 will be referred to as 33-GF-PA-6,6. And a transparent amorphous polyamide, will be referred to as PA-A.
The vibration welding process is ideally suited to the welding of thermoplastic parts along flat seams. The process can also accommodate seams with small out-of-plane curvature. This technique offers several advantages for joining large flat-seamed thermoplastic parts: relatively short cycle times, simple equipment, and insensitivity of the process to weld surface preparation. In contrast to adhesive bonding, no foreign material is introduced, so that the weld interface is of the same material as the parts to be welded (3).
Hot-tool welding, is a widely used technique in which the surfaces to be joined are brought to the "melting temperature" by direct contact with a heated metallic tool. In some cases, such as joining of plastic pipes, the surfaces to be joined are flat, so that the tool is a hot plate. However, in many applications, such as in automotive headlamps and rear lights, doubly curved joint interfaces require complex tools that allow the hot surfaces to match the contours of the joint interface. Applicability to complex geometries is one of the major advantages of this process (3).
Some data on the vibration (4-8), hot-tool (9, 10), and orbital (11) welding of unfilled and glass and particulate filled PA-6 and PA-6,6 are available. However, in most cases the weld process conditions under which the welds were made and tested have not adequately been specified. The contents of these references are discussed in greater detail in the sections on Vibration Welding and Hot-Tool Welding in this paper.
VIBRATION WELDING PROCESS
In vibration welding, frictional work done by rubbing two parts along their common interface is used to generate heat to melt the interfacial material. Welding is achieved by allowing the molten interfacial film to solidify. The main process parameters are the weld frequency, n, the amplitude of the vibratory motion, [alpha], the interfacial weld pressure, [P.sub.0], and the weld time.
Details of the phenomenology of vibration welding (12, 13) and analyses of this welding process (14-16) are available. During welding, the externally imposed interfacial weld pressure causes the molten interfacial film to flow laterally outward, thereby resulting in the two parts coming closer. The decrease, [eta] = [eta](t), in the distance between two parts caused by this lateral outflow is called weld penetration. Extensive tests on polymers show that the welding process can be divided into four phases: solid friction, transient flow, steady-state flow, and solidification (12). (i) During the first phase Coulomb friction causes the solid interface, which is subjected to a normal pressure [p.sub.0], to heat up to the "melting" temperature of the plastic. In this phase the penetration is zero. (ii) In the second, unsteady phase the interfacial material then begins to melt and flow laterally outward relative to the direction of vibratory motion. (iii) A steady state is attained in phase three during which the penetration rate has a steady-state value. (iv) Phase four starts when the vibratory motion is stopped. Under the constant pressure [p.sub.0], the molten fluid in the film continues to flow outward while it cools in the absence of heat input. This process ends when the remaining material solidifies completely, resulting in a weld at the interface.
The weld penetration [eta] is the most important parameter affecting weld strength. Extensive experiments have shown that vibration welds of all thermoplastics--neat resins, blends, filled resins, structural foams, and welds between dissimilar resins--exhibit the four phases of welding. Experiments on many thermoplastics--polycarbonate (17); poly(butylene terephthalate), poly(phenylene oxide), and polyetherimide (18)--have shown that in neat resins very high static weld strengths, equal to that of the resin, can be achieved when the penetration exceeds a critical threshold, the penetration at the beginning of the steady-state phase. And the weld strength drops off for penetrations below this value. This threshold is affected by the thickness of the part being welded; the threshold increases with part thickness (19). Additional penetration into the steady-state phase does not affect weld strength in neat resins (17, 18) in blends (18, 20-22), in chopped glass-filled and particulate-filled resins (4, 8, 23-25) and in structural foams (26); the strengths of welds between dissimilar materials can continue to increase, however (21, 27, 28).
The preceding discussion applies to the normal mode of vibration welding, in which the vibratory motion is parallel to the seam being welded, that is, at right angles to the thickness direction. In cross-thickness vibration welding, in which the vibratory motion is along the thickness direction, cooling of the molten film at the edges, where the melt is exposed to air in each cycle, can adversely affect weld strength (29).
As already mentioned, some data on the welding of unfilled and filled polyamides are available. However, in most cases the weld process conditions under which the welds were made and tested have not adequately been specified. The available data on the vibration welding of these materials will be reviewed briefly.
Reference 4 gives data on the strengths of both normal and cross-thickness vibration welds of injection-molded specimens cut from plaques of a polyamide 6,6 (PA-6,6), a heat stabilized PA-6,6 (HS-PA-6,6), a 40 wt% glass-filled PA-6,6 (40-GF-PA-6,6), and a mineral particulate-filled PA-6,6 (PF-PA-6,6) for which the filler content has not been specified. The plaque used in the weld study had a thickness of 3.3 mm (8). The actual materials used (grades or compositions), the mold geometry, and molding conditions, and have not been identified. All of the tests were done at frequency of 240 Hz and a weld amplitude of 0.75 mm using weld time control. The weld time was varied in the range of 1-7 s. A series of tests on PA-6,6, in which the weld pressure was varied in the range of 1-9 MPa, indicated an optimum weld pressure of 7 MPa. The tests on all other materials were conducted at a fixed weld pressure of 7 MPa. The materials used had the following tensile strengths: PA-6,6, 55 MPa; HS-PA-6,6, 51 MPa; 40-GF-PA-6,6 , 79 MPa; PF-PA-6,6, 77 MPa. The stain rate at which tensile tests were conducted on the materials and welds is not specified. The maximum relative percent (longitudinal, cross-thickness) weld strengths obtained in these materials were (92, 97), (90, 43), (55, 58), and (79, 90), respectively. The corresponding weld zone (longitudinal, cross-thickness) thicknesses in millimeters were (0.60, 0.60), (0.064, 0.036), (0.040, 0.040), and (0.068, 0.080), respectively.
Reference 5 discusses the formation of bubbles in the weld zone of PA-6 vibration welds resulting from evaporation of absorbed moisture, and the effects of such bubbles on weld strength. In this material, test pieces stored for long periods in a 230[degrees]C, 50% relative humidity (RH) atmosphere absorb a moisture content of approximately 3%. The tensile strength of PA-6 is a strong function of the moisture content. The tensile strengths measured at moisture contents of 0.15, 3.4, and 7.4 wt% were, respectively, about 80, 32, and 30 MPa. In vibration welding of nylon, the temperatures in the molten weld zone are expected to be above 220[degrees]C. Use of the boiling point versus pressure curve for water shows that at 220[degrees]C vapor formation, and hence bubble formation, can be prevented at weld pressures higher than 5 MPa. Welds made at a frequency of 240 Hz, a weld amplitude of 0.75 mm, weld pressures of 2, 4, and 7 MPa, and weld times of 2, 4, and 6 s, on 3-mm-thick specimens having moisture contents of 0.15, 3.4, and 7.4 wt%, showed that the optimum weld strengths obtained are equivalent to the base strength of the (moist) material. Although higher weld pressures inhibit the formation of vapor bubbles in the weld, bubble formation cannot be eliminated altogether, even for material with very little moisture content. The low pressures in and near the weld bead results in bubble formation. While weld strength cannot be increased through predrying, it does result in fewer bubbles in the weld bead, or flash.
Reference 6 discusses the vibration welding of two 30 wt% glass-filled nylon 6 (PA-6) and nylon 6,6 (PA6,6) grades: Dupont Zytel[R] 73G30 (30-GF-PA-6) and Zytel[R] 70G30 (30-GF-PA-6,6). Welds were made in both dry as molded (DAM) and 50% relative humidity conditioned materials. The vibration welds were made at a weld frequency of 206 Hz, a weld amplitude of 0.8 mm, a weld pressure of 1.8 MPa, and weld penetrations of 1, 2, and 2.5 mm. Tests were done on specimens cut from both flow and cross-flow directions of molded plaques. The effect of weld pressure was assessed through welds made at a fixed weld penetration of 2 mm in which the weld pressure was varied in the range of 1.8-20 MPa. The tensile strengths of the welds were measured at test temperatures of 23, 80, and 120[degrees]C. (The strain or displacement rate is not specified.) The tensile weld strengths of (30-GF-PA-6 and 30-GF-PA-6,6), determined at 23[degrees]C in MPa, were (63.4, 42.7) for DAM flow-direction specimens; (56.1, 39.6) for DAM cross-fl ow direction specimens; (36.9, 33.2) for 50% RH flow-direction specimens; and (35.5, 29.3) for 50% RH cross-flow direction specimens. At elevated temperatures, 30-GF-PA-6,6 gives higher weld strengths than 30-GF-PA-6 regardless of material conditioning and specimen orientation. For both materials, welds of 50% RH conditioned material have significantly lower strengths at 23[degrees]C than welds of DAM materials. At 23[degrees]C, welds of flow-direction specimens had strengths up to 20% higher than welds on cross-flow direction specimens. At 120[degrees]C, welds of DAM material were not sensitive to specimen orientation. For both directions, 30-GF-PA-6,6 had higher weld strength. Increasing test temperatures resulted in reduced weld strengths in both materials. At 120[degrees]C, 30-GF-PA-6,6 had up to 28% higher weld strength than 30-GF-PA-6. Increasing weld pressure results in lower weld strengths in both materials.
Reference 7 discusses the vibration welding of unfilled and glass-filled nylon 6 and nylon 6,6. The welds were made at a frequency of 240 Hz, weld amplitudes in the range of 1.02-1.80 mm, weld times in the range of 4-25 s, and a maximum clamp load of 4.4 kN-the actual weld pressure is not specified. Molded specimens (101.6 x 76.2 X 6.35-mm) were welded on the 101.6 X 6.35-mm surfaces. Strength data are reported for "optimized" weld process conditions that give the highest weld strengths, but these optimum conditions are not specified. An interesting finding is that the average fiber loading in the flash (bead) material from 33 wt% glass-filled nylon 6 (Honeywell Capron[R] 8233G HS) samples welded at different welding conditions was 32.29 [+ or -] 0.25 wt%, approximately 0.5 wt% to 1 wt% lower than the fiber content of the bulk, 33.01 [+ or -] 1.21 wt%. At 33.48 wt%, the glass content in the flash from a 33 wt% glass-filled nylon 6,6 (Capron[R] 5233G HS) sample was approximately 0.5 wt% lower than in the bulk (33.94 wt%). Also, a comparison of the fiber length distributions in the flash and base materials shows that fiber breakage in the weld zone is small. In six grades of PA-6 (Capron[R] 8202G HS, Capron[R] 8230G HS, Capron[R] 8231G HS, Capron[R] 8232G HS, Capron[R] 8233G HS, and Capron[R] 8235G HS), having glass fiber wt% contents of (0, 6, 14, 25, 33, and 50), optimum weld strengths (MPa) of (79.3, 83.1, 90.7, 90.2, 85.2, and 80.5) were demonstrated. Note that in each case, the weld strength of the glass-filled material is higher than that of the neat resin (79.3 MPa). For the glass-filled nylon 6 studied, the highest weld strength is attained for a glass filler content in the range of 14-25 wt%.
Reference 8 evaluates the effect of weld specimen thickness through 240 Hz welds of 2- and 4-mm-thick specimens of PA-6,6 and 40-GF-PA-6,6, at two weld amplitudes of 0.5 and 0.75 mm. The mean tensile strengths of the 2- and 4-mm-thick PA-6,6 specimens were 53 and 78 MPa, respectively. The mean tensile strengths of the 2- and 4-mm-thick 40-GF-PA-6,6 specimens were 130 and 155 MPa, respectively. (Strain rates for the tests not specified.) In the 3-mm-thick PA-6,6 specimens the highest weld strength of about 51 MPa is attained at a weld pressure of 2 MPa and a weld amplitude of 0.75 mm. In the thicker specimens a maximum weld strength of about 65 MPa is obtained at both weld amplitudes. The paper describes novel tests on vibration welds of a complex hexagonal part with three ribs connected to the middle three alternate faces of the hexagon. The six edges see different weld modalities from longitudinal to cross-thickness, to mixed welds. The paper discusses the use of the data obtained for quality control purpos es.
References 10 and 11 discuss the tensile strengths of 33 wt% glass filled PA-6, PA-6,6, and 30 wt% glass-filled PA-6,6-co-PA-6 copolymer and PA-4,6 to themselves and to each other. The actual grades have not been identified in the paper. (Note that the melting points of PA-6, PA-6,6, PA-6,6-co-PA-6 copolymer, PA-4,6, and high-temperature resistant PA are, respectively, 223, 261, 238, 290, and 300[degrees]C.) The weld strengths of 33-GF-PA-6, 33-GF-PA-6,6, 30-GF-PA-6,6-co-PA-6, 30-GF-PA-4,6, and 35-GF-PA-HTN to themselves at 23[degrees]C, DAM conditions were, respectively, 85.6, 83.2, 84.9, 59.8, and 57.5 MPa. The weld strengths of dissimilar nylons at 23[degrees]C, DAM were: 33-GF-PA-6 to 33-GF-PA-6,6, 85.2 MPa; 33-GF-PA-6 to 30-GF-PA-4,6, 63.8 MPa; 33-GF-PA-6 to 35-GF-PA-HTN, 59.1 MPa; 33-GF-PA-6 to 30-GF-PA-6,6-co-Pa-6, 85.0 MPa; 33-GF-PA-6,6 to 30-GF-PA-4,6, 68.7 MPa; 33-GF-PA-6,6, to 35-GF-PA-HTN, 63.3 MPa; and 33-GF-PA-6,6, to 30-GF-PA-6,6-co-Pa-6, 84.8 MPa. The paper also gives the weld strengths of 40 -PF-PA-6, 15-GF-25PF-PA-6, and 33-GF-PA-6--having tensile strengths of 89.6, 138, and 185 MPa, respectively--as 83.8, 88.4, and 85.6 MPa, respectively.
DISPLACEMENT CONTROLLED HOT-TOOL WELDING
The phenomenology of the hot-tool welding process is described in detail in Reference 30, which also lists references relating to analyses of this process. This welding essentially has four phases: In phase one, the parts are brought in contact with the hot-tool, and a relatively high pressure is used to ensure complete matching of the part and tool surfaces. The lateral outward flow of the molten plastic adjacent to the hot tool results in a displacement of the parts towards the hot tool surfaces. During phase one, this displacement of the parts is restricted to a predetermined distance by means of mechanical stops. In phase two, the parts are held in place against the stops for a predetermined time to allow the molten layer to grow. When a sufficient film thickness has been achieved, the part and tool are separated and the molten surfaces of the parts to be joined are then brought together (phase three), and held under pressure until the weld solidifies (phase four). Mechanical stops are again used to inhi bit the motion of the parts, thereby allowing the molten film to solidify solely by heat conduction, without any gross flow.
With reference to the schematic in Fig. 1, the essential parts of a displacement controlled welding machine consist of the hot-tool assembly having two exposed hot surfaces, two fixtures for holding the parts to be welded, means for bringing the parts in contact with the hot surfaces and then bringing the molten surfaces together to form the weld, and adequate timing and displacement controls. The left-hand side shows one half of the hot-tool assembly, comprising an electrically heated block on which interchangeable hot-tool inserts can be mounted. The hot-tool assembly has mechanical stops [S.sub.H], the surfaces of which are offset from the hot-tool surface by a distance [[delta].sub.H] The hot-tool assembly can be moved in and out of the configuration shown in the figure along the direction indicated.
The part to be welded is gripped in a fixture (right-hand side of Figure) that can be moved to and fro in a direction at right angles to the allowable motion for the hot-tool assembly. This fixture has mechanical stops [S.sub.p] that are aligned with the hot-tool stops [S.sub.H]. For welding, the fixture is moved to bring the part into contact with the hot-tool surface, and a pressure is applied to maintain this contact. When the surface temperature reaches the melting point of the plastic, the externally applied pressure causes the molten material to flow laterally outward, thereby inducing a leftward motion of the part. The decrease in the part length caused by the outflow of molten material is called the penetration [eta].
Initially, very little flow occurs and the molten film thickens. The flow or penetration rate begins to increase with time. The penetration (or part motion) will not change after the part stops [S.sub.p] come into contact with the hot-tool stops [S.sub.H] as shown in Fig. 1. Let the elapsed time from the instant that the part touches the hot-tool surface to the instant when the stops come into contact be [t.sub.0], and let the corresponding penetration, the melt penetration, be [eta] [[delta].sub.0] (Fig. 1). This thickness of material will melt and flow out laterally to form a part of the weld "bead." Continuing contact with the hot-tool surface after time [t.sub.0] will cause the molten layer to thicken with time, with no additional penetration. With increasing time, thermal expansion in the portion of the part heated by conduction will cause more material to flow out, resulting in an apparent increase in [[delta].sub.0] Let the duration of this film buildup phase be [t.sub.M] and let the thickness of the molten layer be [[delta].sub.M] as shown. In the changeover phase, the parts are pulled away from the hot-tool, the hot-tool is retracted, and the molten surfaces are brought into contact-thereby initiating the joining phase. Let the duration of this changeover phase be [t.sub.c]. After the molten surfaces touch, the applied joining pressure squeezes out the molten material laterally, resulting in a further penetration. During this squeezing motion, heat transfer from the melt results in a cooling and in an eventual solidification of the melt.
For dimensional control [t.sub.M] should be large enough to ensure that [[delta].sub.M] [greater than] [[delta].sub.H]. [[delta].sub.H]. For this case, the total penetration on each of the halves being welded will be [delta] = [[delta].sub.0] + [[delta].sub.H], so that the overall (warm) part length will decrease by 2[delta], if thermal expansion effects are neglected. Let the initial lengths of the parts before welding be [l.sub.1] and [l.sub.2], and let the length of the welded part be [l.sub.0] Then, AL = [l.sub.1] + 12 - 10 is the thickness of the material that flowed out into the weld bead. If the stops come into contact during the joining phase (for which [[delta].sub.M] [[delta].sub.H] and thermal expansion effects are neglected, then the expected change in length should be 2[delta]. However, if [[delta].sub.M] [less than] [[delta].sub.H], then the stops will not come into contact and the change in length should be less than 2[delta]. Thus, if thermal expansion effects are neglected, [delta][eta] = 2[delta] - [delta]l is a measure for whether or not the stops come into contact: stops do and do not contact when [delta][eta] = 0 and [delta][eta] [greater than] 0, respectively. Reference 30 discusses a procedure to account for thermal expansion effects.
Clearly, [[delta].sub.0] by itself does not contribute to the welding that occurs during the joining phase; this material just flows outward into the bead. A small value of 80 is required to compensate for part surface irregularities and for ensuring that contaminated surface layers flow out before the joining phase. The machine setting [[delta].sub.H] (Fig. 1) controls the weld penetration, the penetration = [[eta].sub.j] = [[delta].sub.H] during the joining phase.
In this paper, the total time [t.sub.H] = [t.sub.0] + [t.sub.M] [approximate] [t.sub.M] for which the specimen is in contact with the hot-tool will be referred to as the heating time; melt penetration will refer to the distance [[delta].sub.0] (Fig. 1); weld penetration will refer to the distance [[delta].sub.H]; and the time [t.sub.w] will be referred to as the seal time.
In principle, the hot-tool welding process can be used to weld any polymer that melts on heating. Data are available for the hot-tool welding of many unfilled and filled resins (9, 30-40). By using different hot-tool temperatures for the two parts of an assembly, it is also possible to weld dissimilar materials (41-46).
The available data on the hot-tool welding of polyamides will be reviewed briefly. However, the weld process conditions under which the welds were made and tested have not adequately been specified.
Reference 9 gives hot-tool weld strength data on for 20, 30, and 40 wt% glass-filled PA-6, which will be referred to, respectively, as 20-GF-PA-6, 30-GF-PA-6, and 40-GF-PA-6. The strengths of the PA-6, 20-GF-PA-6. 30-GF-PA-6, and 40-GF-PA-6, were 90.0, 152.1, 185.8, and 201.3 MPa, respectively. The weld strengths attained in these materials were 52.1, 81.2, 90.3, and 80.8 MPa, respectively. These weld strengths represent relative strengths of 58. 53, 49, and 40% based on the strengths of the filled systems, and 58, 90, 100, and 90% based on the strength of the unfilled resin.
Reference 11 compares the vibration and hot-tool weld strengths of 6-GF-PA-6, 25-GF-PA-6, and 33-GFPA-6, which have tensile strengths of 85, 160, and 185 MPa, respectively. The base unfilled PA-6 used in these resins had a tensile strength of 79.3 MPa. The (vibration, hot-tool) weld strengths for these three materials, in MPa, are (83.1, 78.2), (90.2, 89.8), and (85.2, 84.5), respectively. The hot-tool weld strength of a 45-GF-PA-6 is given as 80.3 MPa. This paper also gives the (vibration, hot-tool) weld strengths of a 33GF-PA-6,6 as (83.6, 88.8) MPa; the base strength of the corresponding unfilled resin was 185 MPa.
The five commercial grades of nylons studied in this paper are: First, Capron[R] XPN 1250, essentially a general-purpose grade of polyamide 6 that will be referred to as PA-6. The second, Zytel[R] 101 NCO10--a general purpose, molding grade of polyamide 6,6--will be referred to as PA-6.6. The hot-tool welding of this material is also assessed. The third, Zytel[R] FE3705, is also a polyamide 6,6--essentially the same material as Zytel 101 but with a sharper molecular weight Distribution--will be referred to as PA-6,6-X. The fourth, Zytel[R] 7OG33HS1L NC010, is a heat stabilized 33 wt% glass reinforced polyamide 6,6 that will be referred to as 33-GF-PA-6,6. And fifth, Zytel[R] 330 NCO 10, a transparent amorphous polyamide, that will be referred to as PA-A.
The melting and glass transition temperatures of these materials and their nominal mechanical properties are listed in Table 1. Note the well-known differences in the strengths and strains to failure between undried and dried polyamides, the latter exhibiting higher strengths. Note also that the transition temperature of these resins depends on the moisture content, which depends on the relative humidity of the environment to which the material is exposed.
Most of the data in this paper were obtained from welds on 25.4 x 76.2-mm specimens cut from injection molded plaques with nominal thicknesses of 3.2 and 6.3 mm. Eight specimens were cut from the 152 X 203-mm injection molded plaques that were gated at the 152-mm edge (gate B in Fig. 2), as per the layout shown in Fig. 2. The edges of each specimen were machined to obtain rectangular blocks of size 76.2 X 25.4 mm X thickness for assuring accumte alignment of the surfaces during butt welding along the 25.4 mm X thickness edges.
Some of the data on the vibration welding of PA-6,6 were obtained by welding the 50.84 X thickness edges of 25.4 x 76.2-mm specimens. These wider specimens were used to obtain welds at low weld pressures.
The glass-filled specimens of 33-GF-PA-6,6 were individually numbered according to the scheme shown in Fig. 2 (24). Welds were conducted on sets of mating specimens from the same plaque. In this way it was possible to track variations across plaques due to fiber orientations. Fiber orientation in the specimens, which depends both on the location in the specimen as well as on its thickness, was not characterized. However, for purposes of comparison, five 152 X 25-mm specimens were cut from the 152 X 203-mm plaques. These specimens were subjected to the same strength tests as the welded specimens, thereby providing an average strength for evaluating the strengths of the welded joints.
Both vibration and hot-tool welds of a pair of 25.4 x 76.2-mm specimens results in a 152.4 X 25.4-mm x thickness bar. The vibration welds of a pair of 50.8 X 76.2-mm specimens results in a 152.4 x 50.8-mm X thickness bar. Such welded bars were sawed through the center to give a pair of a 152.4 X 25.4-mm X thickness bars. Each rectangular bar is routed down to a standard ASTM D638 tensile test specimen with a but joint at its center. The tensile bar, which has a transverse butt weld at mid length, is then subjected to a constant displacement rate tensile test in which the strain across the weld is monitored with a 25.4-mm gauge-length extensometer. All the weld strength tensile tests reported in this paper were done at a nominal strain rate of 0.01 [s.sup.-1].
The weld flash, or "bead," was not removed, and the weld strengths were obtained by dividing the load at failure by the original cross-sectional area of the specimen. Furthermore, the 25.4-mm gauge-length extensometer can grossly underestimate the local strain in the failure region once strain localization sets in, so that the significance of the reported failure strains [eruo]0 should be interpreted with care. These values only represent the lower limit of the failure strain at the weld.
The vibration welds were made on a research welding machine in which all the process parameters-the weld frequency, amplitude, pressure, and time-can be independently controlled (12). Also, in this machine, the weld motion can be stopped at a prescribed penetration. The data were obtained in the normal mode of vibration welding, in which the vibratory motion is normal to the specimen thickness (29). The data in this paper were obtained at a fixed weld frequency of n 120 Hz and a weld amplitude of a 3.175 mm. The weld pressures were varied in the range of [p.sub.o] = 0.26 to 3.45 MPa.
The hot-tool welds on PA-6,6 specimens were made on a commercially available (Hydra-Sealer Model VA-1015, Forward Technology Industries, Inc.) dual platen hot-tool welding machine. On this machine, the offset [[delta].sub.H], called the weld penetration, of the hot-tool stop [S.sub.H] from the hot-tool surface (Fig. 2) can only be changed by inserting shims between the electrically heated hot-tool block and the stops, which are fastened to the block surface by means of screws. All the data in this paper were obtained at a fixed melt penetration of [[delta].sub.0] = 0.13 mm, two weld penetrations of [[delta].sub.0] = 0.25 and 0.66 mm, and a seal time of 10s. The weld specimens are pneumatically gripped in special fixtures that accurately align the specimens during the welding cycle. Each grip is provided with a micrometer that can be used to accurately set the distance [delta] by which each specimen protrudes beyond the stops [S.sub.p]; any variations in the lengths of the specimens can easily be compensated f or. In this machine, the times [t.sub.0] and [t.sub.M] cannot be resolved, only the total heating time [t.sub.H] = [t.sub.0] + [t.sub.M] can be set and measured. However, for [[delta].sub.0] [much less than] [[delta].sub.H], [t.sub.0] should be much smaller than [t.sub.M]. A fixed changeover time [t.sub.c]--measured from the instant the heated specimens are pulled back from the hot-tool to the instant the molten films are brought back into contact--of about 1.24 s was used; the corresponding average changeover velocity seen by the specimen molten surfaces was about 118 mm [s.sup.-1]. The welding, or joining, time [t.sub.w]--measured from the instant the molten films are brought into contact to the instant the (solidified) welded parts are released--can be preset for on this machine. For the 3.2-mm-thick welds (specimen cross sections of thickness X 25.4 mm), the nominal weld pressure (based on the air pressure and the piston cross-sectional area) was 6.9 MPa.
Strength of PA-6 Vibration Welds
Strength and ductility data for 120 Hz welds of 6.35-mm-thick, undried and dried Capron XPN 1250 specimens, for a weld amplitude of 3.175 mm, at two weld pressures (0.9 and 3.45 MPa). and three nominal weld penetrations of 0.13, 0.25, and 0.51 mm are listed in Table 2. The actual penetrations for the undried and dried specimens are listed, respectively, in columns 2 and 3. The last two columns in this table lists the relative weld strengths, [[sigma].sub.R] = [[sigma].sub.w]/[[sigma].sub.0]--the ratio of the weld strength, [[sigma].sub.w], to the ultimate strength, [[sigma].sub.0], of the material--based on a tensile strengths [[sigma].sub.0] = 62.0 and 67.7 MPa for the undried and dried materials, respectively.
This limited data set shows that PA-6 welds well. High relative weld strengths can be achieved for nominal weld penetrations as low as 0.25 mm. The last column in Table 2 shows that 100% strength with high strains to failure can be obtained in the dried material at the lower weld pressure of 0.9 MPa for relatively low penetrations; the strength is lower at the higher weld pressure of 3.45 MPa. For the undried material, the relative weld strengths are lower at the lower weld pressure, but very high strengths are obtained at the higher weld pressure. One reason for this difference is that in the undried material the absorbed moisture results in small bubble in the weld zone, causing a reduction in weld strength. At the higher weld pressure, the formation of the bubbles is suppressed, resulting in higher weld strength . These one point data, without replicates, do not give a feel for the scatter in strength, which is known to be high in the dried material .
That 100% relative weld strength can be attained in 120 Hz vibration welds of PA-6 is consistent with the results for 240 Hz welds [5, 6]. Note the base strengths for DAM PA-6, given as 80 and 79.3 MPa in Refs. 5 and 6, respectively, are different from 67.7 MPa measured for the material used in this study. Some of the lower strength may be attributed in inadequate drying of the specimens prior to testing.
Strength of PA-6,6 Vibration Welds
Strength and ductility data for 120 Hz welds of 6.1-mm-thick Zytel 101 dried specimens, for a weld amplitude of 3.175 mm, at six weld pressures (0.26, 0.35, 0.52, 0.9, 1.72. and 3.45 MPa), and three nominal weld penetrations of 0.25, 0.50, 1.20, and 2.5 mm are listed in Table 3. The last two columns in this table lists, respectively, the strain at failure, and the relative weld strengths based on a tensile strengths = 78.5 MPa.
While most of the welds were made on 25.4 X 76.2-mm specimens, some of the data were obtained by welding the 50.84 X thickness edges of 25.4 X 76.2-mm specimens. These wider specimens were used to obtain welds at low weld pressures. The weld on a pair of 50.8 X 76.2-mm specimens results in a 152.4 X 50.8-mm X thickness bar. Such welded bars were sawed through the center to give a pair of a 152.4 X 25.4-mm X thickness bars, resulting in a pair of weld strengths for each test condition. Asterisks in column one of Table 3 indicate data obtained from such wider specimens.
The data in the last column show that 100% relative weld strength can be obtained in the dried material for weld pressures in the range of 0.52-0.9 MPa and nominal weld penetrations in the range 0.25-0.5 mm. The failure strains are also very high, almost the same as that for the base material. Clearly, PA-6,6 welds extremely well.
Welds made at 240 Hz on a different PA-6,6, which had a tensile strength of 55 MPa, achieved 92 and 97% relative weld strengths, in normal and cross-thickness mode welding, respectively . The bulk of the data were obtained at a relatively high weld pressure of 7 MPa, which may explain the reduced weld strength, since the present study shows reduced weld strength at weld pressures of 1.72 and 3.45 MPa. For a heat stabilized PA-6,6, which had a tensile strength of 51 MPa, 240 Hz welds at a weld pressure of 7 MPa resulted in normal and cross-thickness mode relative weld strengths of 90 and 64%. respectively.
Strength of PA-6,6 Hot-Tool Welds
Strength and ductility data for 3.2-mm-thick undried and dried PA-6,6 specimens, at a nominal strain rate of 0.01 [s.sup.-1], as functions of the hot-tool temperature and the heating time, are listed in Table 4. The PA-6,6 undried and dried specimens had yield strength of [[sigma].sub.0] = 63.5 and 72.6 MPa; the corresponding yield strains were = 21.4 and 19.3%. The melt and weld penetrations were maintained at 0.13 and 0.25 mm, respectively, and the seal time was kept constant at 10 s. The first column in this table shows that the hot-tool temperature was varied between 260 and 380[degrees]C. The second column shows the three heating times used (10, 15, and 20 s). For the undried material, columns 3, 5, 7, and 9 list, respectively, the weld strength, the failure strain, the change in length [delta]l after welding, and the differential penetration [delta][eta]. Columns 4, 6, 8, and 10 list the corresponding data for the dried material. Data for a melt penetration of 0.66 mm, all other conditions being the sa me as for the data in Table 4, are listed in Table 5.
The data in Table 4 show maximum weld strengths of 29.3 MPa and 72.6 MPa for the undried and dried material, respectively. The corresponding relative weld strengths are 46 and 36%, and the corresponding yield strains are about 1.1%. For the higher melt penetration of 0.66 mm (data in Table 5) the highest weld strengths attained in the undried and dried materials were 36.7 and 39.1 MPa. The corresponding relative weld strengths are 57 and 54%, and the corresponding yield strains are about 1.5%. These hot-tool weld strengths are much lower than the strengths demonstrated in vibration welds. Also, this large difference between the maximum vibration and hot-tool weld strengths is the largest observed in any neat resin. Clearly, relatively weld strengths more than about 60% of the base resin cannot be produced in hot-tool welds of PA-6,6.
As a comparison, Reference 9 reports a relative hot-tool weld strength of 58% in a PA-6 having a resin tensile strength of 90.0 MPa.
Earlier, it was argued that if thermal expansion effects are neglected then the differential penetration [delta][eta] [greater than or equal to]0, and that stops do and do not contact when [delta][eta] = 0 and [delta][eta] [greater than]0, respectively. The last two columns in Table 4 (data for the smaller weld penetration of 0.25 mm) show that [delta][eta] only has negative values, both for the undried and dried materials. However, for the larger weld penetration of 0.66 mm, (Table 5) [delta][eta] is mostly positive over a wider range of low hot-tool temperatures. One explanation for this discrepancy would be errors in the measurements of [[delta].sub.o] and the weld penetration [[delta].sub.H]. Instead of the two stops shown in the schematic in Fig. 1, contact is actually determined by four stops on each side. The difficulty in establishing even contact among the four stops on each side could result in errors in [[delta].sub.o] and [[delta].sub.H]. Although this discrepancy has been addressed and analyzed b efore (30, 38-40). it will not be discussed further in view of the rather low weld strengths in hot-tool welds of PA-6.6.
Strength of PA-6,6-X Vibration Welds
The data in Table 3 are only for dried PA-6,6 (Zytel 101). To assess the effects of drying, weld tests were done on both undried and dried specimens of Zytel[R] FE3705--essentially the same material as Zytel 101 but with a sharper molecular weight distribution--referred to as PA-6,6-X. Note from Table 1 that the dried version of this material had a higher strength and strain to failure than dried PA-6,6. Strength and ductility data for 120 Hz welds of 6.35-mm-thick undried and dried specimens of PA-6,6-X, for a weld amplitude of 3.175 mm, at two weld pressures (0.9 and 3.45 MPa), and three nominal weld penetrations of 0.13, 0.25, and 0.51 mm are listed in Table 6. Clearly, high strengths, equal to that of the base resin, can be obtained in the undried material at a weld pressure of 0.9 MPa. Just as in PA-6,6, the weld strengths are lower at the higher weld pressure of 3.45 MPa in both the undried and dried PA-6,6-X. Note that the tensile strengths of the dried PA-6,6-X and PA-6,6 were 85.3 and 78.5 MPa, respe ctively.
Strength of 33-GF-PA-6,6 Vibration Welds
Strength and ductility data for 120 Hz welds of 6.3mm-thick Zytel 70G33HS undried and dried specimens, for a weld amplitude of 3.175 mm, at three weld pressures (0.52, 0.9, and 1.72 MPa), and two nominal weld penetrations of 0.25, 0.51 mm are listed in Table 7. The last column in lists the pairs of specimens that were welded together to track variations across plaques caused by differences in fiber orientation. An idea of the strength variation caused by fiber orientation can be had from the strength variation in five tensile dogbone specimens cut along the length direction from one plaque. The measured strengths were 166.9, 171.7, 175.8, 149.6, and 155.1 MPa, with an average of 163.8 MPa. The corresponding strains were, respectively, 3.4, 3.3, 3.3, 2.6, and 2.7%, with an average of 3.06%. The relative weld strengths in column six of this table are based on this average tensile strength of 163.8 MPa. At the two lower weld pressures (0.52 and 0.9 MPa) relative weld strengths in the range of 54-57% were obtain ed.
As a comparison, Reference 4 gives relative weld strengths of 55 and 58% for 240 Hz normal and cross-thickness welds, respectively, of 3.3-mm-thick 40-GF-PA-6,6 specimens, the material for which had a tensile strength of 79 MPa. Reference 6 gives the room-temperature strengths of 206 Hz welds of undried and dried 30-GF-PA-6,6 as 45 and 65 MPa. While the relative weld strengths cannot be determined because the base tensile strength is not given, the paper does show how the weld strength decreases as the test temperature is raise from 23 to 120[degrees]C. References 7 and 10 list a weld strength of 83.2 MPa for a 33-GF-PA-6,6.
Strength of PA-A Vibration Welds
Strength and ductility data for 120 Hz welds of 6.35-mm-thick Zytel 330 undried and dried specimens, for a weld amplitude of 3.175 mm, at two weld pressures (0.9 and 3.45 MPa). and three nominal weld penetrations of 0.13, 0.25, and 0.51 mm are listed in Table 8. The last two columns in this table list the relative weld strengths of dried and undried specimens based on tensile strengths [[sigma].sub.0] = 102.8 and 120.0 MPa, respectively. The dried material exhibits higher weld strengths at all the six conditions. Except for one weld condition, the relative weld strengths are also higher for the dried material, for which relative weld strengths in the range of 90-97% have been demonstrated. The highest strengths are achieved at a nominal weld penetration of 0.25 mm at the lower weld pressure of 0.9 MPa.
Vibration welding produces excellent joints in both polyamide 6 and polyamide 6,6; weld strengths equal to those of the base resins can easily be obtained. Obtaining such high strengths requires the use of relatively low weld pressures in the range of 0.52-0.9 MPa.
Hot-tool welds of polyamide 6,6 do not have such high strengths. The highest relative weld strengths obtained in the undried and dried material were 57% and 54%, respectively.
In 33 wt% glass-filled polyamide 6,6. relative weld strengths in the range of 54-57% were obtained at weld pressures in the range of 0.52-0.9 MPa in 120 Hz vibration welds.
In the amorphous polyamide, relative weld strengths in the range of 90-97% have been demonstrated in the dried material.
The contributions of K. R. Conway, who carried out all the testing, and the inputs of L. P. Inzinna are greatly appreciated.
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Table 1. Mechanical Properties of several Polyamide Grades. Tensile strength MPa Melting (glass transition) Material Grade temperature [degrees]C Undried PA 6 Capron XPN 1250 220 (50) 62.0 PA 6,6 Zytel 101 NC010 262 * -- PA 6,6-X Zytel FE3705 262 75.4 33-GF-PA-66 Zytel 70G33HS 262 -- PA-A Zytel 330 NC010 ** 102.3 Strain at failure ** % Material Dried Undried Dried PA 6 67.7 2.26 2.61 PA 6,6 78.5 -- 4.50 PA 6,6-X 85.3 3.43 7.46 33-GF-PA-66 163.8 -- 3.06 PA-A 120.0 6.78 6.34 (*)Glass transition temperature: 70[degrees]C for dry as molded; 15[degrees]C at 50% relative humidity. (**)Glass transition temperature: 125[degrees]C for dry as molded; 80-90 [degrees]C at 50% relative humidity. (***)Strain at peak stress. Table 2. Strengths and Ductilities of 120 Hz Vibration Welds of 6.35-mm-Thick Capron XPN 1250 Specimens for a Weld Amplitude of a = 3.175 mm, at Two Weld Pressures and Three Weld Penetrations. Weld penetration Weld time Weld strength mm s MPa Weld pressure MPa Undried Dried Undried Dried Undried Dried 0.90 0.19 0.17 2.9 1.6 40.4 71.7 0.90 0.31 0.29 3.7 1.7 57.5 70.1 ** 0.90 0.54 0.54 2.8 2.4 73.2 ** 58.6 ** 3.45 0.17 0.17 1.2 0.8 69.8 62.3 3.45 0.28 0.27 1.2 0.8 65.0 50.2 3.45 0.54 0.53 1.6 1.3 59.4 57.7 Relative Strain at failure weld strength * % % Weld pressure MPa Undried Dried Undried Dried 0.90 1.51 3.42 65 106 0.90 2.22 3.08 93 104 0.90 4.15 2.32 118 87 3.45 3.00 2.49 113 92 3.45 2.83 1.83 105 74 3.45 2.44 2.27 96 85 (*)Based on a tensile strenght of 62.0 MPa for the undried material and 67.7 MPa for the undried material. The corresponding mean strains at failure are 2.26 and 2.61%, respectively. (**)Specimen failed away from the weld. In these specimens the failure surfaces show fracture surfaces with striations radiating from a point. Table 3. Strengths and Ductilities of 120 Hz Vibration Welds of Dried 6.1-mm- Thick Zytel 101 Specimens for a Weld Amplitude of a = 3.175 mm, at Six Weld Pressures and Two Weld Penetrations. Weld Weld Weld Weld Strain Relative pressure penetration time strength at failure weld strength *** MPa mm s MPa % % 0.26 * 0.27 6.0 10.1 0.32 13 0.26 * 0.27 6.0 13.0 0.37 17 0.26 * 0.52 7.0 80.8 5.05 103 0.26 * 0.52 7.0 31.9 1.05 41 0.35 * 0.26 4.2 79.4 4.30 101 0.35 * 0.26 4.2 14.8 0.44 19 0.35 * 0.51 5.1 65.6 2.44 84 0.35 * 0.51 5.1 49.9 1.64 64 0.52 * 0.26 3.0 80.8 4.54 103 0.52 * 0.26 3.0 60.1 2.08 77 0.52 * 0.50 3.4 80.7 4.83 103 0.52 * 0.51 3.4 79.6 4.49 101 0.52 0.26 3.2 79.4 4.42 101 0.52 0.27 3.0 79.0 ** 4.32 101 0.52 0.51 3.7 78.4 4.47 100 0.52 0.51 3.7 78.5 4.79 100 0.52 1.29 5.8 59.8 2.10 76 0.90 0.26 2.1 80.1 4.86 102 0.90 0.27 2.6 80.2 4.30 102 0.90 0.26 2.3 79.6 4.37 101 0.90 0.50 2.5 80.1 - 102 0.90 0.51 2.9 79.8 4.27 102 0.90 0.52 2.9 56.8 1.88 72 0.90 1.27 4.8 79.8 4.74 102 0.90 2.55 8.0 62.8 2.10 80 1.72 0.26 1.5 63.8 2.37 81 1.72 0.51 2.0 72.3 2.91 92 3.45 0.25 1.2 63.3 2.08 81 3.45 0.52 1.8 75.2 3.10 96 (*)Welds done on 50.8-mm X thickness edges of 50.8 X 76.2-mm specimens. Each welded bar was cut to give two 25.4-mm wide welded bars. (**)Specimen failed away from the weld. (***)Based on a mean tensile strength of 78.5 MPa. The mean strain at failure is 4.5%. Table 4. Strength and Ductility Data for Hot-Tool Welds of 3.2-mm-Thick Undried and Dried Zytel 101 Specimens, at a Strain Rate of = 0.01 [s.sup.1], as Functions of the Hot-Tool Temperature and the Heating Time. The Melt and Weld Penetrations Were Maintained at 0.13 and 0.25 mm, Respectively, and the Seal Time Was Kept Constant at 10 s. Weld Failure Strength * Strain ** [delta]/ Hot-Tool Heating MPa % mm Temperature Time [degrees]C s Undried Dried Undried Dried Undried 260 10 (a) -- -- -- -- 275 10 (b) -- -- -- -- 290 10 10.4 9.8 0.39 0.32 0.93 305 10 19.0 20.8 0.93 0.73 0.97 320 10 20.9 24.7 0.90 0.85 0.98 335 10 27.5 -- 2.22 0.71 1.10 350 10 15.7 -- 0.66 -- 1.18 365 10 13.8 -- 0.56 -- 1.23 380 10 -- -- -- -- -- 260 15 (b) -- -- -- -- 275 15 (b) -- -- -- -- 290 15 23.6 22.8 1.15 0.78 1.02 305 15 19.0 26.0 0.83 0.85 1.11 320 15 29.3 19.1 1.44 0.61 1.11 335 15 18.5 20.8 0.85 0.71 1.21 350 15 10.9 -- 0.46 -- 1.17 365 15 9.5 -- 0.42 -- 1.24 380 15 -- -- -- -- -- 260 20 (b) -- -- -- -- 275 20 17.9 -- 0.81 -- 0.95 290 20 14.1 21.7 0.56 0.71 1.10 305 20 25.6 20.0 1.15 0.68 1.14 320 20 20.1 12.0 (c) 0.95 0.39 1.10 335 20 13.2 22.5 0.61 0.73 1.15 350 20 11.6 -- 0.51 -- 1.22 365 20 13.2 -- 0.56 -- 1.21 380 20 -- -- -- -- -- Differential Penetration [delta]n Hot-Tool [10.sup.2] mm Temperature [degrees]C Dried Undried Dried 260 -- -- -- 275 -- -- -- 290 0.81 -17 -5 305 0.89 -21 -13 320 1.03 -22 -27 335 1.11 -34 -35 350 -- -42 -- 365 -- -47 -- 380 -- -- -- 260 -- -- -- 275 -- -- -- 290 0.95 -26 -19 305 1.07 -35 -31 320 1.19 -35 -43 335 1.21 -45 -45 350 -- -41 -- 365 -- -48 -- 380 -- -- -- 260 -- -- -- 275 -- -19 -- 290 1.03 -34 -27 305 1.10 -38 -34 320 1.07 -34 -31 335 1.18 -39 -42 350 -- -46 -- 365 -- -45 -- 380 -- -- -- (*)Based on a tensile strength of 83.5 MPa for the undried material and 72.6 MPa for the undried material. The corresponding mean strains at failure ae 21.4 and 19.3%, respectively. (a) Did not weld. (b)Specimen broke while routing. (c) This specimen had an abnormal amount of debries on the weld surface. Table 5. Strength and Ductility Data for Hot-Tool Welds of 3.2-mm- Thick Undried and Dried Zytel 101 Specimens, at a Strain Rate of [epsilon] = 0.01 [s.sup.-1], as Functions of the Hot-Tool Temperature and the Heating Time. The Melt and Weld Penetration Were Maintained at 0.13 and 0.66 mm, Respectively, and the Seal Time Was Kept Constant at 10 s. Weld Failure Strength * Strain ** [delta]/ MPa % mm Hot-Tool Heating Temperature Time [degrees]C s Undried Dried Undried Dried Undried 260 10 -- -- -- -- -- 275 10 (a) -- -- -- -- 290 10 (b) -- -- -- -- 305 10 16.2 -- 0.81 -- 0.90 320 10 23.5 25.4 1.30 0.99 1.05 335 10 30.6 28.1 1.78 1.10 1.24 350 10 22.3 31.9 0.98 1.27 1.18 365 10 35.0 31.0 1.85 1.20 1.45 380 10 32.5 -- 1.72 -- 1.43 260 15 -- -- -- -- -- 275 15 (b) -- -- -- -- 290 15 24.8 -- 1.26 -- 0.88 305 15 30.9 -- 1.67 -- 1.11 320 15 28.3 26.7 1.52 1.02 1.21 335 15 30.7 31.2 1.69 1.27 1.41 350 15 34.6 25.7 1.84 0.98 1.41 365 15 34.4 29.1 1.86 1.06 1.61 380 15 29.2 -- 1.51 -- 1.81 260 20 -- -- -- -- -- 275 20 -- -- 0.87 -- -- 290 20 21.5 -- 1.06 -- 0.93 305 20 24.7 -- 1.30 -- 1.18 320 20 30.5 30.3 1.70 1.17 1.37 335 20 33.2 39.1 1.92 1.51 1.51 350 20 36.7 27.6 1.90 1.01 1.53 365 20 27.3 22.2 1.27 0.77 1.81 380 20 22.9 - 1.11 -- 1.86 Differential Penetration [delta][eta] [10.sup.-2] mm Hot-Tool Temperature [degrees]C Dried Undried Dried 260 -- -- -- 275 -- -- -- 290 -- -- -- 305 -- 68 -- 320 1.00 53 58 335 1.11 34 47 350 1.32 40 26 365 1.34 13 24 380 -- 15 -- 260 -- -- -- 275 -- -- -- 290 -- 70 -- 305 -- 47 -- 320 1.19 37 39 335 1.39 17 19 350 1.43 17 15 365 1.56 -3 2 380 -23 -- 260 -- -- -- 275 -- -- -- 290 -- 65 -- 305 -- 40 -- 320 1.11 21 47 335 1.52 7 6 350 1.61 5 -3 365 1.65 -23 -7 380 -- -28 -- (*)Based on a tensile strength of 63.5 MP a for the undried material and 72.6 MP a for the dried material. The conesponding mean strains at failure are 21.4 and 19.3% respectively. (a) Did not weld. (b) Specimen broke while routing. Table 6. Strengths and Ductilities of 120 Hz Vibration Welds of 6.35-mm- Thick Zytel FE3705 Speciments for a Weld Amplitude of a = 3.175 mm, at Two Weld Pressures and Three Weld Penetrations. Weld penetration Weld time Weld strength mm s MPa Weld pressure MPa Undried Dried Undried Dried Undried Dried 0.90 0.16 0.15 3.7 1.8 46.7 56.7 0.90 0.29 0.28 3.9 2.2 79.1 ** 78.8 0.90 0.54 0.54 3.8 3.0 80.5 83.3 ** 3.45 -- 0.15 -- 0.8 -- 68.5 3.45 0.29 0.28 1.5 1.2 69.8 68.4 3.45 0.54 0.53 2.1 1.8 73.5 72.6 Relative Strain at failure weld strength * % % Weld pressure MPa Undried Dried Undried Dried 0.90 1.71 1.98 62 66 0.90 4.54 3.47 105 92 0.90 4.49 4.81 107 98 3.45 -- 2.66 -- 80 3.45 2.71 2.66 93 80 3.45 3.00 2.88 97 85 (*)Based on a tensile strength of 75.4 MP a for the undried material and 85.3 MP a for the dried material. The corresponding mean strains at faiture are 3.43 and 7.46%, respoctivety. (**)Specimen failed away from the weld. Table 7. Strengths and Ductilities of 120 Hz Vibration Welds of Dried 6.3-mm- Thick Zytel 70G33HS Specimens for a Weld Amplitude of a = 3.175 mm, at Three Weld Pressures and Two Weld Penetrations. Weld Weld Weld Strain at Relative Weld MPa penetration Time Strength Failure weld strength * Pressure mm $ MPa % % 0.52 0.27 5.6 92.6 1.20 57 0.52 0.27 4.6 89.4 1.17 55 0.52 0.52 5.7 89.1 1.17 54 0.52 0.52 5.7 90.2 -- 55 0.90 0.26 3.3 89.2 1.10 54 0.90 0.27 3.2 93.1 1.05 57 0.90 0.27 3.4 91.6 1.17 56 0.90 0.51 3.8 88.8 1.07 54 0.90 0.53 4.5 91.3 1.12 56 0.90 0.53 4.0 91.4 1.03 56 1.72 0.27 2.0 87.0 1.05 53 1.72 0.51 2.5 87.1 1.05 53 Weld MPa Specimen Pressure pairs 0.52 (1, 5) 0.52 (2, 6) 0.52 (1, 5) 0.52 (2, 6) 0.90 (3, 7) 0.90 (1, 5) 0.90 (2, 6) 0.90 (3, 7) 0.90 (3, 7) 0.90 (4, 8) 1.72 (4, 8) 1.72 (4, 8) (*)Based on a mean tensile strengths of 163.8 MPa. The mean strain at failure is 3.06%. Table 8 Strengths and Ductilities of 120 Hz Vibration Welds of 6.35-mm-Thick Zytel 330 Specimens for a Weld Amplitude of a = 3.175 mm, at Two Weld Pressure and Three Weld Penetrations. Weld penetration Weld time Weld strength mm s MPa Weld pressure MPa (psi) Undried Dried Undried Dried Undried 0.90 0.16 0.15 0.17 0.18 67.8 0.90 0.29 0.28 0.34 0.31 72.0 0.90 0.54 0.54 0.58 0.57 75.2 ** 3.45 -- 0.15 0.17 0.16 55.4 3.45 0.29 0.28 0.32 0.30 103.3 3.45 0.54 0.53 0.56 0.55 62.4 Relative Strain at failure weld strength * % % Weld pressure MPa (psi) Dried Undried Dried Undried Dried 0.90 100.3 2.59 -- 66 84 0.90 109.4 ** 2.88 4.93 70 91 0.90 99.1 3.08 3.93 73 83 3.45 106.8 2.03 ** 4.81 54 89 3.45 116.0 ** 6.91 6.76 100 97 3.45 105.2 ** 2.30 4.44 61 88 (*)Based on a tensile strength of 102.8 MPa for the undried material and 120.0 MPa for the dried material. The corresponding mean strains at failure are 6.78 and 6.34%, respectively. (**)Specimen failed away from the weld.
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|Author:||STOKES, VIJAY K.|
|Publication:||Polymer Engineering and Science|
|Article Type:||Statistical Data Included|
|Date:||Aug 1, 2001|
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