KR100437249B1 - Vibration welding method of thermoplastic joints - Google Patents

Abstract

The present invention provides an improved method of vibration welding a thermoplastic joint. Welding is performed by vibrating the two fiber reinforced thermoplastic parts under pressure along a common interface to generate frictional heat to melt the surfaces together. Fibers from at least one surface penetrate the weld and the other side. As a result, the welded, fiber-reinforced thermoplastic surface has enhanced tensile strength than has ever been achieved. Vibration welding of a reinforced thermoplastic surface according to the present invention results in a maximum tensile strength as high as about 120% of the weld formed on the unreinforced surface of the corresponding thermoplastic material.

Description

Vibration welding method of thermoplastic joints

The use of thermoplastics instead of metals in automotive applications, such as air intake systems, has recently increased. By 2010, it is estimated that 21.4 million air intake manifold components will be manufactured using welding techniques. The present invention relates to an improved method of vibration welding a thermoplastic joint and to a vibration welded article produced by the method.

Vibration welding of thermoplastics such as nylon 6 and nylon 66 is well known in the art. "Vibration Welding of Thermoplastics, Part I: Phenomenology of the Welding Process", VKStokes, Polymer Engineering and Science , 28, 718 (1988); VK Stokes, "Vibration Welding of Thermoplastics, Part II: Analysis of the Welding Process", Polymer Engineering and Science , 28, 728 (1988); VKStokes, "Vibration Welding of Thermoplastics, Part III: Strength of Polycarbonate Butt Welds", Polymer Engineering and Science , 28, 989 (1988); VK Stokes, "Vibration Welding of Thermoplastics, Part IV: Strengths of Poly (Buthylene Terephthalate), Polyetherimide, and Modified Polyphenylene Oxide Butt Welds", Polymer Engineering and Science , 28, 998 (1988) and CB Bucknall et al., "Hot Plate Welding of Plastics: Factors Affecting Weld Strength ", Polymer Engineering and Science , 20, 432 (1980).

Vibration welding may be performed by vibrating the two components under pressure along their common interface to generate frictional heat, fusing and fusing their surfaces. Vibration welding is a fast and inexpensive way to join parts of varying sizes and irregular shapes. Conventionally, vibration welding has been used in applications with less load. Extended use of engineering plastics in automotive underhood applications such as air intake manifolds, air filtration housings and resonators would be desirable to save weight and cost. However, until now it has not been possible to obtain adequate weld strength for such applications. Welding results are very sensitive to parameter uniformity and minor changes in parameters can produce significant changes in weld quality. Vibration welding parameters such as pressure, frequency, amplitude, vibration (welding) time, stop time, and weld thickness affect the tensile strength of the weldment.

The present invention relates to vibration welding, and more particularly, to vibration welding of thermoplastic joints.

It is an object of the present invention to provide a method of vibration welding a fiber reinforced thermoplastic resin surface to provide a weldment with greater tensile strength to date.

U.S. Patent 4,844,320 teaches that weld strength is not affected above a certain level by weld amplitude or weld time. In conventional vibration welding, the weld is formed at a vibration amplitude of 0.03-0.70 inches. In contrast, the inventors found that welding amplitude and welding time are very important criteria for increasing weld strength. Vibration welding in the present invention utilizes a vibration amplitude of at least about 0.075 inches. Vibration welding on conventional reinforced thermoplastic surfaces has been measured to obtain a maximum tensile strength of about 80% of the weld formed by the unreinforced surface of the corresponding thermoplastic. For glass fiber reinforced thermoplastics, this reduced tensile strength is due to the change of glass fiber orientation in the welded joint. According to the present invention, vibration welding of the reinforced thermoplastic surface results in a maximum tensile strength as high as about 120% of the weld formed on the unreinforced surface of the corresponding thermoplastic. This is because fibers from at least one surface penetrate both the weld and the remaining surface. This provides unexpected tensile strength added to the weld.

The present invention provides a method of attaching a first surface comprising a fiber reinforced first thermoplastic composition to a second surface comprising a second thermoplastic composition,

That way

Contacting the first and second surfaces; And

Vibrating welding the contacted first and second surfaces under conditions sufficient to form a weld consisting of a mixture of the first and second thermoplastic compositions between the first and second surfaces.

Characterized in that the fiber from the first surface penetrates both the weld and the second surface.

The present invention also includes a first surface comprising a fiber reinforced first thermoplastic composition,

A second surface comprising a second thermoplastic composition in contact with the first surface, and a weld comprising a mixture of first and second thermoplastic compositions between the first and second surfaces,

Vibration welded articles are provided in which fibers from the first surface penetrate both the weldment and the second surface.

Vibration welding techniques and apparatus for performing vibration welding are well known in the art as illustrated in US Pat. No. 4,844,320. Interfacial heating by friction for vibration welding to thermoplastics; Unsteady melting and flow of material laterally; Melting zone setting in steady state conditions; And irregular flow and solidification of the material in the weld zone upon vibration stop. Welding may be performed by a standard vibration welding apparatus that has been modified to obtain the parameter conditions required by the present invention. Important parameters include pressure, amplitude, frequency, welding cycle time and stop time.

Vibration welding machines are commercially available as Mini-Vibration Welder and 90 Series Vibration Welders Model VW / 6 from Branson Ultrasonics Corporation, Danbury, Connecticut. However, they must be adjusted because their graded amplitude range is 0.040-0.070 inches at 240 Hz output frequency. Vibration welding may be performed by bringing the first thermoplastic surface and the second thermoplastic surface into contact with pressure. It is preferred that at least one and preferably both thermoplastic surfaces are fiber reinforced. The surfaces to be welded are brought into contact with each other and the interface between the surfaces is kept at a predetermined pressure, for example by placing them on the platform under pressure applied by air or hydraulic cylinders. One surface is then subjected to a linear reciprocating motion with respect to the other surface to generate heat friction, and the surface is melted to mix the thermoplastics from the first and second surfaces. Prior to welding, the fibers in the fiber reinforced thermoplastic are substantially unoriented. In conventional vibration welding techniques, the thermoplastic surfaces in contact melt and mix to form a weldment, but the fibers in the welds are oriented only within their weld face. On the other hand, when vibration welding is performed according to the present invention, the surface or the fiber reinforcing the surfaces is pressed into the opposing contact surface to obtain a weld strength which has not been achieved so far when the weld is cooled.

According to the invention, the two thermoplastic surfaces to be welded consist of any compatible thermoplastic polymer material. Suitable thermoplastic polymers include, but are not limited to, polyamides, polyesters, polycarbonates, polysulfones, polyimides, polyurethanes, polyethers, vinyl polymers, and mixtures thereof. Polyamides such as nylon 6 and nylon 66, for example Capron available from AlliedSignal Inc. of Morristown New Jersey 8233G HS Nylon 6 and Capron 5233G HS Nylon 66 and Petra available from AlliedSignal Inc. Most preferred are polyesters, such as 130 polyethylene terephthalate. Dissimilar thermoplastic surface materials can also be used if they are mixed miscible. At least one and preferably both thermoplastic surfaces are preferably fiber reinforced. Suitable reinforcing fibers include, but are not limited to, materials that do not soften (lose stiffness) even at temperatures up to about 400 ° C., typically used in injection molding. Preferably the fiber reinforcement comprises materials such as glass, carbon, silicon, metals, inorganics, polymer fibers and mixtures thereof. Most preferred is glass fiber reinforcement. According to a preferred embodiment, the fibers are rigid and have a diameter of 8-12 μm, preferably about 9-11 μm and most preferably about 10 μm. Preferred fiber lengths are about 120-300 μm, more preferably about 130-250 μm and most preferably about 140-200 μm. In a preferred embodiment, the fibers comprise about 6-40%, more preferably about 13-25% by weight of the thermoplastic composition.

The linear peak-to-peak displacement or frictional distance of one surface on another surface is the vibration amplitude. In a preferred embodiment, the vibration amplitude is at least about 0.075. More preferably, the vibration amplitude is about 0.075-0.15 inches, most preferably about 0.075-0.090 inches. The above-mentioned amplitude is a value at a nominal output vibration frequency of 240 Hz. At other vibration frequencies, the amplitude will change. For example, at a nominal output oscillation frequency of 120 Hz, the preferred oscillation amplitude will be at least about 0.09 inches, more preferably about 0.13 inches to about 0.16 inches, and most preferably will range from about 0.135 inches to 0.145 inches. Vibration amplitudes for other frequencies can be easily measured by one skilled in the art.

According to a preferred embodiment, the contact surface is maintained perpendicular to the surface under pressure of about 0.6-1.5 MPa during vibration welding. More preferably the pressure is about 0.6-1.2 MPa and most preferably in the range of 0.7-0.8 MPa. The vibration or friction time is preferably about 2-7 seconds, more preferably about 4-6 seconds. The stopping time or cooling time during which the pressure is maintained after the vibration is stopped is preferably about 2-8 seconds, more preferably about 4-5 seconds. The weld thickness is preferably about 160-400 μm, more preferably about 200-350 μm and most preferably about 250-330 μm.

When vibration welding is performed under these conditions, a portion of the fiber from the reinforced surface penetrates into the weld and its opposite surface. When both surfaces contain reinforced thermoplastic, part of the fiber from each surface penetrates both the weld and the opposing surface. In a preferred embodiment, the fraction of fibers (by tensile strength) measured from one or both reinforced surfaces penetrating into opposing surfaces is about 2-8%, preferably about 4-8%, and more preferably Preferably in the range of about 5-8%. As a result of the vibration welding process of the present invention, the weldment of the reinforced thermoplastic surface to the other thermoplastic surface obtains a greater maximum tension as compared to the weld formed on the unreinforced surface of the corresponding thermoplastic material. The tensile strength of the vibration weldment of the reinforced thermoplastic surface is in the range of at least about 85%, preferably about 85-120%, of the weld formed on the unreinforced surface of the corresponding thermoplastic material. Without being bound by a particular theory, it is assumed that the vibration welding parameters of the present invention allow the fiber to penetrate from one reinforced surface to another. For example, pressure applications and oscillation times and amplitudes should help push fibers from one molten surface into another. Too small a weld thickness or too high a fiber load will result in insufficient space for fiber rotation, thereby inhibiting the fiber from crossing into opposing surfaces.

The following examples are intended to illustrate the invention. Substitution of the fractional parameters and component elements of the photosensitive coating composition components will be apparent to those skilled in the art and is within the spirit of the present invention.

Example 1

Capron available from AlliedSignal Inc. of Morristown New Jersey 8233G HS Nylon 6 and Capron 5233G HS nylon 66 pellets were injection molded into 3 "x 4" x 1/4 "and 3" x 4 "x 1/8" blocks containing nominally 0-50 weight percent glass fiber reinforcement. The same block was welded together with a small-vibration welder or 2400 series welder from Branson Ultrasonics Corporation using the following parameters: maximum clamp load 4.5 kN; Welding amplitude 0.762-2.28 mm (0.030 "to 0.090"): Welding time 4-8 seconds, nominal welding frequency 240 Hz.

The welding parameters, ie pressure (load), amplitude and time, were changed to optimize the tensile strength of the welded joint. Only samples that yielded greater tensile strength than the base unfilled material were selected and the shape of the weld was studied. Details of the area interface and fiber orientation were included in this analysis. Optical microscopy was used to characterize the sample, while image analysis was used to quantify the fiber length.

Analysis of Fiberglass Loads in Welds

Researched Injection Molded Capron The nominal fiber load of the nylon 6 part was in the range of 0-50% by weight. However, if the fiber or nylon substrate is preferably pushed away from the weld as the joint is formed, the actual fiber load at the weld will vary widely. In order to determine whether the fiber load in the excess flow zone in the weld differs from that in the bulk material, the weight percentage of the fiber was determined by taking an excessive weight difference before and after the substrate was pyrolyzed. 7 Caprons processed under different welding conditions The results of the 8233G HS nylon 6 sample are summarized in Table 1 below. As a result, the fiber loading of the various nylon 6 materials was about 0.5-1% by weight lower than the bulk composition.

For nylon 66, the capron glass content in the weld flash Measurements were taken from 5233G HS nylon 66 samples. The results are shown in Table 2 below and the fiber load of nylon 66 in the weld flash was about 0.5% lower than the bulk composition. These fiber content deviations were rather small and the accuracy in measuring the fiber content was also accurate.

Glass fiber length analysis at the weld

To measure the excessive breakage of the fiber at the weld, fiber length analysis was performed. The fiber length of the fibers from the flash (recovered from the pyrolytic ash) was measured by optical microscopy and image analysis. Glass fiber samples were extracted from the ash and dispersed on glass slides with 2,2,2-trifluoroethanol (TFE) solvent. Ten optical tissue photographs were taken from each sample and a total of 1000-2000 fibers were digitized and measured with an image analyzer. Table 3 summarizes the results. This analysis showed that the averaged fiber length of all samples was in the range of 120-180 μm. This is comparable to the average fiber length of the sample measured from the original molded tension bar deviating from the area of the weld. Further studies of the weld fracture surface by scanning electron microscopy suggested that there is no excessive fracture of the fiber in the weld.

Analysis of Glass Fiber Orientation Distribution in Welds

The fiber orientation distribution (FOD) of the glass fibers (GF) at the welds was examined by optical and scanning electron microscopy. For each sample, both planar and through thickness sections were prepared and polished metallographically for preparation for optical microscopy studies. Optical tissue photographic results at relatively low magnifications (25 and 50 times) showed typical FOD around the weld as well as fiber orientation in the weld. Optical tissue photographs were taken from the polished sections of the nylon 6 sample with 6% by weight, 14% by weight GF, 25% by weight GF, 33% by weight GF and 50% by weight GF, respectively. Tissue photographs showed fiber orientation in all cases near and out of the weld zone. In addition, the apparent thickness of the weld can be measured directly at the location indicated by the FOD change in the tissue photograph. Note that for samples with GF 14 and 25% by weight, there is clear evidence for some fibers oriented in the tensile direction perpendicular to the welding plane. It is noted that the reinforcing effect at the optimized welding conditions appears to be independent of the glass fiber orientation in the molded plaque selected for welding.

Tensile strength of welded joint

For each vibration welding condition (ie set pressure, amplitude and welding time), ten specimens were tested under standard ASTM D638M-93 tensile test procedure for plastics. The results for weld joint tensile strength at optimized weld parameters are summarized in Table 4 below. The effect of glass fiber loading on the tensile strength was investigated. The results showed that all weld joint samples had greater tensile strength than unreinforced nylon 6. For the reinforced nylon 6 material, the maximum tensile strength was 93.1 Pa. It formed near 14-25% by weight glass fiber load. Compared to the unreinforced material with a tensile strength of 79.3 MPa, the maximum weld strength measured by the reinforced grade was found to improve the weld joint tensile strength by 17%.

The tensile strength of the welded nylon 6 material was found to be slightly (about 4%) greater than nylon 66 welded under the same welding and reinforcement conditions. This data also showed that the fiberglass / nylon 66 composition at the interface was similar to the bulk composite. The greater weld strength of glass filled nylon 6 observed at optimum welding process conditions may be due to several factors. For nylon 6, several percent of the glass fibers appeared to intersect the weld plane at the interface, depending on the selection of some compositions and welding parameters. The width of the weld around 200-300 μm is comparable to the average length of the fiber. This is not limited to the fact that the mobility of the fiber moves in a direction other than the main flow direction of the resin during welding, that is, the fiber moves along the flow direction as in a narrow weld. The weld thickness observed in the tissue photograph can be plotted as a function of fiber load. The weld thickness is found to be maximum at 14% by weight fiber loading. This maximum was formed at several locations (14-25 wt% glass fiber (GF)) as at the tensile curve maximum. This further suggests that the thickness of the weld has a positive effect on the tensile strength of the welded joint. Weld performance was studied as a function of the glass fiber orientation distribution in GF nylon 6 plaques by preparing weld specimens in orientations other than the prevailing fiber orientation. These data suggest that the fiber orientation obtained in the region of the weld at the weld interface is independent of the predominant orientation of the glass fibers in the bulk nylon 6 adjacent the weldment. These data for linear vibration welded polyamide butt joints have been shown to increase up to 35% in tensile strength compared to previously published data.

As described above, vibration welding of the reinforced thermoplastic surface according to the present invention may yield a maximum tensile strength as high as about 120% of the weld formed by the unreinforced surface of the corresponding thermoplastic material.

Claims (9)

Contacting the first surface comprising the fiber reinforced first thermoplastic resin composition and the second surface comprising the second thermoplastic resin composition; And The contacted first and second surfaces are vibrated welded under conditions suitable to form a weldment consisting of a mixture of the first and second thermoplastic compositions between the first and second surfaces and the fibers from the first surface are welded. Vibration welding method of a thermoplastic resin joint comprising a; and the step of allowing to penetrate both (part) and the second surface. The thermoplastic resin of claim 1, wherein each of the first and second thermoplastic resin compositions is selected from the group consisting of polyamides, polyesters, polycarbonates, polysulfones, polyimides, polyurethanes, polyethers, vinylpolymers, and mixtures thereof. And a resinous polymer. The method of claim 1 wherein the fiber comprises a material selected from the group consisting of glass, carbon, silicon, metals, inorganics, polymers and mixtures thereof. The method of claim 1 wherein the fiber is present in the reinforced first thermoplastic resin composition in an amount of about 6-40% by weight, based on the weight of the first thermoplastic composition. The method of claim 1 wherein the fibers are present in both the reinforced first thermoplastic resin composition and the reinforced second thermoplastic composition in an amount of about 6-40% by weight, based on the weight of each thermoplastic resin composition. Way. A first surface comprising a fiber reinforced first thermoplastic composition, A second surface comprising a second thermoplastic composition in contact with the first surface, Consisting of a mixture of the first and second thermoplastic compositions, A weld between the first and second surfaces, wherein An oscillating welded article, wherein fibers from the first surface penetrate both the weld and the second surface. 7. The method of claim 6, wherein the second thermoplastic composition is fiber reinforced and the fibers from the second surface penetrate both the weld and the first surface. 7. The thermoplastic polymer of claim 6, wherein each of the first and second thermoplastic compositions is selected from the group consisting of polyamides, polyesters, polycarbonates, polysulfones, polyimides, polyurethanes, polyethers, vinyl polymers, and mixtures thereof. Method characterized by that. 7. The method of claim 6, wherein the fiber is made of a material selected from the group consisting of glass, carbon, silicon, metals, inorganics, polymers and mixtures thereof.