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Conference Proceedings

A Rheological Model for Thermoplastic Resins Melt
Viktor V. Skatchkov, Alexandra I. Savchenkova, May 2004

A new rheological model of polymer melt was developed to describe viscosity-shear rate curves utilizing a four parameters equation based on Guassian processes approach for regression description of melt properties. Four parameters of the model (Newtonian viscosity at “zero” shear rate, viscosity and shear rate at inflection point, and dispersion of the rate of change of the viscosity) were found to be a function of polymer chain structure, molecular weight and temperature. The model provides precision description in a wide range of conditions of shear deformation of the polymer melts, solutions, blends and alloys.

Experiments in Micro-Welding of Polycarbonate with Laser Diodes
David Grewell, Avraham Benatar, May 2004

Polymer use in micro-devices, especially in the medical industry has been rapidly increasing. During assembly of micro-devices it is desirable to produce weld joints that are about 100 ?m in width. This paper reviews the use of fiber coupled laser diodes in conjunction with special lenses to produce spot sizes between 25 and 50 ?m in diameter for through transmission infrared welding technique. Studies were completed to evaluate the effect of travel speed, power density and pressure on weld quality for polycarbonate and polystyrene. It was found that process parameters are extremely critical in producing consistent welds. In addition, new testing techniques had to be developed to allow quantitative measurements to be made on weld strength due to relatively small weld area. Micrographs of the resulting welds revealed evidence of ablation at high heat inputs. Finite element analysis of the mechanical tests showed that the localized weld strength approached the yield strength of polycarbonate.

Modeling Heat Flow for a Moving Heat Source to Describe Scan Micro-Laser Welding
David Grewell, Avraham Benatar, May 2004

Polymer use in micro-devices, especially in the medical industry has been rapidly increasing. During assembly of micro-devices it is desirable to produce weld joints that are about 100 ?m in width. This paper reviews the modeling of heat flow during through transmission infrared micro-welding of plastic using fiber coupled laser diodes. Two models were used to predict temperature distributions within welded samples. Both models were based on a moving heat source and moving coordinate system. For the simpler model a moving point heat source was used and for the more complex model a Gaussian distributed heat source was used. It was found that the distributed model can accurately predict temperature fields in plastic laser welds for all ranges of the parameters evaluated. However, the point heat source model was only able to accurately predict temperature fields with a relatively small laser focal spot (25 ?m). In addition it was found that for micro-welding of plastics, when the dimensionless distribution parameter is less than two, a point heat source model predicts similar widths to those predicted by a distributed heat source model.

Measurement of Residual Stresses in Clearwelds Using Photoelasticity
Satish Anantharaman, Avraham Benatar, Nicole Woosman, Scott Hartley, May 2004

Residual stresses are detrimental to a plastic joint for a number of reasons. They lead to reduced strength and fatigue life in joints, act as stress concentrators and cause crazing, cracking when exposed to solvents. In this paper, the residual stresses in Clearweld® joints were measured using photoelasticity. This interference based technique was used in conjunction with a stress separation algorithm to quantify the maximum residual stress level and the stress distribution in the weld region. Also, the effects of process parameters like welding speed, power and ink solvents on residual stresses were evaluated. The GE solvent test was also employed for comparison with the photoelasticity results. A comparison of the residual stresses between various joining processes was also made.

Diode Laser Characterization and Measurement of Optical Properties of Polycarbonate and High-Density Polyethylene
Moonyeong Rhew, Abbass Mokhtarzadeh, Avraham Benatar, May 2004

In recent years, the use of high power diode lasers for through transmission laser welding (TTLW) of thermoplastics has increased rapidly due to the many advantages that they provide, mainly their compact size and low cost. The diode laser output can affect the heating rate and uniformity, making it important to characterize the diode laser in any welding application. In this study, diode laser bar characterization included measurement of the power efficiency, beam shape, and intensity distribution. Those measurements were performed with and without a proprietary fiber bundle provided by Branson Ultrasonics, which improved the uniformity of power intensity. In TTLW laser beam reflection, absorption and scattering as it passes through the transparent part affects the power that reaches the weld interface. Therefore, it was important to study the transmittance and reflectance of polycarbonate and high-density polyethylene. The effects of thickness and beam incident angle on transmittance and reflectance were also measured.

Measurement of Residual Stresses in Laser Welded Polycarbonate Using Photoelasticity
Satish Anantharaman, Avraham Benatar, May 2004

Residual stresses are detrimental to the strength of plastic joints. They lead to reduced strength and fatigue life in joints, act as stress concentrators and cause crazing and cracking when parts are exposed to solvents. In this paper, photoelasticity is used to measure the residual stresses in laser welded polycarbonate. Photoelasticity, an interference based technique, was used in conjunction with a stress separation algorithm to quantify these stresses along and perpendicular to the weld line. The GE solvent test was also employed to serve as a comparison to the photoelasticity results. A comparison of the residual stresses between laser welded samples and hotplate welded samples have also been made.

Effect of Polypropylene Rheology on the Vibration Welding Process
E. Lebaut, P.J. Bates, M. Kontopoulou, May 2004

Vibration welding is a joining technique to assembly thermoplastic components. Meltdown-time profiles and assessment of weld microstructure are commonly used to characterize the behavior of polymers during vibration welding. The aim of this work is to establish relationships between the rheological properties of molten polymers and their meltdown rate during vibration welding. Two polypropylene homopolymers with different molecular weights resulting in different rheological properties were studied. Vibration welding was carried out using a butt-weld geometry and meltdown-time profiles were measured. Significant discrepancies between experimental results and theoretical predictions based on the simple model developed by Stokes suggest the presence of significant elastic effects.

Real Time Temperature Measurement of Nylon 66 Butt-Joints during Vibration Welding
X.P. Zou, G. Park, V. Sidiropoulos, M. Kontopoulou, P.J. Bates, May 2004

Modeling the vibration welding process requires accurate knowledge of the melt temperature at the interface. Due to technical difficulties related to the very small molten film thickness, little work has been done to date on measuring the weld temperature under real time conditions. This paper presents a novel technique for measuring the weld temperature in real time. It involves inserting a 25 ?m thermocouple into one of the welding parts in close proximity to the weld zone. During vibration welding, the thermocouple works its way to the weld interface and records the melt temperature. The experimental data from vibration welding nylon 66 butt joints indicate that the melt temperature at the weld interface is within 15°C of the onset of polymer melting. The temperatures measured in the solid phase prior to entering the melt film are consistent with theoretical models for heat conduction into solid plates.

Heated Tool Welding of Thermoplastic Polyolefin (TPO)
Chung-Yuan Wu, Abbass Mokhtarzadeh, Moonyeong Rhew, Avraham Benatar, May 2004

This study focused on the weldability of two specific thermoplastic polyolefins (TPO-A and TPO-B) using heated tool welding. A three-factor (heating temperature, heating time, and welding pressure) and three-level design matrix was used to perform the welding. Two statistical methods, three-factor two-level design of experiments (DOE) and Box Behnken method, were used to analyze the weld results. In addition, vibration welding of these TPOs was also used to compare the weldability. For heated tool welding, the maximum joint strength was 88% of the bulk strength for TPO-A and 76% of the bulk strength for TPOB. For vibration welding, the maximum joint strength was 65% for TPO-A and 56% for TPO-B. While heated tool welding provided stronger joints compared to vibration welding, it had a longer cycle time. The two statistical methods provided similar results indicating that the simple three-factor two-level design of experiments was a valid screening method for heated tool welding of TPO.

The Effects of Weld Geometry and Glass-Fiber Orientation on the Mechanical Performance of Joints – Part II: Kinetics of Glass-Fiber Orientation and Mechanical Performance
Val A. Kagan, Christopher Roth, May 2004

The mechanical performance of injection molded short glass-fiber reinforced thermoplastic components is anisotropic and is highly dependent on the fiber orientation and distribution. Similarly, the bulk and short and long-term mechanical performance at the weld is influenced by these fibers and the specific welding technology used as related to melt-pool formation.The purpose of this analysis is to show:the short-fiber orientation (analytical and simulation data) and distribution at the pre-welded bead, ribs and wall areas;advantages of SigmaSoft injection molding simulation software, which utilizes full three dimensional fiber representation of any molded part;the mechanical performance of welds with optimized geometry (US Patent 6,447,866).Findings on the mechanical performance of butt-joints with different designs and localized geometry will help designers and technicians with plastic part design optimization. In a previous ANTEC paper (Part I), we related these findings to the kinetics of welds and part design issues for straight and T-type butt-joints.

Feasibility of Selected Methods for Embossing Micro-Features in Thermoplastics
David Grewell, Abbass Mokhtarzadeh, Avraham Benatar, Chunmeng Lu, L. James Lee, May 2004

During the last few decades the use of MEMS (Micro-Electro-Mechanical-Systems) has been steadily increasing in a number of industries, and especially in the medical industry. One application for MEMS is in micro-fluidic devices that rely on micro-channels (10 to 200 ?m wide and deep) to direct and analyze fluids for medical diagnostics. Current methods for producing these features, including hot embossing and micro-injection molding, can be slow (1 to 10 minutes cycle time), are only amendable to batch processing and expensive. Fast surface heating embossing methods have the potential of producing micro-channels rapidly and inexpensively. Three embossing methods were studied: ultrasonic, infrared radiation (IR) heating and hot gas heating. For IR and hot gas heating, a cold tool with the micro-features was pressed onto the surface immediately following heating. Similarly, for ultrasonic embossing the micro-features were machined on the surface of the horn. It was found that cycle times as short as a few seconds were achieved and the quality of the features was similar to those seen in injection molding. In addition FEA studies were conducted to simulate polymer flow during embossing.

3D-Laser Transmission Welding
E. Haberstroh, R. Luetzeler, May 2004

Contour welding is a variant of the laser transmission welding that offers the highest flexibility relative to the weld geometry. In this process the laser beam is translated along the weld line using a robot. This paper reviews the results of welding experiments using a proprietary box geometry with a three-dimensional weld line. It was found that low leakages and high burst pressures can be achieved with optimized process parameters for Polyamide or Polyacetale. In addition, short welding times (a few seconds) were demonstrated. Thus, this process is well suited for mass production of complex plastics parts. It was also seen that the process is relatively robust and weld quality is relatively independent of parameter settings (over the ranges evaluated).

Through Transmission Laser Welding of Polycarbonate and High-Density Polyethylene
Moonyeong Rhew, Abbass Mokhtarzadeh, Avraham Benatar, May 2004

Through Transmission Laser Welding (TTLW) of thermoplastics is a relatively new joining process with many advantages for design and manufacturing of various components in electronic, medical and automotive industries. The use of high power diode laser systems has made TTLW a cost effective process in welding of many amorphous and semicrystalline polymers. In this work, a laser welding system, comprised of a power supply and a diode laser with a Branson proprietary fiber bundle, was used to experimentally study TTLW of polycarbonate (PC) and high-density polyethylene (HDPE). The effects of welding power (measured laser power at the interface), heating time, and welding pressure on joint strength were studied. Maximum weld strength of about 95% the bulk strength of PC and HDPE were achieved.

Overlap Welding of Thermoplastic Parts without Causing Surface Thermal Damage by Using a CO2 Laser
Yasuo Kurosaki, Tomoya Matayoshi, Kimitoshi Sato, May 2004

This paper deals with the principle and applications of a novel infrared laser welding procedure for overlapped thermoplastic parts. Features of experiment, using a CO2 laser as a radiation heat source and numerical simulation of heat transfer phenomena combined with radiation and conduction in the welding process, are demonstrated. Not only high weld strength but also excellent surface quality of welded regions is essential for overlap welding of plastics in industrial applications.The current welding procedure was developed using a combination of penetration infrared radiation heating process and thermal diffusion cooling process by a solid material which is transparent to infrared radiation as a heatsink. The solid heatsink placed in contact with an irradiated surface of overlapped thermoplastic parts during radiation heating. This welding procedure is able to achieve both high weld strength and excellent surface appearance without causing surface thermal damage, as is often suffered in conventional direct infrared radiation welding process without a solid heatsink. In addition, the pigmentation of the welding material to increase absorption of radiation is unnecessary for this procedure.

Technical Review of the Four Major Thermal Press Applications: Staking/Swaging, Inserting, Degating, Part Marking
Thomas R. Kirkland, May 2004

Thermal presses are used primarily in four applications with regard to assembly (decorating) of thermoplastic parts: staking/swaging, inserting, degating and part marking. Thermal staking/swaging and inserting are generally thought of as competitor processes to ultrasonic, while degating operations with heated tooling are thought of as an augmentation to degating by force alone. Part marking such as date- or lot-coding and serializing is another area where these machines can be applied. This paper discusses these four applications areas and references competing processes to highlight the strengths and weaknesses of utilizing modern thermal presses for these applications.

Optical Correction for Heat Buildup in the Center of TTIr Plastics Welds
Scott Caldwell, David Grewell, May 2004

Through Transmission Infrared (TTIr) laser welding of plastics often results in voids forming in the center of the weld. These voids can lead to weak and unattractive welds. Their formation is due to non-uniform temperature distributions within the weld zone and out gassing of volatiles (such as moisture). This non-uniform temperature distribution has been demonstrated not only by a Gaussian laser light distribution but also by an even light distribution depending on the joint/part design. This paper reviews the development of tailored optics that re-shape the distribution of typical light/laser sources in order to promote uniform temperature distributions. It was seen in FEA models that by using uniform heat distributions, uniform temperature fields were produced in butt joint configurations. In addition it was seen that a distribution with high heat input on the outer edges produced uniform heating in lap shear joint configurations. Laboratory experiments verified these FEA predictions, and strong and attractive welds were generated.

Laser Welding of Polypropylene to Thermoplastic Polyolefins
Chung-Yuan Wu, Michael Cherdron, Mark Douglass, May 2004

Polypropylene (PP) and thermoplastic polyolefin (TPO) are currently used in many automotive applications. However, the weldability of these two materials using through transmission scanning laser welding has not yet been reported. This study focused on the effects of color and welding parameters on lap shear joint strength. Three colors, black, blue and tan, as well as three welding parameters, laser power, weld time and scanning speed, were used to evaluate the weldability. The samples were welded using a 200 W flashlamp-pumped Nd:YAG laser. For the 1.06 ?m wavelength, it was found that 3.2 mm thick natural PP has a transmission rate of 29%. It was also found that the black TPO had the most laser absorption, followed by the blue TPO and then the tan TPO. Therefore, the black TPO required the least amount of welding time to reach the maximum joint strength. In addition, as the scanning speed was reduced, the time required to reach maximum joint strength was also reduced.

Modeling the Bond Formation Development between Polymer Filaments in FDM Prototypes
C.T. Bellehumeur, L. Li, Q. Sun, P. Gu, May 2004

Fused Deposition Modeling (FDM) processes have the capability to fabricate parts with locally controlled properties by changing deposition density and deposition orientation. The integrity and mechanical properties of parts are largely determined by the bonding quality realized among polymer filaments. This paper reports a theoretical study of the mechanical properties of FDM prototypes, heat transfer analysis of the FDM process and modeling of the bond formation among ABS filaments. Thermal analysis of the FDM process resulted in an estimation of cooling profile of the extruded filaments. Quantitative predictions of the degree of bonding achieved during the filament deposition process were made. The model was used to estimate the effects of different manufacturing parameters in the FDM process.

Cracking of Resin Rich Layer Joined to Tank Wall Due to Fluctuating Liquid Level
Jack E. Helms, Michael W. Guillot, May 2004

Composite laminate tanks are used in corrosive services in chemical process plants. The inner surface of tanks usually consist of a glass reinforced layer that is mostly resin and is joined to the tank structure to form a corrosion barrier. A large diameter, open top, composite laminate tank containing a hot brine solution suffered vertical cracking in the corrosion barrier during normal process operations. The process involved relatively rapid changes in the liquid level at different times during each day. Vertical cracks were discovered in the corrosion barrier by plant inspectors during a routine plant turnaround. Finite element modeling was used to demonstrate that the cracking was due to transient thermal stresses near the liquid vapor interface that resulted from the fluctuating liquid level and natural convection from the tank wall in cooler weather. In this research, the effects of the amount of glass reinforcement in the resin rich corrosion barrier were also studied. The outer surface of the tank was insulated, but the insulation does not appear to have been a factor in the cracking.

Fast Joining of Composite Pipes Using UV Curing FRP Composites
Su-Seng Pang, Guoqiang Li, H. Dwayne Jerro, Jerry A. Peck, Michael A. Stubblefield, Saleem Hasan, May 2004

For this paper, twelve composite pipe joints were prepared. Among them, six were prepared using ultraviolet (UV) curing E-glass fiber reinforced vinyl ester composites and six were prepared using ambient environment curing E-glass fiber reinforced vinyl ester composites as control. Filament wound E-glass fiber reinforced vinyl ester composite pipes were used. Each section of pipe was 304.8 mm long with a 101.6 mm inner diameter. The wet lay-up technique was used to prepare the test samples. The curing time for the UV cured samples was 40 minutes, while the curing time was 24 hours for the control samples. Both internal pressure tests and four-point bending tests were conducted on the UV cured and control samples. The test results show that the UV cured FRP wrapped composite pipe joints achieved nearly the same bending strength as the control samples. However, the internal pressure rating achieved by the UV cured FRP coupled joints were lower than those achieved by the control samples. Based on the test results, the UV curing FRP can be used in joining composite truss structures and composite frame structures. Further investigation is required in order for the UV cured FRP joined pipes to be used to transport liquids or gases under pressure.







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