Abstract
A study of polyvinylchloride-coated woven polyester fabric welding potential was conducted using continuous ultrasonic welding machines. The effect of cooling air, anvil wheel status, anvil wheel width, material surface contact, and welding gap on seam strength was studied. Three main welding parameters with different levels were selected based on 5 and 10 mm welding widths using old and new anvil wheels with and without cooling air. A lapped type of seam was applied under full factorial design. A microstructure was captured to examine the formation of welding joints, and seam tensile properties were determined. Comparative analysis of comparable welding parameters was analyzed for a gap against pressure and amplitude against power. The actual weld phenomenon was also analyzed based on the recorded machine parameters. The results showed that auxiliary parameters had a significant effect on seam strength. A microscopic image of a welded seam indicated that cooling air reduced the number and size of holes produced. Weld seam with controlled pressure or power provided higher seam strength than that of the controlled gap or amplitude. The actual phenomenon of welding parameters was important to evaluate weld seam quality, whereby the obtained results indicated good quality at lower power and pressure.
1. Introduction
Ultrasonic sealing provides many benefits as an alternative for joining fabrics made of thermoplastic polymer containing a significant amount of thermoplastic content. Compared with other plastic bonding techniques, it is an exceptionally fast process and allows the material to heat, weld, and cool very quickly. It is extremely safe and highly targeted to reduce the risk due to excess electrical energy. It produces minimal, localized, and quickly dissipated heat that minimizes the thermal impact on the material, reduces the chances of excess heat, and saves energy consumption. It functions with a high level of reliability, which results in minimal concern about equipment failures and faulty welds. It can even be automated and produces a very clean and precise high-quality joint. It produces no plastic flash or deformation, resulting in a clean, nearly invisible seam that rarely requires any touch-up work. It is very cost-effective in terms of material usage because the process does not use connective bolts, solder, or adhesive material [1,2,3,4]. The main thing that potentially limits the use of ultrasonic welding is the limitation on material, size, and joint type, including investment cost, as in other bonding techniques. Thus, the ultrasonic welding method is one of the innovative technologies applied to bond-coated hybrid textile materials [1,2,4], and used to achieve an impermeable seam for technical textile applications such as aircraft and clothing in contaminated environments [1,2,3,4,5] as well as roof covers and tents for weather protection purposes. Even though ultrasonic welding is a promising technology for bonding hybrid textile materials, there have still been very few research papers published regarding the auxiliary welding parameters of this process and their influence on the quality of the welded seam in the open literature in this field, especially for polyvinylchloride (PVC)-coated hybrid textile materials commonly used for tents. Furthermore, the actual welding phenomenon and mechanism of this technology are not yet understood fully. To clarify these issues further, this experiment focused on determining the influence of cooling air, anvil wheel status, anvil wheel width, material surface contact, and welding gap between the anvil wheel and sonotrode on the formation of welding joints in the case of PVC-coated hybrid textile material using a continuous ultrasonic welding approach to recognize some main trends in the relations and to assess superior seam strength and quality yielding parametric levels of ultrasonic welding. The actual welding phenomenon was also analyzed to estimate the seam weld quality and the extent of weld defect during welding. Light scanning microscopic images of the bonded joints at different positions were taken to investigate the interfacial microstructure and the bond locations of the materials. Moreover, a comparative analysis of comparable welding parameters on seam strength for welding gap against welding pressure force and amplitude against welding power is also discussed in detail. Various results at constant speed are analyzed and critically commented on after reviewing the state of the art, materials, methods, and machines used for this study are explained. Generally, the effect of auxiliary welding parameters on seam strength, comparative analysis of comparable main welding parameters, and analysis of actual welding phenomena, including joint formation quality, are the main contents of this research.
2. State-of-the-Art
Ultrasonic welding is an industrial process whereby high-frequency ultrasonic acoustic vibrations are locally applied to workpieces being held together under pressure to create a solid-state weld [6]. The assembly process is performed by the melting and bonding of the material [7]. Ultrasonic welding is commonly used for plastics, and its practical application for rigid plastics was completed in the 1960s. At this point, only hard plastics could be welded. Robert Soloff and Seymour Linsley developed the first ultrasonic method or press for welding rigid thermoplastic parts in 1965, and this new technology was first applied in the toy industry; the first car made entirely out of plastic was assembled using ultrasonic welding in 1969 [8]. Ultrasonic welding continues to be a rapidly developing field due to its advantages. Nowadays, it is used for a multitude of applications in the automotive industry, medical and hygienic products, sports, work and protective wear, covering and packaging, underwear, filter, and technical textiles, as Boz and Erdoğan reported [9].
Ultrasonic welding of thermoplastics causes local melting of the plastic due to the absorption of vibrational energy along the joint to be welded. Understanding of ultrasonic welding has increased with research and testing. The invention of more sophisticated and inexpensive equipment and increased demand for plastic and electronic components has led to a growing knowledge of the fundamental process. However, many aspects of ultrasonic welding still require more study, such as relating weld quality to process parameters, auxiliary welding parameters, and actual weld phenomenon. Wu et al. [10,11] implemented the design of an experiment on polyolefin to get a proper understanding of ultrasonic welding and vibration welding, and have investigated that the amplitude of vibrations is a dominant factor for weld strength in both welding processes. They also employed an ultrasonic welding technique for welding plastic with various geometries [10,12]. Mahmut [3] analyzed the tensile property of ultrasonic seam based on polypropylene, polyester, and polyamide/polyester blend of thermal-bonded nonwoven fabrics to investigate the effect of the ultrasonic seam, fiber type, fabric area density, and bonding surface on ultrasonic seam strength and elongation at break properties. He stated that ultrasonic seam tensile strength increased in a way parallel to the increase in fabric area density for all fabrics used in his study, and the rollers were effective in ultrasonic seam tensile strength in a way parallel to the increase in the sewn surface. He has also reported that the polypropylene fabric has the highest seam tensile strength, and ultrasonic sewing is an effective method for assembling nonwoven fabrics; however, a high ratio of polyamide affected the ultrasonic seam strength negatively [3].
Subhas and Renuka [4,13] examined the bond location at the interface based on the image of scanning electron microscopy and temperature measurement. They found adequate seam strength under some sealing conditions for polyester and spectra fabrics using continuous and discontinuous ultrasonic welding machines and investigated higher seam efficiency for polyester fabric than that of spectra fabric. Muhmut et al. [14] studied the ultrasonic seam tensile and elongation properties on spun-bond and melt-blown 100 percent polypropylene and 100 percent polyester nonwoven fabrics to investigate the effect of roller rows, fiber types, fabric area density, and production methods according to three different roller rows. They found the highest seam strength and elongation at four rows of roller, which means the ultrasonic sewing surface area affected the seam strength, whereas the lowest seam strength and elongation properties were obtained at two rows of roller for all nonwoven fabrics and discovered fabric area density affected the seam strength. These results implied that an increase in the area density of the fabric and the row rollers can lead to an increase in the tensile strength. They highlighted that the elongation at break values is proportional to the density and row rollers. In addition, they reported that spun-bond polypropylene and spun-bond polyester fabrics had higher seam strength and elongation than melt-blown polypropylene and melt-blown polyester nonwoven fabrics. As they stated further, polypropylene nonwoven fabrics had higher seam tensile strength and elongation than polyester nonwoven fabrics. This is due to the application temperature of the ultrasonic sewing that closes at the melting point of the polypropylene fiber [14]. In another study, ultrasonic welding was applied for bonding sailcloth using different types of anvil wheels. Under the welding conditions of this paper, the bonding strength of the bonding joints can be increased with suitable engraving, speed, and amplitude of the ultrasonic system [15].
3. Materials and Methods
3.1. Materials
A hybrid textile (H5571-0283-ECO) material used in this study was a plain weave construction having 100 percent air-jet polyester filaments in both warp and weft directions at 1100 dtex thread density and coated with PVC using a plasticizer to make the material more flexible and durable. It was provided by a HEYtex Bramsche GmbH Company in Germany as a common tent material for light structures such as pavilions, large and warehouse tents, hall structures, roofs, or weather protection during all seasons. The construction was 8 x 8 ends and picks per centimeter. The fabric weight was measured at 639 g/m2 according to the DIN EN ISO 2286-2 standard and the thickness at 0.52 mm was measured according to the ISO 5084 standard. This material had a melting temperature range of 250–260°C for polyester, which was somewhat higher than that of PVC used for coating at a range of 150–160°C, whereas the substance density was 1.39 g/cm3 and 1.30 g/cm3 for polyester and PVC, respectively. According to the producer [16], the material had shown high-quality flame retardant, heat, and cold-resistant properties according to the various standards stated in Table 1. This is because of the material’s chemical composition and type of molecular structure (crystalline or amorphous). PVC has an amorphous structure that is directly related to the polar chlorine atoms in its molecular structure. However, it has completely different features in terms of performance and functions compared with other plastics that have only carbon and hydrogen atoms in their molecular structures. Chemical stability is a common feature among substances containing chlorine and fluorine. This applies to the selected hybrid textile material that inherently possesses superior fire-retarding properties due to its chlorine content even in the absence of fire retardants, and durability due to its ability to resist oxidation by atmospheric oxygen.
Physical and mechanical properties of H5571-0283-ECO tentorium 650 [17] material
| Specifications | Standards | Parameter |
|---|---|---|
| Base fabric | 100% polyester | DIN ISO 2076 |
| Coating material | 100% PVC | DIN ISO 2076 |
| Total weight | approx. 650 g/m2 | DIN EN ISO 2286-2 |
| Tensile strength (w/f) | 2700/2500 N/5cm | DIN EN ISO 1421-1 |
| Tear resistance (w/f) | 270/250 N | DIN 53363 |
| Welding adhesion | approx. 130 N/5cm | IVK 3.13 |
| Flex resistance | at least 100,000 bends | DIN 53359 A |
| Cold resistance | −30°C | DIN EN 1876-1 |
| Flame retardancy | Flame retardant | DIN 4102 B1 |
| Possible application | Tents | - |
Ultrasonic welding was carried out using a new generation PFAFF 8311 continuous ultrasonic machine (cf. Figure 1), with a 400 W ultrasonic generator and 35 kHz frequency, produced by a company of PFAFF Industrie Systeme und Maschinen GmbH, Germany. It is the first machine used to measure force during welding and keep it constant, a real-world first and a quantum leap in textile ultrasonic welding, in addition to regulating the speed and welding energy. All welding parameters are measured and controlled in a new touch control panel with an integrated SD card reader and USB slot through user-friendly icons in a simple operation. PFAFF has an innovative dual roller system and its cutting wheel can be switched on through a motor. It has a new modular system with many options such as a motorized puller, single parallel puller, lighting from above and below for better recognition of the lower layer, seam cooling from above for rapid solidification, and cross markers through LED for a precise starting position. It is also equipped with differential feed and a separate drive for sonotrode and anvil wheel, which means smooth, non-distorted seams are possible to produce or the possibility of adding some fullness. PFAFF uses titanium sonotrodes with maximum welding width of 10 mm, whereas their anvil wheel is available as 3, 5, or 10 mm welding width and can be selected according to the anvil wheel. Using sonotrode and anvil wheel, the maximum weld width of 10 mm could be achieved. This machine allows welding speed ranging from 0.1 to 11 m/min, welding power from 5 to 40 W with the range amplitude from 30% up to 100%, and welding pressure force from 0 to 500 N with the range gap from −1.6 up to 5 mm. The seam end detection and material detection-like seam transitions are incorporated as smart functions, and all proven features of the previous ultrasonic models are integrated into this machine as well.
(a) New generation PFAFF 8311 continuous ultrasonic machine; (b) motorized puller; (c) seam cooling.
Ultrasonic welding machines of the seamsonic series combine all the physical advantages of ultrasonic welding with the whole range of technological sewing experiences. On the PFAFF 8311, the workpiece is held between the sonotrode and the anvil wheel and welded continuously under pressure. When welding continuously by the ultrasonic method, the material to be welded will be subjected to rapidly changing pressure vibrations. The heat develops because of molecular vibrations beneath the material surface, for thin materials within the immediate vicinity of the actual weld. Ultrasonic welding with the seamsonic is a modern, innovative, and economic alternative and complementary to conventional sewing technology. If assembling laminated, coated, clothing fabrics with a high share of polymer and technical nonwovens is required in particular to get, the use of the seamsonic is the first choice. Thereby, the working range of selected material for this study is 40–100 W, 1–3 m/min, and 40–300 N for 5 mm welding width and 60–120 W, 1–3 m/min, and 40–350 N for 10 mm welding width respective of welding power, speed, and pressure force according to the preliminary experimental investigation on the material. A flat or plain anvil wheel was selected for welding the test samples considering the application area of the material (cf. Table 1).
3.2. Methods
All measurements were carried out under standard testing climatic conditions at a temperature of 20 ± 2°C and 65 ± 4 % relative humidity after conditioning for 24 hours according to the DIN EN ISO 139 standard. Ultrasonically welded seams were tested according to the tensile strength in a warp direction, and its morphological structure was used to examine the effective weld locations at the joining interface. The test was selected considering the end-use application of the material. Welding was done for 5 and 10 mm welding widths using new and old anvil wheel status with and without cooling air to investigate the effect of cooling air, anvil wheel status, anvil wheel width, material surface contact, and welding gap between the sonotrode and anvil wheel. Comparative analysis of comparable welding parameters on seam strength was done for welding gap against welding pressure force and amplitude against welding power to investigate the comparability of those welding parameters. This is because the machine allows adjusting either a welding gap or welding pressure force and amplitude or welding power for one particular welding scenario, and the rest has set an unselected parameter automatically. The actual phenomenon of ultrasonic welding parameters was also investigated by converting the binary data from the machine into text data using PFAFF software called WDM8311.exe and then by converting the text data into a CSV file format using a Python code that was prepared for this particular welding machine; we only tried to present the parameters having variation during welding in this paper.
During welding, a suitable lapped type of seam was produced by placing one edge of the textile material on the top of another as the seam allowance to be 20 mm [17,18,19], which is higher than the width of the anvil wheel. For both 5 and 10 mm welding widths, two different groups of welding parameters were used considering three factors at different levels. The selected levels as per the preliminary experiments were 150, 225, and 300 N for pressure force, and 70 and 100 W for power at 2 m/min welding speed as a first welding group, and 200, 275, and 350 N for pressure force, and 90 and 120 W for power at 2 m/min welding speed as a second welding group. For both the first and second welding groups, 96 different welding combinations were designed by changing the status of the anvil wheel, cooling air, and width of the anvil wheel. Thereby, 460 samples were bonded ultrasonically and tested their maximum tensile strength to investigate the effect of cooling air, anvil wheel status, and anvil wheel width on seam strength. However, 100 samples were prepared and measured on the other hand to investigate the effect of material surface contact and welding gap between the sonotrode and anvil wheel. For the case of welding gaps, 0.0, 0.2, 0.4, 0.6, and 0.8 mm welding gaps at 100 W welding power and 2 m/min welding speed were used in warp and weft welding direction, with a cooling air effect under the 5 mm anvil wheel width. Smooth to smooth, smooth to rough, rough to smooth, and rough to rough material contact were considered at 300 N welding pressure force, 100 W welding power, and 2 m/min welding speed in warp and weft welding direction with and without cooling air effect under 5 mm anvil wheel width for the case of material surface contact.
One of the most important factors for outdoor technical application is seam durability. Tensile strength was chosen to characterize seam durability because it could be used to judge the joined behavior between adjacent hybrid textile materials. The tensile strength of the ultrasonic weld sample was tested on the Zwick/Roell-Zmart.Pro strip tensile testing machine with a rate of extension (constant testing speed) of 100 mm/min and gauge (clamping) length of 200 mm according to the DIN EN ISO 13935-1 standard. As per the testing standards, the samples were cut into the size of 250 mm x 300 mm in width and length, respectively, and subsequently welded in a weft direction [19,20]. Then the welded samples were cut into five different 50 mm width samples. In a position such that the seam line was in the center of the gauge length, the prepared sample was clamped. We observed the required maximum force to rupture the seam perpendicular to the extension direction. Observation should be made to make sure that the seam failure was due to rupture, not due to fabric tears. If the fabric breaks, the results should not be used, and the test should be repeated for another sample. Usually, more than five samples were prepared for contingency. Thereby, the seams rupture at the seam line due to ultrasonic bond breakage was only considered in the research. The value of the test result was presented in terms of maximum force and elongation at maximum force for tensile strength. The average value of the five samples is shown in each combination.
4. Results and Discussions
4.1. Effect of Auxiliary Welding Parameters on Seam Strength
Auxiliary parameters are welding parameters that are used to support or help the seam quality and strength during welding. It is therefore important to produce a good quality seam and reduce welding defects. In ultrasonic welding, welding pressure force, power, amplitude, speed, and the gap between the sonotrode and the anvil wheel are the main welding parameters, whereas cooling air, anvil wheel status or condition of the anvil wheel, the width of the anvil wheel, the pattern of anvil wheel or engraving, and surface contact of materials have also been included as auxiliary ultrasonic welding parameters. Some of the auxiliary welding parameters are not mandatory but can be essential for good quality products. Cooling air is compressed air that facilitates rapid cooling or solidifies the molten polymer to gain its final shape. It is required to have some air nozzle provided on the machine. Anvil wheel status is a condition under which the anvil wheel is used. The old anvil wheel refers to the wheel used for a while, whereas the new anvil wheel refers to a wheel that has never been used before. Anvil wheel pattern is the engraving of the anvil wheel contact surface. It can be an engraved roller with a continuous pressing surface (flat or plain, single or multiple continuous lines, or an anvil wheel with an engraved sinusoid or zigzag pattern) or a discontinuous pressing surface (dotted weld, weld with a series of discontinuous lines). Anvil wheel width is the total welding width of the anvil wheel excluding the curved edge that chamfered. Surface contact of materials has referred to the contact between the materials at the welding interface. However, this research considers all parameters mentioned above as auxiliary ultrasonic welding parameters, except the pattern of the anvil wheel. This is due to the application area of the material that needs a flat or plain anvil wheel as stated above and mentioned in Table 1. Instead of the anvil wheel pattern, the research included the effect of the welding gap between the sonotrode and anvil wheel on seam strength even if it is the main ultrasonic welding parameter. For the study purpose, two different welding groups were prepared at constant welding speed as mentioned above and shown in Figure 2.
Working plan and graphical abstract.
Effect of Cooling Air during Welding
It was demonstrated from Figures 3a and 3b that the seam strength of the ultrasonic bonds was obtained using a 5 mm old anvil wheel for the first and second welding groups, respectively, whereas, Figures 4a and 4b illustrate the seam strength of the ultrasonic bonds obtained using a 5 mm new anvil wheel for the first and second welding groups, respectively. The percentage of seam strength difference between the cooling air and without cooling air was analyzed for the 5 mm old and new anvil wheels. From the analyzed results, the percentage of seam strength difference between the cooling air and without cooling air ranged from 0.95% to 5.44% and 0.84% to 11.09% for the 5 mm old anvil wheel, and from 0.32% to 5.82% and 2.23% to 14.43% for the 5 mm new anvil wheel in the first and second welding groups, respectively. Thus, the highest difference of 5.82% was obtained in the medium welding pressure force (225 N) and higher welding power (100 W) at 2 m/min welding speed, while the lowest (0.32%) was shown in the lowest welding pressure force (150 N) and higher welding power (100 W) at 2 m/min welding speed for the first welding group, whereas for the second welding group, the highest seam strength difference of 14.43% was found at 2 m/min welding speed in the lowest welding pressure force (200 N) and higher welding power (120 W), while the lowest (0.84%) was attained in the lowest welding pressure force (200 N) and lower welding power (90 W) at 2 m/min welding speed.
Effect of cooling air for 5 mm old anvil wheel at 2 m/min welding speed.
Effect of cooling air for 5 mm new anvil wheel at 2 m/min welding speed.
Figures 5a and 5b illustrate the seam strength of the ultrasonic bonds obtained using a 10 mm old anvil wheel for the first and second welding groups, respectively. On the other hand, Figures 6a and 6b demonstrate that the seam strength of the ultrasonic bonds was obtained using a 10 mm new anvil wheel for the first and second welding groups, respectively. The percentage of seam strength difference with and without the cooling air was analyzed for the 10 mm old and new anvil wheels. From the analyzed results, the percentage of seam strength difference between using the cooling air and no cooling air ranged from 0.79% to 10.81% and 0.46% to 16.25% for the 10 mm old anvil wheel, and from 1.28% to 14.24% and 0.24% to 2.59% for the 10 mm new anvil wheel in the first and second welding groups, respectively. Thus, the highest seam strength difference of 14.24% was obtained in the medium welding pressure force (225 N) and lower welding power (70 W) at 2 m/min welding speed, while the lowest (0.79%) was shown in the highest welding pressure force (300 N) and lower welding power (70 W) at 2 m/min welding speed for the first welding group. In contrast, the highest seam strength difference of 16.25% was investigated at 2 m/min welding speed in the medium welding pressure force (275 N) and the lower welding power (90 W), while the lowest (0.24%) was attained in the lowest welding pressure force (200 N) and lower welding power (90 W) at 2 m/min welding speed for the second welding group.
Effect of cooling air for 10 mm old anvil wheel at 2 m/min welding speed.
Effect of cooling air for 10 mm new anvil wheel at 2 m/min welding speed.
Moreover, the higher percentage of seam strength difference with the cooling air and without the cooling air was observed in the second welding group than that of the first. Because the tensile strength was highly influenced by the main welding parameters, the bonding force between fabrics due to ultrasonic energy created a higher influence on the tensile force of the weld seam when the cooling air was activated. When the welding pressure force increased from the lowest to the highest value, the tensile strength of the bond slightly increased and the percentage of seam strength difference was also increased with increasing welding power for both welding groups. According to these results, it can be concluded that the bonding force of ultrasonic weld seam, based on 5 and 10 mm welding widths and old and new anvil wheels, caused a much higher tensile force when cooling air was activated during welding than that of the tensile force without the cooling air effect; hence, cooling air in ultrasonic welding technique had a significant difference in seam strength because after the ultrasonic vibration is stopped, the ultrasonic welding process enters the final step of cooling and resolidification. During this step, the molten polymer solidifies and gains its final shape. A supportive cooling method, therefore, facilitates rapid cooling. For semi-crystalline polymers inside the coating, woven polyester, the cooling rate determines the final microstructure, and therefore, the mechanical properties of the joint. Even if PVC is an amorphous plastic with no phase transition, it does not significantly shrink during cooling. These findings were also proved by the morphological structure of the light scanning microscope cross-sectional image at 1000 µm shown in Figure 20. The morphological structure showed a higher number of holes or heat-affected areas on the lower side of the seam than on the upper. This is due to the position where the cooling air nozzle is located on the machine. The cooling air nozzle is mounted on the upper side next to the anvil wheel in the welding direction and activating the cooling air during welding is recommended.
Effect of Fabric Surface Contact at Welding Interface
When the surface contact between the materials was changed from smooth-smooth to smooth-rough, smooth-rough to rough-smooth, and rough-smooth to rough-rough, the tensile strength of the weld seam slightly increased by 4.53%, 11.03%, and 2.32% using cooling air and 6.87%, 6.8%, and 6.37% without cooling air at 100 W welding power, 2 m/min welding speed, and 300 N welding pressure force under 5 mm anvil wheel width in warp welding direction as shown in Figure 7a, respectively. It was also shown in Figure 7b that the seam strength of the ultrasonic bond was slightly increased by 9.69% and 6.88% for 150 N welding pressure force and 42.13% and 1.39% for 300 N welding pressure force as the material's surface contact changed from smooth-rough to smooth-smooth and smooth-smooth to rough-rough using 5 mm anvil wheel width without the cooling air effect at 2 m/min welding speed and 100 W welding power in the weft welding direction, respectively. An exceptional change was observed in the weft welding direction when the material's surface contact changed from smooth-rough to smooth-smooth than the warp. This is due to the surface texture difference in warp and weft direction as well as the irregularity in the coating surface. The highest seam strength value of 863 and 1075 N was obtained in rough-to-rough material surface contact for warp and weft welding direction, respectively, whereas, the lowest value of 651 and 533 N was revealed in smooth to smooth and smooth to rough material surface contact for warp and weft welding directions, respectively.
Effect of material surface contact for 10 mm anvil wheel without cooling air at 2 m/min welding speed.
According to these results, it can be concluded that the material surface contact affected the tensile strength of the weld seam, and the higher bond strength was achieved at rough-to-rough material surface contact for both welding directions because during the ultrasonic welding process, the material experiences thermal and acoustic softening. Thermal softening is caused by heat generated due to the friction at the material interface and volumetric heat generation due to hysteresis energy loss during cyclic plastic deformation in the material. Acoustic softening is the second source of material softening and is described as the reduction in the apparent static stress necessary for plastic deformation in material under the influence of ultrasonic energy. Friction heating occurs at the interface between the materials as the motion of the sonotrode causes the two surfaces to move relative to each other. Work done by friction is dissipated as heat over the contact area. The rate at which work is done (i.e., power) is the product of the force of friction and the average oscillatory speed, and frictional heat generation flux is expressed in terms of applied pressure, frequency, amplitude, and coefficient of friction. The total thermal weld energy is also proportional to welding time, pressure force, amplitude, and coefficient of friction, and inversely proportional to welding speed, according to which the coefficient of friction can vary significantly depending on the specific material and the specific ultrasonic welding process parameters. Thus, the coefficient of friction can vary throughout welding time as surface conditions change and subsequent bonding occurs. This observation was supported by previous research by Kelly et al. [21,22] and Koellhoffer et al. [22,23].
Effect of Anvil Wheel Status or Condition during Welding
It was illustrated from Figures 8a and 8b that the seam strength of the ultrasonic bonds was achieved using 5 mm anvil wheel width with cooling air for the first and second welding groups, respectively, whereas Figures 9a and 9b show the seam strength of the ultrasonic bonds obtained using 5 mm anvil wheel width without cooling air for the first and second welding groups, respectively. The percentage of seam strength difference between the old and new anvil wheel was analyzed with and without cooling air effect for the 5 mm anvil wheel width. From the analyzed results, the percentage of seam strength difference between the old and the new anvil wheel ranged from 3.37% to 12.19% and 4.36% to 20.51% for the 5 mm anvil wheel width using cooling air effect, and from 0.2% to 13.92% and 0.84% to 15.78% for the 5 mm anvil wheel width without cooling air effect in the first and second welding groups, respectively. Thus, the highest difference of 13.92% was obtained in the medium welding pressure force (225 N) and higher welding power (100 W) at 2 m/min welding speed, while the lowest (0.2%) was shown in the highest welding pressure force (300 N) and lower welding power (70 W) at 2 m/min welding speed for the first welding group. For the second welding group, the highest seam strength difference of 20.51% was found at 2 m/min welding speed in the highest welding pressure force (350 N) and higher welding power (120 W), while the lowest (0.84%) was attained in the lowest welding pressure force (200 N) and higher welding power (120 W) at 2 m/min welding speed.
Effect of anvil wheel status for 5 mm anvil wheel with cooling air at 2 m/min welding speed.
Effect of anvil wheel status for 5 mm anvil wheel without cooling air at 2 m/min welding speed.
Figures 10a and 10b demonstrate the seam strength of the ultrasonic bonds obtained using 10 mm anvil wheel width with cooling air for the first and second welding groups, respectively. On the other hand, Figures 11a and 11b illustrate that the seam strength of the ultrasonic bonds was obtained using a 10 mm anvil wheel width without cooling air for the first and second welding groups, respectively. The percentage of seam strength difference between the old and new anvil wheel was analyzed with and without cooling air effect for 10 mm anvil wheel width. From the analyzed results, the percentage of seam strength difference between old and new anvil wheels ranged from 0.53% to 10.74% and 1.49% to 12.26% for 10 mm anvil wheel width using cooling air effect, and from 1.01% to 14.05% and 0% to 7.21% for 10 mm anvil wheel width without cooling air effect in the first and second welding groups, respectively. Thus, the highest seam strength difference of 14.05% was obtained in the medium welding pressure force (225 N) and lower welding power (70 W) at 2 m/min welding speed, while the lowest (0.53%) was shown in the highest welding pressure force (300 N) and lower welding power (70 W) at 2 m/min welding speed for the first welding group. In contrast, the highest seam strength difference of 12.26% was investigated at 2 m/min welding speed in the highest welding pressure force (350 N) and lower welding power (90 W), while the lowest (0 %) was attained in the highest welding pressure force (350 N) and higher welding power (120 W) at 2 m/min welding speed for the second welding group.
Effect of anvil wheel status for 10 mm anvil wheel with cooling air at 2 m/min welding speed.
Effect of anvil wheel status for 10 mm anvil wheel without cooling air at 2 m/min welding speed.
Furthermore, a higher percentage of seam strength difference between the old and new anvil wheel was observed in the second welding group than that in the first. The bonding force between fabrics due to ultrasonic energy created a higher influence on the tensile force of weld seam when the old anvil wheel was used. When the welding pressure force increased from the lowest to the highest value, the tensile strength of the bond slightly increased and the percentage of seam strength difference was also increased with increasing welding power for both welding groups. According to these results, it can be concluded that the bonding force of ultrasonic weld seam, based on 5 and 10 mm welding widths with and without the cooling air effect, caused a much higher tensile force when the old anvil wheel was used during welding than that of the tensile force using the new anvil wheel; hence, the old anvil wheel had a significant difference in seam strength. These findings were also proved by the light scanning microscope surface image of the old and new anvil wheel at 1000 µm, shown in Figures 19a and 19b, respectively. The result showed that a smaller and larger number of cracks were observed in the new anvil wheel than in the old. However, the old anvil wheel had shown such a pattern that was taken from the sonotrode pattern due to their frequent welding effect. This is because the new PFAFF 8311 machine is used a sonotrode with a pattern or engraving. This pattern may be transferred into the anvil wheel through the time when frictional contact between them is produced. A light scanning microscope surface image of the old anvil wheel did not show serious damage or problems during welding and suggested using an old anvil wheel for this particular welding scenario.
Effect of Welding Gap during Welding
When the welding gap between the sonotrode and anvil wheel increased from 0.0 to 0.2, 0.2 to 0.4, 0.4 to 0.6, and 0.6 to 0.8 mm, the tensile strength of the weld seam slightly increased by 30.95%, 4.43%, −3.53%, and 6.72% at 100 W welding power and 2 m/min welding speed for 5 mm anvil wheel width with cooling air effect in weft welding direction as shown in Figure 12b, respectively. An exception to this rule was presented by the welding gap of 0.6 mm. While for 5 mm anvil wheel width in warp welding direction, the tensile strength of the weld seam slightly increased by 3.0%, 6.83%, 2.91%, and 4.69%, as shown in Figure 12a. Because gap reduction led to increasing contact between materials and welding tools and, therefore, caused the available time for energy coupling to increase. When the welding gap was reduced, the material temperature increased significantly providing constant welding pressure force, and the heat distribution within the joining material was improved to a certain extent or equalized depending on the material compressibility. The welding gap is adjusted to ensure energy transmission and bonding between the fabric surfaces.
Effect of welding gap for 5 mm old anvil wheel width with cooling air at 2 m/min welding speed.
It may be inferred from Figures 16a and 16b that the highest seam strength value of 819 and 1045 N was obtained in the highest welding gap of 0.8 mm at 2 m/min welding speed and 100 W welding power, while the lowest value of 522 and 874 N was revealed in the lowest welding gap of 0.0 mm at 2 m/min welding speed and 100 W welding power for weft and warp welding directions, respectively. These results showed that the welding gap had a positive effect on the tensile strength of the weld seam. As the welding gap decreased, the effect of the horn cross section on the sample at the location of the horn became deeper and created hot compaction that affected the bonding between the fabric layers. The polymer viscosity was also increased at the lower welding gap and may be attributed to the reduction of free volume due to packing [4]. Hence, an optimal welding gap is necessary, and too small a welding gap caused the material to deform. According to these results, it can be concluded that the tensile strength of the bond slightly increased with the rising welding gap between the sonotrode and anvil wheel for both welding directions. The highest value of seam strength was observed in the warp welding direction as compared to the weft, and the seam strength showed an increment of up to 36.26% and 16.36% in the weft and warp welding direction as the welding gap changed from the lowest to highest, respectively.
Effect of Anvil Wheel Width during Welding
It may be inferred from Figures 13a and 13b that the seam strength of the ultrasonic bonds was obtained using an old anvil wheel with a cooling air effect for the first and second welding groups, respectively, whereas, Figures 14a and 14b illustrate the seam strength of the ultrasonic bonds obtained using an old anvil wheel without cooling air effect for the first and second welding groups, respectively. The percentage of seam strength difference between the anvil wheel width of 5 and 10 mm was analyzed with and without the cooling air effect for the old anvil wheel. From the analyzed results, the percentage of seam strength difference between the 5 and 10 mm anvil wheel width ranged from 33.06% to 90.53% and 30.97% to 51.95% for the old anvil wheel using cooling air, and from 28.39% to 91.07% and 36.39% to 57.08% for the old anvil wheel without the cooling air effect in the first and second welding groups, respectively. Thus, the highest difference of 91.07% was obtained in the lowest welding pressure force (150 N) and lower welding power (70 W) at 2 m/min welding speed, while the lowest (28.39%) was shown in the medium welding pressure force (225 N) and lower welding power (70 W) at 2 m/min welding speed for the first welding group. For the second welding group, the highest seam strength difference of 57.08% was found at 2 m/min welding speed in the medium welding pressure force (275 N) and higher welding power (120 W), while the lowest (30.97 %) was attained in the lowest welding pressure force (200 N) and lower welding power (90 W) at 2 m/min welding speed.
Effect of welding width for old anvil wheel with cooling air at 2 m/min welding speed.
Effect of welding width for old anvil wheel without cooling air at 2 m/min welding speed.
Figures 15a and 15b demonstrate the seam strength of the ultrasonic bonds obtained using a new anvil wheel with a cooling air effect for the first and second welding groups, respectively. On the other hand, Figures 16a and 16b illustrate that the seam strength of the ultrasonic bonds was obtained using a new anvil wheel without cooling air effect for the first and second welding groups, respectively. The percentage of seam strength difference between the anvil wheel width of 5 and 10 mm was analyzed with and without the cooling air effect for the new anvil wheel. From the analyzed results, the percentage of seam strength difference between the 5 and 10 mm anvil wheel width ranged from 28.4% to 93.97% and 41.8% to 59.72% for the new anvil wheel using cooling air, and from 11.93% to 88.53% and 40.61% to 61.34% for the new anvil wheel without the cooling air effect in the first and second welding groups, respectively. Thus, the highest seam strength difference of 93.97% was obtained in the lowest welding pressure force (150 N) and lower welding power (70 W) at 2 m/min welding speed, while the lowest (11.93%) was shown in the medium welding pressure force (225 N) and lower welding power (70 W) at 2 m/min welding speed for the first welding group. In contrast, the highest seam strength difference of 61.34% was investigated at 2 m/min welding speed in the highest welding pressure force (350 N) and higher welding power (120 W), while the lowest (40.61 %) was attained in the lowest welding pressure force (200 N) and lower welding power (90 W) at 2 m/min welding speed for the second welding group.
Effect of welding width for new anvil wheel with cooling air at 2 m/min welding speed.
Effect of welding width for new anvil wheel without cooling air at 2 m/min welding speed.
Moreover, the highest percentage of seam strength difference between the anvil wheel width of 5 and 10 mm was observed in the second welding group than that of the first. The bonding force between fabrics due to ultrasonic energy created a higher influence on the tensile force of the weld seam when the anvil wheel width of 10 mm was used. When the welding pressure force increased from the lowest to the highest value, the tensile strength of the bond slightly increased, and the percentage of seam strength difference was also increased with increasing welding power for both welding groups. According to these results, it can be concluded that the bonding force of ultrasonic weld seam, based on the old and new anvil wheel with and without a cooling air effect, caused a much higher tensile force when the 10 mm anvil wheel width was used during welding than that of the tensile force using the 5 mm anvil wheel width; hence, the 10 mm anvil wheel width had a significant difference in seam strength. It is suggested using a 10 mm anvil wheel during welding depending on the application area. This is because the impact of the welding pressure force decreased when the welding width of the anvil wheel increased. After all, the amount of stress developed in the welding area was inversely proportional to the welding width of the anvil wheel. Due to a higher effect of welding pressure force, a developed frictional work was decreased in the lower welding width of the 5 mm anvil wheel than in the higher welding width of 10 mm, and dissipated friction (due to surface effect) caused a higher plastic dissipation for the lower welding width of the anvil wheel than the higher. Thus, a higher plastic dissipation caused a higher material deformation that resulted in a lower weld seam tensile strength for the lower welding width of the anvil wheel than the higher. This observation was supported by research [17,24], according to which a lower welding width of the anvil wheel led to more intensive stress development in the interface, which resulted in a decrease in the strength of the weld seam. A similar observation was also made by research [17,25,26] that further increasing the welding pressure forces decreased the developed frictional work in the interface.
4.2. Comparative Analysis of Comparable Welding Parameters on Seam Strength
Comparative Analysis of Gap against Pressure Force
When the welding power increased from 40 to 55, 55 to 70, 70 to 85, and 85 to 100 W, the tensile strength of the weld seam slightly decreased by 3.44%, 5.13%, 1.06%, and 30.06% at 0.0 mm welding gap and 2 m/min welding speed for the 5 mm old anvil wheel width without the cooling air effect in warp welding direction, as shown in Figure 17a, respectively. On the contrary, it had shown a slightly increasing modus at a constant 100 W welding power and 2 m/min welding speed with the rising welding gap, as mentioned in Figure 12. It can also be inferred from Figure 17b that the tensile strength of the weld seam slightly increased up to 90 W by 5.76% and 11.57% and then decreased up to 120 W by 3.29% and 18.14% as welding power increased from 60 to 75, 75 to 90, 90 to 105, and 105 to 120 W at 0.0 mm welding gap and 2 m/min welding speed for the 10 mm old anvil wheel width without the cooling air effect in warp welding direction. This is due to the difference in stress development between the 5 and 10 mm anvil wheel widths and is explained in the effect of the anvil wheel width section. The actual welding gap was ranged as presented in Table 2 for 5 and 10 mm of old anvil wheel without the cooling air effect at a constant welding speed of 2 m/min. The data were taken from the machine record. These results showed that the machine automatically measured and set the appropriate welding gap for each welding pressure force used as an input during welding when pressure force was a control variable. According to Figure 17c, higher seam strength was observed when the welding pressure force was controlled at 150 and 300 N than the seam strength when the welding gap was controlled at 0.0 mm. Furthermore, it was noted that the highest seam strength value of 932 and 1729 N was obtained in the lowest (40 W) and medium (90 W) welding power at 0.0 mm welding gap and 2 m/min welding speed, while the lowest value of 622 and 1417 N was revealed in the highest welding power of 100 and 120 W at 0.0 mm welding gap and 2 m/min welding speed for the 5 and 10 mm anvil wheel widths, as shown in Figures 17a and 17b, respectively.
Actual welding gap result for the 5 and 10 mm old anvil wheels without cooling air at 2 m/min welding speed.
| Welding Parameters | For 5 mm Old Anvil Wheel | Welding Parameters | For 10 mm Old Anvil Wheel | ||
|---|---|---|---|---|---|
| Power 70 W | Power 100 W | Power 90 W | Power 120 W | ||
| Pressure force 150 N | −0.299–0.624 mm | −0.261–0.582 mm | Pressure force 200 N | −0.254–0533 mm | −0.170–0.488 mm |
| Pressure force 225 N | −0.452–0.440 mm | −0.413–0.397 mm | Pressure force 275 N | −0.544–0.380 mm | −0.541–0.342 mm |
| Pressure force 300 N | −0.564–0.277 mm | −0.543–0.240 mm | Pressure force 350 N | −0.545–0.220 mm | −0.675–0.202 mm |
Welding gap against pressure force for the 5 and 10 mm old anvil wheel widths without cooling air at 2 m/min welding speed.
Comparative Analysis of Amplitude against Power
As the welding amplitude increased from 35% to 40%, 40% to 43%, and 43% to 45 %, the tensile strength of the weld seam slightly increased by 62.12% for the warp welding direction and 11.04 % for the weft welding direction and then started to decrease by 8.83% and 10.07% for the warp welding direction and 35.09% and 4.84% for the weft welding direction at 150 N welding pressure force and 2 m/min welding speed for the 5 mm old anvil wheel width with the cooling air effect shown in Figures 18a and 18b, respectively. These results showed that the weld seam was difficult to produce using the lowest (30%) and highest (50%) welding amplitude at the lowest welding pressure force of 150 N for both welding directions. The tensile strength of the weld seam slightly increased by 73.65% for the warp welding direction and 51.35% for the weft welding direction as the welding amplitude increased from 30% to 35% and then started to decrease by 29.03% for the warp welding direction and 45.66% for the weft welding direction as the welding amplitude increased from 35% to 40% for 225 N welding pressure force and 2 m/min welding speed of the 5 mm old anvil wheel width with the cooling air effect shown in Figures 18a and 18b, respectively. It was pointed out that the weld seam was difficult to produce starting from 43% welding amplitude up to 50% at 225 N welding pressure forces for both welding directions. It can also be inferred from Figures 18a and 18b that the tensile strength of the weld seam slightly increased by 28.85% for the warp welding direction, but it slightly decreased by 28.12% for the weft welding direction as the welding amplitude increased from 30% to 35% for 300 N welding pressure force and 2 m/min welding speed of the 5 mm old anvil wheel width with the cooling air effect, respectively. It was noted that the weld seam was difficult to produce starting from 40% welding amplitude up to 50% at 300 N welding pressure forces for both welding directions. A similar observation was explored in Figures 18c and 18d, which were constructed for the 10 mm old anvil wheel width using the cooling air effect under warp and weft welding directions. However, the difference was noted on the lowest welding pressure force at a 35% welding amplitude, and it is evidence for the reason explained in the effect of the welding width section. This is attributed to the fact that stress development for the 5 and 10 mm anvil wheel widths was observed. The actual welding amplitude was ranged as presented in Table 3 for 5 and 10 mm of the old anvil wheel with the cooling air effect at a constant welding speed of 2 m/min. These results showed that the machine automatically measured and set the appropriate welding amplitude for each welding power used as an input during welding when power was a control variable. According to these results, it can be concluded that higher seam strength was observed when the welding power, rather than the welding amplitude was controlled. Because when the welding power was controlled at 70 W with 150 N welding pressure force and 2 m/min welding speed, the machine set the welding amplitude by itself between 30% to 34%, but when the welding amplitude was controlled at 30% with 150 N welding pressure force and 2 m/min welding speed, the seam cannot be produced.
Welding amplitude against power for the 5 and 10 mm old anvil wheel widths with the cooling air at 2 m/min welding speed.
Actual welding amplitude result for 5 and 10 mm old anvil wheels with the cooling air at 2 m/min welding speed.
| Welding Parameters | For 5 mm Old Anvil Wheel | Welding Parameters | For 10 mm Old Anvil Wheel | ||
|---|---|---|---|---|---|
| Power 70 W | Power 100 W | Power 90 W | Power 120 W | ||
| Pressure force 150 N | 30–34% | 35–43% | pressure Force 200 N | 32–38% | 35–42% |
| Pressure force 225 N | 29–37% | 32–37% | pressure force 275 N | 30–36% | 18–40% |
| Pressure force 300 N | 29–34% | 30–37% | pressure force 350 N | 13–31% | 11–37% |
Microscopic cross-sectional view of (a) old anvil wheel and (b) new anvil wheel.
4.3. Actual Phenomenon of Ultrasonic Welding Parameters
An actual welding phenomenon is an existing act or fact that is observed during welding. In other words, it refers to a fact or situation that exists and can be seen as especially unusual or interesting. The actual phenomenon of ultrasonic welding parameters was investigated by taking the binary data from a PFAFF ultrasonic welding machine, which was saved after welding for each welding combination. Using the binary data, the PFAFF software termed WDM8311.exe converted the binary data into text. And then the text data were converted into a CSV file format using the prepared Python code that was written for this particular welding machine scenario. The minimum and maximum range of actual welding phenomena are presented in Table 4 for the 5 and 10 mm old and new anvil wheels with and without the cooling air effect at a constant welding speed of 2 m/min with respective welding amplitude, power, pressure force, gap, and distance.
Range of actual welding parameters result for the 5 and10 mm old anvil wheels with and without the cooling air at 2 m/min welding speed.
| Actual Welding Parameters | 5 mm Old Anvil Wheel | 10 mm Old Anvil Wheel | 5 mm New Anvil Wheel | 10 mm New Anvil Wheel | |||||
|---|---|---|---|---|---|---|---|---|---|
| Min. | Max. | Min. | Max. | Min. | Max. | Min. | Max. | ||
| Amplitude (%) | with cooling air | 11–35 | 31–43 | 28–32 | 29–43 | 29–36 | 29–43 | 12–32 | 30–46 |
| without cooling air | 11–36 | 29–46 | 12–31 | 29–45 | 12–36 | 31–47 | 28–32 | 30–46 | |
| Power (W) | with cooling air | 29–110 | 73–140 | 61–111 | 77–178 | 67–113 | 73–129 | 61–113 | 77–163 |
| without cooling air | 47–94 | 74–158 | 60–116 | 80–163 | 36–112 | 75–149 | 59–112 | 80–190 | |
| Force (N) | with cooling air | 74–246 | 154–376 | 52–311 | 154–379 | 132–345 | 154–355 | 61–292 | 154–358 |
| without cooling air | 59–312 | 156–370 | 54–259 | 168–360 | 68–303 | 154–355 | 55–273 | 168–384 | |
| Gap (mm) | with cooling air | −0.633–0.544 | 0.062–0.64 | −0.724–0.552 | 0.19–0.612 | −0.026–0.607 | 0.061–0.64 | −0.629–0.601 | 0.22–0.65 |
| without cooling air | −0.639–0.009 | 0.075–0.624 | −0.675–0.17 | 0.195–0.63 | −0.547–0.446 | 0.044–0.615 | −0.691–0.267 | 0.208–0.638 | |
| Distance (mm) | With Cooling Air | −390–7729 | 6410–8166 | −860–6998 | 7755–8254 | 3639–8129 | 6426–8524 | −370–8079 | 7921–8640 |
| without cooling air | −590–1729 | 6510–8375 | −807–810 | 7675–8443 | −261–7329 | 6227–8267 | −576–7030 | 7807–8490 | |
We tried to present eight welding combination results among 96 welding combinations, which represented and showed the actual phenomena of welding amplitude, power, pressure force, gap, and distance during welding situations. These results showed the variation of actual welding phenomena of amplitude, power, pressure force, and distance in between the minimum and maximum values; cf. Figures 20-1a, 20-1b, 20-2c, 20-2d, 20-3e, 20-3f, 20-4g, and 20-4h. This is due to various reasons. The main reason is the sonotrode pattern or engraving and the material properties. A patterned sonotrode structure caused variation in the welding gap, material thickness depends on the material compressibility, and applied pressure force and time were performed, which led to a variation in the mentioned properties. Results found in this paper are necessary to estimate the quality of welded seam during welding. The extent and place of a welding defect can be estimated based on the extent of the variation on the discovered graph according to analyzed actual welding parameters. Based on these results, it can be concluded that a good quality weld seam was obtained in an old anvil wheel using the cooling air effect for both the 5 and 10 mm anvil wheel widths at a lower welding pressure force and with power up to medium levels. These findings were also supported and proved by the morphological structure of the light scanning microscope cross-sectional image at 1000 µm; cf. Figures 20-1a, 20-1b, 20-2c, 20-2d, 20-3e, 20-3f, 20-4g, and 20-4h. The morphological structure showed a higher number of holes or heat-affected areas when the welding pressure force and power were increased.
Microscopic cross-sectional view and actual welding phenomena of ultrasonic welding parameters for 150/70/2 (a) with cooling air and (b) without cooling air using 5 mm new anvil wheel.
Microscopic cross-sectional view and actual welding phenomena of ultrasonic welding parameters for 300/100/2 (c) with cooling air and (d) without cooling air using 5 mm new anvil wheel.
Microscopic cross-sectional view and actual welding phenomena of ultrasonic welding parameters for 200/90/2 (e) with cooling air and (f) without cooling air using 5 mm new anvil wheel.
Microscopic cross-sectional view and actual welding phenomena of ultrasonic welding parameters for 275/120/2 (g) with cooling air and (h) without cooling air using 5 mm new anvil wheel.
5. Conclusions
The effects of cooling air, anvil wheel status, anvil wheel width, material surface contact, and welding gap created a significant difference in seam strength. A higher tensile strength of the ultrasonic weld seam was obtained when the cooling air was activated during welding for the 5 and 10 mm welding widths under the old and new anvil wheel. The material surface contact affected the tensile strength of the weld seam, and the higher bond strength was achieved at rough-to-rough material surface contact for both welding directions. A higher tensile strength of ultrasonic weld seam was observed on the old anvil wheel than that of the new anvil wheel for the 5 and 10 mm welding widths with and without the cooling air effect. The tensile strength of the bond slightly increased with the rising welding gap between the sonotrode and anvil wheel for both welding directions. The seam strength showed an increment of up to 36.26% and 16.36% in the weft and warp welding direction as the welding gap changed from the lowest to the highest, respectively. A higher tensile strength of ultrasonic weld seam was observed on the 10 mm anvil wheel width than on the 5 mm anvil wheel width for both old and new anvil wheels with and without the cooling air effect. Higher seam strength was observed when the welding power and pressure force were controlled than if the welding amplitude and gap were controlled. A good quality weld seam was found in old anvil wheel status using the cooling air effect for 5 and 10 mm anvil wheel widths at a lower welding pressure force and power up to medium levels. A higher number of holes or heat-affected areas were observed on the lower side of the seam than on the upper. The investigated result is of importance for adaptation for weather protection and industrial applications.
Acknowledgments
The authors would like to thank the Institute of Textile Machinery and High-Performance Material Technology (ITM), the German Academic Exchange Service (DAAD), the Ministry of Science and Higher Education (MOSHE), and the Ethiopian Institute of Textile and Fashion Technology (EiTEX) for their valuable support for this research and appreciate the PFAFF GmbH for allowing us to work on their machine; we also present special thanks for Mr. Tilo Pilling for his valuable assistance during testing.
Funding
This research was funded by the German Academic Exchange Service (DAAD) through the EECBP Home Grown Ph.D. Scholarship Program 2019. The article processing charge (APC) was funded by the publication fund of the TU Dresden and Saxon State and University Library Dresden (SLUB).
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