Forward to Better Understanding of Optimized Performance of Welded Joints: Local Reinforcement and Memory Effects for Polyamides

Abstract

A comparative study of the mechanical performance of welded polyamide joints is evaluated. Under optimized welding (linear and orbital vibration, hot plate, transmission laser) conditions, the tensile strength of welded polyamide/nylon (filled and fiber-reinforced) is close or slightly higher (up to 14%) than the tensile strength of the base polymer (non-filled polyamide). In this study, the influence of two important effects (local reinforcement and "memory") on the mechanical performance of polyamide/nylon welds is analyzed and discussed. The results presented in this study will help plastic part designers, material developers and manufacturers, choose optimized welding conditions for polyamide/nylon parts in a wide range of industrial applications. For a better understanding of the role and influence of the processing temperature of the melt (in injection molding) and weld-melt (in welding) on mechanical performance of semi-crystalline molded (welded) thermoplastics, we performed a comparative study for polyamide/nylon 6 and polyamide/nylon 66 (non-filled and fiberglass reinforced) plastics. Mechanical performance of injection molded and welded nylon was evaluated using static (tensile and flexural) and dynamic (impact, DMA) tests. The static (tensile and flexural) and dynamic mechanical (DMA) properties were evaluated at a wide range of end-use temperatures, typical for welded nylon parts in automotive under-the-hood, small engines for lawn & power, and similar applications. Melt temperatures (for an injection molding) were varied from 225 °C to 310 °C. These values are significant above (up to 87 0 C) to the melt point of nylon 6 (T mp = 223 °C). Presented results will help product developers, designers, technologist, and manufacturers, by given them suggestions on the optimized temperature conditions of a melt and weld-melt inter-phase area. Comprehensive studies of the mechanical performance of welded polyamide 66 with respect to plastic composition were published by H. Potente, M. Uebbing and E. Lewandowski [7]. A comparative study of nylon 6 and nylon 66 welded joints, influenced by temperature and moisture, was published by I. D. Froment [8]. D. Grewell, in a comprehensive study [9] for the orbital welding technology, repeatedly achieved similar [3] tensile strength for PA 6 joints. Presented in these studies [7-9] are results on mechanical performance of PA 6 and PA 66 joints were applied [10-14, etc.] in the design of vibration welded air intake manifolds (AIM), resonators, etc. Reported in [7-11] tensile strength data for welded joints are very similar for both plastics (PA 6 and PA 66) and is equal to 65-72 MPa (for 30-35 wt.% fiberglass reinforcement). Capron ® is a registered trademark of BASF Corporation.

Reinforcement Challenges and Solutions in Optimized Design of Injection Molded Plastic Parts

“…Also in a previous report to SPE 2001 (Antec), our findings revealed the effects of local reinforcement in the weld inter-phase, on linear vibration welding techniques [12]. In a presentation at SAE 2001 we discussed the kinetics of the weld melt temperatures for various nylons using linear vibration and hot-plate welding technologies [8]. Table 1.…”

“…In our report to SPE 2000 (Antec) we associated these maximum temperatures with "memory effects" of semi-crystalline thermoplastics [12]. All of our results presented at SAE and Antec [8][9][10][11][12] were produced for straight butt-joints ( Figure 3), with similar and dissimilar ( Figure 3b, Table 1) weld thickness and made with varying linear and orbital vibration welding parameters (Table 2), such as weld amplitude, weld pressure, melt-down, hold/cooling time, thickness of inter-phase. T-type joints ( Figure 3c) are very commonly used in many applications [1-4, 6-7, 13-14], where welded reinforced thermoplastics (such as nylon, PET, etc.)…”

“…Precise, improved design of injection molded and subsequently welded parts requires the use of specific engineering properties, as related to optimized rib and weld performance and may influence end-use part performance [1][2]. Previously, the linear vibration welding process and short-term mechanical performance of welded joints was described in [3][4][5][6][7][8][9][10][11]. Also in a previous report to SPE 2001 (Antec), our findings revealed the effects of local reinforcement in the weld inter-phase, on linear vibration welding techniques [12].…”

Recent Advances and Challenges in Induction Welding of Reinforced Nylon in Automotive Applications

“…Previously we analyzed and demonstrated basic technical advantages of vibration welding process for various nylon-based plastics. It was reported previously [13] that for glass-fiber reinforced nylon, the maximum weld strength for the butt-joint is approximately equal to or less than the strength of the matrix or base material ( Figure 7).…”

“…Optimizing reduced pressure is a key parameter for many welding processes. More detailed results related to optimization of linear vibration welding of nylon may be obtained from [5][6][12][13][14].…”