Hot Pin Welding of Thin Poly(vinyl chloride) Sheet James D. Van de Ven, Arthur G. Erdman Mechanical Engineering Department, University of Minnesota, Minneapolis, Minnesota 55455 This paper develops a method of welding two thin sheets of poly(vinyl chloride) (PVC) with a heated pin, thus allowing construction of a relationship between the weld temperature and weld strength. Constructing a relationship between weld strength and temperature is necessary for modeling many welding processes, including laser transmission welding. An experimental approach to establishing this relationship is required because of the complex melting behavior of PVC. The designed experimental device uses a single heated pin to weld samples by using varying pressure and temper- ature for one second dwell time. An electro-mechani- cal loadframe pulled the welded samples until joint fail- ure occurred, thereby allowing determination of the weld strength. An experiment varying welding pin tem- perature and joining pressure found the temperature to be a highly significant determiner of weld strength, while the pressure was found to be not significant. A transient numerical heat transfer model was used to calculate the weld interface temperature for each pin temperature. The relationship established in this paper can be used to predict the weld strength from the tem- perature output from models of alternative welding methods. J. VINYL ADDIT. TECHNOL., 13:110–115, 2007. ª 2007 Society of Plastics Engineers BACKGROUND Laser transmission welding (LTW) is a promising plas- tic-joining alternative that creates a subsurface weld. Much work has focused on creating numerical models of the LTW in order to predict the material temperature and pressure for a specific set of input parameters [1–6]. Relating the weld pressure and temperature predicted in these models with the actual weld quality is critical to evaluating the model output. During previous modeling of LTW, different ap- proaches have been taken in quantifying the properties necessary for a satisfactory joint. Some researchers report the temperature distribution from the model and do not address the interpretation of these values [4]. A more common approach is to assume a satisfactory weld is cre- ated when a designated temperature, typically the melt temperature, is exceeded [2, 5]. The author is unaware of any previous work experimentally relating LTW model output parameters with weld quality. The melting temperature of polyvinyl chloride (PVC) is not well-defined, owing to the large distribution in crys- talline particle size. This variation in particle size results in a very broad melting range, which is characterized by particulate flow [7]. While the flow of material, as required for welding, could be modeled with molecular diffusion kinetic equations for many thermoplastics, par- ticulate flow in PVC requires an experimental model. As a rough estimate, the onset of flow in PVC is at approxi- mately 1758C [8]. Relating PVC weld temperature and weld strength has received attention in hotplate welding research. The heat- ing time during hot plate welding is typically between 10 and 20 s [9], approximately one or two orders of magni- tude greater than in LTW. In hot plate welding, the tem- perature of the material can be carefully controlled, thus making the results valuable for knowledge in the LTW field, where the material temperature is difficult to verify. Results from experiments by V. Stokes show that PVC welds created above 2188C achieve strength in excess of 90% of the parent material tensile strength. This same work finds a slight decrease in weld strength at tempera- tures above 2888C [9]. This decline quite likely is due to material decomposition during the long heating time. Work by Grewell and Benatar in the field of impulse welding found the weld strength to be a strong function of the temperature history of the two faying surfaces, not a single temperature [10]. Relatively little work in the LTW field has studied the influence of pressure in the weld zone, beyond assuring material contact. Further work by Grewell found that opti- mal weld strength was achieved with a clamp pressure near 2.2 MPa [11]. Work by Potente et al. found that the maximum weld strength is achieved at a clamping pres- sure near 1.5 MPa, yet the overall influence of weld pres- sure around this value was found to be insignificant because of the large amount of variation in the data [12]. It is interesting to note that both of these works found a Correspondence to: James D. Van de Ven; e-mail: vandeven@me.umn.edu Contract grant sponsor: Andersen Corporation. DOI 10.1002/vnl.20111 Published online in Wiley InterScience (www.interscience.wiley. com). Ó 2007 Society of Plastics Engineers JOURNAL OF VINYL & ADDITIVE TECHNOLOGY——2007