Study on the thermo-compression bonding of thermoplastic polyurethane (TPU) plates of significant thickness difference by indentation

When a thin plate is placed on a thick plate for thermo-compression bonding, unbalanced melting may lead to insufficient bonding. In this study, a heated conical indenter and a set of flat compression dies are adopted to solve this problem. When the indenter is pressed on the combined layers, the thin plate is penetrated first and the indenter progresses into the thick plate up to a predetermined depth. Immediately after the indenter is removed, the melted site is compressed by a set of the flat dies at room temperature; the bonding is complete after cooling. Experiments were conducted to investigate the effects of the process parameters on the bond strength. The major parameters were indenter temperature, duration of indentation, compression load, method of cooling, angle of the indenter, indentation depth, and duration of compression. As a result of the orthogonal array tests, it was confirmed that the indenter temperature has the greatest influence on the bond strength.