Name two common defect modes in spin welds and their typical root causes.

• A. Cold welds due to insufficient heat or dwell time, and burn-through due to excessive heat or prolonged dwell.
• B. Cracks due to misalignment, porosity due to moisture.
• C. Delamination due to wrong materials, overdosing adhesives.
• D. Weak surface due to roughness.

Answer: (A)

Spin welding relies on friction at the joint interface to heat and fuse the thermoplastic surfaces. Two common defect modes are cold welds and burn-through. A cold weld happens when there isn’t enough heat generated or the dwell time is too short, so the interface doesn’t melt sufficiently to form a strong bond. The joint ends up weak because the materials haven’t fused. Burn-through occurs when heat input is too high or the dwell time is too long, causing excessive melting that can pit or burn through the material and create a through-hole or damaged area, compromising strength. To avoid these, balance factors like rotation speed, friction pressure, axial force, and dwell time to achieve proper fusion without overheating. Other listed issues—cracks from misalignment, porosity from moisture, or adhesive-related defects—aren’t the typical spin-weld failure modes driven by heat control in the same direct way.