In plastic assembly, infrared welding and hot plate welding are both common thermal bonding methods. However, both processes inevitably produce flash—excess molten plastic squeezed out during welding. This article will explain why infrared welding is better at reducing flash, and what kind of weld line design should be used to avoid poor appearance caused by flash.
Why there’s flash?
Flash forms because welding requires melting plastic surfaces and applying pressure to ensure a strong bond. This pressure squeezes the molten plastic out of the original plane, forming a new connecting structure—and the excess part of this structure is what we call flash. Issues such as uneven heating or inconsistent/non-uniform plastic parts will aggravate flash. Crucially, flash isn’t useless—it’s part of the weld that maintains joint strength. Scraping it off weakens the bond, risking cracks or separation, and may damage the product’s appearance or sealing ability.
Advantage of IR welding machine
A major advantage of infrared welding is less flash compared to hot plate welding. The difference lies in heating methods: hot plate welding uses direct contact, which heats surrounding plastic excessively, creating more flash. Infrared welding uses non-contact radiation, heating only the target weld area. This controlled heating limits molten plastic volume, reducing flash.
Welding line design to help improve
To further minimize flash and ensure a good appearance, proper weld line design is key: 1. Choose the right structure (stepped for thin parts, grooved for thick sealed parts, shear-type for semi-crystalline plastics like PA/POM). 2. Control dimensions precisely (spigot size ~1/3 of wall thickness, fitting gap 0.05-0.2mm). 3. Add a small flash trap (groove) near the weld line to catch excess plastic. 4. Place the weld line in even-thickness areas and add a gentle guide slope for alignment.
In short, infrared welding’s precise heating reduces flash. Combining this with scientific weld line design helps eliminate flash, creating high-quality plastic products that meet strict appearance requirements in industries like automotive and electronics.
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