Adhesive is the easy way to join PP and the first thing to fail in service – on hot surfaces, in wash-down areas, under load over time. Welding removes the adhesive problem entirely by making the joint out of the same material as the parts. The question is which method suits your geometry.
Hot air welding
A heated air stream softens the parent material and a filler rod of the same polymer is fed into the joint. It is the most flexible method: it works on complex geometry, on-site, and on assemblies too large to fit a machine.
The output quality depends almost entirely on the operator. A good hot-air weld is strong and watertight; a poor one looks similar and delaminates later. It is also slow, which limits it to smaller production volumes.
Best for: repairs, low volume, awkward shapes, work done on site.
Hot wedge welding
A heated wedge runs between two overlapping sheets and softens both, which are then pressed together by rollers. The result is a continuous, repeatable seam with much less operator dependence than hot air.
It is the standard method for long linear seams and it is fast. The limitation is geometry – it needs two flat sheets with a straight, overlapping joint. Corners and complex shapes have to be done by another method or by overlapping separate seams.
Best for: long straight seams, panel-to-panel joining, membrane-type work.
Ultrasonic welding
High-frequency vibration generates heat exactly at the interface between two parts, so the weld forms where you want it and nowhere else. Cycle times are short, it is highly repeatable, and it leaves no visible weld bead.
The constraint is tooling: a horn matched to the joint geometry, and a joint design that concentrates energy at the interface. It suits volume production of a fixed design and is uneconomic for one-offs.
There is also a limitation with honeycomb specifically. Ultrasonic welding works best on solid or thin sections; a honeycomb core does not transmit energy predictably, so the weld usually has to be at a skin-to-skin interface rather than through the core.
Best for: high-volume assemblies, small parts, cases where appearance matters.
What to consider before choosing
- Joint geometry – flat overlap, corner, or something more complex
- Production volume – one-offs and millions need different answers
- Whether the joint must be watertight
- Load direction – a weld is strong in shear along the seam and weaker in peel
- Appearance – whether a visible weld bead is acceptable
- Access – whether the joint can be reached by a machine or only by hand
Joint design matters more than method
A weld is not a repair for a bad joint design. Load a welded seam in peel and it will open regardless of how well it was made; load it in shear and it will hold. Where a joint has to resist peeling, redesign it so the load goes into shear, or add mechanical fastening alongside the weld.
We see more failures from joint geometry than from welding technique.
What we can do
We fabricate welded honeycomb panel assemblies and use hot air, hot wedge or ultrasonic depending on the joint and the volume. Send us the assembly drawing and we will tell you how it should be joined – and if a design change would make the joint considerably more reliable, we will say so at quotation stage.