Looking for plastic sealer that can go round corners

Given that this is a DIY forum why not make one yourself? I haven't made one but I suspect that all you need is a short length of resistance wire, a USB PSU or salvaged PC PSU (experimentation required), a couple of MDF offcuts, a hinge, a suitable switch and a way of tensioning the wire.

I have seen machines like that with an autofeed table but they're factory priced. You could probably use a spare heating element & old transformer, or perhaps one from an impulse type, to make something. A wheel has to run hotter because the flat surface on an impulse has more dwell time than you'd get from a moving wheel. (You can also drive some metal blades from a soldering gun, one plus a wide curved wire blade might just be all you need.)

I've never had any difficulty doing shorter welds with the impulse, the excess plastic just hangs out the front. Presumably you want to do welds with unwelded plastic at both ends.

The product description seems f***ed-up on their website (shopify error? "Liquid error (product-form line 1): include usage is not allowed in this context")

But this sort of thing?

Yes, I've seen them too but I still don't see how they would do what I want. They seem to be aimed at doing seams parallel (and not far from) an edge. I want to do seams away from an edge. For example I want to stick two 10cm (or so) wide strips together in a T formation.

That's *exactly* the sort of thing I was hoping might exist, thank you. It's a bit pricey but given that their impulse sealers are also similarly rather pricey maybe I can find a similar device (eBay, AliExpress) for less money. Now I know that such a thing exists and I have some sort of name/description I may have more chance of finding one.