Filing is concentrated at the top of the ranked list: the five largest assignees together hold 3,245 records, 19.4% of all 16,688 records in scope, and the ten largest hold 4,243, or 25.4%. That leaves roughly three-quarters of the field spread across a long tail of single- or few-filing entrants, including universities and component suppliers. The leader alone accounts for 986 records, well ahead of the rest of the ranked group, but no single company controls a majority of the field.

The overwhelming majority of filings, 79.1% of the 16,688 records, sit in IPC class B23K covering welding, soldering and brazing generally, confirming the core use case is metal joining. Beyond that core, smaller but consistent clusters appear in railway vehicle bodies, alloys, batteries and sheet-metal working, which shows the process is increasingly claimed as a joining step for specific end products — battery packs, rail car bodies, formed sheet assemblies — rather than only as a generic process. Filers building for a specific end application should expect to see prior art in both the general welding class and the class matching their end product.

Annual filings rose from 744 in 2017 to a peak of 959 in 2020, then eased to 747 by 2024, a -17% change over the 2021-2024 window, which is the most recent span that can be treated as complete. Numbers for 2025 and 2026 in the raw data look lower still, but that reflects publication lag of roughly 18 months rather than a real drop in filing activity. Based on the complete years, the field has passed its filing peak but remains active rather than declining sharply.

China leads as a receiving office with 5,185 records, ahead of the United States at 2,892, the European Patent Office at 1,802, Japan at 1,756, the WIPO PCT route at 933 and South Korea at 854. This spread indicates the technology is filed for protection across all the major manufacturing economies rather than concentrated in one jurisdiction, so a freedom-to-operate review needs to cover China, the US and Europe at minimum, with Japan and Korea close behind.

US20210023650A1, filed by JFE Steel Corporation and published 2021-01-28, claims a specific double-sided friction stir welding architecture: a pair of rotating tools placed on opposite faces of a metal plate, rotating in opposite directions, plus the apparatus and method built around that configuration. It blocks that specific counter-rotating, opposed-tool arrangement, not single-sided friction stir welding with a backing anvil, and not the base pin-tool or process patents that predate it by two decades. Anyone developing a double-sided or dual-tool stir-welding system should check their tool rotation and positioning scheme against this claim specifically rather than assuming all double-sided approaches are blocked.