Kennametal Inc v Pramet Tools SRO & Anor

A product claim must be construed with sufficient certainty for the skilled person to identify the claimed physical feature without elaborate experiments. A substantially straight cutting-edge region must be distinguishable from a continuation of an adjacent curve and sufficiently long to perform its stated surface-finishing function. Under section 60(2) of the Patents Act 1977, the knowledge or obviousness requirement concerns the intended use of the supplied means, not whether the supplier appreciates that the means possess every claim feature. A patent may nevertheless lack inventive step where the claimed modification would have been an obvious way of implementing the prior art.

The claimant alleged that inserts manufactured and supplied by the defendants indirectly infringed claim 1 of the claimant’s patent for a high-feed face-milling cutter. The defendants denied infringement and counterclaimed that the patent was invalid in light of Japanese Patent No. 52-103081 (Dijet) and European Patent Application No. 1,260,298 (Nagashima).

The central issues were the construction of “substantially straight cutting edge region” and “secondary conical clearance surface”, whether the Pramet inserts possessed the relevant features, whether section 60(2) was satisfied, and whether claim 1 was novel and inventive.

1. Construction. Claim 1 required a substantially straight cutting-edge region that could be identified by the skilled person on examination of the insert. A minute section indistinguishable in practice from an adjacent arc would not satisfy the claim. The feature was part of the characterising portion, intended to distinguish the invention from prior art and to provide a sufficiently long wiping surface for high-feed milling. The court therefore rejected the claimant’s broader construction.
2. The requirement for a secondary conical clearance surface did not demand precise geometrical conical geometry. In context, a surface having the relevant clearance function could satisfy the requirement despite a small difference in radii. The Pramet inserts therefore had secondary conical clearance surfaces.
3. Infringement. The Pramet inserts had no substantially straight region perpendicular to the cutting axis. Their design drawings and manufacturing evidence showed continuous curves, and the experimental evidence did not establish the alleged 0.2 mm region. The inserts therefore did not infringe.
4. Section 60(2). The knowledge or obviousness requirement concerned the use intended for the supplied means. It did not require the supplier to know that the means possessed a technically difficult-to-identify claim feature or to understand that the resulting combination infringed. The court accepted the reasoning in Qualcomm Incorporated v Nokia Corporation [2008] EWHC 329. The point was hypothetical because infringement had already failed.
5. Validity. On the construction adopted, claim 1 lacked inventive step in light of Figure 21 of Nagashima. It was also obvious in light of Figures 7 and 8, because adding a substantially straight region to improve surface finish was an obvious alternative for the skilled person. Had the claimant’s broader construction been accepted, the claim would additionally have been anticipated and obvious in light of Nagashima and Dijet.
6. The infringement claim consequently failed, and the patent was held invalid for lack of inventive step.