Cutting Tool Failure and Jigsaw Blade Metallurgical Failure Investigation
LPD Lab Services frequently carries out failure investigations and consultancy on metal products and components. In the manufacturing industry, reliable tooling can increase the production rate and decrease the scrap rate, improving profit. It is not only the tooling that matters, but also the manner in which it is applied.
The following illustrative metallurgical examination was performed on jigsaw blades that were reported to have failed when cutting aluminium sheet, leading to a drastic reduction in the production rate and high cutting blade failures. Determining the root cause required an experienced metallurgist with suitable process experience and direct access to optical microscopy, metallography capabilities, chemical analysis and hardness testing to assess mechanical properties.
Visual and Low Magnification Optical Examination
Visual inspection and optical microscopy revealed that the blades that were failing to cut in production were in fact not damaged, but that the teeth had been clogged up with plastically deformed aluminium. This indicated that the aluminium was too soft the be cut as intended; it smeared and adhered to the blade instead. No lubricant was used.
Compositional Analysis by Inductively Coupled Plasma – Optical Emission Spectroscopy ICP-OES
The composition of the jigsaw blade material, determined by ICP-OES and Leco Carbon and Sulphut IR analysis, indicated it to be a high speed tool steel, which is typically used for manufacturing cutting tools, so the tool was adequate for use.
Metallography
Metallography, using optical microscopy, was performed on a polished and chemically etched cross-section from a jigsaw blade. It had very fine grains of tempered martensite and randomly dispersed primary carbides, indicated it to be in the hardened and tempered condition.
Hardness Testing
The jigsaw blades had a Vickers hardness of 744 HV, which confirmed that the heat treatment had been done correctly. The hardness of the aluminium sheet was 28.6 HV, which was significantly soft.
Metallurgical Failure Analysis Findings, Consultancy and Product Improvement
The jigsaw blades did not fail, but rather the cutting operation needed to be changed by employing a suitable lubricant to reduce friction and heat, and thereby prevent the extremely soft aluminium from sticking to the blade and clogging up the teeth. Removing the adhering aluminium from the blades left them intact and fit for use. The blades had the correct composition, microstructure and hardness to function properly as a cutting tool.
Cutting Tool Failure and Jigsaw Blade Metallurgical Failure Investigation Report.