Diamond and Related Materials 13 (2004) 843–847 0925-9635/04/$ - see front matter  2003 Elsevier B.V. All rights reserved. doi:10.1016/j.diamond.2003.11.018 Cutting forces evolution with tool wear in sintered hardmetal turning with CVD diamond M. Belmonte , F.J. Oliveira , J. Sacramento , A.J.S. Fernandes , R.F. Silva * a a b c a, Department of Ceramics and Glass Engineering, CICECO, University of Aveiro, 3810-193 Aveiro, Portugal a High School of Technology and Management, Agueda, Ap. 473, 3751 Agueda, Portugal b ´ ´ Department of Physics, University of Aveiro, 3810-193 Aveiro, Portugal c Abstract The cutting forces evolution is investigated during the dry turning of sintered hardmetal (WC-25 wt.%Co) with chemical vapour deposition (CVD) diamond brazed tools. The effect of the cutting speed (v), feed (f ) and depth of cut (d) in the cutting forces is analysed, being found a clear relationship between tool forces, tool wear and workpiece surface finishing. The chosen test conditions (vs40mmin , f s0.03 mm rev. and ds0.1 mm) allow to set up a threshold main cutting force value of 35 y1 y1 N below which excellent workpiece finishing is assured with low cutting tool damage. Flank tool wear, besides cratering on the rake tool face and hardmetal deposition on the tool surface, are the main damage modes of the cutting tools.  2003 Elsevier B.V. All rights reserved. Keywords: Tool wear; Cutting force; Chemical vapour deposition (CVD); Diamond 1. Introduction Sintered hardmetal components are widely used as dies for metal stamping, forging and laminating pro- cesses. Superhard cutting tools such as polycrystalline diamond (PCD) and cubic boron nitride (CBN) are being increasingly employed in the industry for hard- metal parts finishing due to their benefits in terms of reduction in the operation time, the machining of com- plex geometries and in the elimination of cooling lubri- cants. The selection of PCD or CBN tools is associated to the binder phase content, typically cobalt, of the workpiece w1x. Therefore, for Co contents lower than 18 wt.%, PCD is a better option than CBN due to its higher abrasion resistance. However, binder contents above 18 wt.% produce an increase of the carbon solubility in the PCD tool leading to detrimental effects in its wear resistant properties. Therefore, CBN with a higher ther- mal and chemical stability than PCD is used for Co contents above 18 wt.%. Chemical vapour deposited (CVD) diamond brazed tools can be an excellent alter- nativetobothPCDandCBNonesforhardmetalturning, because they are harder than CBN tools, and present *Corresponding author. Tel.: q351-234370243; fax: q351- 234425300. E-mail address: rsilva@cv.ua.pt (R.F. Silva). betterchemicalandthermalstabilitythanPCDmaterials. Thus, CVD could be used for machining hardmetal workpieces with different ranges of hardness, WC grain size and Co content without need to have several types of cutting tools. Despite many works can be found concerning the use of CVD diamond tools for turning different workpiece materials such as metal-matrix composites w2–4x, alu- minium alloys w5–7x or carbon fibre reinforced carbon composites w8x, only very few papers are related to the machining of hardmetal materials w9,10x. The increasing degradation of a cutting tool during the machining operation will lead to a worsening of the workpiece surface finishing. The limit where that deg- radation starts to affect the workpiece finishing can be detected in situ by monitoring the cutting forces during the turning process. Therefore, the accuracy of machin- ing operations will be improved, and at the same time the tool and the workpiece analysis after each run is avoided. Although there are some works devoted to the establishment of a relationship between the tool wear and cutting forces w11,12x, none of them refers to hardmetal turning with CVD diamond tools. In the present work, CVD diamond thick free-standing films were grown and brazed onto WC-Co insert holders to be used for turning sintered hardmetal (WC-25