Abstract
The effect of sharpness angle on tool wear and the effect of tool wear on machined surface roughness were investigated in wood flour/polyethylene composite (WFPEC) peripheral up-milling using cemented tungsten carbide (TC) tools. It was shown that nose width and edge recession increased with increasing feeding length. During the milling process, the wear of the nose width was smallest for the tool with a sharpness angle of 45°, followed by tools with sharpness angles of 55° and 65°. The wear of edge recession was highest for the tool with a sharpness angle of 45°, followed by tools with sharpness angles of 55° and 65°. The nose width increased with increasing sharpness angle, the edge recession decreased with increasing sharpness angle, and the machined surface roughness increased with increasing sharpness angle after a feeding length of 40 m. The nose width had a positive effect on the machined surface roughness, and the machined surface roughness increased with increasing nose width. The edge recession had little effect on the machined surface roughness. The clearance face roughness of the worn tool increased with increasing sharpness angle. The analysis of the SEM micrographs and EDS of the clearance face of the worn tool showed that the wear mechanisms of the cemented tungsten carbide tool were oxidation and abrasion in the range tested during cutting. Thus, a slight wear of the edge recession is gained in exchange for a lower machined surface roughness by decreasing the sharpness angle.
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Tool Wear and Machined Surface Roughness during Wood Flour/Polyethylene Composite Peripheral Up- milling using Cemented Tungsten Carbide Tools
Xiaolei Guo,a,* Mats Ekevad,b Anders Grönlund,b Birger Marklund,band Pingxiang Caoa
The effect of sharpness angle on tool wear and the effect of tool wear on machined surface roughness were investigated in wood flour/polyethylene composite (WFPEC) peripheral up-milling using cemented tungsten carbide (TC) tools. It was shown that nose width and edge recession increased with increasing feeding length. During the milling process, the wear of the nose width was smallest for the tool with a sharpness angle of 45°, followed by tools with sharpness angles of 55° and 65°. The wear of edge recession was highest for the tool with a sharpness angle of 45°, followed by tools with sharpness angles of 55° and 65°. The nose width increased with increasing sharpness angle, the edge recession decreased with increasing sharpness angle, and the machined surface roughness increased with increasing sharpness angle after a feeding length of 40 m. The nose width had a positive effect on the machined surface roughness, and the machined surface roughness increased with increasing nose width. The edge recession had little effect on the machined surface roughness. The clearance face roughness of the worn tool increased with increasing sharpness angle. The analysis of the SEM micrographs and EDS of the clearance face of the worn tool showed that the wear mechanisms of the cemented tungsten carbide tool were oxidation and abrasion in the range tested during cutting. Thus, a slight wear of the edge recession is gained in exchange for a lower machined surface roughness by decreasing the sharpness angle.
Keywords: Wood flour/polyethylene composite; Cemented tungsten carbide tools; Up milling; Sharpness angle; Tool wear; Surface roughness
Contact information: a: Faculty of Material Science and Engineering, Nanjing Forestry University, Nanjing 210037, China; b: Division of Wood Science and Engineering, Luleå University of Technology, Skellefteå 93187, Sweden; *Corresponding author: youngleiguo@hotmail.com
INTRODUCTION
Wood flour/polyethylene composite (WFPEC) is one type of wood plastic composite (WPC). Currently, WFPEC is the most attractive composite because the material has advantages in terms of low cost, high strength, biodegradability, recyclability, and environmental safety (Hamdan et al. 2010; Segerholm et al. 2012). It is widely used in the construction, automotive, and packaging industries (Hong et al.2010; Klyosov 2007; Selke and Wichman 2004). With the use of WFPEC in a broadening range of applications, second processing requirements for the final product, such as turning, routing, milling, and sawing, are emerging (Saloni et al. 2011). However, the machining of wood flour reinforced plastic composites is different from that of conventional wood and wood-based materials and can cause excessive tool wear (Saloni et al. 2011). Because WFPEC contains two material phases with drastically different mechanical and thermal properties, there are complicated interactions between the matrix and the reinforcement during machining.
Cemented tungsten carbide tools consist primarily of a large volume fraction of fine grain refractory metal carbide in a metal binder (Brookes 1979). They are widely used in wood and wood-based materials cutting (Bayoumi et al. 1983). For almost three decades, the use of cemented tungsten carbide cutting tools in the wood working industry has provided significant improvements in tool life, primarily because of the superior hardness of these alloys. Recently, cemented tungsten carbide tools have been applied in the WPC cutting process. Despite their wide use in the metal and wood working industries, little information is known concerning their machinability in wood plastic composites.
Tool wear and machined surface roughness are two important aspects that reflect tool performance during the machining of composite materials. The wear of the cutting tool is the process that makes a usable tool unfit for continued use. During the cutting of materials, several wear mechanisms may simultaneously contribute to the general wear of the cutting tool. Among these wear mechanisms are gross fracture or chipping, abrasion, erosion, micro fracture, chemical and electrochemical corrosion, and oxidation (Sheikh-Ahmad 1999). The wear of a cutting tool is significantly affected by several factors during the machining process, which consist of tool geometry and cutting parameters. Alternatively, machined surface roughness is an important characteristic that describes the quality of the machined surface, which is, in most cases, a technical requirement for machined products. In addition, the surface roughness also affects several attributes of machined parts, such as adhesion, friction, and water absorption (Ayrilmis 2011; Buyuksari et al. 2010, 2011; Soury et al.2013).
The sharpness angle is the most important parameter for cutting. There is a direct influence of the sharpness angle on cutting tool strength, tool wear, and machined surface quality. The objective of this work was to investigate the effects of sharpness angle on tool wear and the effect of tool wear on machined surface roughness during cutting of WFPEC. The study of tool wear processing and the fundamental mechanisms of wear may lead to data that will indicate whether wear is truly unavoidable, and if so, a feasible means of minimizing wear during the cutting of one type of composite material, WFPEC.
EXPERIMENTAL
Materials
The WFPEC used as the test samples in these experiments was supplied by the Polyplank Company (Sweden). The samples (n = 4), with the dimensions of 1000 mm (L) × 140 mm (W) × 25 mm (T), consisted of 48 wt.% pine (Pinus sylvestris L.) wood, 13 wt.% talc, and 34 wt.% polyethylene, as well as some additives such as pigments and lubricants. The wood particles were screened through a sieve with a mesh size of 0.7 mm × 2.1 mm.
Methods
Experimental set up
Up-milling was adopted for the cutting test of tool wear using a Model TF130 milling machine manufactured by the SCM Group (Rimini, Italy) with a mechanical feed mechanism, as shown in Fig. 1. The samples were machined using a single cutting edge. The cutting head (diameter of 154 mm) was made for two blades, so a blunt counterweight was inserted into the opposing slot to balance the cutting head (Fig. 2) and avoid any effect of small differences between the teeth to maintain constant cutting conditions. The cutting edge, which consists of 10% cobalt, 89.5% tungsten carbide, and 0.5% other compounds, was provided by Sandvik Hard Materials (Sandviken, Sweden). The Vickers hardness (HV30) was 1600 and the Rockwell hardness (HRA) was 92.1.
Fig. 1. The SCM milling machine used in this study