Effect of Multi-Coats of Cutting Tools on Surface Roughness in Machining AISI 1045 Steel

In this study, orthogonal machining tests in dry turning method are performed on (AISI 1045 St.), in order to examine the influences for the type and number of coatings on surface roughness. The cutting tools used are (TiN, TiN/TiC, and TiN/Al 2 O 3 /TiC); multiple layers coated cemented carbide inserts. The tests are performed at five different cutting speeds (80, 112, 155, 220 and 300) m/min, while the feed rates are kept to be (0.08, 0.11, 0.14, 0.16 and 0.2) mm/rev respectively, at constant depth of cut and tool geometry. The results showed that (TiN/TiC) coated cutting tools gave best results for surface finish compared with TiN/Al 2 O 3 /TiC , TiN and uncoated tool, for all the selected machining conditions. The experimental results showed that, when the cutting speed is increased from (80-300)m/min and feed rate is reduced by (250%), the values of surface roughness is decreased by: (20%) for uncoated tool insert ,(27%) for single coated layer insert (TiN), (55%) for double coated layer insert (TiN/TiC) and (49%) for triple coated layer insert (TiN/Al 2 O 3 /TiC).

The surfaces are classified according to tactile feeling and the naked eye; Surface qualities are designated in four different forms: coarse, rough, medium and fine.Kopac and Bahor (1999)[3], studied the changes in surface roughness depending on the process conditions in tempered (AISI 1060 and 4140 steels), found cutting speed to be the most dominant factor if the operating parameters were chosen randomly.They also reported that, for both steel types, the cutting tools with greater radius cause smaller surface roughness values.Similar studies were published by Yuan et al. (1996)[4] and Eriksin and Ozses (2002)[5].Gokkaya et al. (2004)[6] investigated the effect of cutting tool coating material on the surface roughness of (AISI 1040 steel).In their study, the lowest average surface roughness was obtained using cutting tool with coated (TiN).A (176%) improvement in surface roughness was provided by reducing feed rate by (80%) and a (13%) improvement in surface roughness was provided by increasing the cutting speed by (200%).The cutting tool is the most critical part of the machining system today approximately (85%) of carbide tools are coated, almost exclusively by the chemical vapor deposition (CVD) process [1].Yusuf Sahin et al. (2004)[ 7] studied the effect of PVD coated ceramic tools on surface roughness in turning of (AISI 1040 carbon steel) under different cutting conditions of cutting speed, feed rates and depth of cut.The established equations clearly show that the feed rate has greater effect on surface roughness followed by the cutting speed.However, it is increased with increasing the feed rate but decreases with increasing the cutting speed and the depth of cut.

2-Surface Roughness Parameters
Surface roughness could be specified in many different parameters.Due to the need for different roughness parameters were developed.Some of the popular parameters of surface finish parameters in a wide variety of machining operations, a large number of newly developed surface specifications are described as follows: where R a = the arithmetic average deviation from the mean line.L = the sampling length.y = the ordinate of the profile curve.
It is the arithmetic mean of the departure of the roughness profile from the mean line.An example of Eng.&Tech.Vol.26.No.12 ).The machining conditions are selected as recommended in the standard (ISO 3685).
Cutting tools are made of tungsten based cemented carbide (P20), surface roughness was measured by a (Talysurf4) and measurements were repeated (3) times.To measure the surface roughness formed by machining the workpieces, the cut-off length was taken as (0.8) mm and the sampling length as (5.6) mm.For the turning operations, a (TOS) type (SN50) universal lathe was used under orthogonal machining conditions.Specifications of the lathe are mentioned in table (4).

4-Results and Discussion
This paper demonstrated that the cutting speed had a significant impact on surface roughness despite its complex nature of impact.In a certain range, the surface roughness improves as the cutting speed increases.
However, the surface roughness will deteriorate due to many reasons as well as chatter when speeds reach a certain region, after this region, the surface roughness will be found to improve again.The average surface roughness values (R a ) obtained by orthogonal cutting conditions for five values of cutting speeds and five values of feed rates, using four different cutting tools in order to investigate the effects of coating layers on surface roughness of machined surfaces.According to the coating type and number of layers, the results show that the lowest average Eng.&Tech.Vol.26.No.12,2008Effect of Multi-Coats of Cutting Tools on Surface Roughness in Machining AISI 1045 Steel surface roughness was obtained when using double layer coated insert tool (TiN/TiC), followed by triple layer coated insert tool (TiN/Al 2 O 3 /TiC) and then by single layer coated insert tool (TiN).The highest average surface roughness is obtained in machining by uncoated cemented carbide tool tip.Table(5) shows the final results for the experimental tests needed for this paper, the table shows one hundred tests being achieved in order to select the optimum cutting conditions related to the type of coating and surface roughness.Fig (2,3,4,5and 6) shows the relation between cutting speed and surface roughness for various coated tools and uncoated one, the figures show that when the cutting speed is increased from (80 to 300)m/min , the feed rate is reduced from(0.2-0.08) mm/rev, the surface roughness is reduced by (14-24)% for uncoated tool, (23-31)% for (TiN) coated insert, (20-41)% for (TiN/TiC) coated insert, (21-32)% for (TiN/Al 2 O 3 /TiC) coated insert.The reason for the lower average surface roughness obtained from the tools coated with (TiN/TiC) could be that the insert coated with (TiN/TiC) have a higher coefficient of friction and thermal conductivity compared with the other (3) tools.The roughness values obtained are high, possibly due to the ductility of the (AISI 1045 Steel).The improvement in surface roughness depending on the augmentation of cutting speed is an expected feature and improving the surface roughness by increasing the cutting speed is a widespread method according to the literature [1, 11, 12, 13, and 14].The improvement in surface roughness can be explained due to easier deformation process, because of the increasing temperature at high speeds, i.e. the easy deformation of workpiece type at the cutting side beyond the tip radius, and chip flow zone occurring at these high temperatures.For double layer coated insert tool (TiN/TiC), at low feeds (0.08)mm/rev, and low cutting speed (80)m/min, the considerable improvement is achieved from R a =(3.2 -1,9) µm, i.e. (41%) by increasing the cutting speed till it reaches to (300) m/min i.e. by about (275% ), that reveals the effect of cutting speed on the surface roughness clearly.Table (5) shows that the surface roughness is affected by the cutting tool coating material, cutting speed and feed rate.The surface roughness values obtained by using (TiN/TiC) coated tool is lower than those obtained by using (TiN/Al 2 O 3 /TiC), (TiN) coated, and uncoated cutting tool.Again, this difference is more considerable at lower cutting speeds.The better surface features of (TiN/TiC) coated tools may be due to the smaller friction coefficient of this type than the others, and the developing temperature.At lower cutting speeds (80 m/min), depending on the developing low temperatures at the tool-chip interface region, the developing high temperatures at high speeds facilitate the occurrence of flow zone, Consequently, the differences between the surface roughness values obtained by using each of the (4) sets are decreasing.

Fig
Fig.(4): Relation between cutting speed and surface roughness for various coated tools at (S= 0.14) mm/rev.