SCM440(ISO:42CrMo4), alloy steel for structuring, is widely used material in industry fields such as power bolt, crankshaft, gears, couplings, etc. Heat treatment is mainly conducted for SCM440’s hardness. Turning operation is called hard turning, which makes its hardness HrC 45 or more. This hard t...
SCM440(ISO:42CrMo4), alloy steel for structuring, is widely used material in industry fields such as power bolt, crankshaft, gears, couplings, etc. Heat treatment is mainly conducted for SCM440’s hardness. Turning operation is called hard turning, which makes its hardness HrC 45 or more. This hard turning has been replacing grinding process and drawing more attentions. Because it has various advantages such as reducing the processing time and cost, as well as using environmentally friendly process of dry machining. Suitable tools for hard turning are ceramic tools, PCD tools, CBN tools, and CBN tools are most widely used. Thus, studies on the cutting characteristics of hard turning, the performance of CBN tools, and the theoretical analysis for these have been active abroad as well as locally, yet, there are still many things to be identified. In this paper, changes in cutting resistance and surface roughness in accordance with changes in cutting conditions were identified utilizing Low CBN tool and Low CBN tool coated with TiN coating and TiAlN coating during hard turning operations. And tool wear trends of Low CBN tools have been observed through SEM photographs and EDX analysis. In addition, in order to determine the tools’ life span effect for different types of coatings, factors affecting on the cutting length until the end of tools’ life were identified using the Taguchi method analysis, which is the design of experiments. When optimum processing conditions were selected, the extent of the tools’ life span is extended and the extent of the economic benefits were obtained and analyzed. The fact whether the tools’ wear and failure could be detected using neural networks was identified and the following conclusions could be deduced: 1. The thrust force and the cutting force tended to increase with the feed rate at an identical cutting speed because of the increase of cutting volume and the thrust force has shown greater increase. 2. At an identical feed rate, there was no change in the cutting force or the thrust force even though the cutting speed has been increased. But it is considered to be appropriate to set the maximum cutting speed at 250m/min or less. Because the tools’ life span will be shortened if the cutting speed is increased in order to reduce the processing time. 3. When Low CBN, TiN coated tool, TiAlN coated tool were compared under identical cutting conditions, TiAlN coated cutting tools has the highest cutting resistance and TiN coated cutting tools had the lowest among the three tools. 4. As for surface roughness, Low CBN appeared to be the most excellent next to the TiN coated tool and the TiAlN coated in order. All three types of tools were corresponding to 0.2~1.6㎛ which is the average surface roughness of precise manufacturing. They were found to be excellent surface roughness which even can replace grinding. 5. Through SEM photographs and EDX analysis of Low CBN tools, it was confirmed that abrasive wear occurs on flank face and adhesive wear mainly occurs on crater. And these wears were reduced in the TiN coating tools and TiAlN coating tools. 6. The maximum cutting speed appeared to be 150m/min or less in order to prevent tool breakage by chipping wear during interrupted cutting. And it was observed that there’s no chipping wear prevention effect by coating treatment. 7. Analyzing through design of experiments of Taguchi method, it appeared advantageous to set the feed rate slow when the cutting length is considered, while it is advantageous to set the feed rate fast when considering the cutting volume. In addition, the cutting speed was confirmed to be the biggest factor affecting the tools’ life span compared to the feed rate or the cutting tools. 8. When the cutting length was compared until the condition has reached Taguchi Method’s optimal cutting conditions as cutting speed of 176m/min, feed rate of 0.090mm/rev. Frank wear length of 0.15mm, tools’ life span has improved by 25%, 37.5% respectively for the TiN coated tools, TiAlN coated tools compared to Low CBN tools. 9. From economic standpoint of view, the economic benefit of coating treatment was judged to be sufficient. With 10% of Low CBN coating cost, the life span has improved by 100% and 150% respectively for the TiN coated tools, TiAlN coated tools in the case 4 corner insert. 10. The possibility for practically applying field’s automation or unmanned process was confirmed if a back-propagation neural network is used, whose input data are based on the tools’ wear length through the tool microscope and cutting resistance signal from the tool dynamometer. Key word : SCM440, Hard Turning, Low CBN, TiN coating, TiAlN coating, SEM, EDX, frank wear, crater wear, Taguchi method, neural network technology.
SCM440(ISO:42CrMo4), alloy steel for structuring, is widely used material in industry fields such as power bolt, crankshaft, gears, couplings, etc. Heat treatment is mainly conducted for SCM440’s hardness. Turning operation is called hard turning, which makes its hardness HrC 45 or more. This hard turning has been replacing grinding process and drawing more attentions. Because it has various advantages such as reducing the processing time and cost, as well as using environmentally friendly process of dry machining. Suitable tools for hard turning are ceramic tools, PCD tools, CBN tools, and CBN tools are most widely used. Thus, studies on the cutting characteristics of hard turning, the performance of CBN tools, and the theoretical analysis for these have been active abroad as well as locally, yet, there are still many things to be identified. In this paper, changes in cutting resistance and surface roughness in accordance with changes in cutting conditions were identified utilizing Low CBN tool and Low CBN tool coated with TiN coating and TiAlN coating during hard turning operations. And tool wear trends of Low CBN tools have been observed through SEM photographs and EDX analysis. In addition, in order to determine the tools’ life span effect for different types of coatings, factors affecting on the cutting length until the end of tools’ life were identified using the Taguchi method analysis, which is the design of experiments. When optimum processing conditions were selected, the extent of the tools’ life span is extended and the extent of the economic benefits were obtained and analyzed. The fact whether the tools’ wear and failure could be detected using neural networks was identified and the following conclusions could be deduced: 1. The thrust force and the cutting force tended to increase with the feed rate at an identical cutting speed because of the increase of cutting volume and the thrust force has shown greater increase. 2. At an identical feed rate, there was no change in the cutting force or the thrust force even though the cutting speed has been increased. But it is considered to be appropriate to set the maximum cutting speed at 250m/min or less. Because the tools’ life span will be shortened if the cutting speed is increased in order to reduce the processing time. 3. When Low CBN, TiN coated tool, TiAlN coated tool were compared under identical cutting conditions, TiAlN coated cutting tools has the highest cutting resistance and TiN coated cutting tools had the lowest among the three tools. 4. As for surface roughness, Low CBN appeared to be the most excellent next to the TiN coated tool and the TiAlN coated in order. All three types of tools were corresponding to 0.2~1.6㎛ which is the average surface roughness of precise manufacturing. They were found to be excellent surface roughness which even can replace grinding. 5. Through SEM photographs and EDX analysis of Low CBN tools, it was confirmed that abrasive wear occurs on flank face and adhesive wear mainly occurs on crater. And these wears were reduced in the TiN coating tools and TiAlN coating tools. 6. The maximum cutting speed appeared to be 150m/min or less in order to prevent tool breakage by chipping wear during interrupted cutting. And it was observed that there’s no chipping wear prevention effect by coating treatment. 7. Analyzing through design of experiments of Taguchi method, it appeared advantageous to set the feed rate slow when the cutting length is considered, while it is advantageous to set the feed rate fast when considering the cutting volume. In addition, the cutting speed was confirmed to be the biggest factor affecting the tools’ life span compared to the feed rate or the cutting tools. 8. When the cutting length was compared until the condition has reached Taguchi Method’s optimal cutting conditions as cutting speed of 176m/min, feed rate of 0.090mm/rev. Frank wear length of 0.15mm, tools’ life span has improved by 25%, 37.5% respectively for the TiN coated tools, TiAlN coated tools compared to Low CBN tools. 9. From economic standpoint of view, the economic benefit of coating treatment was judged to be sufficient. With 10% of Low CBN coating cost, the life span has improved by 100% and 150% respectively for the TiN coated tools, TiAlN coated tools in the case 4 corner insert. 10. The possibility for practically applying field’s automation or unmanned process was confirmed if a back-propagation neural network is used, whose input data are based on the tools’ wear length through the tool microscope and cutting resistance signal from the tool dynamometer. Key word : SCM440, Hard Turning, Low CBN, TiN coating, TiAlN coating, SEM, EDX, frank wear, crater wear, Taguchi method, neural network technology.
Keyword
#Hard Turning Low CBN coating tool
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