Determining the Effective Conditions for Machining ...

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ScienceDirect Procedia Engineering 129 (2015) 116 – 120

International Conference on Industrial Engineering

Determining the effective conditions for machining fabrication procedures based on the cutting process energy patterns Karpov A.V.a*

a

Murom Institute of Vladimir State University, Orlovskaya Street, Murom, 602264, Russia

Abstract The article is devoted to the rational consumption of energy resources during the metal-cutting tools processing blanks of machine component parts in machine-building production. A scientific and methodological approach to the establishment of energy-efficient processing conditions is proposed, being based on the optimization of fabrication procedures according to new energy efficiency criterion. A study of advantages and disadvantages of known methods of fabrication procedures optimization according to the criterion of the lowest specific energy intensity has been conducted. A new integral indicator of energy efficiency of cutting operation is deefined as a ratio of constructional material specific energy intensity to the specific energy consumption in the cutting area. The methods of determining the energy efficiency figure with respect to the properties of the processed material, the behaviors of its deformation and fracture, type of formed chippings and technological purpose of processing are offered. The optimization of machining fabrication procedures with the new criterion in place permits the 1822%reduction of energy costs in the cutting area in comparison to the applied processing conditions. © 2015 The Authors. Published by Elsevier Ltd. © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license Peer-review under responsibility of the organizing committee of the International Conference on Industrial Engineering (ICIE(http://creativecommons.org/licenses/by-nc-nd/4.0/). 2015). Peer-review under responsibility of the organizing committee of the International Conference on Industrial Engineering (ICIE-2015) Keywords: Machining fabrication procedures, cutting system, optimization of fabrication procedures, energy intensity, energy efficiency, optimal cutting conditions

1. Introduction In comparison with other industries mechanical engineering is characterized by high materials consumption and energy intensity of products. The proportion of the energy component in the costs of engineering products that were manufactured previously in the Soviet Union, did not exceed 5-7 per cent, and in the last decades in Russia and some Eastern European countries the one has increased up to 20-25 per cent with the trend to further increase.The

* Corresponding author. Tel.: +7-492-347-7125; fax: +7-492-347-7128. E-mail address: [email protected]

1877-7058 © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license

(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of the International Conference on Industrial Engineering (ICIE-2015)

doi:10.1016/j.proeng.2015.12.018

A.V. Karpov / Procedia Engineering 129 (2015) 116 – 120

significant part of the manufacturing stage of machine-building productions the machining fabrication procedures occupy - they have 60-70 percent of the total labor intensity of manufacturing of machine parts. Formation of one ton of chippings is accompanied by average consumption of 450-600 kW·h of electricity, and according to this indicator the products of Russian enterprises is 1.5-2.5 times more expensive than similar products of Largest Economies of Western Europe. In Germany, Sweden, France, at the stage of development and certification of fabrication procedures, along with the criterion of the lowest costs, already a lot of decades such criteria as specific energy intensity and metal removal per power unit are applied [5, 9]. Thus, increase of machining of fabrication procedures by optimization of the energy costs to implement them is relevant task for the machine-building complex of Russia and number of European countries. However, up to now the unified methodology that permits to carry out such optimization in terms of operating production is not built up. 2. Purpose of Research To create scientific and methodological approach to defining such conditions of machining fabrication procedures under which the required quality degree of the produced surfaces, cutting tool durability and the performance will be ensured due to sufficient (minimum required) amount of power consumption. 3. Results and Discussion We think that the complex task of increase of the energy efficiency of machining fabrication procedures shall be resolved on the basis of three trends: x x x

reduction of energy consumption in the cutting area by means of both determining and applying of economic conditions of execution of each manufacturing operation, manufacturing step and tool travel; reduction of power wastes in the mechanical part of a drive of metal-cutting machinery; reduction of power wastes in the electrics of a drive of metal-cutting machinery.

The first trend is subject matter of this article, because in particular this work that is performed by the cutting tool in the cutting area, and determined by the rules of chip production, sets ultimately, the total amount of energy, consumed by the motor of the machine tool station from the mains [4]. The intensity of the cut work depends primarily on the type and physic-mechanical properties of process material. However, the constructional material is usually given by drawing of part, in consequence of which the one is uncontrollable factor as for cutting system. Except for type and properties of process material, the following factors have an effect on intensity of cutting work: the state of the surface layer of the blank, the thickness and width of the shear layer, the type and properties of tool material, geometrical parameters of active part of cutting tool, cutting conditions, characteristics of lubricating processing means and other conditions of execution and parameters of the cutting operation, which together form the group of controllable factors of cutting system. Effective values of controllable factors of any system, including cutting system, shall be determined on the basis of on optimization techniques [7, 8, 13]. Specific energy intensity of the cutting process (valid synonyms - "specific cutting work," "specific energy consumption of cutting", "density of the cutting work") numerically characterizes the quantity of energy, expended by the cutting tool to separate as chippings the unit volume of the sheared off layer of blank (preliminary ("rough") stages of processing), or to form area unit of new surface of part (final ("finishing") stages of processing) [13, 15]. Specific power consumption is, in fact, universal physical efficiency factor of the cutting operation. The less value of the specific energy intensity when maintaining the desired processing results (performance, tool life, processed surface quality) is, the more effective the values of controllable factors cutting systems are. The advantages of the specific energy intensity of the cutting operation include simplicity of its definition by means of both theoretical and experimental methods. We will give a number of disadvantages that we found at time of approbation of methods of fabrication procedures optimization in accordance with criterion of the least specific energy intensity.

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Firstly, the specific energy intensity is dimensional indicator and the one does not permit to determine what part of the energy is spent directly on the deformation and (or) the destruction of unit volume of the sheared off layer, or formation of unit area of new surface, and some portion of energy is spent on the mechanical and physic-chemical processes that inevitably accompany the chip formation. Secondly, using the factor of the specific energy intensity, it is difficult to compare the level of energy, developed in the cutting area, with the marginal energy state of constructional material that is determined by rules of its deformation and damage. Thirdly, the manipulation with specific energy intensity, represented by the ratio of cutting work to the volume of the sheared layer, assumes isotropy of material per cross-section of chippings (the outer layer of the chippings is "equaled" in the properties with near-cutter one) [11]. So, in the most energy-consuming small-scale production when the blanks with considerable allowances and lapping (rolled metal, castings, forged forgings, welded constructions) are used, the specific energy intensity of individual operating stroke shall be determined by the following ratio [6]: e

A V

N , V0

(1)

where A – is a cutting work; V – is a volume of the material, separated in the form of chippings; N – is a cutting power (work of cutting per unit time); V0 – is a productivity (volume of chippings, separated per unit time). The fourth, the specific energy intensity is proportional one to the cutting power, at that the power is assumed to be constant during the entire time of operating stroke that is true only for stationary cutting and it occurs rarely [10]. Taking into account presented comments as an integral characteristic of the effectiveness of machining, we propose the dimensionless factor K - "Energy Efficiency of the cutting operation" [4, 8]

K

'w V nc Ⱥc

'w V Wc

,

(2)

nc ³ N W dW 0

where ǻw – is a specific energy intensity of processed material; V – is a volume of processed material that was exposed; nc – is a number of cycles of cutting power changes N(Ĳ) during the tool travel; Ac – is a cutting work for time Ĳc of one cycle of power change. Applied in machine building the methods of blanks processing with metal-cutting tools it is possible to divide into 4 groups, depending on the pattern of change of cutting power during the time of tool travel: pattern 1 - steady mode (power is constant); pattern 2 - power increases monotonically up to the maximum value and then the one decreases rapidly; pattern 3 - power increases intensively up to the maximum value and then the one decreases monotonically; pattern 4 - power changes according to parabolic law. Under duration of one cycle of change Ĳɫ of cutting power, we mean either full-time of tool travel during steady mode (pattern 1), or period of time during which there is complete single change of cutting power during non-steady behavior (patterns 2-4). On the basis of the proposed schemes of change of power, the expressions of the cutting power Ac that is carried out by machining tool during Ĳɫ time that made possible to calculate factor K and thereby quantify the energy efficiency of different methods of machining. Specific energy intensity of process able material ǻw, we will interpret as a critical excess of internal energy of unit volume of the material, i.e. as the difference between the limit [u] level and initial u0 one of volumetric density of the internal energy

'w

>u @ u0 .

(3)

As basis of determination of the value of [u] for wide range of constructional materials, we put energy concept of destruction: the volume of the material is destroyed, if the accumulated in it energy has reached the limit value as a result of external influence. The body is considered as destroyed one if at least one of its local volumes of the internal energy density has increased up to critical value [u].

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Critical delta of internal energy can be determined from different points, such as with usage of indicators of thermo physical properties of the material [3, 14]: Ɍs

'w

>u @ u0 ³ ɋp U dT | ɋp U Ɍ s Ɍ 0 ,

(4)

Ɍ0

where Cp - average specific heat capacity of the material; ȡ - density; Ts - melting point; T0 - initial temperature. Calculation of the specific energy intensity of material ǻw through thermo physical properties we recommend to use for grinding [12], as well as at time of final (finishing) edge cutting machining, accompanied by the formation of continuous chip and occurrence of area of plastic contact of chippings with cutter face (cutting of blanks of lowcarbon steel or nonferrous wrought alloy, the thickness of sheared layer is 0.1-0.5 mm, cutting velocity is 300 m/min or more). Interpretation and definition of value ǻw during preliminary edge cutting machining we offer to carry out depending on the type of produced chippings, since the type of chippings is stipulated by the mechanism and intensity of deformation of the material of the sheared layer. When cutting materials with formation of shearing chip we assume ǻw that will equal to maximum density of work of tangential stresses in the conventional shear area. So, during semi finishing work of carbon and alloy-treated steel the value ǻw can be calculated as the work of tangential stresses in the conventional shear area, if we take the value of relative shear İ = 2.5:

'w W H where W

1.5 V , 1 1.7 \

(5)

0.6 V - is the resistance of the processed material against flow shear; ȥ – uniform relative necking of 1 1 .7 \

material. The proposed figure of energy efficiency of the cutting operation Ʉ meets requirements, maintained as to the criteria of fabrication procedures optimization. Firstly, this figure represents the "Energy Efficiency" of the cutting operation and, consequently, the one has the physical meaning. Secondly, it is simply and unambiguously described in mathematical form. Third, the one can be reduced to the objective function of K ĺ max pattern, the arguments of which are the controllable factors of cutting system. Thus, the optimization of machining fabrication procedures per K ĺ max criterion permits to determine the energy-saving values, driven by factors of cutting operation. In terms of K figure it is possible to compare the effectiveness of alternative methods of surface treatment, design the optimal structure of fabrication procedure of manufacturing of part. With respect to the individual manufacturing step or operating stroke it is possible to assign the brand of tool material, the values of the geometric parameters of active part of cutting tool, cutting depth, feed velocity, cutting velocity, and other conditions, related to the highest value of K. Algorithm of optimization per criterion of the highest energy efficiency of the cutting operation was implemented by us in the form of software package in Delphi environment, when used in respect of lathe turning, drilling, milling of blanks made of carbon and alloy-treated steels, gray and ductile iron. 4. Conclusion Fulfillment of K ĺ max condition at the preliminary stages of processing corresponds to such values of the geometric parameters of active part of cutting tool and cutting parameters under which due to minimum required energy costs, it is possible to provide required performance and durability of machining tool. Fulfillment of K ĺ max condition at the finishing stages of processing corresponds to such values of the geometric parameters of active part of cutting tool and cutting parameters under which due to minimum required energy costs, it is possible to provide required quality rating of machined surface of part. Power consumption reducing in the cutting area at time of switch to the optimal cutting conditions runs to 1822% in comparison with used at present time technological conditions of specified processing techniques.

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