Influence of the undeformed chip cross section in finishing turning of Inconel 718 with PCBN tools

Influence of the undeformed chip cross section in finishing turning of Inconel 718 with PCBN tools

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Procedia CIRP 00 (2018) 000–000

www.elsevier.com/locate/procedia

Procedia CIRP 00 (2017) 000–000 Procedia CIRP 77 (2018) 122–125 www.elsevier.com/locate/procedia

8th CIRP Conference on High Performance Cutting (HPC 2018)

28th CIRP Design Conference, Maysection 2018, Nantes, France Influence of the undeformed chip cross turning of in finishing Inconel 718 with PCBN tools. A new methodology to analyze the functional and physical architecture of a b a Diego Infante-García *, an Joséassembly Diaz-Álvarez , José-Luis Canteroafamily , Ana Muñoz-Sánchez , existing products for oriented product identification a

Maria-Henar Miguéleza PaulEngineering. Stief *, Universidad Jean-Yves Alain Etienne, Ali Siadat(Madrid), 28911, Spain; Department of Mechanical CarlosDantan, III de Madrid, Avda. de la Universidad 30 Leganés

a

b Department of Aerospace Engineering. Universidad Carlos III de Madrid, Avda. de la Universidad 30 Leganés (Madrid), 28911, Spain; École Nationale Supérieure d’Arts et Métiers, Arts et Métiers ParisTech, LCFC EA 4495, 4 Rue Augustin Fresnel, Metz 57078, France * Corresponding author. Tel.: +3-491-624-8754; E-mail address: [email protected]

* Corresponding author. Tel.: +33 3 87 37 54 30; E-mail address: [email protected]

Abstract

Abstract

Inconel 718 is a difficult-to-cut material due to its poor thermal conductivity, severe work hardening and high strength at high temperature. Machining of Inconel 718 towards with Polycrystalline Cubic Boron Nitride (PCBN) tools atDue hightospeed in finishing operations In today’s business environment, the trend more product variety and customization is unbroken. this development, the need of mayand leadreconfigurable to brittle fracture in the cutting because of the lowvarious toughness of PCBN insertsfamilies. in comparison to other cutting production materials. agile production systemstool emerged to cope with products and product To design and optimize PCBN as inserts shaped with the large tip radius arematches, commonly usedanalysis to remove smallarevalues of Indeed, depth ofmost cut of in the order to counteract these systems well as to choose optimal product product methods needed. known methods aim to aspects. When applying multipass turning strategies with this configuration, a significant peak may occur in the response of the analyze a product or one product family on the physical level. Different product families, however, may differ largely in terms of the number and machining forces at This the end the pass in the second and successive This fact mayfamily also be present when turning inner nature of components. fact of impedes an efficient comparison and choice passes. of appropriate product combinations for the production profiles or into a shoulder. The increase of the undeformed chip cross section and the high specific cutting forces of Inconel 718 system. A new methodology is proposed to analyze existing products in view of their functional and physical architecture. The aim is to cluster giveproducts rise to this peakassembly of the machining forces. In thisfor work, different tests involving multipass turning Inconel 718 have these in new oriented product families the optimization of existing assembly lines finishing and the creation of in future reconfigurable been carried out Based in order to study theChain, magnitude of thestructure peak forces different cutting conditions. A PCBN toolareatidentified, high cutting assembly systems. on Datum Flow the physical of thefor products is analyzed. Functional subassemblies and withanalysis coolantishas been employed feed rates depths of cut. On the(HyFPAG) other hand, an output analytical study of the aspeed functional performed. Moreover,ata different hybrid functional andand physical architecture graph is the which depicts similarity between by providing design support both, performed production in system and product designers. An machining illustrative undeformed chipproduct sectionfamilies at the end of each turning pass hasto been orderplanners to determine its relation to the example of a nail-clipper is used explainthat the proposed methodology. An industrial caseare study on tworelated productto families of steering columns of peak forces. The results havetoshown these peaks in the machining forces strongly the tool tip radius and the thyssenkrupp Presta France is then carried out at to the giveend a first of the proposed approach. cutting parameters. The machining force of industrial a turningevaluation pass can increase significantly their values during a short interval. ©Consequently, 2017 The Authors. byinfluence Elsevier B.V. this Published effect may tool wear progression leading to a premature breakage of the tool. Peer-review responsibility of the scientific of theaccess 28th CIRP Conference 2018. license © 2018 Theunder Authors. Published by Elsevier Ltd. committee This is an open articleDesign under the CC BY-NC-ND © 2018 The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/3.0/) This is anAssembly; open access article underFamily the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) Keywords: Design method; identification Peer-review under responsibility of the International Scientific Committee of the 8th CIRP Conference on High Performance Cutting (HPC Selection and peer-review under responsibility of the International Scientific Committee of the 8th CIRP Conference on High Performance 2018). Cutting (HPC 2018). Keywords: Inconel; undeformed chip section; PCBN.

1. Introduction

of the product range and characteristics manufactured and/or assembled in this system. In this context, the main challenge in Due to the fast development in the domain of modelling and analysis is now not only to cope with single 1. Introduction and an ongoing trend of digitization and Finishingaoperations of Inconel 718 usually performed with communication products, limited product range orare existing product families, Polycrystalline Cubic Boron Nitride (PCBN) using low depths digitalization, manufacturing enterprises are facing important but also to be able to analyze and to compare products to define Inconel in 718today’s is a nickel-based superalloy owing elevated new of cut (d) and feed rates (f) be [3].observed Under these conditions, it has challenges market environments: a continuing product families. It can that classical existing resistance to corrosion and high fatigue, creep and tensile been experimentally tested that a significant peak in the tendency towards reduction of product development times and product families are regrouped in function of clients or features. strength at high temperature. Therefore, it is widely employed machining forces may occur at the end of the pass in the second shortened product lifecycles. In addition, there is an increasing However, assembly oriented product families are hardly to find. in the aeronautical industry under andOnsuccessive when products applyingdiffer multipass demand of customization, beingforat critical the samecomponents time in a global the productpasses family level, mainly turning in two extreme conditions, such as blades or disks in gas turbines [1]. strategies. This phenomenon is related to the undeformed competition with competitors all over the world. This trend, main characteristics: (i) the number of components and (ii)chip the Furthermore, Inconelthe 718development is considered from one ofmacro the most section increase at (e.g. the end of the pass and theelectronical). high specific which is inducing todifficult micro type of components mechanical, electrical, to cut materials duediminished to its poorlot thermal severe cutting forces of Inconel 718 (see Figure 1). Furthermore, the markets, results in sizes conductivity, due to augmenting Classical methodologies considering mainly single products work hardening and high strength at high temperature [2]. product varieties (high-volume to low-volume production) [1]. or solitary, already existing product families analyze the To cope with this augmenting variety as well as to be able to product structure on a physical level (components level) which 2212-8271 possible © 2018 The optimization Authors. Publishedpotentials by Elsevier Ltd. an open access causes article under the CC BY-NC-ND license an efficient definition and identify in This the is existing difficulties regarding (http://creativecommons.org/licenses/by-nc-nd/3.0/) production system, it is important to have a precise knowledge comparison of different product families. Addressing this Peer-review of the International Scientific Committee of the 8th CIRP Conference on High Performance Cutting (HPC 2018).. 2212-8271 ©under 2018responsibility The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) Selection © and peer-review under responsibility of the International Scientific Committee of the 8th CIRP Conference on High Performance Cutting 2212-8271 2017 The Authors. Published by Elsevier B.V. (HPC 2018). Peer-review under responsibility of the scientific committee of the 28th CIRP Design Conference 2018. 10.1016/j.procir.2018.08.246

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Diego Infante-García et al. / Procedia CIRP 77 (2018) 122–125 Infante-García et al./ Procedia CIRP 00 (2018) 000–000

large tip radius usually used in PCBN tools produces a high variation of the undeformed chip cross section. Machining forces has a significant value from the point of view of the workpiece surface integrity and tool wear when analysing finishing operation. Furthermore, a rapid increase of the machining forces may cause premature tool breakage because of the relative PCBN tool brittleness or may induce plastic deformations in the workpiece [4]. The prediction of the machining forces is usually performed by the Kienzle force law [5], based on the specific cutting force obtained through the calculation of the undeformed chip section. However, it has been demonstrated that the Kienzle force law is only valid if the ratio between the width and thickness of the undeformed chip section is higher than four [6]. On the other hand, the approach developed by Meyer et al. [7], based on the Altintas force law [8], can be satisfactorily applied to a cutting ratio smaller than four. This model takes into account the undeformed chip section geometry by calculating the effective length of the cutting edge (L) and the average undeformed chip thickness (hm). In this work, tests of multipass turning operations in Inconel 718 with a PCBN tool have been carried out in order to study the magnitude of the peak forces and the tool wear progression at the end of each pass for different cutting conditions. Furthermore, the undeformed chip section increase has been calculated and related to machining peak force values. Finally, the peak machining force values have been analysed following the model proposed by Denkena and Köhler [6]. 2. Materials and Methods Inconel 718 hardened by solution heat treatment and aged (round bar: diameter 100mm and length 130mm) was the workpiece material employed for all the experiments. The chemical composition is 53.02% Ni, 18.49% Cr, 18.12% Fe, 5.4% Nb, 3.06% Mo, 0.96% Ti, 0.55% Al, 0.1% Co, 0.06% Si, 0.05% Cu, 0.06% Mn and 0.03% C. The mechanical properties of the alloy are shown in Table 1. Table 1. Mechanical properties of Inconel 718. Property Tensile strength

1210 MPa

Yield strength

1110 MPa

Density

8.19 g/cm3

Hardness

42 HRC

Tests have been carried out using rhomboid shaped inserts of PCBN supplied by Mitsubishi. The insert has CBN content of 60%, 4 cutting edges, grain size around 2 microns and TiN binder with alumina whisker reinforcement. The tool geometry is shaped with nose radius (rε) of 0.8mm mounted on an 80° rhombic negative insert, cutting edge radius of 15 microns and chamfer honing (0.05mm width and an angle of -15°). The insert was fixed in the external tool holder PCLNR2525M12. After mounting in the tool holder, the inserts displayed principal and minor cutting edge angles of 95° and 5° respectively, a clearance angle of 6° and a normal rake and inclination angles of -6°. Machining experiments were carried

123

out using a lathe Pinacho Smart 6/615 equipped with a dynamometer (Kistler 9257B) able to measure the forces in 3 axes. The forces (Fi) were measured in the three axes aligned with cutting force (Fc), feed force (Ff) and passive force (Fp). All experiments were conducted in a configuration where the tool displacement direction was parallel to the lathe axis into a shoulder with constant cutting speed. The cutting speed (Vc) was 300m/min and coolant was supplied at a constant pressure of 7.5bar. The shoulder was previously machined with the same tool in order to leave a difference of at least 5mm between both diameters. The machining length was 10mm for all the tests. The selected cutting parameters cover the range normally used for finishing operations in superalloys. Table 2. Test matrix (symbol √ denotes test undertaken). Tool material

f [rev/min]

d=0.15mm

d=0.25mm

d=0.5mm

0.07







0.1







0.15







PCBN

The undeformed chip geometry is taken into account to evaluate the machining forces, the calculation of the undeformed chip cross section (A0), effective length of the cutting edge and average undeformed chip thickness are necessary. According to [6,7], the following equations are applied:

4r 2  f 2  1   A0  d· f  · f · r   3  2  

(1)

r d 1  eff  arccos  2 r

(2)

L  2 eff ·r

(3)

A L

(4)

hm 

Computer-aided design software was used to analyse the undeformed chip cross section increase. Fig. 1 shows the description of the undeformed chip cross section at the end of the pass when the tool approaches the shoulder.

Fig. 1. Cross section of the tool and undeformed chip section as the tool approaches the shoulder for rε =0.8mm, f=0.15mm/rev and d=0.25mm.

Diego Infante-García et al. / Procedia CIRP 77 (2018) 122–125 Infante-García et al./ Procedia CIRP 00 (2018) 000–000

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Furthermore, the machining force values have been analysed by calculating the incremental machining forces (Fi’) (Eq. 5) [7]. In addition, following the approach of Meyer et al. [7], the Altintas force law expressed in terms of the average undeformed chip thickness (Eq. 6) has been used to describe the interrelation of Fi’ and hm.

Fi L

(5)

 Fi ' Kic ·hm  Kie

(6)

Fi ' 

The edge cutting coefficients (Kie) are related to the friction along the effective cutting length. The cutting force coefficients (Kic) describe the force component due to shearing of the work material and chip-rake face friction [7].

Table 3. Values of the undeformed chip section increase in percentage terms. ∆A0-max /A0 [%]

d=0.15mm

d=0.25mm

d=0.5mm

f=0.07mm/rev

366.51

227.19

104.39

f=0.1mm/rev

325.48

209.85

98.81

f=0.15mm/rev

265.98

183.73

90.45

Fig. 3 shows the relative differences of the machining forces (∆Fi/Fi0) against the relative differences of the undeformed chip section. As Fig. 3 indicates, the feed force component and the passive component have undergone the highest and the lowest increase in relative terms, respectively. Furthermore, the relationship is not completely direct between both variables. However, it exists a linear relationship between ∆Fi/Fi0 and ̅̅̅2̅ = 0.91 ± 0.05). ∆A0-max/A0 (𝑅𝑅 400

3. Results

350 300 250

∆Fi/Fi0 [%]

All the results presented in this section are obtained using fresh tools. As it is shown in Fig. 2, the machining forces suddenly increase at the end of the pass. This fact has been observed in all tests conducted, but with different magnitude and interval. The highest increment experimented was for the case of feed rate 0.07mm/rev and cutting depth 0.15mm where the machining forces increased up to 387%.

3

200 150 100 50

0

80

130

180

230

280

330

380

∆A0-max/A0 [%] ∆Fc/Fco

∆Ff/Ffo

∆Fp/Fpo

Linear (∆Fc/Fco)

Linear (∆Ff/Ffo)

Linear (∆Fp/Fpo)

Fig. 3. Graphic of the relative differences of the machining forces and undeformed chip section.

Fig. 2. Machining force signal during three different tests.

Table 3 shows the relative differences of the undeformed chip section (∆A0-max/A0), in terms of percentage, between the chip cross section during regular conditions (A0) and when the tool approaches the shoulder (Amax). It can be noticeable in Table 3 that ∆A0-max/A0 is higher as the depth of cut and feed rate decrease.

On the other hand, Fig. 4 displays the experimental results of the incremental machining force values against the average undeformed chip thickness for the peak forces at the end of the test (using Lmax and Amax as described in Fig. 1). For the experiments with a cutting depth of 0.5mm, the undeformed width of chip is four times higher than the undeformed chip thickness. Therefore, these results have been excluded in the calculation of the incremental machining force values. Nevertheless, the relationship of incremental machining force ̅̅̅2̅ = 0.96 ± 0.02) values shows a stronger linear tendency (𝑅𝑅 when employing the average chip thickness as described by the Altintas force law (Eq. 6).

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4. Conclusions

300 250

Fi' [N/mm]

200 150 100 50 0

125

0,04

0,06

0,08

0,1

0,12

hm [mm] Fc'

Ff'

Fp'

Linear (Fc')

Linear (Ff')

Linear (Fp')

Fig. 4. Experimental results of the maximum incremental machining force values against the average undeformed chip thickness.

The rapid development and magnitude of the peak forces influence the tool wear progression. As shown in Fig. 5, a premature notch along the cutting edge is observed after the test with cutting depth 0.5mm and feed 0.15mm/rev. The low machinability of Inconel 718 along with the brittleness of PCBN tools lead to a premature breaking of the cutting tool when this phenomenon is not taken into account in conventional turning.

Fig. 5. Tool flank face after the test with cutting depth 0.5mm and feed 0.15mm/rev.

In this paper, the influence of the undeformed chip cross section in finishing turning of Inconel 718 with PCBN inserts was investigated. The experimental results have shown that there is a significant peak in the machining forces at the end of the pass when turning into a shoulder after the second and successive passes. The main factor that contributes to the peak forces is the increase of undeformed chip cross section during a short interval. Thus, the progression of tool wear is significantly influenced. In conclusion, this effect has to be considered during the definition of the machining strategy. Regarding the magnitude of these peak forces, it has been demonstrated that the increase of the machining forces and the undeformed chip section, in terms of relative difference, is higher as the depth of cut and feed rate decrease. Furthermore, it has been established the relationship between the relative differences of the undeformed chip section and of the machining forces. On the other hand, the machining process of the peak forces can be described by taking into account the geometrical contact conditions between the tool and workmaterial and employing the Altintas force law. Acknowledgements This work was supported by the Spanish Ministry of Economy and Competitiveness and FEDER program under grant DPI2014-56137-C2-2-R. References [1] Reed R. The superalloys : fundamentals and applications. Cambridge University Press, 2006. [2] Díaz-Álvarez J, Cantero JL, Miguélez H, and Soldani X. Numerical analysis of thermomechanical phenomena influencing tool wear in finishing turning of Inconel 718. Int. J. Mech. Sci. 82; 2014. p. 161–169. [3] Cantero JL, Díaz-Álvarez J, Miguélez MH, and Marín NC. Analysis of tool wear patterns in finishing turning of Inconel 718. Wear 297, No. 1–2; 2013. p. 885–894. [4] Braghini A and Coelho RT. An investigation of the wear mechanisms of polycrystalline cubic boron nitride (PCBN) tools when end milling hardened steels at low/medium cutting speeds. Int. J. Adv. Manuf. Technol. 17, No. 4; 2001. p. 244–251. [5] Kienzle O and Victor H. Spezifische schnittkräfte bei der metallbearbeitung. Werkstattstech. und Maschinenbau 47, No. 5; 1957. p. 224–225. [6] Denkena B and Köhler J. Consideration of the form of the undeformed section of cut in the calculation of machining forces. Mach. Sci. Technol. 14, No. 4; 2010. p. 455–470. [7] Meyer R, Köhler J, and Denkena B. Influence of the tool corner radius on the tool wear and process forces during hard turning. Int. J. Adv. Manuf. Technol. 58, No. 9–12; 2012. p. 933–940. [8] Altintas Y and Engin S. Generalized modeling of mechanics and dynamics of milling cutters. CIRP Ann. - Manuf. Technol. 50, No. 1; 2001. p. 25–30.