Trochoid milling of carbon fibre-reinforced plastics (CFRP)

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Procedia CIRP 00 (2018) 000–000

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Procedia CIRP 00 (2017) 000–000 Procedia CIRP 77 (2018) 375–378 www.elsevier.com/locate/procedia

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

Trochoid 28th milling of carbon fibre-reinforced plastics CIRP Design Conference, May 2018, Nantes, France (CFRP) a Geiera,the *, Tibor Szalaya, István A new methodologyNorbert to analyze functional and Biró physical architecture of Budapest University of Technology and Department of Manufacturing Scienceproduct and Engineering,family Egry J. Streetidentification 1., Budapest 1111, Hungary existing products forEconomics, an assembly oriented * Corresponding author. Tel.: +36-1-436-2641. E-mail address: [email protected] a a

Paul Stief *, Jean-Yves Dantan, Alain Etienne, Ali Siadat Abstract École Nationale Supérieure d’Arts et Métiers, Arts et Métiers ParisTech, LCFC EA 4495, 4 Rue Augustin Fresnel, Metz 57078, France fibre-reinforced (CFRP) hasE-mail good address: specific [email protected] mechanical properties, it is, therefore, an often used structural material in the high*Carbon Corresponding author. Tel.:plastic +33 3 87 37 54 30;

tech industries. Due to the anisotropy and inhomogeneity of CFRP, the machining properties are highly depending on the cutting directions. Based on previous experimental works, a new trochoid tool patch was developed in order to minimise cutting force and uncut fibres when milling unidirectional CFRP. The main objective of the present work is to test and analyse the effect of the special trochoid milling technology on the quality parameters (surface roughness and characteristics of uncut fibres) of machined unidirectional CFRP specimens. The machining Abstract experiments were analysed using digital image processing (DIP) method. The influence of the chosen independent variables (cutting tool and patch)business were analysed at fixedthe process (cutting speed, feedand rate,customization depth of cut).isItunbroken. was foundDue that to thethis quality of the machined edge Intool today’s environment, trend parameters towards more product variety development, the need of is better the new trochoid milling technology is applied. agile and when reconfigurable production systems emerged to cope with various products and product families. To design and optimize production © 2018 as The Authors. Published Elsevier Ltd. This is an open access articlemethods under the BY-NC-ND license systems well as to choose theby optimal product matches, product analysis areCC needed. Indeed, most of the known methods aim to © 2018 The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/3.0/) analyze a product or one product family on the physical level. Different product families, however, may differ largely in terms of the number and This is an open access article under the International CC BY-NC-ND licenseCommittee (https://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the Scientific of the 8th CIRP Conference on Highcombinations Performance for Cutting (HPC nature of components. This under fact impedes an efficient and choice of appropriate family thePerformance production Selection and peer-review responsibility of thecomparison International Scientific Committee of product the 8th CIRP Conference on High 2018). system. new 2018). methodology is proposed to analyze existing products in view of their functional and physical architecture. The aim is to cluster CuttingA(HPC these products in new assembly oriented product families for the optimization of existing assembly lines and the creation of future reconfigurable Keywords: CFRP; trochoid milling; machinability; uncut surface roughness assembly systems. Based on Datum Flow Chain, thefibres; physical structure of the products is analyzed. Functional subassemblies are identified, and a functional analysis is performed. Moreover, a hybrid functional and physical architecture graph (HyFPAG) is the output which depicts the similarity between product families by providing design support to both, production system planners and product designers. An illustrative example of a nail-clipper is used to explain the proposed methodology. An industrial case study on two product families of steering columns of 1. Introduction compression end mill. They showed that the roughness in thyssenkrupp Presta France is then carried out to give a first industrial evaluation of the proposed approach. climb milling is lower than that in down milling. Wang et al. © 2017 The Authors. Published by Elsevier B.V. Carbon fibre-reinforced polymer (CFRP) is widely used in [5] analysed burr formation mechanisms in CFRP and showed Peer-review under responsibility of the scientific committee of the 28th CIRP Design Conference 2018.

the high-tech industries. However, it is difficult-to-cut due to that the fibre cutting angle is a key factor for determining the wearburr formation. They, as well as Slamani et al. [6] effect of the carbon fibres [1, 2]. Fibre-cutting-angle (θ) is an characterised the machined CFRP edge-damages with the independent variable to describe the effect of the anisotropy distance from the milled edge to the free end of the uncut and inhomogeneity of such long-fibre-reinforced composite fibres. 1. Introduction of the product range and characteristics manufactured and/or materials [3]. It can be defined by two ways: θcc is the angle assembled in this system. In this context, the main challenge in between the cutting speed (vcc) and the direction of the fibres Due to the fast development in the domain of modelling and analysis is now not only to cope with single (k), or θff, which is the angle between the feed rate (vff) and the communication and an ongoing trend of digitization and products, a limited product range or existing product families, direction of the fibres (k). In the case of orthogonal cutting of digitalization, manufacturing enterprises are facing important but also to be able to analyze and to compare products to define unidirectional carbon fibre-reinforced polymer (UD-CFRP) challenges in today’s market environments: a continuing new product families. It can be observed that classical existing composites, the θcc is constant during machining, as can be tendency towards reduction of product development times and product families are regrouped in function of clients or features. seen in Fig.1. However, in the case of milling, θcc is alternate, shortened product lifecycles. In addition, there is an increasing However, assembly oriented product families are hardly to find. because the angle, how the cutting edge gets contact with the demand of customization, being at the same time in a global On the product family level, products differ mainly in two fibres, is changing with the rotation of the tool. However, θf Fig. 1. Definition fibre-cutting-angle competition with competitors all over the world. This trend, f main characteristics: (i) theof number of components (θcc and θff) and (ii) the can be a constant when milling UD-CFRP. which is inducing the development from macro to micro type of components (e.g. mechanical, electrical, electronical). Gara et al. [4] investigated the influence of process In a previous research [7], investigated ff was markets, results in diminished lot sizes due to augmenting Classical methodologies considering mainly single products the effect of θ parameters on surface roughness in slotting of CFRP using a on solitary, the cutting force and uncutproduct fibres, in the case of milling product varieties (high-volume to low-volume production) [1]. or already existing 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 Keywords: Assembly; Design method; Family identification the anisotropy, inhomogeneity and the strong abrasive

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.2018.09.039

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Norbert Geier et al. / Procedia CIRP 77 (2018) 375–378 Author name / Procedia CIRP 00 (2018) 000–000

UD-CFRP. It was found that cutting force and uncut fibres are minimum at a θf of 100°. Furthermore, the cutting force and the amount of uncut fibres are unfavourable, when the θf is 0° (=180°). The main objective of the present study is to develop a special trochoid tool patch and analyse its influence on the surface roughness and characteristics of uncut fibres at a difficult set-up (θf=0°) 2. Measuring and evaluation methods Digital image processing (DIP) was used in this study in order to evaluate the characteristics of uncut fibres at the milled edge of the workpieces. This tequnique is widely used by researchers [2, 8]. The main steps of DIP can be seen in Fig. 2.

Ab  c

11 ln

n

 i 1

pmi 

11 ln

n

a

(1)

bi

i 1

, where c (mm2/pixel) shows the area of one pixel; l (m) is the length of the evaluation section, pm (pixel) is the number of the measured (black) pixels on the analysed image and ab=cpm (mm2) is the area of uncut fibres in a window. Ab shows the area (mm2) of uncut fibres on a unit workpiece-edge length (m). The average of the highest uncut fibres (X) on the machined edge is expressed by Eq. (2).

X

1 n

n

x

(2)

i

i 1

, where n (-) is the number of the windows and x (mm) is the highest uncut fibre in a window. As can be seen in Fig. 3b, the biggest distance between the edge of the specimen and the highest top of the uncut fibres are determined in all windows, then the average is calculated. Fig. 2. Digital image process of the milled UD-CFRP edges.

At the first step, the images were binarized (into black and white pixels) using grey scaled colour histogram, then those were cut to the image-size of 1280x500 pixels. This cut images include just the uncut fibres (as can be seen in Fig. 2c) and can be analysed by a window-method: As can be seen in Fig. 3, the image is distributed by windows (i=1…n) and the optimisation parameters (abi and xi, explained below) are calculated in every windows. Then, the average of them is calculated as expressed by Eq.(1) and (2) in order to characterise uncut fibres.

Fig. 3. Calculation process for the parameter of (a) average specific area of uncut fibres (Ab); and (b) average of the highest uncut fibres (X)

Two optimisation parameter is defined in this study to describe the characteristics of uncut fibres:  Average specific area of uncut fibres (Ab - mm2/m)  Average of the highest uncut fibres (X - mm) The average specific area of uncut fibres (Ab), expressed by Eq. (1).

3. Experimental setup and cutting conditions The workpiece is a hand lay-up made, 25 mm thick unidirectional carbon fibre-reinforced polymer (UD-CFRP). The milling experiments were carried out on a Kondia B640 machining centre (max. 12,000 rpm), equipped by a NILFISK GB733 vacuum cleaner (14.7 kPa). The surface roughness of the milled wall-surface (vertical) was measured by a Mitutoyo SJ-400 contact profilometer. Furthermore, a Dino-Lite AM4013MT digital microscope was used to take pictures of the milled workpiece edges with a magnification of 70x. Two, special compression end mills were used in this study, as can be seen in Fig. 4. The end mills differ only by the amount and size of the cutting teeth (tool geometries are identical). Both of the cutting tools were developed by the FRAISA in order to produce good-quality surface without delamination and to decrease tool-wear during milling of CFRP. The important data of the tools are listed in Table 1.

Fig. 4. Compression end mills used in this study: (a) FRAISA 20360.450 (coarse tooth); (b) FRAISA 20340.450 (medium tooth) Table 1. The list of compression end mills used Sign

Compression tool

Diameter

Tooth

Tool A

FRAISA 20340.450

ø10

coarse

Tool B

FRAISA 20360.450

ø10

medium

Two different milling strategies were used in this study (as can be seen in Fig. 5):



Norbert Geier et al. / Procedia CIRP 77 (2018) 375–378 Author name / Procedia CIRP 00 (2018) 000–000

 Conventional milling (the vector of the feed rate (vf) is parallel to the edge of the workpiece (x), the tool center point is on one line during machining)  Special trochoid milling (the tool center point is on a special tool path, the fibre-cutting-angle (θf=100°) is constant on the main cutting patch).

When the trochoid milling tool patch was applied, the surface roughness of the milled surface was not changed significantly compared to the conventional case. The surface milled by the Tool A (Ra=19.61 μm and Rz=90.5 μm) still more-times coarse than the surface machined by the Tool B (Ra=2.35 μm and Rz=21. 7 μm).

a Surface roughness (μm)

80

Tool A

60 20 0 -20

0

1

4. Results and discussion

Surface roughness (μm)

Experiments were designed using full factorial design table. Independent variables (category factors) are the cutting tool (Tool A, Tool B) and the milling technology (conventional, trochoid) both of them with two levels. Other process parameters were fixed based on previous studies [1, 7] and suggestions by tool-producers: cutting speed (vc=160 m/min), depth of cut (ap=15 mm), feed rate (vf=1528 mm/min) and climb milling (down milling) technology.

2

3

4

5

-40 Length (mm)

80

b

Tool B

40

-60 Fig. 5. Schematic drawing of the tool patch of the conventional and the special trochoid milling when machining UD-CFRP. G1 movements are interpolated and G0 movements are rapid

377 3

Tool A

60

Tool B

40 20 0 -20

0

1

2

3

4

5

-40 -60

Length (mm)

Fig. 6. Surface roughness profile of the milled surface when (a) conventional and; (b) trochoid milling tool path was applied.

4.2. Characteristics of uncut fibres

Measured data and taken images were analysed using the Wolfram Mathematica, the Irfan View and the Microsoft Excel software. Experimental results are listed in the Table 2. Table 2. Experimental results Tool

Technology

Ra (μm)

Rz/Ra (-)

X (mm)

Ab (mm2/m)

A

conventional

18.84

4.77

2.068

295.6

B

conventional

3.74

7.97

2.029

218.8

A

spec. trochoid

19.61

4.79

0.362

23.6

B

spec. trochoid

2.03

12.28

0.301

21.1

4.1. Surface roughness Surface roughness profile was measured by the Mitutoyo instrument, then average surface roughness (Ra), roughness depth (Rz) and ratio of Rz/Ra were calculated. This process was repeated five times in the case of every experimental setup, then the averages were calculated and used to characterize the milled surfaces. Surface roughness values are listed in the Table 2. Surface roughness profile can be seen in Fig. 6a, in the case of conventional milling tool path was applied. It is clear from the figure, that the surface roughness machined by the Tool A (Ra=19.46 μm and Rz= 87.2 μm) is more-times coarse than the surface milled by the Tool B (Ra= 3.13 μm and Rz= 24.8 μm).

It can be seen in Fig. 7, that the machined UD-CFRP edge is almost free of uncut fibres in the case of trochoid milling was applied. However, in the case of conventional milling, the quantity of uncut fibres is highly considerable. The reason of this difference can be explained by the following:  The fibre cutting angle (θf) is fixed at a constant level of 100° in the case of trochoid milling. The cutting force, delamination and uncut fibres are possibly therefore lower than in the case of conventional milling, when the fibre cutting angle (θf=0°) was not set up based on any previous knowledge.  In the case of trochoid milling, the radial depth of cut was never as big, as in the case of conventional milling (ae=50% of tool diameter). Furthermore, the chip section was smaller, it decreased possibly the cutting force and speed of tool wear too.  The end mill (with special trochoid tool patch) is roughing (with θf=100°) and finishing (with θf=0°) after each other in every period (as can be seen in Fig. 5), not like in the case of conventional milling. This finishing movements could cut the fibres more efficiently than in the case of conventional milling. The average specific area of uncut fibres (Ab) is more than ten times smaller in the case of special trochoid milling of UD-CFRP than in the case of conventional milling tool patch was applied, as can be seen in Fig. 8.

Norbert Geier et al. / Procedia CIRP 77 (2018) 375–378 Author name / Procedia CIRP 00 (2018) 000–000

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5. Conclusion In the present study, UD-CFRP was machined with compression end mills using conventional and special trochoid milling tool patch in order to analyse the influence of them on the quality parameters of the milled surfaces of the specimen. According to the present study, the following conclusions can be drawn:  Better-quality features could be machined in UDCFRP by using the new trochoid milling tool patch.  Uncut fibres were characterized by a new parameter: average specific area of uncut fibres.  In the case of trochoid milling tool patch was applied, the surface roughness of the milled surface was not changed significantly compared to the conventional case.  It was found that the vertical-projected area of uncut fibres is more than ten times smaller when special trochoid milling than conventional milling tool patch was applied.  Furthermore, no significant difference was found between the analysed compression tools from the point of view of characteristics of uncut fibres. Acknowledgements

Fig. 7. Images of the milled UD-CFRP edges when (a) conventional with Tool A; (b) special trochoid tool patch with Tool A (c) conventional with Tool B; and (d) special trochoid tool patch with Tool B was applied. 3.5 3 2.5

2 AbA(mm2/cm) b (mm /cm)

(mm) XX (mm)

2

References [1] [2]

1.5 1

[3]

0.5

0

The authors would like to acknowledge the support provided by the CEEPUS III HR 0108 project. This research was partly supported by the EU H2020-WIDESPREAD-012016-2017-TeamingPhase2-739592 project “Centre of Excellence in Production Informatics and Control” (EPIC). Furthermore, authors would like to acknowledge the support provided by the FRAISA.

Tool A Tool A trochoid Tool B Tool B trochoid conventional conventional

Fig. 8. Average specific area of uncut fibres (Ab) and average length of the highest uncut fibres (X)

Fig. 8. shows also that the average length of the highest uncut fibres (X) is more than five times smaller (in the case of both cutting tool) when the special trochoid tool patch was applied, then the conventional one. Furthermore, no significant difference was found between the analysed compression tools from the point of view of characteristics of uncut fibres. For further industrial application of the presented technology, it is necessary to improve tool patch and optimise process parameters in order to increase cutting performance and efficiency.

[4] [5]

[6]

[7] [8]

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