Selection strategy for milling parts on CNC machines

Selection strategy for milling parts on CNC MACHINES Adam ZALEWSKI Sergiusz Sobieski

Authors: Adam Zalewski ([email protected]), Warsaw University of Technology, Poland Sergiusz Sobieski ([email protected]), TIZ Implements, Poland How to cite: A. Zalewski, S. Sobieski. Selection strategy for milling parts on CNC MACHINES. Advanced Technologies in Mechanics, Vol 2, No 2(3) 2015, p. 9–23. DOI: 10.17814/atim.2015.2(3).18

Abstract Practical knowledge and experience of engineers, CNC programmers, operators related to the implementation of production tasks in the workshop are essential. Every day, developed, perfected for companies specialty, “technological knowledge base “, is a specific, dedicated to the particular conditions of the key to success – the “know -how “in the concrete conditions of production. This knowledge can be relatively easily processed and developed, in particular with regard to the development of technology in the CAM. Additionally subjected to simulation analysis allows comparison of different strategies and variations of part in the design of technology. Several years of authors experience in the analysis of the work ‘s CAM systems in many companies has enabled the formulation of universal principles of numerical simulations that take into account the individual characteristics of the workpiece and the specificity of the selected CNC machine with accessories. Conducted research on the production based on Catia V5 program and Mastercam X6 confirmed the validity of this approach and helped to correcting some of the assumptions developed algorithm. Keywords: CAM, CNC, simulation, strategy

Introduction

For over 30 years are developed CAM systems. Since then, various methods of tool path design are regularly verified in hundreds of manufacturing plants. In the quest for efficient production of offered tool path strategies relative to the workpiece, which provide a stable load on the tool, efficient machining, satisfactory period of tools work before the tool change and the quality of the surface finish. Draws attention to the large number of available solutions on the same technological task. When designing a technological process, technologist has many possible uses of tools of different diameter, length (reach), indexable or monolithic, different numbers of cutting edges, www.atim.media.pl 9

2/2015

ADVANCED TECHNOLOGIES IN MECHANICS

ISSN 2392-0327

with different price, method of operation, cooling, and finally, with different cutting parameters. Which tool to choose? What strategy of the tool will be the best? What are the cutting parameters for the selected strategy will be optimal? The article describes the drop-down simulation method for comparing multiple machining of the same parts. This approach can be classified as numerical methods. By limiting the analysis to the specific case, the discussion comes down to a finite number of solutions to the discrete nature. The results of calculations of partial depend on: ■■ types of tools (milling cutters in this case); ■■ cutting parameters; ■■ assumed operating conditions (cooling type, method of removal of chips, fixing ■■ of the workpiece, tool holder, machine kinematics and dynamics, the type and parameters of movement such as auxiliary input tool material); ■■ algorithms CAM software used to develop the tool pass on the basis of the cutting parameters definition. Type tool is related to the shape and dimensions of the part, the requirements as to the accuracy and surface quality. Tool selection restricts the ability of the machine, fixing and price. The scope of the analysis described below can be limited only to existing tools, or check whether the purchase of the new will be a good project. Cutting parameters are a very important element of the analysis. They depend on many factors. Designated in theory is verified experimentally. In particular, the radial depth of cut ae, axial depth of cut ap and feed speed Vf, will affect the result of the analysis. Conditions of the tool work significantly narrow the field of application of cutting parameters. In this case they are described parametrically, i.e. based on previously machining operations performed on different machines, introducing a limitation in the possibility of their effective use. They are expressed either numerically or factors such as nmax, Pmax, Mmax, Fmax, the area of machining, type of cooling, vibration damping ability and stiffness. This allows for conducting simulations in relation to specific conditions and chooses the best solution for a given machine. Most modern, professional CAM software offers machining strategies appropriate to perform practically every part. Depending upon the path calculation algorithms in different CAM programs, form the tool movement path can be different. The differences may relate to its efficiency, the machining time or the tool life. In this case it isn’t comes to choosing a better CAM program, but a comparison of the strategies under a particular set of solutions. In carrying out the analysis on the basis of one, the same CAM program, the simulation allows the use of the best available approach in this case. The study used a parametric record machining technology to create a “predefined” CAM technology (called templates). Once developed and proven technology can thus be “imposed” on another model of the workpiece. This provision also allows for the automatic design of many cases of tool paths (processing strategy) and various cutting parameters (variants within the same strategy) machining the same parts. 10 www.atim.media.pl

Selection strategy for milling parts on CNC MACHINES

The same shape of the workpiece can be achieved employing different strategies movement of the tool. This usually results in a different shape of the trajectory of the tool and a different path travelled by the tool during machining. In turn, for the same machining strategy, tool path has a similar shape. In the simulations, the following variants of machining (in a single strategy) examines the use of tools of the same type but with different diameters Df, matched in each case the parameters such as radial depth of cut ae and axial depth of cut ap [9]. As a result of the removal of the same volume of material in each case requires a different tool paths and the use of other feed speed Vf. It is difficult to realize in practice constant crosscutting layer at any time, especially when machining complex shape parts. To achieve a constant volumetric efficiency machining can be used to adjust the feed rate Vf [lit.]. Changing the feed rate can also apply to those phases of the tool work, which significantly changed the direction of motion (for example corners, small arcs). This is in turn related to the requirements of the machines servo geometrical precision and its dynamic capabilities. The total tool path includes a number of phases of the tool work, which has not reached it assumed the cutting parameters (eg commuting, departures, short crossing the border material). The road and the speed of movement of the tool are adapted to local machining needs. Given so many opportunities to change the path (trajectory) of the tool and feed rate, it is difficult to analytically determine the actual processing time. Comprehensive analysis enables the simulation of machining CAM system even at the design stage of the process. Note the very broad range of factors, which may be taken into account (for example in the form of modified coefficients of simple experimental). Often assessment of the proposed machining operation is based on idealized cutting conditions, reduced to simplified models. In this case, it is possible to simulate different cases complicated processing (geometrically and technologically) part, in relation to the specific conditions in the workshop. Use predefined CAM technology dramatically accelerates the design processing, uses collected to date experience and knowledge of the company’s employees on the use of specific equipment and instrumentation. During the analysis of the various processes it is easy to select another CNC machine and for her to receive the full results will be even more different from the previous ones, the greater are the differences in capabilities of machines. Each time, however, it should be the best solution for each case. Similarly, designing similar geometrically and technology machining parts process, you can get a completely different solution, as for example, change the number of tool pathes for removing a given volume of material associated with the current parameters ae and ap. An optimal solution may therefore be to apply a completely different tools and machining strategies. Complete this analysis without the effective use of modern CAM programs, assisted techniques, knowledge bases, it does not seem easy to obtain (if at all possible). www.atim.media.pl 11

2/2015


ISSN 2392-0327

dŚĞŐĞŶĞƌĂůǁĞĂŬŶĞƐƐŽĨƚŚĞƐŝŵƵůĂƟŽŶƉƌŽĐĞƐƐŝƐŝƚƐƉŽƚĞŶƟĂůŝŶĐŽŵƉĂƟďŝůŝƚǇǁŝƚŚ ƚŚĞĂĐƚƵĂůŝŵƉůĞŵĞŶƚĂƟŽŶ͘dŚĞƉƌŽƉŽƐĞĚƐŽůƵƟŽŶŝƐďĂƐĞĚŽŶƚŚĞƵƐĞŽĨǀĞƌŝĮĞĚ ĚĞĐĂĚĞƐDƉƌŽŐƌĂŵƐ͕ǁŽƌŬŝŶŐŽŶƚŚĞƉĂƌĂŵĞƚĞƌƐƚĞƐƚĞĚŝŶƚŚĞǁŽƌŬƐŚŽƉ͕ƐƵƉƉůĞŵĞŶƚĞĚďǇŬŶŽǁůĞĚŐĞŽĨEŵĂĐŚŝŶĞƐĂŶĚĞǆƉĞƌŝĞŶĐĞƐƉĞĐŝĮĐƚĞĂŵŽĨƚĞĐŚŶŽůŽŐŝƐƚƐ͘ ƵƚŽŵĂƟĐĐŽŵƉĂƌŝƐŽŶŽĨĚŽǌĞŶƐŽĨĂůƚĞƌŶĂƟǀĞƉƌŽĐĞƐƐĞƐƋƵŝĐŬůǇĚĞƚĞƌŵŝŶĞƐƚŚĞĂƌĞĂ ƉŽƚĞŶƟĂůůǇƚŚĞďĞƐƚƐŽůƵƟŽŶ͕ďĞĐĂƵƐĞŽĨƚŚĞĚŝīĞƌĞŶƚĞǀĂůƵĂƟŽŶĐƌŝƚĞƌŝĂ;ƟŵĞ͕ĐŽƐƚ͕ number of tools used, the type of machine).

1. Analysis of different strategies and implementation variants of machining operation dŚĞĂŝŵŽĨƚŚĞƐƚƵĚǇǁĂƐƚŽƌĞĚƵĐĞƚŚĞƉŽƌƟŽŶŽĨƚŚĞƉƌŽĐĞƐƐŽĨŵĂĐŚŝŶŝŶŐƉĂƌƚƐ ƉƌŽĚƵĐĞĚŝŶƐĞƌŝĞƐďǇĂƚůĞĂƐƚϮϬй͘^ĞĂƌĐŚĨŽƌĂůƚĞƌŶĂƟǀĞƐŽůƵƟŽŶƐƚŽĂƉĂƌƟĐƵůĂƌ ĐĂƐĞ͘dŚĞƵƐĞŽĨƚŚĞĐŽŶĐĞƉƚŽĨĂƵƚŽŵĂƟĐĐŽŵƉĂƌŝƐŽŶŽĨƉƌĞͲĚĞĮŶĞĚƚĞĐŚŶŽůŽŐǇŚĂƐ ůĞĚƚŽƚŚĞĐƌĞĂƟŽŶŽĨĂƉƌŽƚŽƚǇƉĞĂŶĂůǇƟĐĂůƚŽŽůŝŶĂƟĂǀϱĞŶǀŝƌŽŶŵĞŶƚĂŶĚƉĂƌĂůůĞů DĂƐƚĞƌĐĂŵyϲ͕ǁŚŽƐĞƉƌŝŶĐŝƉůĞŽĨŽƉĞƌĂƟŽŶŝƐƐŚŽǁŶŝŶĮŐƵƌĞϭ

&ŝŐ͘ϭ͘dŚĞǁŽƌŬĂůŐŽƌŝƚŚŵďĂƐĞĚŽŶƉƌĞĚĞĮŶĞĚŵĂĐŚŝŶŝŶŐƐƚƌĂƚĞŐŝĞƐ͕ǁŚŝĐŚĂƌĞĚŝƌĞĐƚĞĚƚŽŵĂĐŚŝŶŝŶŐƉĞƌĨŽƌŵĂŶĐĞ

hƉŽŶƌĞĐĞŝƉƚŽĨĂŶĞǁŽƌĚĞƌ͕ĂŶĚƚŚĞĂŶĂůǇƐŝƐŽĨƚŚĞϯŵŽĚĞů;ƐƚĞƉϭͿ͕ĨŽůůŽǁĞĚďǇ ƐĞĂƌĐŚƚĞĐŚŶŽůŽŐŝĐĂůůǇƐŝŵŝůĂƌĐĂƐĞŝŶĞĂƌůŝĞƌƐƚƵĚŝĞƐŽĨD͘^ƚĞƉϮĐŽŶƐŝƐƚƐŝŶůŝŶŬഩ12 www.atim.media.pl


ing the existing predefined strategy (and variants) with the new model, and adapts them to your own specific requirements of the order and the technical capabilities of the workshop. In step 3, the automatic conversion of different machining strategies first, and then the various options within the selected strategy. Reports in the form of graphs in step 4 allow the selection of solutions to develop a detailed (create a list of requirements, workshop documentation, programs, NC) in step 5. In the article [1] devoted to the analysis focuses on the analysis of different machining options into a single strategy (comparison of different ap, ae, Vf, Vc, to work with the same tool). Efforts to get a similar power P [kW] and the average volumetric efficiency cutting Qv [cm3/min]. Other cutting parameters were selected in accordance with the tools manufacturer.

variant

Table 1. Example of selection cutting data for milling of flat cylindrical cutter D16 (16 mm diameter [11,12]) for the individual variants ae [mm]

ap [mm]

n [rpm]

vf [mm/min]

fz [mm/z]

P [kW]

Qv [cm3/ min]

vc [m/min]

L [m]

1

3

5

4516

3775

0,209

3.1

57

227

131

2

5

5

2964

2431

0,205

3.2

61

149

164

3

8

5

2653

1349

0.127

3

54

133

119

4

8

5,3

2646

1323

0,125

3,2

56

132

85

5

12

5

2924

936

0.08

3.4

56

147

106

6

16

5

2646

624

0,059

3.3

50

133

82

7

16

3

2666

1248

0,117

3,4

60

134

141

8

12

3

3104

1601

0,129

3,2

58

156

147

9

8

3

3601

2535

0,176

3,2

61

181

155

10

5

3

4675

3404

0,182

2,8

51

235

116

11

3

7

4138

2516

0,152

3,1

53

208

111

12

5

7

3283

1536

0,117

3,2

54

165

116

13

8

7

2924

948

0,081

3,3

53

147

102

14

12

7

2606

615

0,059

3,3

52

131

93

15

16

7

1771

425

0,06

3,1

48

89

67

16

16

10

1671

287

0,043

3,2

46

84

54

17

12

10

2069

414

0,05

3,3

50

104

55

18

8

10

2129

605

0,071

3,1

48

107

68

19

5

10

2447

1038

0,106

3,2

52

123

77

20

3

10

3143

1785

0,142

3,2

54

158

86

21

8

13

2109

456

0,054

3,2

47

106

52

22

5

13

2208

777

0,088

3,2

51

111

76

23

3

13

2745

1373

0,125

3,3

54

138

78

www.atim.media.pl 13

2/2015


ISSN 2392-0327

Each of the analyzed cases was technically correct, and the differences at the time the procedure mainly due to the varying length of the path of movement of the tool. The shape of the tool path was close every time (this was due to the same strategy), but the length of the tool path (road) differ because of the different parameters ap, ae, and this resulted in a variable number of passes of the tool relative to the shape and dimensions of the workpiece. Founded feed rate Vf, was subjected to a small, local changes due to the movement phase tool (arrive, depart), but without the requireAdam Zalewski ment to maintain a constant volume ofand cut. Sergiusz Sobieski 500 450 400 350 300 250 200 150 100 50 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Simulated time of machining in sec. [s]

There were considerable variation analysis results (fig. 2).

machining variant Fig. 2. Comparison of the total time and the time of cutting machining of different variants of the same strategy

(“Outward in the orderand of the options in Table 1 [1] (red – of total time, blue variants – machiningoftime). Figure 2 Comparison ofhelical”) the total time the timepresented of cutting machining different the same strategy ("Outward helical") in the order of the options presented in Table 1 [1] (red – total time, blue – machining time).

Sequence variants from No. 1 to No. 23 are in line with developed cutting data table

Sequence(Table variants from 1 to No. 23 arerandom, in line as with developed data table (Table 1, 1, [1]). ThisNo. order is somewhat is apparent fromcutting the accepted [1]). This order random, asOnistheapparent from2 itthe order orderisofsomewhat conducted experiments. basis of figure canaccepted be concluded that of conducted minimal and2thus cutting which would will characterize experiments. On the processing basis of time, Figure it can be data, concluded that use, minimal processing time, and the variations. This analysis allows the comparison of different variants of the same allows the thus cutting data, which would use, will characterize the variations. This analysis milling parts. It should increase the radial or axial depth of cut? Machined with a large comparison ofcross-section different variants of the same milling parts. It should increase the radial or axial cut layer and apply a small ap, ae, but a greater feed rate Vf? It also aldepth of cut? Machined large ranges cross-section cut which layer clearly and apply a the small a p , ae, but a greater lows you to with bypassa these cutting data, extend machining due to the mismatch shapes of the part, whichdata, resultswhich in significant feed rate V f ? time It also allows you tobetween bypassthethese ranges cutting clearly extend the prolongation of the tool path. machining time due to the mismatch between the shapes of the part, which results in significant path strategies usually have other shapes trajectory of the tool. This is prolongation ofDifferent the tooltool path. due to the shape of the usually workpiece, theother type ofshapes tool, machining type roughing Different tool path strategies have trajectory of (e.g., the tool. This is due to the or finishing) and manufacturing concept. shape of the workpiece, the type of tool, machining type (e.g., roughing or finishing) and manufacturing concept. Examples of different traffic strategies tools for rough milling open pocket shown in the following examples (Figure 3): 14 www.atim.media.pl


Examples of different traffic strategies tools for rough milling open pocket shown in the following examples (fig. 3): a)

b)

c)

d)

e)

f)

g)

h)

i)

j)

k)

l)

Fig. 3. Examples of various strategies open pocket milling (a-Trochoidal deep, c-Trochoidal + blend, d-pocket HSM, e- open pocket, pocket f-2, G-blend1, h-contour, and dynamic-2, j - pocket 2, k-Trochoidal shallow, l-Plunge)

Comparison of machining strategies and options for the same part should be based on specific criteria such as: ■■ processing time; ■■ cost of machining (cost of tools, power consumption, cost engineering, cost of inputs, etc.); ■■ quality of the machined surface (e.g., changes in the workpiece as a result of the cutting process, the size and shape machining allowance left); ■■ characteristics of the cutting process(chip form, the method of the chip evacuation, a cooling method, the impact of tool wear or damage tool, process stability, resistance to interference, the impact OUPN rigidity and vibration , etc.); ■■ cost of investment in means of production (purchase of new tools, tooling, equipment, CNC machine tools, etc.).


2/2015


ISSN 2392-0327

Match the optimal strategy - and within it - the best implementation variant machining procedure-selected parts based on all of these criteria is not easy [1]. The more that in some cases may lack sufficient data to effectively analyse these criteria. Therefore proposed that the following steps to follow: a level sufficient to conduct the theoreti1) Estimation of the necessary values at cal analysis, 2) Examine using simulation methods (CAM) of all selected cases. 3) Preparation of reports comparing different solutions and potentially the best choice due to the adopted criteria.

2. Research conducted

In order to reduce the input data selection area for machining simulation, the following assumptions proposed: ■■ Initial value of the theoretical power P [kW] and the volumetric capacity of cut Q [cm3/min] were determined on the basis of previously implemented technology. Subsequent trials cutting machining operations were corrected, depending on the running machining. ■■ Suitable for cutting parameters resulted from technical limitations of the industrial partner of the project and had to be possible to use in specific production conditions (the project was implemented in cooperation with a large manufacturing factory). ■■ Minimum cost of investment in the means of production (e.g. the cost of new tools, the cost of installing additional cooling air). ■■ Design strategies and machining options in such a way that the cutting process is at least satisfactory because of the estimated tool life. ■■ Analyses were performed only for roughing and surface roughness after machining was not particularly important. ■■ Basic criterion for the comparison was the duration of the machining, and criteria supporting the cost of tools and tool life (calculated theoretically as parameters correlated with the working conditions and the way the tool during cutting. Auxiliary criteria are described in [1]). We analysed the treatment of open pocket measuring about 40x60x45 mm (simplified outline of the pocket is shown in figure 3) performed serially in steel with properties similar to stainless steel SAE-9310-HB330 (approximately 35 HRC). The task was the removal of about 111 cm3 of material in the shortest time (and the conditions described above). These experiments were carried out on the machine 3 axis DMC-104V (Pmax=20 kW, Mmax=100 Nm, nmax=12 000 obr/min) with Siemens 840 control system. Taken trochoidal machining test strategy, one tool with the different variants of the cutting parameters.

16 www.atim.media.pl

Wariant

Wariant

ae

[mm]

ae

n

ap

[mm]

n

ap

v

f

Qv

P

v

M

T

3 f z c c Selection strategy for milling[cm parts MACHINES [obr/mi / on CNC [mm/min] [mm/ostrze] [kW] [m/min] [Nm] [s] n] min]

vf

fz

Qv

P

vc

Mc

T

W1 47,98[obr/mi 4158 1518 [mm/ostrze] 0,073 [kW] 8,5[cm /117[m/min] 209 [Nm]19 [s] 220 [mm]1,6 [mm] [mm/min] Table 2. Example of cutting parameters for milling of flat cylindrical cutter n] min] D16 (16mm diameter [11,12]) 372 for the 2507 individual variants of trochoidal W2 0,8 47,98 5013 0,100 7,0strategy 96 252 13 3

240 8,5 P8,6117Q120 209 v252 19 16 220 v T c [cm3/ Mc [Nm] [mm] [obr/min] [mm/min] [mm/ostrze] [kW] [m/min] [s] 188 W2 W4 145252 269 13 18 372 0,8 1,0[mm] 47,9847,98 50135352 25073024 0,1000,113 7,0 1096 min] 220 165 W3 W5 10120117 144252209 252 1619 19 240 1,0W11,2547,98 50135013 25072406 1,6 47,98 47,98 4158 1518 0,1 0,096 0,073 8,6 8,5 372 188 W4 1,0 47,98 5352 5013 3024 2507 0,113 0,100 10 7,0 14596 269252 1813 W2 0,8 47,98 Wariant

W1 W3 5013 0,1fz 1,6 1,0 47,98 ae 47,98 a4158 n15182507 vf 0,073 p

Table of cutting 5013 parameters for milling of flat cylindrical cutter D16 (16mm [11,12]) for the 240 165 W5 2 Example 1,25 47,98 2406 19diameter W3 1,0 47,98 5013 2507 0,096 0,1 10 8,6 144120 252252 16 individual variants of trochoidal strategy 188 W4

1,0

47,98

5352

3024

0,113

10

145

269

18

165 for the Table 2 Example of cutting parameters for milling of flat cylindrical cutter D16 (16mm diameter [11,12]) W5 results 1,25 for47,98 5013 2406 0,096 10 machining 144 252 19 The following the individual machining strategy trochoidal open pockets: variants of trochoidal strategy

The following results for the machining strategy trochoidal machining open pockets machining time [s]

372 400machining strategy The following (fig. results trochoidal machining open pockets: 4): for the

machining time [s]

400 300 200

300 200

240

220372 240

100220

188

188

165

0

100

W1

W2

W3

165

W4

W5

machining variant

0 W1

W2

W3

W4

W5

Cutting power [kW]

Cutting power [kW]

machining for five variants. 8000Figure 4 Comparison of the machining time during trochoidal 12 10 10 Example of chips after machining. version W5 (grid having a side of 5 mm). 6000 10 8,6 8,5 6000 5013 5013 5013 7 8 4000 8000 12 10 10 4000 6 6000 10 8,6 8,5 6000 5013 5013 5013 4 7 8 20004000 2 4000 6 0 0 4 2000 W1 W2 W3 W4 W5 W1 W2 W3 W4 W5 2 machining variant machining variant 0 0 W1 W2 W3 W4 W5 W1 W2 W3 W4 W5 Figure 4 Comparison of spindle andcutting cutting power during trochoidal machining for 5 variants Fig. 4. Comparison of spindlespeed speed and power during trochoidal machining for 5 variants, machining variant machining variant and the machining time. Example of chips after machining rpm speed

rpm speed

machining variant Figure 4 Comparison of the machining time during trochoidal machining for five variants. Example of chips after machining. version W5 (grid having a side of 5 mm).

Figure 4 Comparison of spindle speed and cutting power during trochoidal machining for 5 variants


2/2015


200

19

20

150

117

100

96

145

120

cutting torque [Nm]

volumetric capacity [cm3/min]

ISSN 2392-0327

Adam Zalewski and Sergiusz Sobieski 144

50

18

19

W4

W5

16 13

15 10 5 0

0 W1

W2

W3

W4

W1

W5

W2

W3

machining variant

machining variant

Figure 5Fig. Comparison maximum volumetric capacity duringand cutting cutting during trochoidal 5. Comparisonofofthe the maximum volumetric capacity during cutting cutting and torque during torque trochoidal machining forfive thevariants five variants machining for the

ae

[mm]

Table 3. Example of cutting parameters for each milling strategy (D16 – 16 mm diameter of flat cylindrical cutter, D42, D40 – 42 and 40 mm diameters of an indexable Q head cutter [11,12]) v

ap

[mm]

strategy

strategy

Trochoidal machining 3b)isischaracterized characterized cutting movements and moveback movements; Trochoidal machining(Fig. (fig. 3b) by by cutting movements and back in this case, the inmaximum volumetric (Fig. 5 (fig. a) refers only totocutting ments; this case, the maximum efficiency volumetric efficiency 5a) refers only cutting movement. The average volumetric productivity of cut applies to the applies entire tovolume of volume material removed movement. The average volumetric productivity of cut the entire of material removed in relation to the machining time. in relation to the machining time. Practical checking workshop selected machining variantstheshowed Practical checking on on workshop selected machining variants showed possibilitythe of possibility of significantly exceeding the assumed parameters: cutting power and volume significantly exceeding the assumed parameters: cutting power and volume efficiency efficiency 3 /min). The best(variant case (variant was (which initially amounted 3.4 54cm3/min). kW and 54 cmThe (which initially amounted to 3.4kWtoand best case 5) was5)achieved shorter shorter machining time compared the standard by 56%. further This hasexperiments machining achieved time compared to the standard output byto56%. This hasoutput encouraged encouraged further experiments related to the change of milling strategies. Here related to the change of milling strategies. Here discrepancy obtained the machining time was even discrepancy obtained the machining time was even greater, and changing parameters greater, and changing parameters such as power of cut, the moment of cut went far beyond such as power of cut, the moment of cut went far beyond the planned framework. the planned The following cites athat selection Theframework. following comparative analysiscomparative cites a selectionanalysis of experiments illustrateof theexperiments that illustrate the potential savings in processing time the(confirmed theoretical analysis potential savings in processing time resulting from theresulting theoreticalfrom analysis (confirmedininpractice). practice).

ae [mm]

n

[rpm]

vf

[mm/min]

23,09

3561

n vf fz [rpm] [mm/min] [mm/z]

P [kW]

3,3 10,0

1,6

S2

1,25

S147,98 1,6

23,09 5013

3561 24061271

S3

7,68

S2

1,25

47,98

S3

7,68

46,18

5013960 2406 (plunge)960 1200 (plunge)

40

2.8

40

P

[kW]

ap [mm]

S1

S4

fz

[mm/z]

46,18

S4

2.8

1200

1050

1271

480

1050

0,089

480

0,089 0,096 0,096

0,2

0,2

0,11

0,11

3,3

vc

[cm3/

47

tools

8,8

600

D16

8,8 252

60019,0D16

165

D16

158

19,0

165

D16

60

D42

95,5

60

D42

31

380

380

D40

179

47144,0 179

308 (max) 252 144,0 111 (averange) 308 (max) 12 158 111 (averange) 3,4 53

10,0

12

3,4

T

[m/min] Qv min] Mc vc [cm3/ [m/min] [Nm] min]

53

131

131

Mc

[Nm]

T [s]

[s]

tools

95,5 31

D40

Table 3 Example of cutting parameters for each milling strategy (D16 -16mm diameter of flat cylindrical cutter, Compared below (fig. 6, 7, 8) the use of four tools in four machining strategies which, D42, D40 – 42 and 40 mm diameters of an indexable head cutter [11,12])

after theoretical analysis have been reviewed in the workshop. Compared respectively two trochoidal machining strategies (differing substantially parameters) - S1 and S2, Compared (Fig.(S3) 6, 7, ofmachining four tools(contour) in four machining strategiesinwhich, after plungebelow machining and8)a the stepuse over - S4. The differences theoretical time analysis have the been reviewed in theonworkshop. Compared two trochoidal and during simulated execution the machine are usuallyrespectively of a few percent.

machining strategies (differing substantially parameters) - S1 and S2, plunge machining (S3) and a step 18 over www.atim.media.pl machining (contour) - S4. The differences in time and during the simulated execution

Selection strategy for milling parts on CNC MACHINES Adam Zalewski and Sergiusz Sobieski Adam Zalewski and Sergiusz Sobieski

600 500 400 300 200 100 0

machining time [s]time [s] machining

machining time [s]

on the machine are usually of a fewAdam percent. Taking account the actual dynamic properties Zalewski andinto Sergiusz Sobieski Taking into are account the of actual dynamic properties of theaccount machine, compatibility on the machine usually a few percent. Taking into thetheactual dynamic properties of the machine, the compatibility with thehigher. simulation was even higher. with the simulation was even of the machine, the compatibility with the simulation was even higher. on the machine are usually of a few percent. Taking into account the actual dynamic properties 700 600 the simulation was even higher. of the machine, the compatibility with 700 600 500 700 400 600 300 500 200 400 100 300 2000S 1 100 0

600

380

600

165

165

60

380 380

60

165

S2 S3 S4 60 S1 S2 S3 S4 machining strategy machining strategy S1 S2 S3 S4 Figure 6Fig.Comparison ofofthe timeduring during machining4 strategies for 4 strategies 6. Comparison themachining machining time machining Figure 6 Comparison of the machining time duringfor machining for 4 strategies machining strategy

rpm speed rpm speed

Figure 7 (b) shows the instantaneous, maximum volumetric efficiency in the procedure. average 7 Comparison of the power (a) and volumetric (b)cutting ofthe machining for The 4 strategies FigureFigure shows instantaneous, maximum volumetriccapacity efficiency in cutting procedure. The average 7.7 (b) (b) showstheas the maximum efficiency intime) the in cutvolumeFigure efficiency (calculated theinstantaneous, volume of material removed involumetric relation to the machining this case volume efficiency (calculated as the volume of time) in this case 3 3 material removed3 in relation to the machining 3 ting procedure. The average volume (calculated asthe the volume mawas respectively /min(S1), 40,3 cmefficiency /min (S2), 111efficiency cm /min (S3), 17,5 cmprocedure. /minof (S4) Figure 7was (b) respectively shows11,1cm the instantaneous, maximum cutting The average 11,1cm3/min(S1), 40,3 volumetric cm3/min (S2), 111 cmin3/min (S3), 17,5 cm3/min (S4) terial relationas to machining in inthis caseto was respectively volumeremoved efficiency in (calculated the the volume of materialtime) removed relation the machining time) in this case 3 33 3 respectively /min(S1), /min (S2), 11117.5 cm3/min (S3), 17,5 /min (S1), 40.311,1cm cm3/min (S2), 40,3 111 cm cm /min (S3), cm3/min (S4).cm /min (S4) 11.1 cm3was 6000 120 6000 120 95,5 95,5 5000 100 5000 100 6000 120 4000 4000 80 95,5 80 5000 100 3000 3000 60 60 4000 80 31 2000 40 31 2000 40 3000 60 19 19 1000 20 8,8 1000 31 20 8,8 2000 40 19 0 0 0 10000 20 8,8 S1 S1 S 2 S 3 S 4 S 1S 2 S 2S 3 S 3S 4 S4 S1 S2 S3 S4 0 0 machining strategy machining strategy machining strategy machining strategy S1 S2 S3 S4 S1 S2 S3 S4 machining strategy machining strategy Figure 8Figure Comparison of cutting torque moment and rotation of the spindle during during machining for 4 strategies 8 Comparison of cutting torque moment and rotation of the spindle machining for 4 strategies rpm speed

cutting torque [Nm]

0

volumetric capacity [cm3/min] volumetric capacity volumetric capacity [cm3/min] [cm3/min]

5

cuttingcutting powerpower [kW] [kW]

10

12 350 12 Figure 6 Comparison of the machining time350 during machining for308 4 strategies 308 300 10 300 250 10 12 15 350 250 308 10 200 144 300 200 144 10 150 250 150 3,4 3,3 10 100 5 3,4 3,3 53 47 200 100 53 144 47 50 150 50 5 3,4 0 100 3,3 0 0 53 47 S 2 S1 S2 S3 S4 S3 S4 50S 1 S1 S2 S3 S4 S1 S2 S3 S4 machining strategy machining strategy 0 0 machining strategy machining strategy S1 S2 S3 S4 S1 S2 S3 S4 Figure 7 Comparison of the power (a) and volumetric capacity (b) of machining forstrategy 4 strategies machining strategy machining Figure 7 Comparison the power and volumetric capacity (b) of Fig. 7. Comparison of theofpower (a) and(a) volumetric capacity (b) of machining for machining 4 strategiesfor 4 strategies 15

cutting torque cutting torque [Nm][Nm]

cutting power [kW]

15

Figure Comparison of cutting moment and rotation of the spindle duringfor machining Fig. 8. 8 Comparison of cutting torquetorque moment and rotation of the spindle during machining 4 strategiesfor 4 strategies


2/2015

IN MECHANICS ADVANCED TECHNOLOGIES Adam Zalewski and Sergiusz Sobieski

ISSN 2392-0327

To compare of different machining strategies were also applied economic To comparethe the effectiveness effectiveness of different machining strategies were also applied economic analysis, analysis, which which in addition to tothe tools (inserts) based on theof expected number of expected in addition theprice price ofof tools (inserts) based on the number machiningmachining operation up to utool change. aspect, however, is not applicable to this article. operation p to tool change.This This aspect, however, is not applicable to this article. In these cases, the machine worked properly throughout the range, and regisIn these cases, the machine worked properly throughout the range, and registered spindle load does tered load does not exceedtools the possibilities of machine tools and not exceed thespindle possibilities of machine and manufacturing process wasmanustable. The tools facturing process was stable. The tools during the assays described during the assays described herein have not been visibly worn, and the cuttingherein process proceeded have not been visibly worn, and the cutting process proceeded without objecwithout objection. According to the authors the most preferred solutions were strategies S3 tion. According to the authors the most preferred solutions were strategies S3 (short time, but the worst surface quality) and S2 (a good time and quality of the surface) of Figure (short time, but the worst surface quality) and S2 (a good time and quality of the 6, 7, 8. surface) of figure 6, 7, 8.

Figure Simulation VR machine, machining, chips Fig. 99Simulation on VRon machine, machining, chips

In relation toimplementation the implementation of the output parameters machiningachieved: achieved: In relation to the of the output parameters of of machining ■■ reduction of total machining time by the use of one pocket plunging to go

reduction of(including total machining by the73%; use of one coarse finishing)time by almost ■■ theplunging differentto variants of the same machining strategy used even three times pocket go coarse (including finishing) by almost 73%; the cutting powerof increased 3.4 kW to 10 kW)used in relation to thetimes origi- the cutting • the different variants the same(from machining strategy even three nally used. Machining works properly; power increased (from 3.4 kW to 10kW) in relation to the originally used. Machining ■■ volumetric efficiency machining for several experiences was much higher works properly; than the input (reference Q = 53.0 [cm3/min]), e.g. for the trochoidal ma• volumetric fornearly several experiences was [cm much higher 3 /min]) andthan the input chiningefficiency was again machining an increase of threefold (Q = 145.0 3 (reference Q = 53.0 [cm3/min]), e.g. for the trochoidal machining was[cm again / an increase for plunging instantaneous volumetric efficiency was even Q = 308.00 of nearly (Q = increase), 145.0 [cm3/min]) and for plunging instantaneous min]threefold (nearly six-fold while maintaining the stability of the proces.volumetric ■■ cuttingwas speed VcQ = 252 m/min[cm3/min] (an increase of nearly 100%)increase), was considered efficiency even = 308.00 (nearly six-fold while maintaining the bestofforthe trochoidal the stability proces. machining with intensive air cooling. • Studies cutting speed Vc = 252m/min (an increase of simulation nearly 100%) considered were conducted to the automatic machining of thewas same part, con- the cerning to many strategies, using a variety of tools and variables. The analysis best for trochoidal machining with intensive air cutting cooling. •

included 200 specific cases (strategies along with variants) machining of the same pocket various to tools. studies inmachining the workshop focused on that part, wouldconcerning to Studies werewith conducted the Inautomatic simulation of those the same be potentially interesting for an industrial partner of the project, and gave a chance many strategies, using a variety of tools and cutting variables. The analysis included 200 specific to verify the theoretical assumptions. Aim of the study was achieved.

cases (strategies along with variants) machining of the same pocket with various tools. In studies in the workshop focused on those that would be potentially interesting for an industrial partner of the project, and gave a chance to verify the theoretical assumptions. Aim of the study was achieved.

4. SUMMARY



Summary

The use of “predefined” CAM technology has many advantages of a universal character, such as [1]: ■■ Use database “technological knowledge”, as predefined processes can be continuously improved and can provide practical solutions to technological achievements specific to the company. ■■ Reduce the requirements of competence designer CAM because predefined processes should facilitate the programming of less experienced employees. ■■ Better sharing of experience among staff designers of technological CAM (developed processes may be available for a number of employees). ■■ Unify of NC programs for CNC machine tools (especially important in large factories). ■■ Easier to estimate the machining time. ■■ Shortening the programming time of CNC machine tools. ■■ Easier to compare the level of technology used in different departments for some parts technologically similar. ■■ Creation scientific basis for raising the qualifications of technologists. ■■ Easy comparison of different strategies and variants, and choose the best solution due to the adopted criteria. The proposed methodology allows for rapid comparison of a large number of possible solutions to a particular machining task in relation to the specific conditions in the workshop. Conducted analysis shows how much potential may lie in comparison to alternative technologies to perform the same operation on a CNC machine milling. Analysis of series-produced parts related to the number of about 1,000 units per year. Despite the large experience of technologists in the implementation of this procedure, it was shown the possibility of shortening the procedure by 50-70%. It is worth noting that the practical nature of the proposed approach stems from the short time of receipt of the report (even counted in the hundreds charts) on the potential effects of the use of the individual solutions and easy comparison of different methods of milling technology. If the technological process is more complex and diverse, the harder it is to answer the question of which strategies and machining options will best in the summary of a whole? Predefined patterns of technology use “locally” knowledge and technical capabilities to using simulation and comparison of multiple solutions within minutes or a few hours to answer the question, what to choose? Carried out off-line analysis relate to individually defined, specific machines and tooling. So we can (already at the stage of the simulation ) included in a range of dynamic capabilities of the processing (machine parameters and factors described in the form of additional technical conditions, such as the recommended speeds, the optimal diameter and maximum length tools, because of for example the possibility of vibration).


2/2015


ISSN 2392-0327

Description of dynamic area characteristics (machine - handle - workpiece - tool) can be systematically developed based on the observation of the subsequent machining tasks. You can in this respect also benefit from additional observation such as modal analysis, which will allow the determination of a set of characteristics of the FRF (frequency response function), for concrete tools and machining conditions. On the basis of the simulations of different strategies and machining options will be used most likely cutting parameters (e.g. limiting the possibility of self-excited vibrations flow). This underlines the same opportunity to take into account in the analysis of real technical conditions for the construction of a workshop-based knowledge base of predefined technology. Therefore started works are related to the model of an expert system to support the work team of technological preparation of production, taking into account the specificities of a particular plant, department, and finally producing a single machine. One of the functions of such a system is to find the best solution (in a short time) machining for use in specific conditions. This will be important both during the design process and the preparation of tenders for subcontractors. References [1] Z alewski A., 2012, Skracanie czasu obróbki na frezarkach CNC na podstawie okresowej analizy warunków skrawania, Inżynieria Maszyn, R. 17, z. 2, 2012 [Shortening time working for CNC milling machines on the basis of periodic analysis of the terms and conditions of cut] [2] K rimpenis A., Fousekis A., Vosniakos G., 2004, Assessment of sculptured surface milling strategies using design of experiments, The International Journal of Advanced Manufacturing Technology, Volume 25, Numbers 5-6, 444-453 [3] Zalewski A., 2012, Dobór parametrów skrawania tej samej części dla różnych strategii obróbki. referat wygłoszony na II-iej Konferencji Naukowej nt.: Obrabiarki Sterowane Numerycznie i Programowanie Operacji w Technikach Wytwarzania Radom – Jedlnia Letnisko, 23 – 25 listopada 2011 r. Artykuł publikowany w Mechaniku 01/2012 [Selection of cutting parameters of the same part for different machining strategies] [4] T oh C.K. Tool life and tool wear during high-speed rough milling using alternative cutter path strategies, 2003, Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture September 1, 2003 217: 1295-1304 [5] M saddek B., Bouaziz Z., Dessein G., Baili M., 2011, Optimization of pocket machining strategy in HSM, International Journal of Advanced Manufacturing Technology, Manuscript Number: IJAMT7891 [6] Zalewski A.: Efektywne wytwarzanie dzięki optymalnej strategii obróbki HSM, Projektowanie i konstrukcje inżynierskie nr. 3(03) grudzień 2007 str. 23-26 [Efficient production through optimal HSM strategy] [7] Zalewski A., 2006, Droga narzędzia podczas frezowania na obrabiarkach CNC, Mechanik 4s. 4/2006 [Tool path milling on CNC machine tools] [8] Rauch M., Hascoët J. Milling Tool-Paths Generation in Adequacy with Machining Equipment Capabilities and Behavior, 2012, Machining of Complex Sculptured Surfaces, 127-155, DOI: 10.1007/978-1-4471-2356-9_4 [9] P rzybylski L.: Strategia doboru warunków obróbki współczesnymi narzędziami, Toczenie – Wiercenie - Frezowanie, Politechnika Krakowska, Podręcznik, Kraków 2000 [10] „ Opracowanie metodyki doświadczalnej weryfikacji sposobu szybkiego doboru parametrów skra wania na potrzeby predefiniowanych strategii obróbki” Sprawozdanie za realizacji projektu CAx, punkt 2.3, 30.12.2011, Warszawa.



[11] „ Opracowanie predefiniowanych strategii obróbki” Sprawozdanie za realizacji projektu CAx, punkt 2.3, 06.2011, Warszawa. [“Pre-defined machining strategies” Report for the project CAx developed in Warsaw University of Technology in co-operation with industrial partner.] [12] „ Zastosowanie mechanizmu efektywnego stosowania predefiniowanych strategii obróbki w środowisku Catia” Sprawozdanie za realizacji projektu CAx, punkt 2.3, 12.2011, Warszawa. [The mechanism of effective use of pre-defined machining strategies in the environment Catia “ Report for the project CAx developed in Warsaw University of Technology in co-operation with industrial partner.] o H. Kim, Byoung K. Choi, “Machining efficiency comparison Direktion-parallel tool path with con[13] B tour-parallel too path” Computer-Aided Design 34 (2002), 89-95, www.elsevier.com/locate/cad [14] A li Lasemi, Deyi Xue, Peihua Gu, “Recent development in CNC machining of freeform surfaces: a state-of-the-art review”, Computer-Aided Design 42 (2010) 641_654, www.elsevier.com/locate/ cad
