 Open Access
 Total Downloads : 527
 Authors : Abhishek Kumar Saroj, Dr. S.C Jayswal
 Paper ID : IJERTV2IS100076
 Volume & Issue : Volume 02, Issue 10 (October 2013)
 Published (First Online): 07102013
 ISSN (Online) : 22780181
 Publisher Name : IJERT
 License: This work is licensed under a Creative Commons Attribution 4.0 International License
Analysis of Different Parameters on Tool Path for Machining Sculptured Surfaces
Analysis of Different Parameters on Tool Path for Machining Sculptured Surfaces
Abhishek Kumar Saroj 1 Dr. S.C Jayswal 2

Department of Mechanical engineering, M.Tech final year student, MMMEC, Gorakhpur, India

Associate Professor in Department of Mechanical engineering, MMMEC, Gorakhpur, India

Abstract
In this paper effect of different parameters on tool path is described. This paper shows that, for machining a surface an appropriate cutter diameter, step over percentage, is required. If they are not in proper range, than machining time increases. So for creating a sculptured surface in CNC milling process effect of different parameters are analyzed and the effect of parameters (like feed rate, step down, effect of tool containment boundaries etc.) on machining time is shown. In this analysis, main purpose is to obtain the minimum machining time for machining process, so different parameters are analyzed with respect to machining time because if machining time is optimal than our production time reduces and production rate increases. This paper analyzed different parameters with respect to machining time and conclusions are given based on the results.
For this analysis all the data is obtained from the software MASTERCAM and analysis is based on the CNC end milling process. Experiments are performed on MSME Tool Room, Jamshedpur under the guidance of Mr. Jyoti for MASTERCAM and Mr. Koyal Mohamed for the CNC end milling process.
Keyword Sculptured surfaces, CNC milling, MASTERCAM, Tool paths, Simulation, Computer integrated manufacturing.

Introduction
In the present time sculptured surfaces are very widely used in different industries like automobiles in which different type of parts generally created with sculptured surfaces are used. These surfaces are used for increasing the performance and giving a good look for the car or other part. A great variety of products, from dies for machining automotive body panels to turbine blades all rely on this technology. Sculptured surface machining (SSM) on a multiaxis NC machine requires application of efficient methods of tool path generation. So an analysis of different parameters which are effecting the machining of tool path is presented in this paper.
In previous paper Simulation of tool path for machining sculptured surface [1] basic idea of creating a surface with the help of basic dimensions and simulation methodology of machining a sculptured surface was given. Effect of parameters on the machining time and various relationships were not analyzed in that paper. So this paper gives the various relationships and effect on parameters on the machining time. Machining time is very important in manufacturing process because if machining time decreases than our production rate increases and cost of the component decreases. So analysis is done for
obtaining optimal machining time in roughing operation because in roughing surface finish does not matters.

Literary survey –
There is a massive body of previous work in the area of cutting toolpath planning in machining sculptured surfaces on multiaxis NC machines. Dragomatz and Mann compiled a comprehensive overview of scientific publications in the field. The problem of toolpath generation was examined by Marciniak [2]. Choi and Jerard proposed a toolpath generation method called the Cspace method [3]. A brief overview of the recent publications in the field of toolpath generation for SSM is presented below. The toolpath generation problem for the NC grinding operation was investigated by Sarma and Dutta [4]. A toolpath generation method for threeaxis milling by using the guide surface was developed by Kim and Choi [5]. Fiveaxis roughing tool paths generated directly from a tessellated representation of a body were investigated in [6]. A cutterpath scheduling method is developed for milling of concave and/or wallbounded surfaces [7]. An accurate and efficient method to generate a NC tool path for a smooth freeform surface in terms of planar cubic B spline curves was developed by Lartigue et al [8]. Kim and Sarma proposed a heuristics based approach to the problem of tool path generation along directions of maximum kinematic performance. Efficient toolpaths in SSM using threeaxis ballend milling are determined in [9]. Forthe Zconstant contour machining, a toolpath generation procedure is presented in [10].

EXPERIMENTATION
In this paper all the experiment are performed on a sculptured surface for roughing operation. Details of generating of this surface and applying simulation are given in paper Simulation of tool path for machining sculptured surface. in actual machining process for generating a surface different parameters are required like optimal diameter of tool, step over percentage, feed rate, depth of cut, step down etc. So for finding the optimal values of these parameters simulating software is used and after applying the experiments for different parameters results are obtained. Here dimensions of the part are given which is used in this experiment as follows

Dimensions of the part
Figure: 1 shown below gives dimension of the part used for machining operation. With the help of these dimensions a sculptured machining surface is created which is discussed in previous paper and after creating surface simulation is performed for roughing operation. So dimensions are as follows
Figure1: Dimension of the Machining Surface
In this figure: 1 top view, front view, side view and isometric view of the part is shown. All the experiments are performed on the surfaces generated by this part this model is created in MASTERCAM software and machining operations are simulated for CNC end milling process. Firstly roughing operation is performed on the surface for removing the excess material than finishing operation is performed.

ROUGHENING OPERATION
Roughening operation is mainly perform for removing the excess material so for this operation appropriate strategy is that which can remove excess material in less time. While removing the material it is very important that the work piece and tool would prevent, from any unwanted defect or damage. In the present investigation various strategies applied on the work piece for the roughing operation, these strategies are available in the machining software MASTERCAM.
There are seven strategies which are followed by the software MASTERCAM. While applying these strategies input data like feed rate, spindle speed, plunge rate, retract rate are constant. Applying these strategies gives the result that which strategy is suitable for roughing operation and also its gives the optimal diameter of the cutter because it is done with different diameter range. These strategies are suitable for different operation for different machining condition the data obtained after applying these strategies are given in the table no 5.1.

EFFECT OF DIAMETER ON DIFFERENT STRATEGIES
There are two parameters are analyzed by this experiment first one its gives appropriate strategy for the operation and second it gives the optimal cutter diameter for machining. Data obtain by simulating software by applying these strategies are given in table no.1. MASTERCAM gives us machining time in hr. min. and sec. but for plotting graphs this is converted into seconds.
TABLE NO. 1 MACHINING TIME FOR DIFFERENT STRATEGIES
Sr.
no.
Tool path strategies
Machining time (Sec.)
Dia 4
Dia 5
Dia 6
Dia 7
Dia 8
1
Zigzag
6680
4405
5947
9461
9934
2
Constant overlap spiral
7526
4650
6296
9917
10166
3
Parallel spiral
7605
4581
6522
10115
10414
4
Parallel spiral clean corners
7903
4781
6773
10336
10779
5
High speed
6332
5111
5366
5532
4918
6
True spiral
9373
5980
8228
11429
12448
7
One way
31582
16795
19976
21810
12448
Relation Between Time Spent in Machining to Different Strategies
30000
25000
20000
15000
10000
5000
0
Strategies
1
2
3
4
5
6
7
Diameter" 4"
6680
7526
7605
7903
6332
9373
31582
Diameter" 5"
4405
4650
4581
4781
5111
5980
16795
Diameter"6"
5947
6296
6522
6773
5366
8228
19976
Diameter "7"
9461
9917
10115
10336
5532
11429
21810
Diameter "8"
9934
10166
10414
10779
4918
12448
12448
Relation Between Time Spent in Machining to Different Strategies
30000
25000
20000
15000
10000
5000
0
Strategies
1
2
3
4
5
6
7
Diameter" 4"
6680
7526
7605
7903
6332
9373
31582
Diameter" 5"
4405
4650
4581
4781
5111
5980
16795
Diameter"6"
5947
6296
6522
6773
5366
8228
19976
Diameter "7"
9461
9917
10115
10336
5532
11429
21810
Diameter "8"
9934
10166
10414
10779
4918
12448
12448
Machining time for these seven strategies with different diameter range are available in seconds. So with the help of this data a graph is plot between machining time and different strategies used in the software.
Tme in seconds
Tme in seconds
35000
Figure 2: Relationship between Time spent in Machining to Different Strategies
Figure :2 show that for a sculptured surface machining time is minimum for a specific diameter of a tool. For this diameter, machining operation gives minimum time. If diameter is varying from this diameter range than machining time increases. As in this study of graph no.1 diameter 5 gives us minimum machining time. So diameter 5 is suitable for machining.
For maximum production less time in machining required. As shown by the graph no.1 minimum machining time is obtained from zigzag tool path strategy. As shown in table no.1 seven strategies used for removing the material from the work piece but Zigzag motion of tool path takes less time so for roughing operation zigzag tool path selected. High speed strategy also gives minimum machining time at some places but it is not suitable for machining because after analysis we check it will not remove the material properly. So high speed strategy is not selected for this analysis.

EFFECT OF STEP OVER PERCENTAGE ON THE MACHINING TIME
From above study, diameter and strategies which is followed for creating the surface is selected. Other parameters like step over percentage for Zigzag motion study is observed in this operations and its data is given in table no. 2 which is shown below
TABLE NO. 2 MACHINING TIME DUE TO STEP OVER PERCENTAGE
Sr.
no.
Step over percentage
Machining time (Sec.)
Dia 4
Dia 5
Dia 6
Dia 7
Dia 8
1
10
20673
16267
14478
16773
15105
2
20
12811
10088
9766
12465
11784
3
30
10054
7996
8116
11326
10909
4
40
8647
6948
7253
10520
10082
5
50
7796
6430
6854
10344
9934
6
60
7488
6058
6420
9725
9715
7
70
6953
5801
6152
9797
9368
8
80
6680
5536
5947
9461
9481
9
90
6415
5321
5870
9552
9144
10
100
6381
5234
5678
9244
9249
In table no. 2 machining time with varying step over percentage is shown, machining time is in seconds. Step over controls the surface finish of the machining material so for in roughing operation surface finish does not have more importance so its high value which gives less machining time safely is considered. Graph between machining time and step over percentage is given in figure: 3 –
Relationship between time in seconds to Step over percentage
25000
20000
Time in seconds
Time in seconds
15000
10000
5000
10
20
30
40
50
60
70
80
90
100
Diameter"4"
20673
12811
10054
8647
7796
7488
6953
6680
6415
6381
Diameter"5"
16267
10088
7996
6948
6430
6058
5801
5536
5321
5234
Diameter"6"
14478
9766
8116
7253
6854
6420
6152
5947
5870
5678
Diameter"7"
16773
12465
11326
10520
10344
9725
9797
9461
9552
9244
Diameter"8"
15105
11784
10909
10082
9934
9715
9368
9481
9144
9249
10
20
30
40
50
60
70
80
90
100
Diameter"4"
20673
12811
10054
8647
7796
7488
6953
6680
6415
6381
Diameter"5"
16267
10088
7996
6948
6430
6058
5801
5536
5321
5234
Diameter"6"
14478
9766
8116
7253
6854
6420
6152
5947
5870
5678
Diameter"7"
16773
12465
11326
10520
10344
9725
9797
9461
9552
9244
Diameter"8"
15105
11784
10909
10082
9934
9715
9368
9481
9144
9249
0
Step over (%)
Figure 3: Relationship between Time (seconds) to Step over percentage
This figure: 3 show that when the value of step over percentage is less it takes more machining time. Its vale is almost same for the 70% to 90% range some deflection is occurs in between 80% to 90%. So 80% step over is selected for further analysis of surface.
After selecting the diameter of the tool its step over percentage and strategy follows during machining. Different other parameters effect on the machining time is analyzed these are given below

EFFECT OF TOOL CONTAINMENT BOUNDARIES
Tool containment boundary is that boundary in which tool done its cutting action during the machining. In other words it is like a fence in between tool move. So for analyzing its effect on machining time two boundaries are selected one is lies on the wok piece outer boundary and other is having greater area than outer boundary of work piece. The data obtained from the software are given in table no.3
TABLE NO. 3 MACHINING TIME DUE TO TOOL CONTAINMENT BOUNDARIES
Sr.
no.
Tool path strategies
Machining time (Sec.)
Tool containment boundary 1 ( lies outside)
Tool containment boundary
2 (lies on the work piece)
1
Zigzag
5536
4405
2
Constant overlap spiral
5743
4650
3
Parallel spiral
5868
4581
4
Parallel spiral clean corners
6144
4781
5
High speed
5754
5111
6
True spiral
8094
5980
7
One way
22568
16795
7, 16795
7, 16795
15000
15000
MACHINING TIME
MACHINING TIME
This data shows that if tool containment boundary increases than machining time increases so it is profitable to use optimal tool containment boundary. Relationship between tis data is shown in figure: 4
Varriation Due to Tool Containment Boundary
Varriation Due to Tool Containment Boundary
25000
25000
7, 22568
7, 22568
20000
20000
5000
5000
0
0
0
1
2
3
4
5
6
7
8
0
1
2
3
4
5
6
7
8
STRATEGIES
STRATEGIES
10000
10000
TCB 1
TCB 2
TCB 1
TCB 2
Figure 4: Relationship between Tool Containment Boundaries
This Figure: 4 shows that if tool containment boundary lies in the outer boundary of the work piece than it is taken less time and for increase in the tool containment boundary is more than it is taken more time.

RELATIONSHIP BETWEEN FEED RATE AND MACHINING TIME
Another parameter which is analyzed for the study is feed rate and machining time. Effect of feed rate on machining time is analyzed in table no. 4 and its relationship is given in graph no.4.
25000
25000
TABLE NO. 4 MACHINING TIME FOR DIFFERENT FEED RATES
Feed rate (mm/ min)
100
200
300
400
500
600
700
800
900
1000
Machining time(sec.)
20846
11277
8087
6493
5536
4898
4442
4100
3858
3620
5000
5000
0
0
100 200 300 400 500 600 700 800 900 1000
FEED RATE
100 200 300 400 500 600 700 800 900 1000
FEED RATE
20000
20000
15000
15000
10000
10000
Machining
time
Machining
time
Machining time
Machining time
Figure 5: Relationship between Feed rate and Machining time
This Figure: 5 show that at lower feed rate machining time increases. As shown in the graph at lower fed rate slope of the graph is more so greater difference in machining time but at increase in feed rate slope of graph decreases and it is low at high values.

EFFECT OF STEP DOWN ON MACHINING TIME
Effect of step down or depth of cut is studied with the help of software and for different vales machining time is calculated the value of step down and corresponding machining time is given in the table no. 5 and its effect is given in graph no. 5
TABLE NO. 5 MACHINING TIME FOR DIFFERENT STEP DOWN
Step down (mm.)
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
Machining time(sec.)
9144
6101
4735
3816
3221
2768
2441
2143
1998
1680
Effect of Stepdown on Machining Time
Effect of Stepdown on Machining Time
10000
9000
8000
7000
6000
5000
4000
3000
2000
1000
0
0.2
0.3
Stepdown
10000
9000
8000
7000
6000
5000
4000
3000
2000
1000
0
0.2
0.3
Stepdown
0 0.2 0.4 0.6 0.8 1 1.2
STEPDOWN
0 0.2 0.4 0.6 0.8 1 1.2
STEPDOWN
0.4
0.4
0.5
0.5
0.6
0.6
0.7
0.7
0.8
0.8
0.9
0.9
1
1
1.1, 1680
1.1, 1680
MACHINING TIME
MACHINING TIME
Figure 6: Relationship between Step down and Machining time
This Figure: 6 show that at lower depth of cut or step down machining time is maximum. At higher depth of cut machining time is minimum but in actual cutting process depth of cut are not increases for a maximum level because if depth of cut increases from the maximum level it can harm the tool. For greater depth of cut greater energy released during cutting so for maximum depth of cut according to a given tool coolant is used during machining process.



Results & Conclusions
In this paper tool path generation strategy for sculptured surface machining has been analyzed and effects of different parameters are checked. Selection of suitable tool path
generation strategy for a sculptured surface, with minimum machining time shows the effectiveness of using software in manufacturing process. For creating a surface in CNC milling various strategies has checked as shown in table no.1 and table no.2 with the help of software MASTERCAM in very less time. So selection of proper strategy is very easy for manufacturer. With the help of machining time for a given surface different parameters are checked like diameter of tool used (figure no.2), step over percentage (figure no. 3), and effect of tool containment boundary (figure no. 4). Other parameters like effect of feed rate and effect of step down are also analyzed (figure no. 5 and figure no. 6). So by using these results optimal tool path selected. So it is analyzed by the above data that use of software in manufacturing process save our time, money, material and manufacturing cost. Tools and work pieces are also prevented from unwanted wear and damage. It is very helpful for creating NC codes of irregular and intricate shapes. Depending upon the above results there are some important points which conclude this paper as follows

Tool path generations strategies for roughening and finishing operation directly depend upon the type of surface and the machining time obtain from strategies are different for different diameter of tool used, for an appropriate diameter of tool gives minimum machining time (figure no.2).

In most of the cases Zigzag motion strategy is tacking least machining time. But it is not applicable for all surfaces. High speed strategy also gives minimum machining time but for this strategy defects are generated so before machining model is checked with the help of simulation as shown in figure no.2& 3.

Values of feed rate & step down are depend upon the nature of the work piece material and tool material if work piece material is hard than it is as low as possible for softer material its value is high with respect to the hard material but for finding a better shape its optimal value is used (figure no. 5 & 6).

For least machining time value of step over percentage should be as high as possible as shown by figure no. 3.

Tool containment boundary of work piece is lie on the outer boundary for finding minimum machining time as shown in figure no. 4.

Codes are automatically generated after finishing the process so actual machining of any part is very easy.

For actual machining process offset is set on the top level of the work piece and cutting is done in negative Z axis so in simulating software work piece is situated at negative z plane.

Codes are generated for machines which are having automatic tool changer so if machine is not having automatic tool changer than codes are modified according to machine.
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