International Interdisciplinary Journal of Scientific Research Vol. 1 No. 3 December, 2014

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DESIGN AND FABRICATION OF A CNC MACHINE FOR

ENGRAVING AND DRILLING

Khan LA 1, Mehtab U

2, Hasan EU

3, Hussain Z

4

1Associate Professor/Associate Dean University of Lahore Islamabad Campus

2,3,4 Department of Mechatronics Engineering, Air University, Pakistan

Abstract

The paper is focused on the research of On-machine measurement system for a CNC multi-axis milling

machine. This research is aimed at the suitable selection of measuring parameters for On-machine

measurement system in order to reach an accurate and reliable quality control of the mechanical part.

Theoretical information and overall concept of research are also presented.

Keywords— CNC multi axis milling machine, on-machine measurement, quality control

Introduction

The importance of improving machine accuracy is well recognized due to increasing demand of reducing the

product dimensional tolerance. Quality control is one of the important parts of production process which can

be performed through many possible ways with different measuring gauges and equipment. New products

following trends of designers and requirements of industrial applications with free form surfaces demand

instruments with high ability of measuring. Regarding many advantages of On-machine measurement

system, the utilization of the system has become a subject of many researchers. These systems allow

controlling the parts directly on the machine tool, and also the process can be integrated directly to the

machining process, whereas the delays from transportation and measuring process performed on coordinated

machine are omitted.

System Overview

The CNC Engraving Machine consists of an X-axis, Y axis (gantry, Cutting table, Spindle, Base & Frame),

and Z-axis linear drive system (plunge arm, frame etc). However, CNC Control card and Computer are the

typical parts of a CNC machine and together formed the complete control unit of the machine. A standard

International Interdisciplinary Journal o

system configuration is shown in Fig

mechanism is used for 3 axis drive sys

mechanism has a high mechanical effici

stepper motors as accurate rotation was

without any compromise at torque.

F

Mechanical Modeling

� � � � �� ��� + ��� = �net (1)

Electrical Modeling

Using Kirchoff’s Voltage Law

V Input = � � �����

� � � � ���

� ������� (2)

The net torque of stepper motor is

� � �m sin � ∆�� (3)

�m = �hold on/rated = 1.5 Nm/A

Substituting (1) in (3)

��� + ��� = �m sin� ∆��

Now, Substituting (2) in (4)

��� + ���= �m sin� ∆�� " �������

l of Scientific Research ISSN: 2200-9833

ig 1, showing the essential parts of a CNC m

ystems as it provides reliability and durability of

iciency and a very low cost of maintenance. The

as required in the process and stepper motor pro

Fig 1 System Flow diagram

1)

2)

3)

(4)

33 www.iijsr.org

machine. Ball screw

of to the system. This

he actuators used were

rovides such accuracy

International Interdisciplinary Journal of Scientific Research Vol. 1 No. 3 December, 2014

3

Taking Laplace

��#�$�#% � &#' � �m sin� ∆�� (�) � � �#�*(5)

� → ,-./0/1-23 4.5 �27-#

� � 8% �9%� � 9%

� � 0.318 �0.0179�% " �6.28�% � 4.01 " 10BCDE

Substituting values in (5)

��#�$4.01 " 10BC#% � 1.5 #' � 1.55�60 " 2� F4.5# �3.21 � 0.05�G

So,

��-� � 0.17 − 0.209.�BI.JK�� � 0.034.�BI.CLM�� (6)

S.No Parameter Value

1. ∆� 2

2. 60

3. M 0.32 kg

4. R 0.0179 m

5. Fc 9.81 N

6. b 1.56 N/s

Table 1 Parameters used for the solution of equations from 1 through 5

Spindle Motor Power Calculations

Input Power = VI

Efficiency = 80%

POutput = 80" � MJNII� W = 7.68 W

P required = �required " 9

�required → Required Torque for routing PCB (Copper + Bakelite or Fiber)

�required = 0.012 Nm

9 = 628.3 OP�)QR

P required = 7.54 W

P required < P Output

Motor can be used.

S.No Parameter Value

1.

RPM

628.3 OP�)QR

2. Input Voltage 12 V

3. Current 0.8 A

4. PInput 9.6 W

Table 2 Parameters used to calculate spindle motor power

International Interdisciplinary Journal of Scientific Research ISSN: 2200-9833 www.iijsr.org

4

Spindle Motor Modeling

RPM = 6000

9 = 628.3 OP�)QR

tm = K Im (7)

E = k 9m (8)

K = N%

J%L.C = 0.019 V/s

G = 1

Ro = G Ed / Im = 15 Ohms

Using Newton’s 2nd

Law of Motion

∑ � � � �� = �M - b9m – �L (3)

IM = �M / K

Using Kirchoff’s Voltage Law

EM = G ED - Ro IM

EF = h 9m

e = ED - EF

EM = Ge + Ro IM (9)

G = 1

So,

�M = K " (ED - h 9m - k 9m) Ro (10)

Substituting equation (5) in equation (3)

�9m + b9m = k/ Ro [Ed - h9m - k 9m] – �L (11)

9m = [JD + (B+K2/ Ro + K h/ Ro) = – �L + K Ed / Ro (12)

B= FC/9 = 0.02/628.3 = �L max / Imax = 0.012 / 0.8 = 0.015

By using the values given in table 3and solving equation (7), we get

9m [(1.28 D +1)] =17 Ed – 6.6 x 104 �L

T, = Static Gain = 17

�, = Disturbance Sensitivity = -6.6 x 104

V , = Time Constant = 1.28 seconds

Natural time constant = J / B = M.WK "NIXYC.NL "NIXY = 3 seconds

Homogenous complimentary solution is

9m (1.28 D + 1) = (17" 2) - 6.6 " 104

(6 " 10-5

)

9m (1.28 D + 1) = 200 (13)

9m (1.28 D + 1) = 0

D = -0.78

9mh = A e-0.78t

Complimentary solution is

9mc = %II

�N.%L ��N�

9m (t) = A e-0.78t

+200

Initial conditions at 9m = 0 and t=0

9m = 0

0 = A +200

A = -200

International Interdisciplinary Journal of Scientific Research Vol. 1 No. 3 December, 2014

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So,

9m (t) = 200 (1 – e-0.78t

)

S.No Parameter Value

1. J

9.54 x 10-5

Nm

2. FC

0.02 (2000

RPM)

3. 9mc

200

Table 3 Parameters used for spindle motor modeling

Ball Screw Calculations

Required Accuracy = 0.0254 mm

Step of motor = 2O

L "(%

CJI) = 0.0254

L = 4.572 mm (Pitch of Lead Screw)

Percentage of Error = 1.57 %

Can be neglected. OK to use

Conclusion

The project started with a machine capable of only point to point motion with many drawbacks (accuracy,

jerks etc).The existing machine features are compared with the professional CNC machine.

After comparison and making the required improvements, the machine is in a position to mill complex

contours on PCB, soft wood and soft metals with considerable accuracy and speed. Achieving this primary

goal is the result of improvements in both electrical and mechanical design. Exploring new software with

better capabilities also helped us in achieving this goal. The workspace and job clamping system is also

improved.

International Interdisciplinary Journal o

Fig 2 Fabricated working model of CN

Fig 3 PCB board engraved by the deve

X-axis

Y-axis

Z-axis

PCB sit-in for engraving and d

Tool

l of Scientific Research ISSN: 2200-9833

CNC engraving and drilling machine

eveloped CNC machine

axis

ing and drilling

33 www.iijsr.org

International Interdisciplinary Journal of Scientific Research Vol. 1 No. 3 December, 2014

7

References

[1] Katsuhiko Ogata, Modern Control Engineering, 4th Edition, Prentice Hall Of India, New Delhi, 2004

[2] Kelly James Floyd, Patrick Hood-Daniel, Build Your Own CNC Machine, 1st Edition, Springer-

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[3] Geoff Williams, CNC Robotics: Build Your Own Shop Bot, 1st Edition, McGraw Hill, New York,

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[4] Seames, S. Warren, Computer Numerical Control, 4th

Edition, Thomson Learning Inc., New York,

2002.

[5] Overby Alan, CNC Machining Handbook: Building, Programming, and Implementation, 1st Edition,

McGraw Hill, New York, 2010.

[6] Madison James, CNC Machining Handbook, 1st Edition, Industrial Press Inc., New York, 1996.

[7] Albert Alan, Understanding CNC Routers, 1st Edition, FPInnovations, Ottawa, 2011.

[8] Valentino James , Goldenberg Joseph, Introduction to Computer Numerical Control, 5th

Edition,

Prentice Hall, New York, 2012