Design and Fabrication of CNC Precision Router

Group 3

M. Ismail Leghari 2013248

M. Shoaib Butt 2013261

Saad Ali 2013318

Sarmad Ishfaq 2013338

Advisor

Prof. Dr. Wasim Ahmed Khan

Background

Expensive Technology- Novel Technology In Pakistan

Import Restriction/Local Development- Need has to catered locally for small industries

Accuracy and Precision- Demand is increasing rapidly

Objectives

Efficiently design and fabricate a 3-Axis CNC router with micron (10-6) level precision.

Incorporate multiple heads per customer demand.-For numerous additive manufacturing processes

Most economical CNC precision router for small scale industries of Pakistan.

Design Part

Initial Design

Final Design

Exploded View

Mechanical Specifications

• Fixed Gantry

• Moving Table

• Bed area = 250mm * 250mm

• ASTM A36 Steel used for the structure

• Machine Weight = 106 Kg

• Box Volume = 25cm * 25cm * 10cm

• Can accommodate multiple 3D Printing Heads

Material Parameters for Ball Screw

Material AISI 6150 alloy steel

Density 7850 kg/m3

Modulus of Elasticity 200 GPa

Poisson Ratio 0.3

Yield Strength 415 MPa

Mathematical Model (To Find Max Beam Deflection Under Action of Load)

Assumption

• The ball screw behaves like a simply supported beam.

• Cross section area the beam is circular.

• As bed has extended size and there is some load over the bed. Uniformly distributed load of 1180 N/m is applied from 0.2m to 0.3m as shown.

• Moment of magnitude 6.4 N.m is also applied at the center of beam at 0.25 m.

Analytical Solution

The following equations were developed to find the maximum displacement of shaft.

𝑦1 =1

E∗

243.85𝑥3−39.77𝑥

d4for 0 < x < 0.2m

𝑦2 =1

E∗

−1001.68𝑥4+1045.075𝑥3−240.388𝑥2−7.72346𝑥−1.6025

d4for 0.2m < x < 0.25m

𝑦3 =1

E∗

−1001.68𝑥4+1045.075𝑥3−305.5775𝑥2−24.86945𝑥−5.67637

d4for 0.25 < x < 0.3m

𝑦4 =1

E∗

−156.86𝑥3+235.295𝑥2−83.2988𝑥−2.43672

d4for 0.3 < x < 0.4m

ABAQUS Solution (FEM)

Comparison of Analytical And Computation Techniques

Major

Diameter

(mm)

Lead

(mm)

Max Deflection

Analytically (mm)

Max Deflection using

ABAQUS (mm)

% Difference

12 4 1.48 1.493 0.878378378

16 4 0.42 0.4128 1.714285714

20 4 0.19 0.194 2.105263158

25 4 0.078 0.0796 2.051282051

32 4 0.029 0.0293 1.034482759

40 5 0.0122 0.01223 0.245901639

50 10 0.0051 0.005046 1.058823529

• Less than 2.1 % difference in calculations from both techniques

• Confirms our methods

Torque and Critical Speed Calculations

• Torque

𝑇 =𝐹.𝑑𝑚

2

𝑙+𝜋𝑓𝑑𝑚

𝜋𝑑𝑚−𝑓𝑙+

𝐹.𝑓𝑐.𝑑𝑐

2

• Single threaded so lead ‘l’ will be equal to the pitch of screw

• Friction coefficient ‘f’, generally the material used for power screws is steel for the screw and the nut is made of bronze. Value is between 0.10-0.15.

λ is a factor determined by the ball-screw support method where:

One end fixed and the other free, λ = 0.59π

Both ends simply supported, λ = π

One end fixed and the other simply supported, λ = 1.25π

Both ends fixed, λ = 1.49π

• Critical Speed

𝑛𝑐𝑟 =𝜆2

𝐿2𝐸∗𝐼∗𝑔

𝛾∗𝐴∗

60

2𝜋

Results of Torque and Critical Speed

Major Diameter

(mm)

Lead (mm) Torque ncr (rpm)

12 4 0.289968099 5702.357764

16 4 0.37384134 7603.143686

20 4 0.457938052 9503.929607

25 4 0.563193885 11879.91201

32 4 0.710668627 15206.28737

40 5 0.888335784 19007.85921

50 10 1.144845129 23759.82402

Static Analysis of the Ball Screw in Solidworks

• Mathematical model in FEM software ABAQUS.

• 3D model is to be checked for deflection in real conditions.

• Boundary conditions and forces applied are shown in Figure .

• Gravity is also taken into account to make the analysis more realistic.

• Maximum deflection due to static loading to be 0.28 mm

Dynamic Analysis of the Ball Screw in Solidworks• Working Parameter and Condition

mm/s rpm rad/s Hz

20 19.1 2 0.32

60 57.3 6 0.95

• To ensure that the natural frequency of the structure does not resonates with the operating frequency

• Natural Modes of Frequency (First 5)

Frequency Number Rad/sec Hertz Seconds

1 1188.5 189.16 0.0052865

2 1192.4 189.77 0.0052695

3 3478.2 553.57 0.0018064

4 3490.9 555.6 0.0017999

5 6929.8 1102.9 0.00090669

Structure operating frequencies (0.32-0.95 Hz) in not within natural frequency range.

Critical Node Response

• Most Critical node is analyzed for the maximum displacement under working conditions

• Results• Max Displacement =

0.19 mm

• Frequency = 0.35 Hz

Justification of Dimension through different analysis• Mathematical model analysis = 0.42 mm

• Static Analysis = 0.28 mm

• Dynamic Analysis = 0.20 mm

Can safely say that our structure is safe from vibrations

Ball Screw Dimension = 16 mm

Fabrication Part

Assembly and Detailed BoQ

Fabrication Details

• Material Used- A36 ( 415 MPa Yield )

• Joining Mechanism- Square Plates- Bolts and Nuts- Pins (Push Fitting)

• Bearings Used- External Flange

(Universal Ball Bearings)

• Noise Reduction Mechanism-Ribs and Fins

3D Printing Heads

Electronics and Software Parts

Electronics

• NEMA 23 motors

• 1.26 Nm Holding Torque

• 2 Phase

• 1.8 degree step angle

• 3A

• TB-6560 stepper motor drivers

• Sharp infrared sensors: range 2cm-15cm

Software

• Raspberry pi

• C sharp Language

• GUI

• I/O configuration

• Compatible with electronics

Future Prospects

• Material removal processes like vertical milling can also be performed on the precision router after few minor modifications.

• Precision can be further enhanced to less than 2 microns by the utilization of micro-stepping.