project report of design and fabrication of abrasive cut off machine

1. INTRODUCTION

A cut-off is one of the most commonly used machinery in the manufacturing process, and almost every workshop has one. It is easy to use, maintainable and cost effective. The task was given to a group of engineers in training to design an abrasive cut-off machine for cutting steel. After considering a few concepts, the final design and calculations were done.

2. User Requirements An abrasive cut-off machine has to completely designed for cutting steel. It must be able to cut 50mm solid steel and 75mm steel pipes. The cut-off Machine should be fitted with safety guards where required and also have an adjustable down stop to the limit the depth of the cut. A mechanism is required for pulling the machine down when someone is cutting.

3. Mission Level · Long live expectancy · Maintainable · Reliable · Functional · Simplicity · Safety · Productivity · Easy to use 1

4. Functional Analysis 4.1 System Level

4.2 System Level Functional Diagram

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4.3 First Level Functional Diagram

4.4 Design Parameters per Function 1.1. Start Motor 1.1.1. Is cutting disc clear of work piece 1.1.2. Press button Start button visible Start button reachable 1.1.3. Pull up Use handle 1.1.4. Press button Start button visible Start button reachable 1.2. Pull Down 1.2.1. Pull handle long enough Hand grip (ergonomics) Enough momentum 3

1.2.2. Finished cutting desired cut achieved 1.3. Cutting 1.3.1. Hold handle down Handle long enough Sparks directed backwards Disc safety guard Cutting machine stationary 1.4.

Pull Up

1.4.1. Press stop button visible Red 1.4.2. Remove work piece Release clamp 1.5. Motor Stop

5. Design Specifications

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Figure 5.1 Forces on the cutting disc and pulley.

6. Concepts & Concept Evaluation 6.1Concept 1

Figure 6.1 Concept 1

In the concept the hinge point is situated at the rear of the machine. Pulleys with V-belts will be used to transmit power from the motor to the arbor shaft. 5

6.2 Concept 2

Figure 6.2 Concept 2

In this concept the hinge is located slightly in front of the motor (if the cutting disc is said to be the front), this will act like a “see-saw”. When the machine is not busy cutting steel, the cutting disc will be kept in the air due to the weight of the motor at the back. Pulleys and a V-belt will be used for power transmission. 6.3 Concept 3

Figure 6.3 Concept 3

Fixing the cutting disc to the motor shaft directly. 6

6.4 Concept Evaluation

Table 6.1 Concept Evaluation

Thus from the evaluation, Concept 1 will be the best option.

7. Block diagram

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8. Design calculations 8.1 Power Transmission and Torque 8.1.1 TORQUE ON SHAFT: P= (2× π ×N×T)/60 3.75×10³= (2×3.14×2950×T)/60 T=12.138Nm=12.138×10³Nmm

8.2 Design of shaft 8.2.1 DESIGN OF SHAFT 1 Material Used: 45C8 [Refer PSG DB page no.1.9] TENSILE STRENGTH=700N/mm² YIELD STRENGTH=350N/mm² TORQUE= (π ×t×d³)/16 8.2.1.1 TORQUE ON SHAFT1: P= (2× π ×N×T)/60 3.75×10³= (2×3.14×2950×T)/60 T=12.138Nm=12.138×10³Nmm. Shear stress t=ultimate strength/factor of safety. FOS=4. t=700/4=175N/mm². 8

[FOS>2.15 [Refer PSG DB page no.7.22] T= (π ×t×d³)/16 12.138×10³= (π ×175×d³)/16 d=7.06mm Normally we use shaft of diameter 20-25mm. 8.2.2 DESIGN OF SHAFT-2 8.2.2.1 TORQUE ON SHAFT2: P= (2×3.14×N×T)/60 3.75×10³= (2× π ×4000×T)/60 T=8.95Nm=8.95×10³Nmm. T= (π ×t×d³)/16 8.95×10³= (π ×175×d³)/16 d=6.38mm Normally we use shaft of diameter 20-25mm. 8.3 DESIGN OF V-BELT AND PULLEY N1=4000rpm N2=2950rpm P=3.75KW

8.3.1 Selection of belt: For P=3.75kw [Refer PSG DB page no.7.58] 9

Select B type belt. 8.3.2 Small pulley diameter: For B dpmin=125mm [Refer PSG DB page no.7.62] demax = dpmax × Fbmax de = equivalent pitch diameter dp = pitch diameter of smaller pulley Fb = small diameter factor For demax [Refer PSG DB page no.7.62] demax=175mm Speed ratio: i =N1/N2 i = 4000/2950=1.35 For i=1.35 Fb=1.1 [Refer PSG DB page no.7.62] demax = dpmax × Fbmax 175=1.1×dpmax dpmax =159mm For standard diameter [Refer PSG DB page no.7.20 R20 series] It should be between dpmin & dpmax dp = 140mm

8.3.3 CENTRE DISTANCE: C/D=1(assume) 10

N1/N2=D/d D=1.35×140=189mm D=200mm for standard diameter [Refer PSG DB page no.7.20 R20 series] C/D=1 C=200mm [Refer PSG DB page no.7.61] Cmin=0.55(D + d) + T For T [Refer PSG DB page no.7.58] Normal thickness T=11mm Cmin = 0.55(200+140) +11 Cmin = 198mm Cmax = 2(D + d) [Refer PSG DB page no.7.61] Cmax = 2(200+140) = 680mm Calculated value of C lies between Cmin & Cmax 8.3.4 LENGTH OF BELT: [REFER PSG DB P.NO:7.61] L=2C + [(3.14/2) × (D + d)] + [{(D-d) ²}/4C] =2×200 + [(3.14/2) × (200+140)] + [{(200-140) ²} / (4×200)] Pitch length: L=938.57mm Nominal inside length: [Refer PSG DB page no.7.59] 11

For nominal inside length corresponding to nominal pitch length (965mm) is 1008mm. Length correction factor Fc=0.83 [Refer PSG DB page no.7.59] 8.3.5 Angle of contact: wrap angle on smaller pulley: Θ=180-[60{(D-d)/C}] =180-[60{(200-140)/200}] Θ =162deg Angle correction factor Fa = (v-v belt) For Θ=163 Fa=0.96 [Refer PSG DB page no.7.68] For service factor [Refer PSG DB page no.7.69] Medium duty Fs=1.1(for up to 10 hrs) 8.3.6 POWER RATING: [Refer PSG DB page no.7.62] KW=[{0.79×S-0.09}-(50.8/de)-{(1.32×10^(-4) ×(S²)}]S S = (π ×d × N)/60 = (π ×4000×140)/(60×1000) S=29.32m/s. de = dp × Fb =140×1.1 de =154mm KW=[[{0.79× (29.32)-0.09}-(50.8/154)-{(1.32×10-4 ×(29.32²)}] ×29.32] 12

KW =4.04 8.3.7 Number of belts: [Refer PSG DB page no.7.70] No. of belt = (P × Fa) / (KW × Fc × Fd) = (3.75×1.1)/(4.04×0.83×0.96) = 0.98 ~1 8.3.8 Final centre distance: [Refer PSG DB page no.7.61] C=A + {[(A²)-B]1/2} A = (L/4)-(3.14× [(D + d)/8]) = (1008/4)-(3.14× [(200+140)/8]) A=118.48mm B= [(D-d) ²]/8 = [(200-140) ²]/8 B=450mm C=A + {[(A²)-B]1/2} C=118.48 + {[(118.48²)-450]1/2} C=235mm

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8.4 SPECIFICATION: 1) 2) 3) 4) 5) 6)

Type of drive=V-belt Belt used =B965-IS2494 Number of belt=1 Smaller pulley diameter=140mm Larger pulley diameter=200mm Centre distance=235mm

9. PART DIAGRAMS 9.1 PULLEY SHAFT AND COUPLING….

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9.2 ABRASIVE WHEEL

9.3 BASE

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ABRASIVE CUT- OFF MACHINE

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10. DESCRIPTION 10.1 Motor

A three phase one horse power motor is used. The motor shaft has key way in

it. A key is used to hold the larger pulley with that of the motor shaft. 10.2 Motor bed Motor bed must withstand heavy shock loads so we use cast-iron material to absorb heavy shocks during operation.

10.3 Pulley There are two pulleys one is larger which we have discussed already and the other is smaller pulley which is connected to arbor shaft.

10.4 Arbor shaft Arbor shaft is the one which connects the smaller pulley and the cut off wheel.

10.5 Bearings Bearings are used to hold the arbor shaft in position. We use two bearings one at smaller pulley side and other at the cut off wheel side.

10.6 Washers and nut Washers are used to hold the abrasive cut off wheel tightly in position.

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10.7 Belt We use A-38 V-belt to connect the two pulleys.

10.8 Vice Vice is used to hold the work piece. It can be adjusted horizontally to have clear cut on the work piece. It has got two jaws one is fixed and the other is movable jaw. The fixed jaw can be swiveled to have a angular cut.

10.9 stoppers Stoppers are provided for the safety measures we use three stoppers to make limits. A stopper is provided in the rear to prevent the motor from dashing the hinge point. Second one is to give limit for the motor bed to come down while the operating lever is pressed. Third one is to limit the depth of cut.

10.10 Cutting disc housing Cutting disc housing is provided to prevent the dust particles and fire to move backwards not affecting the operator.

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11. CONCLUSION & FUTHER DEVELOPMENT This report has discussed the idea of abrasive cut off machine and demonstrating the functionality and performance of the abrasive cut off machine. An overview of the machine has been discussed. A detailed design calculation has been described, offering an economical safer and rather simple, yet reliable, way to meet the requirement of a workshop. It is important to mention that the machine can perform more complex tasks by applying simple modifications on the design. For instance, mounting different sensors in the machine would inform the user of changes in the behavior of the material while cutting. In addition we can modify the operation from manual to automatic for better performance and to reduce the time for operation.

12. REFERENCES www.google.co.in www.scribd.com www.howstuffworks.com www.machinesindia.com

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