JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III MACHINE TOOLS Previous Question Paper (March - 2021 - R13)
Answer any five questions. All questions carry equal marks.
Main
With the help of neat sketch, describe the complete geometry of a single point cutting tool.
Answer
The geometry of a single point cutting tool is defined by several angles and surfaces that control the cutting action. The key elements include:
- Back Rake Angle: The angle between the tool face and the reference plane, measured in a plane parallel to the tool axis. It controls chip flow and tool strength.
- Side Rake Angle: The angle between the tool face and the reference plane, measured in a plane perpendicular to the side cutting edge. It influences the cutting force and chip direction.
- End Relief Angle: The angle between the end flank and the end base, preventing rubbing of the tool against the finished surface.
- Side Relief Angle: The angle between the side flank and the side base, providing clearance for the side cutting edge.
- End Cutting Edge Angle: The angle between the end cutting edge and a line perpendicular to the tool shank.
- Side Cutting Edge Angle: The angle between the side cutting edge and the side of the tool shank, affecting the chip thickness and tool life.
- Nose Radius: The radius at the tip of the tool, which improves surface finish and tool strength.
These angles are typically represented in the American Standards Association (ASA) system or the Orthogonal Rake System (ORS).
During orthogonal cutting of a MS tube at 12m/min with a HSS tool having 15° rake the chip thickness ratio was 0.3 and the friction force on the tool chip interface measured by means of a special set up was 42kgf with coefficient of friction 0.6. Estimate the component of the cutting force's shear angle, shear strain and work done in deformation.
Answer
Given: Cutting velocity V = 12 m/min, Rake angle α = 15°, Chip thickness ratio r = 0.3, Friction force F = 42 kgf, Coefficient of friction μ = 0.6.
1. Shear Angle (φ): Using the relation tan(φ) = (r cos α) / (1 - r sin α):
φ = tan⁻¹(0.3141) ≈ 17.44°
2. Shear Strain (ε): Using the formula ε = cot(φ) + tan(φ - α):
3. Cutting Force Components: Since μ = F / N, Normal force N = F / μ = 42 / 0.6 = 70 kgf. The resultant force R = √(F² + N²) = √(42² + 70²) = 81.63 kgf.
4. Work Done in Deformation: The work done per unit time is the product of shear force Fs and shear velocity Vs. Shear force Fs = R cos(φ + β - α) where β = tan⁻¹(μ) = 30.96°. Fs = 81.63 × cos(17.44° + 30.96° - 15°) = 81.63 × cos(33.4°) = 68.22 kgf. Work done = Fs × Vs, where Vs = V cos(α) / cos(φ - α).
What are the basic objectives of efficient and economical machining practice?
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During an orthogonal machining operation on mild Steel, the results obtained are: uncut chip thickness=0.22mm, chip thickness=0.7mm, width of the cut=2.2mm, rake angle=0°, horizontal cutting force=700N, thrust force=300N. Compute the coefficient of friction between the tool and chip interface. Determine also the ultimate shear stress of the work material.
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Differentiate between single spindle and multi-spindle automatic lathes.
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Sketch and name the parts of a turret lathe. Describe the operations of the parts of the turret lathe.
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Sketch and describe the construction and working of a double housing planer.
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Explain the construction and working of a double column jig-boring machine with a neat sketch.
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A mild steel plate measuring 300mm × 600mm × 40mm is to be shaped along its wider face. The ratio of return time to cutting time is 2:3 and the feed per cycle is 2mm. Tool approach and the over travel respectively are 50mm each. Select a suitable cutting speed and calculate the machining time required for machining the given plate with H.S.S. tools.
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Write about tool holding devices of drilling machine with suitable sketches.
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Explain the tool geometry of milling cutters with neat sketches.
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Give a neat sketch of an Internal pull type broaches and indicate the various terms relating to its teeth. Describe these terms in brief.
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Explain the general considerations in selection of milling cutters. How do you calculate the number of teeth on milling cutters?
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What is honing? Describe in detail about honing and honing tools.
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What are the various factors to be considered in selection of grinding wheel? Discuss each in detail.
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Write short notes on the following: (i) Built-up wheels (ii) mounted wheels and points (iii) Diamond wheels (iv) Rubber bond.
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