This set of Manufacturing Processes Multiple Choice Questions & Answers (MCQs) focuses on “Ultrasonic Machining – 1”.
1. Ultrasonic machining (USM) can be classified as which of the following type of non-traditional machining process?
Explanation: Ultrasonic machining is a non-traditional machining process. USM is grouped under the mechanical group NTM processes. In ultrasonic machining, a tool of the desired shape vibrates at an ultrasonic frequency.
2. Which of the following material is not generally machined by USM?
Explanation: USM is mainly used for machining brittle materials which are poor conductors of electricity and thus cannot be processed by Electrochemical and Electro-discharge machining.
3. Tool in USM is generally made from which of the following materials?
Explanation: The tool material should be such that indentation by the abrasive grits does not lead to brittle failure. Thus the tools are made of tough, strong and ductile materials like steel, stainless steel and other ductile metallic alloys.
4. Under what frequency ultrasonic machining is done?
a) 5—10 Hz
b) 5—10 kHz
c) 12—19 Hz
d) 19—25 kHz
Explanation: Ultrasonic machining is a mechanical type non-traditional machining process. In ultrasonic machining, a tool of desired shape vibrates at an ultrasonic frequency of around 19—25 kHz with an amplitude of around 15 – 50 μm over the workpiece.
5. In ultrasonic machining (USM), the tool is pressed downward.
Explanation: Generally the tool is pressed downward with a feed force. Between the tool and workpiece, the machining zone is flooded with hard abrasive particles generally in the form of water based slurry.
6. In ultrasonic machining, the abrasive particles act as the __________
a) chip carriers
c) finishing particles
d) thickening agent for the slurry
Explanation: During ultrasonic machining, as the tool vibrates over the workpiece, the abrasive particles act as the indenters and indent both the work material and the tool.
7. In case of brittle materials, the material is removed by crack initiation.
Explanation: The abrasive particles, as they indent, the work material, would remove the same, particularly if the work material is brittle, due to crack initiation, propagation and brittle fracture of the material.
8. During USM, cracks are produced due to _____
a) von-mises stresses
b) hertzian stresses
c) principal stresses
d) episodic acute stresses
Explanation: During USM, as the tool vibrates, it leads to the indentation of the abrasive grits. During indentation, due to hertzian contact stresses, cracks would develop just below the contact site then as indentation progresses the cracks would propagate due to increase in stress and ultimately lead to brittle fracture of the work material under each individual interaction site between the abrasive grits and the workpiece.
9. In USM, material removal may occur due to _____
a) fatigue failure
b) fouling failure
c) free flowing impact of the abrasive
Explanation: Other than brittle failure of the work material due to indentation some material removal may occur due to free flowing impact of the abrasives against the work material and related solid-solid impact erosion, but it is estimated to be rather insignificant.
10. Increasing volume concentration of abrasive in slurry would affect MRR in which of the following manner?
a) increase MRR
b) decrease MRR
c) would not change MRR
d) initially decrease and then increase MRR
Explanation: The concentration of abrasive grits in the slurry is related as follow
n = (6AC)/ πdg2,
where n= number of grits
A= total surface area of the tool facing the workpiece
C= concentration of abrasive grits in the slurry
dg= diameter of a grit
Thus above relation shows that any increase in ‘C’ will increase ‘n’ and hence material removal rate (MRR).
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