Answer the following questions (2 x 10)
Define toughness.
Toughness is the ability of a material to absorb energy and plastically deform without fracturing.
Structure of grinding wheel.
A grinding wheel consists of three elements: abrasive grain, bond and pore, as shown in the figure. As the wheel turns at high speed, its innumerable grains quickly grind the workpiece to a beautiful finish and precise measurement.
What is straddle milling?
A straddle is a special form of gang milling where only side and face milling cutters are used. In Straddle milling, two side milling cutters are mounted with the desired distance between them so that both sides of a workpiece can be milled.
State the detriment caused to the mould properties if the moulding sand contains too much clay.
The clay imparts the necessary tensile strength to the moulding sand so that after ramming, the mould does not lose its shape. However, as the quantity of the clay is increased, the permeability of the mould is reduced.
How runner extension is helpful for good casting quality?
Runners are connected channels that convey the molten metal to different parts of the mould. A well-designed running system can regulate the speed of the molten metal, avoid shrinkage and minimise turbulence.
What function is served by the die inserts?
The main purpose of inserts is to create the holes or the running tubes within the piece.
How material is removed in ECM?
In electrochemical machining, the metal is removed due to electrochemical action where the workpiece is made anode and the tool is made the cathode. A high current is passed between the tool and workpiece through the electrolyte. Metal is removed by the anodic dissolution and is carried away by the electrolyte.
What possible errors are caused in EDM?
- The error in cutting accuracy
- Error of surface accuracy
- Faulty cutting speed
- Curl failure
- Failure of automatic threading (insertion failure)
What is meant by the "carbon equivalent" of commercial steel?
The carbon equivalent is a measure of the tendency of the weld to form martensite on cooling and to suffer a brittle fracture. When the carbon equivalent is between 0.40 and 0.60 weld preheat may be necessary.
Why is hydrogen a concern in welding?
Hydrogen atoms are extremely small, highly mobile, and can easily diffuse out of the weld zone and coalesce along discontinuities that are present in the microstructure. Those pockets of hydrogen eventually build stresses that can lead to cracking.
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