AMIE Study Circle Blog

Answer the following (10 x 2) Negative rake angles generally are preferred for ceramic, diamond and cubic boron-nitride tools. Why? Although hard and strong in compression, these materials are brittle and relatively weak in tension. Consequently, negative rake angles (which indicate the larger included angle of the tooltip) are preferred mainly because of the lower tendency to cause tensile stresses and chipping of the tools. If a drill bit is intended only for woodworking applications, what material is it most likely to be made from? Because of economic considerations, woodworking tools are typically made of carbon steel, with some degree of hardening by heat treatment. Tool life can be almost infinite at low cutting speeds. Would you then recommend that all machining be done at low speeds? This reason alone would not justify using low cutting speeds. Low cutting speeds remove less material in a given time which, unless otherwise justified, would be economically undesirable. Lower cut...

Answer the following (2 x 10) Tool life can be almost infinite at low cutting speeds. Would you then recommend that all matching be done at low speeds? Explain. This reason alone would not justify using low cutting speeds. Low cutting speeds remove less material in a given time which, unless otherwise justified, would be economically undesirable. Lower cutting speeds also often lead to the formation of a built-up edge and discontinuous chips, thus affecting the surface finish. Which tool material properties are suitable for interrupted cutting operations? Why? In interrupted cutting operations, it is desirable to have tools with a high impact strength and toughness. The tool materials which have the best impact strength are high-speed steels, and to a lesser extent, cast alloys and carbides. Therefore, one would prefer to use high-speed steels and carbides in interrupted cutting operations. In addition, in these operations, the tool is constantly heated and reheated. It is therefore de...

Answer the following (2 x 10) What is the proof stress? The proof stress of a material is defined as the amount of stress it can endure until it undergoes a relatively small amount of plastic deformation. Specifically, proof stress is the point at which the material exhibits 0.2% of plastic deformation. A straight line offset at 0.2% strain is extended parallel to the linear portion of the graph until it meets the stress-strain curve. The stress at the intersection between this line and the curve is the value of the proof stress. What is the proportionality limit? The proportional limit is defined as the highest stress at which stress and strain are directly proportional so that the stress-strain graph is a straight line such that the gradient is equal to the elastic modulus of the material. What is strain hardening? Strain hardening also referred to as cold working or work hardening, is the process where metals are made stronger and harder through permanent deformation.  Why inten...

Answer the following (2 x 10) What is impact extrusion? Impact extrusion is a manufacturing-related extrusion process that uses a press, along with a punch and dies set, to form metal slugs. It involves placing a metal slug between a punch and die, followed by engaging the press so that it forces the metal slug through the die. Define limiting drawing ratio. The limiting drawing ratio (LDR) test evaluates the deep drawability of sheet metals. It indicates the maximum ratio of circular blanks to the diameter of the die, by deep-drawing the blank into a cup, without crack formation. The limiting drawing ratio (blank diameter/punch diameter) is between 1.6 and 2.2 for most materials. Define arc length and arc crater. Arc crater - Depression formed when the arc melts the base metal. Arc length - Distance between the electrode and the base metal. In SMAW, this distance should be approximately equal to the electrode diameter. What is directional solidification? "Directional solidificati...

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 re...

Answer the following questions in brief (2 x 10)  How is an arc obtained in arc welding? Arc welding is welding using the heat of an arc as a heat source. In arc welding, a positive voltage is applied to the electrode (welding rod/wire) and a negative voltage is applied to the base material. This makes an arc occur from the base material to the electrode. Why is neutral flame extensively used in oxy-acetylene welding? Because it adds nothing to the metal. What Is the significance of roll diameter with reference to the roll-separating force in rolling? Low roll diameter results in the low roll contact area and consequently in the low absolute value of the roll separating force and the torque required for achieving a certain thickness reduction. How do you compare forged components with cast components? Forged steel is generally stronger and more reliable than castings and plate steel due to the fact that the grain flows of the steel are altered, conforming to the shape of the part. ...

Answer the following questions Define ductility Ductility is the physical property of the metal which means if we pull the metal it’s going to stretch rather than break. In other words, a material’s ability to undergo significant plastic deformation under tensile stress before rapture is called the ductile properties of the material. The ductile materials are nickel, copper, steel etc.   Factors affecting tool life Cutting Speed Physical Properties of Work Piece Area of Cut Ratio of Feed to Depth of Cut (f/d) Shape and Angles of Tools Effect of Lubricant Nature of Cutting Wheel dressing Dressing returns the grinding wheel to its original sharpness by removing old grains to reveal the fresh grain underneath. It removes clogs, dulled abrasive grains, and excess bonding material to help minimize vibration, thereby improving surface finish. Sprue well Sprue – a hole where the metal enters the mould. It is ideally tapered to prevent air from entering the casting. Well – forms a cus...