manproexam2

Why is surface finish of rolled products better in Cold rolling than in Hot rolling?

Cold rolling operates below the recrystallization temperature without thermal oxidation, preventing the formation of surface oxide scale that occurs during elevated temperature hot rolling.

What is the difference between Blooms, Slabs and Billets?

Blooms have a square cross-section greater than 150 mm by 150 mm; Slabs have a rectangular cross-section with width at least twice the thickness; Billets have a square cross-section smaller than blooms, typically 40 mm by 40 mm or larger.

What is Forward Slip? Why it is important?

Forward slip is the relative measure of the increase in exit velocity of the rolled strip compared to the roll surface speed. It is important because it reflects material elongation, contact arc friction behavior, and roll speed control.

Define Neutral Point and Draft in Rolling!

Neutral Point is the location along the contact arc where the velocity of the metal equals the surface speed of the roll. Draft is the absolute reduction in workpiece thickness from initial to final state.

Calculate number of rolling passes to deform a plate thickness of 8 mm to 5 mm. Coefficient of friction is 0.15 and roller diameter 500 mm.

Only 1 pass is required. The maximum allowable reduction in a single pass (calculated from the friction coefficient squared times the roll radius) exceeds the required total thickness reduction of 3 mm.

How does Rolling differs from Extrusion process!

Rolling reduces thickness or reshapes workpieces continuously by squeezing them between rotating rolls, whereas extrusion forces a billet through a shaped die opening using a ram.

Explain the difference between Extrusion and Wire Drawing processes!

Extrusion pushes a metal billet through a die opening under compressive force applied from behind, while wire drawing pulls a metal rod or wire through a die orifice under tensile force applied from the front.

What is the purpose of dummy blocks in Extrusion process?

A dummy block is a protective metal disc placed between the ram and billet to prevent hot, soft metal from flowing backward over the ram and to protect the ram head from extreme thermal and mechanical damage.

What is Impact Extrusion? What are applications?

Impact extrusion is a high-speed cold processing method where a punch strikes a metal slug, causing the metal to flow rapidly backward over the punch or forward through a die. Applications include collapsible tubes, aluminum cans, and battery cases.

In an extrusion process Aluminium round billet of 150 mm diameter and 500 mm long is deformed into a channel shape product of 1500 mm long. What is the cross section of the channel produced?

The cross-sectional area of the produced channel is approximately 5890.49 square millimeters (or 1875 pi square millimeters), calculated by applying volume conservation between the initial billet and the extruded channel.

Compare the processes Sizing and Coining!

Sizing squeezes selected surface regions of a part to achieve precise dimensional thickness with minimal lateral metal flow, while coining uses severe compressive force in a closed die to alter thickness across the part and produce high-definition surface detail.

Compare the processes Coining and Embossing!

Coining alters thickness locally through heavy surface squeezing in a closed die without backside impression, while embossing bends sheet metal into thin relief patterns maintaining uniform thickness.

What is the difference between Cold, Worm and Hot forging?

Cold forging occurs at room temperature (below 0.3 times the melting temperature in Kelvin) giving high strength and surface finish; Warm forging occurs between 0.3 and 0.5 times the melting temperature to reduce forces without forming scale; Hot forging occurs above 0.5 times the melting temperature (above recrystallization) for maximum ductility and low required forging forces.

What are the defects in flat rolling?

Major defects include edge cracking (due to low ductility), center split or alligatoring (due to non-uniform tensile stress state), wavy edges (due to roll bending under load), and surface scale or rust marks.

How Seamless tubes produced?

Seamless tubes are produced using rotary tube piercing (Mannesmann process), hot extrusion using a mandrel, or tube spinning over a mandrel.

What are the factors affecting Rolling Forces?

Rolling forces are affected by roll radius, workpiece width, thickness draft, friction coefficient between roll and strip, material flow stress at operating temperature, and application of front or back tension.

What are the advantages and disadvantages of Isothermal forging?

Advantages: uniform material flow, low forging forces, high dimensional accuracy, and elimination of thermal die chilling. Disadvantages: high die material costs, low production rates, required protective atmospheres, and high operating costs.

What is Upset forging? What are applications?

Upset forging increases the cross-sectional area of a workpiece by reducing its length under axial compression. Applications include manufacturing bolt heads, engine valves, rivets, and valve stems.

How to differentiate whether a part is produced by Forging or Casting?

Forged parts feature continuous grain flow lines aligned with the part contour, higher toughness, and no internal porosity. Cast parts exhibit isotropic grain structures, parting lines, and potential internal shrinkage porosity.

What is the difference between Punching and Blanking?

In punching, the slug removed by the die is scrap and the pierced sheet is the desired product; in blanking, the removed piece is the desired product and the remaining sheet is scrap.

What is Spring Back and how to take care of it in Bending process?

Spring back is the elastic recovery of a bent part upon unloading, increasing bend angle and radius. It is compensated for by overbending, bottoming (coining the bend area), or stretch bending.

Differentiate Compound Dies and Progressive Dies!

Compound dies perform multiple shearing operations at a single station in one press stroke, while progressive dies perform sequential operations across multiple stations over consecutive press strokes.

What are the factors on which Recrystallization temperatures depend?

Recrystallization temperature depends on the degree of prior cold work (higher deformation lowers it), initial grain size, metal purity/alloying elements, heating duration, and base metal melting point.

What are the various applications of Metal Spinning?

Metal spinning is used to manufacture axisymmetrical hollow components such as rocket nose cones, parabolic dish antennas, musical wind instruments, cookware, and light reflector cones.

What are typical stages of a Deep Drawing process?

1. Blank positioning and clamping by the blank holder; 2. Punch contact and bending over die radius; 3. Wall drawing and sliding into the die cavity; 4. Cup bottom formation and ejection.

What are the defects in Deep Drawing?

Defects include flange wrinkling (due to compressive instability), wall tearing or fracture (due to high tensile stress), earing along rims (due to planar anisotropy), and surface scoring.

Compare V-bending and Edge bending!

V-bending uses a V-die and punch for bend angles up to 180 degrees in simple set-ups; Edge bending clamps the sheet with a pressure pad while a wipe die bends the overhanging edge up to 90 degrees.

What are Trimming and Shaving in sheet metal cutting ?

Trimming cuts away excess flash or unwanted flange edges from formed components. Shaving removes a tiny amount of material from previously sheared edges to produce smooth, dimensionally precise, square edges.

What are methods of reducing cutting forces in press cutting operations? Explain!

1. Adding shear or bevel angles to punch or die faces so shearing occurs progressively; 2. Staggering or stepping punch lengths in multi-punch setups; 3. Heating the metal sheet to reduce shear yield strength.

Explain Scrap-Strip layout in Blanking and it’s advantages!

Scrap-strip layout is the geometric arrangement of blanks on a metal sheet strip. Advantages include maximizing material utilization percentage, minimizing scrap generation, lowering material costs, and optimizing tool life.