MMP Exam 2

Why is surface finish of rolled products better in cold rolling than in hot rolling

Cold rolling occurs below the recrystal temp which avoids high temp oxidation. Hot rolling a surface produces a worse finish due to atmospheric gasses which can cause oxidation

What is the difference between blooms, slabs, and billets

Blooms are large and square/rectangular and have a cross sectional area of greater than 225 cm². Slabs have an cross sectional area greater than 100 cm² are wide, and used mainly for sheets/plates. Billets are mainly used for bars/rods.

What is forward slip? Why is it important?

The material is exiting the rollers with greater velocity than the rollers, given by S = (Vout - Vr)/Vr. It is important because it gives the roll strip speed relationship that can predict thickness control and operational stability.

Define Neutral point and Draft rolling

The neutral point is where the Material velocity is equal to the rollers velocity. Draft is the reduction in thickness during one rolling pass, d= h0 - hf

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

h_max = u²(r) = diameter reduction per pass. =(.15)²(250) = 5.625. Required is 8-5 = 3mm so only one pass is needed.

How does rolling differ from extrusion

Extrusions is a metal forming process that forces metal through a die to produce a shape with a desired cross sectional area. Rolling compresses the material and reduces its thickness as it passes between rotating rollers.

Explain the difference between extrusion and wire drawing

In extrusion the material is pushed through a die, while in wire drawing a material is pulled through a die.

What is the purpose of dummy blocks in the extrusion process

Dummy blocks are placed between the extrusion ram and the billet so that the ram can push the billet through the die. The block also acts as a intermediate tool that protects the ram from the hot billet and reduces adhesion and wear.

What is impact extrusion. What are its applications?

Liquid metal is forced into a metal die very quickly by a punch striking a metal slug. A common application is the creation of toothpaste tubes, and cans.

In an Extrusion process Aluminum round billet of 150mm diameter and 500 mm long is deformed into a channel shape product of 1500mm long. what is the cross section of the channel produced

A1 L1 = A2 L2, A2= (pi/4)(150)²(500/1500) = 5890.5 mm²

Compare the Coining and Sizing processes

Sizing is a cold-working process primarily used to obtain accurate dimensions and tolerances. Coining produces very fine and intricate details or impressions on the work surface and may locally displace or thin the material.

Compare Coining and Embossing

Coining produces very fine and intricate details or impressions on the work surface and may locally displace or thin the material. Embossing forms raised or depressed designs in sheet metal, generally without intentionally thinning the material.

What is the difference between Cold, Warm, and Hot forging

Cold forging occurs below recrystallization temp and has good surface finish, while strengthening the material via strain hardening. Warm occurs at elevated temps below the recrystallization temp which reduces the required force and improves ductility slightly. Hot forging occurs above the recrystal temp allowing large amounts of deformation to occur, less forces, and giving a poor surface finish.

What are the defects in flat rolling

Possible defects are Wavy edge, zipper cracks, edge cracks and alligatoring. Alligatoring results from non-uniform deformation during rolling and edge cracks are caused by poor material ductility at the rolling temperature.

How are Seamless tubes produced

They are produced from hollowing a billet through hot extrusion over a mandrel, and then cold reduction by tube drawing.

What are the factors affecting Rolling Forces

Affected by thickness reduction, roll diameter/radius, friction coefficient, material deformation resistance, strip and width tension. With Roll diameter/radius and friction be the main factors

What are the advantages and disadvantages of isothermal forging?

The advantages are lower forging loads, better dimensional accuracy, and fine details. The disadvantages include slower processing and expensive high-temperature dies leading to higher costs than conventional forging processes.

What is upset forging and what are its applications

Upset forging uses compressive forging to reduce length while increasing cross sectional dimensions. Its main application is in the production of bolts and screw heads.

How to differentiate whether a part is produced by forging or by casting

A forged part generally has a refined, directional grain flow that follows component geometry and has higher strength and structural integrity. Cast parts can contain porosity and inclusions along with a more randomly oriented grain structure

What is the difference between punching and blanking

Punching produces holes or cutouts in a sheet of metal which are the desired feature. Blanking cuts a portion of sheet metal and leaves the remainder of the sheet for scrap.

What is spring back and how to take care of it in the bending process?

Spring back is the partial return of the metal toward its original flat condition after the bending load is removed due to deformation being partly elastic. it can be controlled by overbending or bottoming, which plasticly deforms the bend region.

differentiate compound Dies and progressive dies

Compound dies perform more than one operation at a single station, allowing internal and external features to be produced simultaneously in one stroke. Progressive dies have multiple workstations, with different operations performed as the workpiece automatically moves from one station to the next.

What are the factors on which recrystallization temperatures depend

The main factor is the melting temperature differences between Pure metals, and metal alloys. Pure metals use 1/3 of the melting temp for recrystallization, and metal alloys use ½ their melting temp. Strain hardening also decreases the recrystal temp.

What are the various applications of metal spinning

Metal spinning uses a mandrel to support the workpiece and is used to produce parts such as the bottoms of large tanks and hoppers. it can also be used to produce sheet metal parts with axisymmetric shapes

What are typical stages of a deep drawing process

The stages are shearing a blank, clamping the blank on the die, stretching the blank into the die cavity with the punch, returning the punch, removing the part and trimming the excess blank

What are the defects in deep drawing

Common defects are wrinkling, Tearing, earing, and surface scratches. Earing produces peaks and valleys in the cup wall, tearing creates a crack near the base.

Compare V-bending and Edge bending

V-bending uses a punch and V-die with the punch pressing the sheet into the V-die to produce the desired angle. Edge bending uses cantilever loading, with a pressure pad holding the sheet against the die while the punch bends the sheet over the edge.

What are Trimming and Shaving in sheet metal cutting?

Trimming removes excess metal surrounding a formed, pre-designed part. Shaving removes a thin strip of metal along the edge of a blanked part to obtain accurate dimensions and improve the edge.

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

The two methods are stepping the punch lengths and providing shear on the punch or die. Stepping reduces the force required at any one time, while shear reduces the area being cut at one time; the total work done remains unchanged

Explain Scrap-Strip layout in Blanking and its advantages

Determines how blanks are positioned and spaced along the sheet or strip, including the required web and material allowances. Advantages include increased material utilization, reduced scrap, and lower material cost. Very useful in progressive-die production to reduce material cost.