Deep Drawing MCQ Quiz in मल्याळम - Objective Question with Answer for Deep Drawing - സൗജന്യ PDF ഡൗൺലോഡ് ചെയ്യുക

Various Metal forming process and their properties are explained in the table given below.

Explanation:

Deep drawing: 

• If the ratio of height to diameter of the product is greater than 0.5 then this drawing operation is known as deep drawing. 

  \(\frac{h}{d_p} \)≥ 0.5

• Deep drawing is the process of converting blank of sheet metal into a cylindrical containers with a flat or hemispherical base.
• It basically consists of die, punch, blank holders.
• After the application of drawing force, the blank of material forms & takes shape of the punch or shape made onto the punch. To avoid frictional resistance between blank & die, the lubricant is used.

Limiting drawing ratio (LDR) : 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 punch, by deep drawing the blank into a cup, without crack formation.

 \(\rm LDR=\frac{Maximum\ blank\ diameter}{Punch\ diameter}\)

Explanation:

For kitchen utensils like cup shape components & hollow components the method followed is deep drawing.

Deep drawing

• Cup drawing or deep drawing is one of the widely used sheets metal forming operations.
• Cup-shaped objects, utensils, pressure vessels, gas cylinders, cans, shells, kitchen sink sets are some of the products of deep drawing.
• In this process, a sheet metal called blank is placed on a die cavity, held in position using a holding plate or holding ring, and pressed against the die cavity using a solid punch.
• The sheet metal attains the shape of the die cavity with a flat bottom.

Wire drawing

• Wire drawing is a cold working process to obtain wires from rods of bigger diameters through a die.
• It is the same process as bar drawing except that it involves smaller‐diameter material.
• To obtain a bright shining surface thin fluid lubricant is obtained.

Extrusion

• Extrusion is a compressive deformation process in which a block of metal (heated billet or slug of metal) is squeezed through an orifice or die opening in order to obtain a reduction in diameter and increase in the length of the metal block.
• It is used to make a hollow rods.

Explanation:

Deep drawing or Cup Drawing:

• It is a process in which a raw material sheet is deformed plastically between the punch and die working process to convert into a cup-shaped component.  
• It is the drawing process in which the height of the mug is more than half the diameter.
• In this process, material flows radially towards the cup cavity to produce a cup-shaped component.
• It is extensively used to manufactured kitchen utensils, soft drink cans etc.

Concept:

In the deep drawing process, the flange portion of a blank experiences different stress states depending on the presence of a blank holder. Without a blank holder, the stress state in the flange can change significantly.

Explanation:

When deep drawing is performed without a blank holder, the material in the flange region is not constrained. This lack of constraint allows the material to move more freely, leading to different stress states:

1. No Significant Stress: Without a blank holder, the material in the flange region is not subjected to significant stress because there is no force applied to hold the material in place. The material can move freely without any restraining force, resulting in minimal stress.

2. Effect of No Blank Holder: The absence of a blank holder means that the material is not compressed or stretched significantly. Instead, it can move into the die cavity with minimal resistance, leading to a state where there is little to no stress in the flange portion.

Conclusion:

Given the above explanation, in the case of deep drawing without a blank holder, the flange portion of the blank experiences no significant stress because there is no force applied to hold and constrain the material.

Correct Answer:

3) No stress in the flange at all, because there is no blank holder

Explanation:

Given:

d = 30 mm, h = 50 mm, t = 0.5 mm

Calculation:

Diameter of blank (D) \(= \sqrt {{d^2} + 4dh}\)

\(D = \sqrt {{{30}^2} + 4\left( {30} \right)\left( {50} \right)}\)

∴ D = 83.06 mm

After first draw (50 % reduction)

\(0.50 = 1 - \left( {\frac{{{d_1}}}{D}} \right)\)

\(\frac{{{d_1}}}{{83.06}} = 1 - 0.5\)

∴ d₁ = 41.53 mm

Second draw (30 % reduction)

\(0.3 = 1 - \left( {\frac{{{d_2}}}{{{d_1}}}} \right)\)

\(\frac{{{d_2}}}{{41.53}} = 0.7\)

∴ d₂ = 29.07 mm

Hence two draws are required and so the correct answer (a) (b) and (c)

Various Metal forming process and their properties are explained in the table given below.

Concept:

Drawing Force = π d₁ t σ_y

d₁ is diameter after first draw, t is thickness of sheet, σ_y is yield strength

Calculation:

Given:

Corner radius (r) = 3 mm, Final diameter of cup (d) = 50 mm, Height of cup (h) = 70 mm

Thickness (t) = 3 mm, σ_y = 560 MPa, Reduction in first draw = 45 %

\(\frac{d}{r} = \frac{{50}}{3} = 16.6\)

\({\rm{Blank\;diameter\;}} = 15 < \frac{d}{r} \le 20\)

D = Blank diameter is given by

\(D = \sqrt {{d^2} + 4dh - 0.5r} \)

\(D = \sqrt {{{\left[ {50} \right]}^2} + 4 \times 50 \times 70 - 0.5 \times 3} \)

D = 128.446 mm

Percentage reduction in the first draw is 45 %

\(1 - \frac{{{d_1}}}{D} = 0.45\)

\(1 - \frac{{{d_1}}}{{128.446}} = 0.45\)

∴ d₁ = 70.6453 mm

Now,

Drawing force in the first draw = πd₁ t σ_y 

Drawing force in the first draw = π × 70.6453 × 0.9 × 560

Explanation:

The direction-dependent behaviour of a material termed as anisotropy. In anisotropic materials, the mechanical properties are different in different directions.

There are two types of anisotropy:

(1) Crystallographic Orientation: From preferred grain orientation

(2) Mechanical fibering: Alignment of impurities, inclusions, voids.

• Anisotropy may be present in plane of the sheet (planar Anisotropy) as well as in its thickness direction (Normal or plastic Anisotropy).
• It is quantified by a factor of anisotropy (or) plastic strain ratio of width to the thickness direction of a uniaxial tensile test specimen made from the sheet, denoted by R.

\(R = \frac{{{\varepsilon _w}}}{{{\varepsilon _t}}} = \frac{{\ln \left( {\frac{{{\omega _1}}}{{{\omega _0}}}} \right)}}{{\ln \left( {\frac{{{t_1}}}{{{t_0}}}} \right)}}\)

In the equation:

0 index: refers to dimensions before the tensile test

1: after the test

• In general, materials are anisotropic & defined by average R̅:

            \(\bar R = \frac{1}{4}\left( {{R_{0^\circ }} + 2{R_{45^\circ }} + {R_{90^\circ }}} \right)\) 

• Planar Anisotropy \({\rm{\Delta }}R = \frac{1}{2}\left( {{R_{0^\circ }} - 2{R_{45^\circ }} + {R_{90^\circ }}} \right)\)

Planar Anisotropy relates to formation of ears in deep drawn cups or in other words ΔR is the degree of the tendency of the sheet to form ears.

* If ΔR > 0, then ears form at 0° & 90° to the rolling direction.

* If ΔR < 0, ears form at 45°.

Explanation:

Deep drawing:

• Deep drawing is a sheet metal forming process in which a sheet metal blank is radially drawn into a forming die by the mechanical action of a punch.
• It is thus a shape transformation process with material retention.
• The process is considered a "deep" drawing when the depth of the drawn part exceeds its diameter.
• This is achieved by redrawing the part through a series of dies.
• The flange region (sheet metal in the die shoulder area) experiences radial drawing stress and tangential compressive stress due to the material retention property.
• Thickness in the drawn cup by the deep drawing process keeps on increasing in the wall region because of compressive hoop stress.
• These compressive stresses (hoop stresses) result in flange wrinkles (wrinkles of the first order).
• Wrinkles can be prevented by using a blank holder, the function of which is to facilitate controlled material flow into the die radius.

For the deep drawing operation, the diameter (D) of the blank needed to make a cup diameter (d) and height (h) in a single pass,

D = \(\sqrt{d^2~+~(4~\times~d~~\times~h)}\)

The process involved in the deep drawing:

• The total drawing load consists of the ideal forming load and an additional component to compensate for friction in the contacting areas of the flange region and bending forces as well as unbending forces at the die radius.
• The forming load is transferred from the punch radius through the drawn part wall into the deformation region (sheet metal flange).
• In the drawn part wall, which is in contact with the punch, the hoop strain is zero whereby the plane strain condition is reached.
• In reality, mostly the strain condition is only approximately plane.
• Due to tensile forces acting in the part wall, wall thinning is prominent and results in an uneven part wall thickness, such that the part wall thickness is lowest at the point where the part wall loses contact with the punch, i.e., at the punch radius.
• The thinnest part thickness determines the maximum stress that can be transferred to the deformation zone.
• Due to material volume constancy, the flange thickens and results in blank holder contact at the outer boundary rather than on the entire surface.
• The maximum stress that can be safely transferred from the punch to the blank sets a limit on the maximum blank size (initial blank diameter in the case of rotationally symmetrical blanks).
• An indicator of material formability is the limiting drawing ratio (LDR), defined as the ratio of the maximum blank diameter that can be safely drawn into a cup without flange to the punch diameter.
• Determination of the LDR for complex components is difficult and hence the part is inspected for critical areas for which an approximation is possible.
• During severe deep drawing the material work hardens and it may be necessary to anneal the parts in controlled atmosphere ovens to restore the original elasticity of the material.