Lecture 8 - Sheet Metal

Question 1

What are the basic deformation processes for sheet metal?

Answer 1

1) Bending
2) Deep drawing
3) Cutting
4) Progressive die

Question 2

What thickness defines sheet metal from other materials?

Answer 2

Sheet metal < 1/4 inch
Plate >1/4 inch
foil or leaf = very thin material

Question 3

What are some advantages to sheet metal parts?

Answer 3

-Good dimensional accuracy
-Good surface finish
-Low productions cost for large quantities
-High strength

Question 4

What conditions would require warm working over cold working?

Answer 4

warm working is performed If the material is quite thick, brittle or deformation is significant, other wise cold working is preferred.

Question 5

List the Cutting Processes

Answer 5

Shearing
Blanking
Punching
Cutoff
Parting
Piercing
Slotting
Notching
Semi-Notching
Perforating
Shaving

Question 6

What is the difference between blanking and punching?

Answer 6

With blanking, the part that is removed from the stock material is the desired part.
with punching the material that is removed is scrap, and the remaining material is the part.

Question 7

What is the difference between Cutoff and Parting?

Answer 7

Cutoff is separating the part from the stock material without any scrap.
Parting separates the part from the material by punching away the material between parts.

Question 8

What is the difference between Piercing and Slotting?

Answer 8

Piercing is typically done with cylindrical shaped punches
Slotting forms rectangular shaped holes in the sheet

Question 9

What is the difference between Notching and Semi-Notching?

Answer 9

Notching is a form of punching that removes material from the outer edge of the blank material.
Semi-Notching removes material from the inside of the blank material

Question 10

When are Shaving and Trimming performed?

Answer 10

Shaving is a secondary or finishing operations. It is used to obtain accurate dimensioning.
Trimming is used to cutoff excess material after the part has been shaped/formed

Question 11

What are the design considerations for the bending process?

Answer 11

Bending allowance
Bending Force
Spring back

Question 12

How do you compensate for Spring back?

Answer 12

Overbending - bending past desired degree and allowing to spring back to desired angle
Bottoming - Involves squeezing the part at the end of the stroke, plastically deforming it in the bend region

Question 13

What are some other bending operations?

Answer 13

Hemming - to eliminate sharp edges, increase stiffness, and improve appearance
Seaming
Curling

Question 14

What is the Drawing process of sheet metal used for?

Answer 14

To make cup-shaped, box shaped, or other complex curved and hollow shaped parts

Question 15

Explain the Drawing Process

Answer 15

A punch applied a force to deform the stock material through a die. A holding force acts on the material that hasn’t made its way through the die. (blank Holder)
As the punch moves further down the die, the material is bent/drawn into the die, then straightened as it passes through the die.
This straightening forms the walls of the cylindric shape.

Question 16

What common defects arise from the Drawing process?

Answer 16

-Wrinkling in the Flange
-Wrinkling in the wall
-Tearing
-Earing
-Surface scratches

Question 17

If the shape change of the stock material is to severe (causes defects) during the drawing process, what can you do to prevent this?

Answer 17

-Blank holder to prevent wrinkling
-Multi-step drawing process known as Redrawing, where the shape change is increased with every step

Question 18

What other drawing process requires multiple steps?

Answer 18

Reverse drawing, where the part is flipped over after initial drawing step, to then draw the part in the opposite direction of the first draw

Question 19

What are some other press sheet metal forming operations are there? (metal tooling processes)

Answer 19

Ironing
Embossing
Lancing
Twisting

Question 20

What are some other press sheet metal forming operations are there? (rubber tooling processes)

Answer 20

Guerin Process
Hydroforming

Question 21

How is Ironing similar to drawing? how is it different?

Answer 21

Like drawing Ironing is the process of punching a stock material through a die.
Unlike drawing, the clearance is smaller than the thickness, thus squeezing the material through the die, creating and more uniform wall thickness

Question 22

What is the Embossing process used for?

Answer 22

Embossing is used to create indentions in the sheet metal part. These indentions can be used for Lettering or strengthening ribs

Question 23

What is Lancing used for?

Answer 23

Lancing is a combination of cutting and bending, creating slits and or tabs. (look up picture)

Question 24

What is the Guerin Process, and what are its advantages and disadvantages?

Answer 24

The Guerin process uses a thick flexible rubber pad to form sheet metal over a positive form block.
Advantages: Low tooling cost
▪ Form block can be made of wood, plastic, or other materials that are easy to shape
▪ Rubber pad can be used with different form blocks
▪ Process attractive in small quantity production
Disadvantages: It is limited to relatively shallow forms, because the pressure developed by the rubber (~10 MPa or 1500 psi) are not sufficient to prevent wrinkling in deep drawing

Question 25

What is the Hydroforming Process, and what are its advantages and disadvantages?

Answer 25

A rubber diaphragm filled with high pressure hydraulic fluid form the work part at around 100 MPa.
Advantages: Good for high production
▪ Setup can be used with different form blocks
▪ Deeper draws can be achieved with the
hydroform process than with conventional deep drawing
▪ Uniform pressure up to 100 MPa creates
uniform wall thickness and prevents tearing at the base of deep drawn part.
Disadvantage:
▪ Relatively high tooling cost

Question 26

What sheet metal forming processes don’t require a press?

Answer 26

Stretch forming
Roll bending and forming
Spinning
High energy rate forming

Question 27

describe Stretch forming

Answer 27

Metal stretched and simultaneously bent to achieve desired shape change.
Can us Standard metal or flexible molds to create shapes

Question 28

Describe Roll bending and Roll forming

Answer 28

Roll bending - Large metal sheets and plates are formed into curved sections using rolls
Roll Forming - Continuous bending process in which opposing rolls produce long sections of formed shapes from coil or strip stock

Question 29

Describe Sheet metal Spinning Process

Answer 29

An axially symmetric part, gradually
shaped over a rotating mandrel, using
a rounded tool or roller
three types include:
Conventional Spinning
Shear spinning
Tube spinning

Question 30

Describe High-Energy-Rate forming and what are the 2 types.

Answer 30

Moving metal into a die, and using large amounts of energy over a very short period of time.
Explosive Forming
Electromagnetic Forming

Question 31

Explain the Explosive forming process and give some examples of applications

Answer 31

A material is placed between water and an evacuated cavity/mold. An explosive charge is detonated, causing a shock wave whose energy is transmitted to force the material into the cavity/mold.
Used for large parts such as boat hulls and aerospace parts

Question 32

Explain the Electromagnetic forming process and give some examples of applications

Answer 32

The sheet metal is deformed by the mechanical force of an electromagnetic field induced into the work part by an energized coil. Best suited for good electrical conductors (copper/ aluminum)
Used for Tubular or cylindrical parts