Week 3 Flashcards
What is the definition of sheet metalworking?;
Cutting and forming operations performed on relatively thin sheets of metal.
What is the typical thickness range of sheet metal?;
0.4 mm (1/64 in) to 6 mm (1/4 in).
At what thickness does sheet metal become plate stock?;
Greater than 6 mm.
What is the usual temperature condition for operations in sheet metalworking?;
Cold working.
What are the advantages of sheet metal parts?;
good dimensional accuracy, High strength
Why are sheet metal parts suitable for large quantities?;
Economical mass production operations are available.
What is the function of ‘punch-and-die’ in sheet metalworking?;
Tooling to perform cutting bending
What is a ‘stamping press’ used for in sheet metalworking?;
It is a machine tool that performs most sheet metal operations.
What are ‘stampings’ in the context of sheet metalworking?;
They are sheet metal products.
What is the process of shearing used for in sheet metalworking?;
To separate large sheets cut part perimeters
What is the purpose of bending in sheet metalworking?;
To strain the sheet around a straight axis.
What is the process of drawing used for in sheet metalworking?;
Forming the sheet into convex or concave shapes.
What is shearing in sheet metalworking?;
It is the process of cutting sheet metal between two sharp cutting edges.
What causes plastic deformation in the shearing process?;
The punch begins to push into the work.
What are the three principal operations in pressworking that cut sheet metal?;
Shearing Blanking
What is shearing in sheet metal cutting?;
It is a cutting operation along a straight line between two cutting edges.
What is the typical purpose of shearing in sheet metal cutting?;
To cut large sheets into smaller sections for subsequent operations.
What is blanking in sheet metalworking?; Sheet metal cutting to separate a piece from surrounding stock
with the cut piece being the desired part
What is the cut piece called in blanking?;
A blank.
What is punching in sheet metalworking?;
Sheet metal cutting similar to blanking where the cut piece is scrap
What is the cut piece called in punching?;
A slug.
What is clearance in sheet metal cutting?;
The distance between the punch and die.
What are the typical values for clearance in sheet metal cutting?;
Typical values range between 4% and 8% of stock thickness.
What issues can arise if the clearance in sheet metal cutting is too small?;
Fracture lines pass each other causing double burnishing and larger force.
What issues can arise if the clearance in sheet metal cutting is too large?;
Metal is pinched between cutting edges and excessive burr results.
How can recommended clearance in sheet metal cutting be calculated?;
By using the formula: c = at
c = clearance
a= allowance
t = stock thickness
What does die size determine in blanking?;
Blank size (D b).
What does punch size determine in blanking?;
Hole size (D h).
How is the blanking punch diameter calculated for a round blank?;
D b - 2c.
How is the blanking die diameter calculated for a round blank?.
D b
How is the hole punch diameter calculated for a round hole?; .
D h
How is the hole die diameter calculated for a round hole?;
D h + 2c.
What is the formula for calculating punch diameter?;
Punch diameter = D b - 2c
What is the purpose of angular clearance in manufacturing processes?;
To allow slug or blank to drop through the die.
What are the typical values for angular clearance on each side?;
0.25 degrees to 1.5 degrees.
What is the formula for calculating cutting force?;
F = S * t * L
Why are cutting forces important in determining press size?;
They help determine the required tonnage for the press.
What does ‘S’ represent in the cutting force formula?;
Shear strength of the metal.
How is ‘t’ defined in the cutting force formula?;
Stock thickness.
What does ‘L’ stand for in the cutting force formula?;
Length of the cut edge.
What is the formula for force (F) in the given solution?;
F = StL
What is bending in sheet metalworking?;
It is straining sheet metal around a straight axis to take a permanent bend.
What happens to the metal on the inside of the neutral plane during bending?;
It is compressed.
What happens to the metal on the outside of the neutral plane during bending?;
It is stretched.
What is V-bending in sheet metalworking?;
It is performed with a V-shaped die.
How is edge bending performed in sheet metalworking?;
It is performed with a wiping die.
What type of production is V-bending suitable for?; .
Low production
Where is V-bending typically performed?; .
On a press brake
What are the characteristics of V-dies used in V-bending?;
Simple and inexpensive.
What is the purpose of edge bending?;
To create a bend in the edge of a workpiece.
Why is a pressure pad required in edge bending?;
To ensure proper contact and support during the bending process.
What is a characteristic of dies used in edge bending?;
They are more complicated and costly.
What happens to the metal during bending if the bend radius is small relative to stock thickness?;
The metal tends to stretch.
Why is it important to estimate the amount of stretching during bending?;
To ensure that the final part length matches the specified dimension.
What is the formula for bend allowance (BA)?;
BA = 2π(α/360)(R + Kbat).
BA = bend allowance
t = thickness
A = bend angle
R=bend radius
kba = factor to estimate bending
When is the value of Kba 0.33 in the bend allowance formula?;
When R < 2t.
When is the value of Kba 0.50 in the bend allowance formula?;
When R ≥ 2t.
What is the formula for BA (Blanking Allowance)?;
BA = 2π(α/360)(R + Kbat).
What is springback in bending?;
It is the increase in the included angle of the bent part relative to the included angle of the forming tool after the tool is removed.
What causes springback in bending?;
When bending pressure is removed elastic energy remains in the bent part
What is springback in bending?;
It shows itself as a decrease in bend angle and an increase in bend radius.
What happens to the work during bending?;
It is forced to take the radius and included angle of the bending tool.
What occurs after the punch is removed in bending?;
The work springs back to radius and angle.8888888888
How is the maximum bending force estimated?;
F = 1.33 * TS * w * t for V-bending
F = 0.33 * TS * w * t for edge bending.
How is the sheet metal blank positioned to create the desired shape in drawing?;
Over the die cavity then the punch pushes the metal into the opening.
What are some products that are manufactured using the drawing process in sheet metal forming?;
Beverage cans & ammunition shells
What does DR stand for in the context of drawing operations?;
Drawing Ratio.
How is the Drawing Ratio (DR) calculated?;
By dividing the punch diameter (Dp) by the blank diameter (Db).
What does a Drawing Ratio (DR) value of 2 indicate?;
It indicates severity of a given drawing operation.
For which shape is the Drawing Ratio (DR) most easily defined?;
Cylindrical shape.
What is the condition for the value of r in the context of cylindrical shape reduction?;
The value of r should be less than 0.50.
What does the thickness-to-diameter ratio (t/Db) represent?;
The thickness of the starting blank divided by the blank diameter.
What is the desirable range for the thickness-to-diameter ratio (t/Db)?;
Greater than 1%.
What happens as the thickness-to-diameter ratio (t/Db) decreases?;
There is an increased tendency for wrinkling.
What is the formula for drawing force in sheet metalworking?;
F = πDpt(TS)(Db/Dp - 0.7)
What does TS represent in the drawing force formula?;
Tensile strength.
What is the formula for holding force in sheet metalworking?;
Fh = 0.015Yπ(Db^2 - (Dp + 2.2t + 2Rd)^2)
What does Y represent in the holding force formula?;
Yielding point.
What is the formula for calculating the drawing ratio?;
Drawing ratio = Blank diameter / Inside diameter.
How do you calculate the reduction in a deep drawing operation?;
Reduction = (Blank diameter - Inside diameter) / Blank diameter.
What is the formula for the thickness-to-diameter ratio in deep drawing?;
Thickness-to-diameter ratio = Sheet metal thickness / Inside diameter.
Based on the given parameters does the deep drawing operation seem feasible?;
Feasibility depends on the calculated drawing ratio
What does DR represent in the given solution?;
DR represents the drawing ratio and is calculated as D b / D p.
How is the reduction in area (r) calculated?;
The reduction in area (r) is calculated as (D b - D p) / D b.
What does the value t / D b represent in the given solution?;
The value t / D b represents the thickness-to-diameter ratio.
Why is the feasibility of the process considered not possible in the given solution?;
The drawing ratio (DR) is too large (greater than 2.0)
the reduction in area (r) is too large (greater than 50%)
What is the purpose of blank size determination in sheet metalworking?;
To ensure the final dimensions of the drawn shape are correct.
How is the starting blank diameter (D b) determined?;
By setting the starting sheet metal blank volume equal to the final product volume.
What assumption is made to facilitate the calculation of blank size?;
Negligible thinning of the part wall.
What are some shapes produced by deep drawing other than cylindrical cups?;
Square or rectangular boxes stepped cups
What unique technical problems do different shapes present in deep drawing?;
Each shape presents its own unique technical problems.
What are some sheet metal forming operations performed on conventional presses?;
Operations performed with metal tooling.
What type of tooling is used for sheet metal forming operations on conventional presses?;
Metal tooling.
What are some sheet metal forming operations performed with flexible rubber tooling?;
Operations performed with flexible rubber tooling.
What does ironing achieve in the manufacturing process?;
It makes the wall thickness of a cylindrical cup more uniform.
What is the purpose of ironing in the production of a drawn cup?;
To achieve a more uniform wall thickness.
What is embossing used to create in a sheet?;
Indentations such as raised lettering or strengthening ribs.
What is the purpose of embossing in manufacturing processes?;
To create indentations in a sheet for various purposes.
What are most pressworking operations performed with?;
Conventional punch-and-die tooling.
What term is sometimes used for high production dies?;
Stamping die.
What is the configuration of a gap frame stamping press?;
It is in the shape of the letter C and often referred to as a C-frame.
How is a straight-sided frame stamping press constructed?;
It has a box-like construction for higher tonnage.
What type of system do hydraulic presses use to drive the ram?;
They use a large piston and cylinder.
What type of operations are hydraulic presses suited to?;
They are suited to deep drawing.
How does a mechanical press convert the rotation of the motor?;
It converts it to the linear motion of the ram.
What type of operations are mechanical presses suited to?;
They are suited to blanking and punching.
What is stretch forming in sheet metal operations?;
A process not performed on presses.
What is roll bending and forming in sheet metal operations?;
A process not performed on presses.
What is spinning in sheet metal operations?;
A process not performed on presses.
What is stretch forming in sheet metalworking?;
It involves stretching and bending sheet metal simultaneously to achieve a shape change.
What happens at the start of the stretch forming process?;
The form die is pressed into the work with force ausing the sheet metal to be stretched and bent over the form.
What is the force responsible for stretching the sheet metal in stretch forming?;
The stretching force (F).
What is the formula for the stretching force in stretch forming?;
F = f L t Yf
How is the die force (Fdie) determined in stretch forming?;
By balancing vertical force components.
What is roll bending used for?;
Forming large metal sheets and plates into curved sections.
How are curved sections formed using roll bending?;
Using rolls.
What is roll forming?;
A continuous bending process using opposing rolls to produce long sections of formed shapes from coil or strip stock.
What is spinning in metal forming?;
A process in which an axially symmetric part is gradually shaped over a rotating mandrel using a rounded tool or roller.
What are the three types of spinning?;
- Shear spinning
What is High-Energy-Rate Forming (HERF)?;
A process to form metals using large amounts of energy over a very short time.
What are the types of HERF processes?;
Explosive forming
Electrohydraulic forming
What is Explosive Forming?;
It is the use of an explosive charge to form sheet (or plate) metal into a die cavity.
How is the energy for forming transmitted in Explosive Forming?;
The explosive charge causes a shock wave whose energy is transmitted to force the part into the cavity.
What are the typical applications of Explosive Forming?;
Large parts typical of the aerospace industry.
What is Electromagnetic Forming in sheet metalworking?;
It is the process where sheet metal is deformed by the mechanical force of an electromagnetic field induced in the workpart by an energized coil.
What is the most widely used HERF process at present?;
Electromagnetic Forming.
What are some applications of Electromagnetic Forming?;
Tubular parts.
