Deep Drawing Process Quiz

Sheet Metal Forming

• Sheet metal forming is a manufacturing process used to create complex shapes from sheet metal
• A sheet metal part is produced using presses, called stamping.
• Low carbon steel is frequently used due to cost-effectiveness and good strength/formability
• Other materials, like aluminum and titanium, are sometimes used for specific applications (e.g., corrosion resistance, aerospace components)
• Sheet metal forming can be performed at room temperature, or hot stamping can be used to increase formability.

Introduction to Shearing

• Sheet metal forming begins with shearing to remove a blank from a larger sheet
• Shearing uses a punch and a die to create shear stresses
• Shearing creates cracks along the edges of the sheet and the slug, leading to separation.
• Burnished surfaces on the hole and the slug result from contact, while rough fracture surfaces develop due to cracks.
• A burr is a thin, raised edge at the sheared edge
• Burr formation is influenced by clearance and material ductility.
• Dull tool edges contribute to large burr formation
• Excessive clearance results in rougher sheared edges, affecting subsequent processing.
• Secondary operations may be required to smooth finished edges.

Punch Force

• Punch force is calculated by multiplying shear strength by sheared area.
• Factors include sheet thickness (T), total length sheared (L), and the Ultimate Tensile Strength (UTS) of the material.
• Punch force decreases as clearance increases.
• Friction between the punch and workpiece increases the punch force.

Other Shearing Operations

• Shearing operations include punching and blanking.
• Die cutting involves fine blanking (smooth sheared surfaces), slitting (using circular blades), and lancing (slitting to create tabs)
• Processes are frequently done using a pair of circular blades, similar to a can opener.

Characteristics of Shearing Dies

• Proper clearance is crucial for product formability and finish.
• Clearance (c) ranges between 2% - 8% of sheet thickness. But can be smaller (1%) for fine blanking or higher (30%) in some cases.
• Soft materials require tighter clearances, while hard materials require larger ones.
• Larger clearances increase sheared area deformation, resulting in a rougher sheared edge, which might need further processing.

Punch and Die Shape

• Shapes are often beveled to control shearing location.
• Compound dies allow multiple operations on the same part at a single station.
• Progressive dies are used for high-volume, multi-stage operations

Formability Tests

• Sheet metal formability measures its ability to change shape without failing

Cupping Test

• The Erichsen test is a cupping test to assess formability by stretching the metal until a crack appears.
• Punch depth at crack point is a key indicator of formability.

Bending Sheets, Plates, and Tubes

• Bending is a common metal forming operation, used in numerous applications
• Outer fibers experience tension, while inner fibers experience compression.
• Bend allowance considers the neutral axis length, bend angle, bend radius, and material thickness.

Minimum Bend Radius

• Minimum bend radius is where cracks first start in outer fibers.
• Bending strain and crack formation depend on bend radius, material thickness, and angle.

Springback

• Springback refers to the tendency of a bent material to return to its original shape slightly after the force is removed.
• Factors influencing springback is the material’s elastic modulus, yield strength, and the ratio of bend radius to material thickness.
• Springback calculations can be approximated using bend radii, before and after.
• Negative springback is also possible when the bend goes back toward a direction opposite of the expected bend angle because of the absence of constraint.

Miscellaneous Bending and Related Forming Operations

• Various techniques like forming, channels, joggles, hemming (flattening), two stage lock seam, offset forming, and different types of bead forming are used to shape metals.
• Tools and dies materials used in shearing operations often include tool steel and carbides. Lubrication is important to minimize wear.

Deep Drawing

• Cylindrical and box-shaped parts are formed using deep drawing.
• The process forces a flat blank into a die cavity, thus forming a cup
• Determining the maximum punch force is complex, but formulas can be used based on blank diameter, sheet thickness, material strength and the punch/die radii.
• Wrinkling can often occur in the drawn flange.
• Wrinkling can be reduced by applying a blank holder.

Metal Forming Processes in Can Manufacturing

• The process for manufacturing two-part aluminum cans is detailed
• Sequence of manufacturing operations needed to shape from a raw blank to a finished can. Methods used in forming operations including blanking, deep drawing, redrawing, ironing, doming, necking, and seaming.