Analysis of Common Forming Types in Stamping Parts Stretching Processes: A Comprehensive Overview of Technical Principles and Application Scenarios

In modern metal processing, stamping drawing is a core process widely used in the automotive, electronics, and aerospace industries. Through the combination of molds and stamping equipment, flat blanks are shaped into thin-walled parts of various complex shapes.

I. Cylindrical Drawing: A Basic and Efficient Forming Method

Cylindrical drawing is one of the most common types of stamping drawing, suitable for manufacturing cylindrical products with flanges. Its characteristics include flat flanges and bottoms, axisymmetric sidewalls, and uniform deformation distribution. For example, metal cans and bearing sleeves in everyday consumer goods often use this process. Key technical points include: The drawing deformation of the blank in the flange area must be uniform to avoid uneven thickness; For deep cylindrical parts, multiple drawing operations are required to prevent material wrinkling or cracking.

II. Conical Drawing: A Dual Challenge of Depth and Angle

Conical drawing is used to manufacture conical or pyramidal containers, such as funnels and lampshades. Due to the large unsupported area of ​​the blank and the small radius of the cone apex, this type of processing is prone to localized thinning or cracking. Solutions include:

1. Stepped stretching method: The blank is first stretched into a stepped transition part, then expanded into a cone shape;

2. Blank holder and draw bead: Increases radial tensile stress to prevent wrinkling.

The forming difficulty of cone-shaped parts increases with depth (h/d ratio) and cone angle (α), requiring precise control of die clearance and the number of stretching operations.

III. Rectangular stretching: Deformation difference between straight edges and rounded corners

Rectangular stretching is mainly used for forming low rectangular parts. Its characteristic is that the stretching resistance at the rounded corners in the flange deformation zone is greater than that at the straight edges, resulting in more severe deformation at the rounded corners. The technical challenges are: The difference in plastic deformation between straight edges and rounded corners needs to be balanced through die design; Sidewall instability must be avoided during multiple stretching operations.

High rectangular parts require rectangular re-stretching, whose deformation pattern is similar to that of deep cylindrical parts, but the stress distribution at the step transition section needs additional consideration.

IV. Complex Shape Stretching Processes: Composite Forming and Precision Control

1. Panel Stretching Processes
Suitable for sheet metal stampings with complex surface shapes (such as instrument panels and decorative panels). Its forming properties are a composite of deep drawing and bulging, resulting in complex blank deformation, requiring high-precision dies and multi-station presses.

2. Flange-Enhanced Hemispherical Stretching Processes
When stretching spherical parts, the blank only partially contacts the top of the punch, easily leading to localized thinning or wrinkling. Solutions include increasing the blank holder force or using a reverse stretching process.

3. Thinning Stretching Processes
By reducing the punch-die clearance, the cylinder wall material is thinned during stretching, thereby eliminating wall thickness deviations and improving surface smoothness. This process is commonly used in the manufacture of high-precision containers (such as cans).

V. Special Processes: Reverse Stretching and Curved Surface Forming

Reverse Stretching Processes: The workpiece from the previous process is stretched in the opposite direction, increasing radial tensile stress to prevent wrinkling, and potentially increasing the stretching coefficient. Suitable for secondary forming of deep box-shaped parts.

Curved Surface Forming: Through non-straight-walled, non-flat-bottomed mold design, the outer flange of the blank is reduced while the inner flange is extended, forming a curved hollow part. Typical applications include automotive body panels and irregularly shaped shells.

VI. Selection Recommendations: How to Match Processes and Requirements?

1. Material Thickness and Plasticity: Thin materials (t/d < 0.15) require multiple stretching or edge pressing; high-plasticity materials (such as stainless steel) are more suitable for complex shape forming.

2. Product Depth and Shape: Deep-drawn parts (h/d > 0.8) require stepped transitions or reverse stretching; non-axisymmetric parts (such as ellipses and dome shapes) require segmented control of deformation.

3. Equipment and Cost: Multiple stretching increases process complexity, requiring multi-station presses; thinning stretching requires extremely high mold precision and is suitable for high-precision applications.

The forming types of stamping part stretching are diverse, ranging from basic cylindrical shapes to complex curved surfaces and thinning stretching. Each process has its applicable scenarios and technical challenges. In actual production, the optimal stretching solution must be selected by considering material properties, product shape, and precision requirements. In the future, with the popularization of intelligent manufacturing technologies, stamping and stretching processes will develop towards greater efficiency and precision, continuously driving technological upgrades in the manufacturing industry.