Sheet metal fabrication processes——Shearing, Blanking, Punching, Piercing, etc.

Metal Shearing Techniques

Shearing methods encompass cold mechanical cutting techniques where sheet metal finds itself sandwiched between two razor-sharp blades utilizing guides or stops. The lower blade (referred to as the die) remains immobile, while the upper blade (known as the punch) swiftly cleaves through the metal with a forceful strike. Typically, both the die and the punch are constructed from tool steel or carbide. As this process unfolds, the sheer force applied places the sheet metal under stress, eventually surpassing the material’s ultimate shear strength, resulting in a clean cut.

Various approaches exist for mechanically slicing sheet metal, but the fundamental principle centers around the utilization of cutting blades within the material. This operation can be executed through a variety of means, including manual, electric, pneumatic, and hydraulic methods.

Typically, these procedures prove more cost-effective when dealing with moderately substantial production quantities, owing to extended setup durations and expenses linked to specialized tooling and dies. In scenarios involving one-off components or limited production runs, alternative cutting procedures like laser cutting often present a more financially viable solution.

Delve into the three primary shearing techniques (shearing, blanking, punching) employed by the metalworking sector, along with their corresponding sub-processes and distinctive attributes.

Shearing Insights

While all the procedures we delve into within this document fall under the category of shearing processes, it’s important to note that the term “shearing” primarily pertains to the act of making linear incisions to separate substantial metal sheets or bar stock. In this method, keen-edged blades are employed to carve their way through the material, ultimately yielding a sheared edge on the flat metal sheet.

Sheet metal shearing or die-cutting serves as a preparatory stage for other cutting methods, granting it versatility in handling metals of varying sheet thickness, up to 6 mm (0.25 inches). A 5-10% allowance based on the metal’s thickness is maintained to permit the sheet to undergo plastic deformation between the upper and lower blades.

The ability to execute seamless sheet metal cutting without the issues of burn-through or chip formation renders it well-suited for softer metals like aluminum, brass, bronze, and low-carbon steel.

  • Advantages

Cost-effective for high-volume production.

Minimizes cutting kerf in contrast to thermal cutting processes.

Facilitates the straightforward creation of large linear cuts across metal sheets of different thicknesses.

  • Limitations

Harder materials such as tungsten may experience delamination, fracturing, or harm to the cutting blades.

Burrs may arise in metals with larger diameters or clearance if secure clamping is not maintained.

Shearing is ill-suited for the intricate shaping of metals.

Blanking Unveiled

Blanking, an intricate method, surgically excises a product from sheet metal with precision. Employing both a punch and die, this procedure unleashes formidable shearing forces to part ways with unwanted material. The resultant shape, gracefully punched out, finds its purpose in specific applications, while the remaining surplus is relegated to the realm of scrap material.

Within the realm of blanking, a die, a guide plate, and a punch collaborate seamlessly. The die, steadfast and positioned beneath the metal sheet, rests securely, guided by the guide plate. The die’s contours faithfully mimic the envisioned cut. It is the punch’s solemn duty to apply measured pressure to the metal sheet, executing the cut with precision.

Blanking welcomes a diverse cast of metals, including aluminum, alloy steel, brass, copper, carbon steel, stainless steel, special alloys, and an array of other ferrous companions. Its applications extend to the realms of automobile components, electronics, and various industrial sectors.

  • Advantages

With strategic planning, generates minimal scrap material compared to traditional punching.

An expeditious process suitable for high-volume production.

  • Limitations

Entails substantial equipment and tooling investment.

Often necessitates follow-up operations to tame the unruly burrs along the edges.

  • Conventional Blanking

Conventional blanking relies upon a singular downward force to extract the desired form from the sheet metal. Its cutting clearance typically hovers around 10% of the material thickness, leading to a more generous helping of scrap in contrast to fine blanking.

  • Fine Blanking

Fine blanking, a distinguished sibling, harmonizes three sources of force (holding force, counterforce, blanking force) instead of the solitary downward impact of conventional blanking. This artful technique orchestrates a symphony of advantages: reduced burr formation, the birth of smoother and flatter edges, and the attainment of tighter tolerances (±0.0003).

The holding force stands sentinel, firmly clamping the metal sheet in place, while the counterforce takes its position beneath the blank’s emergence point. When the blanking force makes its entrance, it bestows pressure upon the cut, propelling the desired shape to freedom from the metal sheet. Fine blanking transcends the realm of mere cutting; it embodies the essence of precision and high-pressure artistry, akin to a cold extrusion process.

Punching Essentials

Punching is the art of creating holes or intricate shapes in metal sheets, resulting in scrap material. It’s a versatile process used across industries.

  • Advantages:
  1. Cost-effective for standard shapes.
  2. Can make dimples and louvers.
  3. No need for additional operations.
  • Limitations:
  1. Time-consuming setup.
  2. Not suitable for one-off parts.
  3. Custom tooling is costly.
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