Basic Knowledge of Sheet Metal Processing – Advantages, Disadvantages, and Cost Reduction Methods

Key Points of Sheet Metal Processing

In sheet metal processing, various methods are used to apply force to sheet-shaped metals to form the target shape, and the principle is related to the properties of metal materials. When a load is applied to a metal material, the distance between the constituent atoms changes, and the material deforms while strain is generated. At this time, the internal force that attempts to restore the metal to its original state comes into play. Therefore, when the load is small, removing the load will allow the metal to return to its original state (elastic deformation). When the load continuously increases beyond a certain point (yield point), the metal can no longer return to its original shape (plastic deformation). If the load continues to increase, the metal will eventually break.
In sheet metal processing, it is important to have the technique of adjusting during processing to achieve the target shape through plastic deformation.

Sheet Metal Processing Procedures

There are roughly eight steps from sheet metal processing to product shipment. Let’s take a look at each process in detail.

1. Development / Programming

Design drawings are often created with 3D CAD, but since sheet metal processing starts from a flat sheet, it is necessary to “develop” the 3D model into a 2D flat pattern using CAD or dedicated software. Once the development drawing is complete, “nesting” is performed to arrange parts efficiently on a standard sheet size to minimize waste, while simultaneously creating machining programs.

2. Blanking / Cutting

This process cuts the outer contour and inner holes of metal sheets. The main processing equipment used are laser cutting machines and turret punch presses.
Generally, laser cutting machines excel in high-speed cutting of outer contours and large holes, while turret punch presses are advantageous for processing many holes and performing forming operations.
There is also a “laser-punch combination machine” that combines the advantages of both. Since each sheet metal manufacturer owns different equipment, it is best to choose the factory according to its available machines when placing an order.

3. Deburring

Regardless of the previous process used, there will be some laser cutting burrs (slag), punch shear burrs, or flash. The deburring process removes these using hand grinders, files, or automatic deburring machines with rotating abrasive brushes.
In sheet metal processing, it is difficult to perform fine dimensional control such as C0.2 or R0.2 as in machining. Therefore, drawing notes like “no burrs” can be ambiguous. A clearer indication would be “remove burrs so that they do not cut hands.” When placing an order, it is recommended to confirm the acceptable level of burr removal with the manufacturer.

4. Bending

The general bending process in sheet metal fabrication involves using a press brake equipped with upper (punch) and lower (die) molds to apply pressure to the cut sheet and bend it at a specific angle.
Since the bending angle may vary depending on material batch and rolling direction, fine adjustments are needed each time, making this process challenging. However, it is one of the most important steps, as the precision of bending greatly affects the ease of welding and the appearance in later stages.
The “press brake” is sometimes called a “bender” or “folding machine,” but all refer to the same equipment.

5. Welding

Welding is a process that joins metals by melting them through heating and solidifying after cooling. In sheet metal processing, TIG welding and laser welding are the main methods.
TIG welding (also known as argon arc welding) uses a tungsten electrode and argon as a shielding gas. It can include filler rods for build-up welding, but since it introduces a large amount of heat, deformation is likely to occur, and the result depends heavily on the craftsman’s skill.
Laser welding, on the other hand, suppresses heat distortion and enables standardized processes. However, since it is generally based on autogenous welding, it is difficult to use for parts requiring build-up and may require different methods.

6. Finishing (Including Surface Treatment)

The finishing process in sheet metal fabrication includes removing heat distortion caused by welding, grinding off weld beads, eliminating burn marks through electrolytic polishing, and performing surface polishing or buffing.

7. Assembly

This step assembles multiple parts using fasteners such as bolts, nuts, and rivets. It is often used in areas where welding strength is not required or where disassembly will be needed later. Assembly work, also known as “fitting” or “mounting,” covers a wide range of operations, from small parts assembly to medium-sized unit assembly and final assembly of entire machines or equipment.

8. Inspection

Before shipment, sheet metal products undergo dimensional and visual inspection.
Dimensional inspection mainly uses calipers, scales, and protractors to verify whether the dimensions, hole positions, and tolerances match the drawings.
Visual inspection checks for scratches and burrs, and some factories also use image measuring instruments or coordinate measuring machines (CMMs).

Main Equipment Used in Sheet Metal Processing

• Laser Cutting Machine
  Uses high-power laser beams to locally melt metal, blowing away molten metal with gas for cutting. Excellent for high-speed cutting of long perimeters or large holes. However, when there are many holes, the number of piercing operations increases, which takes time. With recent advancements in high-power lasers, even piercing operations have become faster.

• Turret Punch Press
  Equipped with multiple small dies mounted on a rotating turret, it punches holes in metal sheets at high speed. Suitable for multi-hole parts and can perform forming operations such as tapping, countersinking, and louver forming. However, cutting outer contours requires many punches and is time-consuming.

• Laser-Punch Combination Machine
  Combines both technologies, allowing blanking and forming in one setup. For example, laser cuts large holes and outer contours, while punching handles holes and forming. This minimizes alignment errors due to fewer setups.

• Deburring Machine
  Modern deburring machines use conveyor belts to hold parts and rotating abrasive brushes to evenly remove burrs, replacing traditional manual methods.

• Press Brake
  The press brake applies pressure from the upper punch onto the lower die to bend the metal. There are mechanical, hydraulic, and servo motor-driven types, with NC-controlled versions being most common today. Automated back gauge movement ensures high precision. The tonnage and working length determine the processable material and thickness.

• Laser Welding Machine
  Laser welding produces deep, narrow welds with minimal heat-affected zones, reducing thermal distortion. Early YAG lasers were known for low deformation and good appearance, but the later fiber laser welders (since around 2015) achieved higher strength and became widely used. Laser welding is especially suitable for thin sheets and easy to operate even by less experienced workers.

• TIG Welding Machine
  TIG welding is an arc welding process commonly used in mechanical sheet metal. It provides excellent airtightness and high joint strength but causes large heat input and thermal distortion. Techniques to minimize or correct distortion require high craftsmanship, hence TIG welding is often referred to as an “artisan skill.”

Materials and Surface Treatment Used in Sheet Metal Processing

Common materials include stainless steel, carbon steel (SPCC, SECC), and aluminum alloys.
The typical thickness ranges from t0.1 mm to 22 mm. Material selection should depend on the product’s purpose and processing characteristics.

Advantages and Disadvantages of Sheet Metal Processing

Advantages:
The greatest advantage of sheet metal processing is its suitability for small-lot and multi-variety production. Stamping, as a representative plastic forming method, is ideal for mass production of identical parts but requires expensive molds for each product, making it costly for small batches.
In contrast, sheet metal processing uses general-purpose equipment and tooling for all steps such as blanking, bending, and welding. It allows flexible design changes and can produce complex shapes from a single sheet through combined operations.

Disadvantages:
Since parts are produced one by one, large-volume production takes time. Moreover, many processes such as welding depend on the craftsman’s skill, making it unsuitable for high-volume production.

Methods to Reduce Costs in Sheet Metal Processing

Here are four ways to reduce costs in sheet metal fabrication:

1. Order Based on the Manufacturer’s Expertise
   Although all are called “sheet metal fabricators,” each company has different equipment. Costs can be reduced simply by matching the job to the manufacturer’s capabilities. For example, laser cutting excels at outer contour and large-hole cutting, while turret punches are ideal for many holes and forming operations. Ordering accordingly can significantly reduce processing costs.

2. Replace Welding with Bending Where Possible
   As mentioned in the TIG welding section, welding relies heavily on skill and tends to be costly. For example, instead of welding two plates at 90°, bending them may be cheaper.
   Riveting is another cost-saving option but must be defined in the drawings as “no welding required.”

3. Review Deburring Requirements
   Specifying “no burrs around the entire perimeter” in drawings significantly increases labor and machine costs. By narrowing deburring to only necessary areas, factories can reduce processing time and cost. Discussing realistic tolerances and quality expectations with the manufacturer can lead to cost savings.

4. Review the Necessity of Build-Up Welding
   Build-up welding is often required to ensure strength, but modern fiber laser welding can achieve sufficient strength without it. Changing the process instead of insisting on build-up can reduce costs while maintaining quality.

Sheet metal processing is a flexible manufacturing technology suitable for small-lot and multi-variety production. However, since it still relies heavily on craftsmanship and intuition, it remains a technically challenging field.
Manufacturing costs vary depending on equipment and methods, so understanding the characteristics of sheet metal processing is essential for efficient design.