Sheet Metal Fabrication: Your Step-by-Step Guide

1. Purpose

To standardize the operation of sheet metal and improve the quality of our products, ensuring customer satisfaction.

2. Scope of application

This applies to sheet metal operations such as the MPX178 digital distribution frame, TYWZ outdoor cabinet, broadband box, components of the JPX-250 main distribution frame, the GXF5-106 stainless steel optical cable junction box, etc.

3. Equipment

The QC12NJDK CNC hydraulic shearing machine, WD67NJDK double-cylinder hydraulic press brake machine, J23 series punch press, ZXJ bench drilling machine, AC/DC arc welding machine, polishing machine, and scale are included in this.

4. Operation process

1. Collect materials

Collect materials from the warehouse according to the order and technical specifications.

2. Take materials

As per the design drawings requirements, raw materials should be collected according to specifications and checked for compliance with the process requirements. To minimize material waste and improve utilization, the nesting method should be optimized through proper calculation.

Measure the distance between the steel plate and the two ends of the retaining plate, as specified in the process card, multiple times. Then, cut a small piece of material to verify that the size is correct. If the size tolerance is within the acceptable range, proceed with the feeding shear. If the size does not meet tolerance requirements, adjust the positioning distance until it meets the specifications.

Before shearing, check if the blade is sharp and secure. Adjust the blade gap based on the thickness of the sheet.

3. Punching

a) Verify that the material, width, length, and thickness of the materials meet the requirements of the drawings.

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b) Choose the appropriate press based on the process requirements.

c) Align the positioning device as per the process sequence and requirements, and punch out the process holes that meet the required specifications.

Related reading: How to Calculate Punching Force?

4. Bending

a) Ensure that the material, width, length, and height of the materials conform to the requirements of the drawings and are free of any contaminants.

b) Choose the appropriate press brake based on the specifications in the drawings.

c) Align the positioning device according to the process sequence and requirements, and carry out the bending process.

d) Reference table for material thickness, bending fillet, and die depth during bending (dimensions in brackets refer to CNC press brake machine specifications).

e) Minimum bending radius for different materials.

f) Table of dimensions for bending fillet expansion.

Related reading: Press Brake Bending Basics

5. Welding

a) Verify that the semi-finished parts transferred from the previous process conform to the requirements of the drawings and other technical documents. If necessary, adjust promptly to meet the specifications.

b) Gather the necessary welding equipment and tools.

c) Arrange the welding sequence as per the requirements of the drawing, generally starting with critical areas and then proceeding to general areas.

d) Choose the type and size of the welding rod and welding current based on the material and welding requirements of the workpiece.

The following current selection methods can be used for reference.

① Welding selection shall be considered from two aspects:

a) Select the appropriate category of welding rods based on the material and welding requirements.

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b) Determine the electrode diameter based on factors such as the thickness of the workpiece, weld geometry, welding specifications, and others.

To improve labor efficiency without compromising welding quality, it is recommended to use larger diameter electrodes. The data in the following table can be used as a reference.

AC/DC electric welding machine

Thickness of weldment (mm)234~56~12>13
Electrode diameter (mm)233~44~55~6

C02 protective cover

NameIron plate
Iron plate
Electrode diameterφ0.8φ0.8
Wire feeding speed5th5th
Current regulation3rd6th

② Selection of welding power source and welding current

a) Selection of Welding Power Source

The welding power source should be selected based on the type of welding electrode. Typically, ferrous metals like low-carbon steel can be welded with either AC or DC power sources. AC welding machines are cost-effective, so it is recommended to use them to save on electricity. However, some materials have poor welding performance and are better suited for DC welding machines, such as cast iron, stainless steel, heat-resistant alloys, copper, aluminum alloys, etc.

b) Selection of Welding Current

The selection should be made based on the type and size of the welding rod. To ensure welding quality (such as avoiding early redness and avoiding penetration), it is recommended to use high current welding. For electrodes with a diameter of 4 to 8mm, the welding current can be roughly calculated using the following formula:

 I =K*D


  • I=current intensity
  • K=coefficient (chalk coated electrode K=36~50, high-quality electrode (thick coating), K=40~60);
  • D=electrode diameter (mm)
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When determining the current based on the calculated value, take the following factors into consideration:

a) Fast heat transfer of the weldment, low operating current, high circuit resistance, and high operating current.

b) If the electrode diameter remains the same, the current for welding thick steel plates is higher than for welding thin steel plates.

The current for vertical and overhead welding should be 15 to 20% lower than for flat welding, and the current for fillet welding should be higher than for flat welding.

6. Grinding

After welding, it is important to properly polish the machined parts to make the surfaces smooth and even, without any missing welding, cracks, splashes, burrs, or other defects.

7. Detection

The machined parts that have undergone the above processes should undergo comprehensive testing in accordance with technical specifications. If they pass inspection, they can then be transferred to the next stage of the process.

8. Plastic spraying

a) The machined parts should be coated with the specified color as per the requirements in the drawings.

b) After plastic coating, the processed parts should have a uniform and smooth surface, with no air holes, sagging, or color variations.

9. Inspection of semi-finished products

The semi-finished products should undergo thorough testing in accordance with technical specifications. If they pass the inspection, they can then be moved to the next stage.

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