The design criteria for welded lap joints involve ensuring adequate weld size, strength, and load-carrying capacity. Here is a step-by-step procedure for designing welded lap joints:
- Determine Material and Thickness: Identify the materials being joined and determine their thickness. Consider the mechanical properties of the materials and ensure they are compatible for welding.
- Calculate Required Weld Size: Determine the required weld size based on the design requirements, including the applied loads and the desired level of strength. The weld size is typically specified as the leg length of the fillet weld.
- Determine Fillet Weld Length: Calculate the required fillet weld length based on the applied loads and the strength requirements. The weld length should be sufficient to provide proper load transfer and to prevent stress concentrations.
- Select Welding Process: Choose the appropriate welding process for the joint based on factors such as material type, thickness, and the desired quality of the weld. Common welding processes for lap joints include shielded metal arc welding (SMAW), gas metal arc welding (GMAW), and flux-cored arc welding (FCAW).
- Determine Welding Parameters: Select the appropriate welding parameters, such as current, voltage, travel speed, and electrode size, based on the chosen welding process and the material being welded. Consult welding procedure specifications (WPS) or welding codes for guidance on selecting the welding parameters.
- Prepare Joint Surfaces: Prepare the joint surfaces by cleaning them thoroughly and removing any contaminants, oxides, or coatings. Ensure proper fit-up and alignment of the lap joint.
- Welding Procedure Qualification: If required by the design codes or specifications, perform a welding procedure qualification test to ensure the weld meets the specified quality and strength requirements.
- Quality Control and Inspection: Implement quality control measures during welding, including monitoring welding parameters, visual inspection of the weld, and non-destructive testing if necessary. Inspect the completed weld joint to ensure it meets the specified criteria.
- Design Verification: Perform structural analysis or calculations to verify the strength and performance of the welded lap joint. This may involve checks for weld size, load-carrying capacity, and the overall joint strength based on the applied loads and the material properties.
Example: Design of a Welded Lap Joint
Given:
- Material: Steel
- Thickness: 8 mm
- Design Load: 10 kN
Step 1: Determine Material and Thickness The material is steel with a thickness of 8 mm.
Step 2: Calculate Required Weld Size Based on the design load and desired strength, let’s assume a required weld size of 6 mm (leg length of the fillet weld).
Step 3: Determine Fillet Weld Length Calculate the required fillet weld length based on the applied load and the desired load transfer efficiency. Let’s assume a required weld length of 80 mm.
Step 4: Select Welding Process Choose the gas metal arc welding (GMAW) process for the joint.
Step 5: Determine Welding Parameters Select the appropriate welding parameters, such as current, voltage, travel speed, and electrode size, based on the chosen welding process and the material being welded.
Step 6: Prepare Joint Surfaces Clean the joint surfaces thoroughly and ensure proper fit-up and alignment of the lap joint.
Step 7: Welding Procedure Qualification Perform a welding procedure qualification test if required.
Step 8: Quality Control and Inspection Implement quality control measures during welding and inspect the completed weld joint.
Step 9: Design Verification Perform structural analysis or calculations to verify the strength and performance of the welded lap joint.
It is important to note that the specific design criteria and formulas for welded lap joints may vary depending on the design codes and standards being used. It is recommended to consult the relevant design code or consult with a qualified welding engineer or structural engineer to ensure accurate and compliant joint design.
