Machine Design
  • Resources
  • Members
  • Directory
  • Webinars
  • WISE
  • CAD Models
  • Advertise
    • Search
  • 3D Printing & CAD
  • AUTOMATION & IIOT
  • Robotics
  • Motion Systems
  • Materials
  • Video
  • Data Sheets
  • Topics
    Industry Markets3D Printing & CADAutomation & IIoTFastening & JoiningMaterialsMechanical & Motion Systems Medical DesignRobotics
    Resources
    Machine Design ResourcesWISE (Workers in Science & Engineering)Company DirectorySearch Data SheetsContributeDigital Edition ArchivesCSIA Exchange
    Members
    ContentBenefitsSubscribe
    Advertise
    https://www.facebook.com/MachineDesignMagazine/
    https://www.linkedin.com/company/10998894
    https://twitter.com/MachineDesign
    https://www.youtube.com/channel/UCXKEiQ9dob20rIqTA7ONfJg
    Thinkstock
    Machinedesign 15812 Welding Lead
    1. Mechanical & Motion Systems

    DFM for Welding

    May 14, 2018
    Welding is one of the least expensive and most reliable ways to join metal to metal. But engineers must design drawings for welding with rules in mind.
    Usha B. Trivedi

    For sheet metals and plates, resistance spot welding remains a widespread choice for joining similar metals. It is inexpensive and the resulting joints are strong and reliable. That’s why resistance welding is so widespread in automobile manufacturing. But to get the most out of the design and welding, the product should be designed for welding. Here are some DFM features that make resistance spot welding more effective and efficient.

    Part thickness. Ideally, parts or plates of equal thickness will result in evenly spread weld nugget (the molten metal that quickly cools and solidifies into a round joint). But most of the time, plate thickness varies, and in such cases spot weld is effective only when the ratio of plate thicknesses is 3:1 or less. Using a filler electrode will produce effective weld nuggets and give the joint adequate strength. And, the plate surface should be flat or coplanar to simplify the welding process.

    Www Machinedesign Com Sites Machinedesign com Files Fig 1 Ratio Of Plate Thickness

    The proper ratio of plate thicknesses should be 3:1 or less. In this case, the upper plate is 2-mm thick and the lower one is 6-mm thick. So, the ratio is 3:1 and within the limit.

    Brackets and stiffeners. Spot welding thermally deforms the pieces being joined with deformation greatest on the thinner piece. Thus, when stiffeners are used to provide added structural stability to the joint, selecting appropriate thickness is important. Stiffeners and brackets should be thinner than or equal to the thickness of the exposed surface of the base plate.

    Weld proximity and edge clearance. To get the best weld quality and strongest joint, the distance between consecutive welds (aka pitch) and between individual welds and the edge of the part (clearance) must meet specific criteria. The pitch should be 10 times the material thickness for the best strength and to avoid any adverse effect on the part. Theoretically, a pitch of 20 times the material thickness reduces the shunting effect (where current travels from the weld being made to a nearby already-made nugget and not enough heat is generated in the joint being formed, making it weaker and unreliable).

    It is also good practice to maintain twice the spot-weld diameter from the center of the weld to edge of the workpiece. This rule also applies to slots and holes midway between the plate surfaces. If this minimum distance is not maintained, the electrode may not apply enough pressure and cracks may develop, leaving a porous weld. Sometimes, it may also lead to excessive burrs or deformation of metal.

    Www Machinedesign Com Sites Machinedesign com Files Fig 2 Spot Weld Diameter

    D = 2d, d = spot weld diameter.

    Www Machinedesign Com Sites Machinedesign com Files Fig 3 Distance Between Weld And Slot Or Holes

    Distance between weld and slot or holes.

    Distance between weld and form. When sheet-metal parts having any kind of form, bend, or draw are to be welded, there should be a minimum distance of a spot-weld diameter (D) plus one bend radius (D + R) between the electrode and form to prevent shunting. Designers should ensure this bare minimum clearance to avoid fabrication errors.

    Www Machinedesign Com Sites Machinedesign com Files Fig 4 Weld Space

    Weld space: distance of form to the center of the spot weld.

    Spot weld overlap region. Spot welding is only done on pieces that are coplanar, so the overlap region of both workpieces has a significant impact on weld quality. It is necessary to have appropriate overlapping lengths of the sheets to attain better dimensional accuracy and join the sheets without large deformation. Usually, the overlap length depends upon the material being welded and its thickness, but is not usually more than 8 mm in diameter.

    Www Machinedesign Com Sites Machinedesign com Files Fig 5 Overlap Region For Spot Weld

    Overlap region for spot weld.

    Projection Welding

    Projection welding, a small refinement of resistance spot welding, uses earlier projections to reduce the consumption of power to make a resistance weld. It also reduces shunting effect—a major limitation of spot welding—allowing for closer weld-to-weld spaces and making it possible to weld the jobs that have smaller flanges.

    Usually, projection welding is used for materials such as low-carbon steels and alloys, as well as aluminum having a thickness around 3.18 mm. But workpieces below 0.25 mm thickness would need spot welding only, as the higher temperatures of projection welding would result in the workpiece collapsing. Projection welding is less expensive than spot welding, but requires precise positioning of workpieces and electrodes, in addition to precise tolerances.

    These design rules ensure that parts are designed with the intent to reduce design revisions and reworks, which will take care of 70 to 80% of the costs. The remaining costs are for manufacturing, which can be minimized by specifying correct processes and methods in the drawings.

    Axial, shear, and bending strength of welds vary as a function of strain generated in the component, and they depend on the pressure generated through the electric current during the welding and the distance of the electrodes from the workpiece. Thus, designers should specify tool clearances in drawings along with standard weld symbols, based on the intended design characteristics.

    Www Machinedesign Com Sites Machinedesign com Files Fig 6 Spot Weld And Tool Clearance

    Spot weld and tool clearance >= 3 mm to avoid interference of the weld gun.

    Www Machinedesign Com Sites Machinedesign com Files Fig 7 Spot Weld Symbol

    Spot weld symbol.

    Following a good design rulebook should reduce rework and waste due to bad welds, but it doesn’t guarantee that the designs will not fail or component will withstand extreme cases. Designs adhering to DFM must still undergo design analysis to ensure the reliability and appropriate functioning in operational conditions. The conventional approach of designing with DFM rule books and then calculating the strength of critical components for optimization will show a dramatic reduction in the overall costs of manufacturing a product.

    If you have any questions regarding DFM for spot welding designs & drawings, please feel free to contact an engineer at Hi-Tech CADD Services.

    Www Machinedesign Com Sites Machinedesign com Files Source Esb Looking For Parts Rev Caps

    Continue Reading

    How a Connected World Requires Product Adaptation and Faster Time-to-Market

    Cobots Double Weld Grinding Efficiency Without Replacing Human Know-How

    Sponsored Recommendations

    Smart Factory Solutions that Connect and Protect from Amphenol RF

    Nov. 28, 2023

    Stay Connected and In Control of Your Future Factories with Littelfuse

    Nov. 28, 2023

    Turn to NKK Switches for the Widest Range of Industrial-Savvy Electromechanical Switches

    Nov. 28, 2023

    Unlocking Operational Flexibility in Manufacturing with Industria IoT

    Nov. 28, 2023

    Voice your opinion!

    To join the conversation, and become an exclusive member of Machine Design, create an account today!

    I already have an account

    New

    Using Natural Language Understanding to Power Productivity

    Intelligent Assistant Platforms Improve Conversations with Industrial Robots

    Natural Language Conversation Assistants Cross Over from Vehicles to Industrial Machinery

    Most Read

    Universal Robots Unveils UR30: Relief for Heavy Lifting

    The Cyber-physical Training Module

    Edge Computing & Gaining Value

    Sponsored

    Stay Connected and In Control of Your Future Factories with Littelfuse

    Unlocking Operational Flexibility in Manufacturing with Industria IoT

    Next-Generation ix Industrial Interconnects From Amphenol Communications Solutions

    Machine Design
    https://www.facebook.com/MachineDesignMagazine/
    https://www.linkedin.com/company/10998894
    https://twitter.com/MachineDesign
    https://www.youtube.com/channel/UCXKEiQ9dob20rIqTA7ONfJg
    • About Us
    • Contact Us
    • Advertise
    • Do Not Sell or Share
    • Privacy & Cookie Policy
    • Terms of Service
    © 2023 Endeavor Business Media, LLC. All rights reserved.
    Endeavor Business Media Logo