Fabricating Techniques and Practices Chapter 21 Fabricating Techniques and Practices

Objectives Explain the various safety issues related to fabrication List the advantages of using custom fabrication parts Demonstrate an understanding of the proper placement of tack welds Demonstrate the use of location and alignment points when assembling a project Explain how to adjust parts to meet the tolerance

Objectives (cont’d.) Describe how to control weld distortion Lay out and trace parts Identify common sizes and shapes of metals used in weldments Describe how to assemble and fit up parts for welding.

Introduction Assembly of the parts to be joined First step in almost every welding operation Basic level: placing two pieces of metal flat on a table and tack welding them together Higher level: assembly of complex equipment, buildings, ships, or other large welded structures No matter how large or complicated the welded structure It is assembled one piece at a time

Fabrication Process of assembling parts to form a weldment Often required by welders Number and type of steps required to complete a project vary Welding projects start with a plan Plans can range from simple to very complex You must learn how to follow a set of drawings to produce a finished weldment

Safety Primary concern for fabrication of weldments Much of larger fabrication work may need to be performed outside an enclosed welding booth Several welders may work simultaneously Notify others of hazards Ventilation is important Lines must be flat on the floor and covered to prevent trip hazards Make sure fabrication is stable

Parts and Pieces Welded fabrications Preformed part advantages Made from precut and preformed parts or hand-cut and -formed parts Preformed part advantages Cost, speed, accuracy, and less waste Custom fabricated part advantages Originals, prototypes, repairs, and custom jobs

Layout Welder must lay out lines and locate points for cutting, bending, drilling, and assembling Always start a layout as close to a corner of the material as possible It is easy to cut the wrong line Some shops have their own shorthand methods for identifying layout lines Process may be affected by several factors Material shape, part shape, tolerance, and nesting

FIGURE 21-13 Marking parts makes it less likely that the wrong one is welded in place. La-Co Markal

Nesting Laying out parts so the least amount of scrap is produced FIGURE 21-21 Parts nested for cutting; note the small blank space left between the parts. MultiCamPix

Kerf Space Space created as material is removed during a cut Width varies depending on cutting process FIGURE 21-23 Angle iron shear. Scotchman

Material Shapes Metal stock Bill of materials form Wide variety of shapes, sizes, and materials Bill of materials form Plate: usually 3/16 inch or thicker and measured in inches and fractions of inches Sheets: usually 3/16 inch or less and measured in gauge or decimals Pipe: dimensioned by diameter and schedule or strength Tubing sizes: always given as outside diameter

Overall Tolerance Amount that a part can be bigger or smaller than it should be and still be acceptable FIGURE 21-35 Small errors on lots of parts can become a big error on the finished assembly. © Cengage Learning 2012

Assembly Assembly process Very large projects Start the assembly Requires proficiency in several areas Very large projects Corner or centerline is established as a baseline Start the assembly Select largest or most central part Identify each part and mark each piece for future reference Layout lines and other markings can be made on the base

Assembly Tools Variety of tools make assembly easier Clamps: temporarily hold parts in place C-clamps, bar clamps, pipe clamps, locking pliers, cam-lock clamps, and specialty clamps Fixtures: aid in assemblies and fabrication of weldments A well-designed fixture allows adequate room for the welder to make tack welds

Fitting Adjusting parts of a weldment so they meet the overall tolerance Not all parts fit exactly as they were designed Slight imperfections in cutting or distortion due to welding, heating, or mechanical damage Some problems can be solved by grinding away the area Other situations may require parts be forced into alignment More aligning force can be applied using cleats or dogs with wedges or jacks

Tack Welding Welds made during assembly to hold all parts of a weldment together so they can be finished welded Several factors to consider Thickness of the metal Length and shape of the joint Welding stresses Tolerance Fitup

Welding Good welding requires more than just filling up joints with metal Welding on an assembly should be staggered Keep arc strikes in the welding joint Striking the arc in correct location on an assembly is more difficult than working on a welding table Be sure you have enough freedom of movement to complete the weld joint Follow all the safety and setup procedures

Finishing Welder may be responsible for finish work Considerations Depends on shop size Considerations Most grinding is done with a hand grinder Grinders must be held securely Painting and other finishes release fumes such as volatile organic compounds (VOC) Special ventilation may be required Most paints are flammable Must be stored well away from any welding

Summary Completing work on a piece of equipment, building, trailer, or other structure One of the greatest experiences as a welder/fabricator Layout and fabrication techniques must be learned Welded structures Enduring monument to your skill as a craftsman Every time you build a project, do it as if it were going to be on display