© 2012 Delmar, Cengage Learning Chapter 21 Fabricating Techniques and Practices.

© 2012 Delmar, Cengage Learning

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 – 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 – 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 – 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– 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

© 2012 Delmar, Cengage Learning Chapter 21 Fabricating Techniques and Practices.

Documents

cengage learning parts

cengage learning welding

cengage learning figure

cengage learning objectives

cengage learning nesting

cengage learning chapter

cengage learning fitting

tolerance slide