1. Fabricating Techniques and Practices
Chapter 21
Fabricating Techniques
and Practices

2. 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

3. 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.

4. 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

5. 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

6. 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

7. 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

8. 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

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

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

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

12. 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

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

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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