Introduction to Basic Manufacturing Processes and ... - always yours

Sheet Metal Work 359
4. Hem (single and double), wired edge, cup and angular joints. These enable
the edges sheet metal part to join the pieces along them.
5. Flanged joint. It is commonly used in sheet metal work frequently in making pipe
connections.
6. Cap joint. It provides another useful form of locked seam joint on sheet metal
component with good appearance and strength. It is generally used for assembling
cross seam of ducts made up of in sheet metal part.
18.5 SHEET METAL OPERATIONS
The major sheet metal operations carried out in sheet metal work are as follows:
1. Cleaning 2. Measuring
3. Marking 4. Laying out
5. Hand cutting 6. Hand shearing
7. Hand forming 8. Edge forming
9. Wiring 10. Joint making
11. Bending 12. Drawing
13. Soldering 14. Circle cutting
15. Machine shearing 16. Nibbling
17. Piercing 18. Blanking
The measuring and marking operations carried over on sheet metal are discussed as
under.
Measuring and Marking
The standard sizes of metal sheets available in the market are quite large. But the
required sheet size for making a component may be smaller and hence a standard size sheet
may have to be therefore cut into several smaller pieces. Each piece must be sufficient for
making one such component as per the needed size. Smaller sizes of sheet metal part are first
decided and are then marked on the larger metal sheet to cut the latter into small pieces
along the marked lines. A little allowance for cutting is always incorporated to the required
overall sizes. The overall dimensions of the required smaller sizes are marked on the larger
sheet with the help of marking tools such as a steel rule, a straight edge, a steel square and
a scriber. The sheet surface may have to be coated with a coloring media so that the scribed
lines arc clearly visible. If circular pieces are needed, a divider or trammel may be used to
mark the circles.
18.6 DEVELOMENT OF PATTERN LAYOUT
Projective geometry forms the basis of successful layout of patterns for making different
jobs in sheet metal work. Most of the patterns are obtained from development of surfaces of
some common geometrical solids like cylinder, prism, pyramid and cone. These shapes may
be required to be developed either in single or in combination. A sheet metal planner should
have a thorough idea of the procedures employed in developing the surfaces of the above
solids and their inter-penetrations.