FABRICATION PROCESS

FABRICATION PROCESS

                     

                            FABRICATION PROCESS

Structural steel fabrication can be carried out in shop or at the construction site. Fabrication of steel work carried out in shops is precise and of assured quality, whereas field fabrication is comparatively of inferior in quality.

Structural steel passes through various operations during the course of its fabrication. Generally, the sequence of activities in fabricating shops is below 

1) surface cleaning 

2)cutting and machining according to drawing 

3)punching and drilling

4)bending rolling and straightening

5)fitting

6)fastening like riveting welding

7)finishing

8) Quality control 

9)surface treatment

10)Transportation

 Surface cleaning:

 Structural sections from the rolling mills may require surface cleaning to remove mill scale prior to fabrication and painting.

 Cutting and machining according to drawing :

Following surface preparation, cutting to length is always the first process to be carried out, and this is done by any of the following methods.

I)Shearing and cropping

II)Flame Cutting or Burning

III) Arc Plasma Cutting

VI)Cold Sawing

 Punching and Drilling
Most fabrication shops have a range of machines, which can form holes for connections in structural steel work. The traditional drilling machine is the radial drill, a manually operated machine, which drills individual holes in structural steel work. But this method has become too slow for primary line production. 

Straightening, Bending and Rolling: 
Rolled steel may get distorted after rolling due to cooling process. Further during transportation and handling operations, materials may bend or may even undergo distortion. This may also occur during punching operation. Therefore before attempting further fabrication the material should be straightened. In current practice, either rolls or gag presses are used to straighten structural shapes. 

Fitting:
Before final assembly, the component parts of a member are fitted-up temporarily with rivets, bolts or small amount of welds. The fitting-up operation includes attachment of previously omitted splice plates and other fittings and the correction of minor defects found by the inspector.

Fastening like riveting welding:
The strength of the entire structure depends upon the proper use of fastening methods. There are three methods of fastening namely bolting, riveting and welding. A few decades back, it was a common practice to assemble components in the workshop using bolts or rivets. Nowadays welding is the most common method of shop fabrication of steel structures. In addition to being simple to fabricate, welded connection considerably reduce the size of the joint and the additional fixtures and plates


Finishing:
Structural members whose ends must transmit loads by bearing against one another are usually finished to a smooth even surface. Finishing is performed by sawing, milling or other suitable means. Several types of sawing machines are available, which produce very satisfactory finished cuts.

Surface treatment:
Structural steel work is protected against corrosion by applying metal or paint coating in the shop or at site.