Clinch fastening

By far the most common fastening method adopted by steel framing fabricators is the self drilling screw, but there are alternatives and most of these have performance characteristics that have found favor in certain circumstances.  In Australia  for instance, welding has been very common in the past and although the strength of connection is possibly superior to all other methods, the toxic fumes given off during the welding process complicates the fabrication, making it uneconomic in most applications. 

Other fastening methods used are; 

Clinching has one characteristic however, that sets it apart from all the others; and that is, it does not involve the introduction of a consumable in the fastening process. 

In recent years, clinch fastening has been identified as a viable alternative for the fabrication of both residential and commercial steel framed construction.  This technology is commonly found in the automotive and appliance industries where fastening of similar light gauge steel is used. 
 

Self Drilling Screws:

Advantages: 

The development of the self drilling self tapping screw has played a significant role in the development of steel framing, for until these screws were developed, the cost of labor made the fabrication of cold rolled steel framing cost prohibitive for most applications.  The principle advantage of screw fixing is the relatively low cost of equipment. 

Disadvantages:

The major disadvantage is the continuous cost of consumables; i.e. screws and labor due to the effort required in the placement of the screw. 

Interestingly, in virtually all cases where screw fixing systems are being demonstrated at trade shows and the like the sales personnel employ upper body strength to force the screw vertically downwards.  This situation very seldom occurs  in the production environment however and even given a situation where the placement of the screw is in this optimum orientation, the continued effort will ultimately reduce operator efficiency over the work period. 
 

Clinching:

In 1982 the BTM Corporation produced a tool for EasySteel Homes Australia, specifically for the fabrication of Steel framing for residential construction.  EasySteel Homes in turn developed manufacturing and assembly techniques in order to optimize this fastening technology. 

In appropriate systems design the connection strength will be closely matched with the structural capacity of the members being joined.  In the case of residential steel framed construction for example; the capacity of the stud in the wall frame configuration can be matched with four (0,18in") clinch joints. 

 Advantages:

In addition to the substantial cost advantage,  the hand gun developed has several practical advantages over the other fastening systems, including the following;

1. The clinching process draws the metals together prior to fastening, thus guaranteeing a neat and close fit.
2. The formation of button is produced in the inside of the connection leaving a flush surface.
3. The joint is produced mechanically, thus requiring little effort from the operator.
4. The joint is produced without noise, fumes, metal swath or debris of any kind. 
    

Disadvantages:

Clinching has some practical restraints that should be addressed in the formulation of a manufacturing scenario and the initial cost of equipment may preclude its adoption in limited production applications. The current tool design is also not generally compatible with traditional on-site building techniques.  The tool must be placed in a position where both sides of the joint can be accessed. 

Steel Frames and Trusses:

The following cost analysis is based on the manufacture of steel wall frames and trusses in a factory, where  effective labor supervision, materials supply and a regulated environment can be controlled.  Extrapolation or interpolation to a situation where this cannot be achieved should be avoided 

Clinch Fastening verses Self Drilling Screw

In the 5 year projected life span of the clinching equipment; the cost savings using the BTM Tog-L-Loc^® exceed $2.8 million.  The figures in the following table reflect the cost of the fastening operation in a medium sized facility.  

Notes: 
(1) Production rate 70,000 square feet of dwellings per month. 
(2) Average number of wall panels per month = 2600. 
(3) Average number of  trusses per month = 2200. 
(4) Average number of connections per 12' wall panel = 144. 
(5) Average number of connections per 28' truss = 100. 
(6) Cycle time assumes 100% effectiveness, i.e.; no screw wastage. 

Summary:

The automotive and appliance industries have developed and implemented fastener technology that reduces costs and simplifies fabrication.  It can be shown that the application of this technology in the steel framed construction industry  using very similar cold rolled and precoated steel will generate remarkable costs savings.