Valley Fastener has an engineering and design team specializing in rivets, cold headed fasteners, tooling, equipment and fastening solutions. We’re dedicated to providing excellence in engineering & design services and committed to providing the highest level of technical expertise for your project. Advanced CAD systems help our engineers optimize the part design, product performance and shorten the product development cycle. VFG offers unmatched custom rivet design and engineering for all applications.
Cold heading or cold forming is the process of manufacturing parts at high speeds by changing the shape of a length of an unheated coiled wire that has been inserted into a die. The wire is fed automatically into a cold heading machine and a predetermined blank of material is cut-off and automatically placed in line with a cavity, called a die. The blank is then subjected to an impact force that is delivered by a punch through one or more forming “blows”. The force and counter force of the blow(s) cause the wire blank material to flow into the die cavity forming the shape of the finished part.
For simple part configurations or when the head diameter or volume of material to be formed is small and the material lends itself easily to “upsetting” (as in most common screws and rivets), one die station and two forming blows are required. For more complex part configurations or parts made from difficult to form material, two or more die stations and multiple forming blows may be required.
The Benefits of Cold Heading/Forming
- Savings in Material: Cold heading scrap loss is as low as 1% compared to turning, shaving or forging where up to 75% (or more) scrap loss is common
- Higher Strength: Cold heading creates continuous, unbroken material grain flow instead of cutting the grains of the fastener
- Longer Life Part: Properly designed cold headed parts are resistant to impact, fatigue and shear failure
- Eliminate Costly Secondary Operations: Often a part can be formed complete in the header, eliminating the need for expensive secondary forming and handling
- Production Rates: Cold heading can produce rate up to 450-500 pieces per minute!
Common Industry Guidelines for Semi-Tubular Rivets
Clinch Allowances for semi-tubular rivets, up to one half-inch diameter are 50% to 70 % of the shank diameter of the rivet, dependent on application. (.50/.70 x shank body diameter of the rivet = clinch allowance)
Shank Length of the Rivet = combined work-piece thickness added to the clinch allowance of the rivet.
Work-Piece Hole Diameter = about 107% of the shank diameter of the rivet. If multiple work-piece holes are used, larger hole(s) to accommodate stack up tolerances are suggested.
Clinch Allowances and Work Piece Holes for Small (non-hardened) Solid Rivets up to 7/16” Diameter
The Reference Clinch Allowance suggested is 100 to 110% of the body diameter.
You add the clinch allowance to the combined work piece material thickness to give you your under head rivet length for most applications.
(1.0/1.10 x rivet shank diameter = clinch allowance)
When a certain length is surpassed in small diameter solid rivets, it is usually unsatisfactory to rivet by press or impact clinching. This is the point where spin or orbital forming of the rivet becomes necessary. As a guide, this point is near where the work piece thickness is greater than five or six times the rivet diameter.
Where spin riveting is necessary, you would add to the work piece thickness an additional reference clinch allowance of 50% to 60% of the diameter of the rivet. The size of the desired spun head and the type of clinch equipment and tooling selected will ultimately determine the clinch allowance. The amount of metal that can be handled in spinning tools is limited and since there is little metal lost in buckle or swelling of the shank, any excess amount of material left for spinning will result in greater tool wear or the potential for application concerns.
There are many variables to consider when designing work piece holes for solid rivets. This is an important consideration to prevent loose joints or rivets that can be damaged due to clinching with excessive force. When a rivet is impact clinched, the shank of the solid rivet is typically designed to swell to completely fill the work piece hole just prior to the complete upset of the formed clinch head. Generally speaking, we suggest adding 3 to 5% to the shank diameter of the rivet for work piece holes (1.03/1.05 x shank body diameter of rivet = work hole diameter).
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