Solid, semi-tubular and tubular rivets are widely used mechanical fasteners. These specific types of rivets are employed in a wide variety of products which may require flexible joints or tightly joined mating components.  Typical solid rivets include flat head, pan head, round head and shoulder type rivets. The head may be of various shapes and the shank must be of sufficient length to accommodate the thickness of the parts to be joined and to allow for the formation of the clinch head. Solid rivets are available in many metals and alloys to meet today's requirements of tensile and shear strength, electrical conductivity, corrosion resistance, appearance and cost. Flat head, pan head and button head rivets are more commonly used for tightly joining mating components. Shoulder-type rivets are normally used for pivoting or hinging joints. A basic requirement of the rivet is that the material must be able to withstand rigorous cold-working without deterioration and provide the desired standards of finish and appearance. Two of the most common types of steels used in rivet manufacturing are SAE 1010 from which cold-headed rivets are made and B1113, or screw machine steel. Brass, nickel-silver, bronze, copper, stainless steel and aluminum alloys are also widely used. In the case of rivets made from SAE 1010, the clinch head can be easily formed and will provide excellent appearance. Rivets of B1113 steel do not lend themselves nearly as well to the riveting process and on this type of rivet the formed closure is usually ragged around the edge and has a poor appearance.  There are four principal ways to clinch solid, semi-tubular rivets or studs-staking, spin roller forming, orbital forming, and radial forming. Each of these have variations in tooling and technique. Each has advantages and disadvantages. 

Staking operations cover a wide range of techniques and applications. Staking in general is a fast low-cost method of heading solid, semi-tubular rivets or studs where a head with a smooth finish is not required. The operation is most likely performed in a press or a rivet setting machine, and clinch formed with a tool having a shaped face. The tool does not revolve. Tool pressure alone reshaped or cuts back the rivet shank, rather than flowing the metal. Speed and low costs are the principal advantages of staking. The performance cycle is rapid, and tools and equipment are of the simplest kinds.   A disadvantage is the lack of holding strength in the staked end. Hence, the method is not recommended for parts which must resist pulling apart in the direction of the rivet and resist high torque on the head. The appearance of a staked rivet is not compatible with high quality work.   

Twin Spin Roller Forming of clinch head: -achieved with Twin-Spin tooling is designed to utilize the combined forces of motion and pressure. The Twin-Spin tool consists of two matching, precision shaped, hardened and polished steel rollers. These are contained in a tool holder just slightly larger than the diameter of the work piece. The rollers distribute a combination of forces which flow the material to the desired shape and size. The material is flowed from the center outward, in a radial series of overlapping waves. Since the material is flowed continuously in these two directions, spin roller forming produces the highest quality grain structure, head integrity, and uniformity of head structure.  In a typical Twin-Spin application such as head-forming on rivets, pins, or staking posts, the tool is brought down on the area to be formed. The free-spinning rollers, driven by contact with the work piece, rotate counter to each other. The two rollers always work diametrically opposed, thus counter balancing each other and applying negligible torque or bending movement to the work piece. Tightness of the fastener - either loose to provide free movement of the assembled parts, or tight to prevent movement - is controlled by roller shape and the amount of pressure applied. Because of the high degree of control achievable with this method of forming, there is no deformation of the pin or the fastener shank. The tightness of the rivet in the joint can be controlled within close limits and with excellent repeatability.  Surface finish is polished in appearance, and head integrity is excellent. The maximum shank diameter of the work piece is limited only by the output of the power head. Depending on size or material, forming cycle time ranges between one quarter to one second.   Possible disadvantages of this method for certain classes of work may be the relatively large diameters of the roller tools, which prevent riveting in extremely close quarters, or the need to use a lubricant with some materials. Carbide tooling is supplied when lubricants can not be used. All Grant Riveter's automatically supply a very thin film of lubrication to the hidden side of the twin spin roll forming die's. Lubrication greatly increases life beyond belief. One set of rollers made from Grant's coated high grade tool steel or made from carbide have been tested in high-end production environments where the dies produced production for over a year. 

Orbital Forming is also commonly used in producing heads on rivets, pins, or posts. Orbital tools are composed of a rotating tool holder and a shaped tool insert. The axis of the tool insert has a definite angular relationship to the axis of the tool holder. The forming end of the insert is located at the intersection of these two axes. The insert does not rotate when in contact with the work piece, and as a result, describes a concentric, conical path…. very much like a top beginning to run out.   The rivet or pin being worked, is "set" by a combination of pressure, high speed spinning action of the holder, and conical rotary motion.   The operation is quiet and produces joints and heads of high quality, at high cycle speeds. Design of tools can be adapted to work in close quarter. Orbital tools can be adjusted to produce a tight or loose assembly, and lubricants may be required for a better finish. Orbital tooling is generally set up to produce extremely tight assemblies where no movement is acceptable.   The disadvantage of the orbital forming process is that the initial tool holder is relatively expensive. However, tool inserts - although more expensive than Twin-Spin rolls- have excellent life. The grain structure of orbital formed heads is not of the quality obtained with Twin-Spin rolls and radial forming. The rivet or pin being worked in an orbital form technique, can not be headed without deformation of the shank under the formed head. The cosmetic's are generally very good.   

Radial Forming is another popular process used in producing heads on rivets, pins or post. Different than the circular motion of the orbital tool, radial riveting passes the tool through a rosette forming pattern. Each rosette path or loop pass through the center, the longitudinal axis of the riveting tool always overlaps the center of the rivet. The material is spread radial from the center outward and looping inward rather than around the center. According to the practitioner the rivet material is spread in a radial manner or formed tangentially overlapping. The operation is quiet and produces joints and heads of high quality and slightly polished in appearance. The tools can be adapted to work in close quarter. Radial forming can be adjusted to produce a tight or loose fastener. The grain structure of a radial formed head is not as high in quality as spin roller formed heads. The control of a joint can be held within limits slightly better than orbital forming but falls short of Grant's Twin Spin roller forming process. The Grant process is much quicker with better results.   

Complexity of radial motion generation is considered by some as a process disadvantage. Other problems encountered are: poor power train wear factors under heavy forming condition; forming tools cost more to manufacture than orbital tool inserts; The rivet or pin being worked, can not be headed without some deformation to the fastener shank; cosmetic appearance is only fair to good; length of forming pass increases cycle time considerably.  

In conclusion, all four principal ways to clinch form solid, semi-tubular rivets or studs by staking, spin roller forming, orbital forming and /or radial forming, all have advantages and disadvantages. Each process has unique in its capabilities. There is no one best process that meets the needs of all heading operations. 

The "Grant" Solution provides the most cost effective way to form or fasten a rivet or component without hindering the performance or the integrity of the rivet or part being fastened. "Grant" employs several processes all adaptable within a single modular unit portable power head riveter. Any "Grant" power head can accept orbital, twin-spin roller forming, multi-spin roller forming, spin-press (burnishing), chamfering tools, drilling and even rolling or cutting threads.  Riveting has grown into an age of modularity and portable riveters. 

There are two basic power head designs that assure a future for riveting assembly. The first is a power head in which the pneumatically, hydraulically or servo-electric advanced piston encloses a precision spindle and bearing shaft assembly. This one design feature allows us to manufacture a durable head, simple to maintain, low in initial cost and economical in operation.   The second is a power head in which the pneumatically or hydraulically operated piston has a complex eccentric shaft arrangement built within the piston. This spindle assembly drives a gear arrangement, which controls the radial rosette forming pattern. The forming tool must complete 360 degrees around the rivet shank.  Because of its complexity maintenance of this type head, along with its high initial cost, remain operational concerns which must be over come. One of the units advantages is that due to minimal side loads it can be operated with simple low cost support fixtures.

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Last modified on Sunday April 20, 2008