Four Special Points to Consider
Posted on 03/27/2019 | by The Orbitform Blog Team
Impact Riveting uses impact force to permanently fasten components together. The quick process helps to minimize cycle time, increase throughput, and lower operating expenses. The most commonly used rivet for impact riveting is a mild steel semi-tubular rivet. The proper rivet geometry is crucial to meet the joint requirements.
Orbitform’s Lab Technicians have helped numerous customers assemble their parts in our Solution’s Lab and helped determine what fastener best fits their application. With over 30 years of experience, we have developed general guidelines to consider when choosing semi-tubular rivets.
There are three critical diameters to consider when choosing a semi-tubular rivet: head diameter, shank diameter, and end-hole diameter. The pull-out force required for the joint will determine the necessary head diameter. Soft materials will require larger diameter heads with greater surface areas to withstand pull-out forces.
The rivet shank diameter can be determined by comparing it to the thickness of the material stack up. Optimally, the ratio between the shank diameter and part thickness should between 1:1 and 1:3 for metal parts (closer to 1:1 for plastic parts).
Once the shank diameter has been determined, you can design the clearance hole to fit the rivet. This is important because too small of a hole can lead to rivet feeding issue or damage to the rivet or part. Generally, the clearance hole should be .010” to .015” larger than the shank diameter.
The rivet end-hole diameter should be about 70-80% of the shank diameter. Larger percentages mean the wall is thinner, which is easier to form and requires less force. However, this may also decrease the strength of the joint.
Another important consideration is the depth of the hole in the end of the rivet. The average depth is 100-125% of the end-hole diameter. Proper hole depth is necessary to prevent the rollset from hitting the body of the rivet and causing shank swell or rivet deformation.
Shank Length & Rivet Stick Out
The shank length is determined by the part stack up thickness and the required rivet stick-out. This stick-out is also known as clinch allowance and is generally between 50-55% of the shank diameter. If the rivet is too long, the parts may not be fastened together tightly. If the rivet is too short, there may not be enough material to clinch the parts together at all.
Mild steel rivets are the most common rivets used for impact riveting. However, different rivet materials may give very different results. For example, harder materials, such as stainless steel, require more force to form. This may increase the chances of shank swell and must be considered when determining shank length. It is vital to be aware of the hardness of rivets when designing parts and to determine the appropriate assembly equipment.
With over 30 years of manufacturing and assembly experience, our lab technicians and engineers have supported tens of thousands of assembly applications. Call us today for help determining the proper rivet size for your part and let us assemble samples in our Solution’s Lab to ensure your part meets your requirements.