What Role Does the Mandrel Play?
Key Points
- The mandrel is the actual working element in the riveting process
- It forms the closing head and thereby determines the quality of the joint
- Without the correct mandrel, defective, unstable, or visually flawed riveted joints result
- The choice of material, shape, and handling of the mandrel must be tailored to the specific application
What Is a Mandrel?
If you want to permanently join metal, plastic, or other materials, blind rivets come into play. But what many people overlook is that the rivet alone does not determine the result. The rivet mandrel is the true heart of the process.
The rivet mandrel is a sturdy metal pin. It sits inside the blind rivet and ensures that the rivet deforms during setting, creating a secure joint. Without it, the rivet remains a hollow tube with no function.
This knowledge is not only relevant for industrial companies. You’ll also encounter the mandrel regularly in automotive bodywork, electrical engineering, and DIY projects.
What is the function of the mandrel?
A mandrel consists of three main parts. The rivet nut body is the long, slender section. It runs through the blind rivet body and protrudes from the tool side. The head is located at the front end and has a larger diameter. It is responsible for causing the rivet to expand when pulled. The predetermined breaking point is located at the rear of the mandrel. At this predefined point, the mandrel breaks off as soon as the required tensile strength is reached.
The process for applying blind rivets consists of three steps.
Insertion: You insert the rivet into the pre-drilled hole. The mandrel protrudes from the hand rivet tool on your side.
Pulling: The hand rivet tool grips the mandrel with its jaws and pulls it back with force. As this happens, the head of the mandrel presses against the rivet. The rivet expands on the back side and clamps the materials tightly together.
Shearing: As soon as the joint is secure, the mandrel shears off at the predetermined breaking point. The remaining mandrel stays inside the blind rivet body and seals it.
This mechanism makes blind rivets particularly practical. You only need access to the workpiece from one side.
How does the mandrel affect the quality of the joint?
The joint quality depends directly on the mandrel. It determines how much force is transferred to the rivet and how uniformly it deforms.
The tensile strength describes how strong the joint is against forces in the longitudinal direction. The shear strength indicates how well it withstands lateral loads. A precisely manufactured mandrel with a cleanly set predetermined breaking point ensures that both values are reliably achieved.
Defects often result from using the wrong mandrel. If it is too soft, it bends instead of forming the rivet. If it is too brittle, it breaks prematurely. If the predetermined breaking point is too deep or not pronounced enough, the mandrel either breaks too early or slips through. In all cases, the joint suffers.
When purchasing, you should look for the following quality characteristics:
- Tolerances: A good mandrel fits exactly into the rivet without wobbling.
- Surface quality: Cracks or irregularities on the rivet nut body lead to uncontrolled breakage.
- Compliance with standards: Look for rivets and mandrels that are tested according to DIN ISO.
- Manufacturer specifications: Combination and size specifications should always be coordinated.
Which mandrel should you buy for which application?
Although the mandrel is an integral part of a blind rivet, it is by no means a minor component. It is the element that determines whether a riveted joint will be reliable or fail. Anyone who skimps on blind rivets and opts for cheap products risks unstable joints and extra work.
For DIYers and occasional projects, sets from the retailer area containing aluminum rivets and matching mandrels are perfectly sufficient. A medium-sized hand rivet tool and an assortment box with the standard sizes (3.2 mm, 4.0 mm, 4.8 mm) cover most tasks.
Rivet Assortments
For professional users and industrial applications, it’s worth investing in high-quality materials made of stainless steel or coated steel. Here, precision directly translates to durability and workplace safety. Choose manufacturers that provide technical data sheets with tensile and shear strength values
Further Information
Conclusion
The mandrel leads an underappreciated existence. Once the job is done, it disappears into the spent mandrel container and remains invisible to the naked eye. Yet it is precisely this component that determines whether a riveted joint holds or fails.
Anyone who focuses only on the rivet and takes the mandrel for granted runs the risk of cutting corners in the wrong place. Inferior material, incorrect dimensions, or an imprecise predetermined breaking point can render even high-quality rivets ineffective.
The good news: With the right knowledge, selecting the right rivet isn’t complicated. Match the material, size, and manufacturer. Purchase rivets that comply with standards. And store your consumables carefully.
