This guide explores the fundamentals of plastic parts riveting connection, including the types of riveting, materials used, and key considerations during design and implementation.
What is Riveting in Plastic Parts?
Plastic parts riveting is a method used to connect plastic components with various materials, such as metals, electrical parts, or fabrics, by forming a mechanical bond. The rivet creates a permanent, non-reversible connection that resists axial and shear forces. Riveting is especially advantageous when dealing with materials that cannot be welded or glued effectively, or when a high-strength, durable connection is needed.
Types of Riveting Connections for Plastic Parts
Plastic parts can be joined using various riveting techniques, each with its own set of advantages and considerations. The most common methods include:
Hot Melt Riveting
Hot Melt Riveting is a contact-type riveting method that uses a heated riveting head to soften the protruding part of the rivet column, which is inserted through the reserved hole in the plastic part. The heated riveting head transfers its heat to the rivet, causing it to soften and become malleable. Once the rivet column is softened, pressure is applied to shape it, forming a permanent rivet head. After cooling, the connection is complete.
Advantages:
- High heating efficiency due to direct heating of the rivet.
- Suitable for applications where a smaller, compact rivet head is required.
- Faster than some traditional methods as it reduces the need for external heating elements (like heating blocks or tubes).
Disadvantages:
- May require specialized equipment for precise heat control.
- The process needs careful control of temperature to prevent overheating or incomplete forming.
Applications: Automotive, electronics, and consumer goods where a secure, compact rivet connection is needed.
Hot Air Riveting
Hot Air Riveting uses a non-contact heating method where hot air is used to heat the rivet column until it becomes soft and malleable. The heating process is divided into two stages:
- Stage 1: The hot air evenly heats the rivet column to a malleable state, ensuring uniform temperature and airflow.
- Stage 2: The cold riveting head then presses down on the softened rivet column to form a permanent rivet head that holds the parts together.
This method relies on the precise application of hot air to heat the rivet column, and the correct fit between the rivet and the holes in the plastic parts is crucial. If the fit is too loose, the softened plastic may not form a secure rivet head.
Advantages:
- Clean, non-contact heating process that avoids pollution, vibrations, and displacement.
- Ideal for precise applications where cleanliness and efficiency are essential.
- No additional heating elements (like tubes) are needed, which can simplify the process.
Disadvantages:
- Temperature control is critical for uniform heating.
- Can be less efficient for large-scale production compared to methods that apply heat directly to the rivet.
Applications: Suitable for precision applications in industries like electronics, medical devices, and thin plastic components where cleanliness and accuracy are crucial.
Ultrasonic Riveting
Ultrasonic Riveting is a contact-type method that uses high-frequency ultrasonic vibrations to generate frictional heat at the contact surface between the rivet post and the welding head. The process occurs in the following steps:
The ultrasonic welding head moves down toward the rivet post that passes through the reserved hole in the plastic part.
The welding head vibrates at ultrasonic frequencies, which generates heat due to friction at the contact points. This heat softens the protruding part of the rivet column.
Once softened, pressure is applied by the welding head to compress and form the rivet, creating a secure connection between the parts.
Advantages:
- Very fast and efficient, especially for small plastic parts.
- Clean, vibration-free process with minimal heat spread, reducing the risk of damage to nearby components.
- Excellent for precision bonding where high accuracy is required.
Disadvantages:
- Requires specialized ultrasonic welding equipment.
- May not be suitable for larger or thicker plastic parts that require a more robust heating method.
Applications: Ideal for industries that require precise, clean, and fast assembly, such as medical device manufacturing, electronics, and high-tech industries.
When to Choose?
Each method has distinct advantages depending on the application, such as the size of the parts, heating requirements, and the desired speed of assembly.
| Method | Hot Melt Riveting | Hot Air Riveting | Ultrasonic Riveting |
|---|---|---|---|
| Strength | Moderate, sensitive to vibration. | High, resistant to vibrations. | Moderate, sensitive to vibration. |
| Speed | 6-60 seconds | 6-10s heating, 2s cooling | Less than 5s |
| Appearance | Bright, easy to draw wires. | Matte surface, no wire drawing | Bright, clean surface |
| Cost | Low | Medium | High |
| Material Fit | Good for non-fibrous plastics. | Works well with most thermoplastics. | Challenging with glass fiber-filled plastics. |
- Hot Melt Riveting is best suited for compact, high-efficiency applications.
- Hot Air Riveting excels in applications requiring clean and uniform heating without contact.
- Ultrasonic Riveting is ideal for high-precision, fast, and clean applications where minimal heat spread is needed.
By understanding these methods and their specific benefits, manufacturers can choose the most appropriate riveting technique for their plastic part assembly needs, optimizing both performance and efficiency in the final product.
Choosing the Right Rivet for Plastic Parts
Riveting processes are most suitable for thermoplastic plastics, which can melt and flow under specific temperatures. These plastics are categorized into amorphous (non-crystalline) and semi-crystalline types, with each type affecting the riveting process differently.
- Amorphous Plastics: These materials have a disordered molecular structure and soften at a distinct glass transition temperature (Tg). They are suitable for all three riveting processes.
- Semi-Crystalline Plastics: These have an ordered molecular structure and a clear melting point (Tm). They are more challenging to rivet, especially with ultrasonic methods, due to their higher melting points and difficulty in absorbing ultrasonic energy.
Additionally, plastics with fillers (e.g., glass fibers) can be difficult to rivet. For hot melt riveting, temperature control is critical to prevent glass fibers from precipitating and causing rough surfaces. In ultrasonic riveting, higher vibration energy is needed to melt the plastic, and excessive filler content may result in weak riveting due to incomplete fusion.
The rivet must be chosen based on the specific plastic material, application requirements, and operating conditions. Commonly used rivet materials include:
- Steel: Offers high strength and durability, making it ideal for heavy-duty applications. However, it may cause stress cracking in brittle plastics.
- Aluminum: Lighter than steel, aluminum rivets are often used in automotive and lightweight applications. They also provide good corrosion resistance.
- Plastic Rivets: These are often used for joining softer or more flexible plastics. They provide a lightweight solution and reduce the risk of cracking.
Rivet design should also be considered, including the shape and length of the rivet, as well as its head type (e.g., flat, domed, countersunk). Proper rivet selection ensures optimal joining strength, while also minimizing the risk of damaging delicate plastic parts during installation.
Common Rivet Columns and Rivet Heads
| / | Rivet Head Type | Suitable for Rivet Column Diameter (D1) | Protruding Column Height (H1) | Rivet Head Diameter (D2) | Rivet Head Height (H2) | Applications |
|---|---|---|---|---|---|---|
 | Semi-Circular Rivet Head (Large Profile) | D1 < 3mm (preferably > 1mm) | 1.5–1.75 * D1 | ~ 2 * D1 | ~ 0.75 * D1 | Low-strength applications (e.g., PCB boards, decorative parts) |
 | Semi-Circular Rivet Head (Small Profile) | D1 < 3mm | ~ 1.0 * D1 | ~ 1.5 * D1 | ~ 0.5 * D1 | Low-strength, fast riveting (e.g., FPC ribbons, metal springs) |
 | Double Semi-Circular Rivet Head | D1 between 2-5mm | ~ 1.5 * D1 | ~ 2 * D1 | ~ 0.5 * D1 | Higher strength fixation needs |
 | Annular Rivet Head | D1 > 5mm | 0.5-1.5 * D1 | ~ 1.5 * D1 | ~ 0.5 * D1 | High-strength applications with large diameters |
 | Flat Rivet Head | D1 < 3mm | ~ 0.5 * D1 | Based on column volume conversion | Based on column volume conversion | Flush rivet head required (e.g., thin plastic parts) |
 | Ribbed Rivet Head | D1 < 3mm | 1.5–2 * D1 | ~ 2 * D1 | ~ 1.0 * D1 | Larger contact area needed with limited space |
Design Considerations for Riveting Plastic Parts
The design of plastic parts intended for riveting connections must account for several factors to ensure successful joining. Key design considerations include:
Hole Design
The hole into which the rivet is inserted must be precisely sized and shaped to allow for proper rivet deformation. The diameter of the hole is generally slightly larger than the rivet shaft, allowing for the rivet to expand or flare when pressure is applied. If the hole is too large, the rivet connection may be weak; if too small, the rivet may not deform properly.
Wall Thickness
The wall thickness of the plastic parts should be appropriate for the rivet being used. Too thin, and the material may crack or deform under pressure; too thick, and the rivet may not have enough surface area for a strong connection.
Material Compatibility
Different plastic materials have varying characteristics in terms of rigidity, flexibility, and heat tolerance. It is important to choose a rivet and joining technique compatible with the specific plastic being used. For example, rigid plastics may require stronger rivets or heat-forming techniques, while flexible plastics may benefit from cold-forming techniques.
Load Considerations
The anticipated load on the riveted connection should be considered. Riveting is typically used in applications that experience shear forces or vibration, so the design must ensure that the rivet can withstand these stresses. Rivet strength can be enhanced by using larger or multiple rivets for added stability.
Stress Distribution
Proper rivet placement can help distribute stresses evenly across the joint and prevent cracking or material failure. Rivets should be positioned at strategic points to reduce stress concentration, ensuring longevity and durability of the connection.
Conclusion
Riveting is a proven, efficient method for joining plastic parts in a wide range of industries. By carefully considering the type of rivet, plastic material, hole design, and stress factors, manufacturers can create secure, long-lasting connections. Whether for lightweight consumer goods or demanding industrial applications, the versatility of riveting continues to make it a valuable solution for plastic assembly.
This article was written by engineers from the BOYI team. Fuquan Chen is a professional engineer and technical expert with 20 years of experience in rapid prototyping, mold manufacturing, and plastic injection molding.
