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Heat staking is a process that reshapes thermoplastic features to form secure mechanical connections with other components. It offers a clean, durable assembly solution when you need to join plastic and metal parts without visible fasteners. It is used across various industries from automotive to medical devices.
How The Heat Staking Process Works
Heat staking, also called thermoplastic staking or thermal staking, is a joining method that uses heat and pressure to join two or more parts where at least one part is made of plastic. The process involves heating, softening, forming, and cooling the plastic feature to achieve the desired joint.
To start the heat staking process, controlled heat is applied to features of a thermoplastic part, such as studs or bosses. This local heating is achieved using a heated tool, heated air, impulse power, or infrared radiation. Tools are often made with brass or aluminum with a PTFE coating to prevent sticking.
As the specific heat-targeted area of the stake (or boss) gets hot, it softens, which allows it to be formed and shaped using applied pressure to create a joint with the mating component. Under light, controlled pressure, the plastic flows and forms a head, which can take various shapes such as dome, flush, hollow, or flared depending on the tooling design.
After the joint is formed, the area is cooled, which causes the plastic to solidify. Cooling under pressure prevents shrinkage or cracks. This creates a secure, permanent mechanical lock with the other component(s).
Heat staking is commonly used to join parts directly, but can also be used in other applications, such as installing threaded inserts.
The Benefits of Heat Staking in Product Development
Heat staking offers several benefits that make it a popular joining method, including:
- Creating strong, repeatable joints
- Joining plastic to metal or PCBs
- Reducing or eliminating consumable costs
- Reliability for assemblies requiring a tight fit
- Creating durable bonds without the need for fasteners or adhesives
In addition, this method doesn’t cause vibration damage to sensitive components, no particulates are generated during the joining process, it’s compatible with coated applications, and is effective for staking in difficult-to-access or restricted areas.
Limitations and Trade-Offs of Heat Staking
There are some downsides to heat staking that should be considered before selecting this method to join your components, including:
- It is slower than other joining methods, such as ultrasonic welding, because of the time needed for the heating/cooling phases.
- The method only works with thermoplastics that can be softened and reshaped with heat.
- Stake heads remain visible unless hidden by design.
- The result is almost always irreversible. Once staked, the joint is difficult to disassemble without damaging the parts. Hollow stake heads, however, do allow a method of disassembly and subsequent reassembly with self-tapping screws.
It’s important to note that heat staking works best with low-melting-point thermoplastics, such as polycarbonate, ABS, or polypropylene. High-melt thermoplastics and/or brittle materials might require adjustments to the process. Also, keep in mind that this method is heat-sensitive, so precise heat control is necessary to avoid issues like warping or weak stakes. Optimal staking temperature depends on the type of plastic and should typically be 60–80% of the material’s melt temperature.
Try our Materials.AI tool for help selecting the right plastic materials for heat staking.
Design Guidelines for Heat Staking
The design guidelines for heat staking are different for every joint type. Table 1 summarizes the design guidelines based on the different types of joints, while Table 2 lists the general design rules that are the same for all joint types.
Table 1. Heat Staking Design Guidelines by Joint Type
| Joint Type | Typical Post Height* | Typical Post Diameter | Geometry & Shape | Notes |
| Dome / Rounded | 1.5–2.0 × post diameter | ≥ 2 mm (common minimum) | Rounded tip forming a smooth head | Provides smooth, low-stress head formation; reduces risk of cracking; ideal for visible surfaces |
| Flat / Cylindrical | 1.5–2.0 × post diameter | 2–3 mm+ depending on load | Flat tip forming a broad head | Produces strong joints with wide load distribution; consistent head formation; easy to produce in high volume |
| Rosette / Flared | 1.5–2.0 × post diameter | Larger base recommended | Petal-like slots or flared geometry | Increases retention and pull-out resistance; prevents rotation; suitable for high mechanical loads or vibration-prone parts |
| Dimpled / Concave | 1.5–2.0 × post diameter* | Similar to a dome | Concave or dimpled top | Controls flash and overflow; improves cosmetic appearance; useful for thin components or precise alignment |
| Hollow / Tubular | ≥ 2 × wall thickness height* | Outer diameter per post design (usually 2–3 mm or proportional to joint strength needs); inner diameter sized for required wall thickness | Cylindrical post with hollow center | Reduces material usage; allows large head formation without excessive melting; supports reassembly with self-tapping screws |
| Knurled / Ribbed | 1.5–2.0 × post diameter | Nominal post diameter + 5–10% for rib depth | Vertical ribs or knurling on the post | Enhances torque and pull-out resistance; tolerates minor misalignment; suited for high-volume production |
| Shouldered Boss | Height per above + shoulder | Boss base ≥ 2 × post OD | Post on the widened boss | Shoulder spreads load; improves joint strength; supports dissimilar material joining; reduces stress on surrounding plastic |
| Multi-Stake Array | Standard post geometry | Multiple smaller posts | Several posts in parallel | Distributes mechanical load across large components; prevents warping or distortion during staking |
| Tapered / Conical | 1.5–2.0 × post diameter | Slight tapered post | Conical geometry for flow control | Promotes self-centering; improves head formation; reduces flash; ensures alignment and repeatability |
| Flush / Recessed | 1.5–2.0 × post diameter | ≥ 2 mm (common minimum) | Stake head formed level with the part surface | Offers clean, flush appearance with no protrusion; excellent for cosmetic assemblies or sealed housings; may require precise temperature control to prevent sink marks |
| * When calculating the post height, always include the thickness of the captured material. For example, a post designed to be 2x as long as its own diameter must still extend through the material to be joined. The total height should therefore equal the post design height plus the thickness of the component being captured. | ||||
Table 2. General Design Rules Across All Types
| Design Rule | Recommended Dimension | Notes |
| Boss Diameter* | 2–3 × stake post diameter | Ensures sufficient plastic volume to form a secure head; reduces risk of cracking or deformation |
| Boss Height | 1.5–2.0 × post diameter | Provides adequate material for forming the stake head; too short can weaken the joint, too tall may cause flash |
| Draft Angle | 0.5–1° per side | Facilitates mold release while maintaining staking geometry; helps maintain boss shape and surface finish |
| Wall Thickness | ≥ 0.6 × boss OD | Prevents sink marks and deformation; ensures structural stability during and after staking |
| Edge Distance | ≥ 2 × post diameter from other bosses/edges | Avoids cracking or heat distortion; ensures adjacent posts or features do not interfere |
| Hole Clearance | +0.05–0.15 mm larger than post | Provides easy insertion and proper alignment; ensures consistent heat transfer and staking quality |
| Tolerance | ±0.05 mm post diameter | Critical for uniform heating and consistent joint strength; reduces variation in head formation across multiple parts |
| * Note: In heat staking design, a post is the molded thermoplastic feature that is heated and formed to create the mechanical lock, while a boss refers to the larger molded base or support structure around that post. The boss provides reinforcement and helps distribute stress during staking. Think of the boss as the supporting feature and the post as the feature being staked. | ||
Heat Staking Applications
Heat staking is utilized in a number of industries, especially those that often require a simple, clean solution where strong and precise bonds are essential. Below are a few examples:
- Consumer Electronics: Housings, enclosures, circuit boards, buttons
- Automotive Industry: Control units, driver assistance sensors, dashboards, locking systems, interior trim, front and rear lights, engine compartments, media guides, batteries, and electric motors
- Medical Industry: Disposable instruments, medical devices, assemblies, casings
- Aerospace Industry: Interior cabin components, wiring harnesses
- Military Applications: Ruggedized electronic equipment, defense system components
Heat Staking for Threaded Inserts
While heat staking is commonly used to directly join plastic and metal components, it is also a reliable method for installing threaded inserts into thermoplastic parts. In this application, a heated tool or ultrasonic horn is used to soften the plastic around a pre-molded hole. The threaded insert—typically made of brass or stainless steel—is then pressed into the softened material. As the plastic cools, it re-solidifies around the insert’s knurled or grooved surface, forming a strong mechanical bond that provides durable, reusable threads.
Heat-staked inserts are ideal for high-torque or load-bearing joints, allowing repeated assembly and disassembly without damaging the plastic. They are widely used in automotive housings, consumer electronics, and medical device enclosures, where precision and strength are critical. Proper design of boss geometry and control of heat and pressure are essential to ensure consistent insert alignment and retention.
Alternatives to heat staking threaded inserts include ultrasonic staking, insert molding, or a press-fit (although the latter is less recommended due to lower pull-out strength and dimensional sensitivity).
Heat Staking vs. Other Joining Methods
Heat staking is not the only method that can be used to join plastics effectively. There are some other options available, each with its own advantages, disadvantages, and ideal use cases.
Ultrasonic Welding
This method uses high-frequency vibrations to fuse plastics. It’s fast, produces clean joints, and is ideal for high-volume production. The downside is that it only works with certain plastics, and the vibrations can damage fragile components. Although slower in some scenarios, heat staking avoids this risk and can also join plastics to metal inserts or PCBs.
Adhesive Bonding
Adhesives are useful when parts can’t handle heat or when different materials that cannot be welded or heat-staked need to be joined. They can create smooth, hidden joints, but their longer curing time slows production, and factors like humidity and temperature could impact the adhesive’s bond strength. Heat staking doesn’t have these issues, but it is limited to thermoplastics.
Mechanical Fastening (Screws & Rivets)
Fasteners are a good option when you want parts that can be taken apart. They’re simple and widely available, but they increase cost, add weight, and require extra design space. They can also loosen over time.
Hybrid Approaches
Sometimes one joining method isn’t enough. Hybrid approaches combine techniques, such as using heat staking for alignment and adhesives for sealing. This can improve strength, durability, or appearance. The trade-off is added complexity and cost compared to heat staking alone.
The table below compares the pros and cons of different plastic joining methods.
Table 3. Comparison Table of Plastic Joining Methods
| Method | Pros | Cons |
| Heat Staking | Plastic-to-metal joining, strong, permanent joints | Slower cycle time, visible heads, limited to thermoplastics |
| Ultrasonic Welding | Very fast cycle times, clean finish | Limited plastic options and not compatible with plastic-to-metal joining, risk of damaging delicate parts |
| Screws & Rivets | Reversible, widely available | Adds cost, increases part count, risk of loosening |
| Adhesives | Smooth, hidden joints that can join heat-sensitive or mixed materials | Long cure times, chemical compatibility issues |
| Hybrid Approaches | Combines the strengths of staking + adhesive or fastener | More complex, higher cost |
Designing for Reliable Heat-Staked Joints
There are many factors that need to be considered in heat-staked joints if you want them to stand the test of time. These include post shape and boss size, wall thickness, and joint shape, as well as the controlled heat and pressure required to form the joint. That’s why it is important to get expert advice to validate your heat-staked joint designs to ensure they will be fully functional and durable.
Need to validate plastic assembly designs? Fictiv provides injection molding, CNC machining, and DFM feedback to help engineers optimize heat staking and other joining methods.
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