INSERTS

While there are many types of threaded inserts serving different purposes, they can be easily summarized as inserts with threads designed to accept a bolt or fastener. They provide advantages by their ability to hold fast in materials of different types and thicknesses.

Various Installation Processes

As mentioned, there are many different installation methods when it comes to threaded inserts. The methods are designed for automation and economy. Let’s discuss the different installation types in more detail.

• Molded-in Installation (Thermosets and Thermoplastic Application)

This method ensures the very best pull-out and torque performance. The process involves machine-directed insertions into the mold. Resin is then added to completely encase the insert, which creates a super strong bond. This approach requires close tolerances between the pins and inserts and achieves a more complicated core with closer tolerances. The process for molded-in installation will often take more time than heat- staking and ultrasonic methods.

• Pressed-in (Thermosets) cold pressed-in installation is the easiest and least costly plastic insertion method, requiring only a basic press for proper execution. Put simply, inserts are pressed into the thermoset plastic mold. This installation process does not result in the same overall strength as other methods due to a weaker bond, but is ideal when cost savings are the priority. Pressed-in inserts remain a highly economical alternative because they are easy to install and typically do not require special auxiliary equipment.
  
  
• Self-tapping  The self-tapping inserts are installed into preformed holes. The insert has external threads which when installed like a screw cut their own threads into the material they are being inserted into. They are generally installed in metals, but can also work in wood and plastics.
  
  
• Thermal  methods of installing threaded inserts include heat-staking and ultrasonic. Thermoplastics can be melted and recast continually and become like liquid when melted and solidify when cooled. The heat-Staking approach is for Thermoplastic use only, and offers high performance along with lower overall costs. This process involves the insert being heated with a thermal press until the insert melts a small part of the hole’s edge while being pushed into the thermoplastic assembly. Melted resin then seeps and fills the knurl pattern to form a firm bond once hardened. This is the most typical thermoplastic insertion process because it is less costly and is amenable to automation processes, allowing multiple insertions at a time. Ultrasonics are also deployed to melt the periphery of the hole. While heat-staking uses heat to melt the hole edge, the ultrasonic method uses a vibration frequency to achieve melting. Unlike heat-staking which is easily controlled, ultrasonic insertion has greater control requirements, as the application of the vibrations needs to be very precise to avoid material damage. The ultrasonic process is less easily automated and is less frequently utilized.
  
  
• Threaded Hole  The threaded hole inserts offer great cost and time savings compared to other methods. The threaded insert is installed into a pre-threaded hole which requires specialized tools for tapping.
  
  

Threaded inserts come in a variety of materials and sizes for installation into plastics, wood, and metal. This variety in configurations make them an ideal and long lasting choice for your application.

Get an Overview of the Project

Before choosing materials or getting into the finer details of installation, it is important to have an overall understanding of the project or component being designed. If you know the purpose and function of your project, the next steps will come a lot easier.

Consider Materials

Depending on the application, the type of material matters a great deal. Two insertion processes— ultrasonic and heat-staking— involve melting previously molded plastic and work with thermoplastics. For thermosets, the options are molding in the insert, or cold pressing the insert in later, where the elasticity of the resin material becomes crucial. The most common material for the threaded inserts is brass, but with ever-increasing sustainability requirements, lead-free alternatives such as stainless steel or aluminum are growing in popularity. Stainless steel offers better strength and corrosion resistance, and aluminum inserts are about 70% lighter than brass.

Think About Application Methods

The installation and application of the threaded insert will be crucial to determining the right insert for the job. With threaded inserts being used in industries such as automotive, industrial, aerospace, and defense, there are a vast number of applications. When making the final decision on inserts it is best to factor in the installation method, the material best suited to your application, and the automation of the installation process.

Knurling

Knurling is a metalworking process where a pattern is cut or rolled onto the outside of a workpiece. For threaded inserts, the knurling pattern directly impacts the strength requirements when it comes to resistance to pulling out or twisting out.

As previously mentioned, the knurling pattern plays a direct role in the strength of the application. Let’s review the different types of knurling patterns below:

• Straight knurls are parallel to the length of the insert. This pattern can be used for all methods of installation but is most often used with ultrasonic, thermal, or press-in installation methods. It is very similar to a diagonal knurl but will not turn slightly during installation like the diagonal due to the straight knurl pattern. It will provide added holding strength for torque and pull-out loads.
  
  
• Diagonal/Helical Knurls can be used with all methods of installation but is more commonly used with ultrasonic, thermal, or press-in installation methods. It will provide added strength for torque and pull-out loads.
  
  
• Non-Knurled are used most often for mold-in applications where no rotational torque resistance is needed. An undercut will be added to provide resistance to pull-out loads. No knurling is applied to the outside of the part.
  
  
• Diamond Knurl pattern is primarily used & recommended for mold-in installation methods. It will provide added holding strength for torque and pull-out loads.
  
  

Assess Strength Requirements

Another important question to ask yourself is the strength requirements of the application. The two factors for strength requirements in an insert are resistance to pull out of the part and resistance to the insert twisting out when the mating fastener is torqued. The length of the insert has a direct impact on its strength. The longer the insert, the greater strength it has. Diameter also impacts the torque capacity of the insert. The greater the diameter of the insert, the more torque capacity.

Buying Threaded Inserts

With industry leading brands available and updated daily, HTF is your go to for Acme Industrial, SI Inserts, and Stanley Engineering Heli-Coil Inserts. Our experts are on hand to help you identify the right insert for your application.

HTF has the most extensive catalog of threaded inserts and they are delivered to you quickly with the best customer service. That’s why the top manufacturers in the industry partner with us. HTF is here to serve—reach out today.