Magnetic assemblies overview
The past few weeks have highlighted how the correct assembly technique is a vital aspect to ensure performance of any application. After a detailed look at the pros and cons of mechanical assembly, insert moulding, over moulding, gluing, ultrasonic welding and brazing. Heat staking is the final assembly technique up for discussion.
What Is heat staking?
Described as a pulsed heat process used to join two or more parts out of which at least one is made of plastic, heat staking involves deforming the plastic material using heat and force at a set process time. The bond is made by partly de-forming the plastic part to fix the other. The process makes it easy to bond metal to plastic, which is why it is commonly used in high volume/low cost applications like automotive, IT and consumer appliances.
The process of heat staking
Basically, the heat staking process can be broken down into four main steps:
- The thermode, with defined cavity, comes down on the stud;
- Force is then applied on the stud and once the required forces is achieved the heating process starts;
- The force together with the pre-set heat will soften the stud and mould it into the required shape and at the same time fix the second part;
- Cool down, still under forces to below glass transition temperature and finally lift the thermode.
Below is a visual representation of the four basic steps discussed above.
Applications using heat staking
With its ability to join plastic with metal, heat staking is used across many applications, to include:
- Attaching metal grilles and screens to plastic frames
- Automotive panel
- Automotive dash mat
- Mobile phone assembly machines
- Antennas in handheld devices
Benefits of heat staking
Heat staking proves beneficial depending upon the application, including:
- Heat staking enables similar and dissimilar materials to be joined.
- Local heating ensures that there is no damage to adjacent materials.
- There are many heat stake shapes available through custom designed tools.
- No mechanical vibration.
- Very simple design guidelines are required for success.
Disadvantages of heat staking
Like everything, heat staking has its drawbacks:
- If formers are too cold they will strain the stake causing stress, which may impact breakages leading to failure.
- Temperature control is difficult to achieve with large multiple staking applications.
- The number of posts heat staked at one time is limited by the configuration design of the parts being assembled.
The heat stake method for assemblies is repeatable, cost-effective and safe, which is why it is widespread popularity is ever increasing within the magnetic assembly industry.
If you require anymore information on any of the assembly techniques discussed over the last few weeks visit our brochure.