Phasa’s heat welding process

The Phasa Heat staking process is used for the assembly of many types of  plastic components, including Automotive interior , exterior and electronic PCBs joining them together using a rivet type, swaging method. Phasa provides a custom made alternative to other less dedicated methods of plastic assembly such as ultrasonic welding and hot tool staking, it is often referred to as hot air cold stake assembly.
The Phasa process is a simple two stage operation providing a cost effective, capable and repeatable method of permanent plastic assembly using multiple moulding extensions in the form of stakes or ribs which are simultaneously heated by a precisely directed non-contact super hot air  from a precision engineered manifold system. Once soft the stakes are reformed and clamped with separate cold forming tools producing a rivet type, tight and secure fixing.

Replacing traditional screwing and metal riveting methods with their inherent process variables and component cost disadvantages as well as future recycling difficulties, the Phasa process gives an economic, clean and quick process with proven Cpk. Values and pull off strengths recorded to an excess of 500N.

When re-formed by Phasa hot air staking, the stake or rib can be made into an ascetically pleasing shaped head being secure and tight helping prevent problems such as “squeak and rattle” a common Automotive interior problem. The Phasa “hot air cold stake” process is equally suitable for joining materials operating in harsh variable environments such as under-bonnet where filters and management sensing systems need to withstand extremes in operating temperature and vibration.

Almost all common thermoplastic materials such as ABS, Polypropylene, POM, Acetal and Nylon, with up to 50% Glass or Talc filling are processed without issue as can higher melt Ulthem or Peek type materials. The substrates staked vary enormously and can have the same or different thermoplastic properties as the moulding material itself, metallic, rubber composite, glass or a PCB, all can be used without damage.

Sizes for the stakes or ribs start at 0.5mm and increase to over 20mm and can be either solid or hollow. It is possible to process over 100 retention points in any one pass, as can a rim of solid material for retaining a lid or bearing by heating and rolling over as a retention feature. Using the Phasa recommended design, a copy of the Phasa free design guide is available giving all the dos and don’ts to give the right fixing.

Where special surfaces such as gloss painting, chrome, polished metal or wood effect are used it is important not to damage or create “sink marks” to the “a surface”, equally for delicate soldered circuits of LED’s and flexible PCB no damage must occur. The Phasa process is precisely controlled throughout and you can be confident in minimising any marking or risk of damage.

There are disadvantages in using just a contact heatstake tool or ultrasonic head, the “contact’ heat from a hot tool or Ultra-Sonic tool at the top of the stake, spreads the material out sideways from the heat to form the typical “Mushroom” head, which is weak at the point where it joins to the stake.

Using contact heated tools it is often difficult to obtain a consistent and capable standard of fixing. Being less suitable for filled Plastic materials they will melt onto and stick to the forming tool often causing stringing of material. After processing there can be an initial ‘Spring Back’ towards the original stake shape, followed by a ‘creep’ over a period of time leaving the completed assembly loose with rattles, squeaks and vibration noises.

Ultrasonic staking has been partially adapted from a plastic welding process, Ultrasonic Tooling often called a Horn or Sonotrode can be expensive to manufacture as they are individually acoustically tuned, undue care causes damaged as can accidental contact with metal, overloading or fatigue failure. Positioning and processing is difficult if staking points are close with different stake heights, shapes and sizes adding to costs.

The Ultrasonic process can cause damage on the mouldings ‘A’ face from a vibration burn when the part is rubbed against the nest. Sensitive components fitted to the assembly such as springs, electronic assemblies and sensors do not react well to the vibrations as do heavy glass filled materials, fully chromed stakes or foamed materials.

Ultrasonic staking working at the top of the audible range can cause distress, protection is advisable but adds additional cost for an acoustic surround and further restriction within the processing area.