ATM has recently opened its in-house plastics joining laboratory. ATM has over 40 years experience of supplying the automation and plastics industries with a diverse range of technologies and solutions for applications such as de-moulding, parts handling and assembly.

With component manufacturer’s now increasingly adding value to their product by performing more of the downstream assembly operations, plastic joining has become a key growth area for the company. This new resource, backed by the extensive experience of their plastic joining specialist, John Neugebauer, enables customer applications to be evaluated ahead of the proposal stage thus determining not only the best process for the application, but also enabling cycle times and process parameters to be defined in advance.

The laboratory has a number of different technologies available for evaluation including Hot Air/Cold Staking, Ultrasonic and Pulse Staking.

Each of the different technologies can be tried and tested on sample parts to determine the process best suited to the materials under evaluation. In some cases, there will be perhaps two or more technologies that can successfully join the parts. One of the technologies may be deemed more appropriate for a specific application depending upon the number of stake points or weld positions, cycle time and aesthetic appearance required

Hot Air/Cold Staking is a traditional joining method which has been used for many years in a multitude of applications. Seen as a simple technology which can be used easily by un-skilled operators, this process is also relatively inexpensive especially where the components have multiple stake positions. The disadvantages of this process however include the fact that for a small number of stake points or tips the process is not particularly energy efficient. The process is not suited to hand held operation and also in some applications, the gap between the hot air nozzle and the stake point is critical if consistent quality is to be achieved. This renders the process less suitable for applications where the component tolerances may not be sufficiently tight. Additionally any concentration of heat energy applied to a confined area containing several stakes may stress relieve a moulded component causing unacceptable distortion.

Ultrasonic welding systems are used extensively for many applications, but as for other joining processes, this too has limitations. When applied to materials with a high glass or mineral fill content (40% to 50%) the ultrasonic process can cause particle fragmentation which is unacceptable in certain safety critical applications found in the production of Aerospace or Military components and automotive seat restraint and air bag applications. The use of ultrasonic welding on electro-mechanical components and PCB’s can also pose a problem due to the high frequency vibrations generated, as can the use of the technology in close proximity of metal components. Consideration must also be given to the noise generated by the process, and appropriate steps must be taken to prevent prolonged operator exposure to the high frequency sound. Ultrasonic welding does however have a number of advantages. It is possible to have a hand held unit, which enables the use of the technology on low volume production or where a dedicated multi-tip machine cannot be justified. The process is also quick and can generally be used on a wide range of materials. Where multi tip applications are required, a number of sonotrodes can be operated from a single generator unit by switching from one tip to another in a pre-defined sequence, thus helping to reduce the overall cost of the machine.

A less well known process, pioneered by ATM, is Pulse-Staking technology. Available as a portable hand held device or integrated into multi head desk top or floor standing machines, Pulse-Staking works by accurately controlling the amount of time a current passes through a specially designed tip which is rapidly heated to the melt temperature of the material being processed. The current is “pulsed” on and off to ensure that the material does not overheat and begin to degrade. At the end of the “pulsed” heating cycles, compressed air is passed through a central tube which rapidly cools the tip and allowing the plastic to solidify rapidly. The small heat affected zone around the Pulse-Staking tip, plus the fact that the process does not generate any vibrations, makes Pulse-Staking ideal for applications on electronic components and PCB’s. The process is also unaffected by the close proximity of metal components and the controlled nature of the heating cycle also makes it more suitable for materials which have a high filler content.
          
Hybrid machine

Selecting the most appropriate process for an individual application can mean that on occasions two different technologies will be used together within a Hybrid machine. One such example was a rotary table welding machine for the production of powder print cartridges. This machine employed ultrasonic technology to weld a plastic cap onto one end of the cartridge housing whilst a multiple tip Pulse-Stake head staked an ID tag in the form of a small PCB at the other end of the assembly. With a very localised heat affected zone and with no vibrations generated from the process, Pulse-Staking was deemed to be the most appropriate technology for this part of the assembly process. This Hybrid machine operates very successfully and is an excellent example of the unbiased approach for every individual application. ATM also has experience with other plastics joining technologies such as Hot Plate Welding, Vibration Welding and Laser Welding.

www.atmautomation.com