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Actually, near and far field refers to the distance from the ultrasonic horn to the weld joint. Typically, when this distance is less than 0.25in or 6mm it is considered ‘Near Field’ or ‘Close Range’ ultrasonic welding. Distances greater than that are generally considered ‘Far Field’ or ‘Long Range’ ultrasonic welding.

As a general rule, the greater the distance, the more difficult it is to get the vibrational energy of the horn transferred to the point of the weld. Materials which are softer often get less polymer chain entanglement at the interface since much of the vibrational energy is absorbed by the part before it reaches the joint.

Parts being designed for ultrasonic welding should take factors such as horn location and joint design early in the design process to ensure success.

-Andy

Basically, the purpose of a higher feed temperature in a reverse profile is to ensure the pellets soften enough to stick to the barrel so they convey to the transition zone for melting.

You should conduct a test to ensure what feed zone temperature is best for your material as different heater bands, screws, and barrels behave differently.

There are many times I have found that the same temperature can be used for both the feed and middle temperature zones.

Processing guides can be a great starting point when setting your temperature zones, but do not always reflect the best settings for your machine.

-Andy

In a D1 (DECOUPLED MOLDING 1) process the first stage is filling and packing, yet a D2 process isolates filling in the first stage. Could you please explain the difference?

A reverse profile is typically used when processing materials such as nylon and LCP. In fact it is quite common for many semi-crystalline polymers. Basically, such polymers have a melting point. The high rear temperature often helps improve conveyance as well as melt the polymer quickly, Once melted, the polymer can often be cooled a little in the front to improve the overall cycle time and meet the desired melt temperature.

Usually the need for a forward or reverse temperature profile should be approached scientifically. The middle barrel temperatures should be set to the desired melt temperature. The front zones are typically adjusted to obtain the desired melt temperature. The rear temperature should be set  to optimize feed and melt consistency.

Historically, low viscosity polymers with high crystallinity tend to process best using a reverse profile… but you should always look to optimize this, since everyone has different screws, barrel, heater bands, thermocouples, and temperature controllers.

Try not to confuse the front temperature with the actual nozzle temperature. The nozzle temperature will be adjusted independently to meet the needs of the specific process, such as avoiding drool or freeze off.

-Andy