Post-Processing for Plastics

1. Laser Marking

Laser marking is a quick and "toolless" process that eliminates the need for surface preparation while giving plastic injection molded parts a high-resolution marking. It offers an alternative to in-mold painting and in-mold graphics, applying decorative marks during the injection molding process. During the laser marking process, the injection molded plastic is subjected to visible surface changes by a solid-state pulsed laser. To get a clear mark, the light emitted by the laser needs to have a wavelength that can be absorbed by the molded plastic. Typically, laser marking is applied to make logos or unique identifiers to parts which require traceability, for example, aerospace components and medical devices.

2. Foil Stamping

Foil stamping is a manufacturing process that the object and the hot plate are pressed together in a short time with the help of a certain pressure and temperature, and the metal foil or colored foil is transferred to the surface of the object according to the graphic requirements of the hot stamping template. Foil Stamping shows good decorative result. The gold, silver, copper or other colors of the metal foil creats a sharp contrast with the surface of the item, which has a high-grade and luxurious visual appearance. At the same time, foil stamping can also increase the water resistance, durability, wear resistance and oxidation resistance of products.

3. Pad Printing

Pad printing is a marking process that transfers a two-dimensional (2D) image onto a three-dimensional (3D) object. The transfer pad is pressed onto a fully inked plate which has etched the desired image, then the ink pad is placed on the injection molded part and pressed onto the surface of the part to transfer the ink and apply the image.

Pad printing can be applied for irregular surface or shape. It is perfect for transmitting detailed images and providing excellent print quality. Fast drying ink speeds up processing time and helps avoid drip, run, or smudge problems that can occur when the ink is applied. However, transfer pads and inks are affected by air pollutants, therefore, quality assurance is a key part of this process.

4. Ultrasonic Welding

Ultrasonic welding is a connection process that uses high-frequency ultrasonic vibration to form a solid welding between two pieces of plastic. The ultrasonic horn vibrates 20,000 to 40,000 times per second while remaining in slight contact with the plastic. This vibration creates friction, which in turn generates enough heat to melt the plastic. To ensure that the part does not move while cooling, a clamping force is applied for a specific holding time. 

5. Heat Stake Inserts

The metal inserts are installed into the plastic boss and housing by heat staking. These inserts are typically threaded to support the use of screws during the assembly of products. With thermoplastic staking, heat is applied to the metal insertion to soften the plastic as it is pushed into the part. The heat staking melts the plastic at a specific temperature and pressure to realize an optimal filling. Attaching moulded plastic enclosures to printed circuit boards (PCBS) is one of the applications for heat staking. This assembly method is used for plastic bosses in automotive door panels as well. In addition, it is also used in the thermal detection of consumer appliances such as coffee machines. For nearly any type of plastic, thermoplastic staking can create strong joints. The use of metal inserts with thin plastic that may split or shatter is also supported by its low insertion force.

Post processing can achieve decorative results. There are several different ways as following to achieve decorative results on aesthetics, identification, orientation or more.

1. Laser Marking

Laser marking uses a laser beam to discolor the material surface to gray or black, resulting in the desired graphics or text. The carved word has no score. The surface of the part is still smooth, and the writing will not wear out.

2. Foil Stamping

Fol stamping using metal foil, rich color, with high-grade sense, can make the product more noble, beautiful. Compared with ordinary printing, foil stamping can enhance the visual effect of the product and improve the value and competitiveness of the product.

3. Pad Printing

Pad printing adopts a color separation printing method, which can print dozens of colors and complex gradient colors, and has a strong color expression. Pad printing has the characteristics of rich color, bright color, clear pattern, smooth and natural.

For functional or joining purpose, there are following two methods to achieve the results. You can choose the best solution for your project.

1. Ultrasonic Welding

Acoustic pulses are transmitted to a plastic part by a resonant vibration tool called a horn, which causes two plastic materials to vibrate against each other. Two parts are heated and fused together by vibration. With this method, different resin families can be joined when their melting temperatures are within 30°F and their compositions are compatible. This technology is quick and the cycle time is short. Assembly speeds of more than 25 parts per minute are possible.

2. Heat Stake Inserts

Heat staking machine connects two different materials using small plastic posts that protrude from the plastic housing by applying controlled heat, time, and pressure using a Heat Embossing head. Usually, the temperature is reached prior to the head being heated. Once heated to the proper temperature dependent on the types of metals and plastics being staked, the head makes contact with the protruding plastic posts and is molded into various forms of heat staked posts. Staggered posts include those that are flat, profiled, dome-shaped, hollow, cross-shaped, and rosette-shaped.