The application of injection molded parts in electronic intelligent devices: Every piece of plastic in your hand is a result of precise engineering.

I. Electronic smart devices use much more plastic than you might think.

When you open a flagship mobile phone, the metal frame might only account for 15%, while the remaining 85% is all plastic and rubber. Smartwatches, TWS headphones, VR headsets, smart speakers, drones - the shells, structural components, buttons, and sealing rings of these devices are almost all produced through injection molding.

The reason is straightforward: Electronic devices need to be lightweight, thin, have good signal quality, be mass-produced at low cost. Metal cannot meet these requirements, and injection molding is the perfect solution.

II. What materials are used for different devices, clearly listed in one document

Smartphones / Tablets 

The frame is made of aluminum alloy or stainless steel, but the back cover, buttons, and camera module support are all injection molded. The mainstream uses PC (polycarbonate) for the transparent back cover, PC/ABS alloy for the frame and buttons, and LCP (liquid crystal polymer) for the antenna partition and SIM card slot - LCP can transmit high-frequency signals, while metals cannot. 

TWS Headphones 

The earphone case is made of PC or PC/ABS, being lightweight yet with good texture. The earplug part is molded with TPE (thermoplastic elastomer) for coating, achieving a combination of softness and hardness in a single process. The charging case shell is made of ABS glossy material, with no need for painting and directly presenting a mirror-like effect. 

Smartwatch 

The case is made of PC or PA12 (nylon 12), which is lightweight and resistant to sweat corrosion. The strap is made of TPU or fluorine rubber, and is formed by a two-color injection molding process. The sealing ring under the dial glass is made of LSR (liquid silicone rubber), and the injection molding accuracy should be controlled within ±0.02mm. 

VR/AR Headsets 

The face shell is made by dual-color injection molding of PC and PMMA, with the front shell being transparent and the rear shell being opaque, all formed in one piece. The lens holder is made of PPS, which is resistant to high temperatures and does not deform. The headband adjustment structure is made of PA66 + GF30, which is strong and lightweight. The total weight of the entire machine is controlled within 300g, and plastic plays a significant role. 

Smart speakers / Smart home devices 

The structural components beneath the speaker mesh are made of ABS, and the bottom counterweight is composed of PP and iron powder. The casing of the floor cleaning robot is made of PP and talcum powder, which is wear-resistant and scratch-resistant. The panel of the smart lock is made of PC/ABS, which is resistant to impact and also resistant to fingerprints. 

III. The core process of electronic injection molding parts, what makes it more difficult than that of household appliances

The precision requirement is one order of magnitude higher

For household appliances, a tolerance of ±0.1mm is considered qualified. However, for electronic parts, the tolerance is ±0.02mm or even tighter. The slot for the SIM card in a mobile phone, the mold line for headphones, and the watch lugs - if they are even a little off, they won't fit. 

Micro Injection (Micro Injection Molding)

The ear tips of TWS headphones and the tiny buttons of smart watches weigh less than 0.1g each. The injection volume of the injection molding machine should be controlled at the 0.1cc level. This is not something that an ordinary injection molding machine can handle. 

Insert Molding

The metal screws, spring clips and FPC cables in mobile phones are directly placed in the mold. During the injection molding process, the plastic encapsulates the metal parts and forms them into one piece. This eliminates the subsequent assembly steps, yet the reliability is even higher. 

Paintless High Gloss Solution

The appearance of electronic products is increasingly emphasizing "bare machine texture". Without painting or electroplating, simply using high-gloss PC or paintless ABS injection molding results in a mirror finish. LG, Sabic, and Covestro all offer mature paintless grades for selection. 

IV. Several Easily-Omitted Details

Signal Penetration Issue

Metals can block signals. Therefore, for any positions in electronic devices that involve antennas, NFC, and GPS, plastic must be used. LCP and PPS are the most commonly used high-frequency penetration materials. 

Heat dissipation issue

The chip generates heat which is dissipated through the heat sink. However, the thermal conductive structure between the heat sink and the plastic casing is also an injection-molded part - made of PA66 + GF30 or a heat-conductive plastic, to transfer the heat from the interior to the surface of the casing. 

Waterproof sealing

For TWS headphones to meet IPX5 standards, and for smartwatches to achieve 5ATM water resistance, it is achieved through ultrasonic welding between the injection-molded parts and a silicone sealing ring, rather than using glue. 

The core characteristics of the injection molded parts for electronic intelligent devices are three words: precision, lightness, and transparency. Precision determines whether they can be installed, lightness affects the feel and battery life, and transparent materials determine the quality of the signal.

The materials and processes in this field are evolving extremely rapidly. LCP, PPS, no-spray, micro-injection - each of these is pushing the boundaries of injection molding forward.