Which one should I choose? Analysis of the competitiveness of metal and plastic bodies

In today's mobile phone market, the war between manufacturers has gradually spread from single configuration to all aspects of a mobile phone, and the "temperament", "feel" and "gloss" of the product are the most difficult to grasp. This highly subjective experience is indeed a difficulty for many manufacturers who are used to competing with marketing slogans and not paying attention to design.

However, the times are progressing, and many manufacturers have begun to follow the so-called experience economy. They began to figure out the design language of their own products and choose different mobile phone materials, hoping to create a unique product temperament. However, in this process, many technical or market problems began to emerge, and they found that the temperament of the product is not so easy to create. Today we will talk about the factor that has the greatest impact on the temperament of the product in terms of technology and experience - the body material.

In fact, it is because metal and plastic are the most widely used materials in mobile phones, and they are also the two most opposite materials in temperament. The author hopes to analyze the advantages and disadvantages of these two materials to let everyone understand the trade-offs between "taking" and "giving up" of some manufacturers.

List of factors that oppose metal and plastic

Let's first take stock of the conflicting factors between metal and plastic: metal is expensive, plastic is cheap; metal is not easy to process, plastic is easy to mold; metal has signal problems, plastic has no signal problems; metal has a good texture, plastic feels cheap; metal is not easy to color, plastic is easy to color; metal is strong, plastic is weak; metal is difficult to repair, plastic accessories are easy to find, etc. Let's start with the metal material.

Aristocratic metal material

The use of metal materials did not originate in the era of smartphones. As early as the era of feature phones, many manufacturers began to use various metal materials. However, the metal materials used at that time were mainly "steel" and "magnesium-aluminum alloy", while the "anodized aluminum" that appeared on the iPhone later was for better wear resistance and coloring effect.

1. Metallic luster & delicate cool feel & heavy

The biggest advantage of using metal materials is that it can give the product a unique luster and touch of metal. The unique cool and delicate touch of metal comes from its good thermal conductivity and dense atomic arrangement structure, and the beautiful metallic luster is because the free electrons inside the metal absorb external light and then release most of the light as visible light. This is why metal appears "shiny" after polishing.

Metal is heavier than plastic, but different metals are heavier to different degrees. For example, magnesium-aluminum alloy is lighter than steel when the strength is similar, but the price of magnesium-aluminum alloy is much more expensive than steel. Therefore, if a mobile phone wants to be as light and thin as possible while maintaining strength, it must use more expensive magnesium-aluminum alloy. But whether it is better to be lighter or heavier, I am afraid everyone has their own opinions. I personally prefer thin and light, but many of my friends say that thin and light mobile phones have no "feel" and are as light as a toy. Therefore, this is a very tangled issue. It depends on how the mobile phone manufacturers weigh it.

2. High strength & high processing difficulty

Xiaomi Mi 4 uses a metal frame to increase strength, but the processing process is also very long.

One of the main characteristics of metal materials is that they are generally strong, and their tensile, compressive and bending resistance are much higher than plastic. This is why many manufacturers use metal materials to make the middle frame, border or back cover even if they don’t use metal to make the phone shell (for example, the polycarbonate shell of the iPhone 5c also has a metal middle frame to enhance the strength of the body). Currently, many mobile phones have to make the borders narrower and narrower in order to fit a larger screen within the limited width of one-handed holding. This will inevitably require higher strength for the borders, so high-strength metal materials have become the first choice for narrow-border mobile phones.

However, the strength of metal materials is not completely equal to the strength of the metal body. If you think that you can use the phone carelessly just because it is made of metal, then if your phone bends when you sit on it, you will be in tears. Although metal is strong, it has poor toughness. Once it is deformed, it is difficult to restore it (especially for phones with aluminum alloy shells).

In addition, it is also because of the strength that metal is more difficult to process than plastic. Generally, the molding of plastic materials only requires one mold, while metal materials need to go through a series of processes such as cutting and grinding. Not only are the processing requirements higher, but the processing time is also much longer than that of plastic. Therefore, in many markets that require quick response, time-consuming and labor-intensive metal shells are difficult to gain an advantage.

3. High hardness, anti-scratch, anti-scratch, difficult to color

iPhone 5 frame easily peels off

Compared with general plastic, metal materials are harder, so metal bodies have a clear advantage in terms of scratch resistance. However, if there is color attached to the body, the color will be scratched off.

This is also a big problem faced by metals, that is, the poor coloring stability. Metals cannot be directly added with colorants during the molding process like plastics, and can only be colored by spraying or electroplating on the metal surface. Although such coloring processes are more complicated and more expensive than plastics, their adhesion ability is far inferior to that of plastics. The only advantage is that these processes can add color rendering to the beautiful metallic luster, making the texture of the whole machine even better.

Apple is good at this kind of craftsmanship, but even Apple has made mistakes here. Everyone should still remember the much-criticized "paint peeling" incident when the iPhone 5 was first released. Apple finally had to reduce the original pure black to a lighter dark space gray on the new generation iPhone 5S to solve this problem (light colors have stronger adhesion than dark colors). Therefore, when manufacturers choose metal bodies, they also have to consider the coloring issue. After all, the market demand for multiple colors is still very strong.

4. Metal Conductor Properties & Signal Issues

Jobs was troubled by the iPhone 4 antenna issue

If we talk about the biggest difficulty in manufacturing metal shell mobile phones, it is naturally the signal problem. No matter how exquisite your shell is, a mobile phone is still a mobile phone, and it still needs to transmit and receive signals. And the good conductor properties of metal will greatly affect the performance of mobile phone antennas, so this is also the reason why many manufacturers are reluctant to use metal shells.

Currently, mobile phones with metal shells (whether it is the frame, middle frame or back cover) generally choose to use other non-conductive media (such as rubber) to separate the metal parts so that the signal can pass smoothly. But even if this can improve the signal problem, the selection of partition materials, the width of the partition, the position of the partition, etc. also cost a lot of research and development costs. Even if such a high price is spent, problems are easy to occur. The most famous example is the "antenna gate" incident of iPhone4.

The solution adopted by iPhone4 is to use the stainless steel frame as two antennas, one for WIFI/GPS/Bluetooth and the other for 3G antenna, and in the middle is the familiar "gap" that causes no signal when held. Due to Apple's design flaw, once you hold the phone with your hands, the human body, a good conductor, will short-circuit the two originally separated "frame antennas", thereby changing the antenna's working length (the antenna length largely determines its resonant frequency, so it will affect the transmission and reception of signals). And because the human body directly contacts the antenna, this will greatly change the antenna impedance, and then cause impedance adaptation problems between the antenna and the terminal, which will also greatly reduce the working efficiency of the entire antenna. Therefore, the "death grip" becomes a very natural thing.

At present, the solutions adopted by other manufacturers are to either directly build the antenna inside to prevent human contact with the antenna; in addition, if an external antenna is to be used, the metal surface must be anodized to form a dense oxide layer to eliminate interference from human hands (the oxide layer is insulating). Of course, there are other methods, such as Apple's iPhone 4S, which uses dual antenna intelligent switching and changing the "partition" position to solve the signal problem. So we can see that the use of metal casing has very high requirements for the antenna design of the mobile phone. Many manufacturers are unwilling to bear such design costs and risks.

Inexpensive and high-quality plastic material

Plastic materials are often seen in our daily life, but the plastics used in mobile phones are somewhat different from the common plastics in our daily life. Take the most mainstream "polycarbonate" for example, its impact resistance and structural strength are much stronger than the common plastics in our daily life, which is why "polycarbonate" has gradually replaced the original "ABS" plastic and become the preferred plastic material of today's manufacturers.

1. Low price & easy to process & cheap feeling

Easy processing is probably the most advantageous feature of plastics. Since plastics are mainly formed by injection molding, pressing and other processes, they are very advantageous in large-scale production, unlike some metal shells that take dozens of hours to complete a production process. This is a great temptation for manufacturers who need to complete a huge supply in a short period of time (such as Samsung).

However, such a process also causes the cheap feeling of plastic to a large extent. Since the plastic processing process will go through the process from solid to molten and then to solid, the shape change caused by such shrinkage makes it difficult for plastic products to maintain a good degree of refinement. Therefore, in the end, the finished plastic product will have many uncontrollable errors at its edges or seams. For example, the back cover is not tightly fitted, there are burrs behind the frame, etc., which will have a great impact on the texture of the mobile phone. In the early days, many manufacturers made plastic mobile phones by first opening the mold, stamping out multiple shell parts in large quantities, and then "assembling" them together. The mobile phones produced in this way often have many small gaps in the body and are easy to fade. So the label of cheap feeling is attached to the head of "plastic".

However, some manufacturers (such as Apple and Nokia) have also begun to use machine tools to process plastics. Specifically, a whole piece of polycarbonate colored plastic is drilled with a drill to create openings and spaces for the camera, speaker, power button, and volume button. This ensures the integrity and refinement of the body, which is why the iPhone 5C and Nokia's Lumia series, although also using plastic bodies, do not give people a cheap feeling at all.

2. Lighter than metal & sufficient strength and hardness

Plastic materials are generally lighter than metal materials, but this statement is not rigorous. There are lighter metals such as "magnesium-aluminum alloys" and heavier plastics such as "polycarbonate". But overall, plastics are still lighter.

Although plastic is light, it can maintain good strength. Take "polycarbonate" for example, its hardness is much higher than that of ordinary plastic, and its strength and fatigue resistance are also excellent (so the saying that Nokia phones can "crack walnuts" has continued from the era of feature phones to the Lumia era). Another excellent feature of plastic is that it has a certain elasticity, that is, the ability to return to its original shape after being impacted. While metal is hard, it is difficult to ensure excellent toughness. Generally, a pit will appear after a fall, or it will bend after sitting. Plastic can have strength while maintaining a certain toughness, which is also a rare advantage of plastic.

3. Easy to color & insulate & little impact on signal

Another advantage of plastic is that it can be made into a variety of colors. Currently, there are two ways to color plastic: spraying and mixing. Of course, mixing is the most advantageous coloring process for plastic. But being easy to color is one thing, and being able to make good-looking colors is another. This requires very high standards for the selection of base materials, the mixing of color matching particles, the temperature during mixing, the degree of mixing uniformity, and the cooling process. If you want to produce a beautiful shell with bright colors and subtle luster like the iPhone 5C or Lumia series, it is still very technically difficult.

The insulating properties of plastics mean that they will not become a hindrance to antennas and signals, which means that there is one less restriction on where to design the antenna inside a mobile phone, where every inch of space is valuable. Don't underestimate this restriction, as it may mean saving huge R&D costs, so the low cost of plastics is also reflected here.

4. Easy maintenance & low replacement cost & removable battery

HTC M8 is the type that is difficult to repair

Strictly speaking, this is not the advantage of plastic itself, but the advantage derived from it. Samsung has been reluctant to give up plastic bodies, and one of the main reasons is that the plastic body can be removed from the battery. Although integrated bodies are becoming more and more popular, once the phone freezes, when you subconsciously want to unplug the battery, you will find that you have no battery to unplug. And didn't the mobile power bank become popular after the integrated body battery could not be removed?

In addition to the removable back cover, the plastic body is also more convenient to repair due to cost reasons. The plastic body can be assembled in a press-fit manner, so it is very convenient to disassemble and assemble in many cases, while metal is more troublesome. Therefore, in terms of repair, plastic also has an advantage.

Cultural reasons why metal is high-end and plastic is cheap

The battle between metal and plastic involves not only the tangible "hard reasons" of performance and actual appearance, but also some cultural "soft reasons".

Plastics and chemical fibers are products of modern chemistry, and they just happened to catch up with industrialized mass production. So from the beginning, they were popular, common, and cheap, which is both the advantage of these materials and the reason why they are not of high quality. So after people's living standards gradually improved, they gradually began to dislike these ubiquitous materials and began to pursue some more "high-quality" materials. This is one of the reasons why many people are unwilling to wear artificial materials and pursue high-quality pure cotton and pure linen.

Whether a material is expensive because it is rare, or rare because it is expensive, this is probably a difficult question. But as a rational person, the value of the material itself also needs to be expressed through the formed product. Just like Lei Jun's austenitic 305 stainless steel, although it is very cheap, after a series of precise processing processes to cut off the extra 290 grams, the remaining frame does not look like a cheap product at all. So materials are ultimately used by people, it depends on how you use them.

As a winner of Toutiao's Qingyun Plan and Baijiahao's Bai+ Plan, the 2019 Baidu Digital Author of the Year, the Baijiahao's Most Popular Author in the Technology Field, the 2019 Sogou Technology and Culture Author, and the 2021 Baijiahao Quarterly Influential Creator, he has won many awards, including the 2013 Sohu Best Industry Media Person, the 2015 China New Media Entrepreneurship Competition Beijing Third Place, the 2015 Guangmang Experience Award, the 2015 China New Media Entrepreneurship Competition Finals Third Place, and the 2018 Baidu Dynamic Annual Powerful Celebrity.