Mohou.com Concise Digital Manufacturing Handbook (3): Understanding Basic Materials

Mohou.com Concise Digital Manufacturing Manual (1): Why Use Digital Manufacturing?

Mohou.com Concise Digital Manufacturing Handbook (2): Comparison between Additive Manufacturing and Subtractive Manufacturing

In this chapter, Mohou.com will work with you all

1.Learn more about thermoplastics, thermosets, and photopolymers (photoresins).

2.Learn more about plastics and similar materials

3.Learn about hard and soft metal materials

4.Choose the right process

Digital manufacturing technology encompasses different processes for processing a variety of materials. In order to choose the most appropriate material to produce your part, you need to understand which materials can be used in which processes and some of the properties of those materials. This chapter from MagicMonkey.com looks at the basics of a few different material categories to help you understand not only what possible material options are available, but also which materials are best suited to your needs.

Learn more about thermoplastics, thermosets, and photopolymers (photoresins).

exist 1967In the 2011 American film “The Graduate”, the hero played by Dustin Hoffman was told that plastic was a promising industry. We have no way of knowing whether the male protagonist shares this view, but over fifty years later we now know that the manufacturing industry must share this view. Plastics are now widely used in the manufacturing industry, including many types of plastics. and plastic-like materials, covering almost all industrial categories, and have become an inseparable part of our lives.

For the uninitiated, there are many different types of plastics. What are the differences and connections between different plastics? This confusion is usually due to the following reasons:

✓ No notion of relationship between the structure of the material and its properties.

✓ The performance of product materials often does not receive enough attention and not enough time and energy is devoted to it.

✓ Even if the above two obstacles are overcome, it is difficult to find accurate data on material properties.

Choosing the right materials for your product involves integrating data from various sources. Data from each source may be incomplete, overlapping, or conflicting. You need to integrate this incomplete or even mutually exclusive data together. For a material, the most important thing to look at is its material data sheet (MDS,Material data sheet), a good suggestion is that you get as much information as possible from this table. More detailed information can sometimes be obtained from design manuals and application notes published by individual material suppliers, which can be used to fill gaps in the material data sheet. Complete and detailed material information is usually only available for high-performance engineering and specialty materials (to show performance superiority), while some common materials may contain missing information. If you really need to learn about a material, in addition to researching information, you may also need to do some experimentation and testing.

thermoplastic

Thermoplastics are plastics that soften above a certain temperature, become moldable, then solidify as they cool, and the process repeats over and over again. Thermoplastics are therefore often used in injection molding and can generally be recycled.

What happens to thermoplastics when they are heated is, in technical terms, a phase change. A very common example of a material undergoing a phase change is water changing to ice at temperatures below freezing and ice changing to water at temperatures above freezing. Below this phase transition temperature, the material is solid, and above this temperature, the material is liquid.

Some common thermoplastics

✓Acetal Acetalalso known as Delrin

✓ Acrylic(Acrylic, PMMA, Polymethyl methacrylate）

✓ Acrylonitrile Butadiene Styrene (ABS,Acrylonitrile butadiene styrene)

✓Nylon Nylon (PA, Polyamide)

✓Polycarbonate (PC Polycarbonate)

✓ Polyethylene (PE Polyethylene)

✓ Polylactic acid (PLA, Polylactic Acid)

✓ Polypropylene (PP, polypropylene)

✓ Polystyrene (PS, polystyrene)

✓ Polytetrafluoroethylene (PTE, polytetrafluoroethylene)also known as Teflon

✓ Polyvinyl chloride (PVC, polyvinyl chloride)

thermoset plastic

The name thermoset can seem a little confusing, especially when compared to thermoplastics (see previous section). A thermoset is a material that hardens irreversibly, rather than being softened by heat. Perhaps the easiest way to remember the difference between the two plastics is that thermoplastics deform reversibly when heated, while thermosets deform permanently.

Thermoset materials can be hardened by a chemical reaction or by radiation, depending on the composition of the material. Liquid silicone is a commonly molded thermosetting material.

Thermosets are generally stronger than thermoplastics and can also be used in various molding processes.

Common thermoset plastics include:

✓Bakelite

✓ Epoxy resin

✓ Melamine

✓ Polyurethane (also found in thermoplastics, but less common)

✓ RTV Silicone

✓ Silicone rubber

photopolymer

Photosensitive polymer is a kind of plastic. Before the liquid state is cured, it is often called photosensitive resin which changes characteristics and undergoes a curing reaction when exposed to light. These plastics are usually cured with UV light and harden very quickly. Photosensitive resins are often used3D Printing and similar processes (such asUVprinting, etc.). Photopolymers tend to be more fragile than other types of plastics and are often unstable when exposed to sunlight or high humidity. Like thermosets, photopolymers undergo an irreversible curing process and cannot soften once cured. when used for3DDuring printing and other processes, the photosensitive resin will solidify layer by layer. usually through aUV The laser head draws (and cures) a layer of the part on the resin, then lowers the table one layer in height before drawing and curing the next layer, and the process continues until the entire part is trained.

Photoresist is one of the important raw materials in digital manufacturing. Many photosensitive resins have been developed to make photopolymers with certain characteristics.

Compare plastic and plastic

From a technical point of view, not everything that looks like plastic is plastic. The performance behavior of thermoset plastics and photopolymers is similar to that of real plastics.“Plastic” is different, although it is normal for ordinary people not to be able to tell the difference. But if you want to become an expert, or just want to learn a little more, it can be fun to compare plastics to similar plastics.

Stereolithography (a commonly used additive manufacturing process that can be shortened to YEARS) The raw material is a photosensitive resin rather than a thermoplastic, so it is different from ordinary engineering-grade resin in some key characteristics. Nonetheless, these plastic-like materials are useful to designers and engineers and can be used for appearance, assembly, and limited functional testing, provided they match the intended final production material within certain dimensions. Often the property that designers and engineers value most is stiffness (the technical term is tensile modulus), so if the raw material is ABS material, it generally refers to the material withABSStiffness is similar, while other material properties can vary significantly.

The most common properties that differ between photosensitive materials and engineering-grade thermoplastics are elongation at break (the amount of stretch before breaking, measured as a percentage) and temperature resistance (the temperature before softening). The elongation at break and temperature resistance of photosensitive polymers are much lower than those of corresponding engineering plastics.

All photosensitive polymers have long-term sensitivity to oxygen, that is, their properties will age and degrade when exposed to oxygen for a long time, and this sensitivity will increase as the temperature increases. A general measure of aging is the relative thermal index (Relative thermal index, RTI). This is currently the best method for measuring the long-term effects of aging on the mechanical and electrical properties of photopolymer machines. RTI Start by measuring key basic properties, then test the sample for aging at multiple temperatures, monitoring its basic properties until they return to their original values. 50%. reach 50% The time required for execution is called failure time.

Choose the right plastic

Without understanding all of a part’s performance requirements, it is impossible to select materials with complete precision. But if it is sometimes unprofitable to carry out too many technical calculations in advance for the selection of materials, then how to choose a suitable material for the product? Below we provide some rules of thumb for quickly choosing plastics:

✓ Try it ABS。 ABS Suitable for many applications. It’s reasonably priced, sturdy, relatively durable, beautiful, and forgiving even if you don’t follow all the standard design rules for plastic parts. However, its melting point is relatively low.

✓ If you need a cheaper, stronger product and appearance is not critical, try polypropylene. (PP)。

✓ If you need to compare ABS For something sturdier or able to withstand higher temperatures, try polycarbonate (computer),PCNot as good asABSNext, tolerant design rules require an understanding of the design rules for plastic parts. .

✓ If you need beauty and transparency, try acrylic (PMMA）。 PMMA It might be a little crunchy.

transparent PC I will compare PMMA More solid, but less aesthetic.

✓ If these rules do not select a suitable material, then you will need to perform mathematical and engineering analysis.

If you plan to use injection molding to make parts, you can machine multiple parts from different candidate target materials before making the mold, and then make the mold after settling on the final material. This is because the mold must match the properties of a specific material during design. The resin will shrink once solidified. Therefore, it may not be possible to use multiple resins in the same mold. affect part size and tolerances as well as accuracy risks.

Recognize hard metals and soft metals

Obviously not all parts are plastic, metal is also common and is often a more suitable choice. There are many types of metals, which can be simply classified as hard metals or soft metals in parts manufacturing.

Soft metals: aluminum, copper, magnesium

Aluminum is the most abundant metal on earth and the third most common element after oxygen and silicon. In fact, aluminum makes up 10% of the total mass of the Earth’s crust.8%！

Aluminum is soft and very ductile, making it unsuitable for mechanical purposes. Aluminum is often mixed with other elements, including silicon, copper, magnesium and zinc, then heat treated to create the strong, lightweight aluminum alloys used today in fuselages, cars and a variety of consumer products.

Another popular lightweight material is magnesium. Magnesium is about two-thirds the weight of aluminum alloys and is almost as strong, making it the lightest of all structural metals. Magnesium is the material of choice for its significant specific resistance. It has excellent damping properties, is easy to machine and can be easily formed or die cast.

Another soft metal is copper, generally divided into brass and copper (purple). Of the two, brass is by far the more versatile copper alloy and is extremely resistant to weathering and corrosion except in high ammonia and acid environments. If you’ve ever replaced a car radiator, soldered a kitchen faucet, or played a horn, you’ve come into contact with brass parts.

Hard metals: steel, stainless steel, titanium, cobalt-chromium and inconel

Some parts must be made of hard metal. The most common metal product is steel, which is primarily composed of iron, the second most abundant element after aluminum. People began making iron thousands of years ago, but it wasn’t until19Large-scale, high-quality steel production did not become possible until the middle of the century.

As with soft metals, small amounts of alloying elements can have a significant impact on the properties of steel.——Cannot be added 1% Carbon and manganese are what make iron brittle and strong.1018steel. Suitable for airplane use 4140 Alloy steel is made from a mixture of equally small amounts of chromium and molybdenum powders.

Through such mixed additions, carbon steel can be hardened to a certain extent and easily welded. But there’s a problem: They rust, making plating or painting essential for almost any application involving carbon steel.

To prevent rust, stainless steel was developed. By increasing the chromium content to at least 10.5%corrosion resistance is greatly improved. Stainless steel is widely used in the chemical industry, textile processing and marine applications. Many stainless steels are also temperature resistant and can withstand 1480 Celsius and above, which is hot enough to turn aluminum, brass, and copper into a pool of fusion.

3Made of stainless steel(The most common include301 302 316wait)contains at least 20% Chromium and a considerable amount of nickel, making it very strong and difficult to process.

17-4PHStainless steel is a versatile and very strong material containing nickel, chromium and copper. Although considered part of the stainless steel family, its machinability in the annealed state can approach superalloy status – which it can easily achieve with heat treatment. 45 CRhardness and1000MPa or higher tensile strength, three times that of carbon steel. It is most often used when a combination of high strength and good corrosion resistance is required.

And then hard metals also include titanium. This lightweight element is often alloyed with aluminum and vanadium to provide a strong, corrosion-resistant material. Like cobalt-chromium alloys, titanium has good biocompatibility and is widely used in screws, pins and bone plates. Titanium is also very attractive to the aerospace industry and high-performance automobile manufacturers, who have strong needs in terms of weight savings.

If you need a particularly strong and durable alloy, you might consider cobalt-chrome or inconel. Inconel contains 50% or more nickel, which gives it excellent resistance over a certain temperature range. It is used to meet extreme requirements such as gas turbine blades, jet engine compressor disks and even the combustion chambers of nuclear reactors and jet engines. Next to nickel in the periodic table is cobalt, which is the main component of cobalt-chromium alloys. Unfortunately, cobalt-chromium and inconel are generally considered difficult to machine, which is why they are more commonly used by direct metal laser sintering. (SLM) Additive manufacturing process.

Choose the right process

Sometimes you will find that the same material can be used in multiple digital manufacturing processes. For example, nylon,ABSSome plastic materials are suitable for 3D Printing, also suitable for machining, injection molding. Likewise, certain metals, such as aluminum and stainless steel, can be used 3DPrint,CNCMachining and other processes.

How to choose between plastics and metals used in different processes? This involves three factors:

✓ End use of the room

✓ Complexity of part design

✓ Production volume

in the next4,5,6In this chapter, we will present the main digital manufacturing tools. Only by understanding these processes can we make the right decisions based on specific situations.