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Choosing the Optimal Material For CNC Machining.

If you find the vast selection of different materials for CNC machining confusing, this blog will tell you how to reduce that number to a manageable level.

Choosing the right material for CNC machining can make all the difference in getting a working part or prototype made at a reasonable price.

Create a shortlist

If you have to wade through a multitude of data sheets, you should

Start by weighting the requirements of the custom machined parts you want to manufacture. First, think about which features are essential, and then consider which would be desirable.  This will allow you to quickly go through the data sheets and reduce the choices to a manageable level.

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Material properties

First, understand what the most common material properties are.

Starch. There are several different types of strength.

One of the most common is tensile strength. Ultimate Tensile Strength (UTS) indicates the tensile load at which an object will break. Fracture strength is measured in megapascals (MPa) or newtons per square meter. A material with low tensile strength typically has an MPa value of less than 100, while a high-strength material has a value of more than 400.

Impact strength or toughness may be another important consideration, and the part may also need to be hard and wear-resistant. Friction can also play an important role. Here, the spectrum ranges from materials with high friction to those that are low-friction and self-lubricating.

Wear resistance versus machinability

At first, you may be considering a material that resists wear and/or abrasion. However, you should not ignore the fact that wear-resistant materials are also difficult to machine. It will take more time and require more tooling to produce the part you need. In other words, it will cost you more. This is what we mean by the term "machinability".

Strength to weight ratio

Strength is important, but in modern manufacturing you often need materials that have a good strength-to-weight ratio. Therefore, you should also consider material density or material weight. This is simply the ratio of weight to volume. This value is often given in kilograms per cubic meter.

Elasticity

This refers to the ability of a material to return to its original shape after being stretched or compressed. Material descriptions contain common terms relating to elasticity. For example, low elasticity is described as plastic, medium elasticity as deformable or tough, and high elasticity as stiff or brittle.

Elongation

Elongation refers to the changed length of a part compared to its original size. In other words, to its stretchability. One often encounters a value that provides information about the so-called elongation at break or elongation at tear. It indicates the length of an object in relation to its original length when it breaks or tears.

Temperature

The operating temperature is the temperature at which a device operates. For plastics, this specification can be further subdivided into a short-term operating temperature (short-term tolerance in minutes or sometimes hours) and a long-term operating temperature.

You may also need to consider the melting temperature of your chosen material.

Thermal conductivity

This value refers to the ability of a material to conduct or transfer heat. In some applications, thermal conductivity is quite desirable, while in others it should be prevented (for example, by insulation).

Electrical conductivity

The ability of a material to conduct electrical current.  For example, copper is a good conductor. In contrast, most plastics are poor conductors or excellent insulators.

Some of the most commonly chosen materials

Given the variety of different metals and plastics, you'll notice that some are more popular than others. Here is a selection of the most common options.

Titanium

Titanium is the top choice in aerospace engineering because it is strong, wear-resistant and lightweight. The problem is that it is difficult to machine, and parts made from it cost significantly more than those made from aluminum or stainless steel. Consequently, you should consider a less costly metal if it doesn't have to be titanium.

Aluminum

Aluminum alloys are easy to machine, have a good strength-to-weight ratio, and are corrosion resistant (especially when anodized). They are widely used in the manufacture of aircraft parts, but also in mechanical engineering, as well as in the production of computer components, cookware and many other applications. It is worth taking a look at the specific properties of various alloys of this metal: The 6000 series is, in a sense, the workhorse, while the 7000 series is stronger and 2000 is intentionally softer to increase fatigue resistance.

Stainless Steel

Stainless steel comes in numerous different grades and qualities to consider. They are all known for their corrosion resistance and excellent mechanical properties.

Alloy 17-4PH.  PH stands for Precipitation Hardenable. Aside from being a stainless steel alloy, this alloy is also very durable, making it well suited for harsh environments where the part may be subject to wear and corrosion. It is used in mold making, aerospace, missile, chemical, food processing, and oil and gas platforms. These alloys are hard and correspondingly expensive to machine.

Two common grades of stainless steel are 304 (also known as A2) and 316 (A4 or marine grade). 304 is stronger and less expensive, while 316 is more corrosion resistant.

The various stainless steels have very different machinability, but all take longer to machine than aluminum.

Other metals

Other metals worth considering are mild and mild steel alloys, as well as copper and brass. They are all suitable for CNC machining, although some are harder and therefore more costly to machine than others.

ABS plastic

ABS plastic is suitable for both injection molding and machining and offers excellent toughness and impact resistance.

Acetal (or Delrin®)

An engineering plastic with high mechanical strength, dimensional stability and comparatively low cost. This combination makes it the most widely used material, for example in gears and sporting goods.

Nylon

Another excellent material is nylon, which combines strength with flexibility. It is used in numerous technical areas, for example in the automotive industry as well as in mechanical engineering.

Polyetherketone (PEEK)

This material is often used as a substitute for metal. It is the all-rounder plastic from which high-end components for aerospace, Formula 1 and medical technology are made. It offers high abrasion and wear resistance, low moisture absorption and a low coefficient of friction.

Polycarbonate

This is one of the most widely used materials in modern manufacturing. It has excellent impact resistance and good temperature resistance and is a real alternative to glass. Polycarbonate and acrylic are naturally transparent, but processing leaves a matte finish. The clarity of the material can be restored by polishing.

Choosing the right material

Admittedly: Choosing the right material can be time-consuming, but with a little research, you can increase the number of materials you're familiar with. As your personal list grows longer, you may save money or come across a material that better suits the needs of the part you want to make. Richconn has already done much of this research for you. The result: 30+ of the most popular materials hand-picked for you.

Selecting a metal or plastic material for CNC machining part can be challenging. Keep the intended function in mind and don't discount any post-processing options.

If you have any questions about our services at Richconn, please contact an applications engineer at sales@richconn.com.cn or +86-0755-28025755. Have a finished design for 3D printing? Upload it now to get a quote.

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