Plastic Material for CNC Machining Prototyping

Prototyping Materials

PMMA (Acrylic Plastic)

 According to the materials used in the production, the prototype model can be divided into plastic prototype and metal prototype.

At present, the mainstream material of the prototype model is plastic. It is due to the large number of applications of plastic products. The prototype model is directly produced with the same material, and the product is real and intuitive. On the other hand, due to the excellent cutting performance and strength of plastics, plastic prototypes, especially ABS plastic prototypes, have become the most widely used prototypes. The processing of metal prototypes is relatively slow. At present, most of the raw materials are aluminum alloys and other easy-to-cut metal materials, mainly for high-end products.

However, the cutting of plastics is not so easy. Plastics have hygroscopicity, poor thermal conductivity, low melting point, poor selection of cutting parameters, and easy melting and deformation. On the other hand, if the cutting amount is too small, the timeliness, economy, and competitiveness of the product model cannot be reflected.
Let’s do a detailed analysis of this.

Plastic Classification

1. Thermoplastic

 Thermoplastics melt or soften when heated, and harden after cooling. This process can be repeated and reversible many times. Such as polyvinyl chloride, polypropylene, polyethylene, polystyrene and their copolymers ABS, nylon, polyoxymethylene, polycarbonate, polyphenylene ether, etc. belong to this category of plastics.
Thermoplastics are easy to process and form and have better mechanical properties. They are engineering plastics with better properties among plastics. However, the heat resistance and rigidity of thermoplastics are generally low.

2. Thermosetting Plastic

 Thermosetting plastics can be cured at a certain temperature after a certain time of heating or adding a curing agent. The cured plastic is hard in texture and does not dissolve in the Ming agent. Heating can not make it soft and no longer plastic. They will decompose if the temperature is too high. Such as phenol, unsaturated polyester, amino, epoxy, pyran, PDAP (diacrylic phthalate), etc. belong to this type of plastic.
Thermosetting plastics have good heat resistance and are not easily deformed under pressure.

Plastic Martial Characteristics

 Plastic has a series of excellent characteristics, such as:

1. Density is small

Usually the density of plastic is 820 ~ 2200Kg /m³, only 1/8 ~ 1/4 of steel,  is about 1/2 of aluminum, which is particularly convenient for prototypes making.

2. Very low thermal conductivity

Generally, the thermal conductivity of plastic is only 1/175 ~ 1/475 of steel.

3. Higher specific strength

If the strength is calculated by weight, some plastics are the strongest materials in modern machinery.

4. Large expansion coefficient

The thermal expansion coefficient of general plastics is about 3~10 times that of metals, so that the size of the parts changes greatly during cutting and use, which causes certain difficulties in cutting, especially when cutting with size tools. The amount of expansion of the material must be considered.

Plastic Material for Prototype Analysis

1 ABS

abs plastic

ABS is the most commonly used prototype model. ABS is a linear polymer material made of acrylonitrile (A), butadiene (B) and styrene (S). It is pale yellow or white. The specific physical properties are shown in the table below. , The density is similar to that of water, the mechanical strength is high, and the cutting performance is good. It can be easily processed by turning, milling, planing and grinding. But the heat resistance is poor, and the heat distortion temperature is 78°C-85°C. Therefore, it is necessary to prevent heat generation during processing.

ABS Properties
Density 1060  (Kg /m³)
Heat distortion temperature 78 – 85  (℃)
Coefficient of linear expansion 8.6-9.9   (10-4/K)
Tensile strength  21-28  (MPa)
Tensile modulus of elasticity 0.7 ~ 1.8  (GPa)

There are formed ABS plates, rods and tubes on the market. When making a prototype model, you can choose appropriate materials according to the shape of the prototype. ABS material has good chemical stability and good colorability. The surface is polished or polished and painted. The surface can be subjected to subsequent treatments such as printing, spraying, and gold spraying as required.

2 PMMA

PMMA (Acrylic Plastic)

PMMA, Polymethyl methacrylate. The main advantage is that it is transparent and can pass through 92% visible light and 73% ultraviolet light. It is especially suitable for models that need to observe the internal structure.

The disadvantage is that the surface hardness is low, the heat resistance is not high, and the thermal expansion coefficient is large. After the plexiglass is processed, the processed surface is relatively rough, no longer transparent, and requires polishing.

PMMA Properties
Density1170 – 1200 (Kg /m³)
Heat distortion temperature95  (℃)
Coefficient of linear expansion7   (10-4/K)
Tensile strength 56-80  (MPa)
Tensile modulus of elasticity2.45 ~ 3.15  (GPa)

PMMA is transparent, translucent, opaque, and the color is colored or colorless. Generally, the production of hand model is colorless and transparent. The plexiglass material has high strength and convenient bonding. It can be bonded with chloroform, acetone, trichloroethane, etc.

3. POM

antistatic pom board

POM is a tough and elastic material that has good creep resistance, geometric stability and impact resistance even at low temperatures. POM has both homopolymer materials and copolymer materials. Homopolymer materials have good ductility and fatigue strength, but they are not easy to process. Copolymer materials have good thermal and chemical stability and are easy to process.

Both homopolymer and copolymer materials are crystalline materials and are not easy to absorb moisture. The high degree of crystallinity of POM leads to a very high shrinkage rate, which can be as high as 2%~3.5%. There are different shrinkage rates for various reinforced materials. Melting temperature: 190~230℃ for homopolymer materials; 190~210C for copolymer materials.

Typical use: POM has a very low coefficient of friction and good geometric stability, especially suitable for making gears and bearings. Because it also has high temperature resistance, it is also used in pipelines, valves, pump casings, etc.

4. PC

PC board

PC polycarbonate is an amorphous engineering material with particularly good impact strength, thermal stability, gloss, anti-bacterial properties, flame-retardant properties and anti-pollution properties. Melting temperature: 260~340℃. The notched impact strength of PC is very high, and the shrinkage rate is very low, generally 0.1%~0.2%.

Combining the advantages and disadvantages of the above-mentioned plastics, it is obvious that they have some very different properties from metals. Therefore, in the cutting process, compared with the metal cutting process, there should be its own unique laws.

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4 thoughts on “Plastic Material for CNC Machining Prototyping”

  1. i, I make wall art and signs with my CNC Router. I have been doing prototypes made out of various inexpensive materials: Foamular from HD, drywall, white insulation foam (for garage doors). Do you have any suggestions?
    Great article!!

    Mick

    1. Hi, Mick,
      You need to tell us your more specific needs before we can give you advice. For example, in our industrial prototypes, if we only consider low prices, our commonly used materials are PVC, PP, etc.

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