How plastics are made: Plastic machining

Plastic is a material that many take for granted. Because it is so versatile and is found just about everywhere, covering just about anything, and can be used to do just about anything, it is important for plastics manufacturers to utilize the best and most efficient processes available.  One such popular plastics manufacturing process is called plastic machining.

How are plastics made?

First, a science lesson.  Plastics are made from organic products such as cellulose, coal, natural gas, salt and crude oil which is a mixture of multiple organic compounds. The process to produce plastic begins with distillation to separate heavy crude oil into fractions or lighter groups composed of hydrocarbon chains that have different size and ae composed of different molecular structure. A key element is naphtha which is a crucial to the production of plastic.

There are two major processes to produce plastic called polycondensation and polymerization. Both of these processes require catalysts to start the reaction. In the process of polymerization, monomers such as propylene and ethylene are conjoined to form a polymer chain. The polymers from this chain carry their own properties, are of varied length, and settle into different structures based on the monomers that compose the chain.

What is Plastic Machining?

plastic machining example

Plastic machining in action

What plastic machining actually does is reducing the large plastic component to a smaller one. Plastic machining is the use of a machine to slowly drill off a piece of plastic to eventually look like the desired product. It is a process where people can program a chisel like device to slowly carve out the plastic to eventually become the desired product. This process is similar to word carving where the product is created through the chiseling of small parts. It is a time consuming process but the product is worth it.

Plastic machining can be used for a variety of different applications, but typically for low volume and custom production. Further, it can be used to create molds to be used for mass production, described in the plastic injection molding process. It is important to understand that this is a time consuming process for specialty materials. It is not reliable or efficient for mass quantity needs.

What Plastic Materials are used in plastic machining?

Finding the right material to be used in plastic machining is important because if the wrong material is used, the product may not be as versatile or correctly used. More often, engineers require certain characteristics in order to make the best quality product.     Here’s some of the characteristics:

Load Strength (psi):

For structural applications,  compression strength (plastic under compression) and tensile strength (plastic in tension), particularly in its ability to withstand rotational wear from the application.  The type of plastic must be able to withstand the machining process, or it may break or tear.

  • Good Choices: Ultem, Peek, PPS, Nylon, Delrin
  • Poor Choices: Teflon, UHMW, LDPE, HDPE, Polypropylene

Structural stability:

Machined plastics are not as  structurally sound as metals, because they can absorb water and have a high coefficient of thermal expansion. The use of a stable plastic will ensure that the material has a low water absorption and thermal expansion coefficient.

  • Good Choices: Peek, PPS, PET, Ultem
  • Poor Choices:  HDPE, Nylon,  LDPE

Resistance to Chemicals:

This is important because the chemical resistance of plastic is variable. Some of the materials have a universal chemical resistance while others are extremely sensitive to chemicals and can crack on exposure.  Making sure that the plastic has a suitable resistance is important in the process of plastic mechanics.

  • Good Choices: Teflon, CTFE, PEEK, UHMW
  • Poor Choices: Acrylic, ABS, Noryl

 Cost:

The cost of the plastic does not outweigh the use of the product from plastic mechanics.

  • Less expensive choices:  Delrin, Polypropylene, HDPE
  • Expensive choices: Peek,   Radel HDPE, PPS

 Advantages of plastic machining:

  • No molds required in the process
  • Single tool used
  • Design can be altered
  • Cost efficient
  • Materials can be utilized
  • Multiple angles can be taken into consideration

 Disadvantages of plastic machining

  • Higher costs to produce plastics
  • Moisture absorption
  • Multiple types of plastic to consider
  • Time consuming
  • Not good for mass production

Plastic machining can be used to produce specific molds and other products in a cost efficient way. It is a growing business and can be used to create versatile adaptable products.