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A Guide to Machining Plastics 

Written by MS
19/10/2020 12:00:33


In last week’s blog, we took a look at the Plastic Injection Moulding Process and its prevalence in contemporary culture that allows for the cost-effective mass-production of items such as syringes and children’s toys. You can read our comprehensive guide on injection moulding here. 
 
To follow on from this topic, we thought this week it might be useful to dive into the world of plastic machining. There are several ways of plastic machining and the reasons one might adopt this method vary, but in this blog, we are going to highlight the main types of machining and reasons for the process. 
 
One of the main benefits of plastics is the wide range of materials available to us. There are incredibly strong plastics such as polycarbonate, but also more malleable materials that can easily be moulded when heated and, in some cases, reformed over and over again (these are known as thermoplastics). 
 
As a result, plastics can often be moulded into a finished component, and complicated shapes, holes and grooves can be cut into the material, allowing for complex and intricate machinery to operate. The sheer availability and adaptability of plastic components now far outperform metal alternatives. 
 
Nonetheless, plastic machining can be a costly process. The tools needed can be expensive and the level of expertise it takes to operate the machinery also leads to an increased cost. Moreover, it may take substantial time to develop an accurate component/product, adding any intricacy to the machining process. 
 
Main Methods of Machining Plastics:
 
CNC Machining:
 
Computer Numerical Control (or CNC) Machining allows for the cutting of complex shapes and components. It is an automated method of manufacturing that utilises a variety of machining tools including milling, sawing and even 3D printing - all of which are operated via a computer. 
 
In short, one can upload a schematic into select computer programmes (such as G-Code and M-Code) that can then be read, interpreted and machined. In addition to plastics, woods, metals, ceramics and/or composites can also be machined via this method. 
 
Milling:
 
The milling process is something that can be dated back to the late-18th century and involves using rotary cutters to remove material from a piece. This can be done on various axes and directions to allow a wide range of products to be created. 
 
Now, the milling process can be operated via computer models, much like CNC Machining, to create precise components. Nonetheless, a milling machine can also be operated by hand as a form of lathe work. 
 
Sawing:
 
Sawing is fairly self-explanatory. It involves the cutting and separating of plastic material. This could be used for cutting large plastic sheets into more workable sizes. 
 
Turning:
 
This a method intended for products or components that need to be round or circular. It involves the spinning of the plastic while a chisel-like element removes the surface and creates a rounder end-product. 
 
Laser Cutting:
 
Laser-cutting is a machining method that is usually reserved for acrylics and cannot, largely, be used for thermosetting plastics. Much like CNC Machining, it utilises a computer model and then cuts the shape uploaded directly on the plastic material. 
 
This process will always leave a high-quality finish as the high-powered laser will effectively melt, burn or vaporize the unwanted material. 
 
Punching:
 
When thinking about punching, it is useful to imagine a cookie-cutter as this process involves using a metal component to, literally, ‘punch’ out shapes into a sheet of plastic. This can usually only be done on more malleable plastics and can be operated via computer or by hand. 
 
Hot-Knife Cutting:
 
This method is like a ‘low-tech’ version of laser cutting. Softer plastics can simply be cut using a heated element or knife. You typically see this method being used to cut foam boards or polystyrene-type plastics. 
 
Water Jet Cutting:
 
In this process, a high-powered jet that consists of a mixture of water and an abrasive substance is used to cut through particularly tough materials. It is primarily reserved to trim fibre-reinforced thermosetting plastics, which one could not cut with conventional knives or through a heat-generating method. 
 
As there is no area of the component heated during the process, its overall structure and intrinsic properties will remain the same. Hence why this machining method can be used to trim or edge components or products. 
 
Ultrasonic Cutting:
 
Ultrasonic cutting is a manufacturing method that uses high frequency, low amplitude vibrations of a tool against a material’s surface, in the presence of abrasive particles, to remove layers from the material itself. Again, this is a method of machining that is computer-operated. 
 
One of the drawbacks of this machining method is it can be slow to remove layers. Drilling deep holes into plastic can also cause issues as the abrasive slurry may not be able to reach far enough into the material.  
 
Nonetheless, the ultrasonic method is perfect for machining more fragile materials, including glass, without breaking or altering the structure as there is no distortion of the material worked. 
 
The Benefits of Machining Plastic Components:
 
As previously mentioned, machining plastics is a key way of creating more complex parts and components. It avoids the high costs of mould-making that come with the injection moulding process, and plastics can typically be machined dry. 
 
The machining process can offer short lead times and allow for test - or trial - pieces to be made easily. This helps you see whether a component operates correctly before committing to the manufacturing of countless products. 
 
Plastic components are quickly becoming more popular than metal counterparts. Plastics are a cheaper material that can operate in a wider range of special environments (ie. high heats, nuclear, and among acids and bases), positioning them as a superior material to, say, steel alternatives. 
 
What’s more, is plastics can be manufactured to become incredibly resistant materials, this will help reduce the maintenance required on any machinery, effectively eliminating expensive and unexpected downtime in your business. Plastics will help you increase productivity. 
 
Compared to metal components, plastics typically create less friction and thereby heat when in operation. This slows the natural wear and tear of plastic components, saving you money in the long run and making your business run more efficiently. 
 
We are experts in plastic components, with over 50 years of experience behind us, that’s why our manufacturing business, Barkston Ltd, services all businesses from OEMs to SMEs and all industries from big pharma to nuclear and even food. If you want to discuss the transition to a plastic-based system, get in contact with our qualified team today: service@barkstonltd.co.uk
 
We hope you have enjoyed this cursory look at the plastic machining process and the primary methods of creating plastic components that work. There are dozens of different machining methods - some are recent inventions while others can be traced back by hundreds of years. 
 
With that said, as the machining process becomes more evolved, we can create more precise and complex plastic components that will serve your business. Plastic machining is a surefire way to create products that improve efficiency and reduce wear and tear. 
 
What plastic process or topic should we explore in next week’s blog? Let us know on social media! We can be found @barkstonplastic on Twitter and Instagram! 
 
 
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