Simple Guide To Plastic Machining, Fitting And Assembly

Plastic parts are produced by many different methods, but they are all divided into three categories: machining, fitting and assembly. The machining includes injection molding, blow molding and thermoforming. After these processes, plastic parts are machined to the final specifications and fitted properly. Lastly, they are fitted and assembled to other parts. Here is a simple guide for all three main processes.

Plastic Machining

The plastic machining is done to already molded and folded parts (as a secondary operation), but it is largely used in the fabrication of flat plastic sheet. People usually compare the plastic machining to metal machining, but these two processes are completely different. Plastic parts are more elastic, require lower melting temperature and exhibit 10 times greater thermal expansion. These differences demand changes in feed rates and cutting speeds. Plastic materials are divided into three different categories: soft plastics, hard plastics and reinforces plastics. To control the temperature during this process, coolants are required. Whether it’s a light cutting oil, water oil or clean compressed air, coolants must be used to prevent any adverse reactions with the plastics being machined.

There are a lot of machining processes that plastic machining includes. The primary types are:

• milling;
• sawing;
• turning;
• drilling;
• routing;
• laser cutting;
• waterjet cutting;

Plastics Fitting And Assembly

When it comes to fitting and assembly, people have been using a variety of methods. The plastic-to-plastic or plastic-to-metal fitting can be either done manually or automatically. For these fitting and assembly methods, there are few essentials:

• Welding – fusion of thermoplastic components;
• Hinges – for parts that require repeated opening/closing;
• Snap fits – essential fasteners that are molded into plastic parts that lock into place when assembled;
• Bonding – for creating strong bonds and permanent joints;
• Mechanical fasteners – rivets, eyelets, and screws.

Welding is one of the most important fitting and assembly methods and it is done in different ways.

• Spin welding – one plastic component is rotated against another stationary component at a great speed;
• Hot-gas welding – performed by passing gas/air over heating elements with a welding gun;
• Ultrasonic welding – high-frequency vibrations are used in the 15,000-40,000 cycles per second range, which results in both surface and inter-molecular frictional heat.
• Vibration welding – one component vibrates against another, generating fictional heat. The vibration can be either lineal or orbital direction.
• Staking – ultrasonic energy is applied to a protrusion that is later passed through the component to be assembled.