Common Secondary Machining Processes In Plastics Manufacturing
Common Secondary Machining Processes In Plastics Manufacturing
During injection molding, the workpiece first undergoes several rough cuttings to help it get close to the finished dimensions and shape. Afterward, there is cutting to achieve the final tolerance and dimension. The processes used include CNC machining, turning, milling, drilling, grinding, and tapping.

The secondary machining process is cost-effective for producing workpieces involving several processes. Several operations follow a planned sequence during the machining process to achieve the best results. Secondary machining processes follow primary manufacturing methods like CNC or injection molding. It's the final stage of manufacturing, and it helps in furnishing the surface finish, tolerance of the parts, and dimensional integrity when they finally come out of the press. Here are some of the common secondary machining processes versatile in plastic manufacturing.


This is a Computer Numerical Control(CNC), a secondary machining process that uses a round cutter to make holes in a workpiece. There are designed drill pressing machines used in this process, but a milling machine can also work. During the working process, waste products, also known as chips, form on the workpiece. However, the shape of the drill usually helps keep the chips off the workpiece, leaving it free of any debris. 


During milling, a multi-point rotary cutter curves gear teeth, deep threads, or slots onto the workpiece. Milling is a secondary machining process that provides a fining coat to the workpiece during the injection molding. In addition, it helps define features and services of the finished product, like contours, holes, pockets, or slots.


The turning process can either be done manually or automatically by rotating the workpiece while a cutting tool moves in a linear motion to create the final tube-shaped piece. The use of CNC allows for higher efficiency, production, and consistency. You can program all the speed, movements, and tooling changes with automatic turning into a computer. The instructions then get to the lathe, which then carries out the completion. The tools used in turning come in various shapes, and depending on the desired outcome, you can place them at varying angles.


A tolerance surface finish is vital in injection molding, which is why surface grinding machining operation comes into the picture. It uses a powered abrasive paste, wheel, or belt, giving the workpiece a fine-tolerance finish. Unlike other secondary machining processes, grinding offers a more precise tolerance modification of using an abrasive turning wheel.

CNC Machining

This automated secondary machining process used in plastic manufacturing helps control several complex pieces of machinery to help create different models of prototypes. These prototypes can be turning, lathes, mills, or grinders. CNC machining gives the major foundation of the machining processes, including modern machinery, chip-making tools, and presses.


Have you ever wondered how bottles get the grooves that allow their caps to fit? Well, this is achieved through tapping. It's the process that uses a conical thread or cylindrical cutting tool to help create grooves on the inside surface of the drilled hole. Like the turning process, you can easily program tapping on a CNC lathe, making a highly efficient and easy threading process. This gives the workpiece a final definite look, which will help determine its function.

Plastic manufacturing and parts assembling are becoming more common. And as such, more goes into designing the right injection mold that will, in turn, be part of an extensive assembly. This calls for late technologies to help handle post-molding operations like conditioning, inserting, and welding. Custom plastic injection molding needs precision which is why you need the expertise of a full-service contract manufacturer.