Injection Molding

Table of Contents

Injection molding is the process of injecting molten plastic into a mold cavity in order to produce a part that is of the shape of that cavity. It is suitable for parts that need to be mass-manufactured, without the need to customize each part differently.

Almost every product we manufacture for our customers will get to a stage where additive manufacturing methods become insufficient and costly in the long run. Getting into injection molding is a serious undertaking and requires a few steps before any investment is made in the actual molds. 

Materials Used in Injection Molding

With injection molding, you can make parts using materials such as:

  • Acrylics (PMMA)

  • ABS 

  • Nylon polyamide (PA)

  • Polycarbonate (PC)

  • Polyethylene (PE)

  • Polyoxymethylene (POM)

  • Polypropylene (PP)

  • Polystyrene (PS) or High Impact Polystyrene (HIPS)

  • Thermoplastic elastomer (TPE)

  • Thermoplastic polyurethane (TPU)

  • Thermoplastic rubber (TPR)

The working principle of the injection molding is as follows,

  1. The feed material is heated to its melting point.

  2. Liquid material is forced through an injection port to fill a formed cavity (mold) at high pressure. 

  3. As the material cools, it solidifies into the shape of the mold. The finished product is then removed from the mold and the cycle repeats.

Injection molding is costly in the short run but economical in the long run. Injection molding has a low defect rate average of 5%. On average, 500 pieces can be produced daily. The average turnaround time from mold design to production is 35 days. If you need detailed lead time predictions for your project, please contact us. 

The maximum size depends on a multitude of factors, but shouldn't be a concern for those making products in the realm of IoT hardware. 

One reason why we say it's crucial to run the whole NPI process for each new project is because of the lock-in that comes with opening a mold. Once the mold is opened (manufactured), it's costly to make changes to the design. Keep in mind that the ownership of the mold belongs to you.

Coloring injection-molded plastics is simple, but getting it right exactly is challenging. Adding colors in the injection molding process can be done by adding dye pellets together with the initial resin pellets before melting the plastics into the mold. These dye pellets are to be adjusted according to your plastic of choice's natural color, which could range from clear, to brown or black. 

Molding and Tooling

Molds are hollowed out structures used to set the shape of the product to be made. These are typically made out of aluminium, steel, copper, and alloys. The material choice for these molds  are different according to the product's material.

Tooling is the process of choosing the appropriate tools: jigs, gauges, molds, cutting patterns, and other equipment appropriate for the product being made. Different products require different tolerance and clearance, which plays a part in deciding on what tools are to be used. Other than that, the product's material is also a core factor to be paid attention to.

Silicon or silicon rubber molds are also commonly used in plastics injection molding since it's relatively cheaper than harder metal molds. Silicon molds are generally flexible, chemical resistant, with great tear strength. These qualities make them appropriate to mold polyesters, polyurethanes, and even low-melting point metals. These silicon molds are often made using SLS 3D printing, which we also support.

Hot Runner System

Hot runner systems are systems of heated components used in injection molds to inject molten plastic particles into the cavity of the mold.

Hot runner systems are heated to ensure that the plastic in the runners and gates remains molten. Since there are heating rods and rings near or in the center of the runner, the entire runner from the nozzle outlet to the gate of the injection molding machine is under a high temperature, the plastic in the runner is kept molten. It is generally not necessary to open the runner to take out the condensed material after shutdown. For this reason, the hot runner process is sometimes referred to as runnerless molding.

Advantages of Hot Runner System

The main advantage of having a hot runner system is that it has negligible remaininog feed inside the mold. This means, it also:

  • Save raw materials and reducing material costs.

  • Shorten the molding cycle and improving machine efficiency.

  • Fewer follow-up processes and increased automation: There's no need to trim the gate and recycle the cold sprue and further processes, which is conducive to production automation.

  • Consistent quality of injection molded parts in multi-cavity molds improves product quality.

  • Reduces the possibility of deformation of thin-walled products, since lower injection pressure is used.

Common situational use of Hot Runner Systems

  • When the overall size of the product is large or when the product wall is thin.

  • When the requirement for product appearance or precision is demanding.

  • When the product yield is high.

  • When the material used in the product is thermally sensitive.

  • When the product requires special materials, such as high viscosity, low stickiness, and high forming temperature materials.

Differences from other manufacturing methods

Injection Molding vs 3D Printing:

If you want to see how different design decisions affect your product, use 3D Printing, if you have finalized your design and secured funds for a manufacturing batch, move to injection molding.

Injection Molding vs Die Casting:

The primary difference between die casting and injection molding processes is that die casting deals with metals and their alloys, while injection molding deals with plastics and polymers.