Understanding Injection Molding and Its Applications

What is Injection Molding?

Injection molding is a manufacturing process for producing parts in large volumes. It is most typically used in mass-production processes where the same part is being created thousands or even millions of times in succession.

Injection Molding Machine

Why Use Injection Molding?

The principal advantage of injection molding is the ability to scale production en masse. Once the initial costs have been paid, the price per unit during injection molded manufacturing is extremely low. The price also tends to drop drastically as more parts are produced. Other advantages include the following:

• Molding is very repeatable. That is, the second part you produce is going to be practically identical to the first one. This is a wonderful characteristic when trying to produce brand consistency and part reliability in high-volume production.

What Is the Downside to Injection Molding?

Upfront costs tend to be very high due to design, testing, and tooling requirements. If you are going to produce parts in high volumes, you want to make sure you get the design right the first time. That is more complicated than you might think.

Sintering is a heat treatment applied to a powder compact in order to impart strength and integrity. The temperature used for sintering is below the melting point of the major constituent of the powder metallurgy material.

After compaction, neighboring powder particles are held together by cold welds, which give the compact sufficient “green strength” to be handled. At sintering temperature, diffusion processes cause necks to form and grow at these contact points.

Sintering in the Powder Metallurgy Process

There are two necessary precursors before this “solid state sintering” mechanism can take place:

• Removal of the pressing lubricant by evaporation and burning of the vapors.
• Reduction of the surface oxides from the powder particles in the compact.

These steps and the sintering process itself are generally achieved in a single, continuous furnace by judicious choice and zoning of the furnace atmosphere and by using an appropriate temperature profile throughout the furnace.

Blow Molding is the process of forming a molten tube (referred to as the parison or preform) of thermoplastic material (polymer or resin) and placing the parison or preform within a mold cavity. The tube is then inflated with compressed air to take the shape of the cavity and cool the part before removing it from the mold.

Blow Molding Manufacturing Processes

There are three main types of blow molding:

• Extrusion blow molding
• Injection blow molding
• Injection stretch blow molding

The main differences among them are the method of forming the parison; either by extrusion or injection molding, the size of the parison, and the method of movement between the parison and blow molds; either stationary, shuttling, linear, or rotary.

Extrusion is a process in which metal or other material is forced through a series of dies to create desired shapes. Many ceramics are manufactured by extrusion because the process allows efficient, continuous production. In a commercial screw-type extruder, a screw auger continuously forces the plastic feed material through an orifice or die, resulting in simple shapes such as cylindrical rods and pipes, rectangular solids and hollow bars, and long plates. In metalworking, extrusion converts a billet of metal into a length of uniform cross-section by forcing the billet through the orifice of a die; aluminum is easily extruded.