In the first few sections of the basics of mold design, we will mainly look at the theory behind mold design. In the subsequent sessions, you will be capable of designing the mold using SolidWorks.
Here is the table of contents for this part down below:
Injection molding is one of the types of large-scale manufacturing processes. In this process, a material is melted and poured (or injected) into a mold and allowed to cool. The hot molten material starts solidifying as the temperature drops to take the shape of the mold.
The raw material used for the injection molding manufacturing process is small plastic pellets, which are known as resins. These resins are dropped in a hopper through which they go into the injection barrel.
The plastic pellets in the injection barrel are driven forward by the rotation of a screw. These plastic pellets get converted into molten plastic due to friction. External heating may also be provided in some cases to melt the raw material.
The molten plastic is then injected through the nozzle into the mold. It then fills the region between the core and the cavity to take the shape of the mold.
The core is the convex region (also called the male part of the mold), which forms the inner surface of the component which is being molded. The cavity is the depression or the concave region (also referred to as the female portion of the mold) and forms the component's outer surface.
The material (molten plastic) filled between the core and the cavity is allowed to cool so that it solidifies before ejection.
The other components that primarily affect the mold are:
From the nozzle, at the end of the injection barrel, the material first enters the sprue. The sprue is a large channel in the mold, which receives the molten material from the nozzle. This sprue channel gets divided into several smaller channels called runners.
The runner carries the molten material to each section of the mold. The connecting channel between the runner and the part is called the gate.
Although there are numerous methods of manufacturing plastic parts, there are certain distinct advantages to using injection molding as a manufacturing method for plastic components.
Microinjection molding is one of the recent innovations in this field, which allows manufacturing plastic parts in micro tolerances. This technique will be useful in the medical industry or in building high-precision devices like watches.
The mold cycle can be defined as the amount of time it takes to complete a single injection molding process. The calculation of this time does not have a well-defined formula and depends on several factors like:
All plastics can be divided into two major types:
|Shape||Can be reshaped by remelting||Cannot be reshaped once formed|
|Surface finish||Very high||Poor|
|Example||PET, polypropylene, polycarbonate||Vinyl ester, epoxy resin|
When thermosets are heated, the polymer chains are attached through a process known as cross-linking, which gives them a permanent 3D shape and makes it more resistant to melting. However, since thermoplastics do not form such cross-links, they can be quickly melted. This property of thermoplastics makes it easier to shape them, which is why they are used to make plastic components using injection molding.
Most of the plastic car components (about 90%) are thermoplastics. As thermoplastics can be remelted and reshaped, they are also recyclable. In applications where excellent surface finish is required, like that of the interiors of luxury cars, thermoplastics will be used.
Generally, thermosets are more durable than their counterparts, thermoplastics. Hence, you can find thermosets in safety equipment like helmets and also in heavy industrial applications like load-bearing.
One of the disadvantages of using thermoplastics is that they cannot withstand high temperatures. So, applications where high-temperature resistance is required, like in engine parts, aircraft landing gears, and satellite structures, thermosets will be preferred.
In the first part, we have covered the basics of mold design in three topics, as discussed in the beginning. In the next section, we'll take a look at:
To start this course, visit Skill-Lync today.
Get a 1-on-1 demo to understand injection modeling course and how it can benefit you from an experienced career consultant.Request a Demo Session