Plastic Injection Molding vs. 3D Printing

Plastic injection molding generally entails making plastic containers using the pelleted or granular plastic resins. For PET bottles, stretch blow molding machine is normally used to achieve the same. In injection molding variety of materials are used, these include the polystyrene, polycarbonate, polypropylene, polyvinyl chloride and others. There are many processes involved in injection molding, these include clamping, injection, solidifying and finally ejecting the product.

On the other hand, the 3D printing process is still generally new given that it has just been on the scene for around five years. Its oddity joined with misguided conceptions for its capabilities of doing well more than plastic injection molding. In 3D molding, materials such as ABS plastic, nylon, steel, wax, PLA, polycarbonate are normally used.

Contrasts between Plastic Injection Molding and 3D Printing

These two procedures are comparable from numerous points of view. For instance, they are both used to make complex shapes from plastic; be that as it may, it is likewise vital to take note of the distinctions. These differences include:

  •    Costs

The forthright expense of 3D printing is low, however, can possibly go up because of misprints. The expense of injection molding is moderately high at first, yet that expense goes down throughout a high-volume generation run.

  •    Technical Issues

Programming glitches keep on plaguing 3D printing however these issues don’t influence injection molding. Settling these issues is regularly expensive and tedious.

  •   Time

Injection molding includes infusing polymers into shape and after that quickly cooling them with the goal that another cycle can begin. On the other hand, the melded type of deposition modeling of 3D printing necessitates that a plastic fiber is melted and used as a drop when making a printed product. This process in 3D printing consequentially takes hours. The outcome is that plastic injection molding is a significantly quicker alternative.

  •    Quality

The quantity of 3D printable materials is also limited when contrasted with the number for injection molding. Parts that are 3D printed will consequently not have indistinguishable properties from injection formed parts. For example, injection shaped parts will have more tightly resistances when contrasted with 3D printed parts.

Those distinctions are the reason most makers pick plastic injection molding more than 3D printing for a genuine generation. Always ensure that you buy a stretch molding machine that will improve the production rate while delivering high-quality plastic products.

Reasons why PET bottles are widely used

PET material also known as PETE is an ideal polyester material for making injection molded parts including bottles and jars. PET is made of elements that have special grades making it good for wide range of application. It is composed of long-chain molecules having repeated units that make it linear thermoplastic. PET blow molding machine is a machine that enables the production of PET bottles through injection molding and blowing processes.

The first step of molding is the production of PET preform through the injection process. The PET material is first heated to form a preform, and while it is hot, it is passed through the injection cavity before it is finally blown to get the desired bottles. A PET material offers a wide range of application that includes bottles for carbonated drinks, water, juice, and beer among others.

Why is PET bottles recommended?

The reason why PET bottles are preferred is that it has the following properties:

  •    Strength– most bottles required for packaging drinks such a beer should have specific qualities. PET material is made of long-chain molecules that can withstand high temperatures, impact, and stretch. This polyester material is also resistant to most chemical products. Industries that make liquid products with reactive elements, PET materials are usually the ideal choice.
  •    Clarity–for drinks made for consumption, clarity is an important aspect. A consumer has to see and check the content before buying it. With PET material, clarity can be achieved easily by subjecting it through a low-level crystallization.
  •    A color-most product is colored and requires clear bottles, PET bottles are clear and will be ideal for displaying soft drinks for consumers.
  •    Purity– most drinks should be packed in containers that can keep the original taste of the drink. For instance, water should be packaged in a plastic container that ensures that it remains odorless and tasteless for long. With PET bottles, it can keep drinks for a long time without getting instilling a foreign flavor.
  •    High melting point– PET materials can withstand up to 270 degrees temperatures; this makes it ideal for most products that are channeled through hot temperatures. With an increase in temperatures, PET bottle molecules usually become mobile making them uncoil instead of breaking.
  •    Barrier– some drinks such as beer requires high performance barriers compared to other CSD applications. Such a product has to go through different channels of distribution, and without proper strength level, it can be affected. PET bottles are usually designed in such a way that it can withstand different levels of temperatures, pressure, humidity, and storage time.

Most PET bottles are made of wear resisting, transparent, corrosion-resistant and wear resistant material. They are widely used for packaging carbonated drinks, water, cosmetics, oils, and pharmaceuticals.

Why a two-stage method is recommended for making PET bottles

Why PET plastics are molded using high temperatures compared to another form of plastics. This is because PET materials have a high melting point of about 270 °C which can sustain high-temperature injection molding. Apart from melting point, PET products are preferred due to their fluidity. In most cases, PET molding uses hot runners where gate valves are selected to ensure management of fluidity is in point. PET molding machine operates in two ways; one is through the hot preform while another one is cold preform where it involves two steps.

Hot preform method (one-step method)

In the hot preform method, one integrated machine incorporates all processes converting the PET granules into complete bottles. The injection molding usually happens by channeling the preform through the injection cavity and then finally stretch blown to come up with a bottle. In this method, there is no heating required as the preforms are molded directly without being stockpiled. Hot preform method is most recommended for small-medium industries that require minimal production scale.

Two-stage method

In the two-step method, it uses two different molding machines. The preform first goes through injection molding first before it is heated again and blown. This process requires an injection molding machine and blow molding machine. The injection machine produces the preform while the other one reheats the preform before it blows.  When acquiring the heating system for the preform, you should first ensure it has low thermal efficiency. This two phase method is suitable for both medium and large scale producers.

 Why is the two-stage method recommended?

Here are the reasons why a two-phase process is preferred and widely used for PET bottles:

  1.   Drying of PET material is done before the injection molding. PET has to be free from moisture, and this is done by dehumidifying drying.
  2.    Plasticizing the PET- during the molding process, you have to compress and rotate the PET pellets in a rotational screw.
  3.    The injection of a molded PET is usually done through an injection cavity and has to be cooled rapidly to make a preform.
  4.    When heating the preform, the temperature level has to be adjusted to produce the correct profile ideal for blowing.
  5.    During the PET bottle production, the hot preform has to be stretched and blown simultaneously to form the required bottles.
  6.    PET container ejector is required where the finished bottle is ejected.

When PET is subjected to high temperatures, its chain-like molecules become mobile making the preform to stretch. With the help of PET molding machine, biaxial orientation can be achieved; in this case, PET is stretched from two different directions at right angles. This makes the molecules to align themselves in the direction of stretch. PET products are usually reliable and can sustain chemicals, impact and different barriers.

Blow Molding

Blow molding, also known as BrE molding, is a manufacturing process where hollow plastics are inflated with hot thermoplastic perform to produce a bottle or a container that conforms to the mold cavity. This process is also used in glass bottles production. Blow molding usually begins by melting down the plastic material into a parison. A parison is made up of tube-like plastic that has a hole where compressed passes through it. After melting, the parison is clamped into a mold, and compressed air is passed through it pushing the plastic out that matches with the mold. When this plastic is cooled and then hardened, the mold will open, and the part gets ejected. There are three main different molding processes namely: •  Injection blow molding •  Extrusion blow molding •  Stretch blow molding Injection Blow Molding In this molding process, the plastic material is melted down and then injected through a core pin before it is rotated. The hot plastic material is then indexed to a bolding station where the material is allowed to cool. When processing PET material, it is critical for the core pin to be cooled. After getting cooled, the bottled made is then indexed to a station where it is ejected. This process compared to extrusion molding process allows precise detail in the threaded (finish) area. There is minimal improvement in physical properties in the injection molding process since there is little orientation occurring. Moreover, the injection process is usually limited to manufacturing relatively small process. Eastapak polymer 1991 is usually implemented in injection and stretch blow molding processes. Stretch Blow Molding Stretch blow process involves the production of objects that are hollow in shape through the biaxial molecular orientation. This orientation provides an enabling environment where physical properties, gas barrier properties, and clarity are enhanced. Stretch blow process is very critical, especially when producing bottles meant for carbonated beverages. There are two distinct techniques of stretch blow molding. One is a one-stage process where injection molding is carried out in perform and then conditioned with proper temperature before getting blown into bottles. This process is continuous and is most useful in making products such as wide-mouthed jars that do not require a high production rate. On the other hand, the two-stage process involves injection molding of plastic material, storing it for a short time and then blowing it up into containers through a reheat-blow machine. This technique is best suited for producing high volume products due to the high cost of RHB equipment and molding. Extrusion Blow Molding This molding process begins by conventional extrusion of material through a parison (hollow tube) before it is indexed into a metal mold for cooling. Air is blown through the tube to inflate material into the shape of the mold then cooled sufficiently before it is open and ejected. The material is usually extruded between open blow molds until it reaches the required length. After the bottle is ejected, the excess plastic is trimmed either from the neck or bottom. In the extrusion process, different kinds of plastic can be processed including the PVC, PP, PC, HDPE, and PETG. It is suitable for the production of small units and requires relatively little capital.