Plastic Extrusion Manufacturing vs. Other Processes | Pexco

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Plastic Extrusion vs. Injection Molding & Other Processes

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Choosing the Right Plastic Manufacturing Process

When you are designing a part that you think is a good candidate for plastic, consider the following factors when selecting a manufacturing process:

Form:  Do your parts require tight tolerances or have complex features?  Your end use and needs determine what is required in your parts.  The geometry of your design may limit conventional manufacturing options, but we can help with design for manufacturing (DFM) optimization to make the best trade-off between price and meeting your specific needs.

Volume/cost: What’s the annual volume of parts you’re planning to manufacture? Some manufacturing processes have high up-front costs for tooling and setup but produce parts that are inexpensive on a per-part basis. Alternatively, some low volume processes have low startup costs, but due to slower cycle times, less automation, and manual labor, cost per part remains high. 

Material: What is the end use of your parts?  What are the environmental stresses on your part (UV, chemical, heat, abrasion, etc.)? The optimal material for a given application is determined by a number of factors. Cost must be balanced against functional and aesthetic requirements. Consider the ideal characteristics for your specific application and contrast them with the available choices in a given manufacturing process.

Lead time:  How quickly do you need parts produced? Some processes create first parts within 24 hours, while tooling and setup for certain high-volume production processes can take months.

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Pexco’s core competency is extrusion and we’re here to help and guide you with your next project!  This list is simply to help you determine the right process for your part.  If you’re still confused, please don’t hesitate to give us a call and we’ll help guide you through the process.

Suited for long, hollow formed applications like tubing, pipes and straws or open profile products such as window frames, flooring molding and edge strips.  It has a much lower cost of entry than other typical forms of plastic manufacturing.

While other forms of molding use extrusion to get the plastic resins into a mold, this process extrudes the melted plastic directly into a die. The die shape, not a mold, determines the shape of the final product.

Extrusion molding involves forcing melted plastic through a die into a shape with a fixed cross section. It’s an efficient way to produce many shapes. Since the plastic is melted from a solid form and then resolidified, only thermoplastics can undergo extrusion. The extruded part is cooled and can be cut or rolled for shipment.

Accounts for about 80% of the durable plastic items we find every day. Suited for high-quality, tight tolerance, high-volume part manufacturing.  Injection molding uses a mold or die made from aluminum or steel. The mold consists of a core side and a cavity side that is placed into a plastic injection molding machine. This machine heats the raw plastic resin pellets until they’re molten, injects them into the empty cavity of the mold under great pressure, and then opens to eject the finished part.

During blow molding, gas pressure is used to force molten resin into a mold cavity. The process is easily controlled and repeatable and is commonly used for transparent plastic drinking bottles. It makes for excellent surface quality but it’s not ideal for thin walls.

Rotational molding also uses a core and cavity mold tool, but the manufacturing process is quite different.

Plastic powder is poured into the cavity of the mold, and the mold placed in an oven. While being heated, the mold is slowly rotated on two axes. Gravity is used to stick the plastic to the tool walls and build up the correct thickness.

Rotational molding is best for large containers with thick walls, such as products for outdoor use like canoes, tubs and playground equipment. 

RIM is most often used in the automotive industry because it produces lightweight parts that have a rigid skin. This skin is easily painted to make body panels, dashboards and other car parts.

Vacuum casting is a great choice for making a small number of high-quality rapid prototypes without a big investment in tools or material.

A master model of any rigid solid (often this is a 3D printed master pattern) is placed into a sealed box that’s then filled with a flexible urethane or silicone. When the master is removed, a cavity is formed inside the mold that can now be filled with plastic resin to form a copy of the original. Vacuum pressure is used to pull air out of the mold so that it fills completely with no air bubbles.

This is a type of vacuum forming, where thin or thick gauge plastic sheet is placed over a die, heated to a temperature that allows the material to become pliable, then is stretched over the surface of the die while vacuum pressure pulls the sheet down and into its final shape.

In industry, it’s used for plastic cups, lids, boxes and plastic clamshell packaging, as well as for auto body parts in thicker gauge material. Only thermoforming plastics are suitable for this process.

The raw material is pre-heated and placed inside the open cavity of a die. A cap or plug is used to close the die and apply heat and pressure, causing the plastic to cure. This process is great for rubber keypad switches, gaskets, O-rings and other soft, pliable thin-walled parts.

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