Short Guide to Finding the Best Plastic Injection Molding Company

Injection molding is a manufacturing process that’s highly popular with organizations that want to produce parts in large volumes. It is generally used in rapid prototyping, and it is invested in when parts need to be manufactured by the thousands or millions in succession, all bearing the same dimensions.

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The molds are typically made of metal and are hollow forms into which molten plastic is injected to make a desired product. Usually, these molds are made from stainless steel, and they have holes cut out in the middle, also known as mold cavities, that are in the shape of the product to be made. The number of mold cavities will vary based on the quantity of individual pieces and components needed during the production cycle.

Understanding the Three Categories of Plastic Injection Molding

Plastic injection molding can be classified into three main categories: (1) single-cavity injection, (2) multi-cavity injection and (3) family injection molding.

Single-Cavity Injection Molding – Single-cavity injection molds are singularly hollow and are used to produce a single piece at a time. This is a cost-effective, highly efficient method for producing parts in a low volume order, or parts that are complex or oversized. Single-cavity injection molding option gives production teams an advantage in that they can focus more attention to each individual piece to make sure there aren’t any flaws such as unfilled portions of the mold, air bubbles, or other types of errors. Finally, this option is not as expensive as a multi-cavity injection mold making the same piece.

Multi-Cavity Injection Molds – Multi-cavity injection molds boast numerous identical hollows. They give manufacturers the advantage of being able to inject molten plastic into all hollows simultaneously to create multiple pieces at once. Therefore, multi-cavity plastic injection molding offers short lead times, increases costs for large volume productions, improved product efficiency, and cuts back on delays.

Family Injection Molds – There are some similarities between family injection molding and multi-cavity plastic injection molding. But rather than having numerous identical hollows, every hollow possesses a different shape. This enables manufacturers to use these molds to create prototypes or even different products that can either be sold as solitary items or sold together in a variety pack. Keep in mind that this method is ideal for producing different pieces made from the same material, but the hollows must be arranged and sized without error. If the family mold is not balanced correctly, the molten plastic won’t be evenly injected and as a result flaws can occur.

When Should Companies Look for Custom Plastic Injection Molding Partners?

Of course, there are several standard injection molds on the market, however, there isn’t a perfect model for every unique project. Companies generally require custom plastic injection molding when products are required with the following:

High Precision Requirements – When it comes to suiting production demands, custom molds are designed down to every fine detail with high precision.

Exacting Standards – When it comes to highly regulated markets like the medical industry or aerospace, custom molds are made according to the client’s exact specifications.

Complex Designs – With custom molds one is not limited to producing standard designs. Rather, they can be tailored to fulfill any component’s size or shape meaning they can create highly complex and unique parts.

What Factors Go into a Successful Plastic Injection Molding Company?

As soon as your team has determined that plastic injection molding is the right manufacturing process, you will need to find the right partner. Laszeray is known for offering the best plastic injection molding services to a wide range of industries, and they can accommodate any project. When looking for the best plastic injection molding services, it is critical to look for the following factors:

• Do they have modern manufacturing equipment?
• What are their design and engineering capabilities?
• Do they use high-quality molding materials?
• Are they committed to the highest standards?
• Do they have the capacities for tight tolerances?

When booking consultations with several plastic injection molding companies, be sure to cover the above points with them to ensure you are truly getting the best plastic injection molding company capable of helping your organization.

Call Laszeray: The Best Plastic Injection Molding Company

Laszeray has the reputation for being the best plastic injection molding company because all our capabilities are achievable under one roof, and we have the best team in the industry. Capable of handling any project, in any industry, of any size, we can cover rapid prototyping, to create large volumes of complex products. Call Laszeray today and tell us all about your project and learn how we can help you get your product to market quickly, with flawless precision, and all while staying under budget.

How Does Injection Molding Work?

Tooling fabrication: Once an injection molding design is finalized the first step in the manufacturing process is to mill the tooling, which is typically fabricated from steel or aluminum. In most cases, the metal block of material is placed in a CNC mill, which then carves out a negative of the final plastic part. Additional treatments like polishing or laser etching can then be applied to the tooling to achieve specific surface finishes.

Part production: The actual production of plastic parts begins by loading resin pellets into a barrel. The temperature of the barrel is raised until the resin pellets reach a molten state and are then compressed. Next, the molten plastic is injected into the metal tool through a runner system, which then feed into the mold cavity through gates. The part then cools down, solidifies, and is ejected from the tool with ejector pins.

Types of Injection Molding

The term injection molding encompasses a handful of processes that inject liquid resin into a tool to form plastic parts. Here are four common types:

Thermoplastic injection molding: Thermoplastic injection molding is the most common type of molding. It injects thermoplastic resin into the mold where the material cools to form the final part.

Liquid silicone rubber molding: Liquid silicone rubber uses thermoset materials and a chemical reaction creates the plastic part.

Overmolding: Overmolding is a process used to manufacturing plastic parts with two or more materials. You’ll often find this on parts to improve grip by adding rubber to the handle.

Insert Molding: Insert molding is process that begins with an insert component placed into the mold before resin enters. The material is then injected and flows around the insert, typically metal, to form the final part. This is frequently used for parts that require metal threads.

Basic Design Principles for Injection Molding

Tolerances
With our injection molding process, we can hold about ±0.003 in. machining accuracy. Shrink tolerance depends mainly on part design and resin choice. It varies from 0.002 in./in. for stable resins like ABS and polycarbonate to 0.025 in./in. for unstable resins like TPE.

Wall Thickness
Wall thickness is important because it can lead to defects such as sink and warp. It is best practice to maintain a uniform thickness throughout an injection-molded part. We recommend walls to be no less than 40 to 60 percent of adjacent wall thickness, and all should fit within recommended thickness ranges for the selected resin.

Core Geometry
Core out parts to eliminate thick walls. You get the same functionality in a good molded part. Unnecessary thickness can alter part dimensions, reduce strength, and necessitate post-process machining.

Draft
Applying draft to molded parts is critical to ensure parts do not warp during the cool down process and it helps the part easily eject from the mold. Applying 1 to 2 degrees works well in most scenarios. If there are vertical faces, we advise incorporating .5 degrees of draft.

Side Actions
A portion of the mold that is pushed into place as the mold closes, using a cam-actuated slide. Typically, side-actions are used to resolve an undercut, or sometimes to allow an undrafted outside wall. As the mold opens, the side action pulls away from the part, allowing the part to be ejected. Also called a “cam.”

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Undercuts
A portion of the part that shadows another portion of the part, creating an interlock between the part and one or both of the mold halves. An example is a hole perpendicular to the mold opening direction bored into the side of a part. An undercut prevents the part from being ejected, or the mold from opening, or both.

Bosses
A raised stud feature that is used to engage fasteners or support features of other parts passing through them. There can be a tendency to design thick bosses which will increase the likelihood of sink and voids in a part. Consider reinforcing bosses with ribs or gussets for extra strength

Gates
A gate is an opening in the injection mold tool that allows resin to enter and fill the cavity. There are three common types of injection molding gates.

• Tab gates are the most common type of gate since it works well with additives and is the most cost effective option.
• Hot Tip gate is best for parts that cosmetic appearance is a priority. These gates can also reduce wear on tooling and flash.
• Pin, Post, or Tunnel gates  are ideal for cosmetic parts that don’t require a vestige. Sometimes not an option depending on material and geometry.

Ribs
A rib is a thin, wall-like feature parallel to the mold opening direction, its used to add strength and support to features like bosses and walls. To prevent sink, ribs should be no more than 60% of the wall’s thickness.

Ejector Pins
Ejector pins are installed in the B-side of the mold and help to release the plastic part from the tool after the part has cooled sufficiently. Designing in sufficient draft can help reduce the need for ejector pins on a part.

Logos and Text
Sans serif fonts will be the easiest to mill into a mold with text. We recommend font larger than 20 pt. and no deeper than 0.010 in to 0.015 in.

Commodity Resins

Polypropylene (PP): PP is a cheap material and good when cosmetics and rigidity aren’t a priority. Chemical resistant and good for living hinge designs.

Polyethylene: High and low density options. Is durable and chemical resistant.

Polystyrene: A hard thermoplastic that is cheap and clear.

Check out our guide to injection molding materials if you want to dig deeper into plastic selection.

Colorants and Resin Additives for Injection Molding

Stock colors from the resin vendor are typically black and natural. Natural might be white, beige, amber or another color. Semi-custom colors are created when colorant pellets are added to natural resins. For available colors, visit our materials page. There is no added charge for our inventory colors. They may not be an exact match and may create streaks or swirls in parts.

Resin Additives

Short glass fibers are used to strengthen a composite and reduce creep, especially at higher temperatures. They make the resin stronger, stiffer, and more brittle. They can cause warp due to the difference in cooling shrink between the resin and the fibers.

Carbon fiber is used to strengthen and/or stiffen a composite and also to aid in static dissipation. It has the same limitations as glass fibers. Carbon fiber can make plastic very stiff.

Minerals such as talc and clay are often used as fillers to reduce the cost or increase the hardness of finished parts. Since they do not shrink as much as resins do when cooled, they can reduce warping. 

PTFE (Teflon) and molybdenum disulfide are used to make parts self-lubricating in bearing applications.

Long glass fibers are used like short glass fibers to strengthen and reduce creep, but make the resin much stronger and stiffer. The downside is that they can be particularly challenging to mold parts with thin walls and/or long resin flows.

Aramid (Kevlar) fibers are like less-abrasive glass fibers only not as strong.

Glass beads and mica flakes are used to stiffen a composite and reduce warping and shrinkage. With high loading, they can be challenging to inject.

Stainless steel fibers are used to control EMI (electromagnetic interference) and RFI (radio frequency interference) typically in housings for electronic components. They are more conductive than carbon fiber.

UV inhibitor for outdoor applications.

Static treatments make resins dissipate static.