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How Injection Molding Works

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How Injection Molding Works

In this post I’m going to explain how injection molding works. Creating polymers is an amazing process. Then there is the question of forming the plastic or rubber into useful objects….another fantastic discipline. One of the most common methods of forming rubber or plastic resins is a process called injection molding. Injection molding is made possible by large machines called injection molding machines.

Material, either rubber or plastic resin is fed to the machine. This can be in the form of a hopper for plastic pellets or an auger for thicker, heavier compounds. Colorants are usually fed to the machine directly after the hopper. The resins enter the injection barrel by gravity though the feed throat. Upon introduction into the barrel, the resin is heated to the appropriate temperature to make it melt.

This now viscous material is injected into the mold by a reciprocating screw or a ram injector. A reciprocating screw provides the advantage of being able to inject a smaller percentage of the total shot1. The ram injector on the other hand, must typically inject at least 20% of the total shot. A screw injector can inject as little as 5% of the total shot. Many factors also come into play such as the type of mold, how the material is injected, etc., effect the shot.

The Plastic mold is a cavity in the machine that receives the material and shapes it accordingly. In order to make the injected material solidify, the mold is cooled constantly to a temperature which makes the solidification possible. The mold plates are forced together, usually by hydraulic force. The clamping force is defined as the injection pressure multiplied by the total cavity projected area. Molds are typically over-designed with regard to the pressures they must endure depending on the material to be cast. In addition, each injectionable material has a calculated shrinkage value associated with that has to be accounted for as well.

Some Typical Complications

Burned or Scorched Parts: Melt temperature may be too high. Polymer may be becoming trapped and degrading in the injection nozzle. Cycle time may be too long allowing the resin to overheat.

Warpage of Parts: Uneven surface temperature of the molds. Non-uniform wall thickness of mold design.

Surface Imperfections: Melt temperature may be too high causing resin decomposition and gas evolution (bubbles). Excessive moisture in the resin. Low pressure causing incomplete filling of mold.

Incomplete Cavity Filling: Injection stroke may be too small for mold (ie. not enough resin is being injected). Injection speed may be too slow causing freezing before mold is filled.

Injection Molding Materials

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Injection Molding Materials

Plastics are used as molted liquid to form the main ingredient in injection molding; the plastics that are used are polymerization, which basically means molecules that have had a chemical reaction and the properties change as a result. Plastics were first on the rise after World War I including new types of plastics called PVC and PS.

PS or polystyrene is a brittle but tough type of cheap plastic that is used to make airplane and car model kits and other little toys like that. They are used in plastic molding because the plastic can break down easily.

PVC has a great and respected reputation as a strong and sturdy plastic; you can do many things with it because of the strength of the material. PVC is used on fencing, pipes and pipe covering. PVC is molded and used in injection molding because when it solidifies it becomes a durable solid materials.

One of the best materials used in molding is nylon. Nylon is also called polyamide. This is the strongest and most flexible material you will ever find. Dupont began manufacturing nylon based products in 1939 and have a great and powerful fiber ever since. Injection molding is only as good as it’s materials.

So these are the materials used in injection molding. want to know more information about injection molding process? Go to https://www.hao-mold.com/

Contract Injection Molding

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Contract Injection Molding

When you are looking for a company to do a terrific job handling your custom injection molding contract. You want to make sure that they can cover your needs. If at all possible, tour the facility of where you are interested in having your work done. But you want to make sure their facility can handle the load.

You want a company that handles both a large and small volume of work. Some companies only will do a certain amount of work therefore they turn down small amount jobs. You want them to provide samples, you want to be able to see what kind of job they will do for you before you contract a huge order and do not like the work.

You want full production abilities, process optimization, and Insert molding and over molding, PPac capabilities. You also want packaging and domestic and international shipping capabilities. The company that you contract for your work, you want to handle the type of job you have for the price that you want.

That is why it is important to tour the facility to see first hand how the company will handle your job load. You want a guarantee that the job you give them will be nothing less than spectacular. This is what contract Plastic molding is all about.

Injection Molding Companies

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Injection Molding Companies

These are some of the top companies in the United States in the injection molding field. If you are looking for a great company with great reputations, check out these companies.

MOCAP, Inc, located in St. Louis, MO. They are a full service company; they are a manufacturer of standard and custom injection molding designs. They use all grades of plastic and they do a lot of volume and can handle as little or as much volume as needed.

Precision Tool & Die located in Derry, New Hampshire. They are an all purpose company, they provide custom manufacturing, service and a general manufacturer. They provide on site molding with perfect injection molds, they also do insert molds, transfer molds and they also do complete designs.

World Class Plastics located in Russell Point, Ohio, this company is also a custom manufacturer, a service and a manufacture company. Their company profile says they are QS9000 registered, they do custom thermoplastic injections, and they fabricate molds and tool design.

The G&F Industries located in Sturbridge, MA, they are a service and manufacture company. They are listed as an ISO 9000 certified company; they have a great reputation in the fabrication of injection Plastic Molding and plastic fabrications that use the injection molding process. They also use a robotic system and a real time production team.

Do you know any other injection molding companies that deserve to be mentioned here?

Injection Molding Questions and Answers

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Here are some frequently asked questions when there are problems in the process of injection molding, here some of the most popular ones and their solutions.

What happens when the molds are brittle and delaminate? The cause may be an improper injection screw. The screw that is used for molding at a low-pressure ratio fro the amount of resin being used; causes the plastic’s molecules to form incorrectly. Basically, a weak molecular structure can cause brittle parts. When this happens de lamination can occur as well. The result will be a to take a pressure reading and record the ratio. This should be performed once every six months.

Another problem may be discoloration; the possible cause for this may be excessive dwell time or what they call residence time. When a part has been discolored or changed the problem is usually found in the residence time. The material stays in the barrel too long, the base will become discolored. What can be done is the heat sensitive materials have to be set at a certain ration. After every injection shot clean out the barrel.

Discoloration may also be caused by an improper plastic mold temp. The hotter the mold is it will keep the material melted for a longer period of time. The temp of the mold should be adjusted to the supplier’s specs on material and cycle times.