Over Molding

Over mold & Over molidng

Over-mold injection molding is the same as insert-molding, where an existing component is loaded into a mold and plastic is molded around it to create a multi-material single part. Insert-molding is most synonymous with combining metal components with plastic in such products as electrical pin connectors. When the term over-molding is used, the metal component is simply replaced with a previously molded plastic part. Single-shot injection molding machines are used to produce both the plastic component and the over-molded plastic. Tooling for injection over-mold injection molding requires two molds; one for the plastic component and one for the over-mold. Over-mold injection molding requires labor to handle the plastic component and load it into the second mold. Over-molding is generally reserved for higher priced parts that can absorb higher machine time and labor costs.

If you are planning to go into a plastic molding business, you should first know the different processes. Choose from a plastic molding process that fits your budget, your expertise, and your resources. In Injection Molding, melted plastic is forced into a mold cavity. Once cooled, the mold can be removed. This plastic molding process is commonly used in mass-production or prototyping of a product. Injection molding machines were made in the 1930’s. This can be used to mass produce toys, kitchen utensils, bottle caps, and cell phone stands to name a few. Plastic molding is a very technical process. It needs experts in this type of manufacturing business for it to be competitive in the market. Therefore, a very scientific and systematic study should be first made before going into this endeavor.

Injection molding is an effective way to make custom parts. Granules of plastic are melted down and then injected into a metal mold; there the molten plastic hardens into a designated shape. Then you open the mold and a new part is removed, inspected and is ready to go. Injection molding is an incredibly versatile form of molding plastics. As with everything, injection molding has its ups and down so it is important that the ends justify the means for your project needs. There are three main components in the injection molding process. The injection apparatus itself which melts and then transmits the plastic, the mold, which is custom designed, and clamping to provide controlled pressure.

Thermoplastic injection molding is molding the most widely used of all plastic processing methods. The injection molding machine reduces pelletized raw material and colorants into a hot liquid. This “melt” is forced into a cooled mold under tremendous pressure. After the material solidifies, the mold is unclamped and a finished part is ejected. Injection molding offers the lowest piece prices available, but tooling prices are generally the highest. Thermoset injection molding is similar to thermoplastic injection molding except that uncured thermoset resins are mixed, injected, and held in the mold until cured. As with thermoplastic molding, the price per piece can be low, but the tooling prices are generally very high.

Purchasing the box, some assorted socket rails, and some additional clips for the socket rails, I took the box home with me to see how well it would stand up as a replacement. The box is quite simple in construction. It’s a plastic injection molded case made of a very thick plastic. The case consists of a flip open lid (with two latches that are padlock compatible) covering a deep top storage area, and three drawers that are very similar to the large rolling tool chests that many professionals and advanced amateur home mechanics have in their garages. When you flip the lid open, the lid will immediately release the latching mechanism for the three drawers. Unfortunately, the lid does not contain any hinges or tethering that prevent it from flopping open and hitting itself on the back of the tool box. This was my only gripe involving the tool box.

Electrical Discharge Machining And Mold Making

   The use of electrical discharge machining is so essential that it is almost impossible to imagine a modern shop without an EDM machine. Many of today’s products simply could not be produced without it. Think of all the cell phones, calculators, IPods, cameras, medical devices and the endless amounts of high tech equipment that are made out of plastic!

Besides the essential role it plays in plastic injection mold making, EDM is used for the precision machining of medical parts, aerospace parts, and other highly specialized products. Electrical discharge machining, including Wire EDM, has also completely changed the way molds are made, as well as other specialized parts.

This is your information source for the EDM die sinker

Graphite  Copper EDM Tooling EDM Oil
EDM Filters Specialty Electrodes Carbide EDMing Surface Finishes

Check out the pages dealing with graphite, graphite dust, copper, dielectric fluid, electrode holders, and machinery.

What about jobs in EDM?

Find out what kind of personality it takes to have electrical discharge machining as a career job. See what the future holds in this high-tech profession.

You can also find educational material that attempts to explain this rather mysterious process. Not so long ago, it was as much black art as science. Today, however, much of the mystery is removed due to CNC controls.

Most shops send their operators to classes put on by the manufacturer of their EDM machine. It is foolish to invest so much money in a machine and skimp on the training! But it happens all the time.

What about EDM and stress?

EDM is quite a stressful occupation, to put it mildly. It may not appear difficult, but the stress levels can be exhausting. Nearly every mold component that is EDM’d is in the final stages of manufacturing. The slightest mistake can become very costly, very quickly.

There is nothing quite like the feeling of coming to work in the morning and seeing your supervisor leaning over the EDM machine staring at your workpiece. Then you find out that you had mixed up two locations and the completely finished cavity block is now completely useless!

Injection Mold Design

Plastic injection molding for producing plastic products

Plastic injection molding is the principal process for producing plastic products or parts of products. Plastic is acknowledged to be a very flexible and cost-effective material that is used in many applications. Although the tooling can be expensive, the cost, per part is very low. Intricate geometries are limited only to the abiltiy to create the injection mold. Things you use everyday, such as the case that houses your monitor, the keyboard on which you type or the mouse on your desk were produced with plastic injection molding.

Plastic injection molding involves the transformation of a plastic solid, usually in the form of granules or pellets, and heating the plastic resin to a specific temperature until it melts. The melt is then forced into a mold made up of two or more dies, where it is forced to “cool”, resulting in producing the desired shape. A specific amount of time passes, usually a few seconds, and the mold is then opened and the part is released. This cycle then repeats continuously until the desired quantity is reached.

Considerations of  Injection Mold Design

The design of the part, and therefore the mold, needs to include draft features (angled surfaces) to make possible the removal of the part from the mold. Typical draft angles are about 1 to 2 degrees for part surfaces which do not exceed five inches. Dimensional tolerance specification will dictate the final cost of the part as well as its ability to be manufactured. If there is a small section of the part which needs higher tolerances, such as the location of a critical feature used for alignment,do not specify a tight tolerance, as an alternative, plan and design for post molding processes such as machining to achieve the desired results.

Radii and Corners

It is very important that uniform wall thickness be maintained at the corners. The internal and external radius need to share the same center point. External radii = internal radii + wall thickness. The minimum radii should not be less than ¼ of the minimum wall thickness. Design for radii to be ½ to ¾ of the nominal wall thickness. When a large amount of stress is going to be present, it is very important to design in larger radius as this will distribute the stress much more evenly.

Wall Thickness

The production of thin wall items such as a clamshell for retail packaging are possible with today’s technology. Products with thick walls are also easily produced. However, parts which require uneven wall thickness present a challenge to the plastic molder manufacturer. Creating a part with a uniform wall thickness and cross section will abridge manufacturing and reduce costs. One issue to be aware of is sinking. Wherever an intersection or “tee” occurs, there will be some degree of sinking. This occurs because thicker walls cool at a slower rate and therefore create this problem.

Ribs

Ribbing should be ½ to two thirds of the nominal wall thickness and less than 3 times the thickness in height.A taper of 1° is usual. Note: as mentioned above, excess thickness can result in shrinkage.An excess in rib height combined with a taper will produce thin areas requiring extra fill time at the mold.

Weld (Part) lines

The location of weld lines needs to be considered by designer before a injection mold is created. Weld lines are formed by the joining of the flow fronts of the plastic during molding. One issue of concern is the that the weld line area is more susceptible to cracks and stress failure.

Bosses

  • Diameter = (Outside Diameter) \ (Inside Diameter) = 2 to 3
  • Thickness = 1/2 to 2/3 nominal wall thickness
  • Gusset Height = 2/3 Height
  • Height = Fastener minimum requirements
  • Taper = 1 deg. all around
  • Diameter Ratio should be minimum ratio of 2., this will reduce risk of failure.

Pressure:

Another factor in the design will be the clamping pressure required to produce the part while the plastic is being injected. Smaller cavities can result in high pressures being required to force the plastic or rubber material to fully fill the mold cavity. This will, in turn, determine the thickness of the mold material, usually steel) as well as the type of machine in which can be used.

Summary:

Many factors must be taken into account when designing a mold for the creation of plastic injection molded parts. Factors such as draft angles, wall thickness, ribbing (not the kidding kind), bosses and weld lines and clamping pressure all come into play when designing a mold that will be used in a plastic injection mold machine. Each facet is important in and of itself, but as a whole, each one affects the others. Therefore the design of a mold for plastic molding can be quite involved. When done correctly, the result will be a mold which will yield thousands, hundreds of thousands, or even millions of parts over it’s lifetime.

Used Injection Molding Machines

Used Injection Molding Machines

There are constantly new techniques and new technology in the industrial world of injection molding. New machines, new plastics, new equipment. There are some companies that keep up with other companies by buying a lot of expensive equipment the second it comes out.

But these are the companies that cost so much because they have to charge more to pay for the price of the new equipment they just bought. But then you have the companies that like to keep using used machinery because they are just as good as new and as the old saying goes if it isn’t broke don’t fix it. Not every company wants to be the fancy company with all new machines.

Some companies want to just be known as the company that did my job in the most outstanding way. They want the recognition for a job well done rather than for the company who spend a lot of money on a piece of new machinery.

Companies that keep using used machinery don’t have to increase their prices and customers like to see that and they will keep coming back to the company that does great work for a great price.

Injection Molding Materials

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.

Contract Injection Molding

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 Machines

Injection Molding Machines

One type of injection molding machine is the Milacron LIM, Liquid Injection Molding; there are many benefits in having this machine over the traditional LIM. This machine has its own controls and especially made soft ware for this product only. It has a low pressure set up for injection setup and it has a closed loop control.

Unlike the traditional LIM this machine has an increased power ejector force, so it can inject the mold quicker. It has a standard injection screw, a cooling plate on both sides, eight new pneumatic valves, and two heat zones on each paten, a 3-stage air ejector. The improvements from the standard LIM also include a revised rear seal on the injector screw and also a revised seal that is on the nozzle.

These machines have a thermo set process that uses a silicone rubber material that is used to be injected into the heat plastic molds. The best part about these Milacron machines is that no other machine can use their software is designed just for their machines and no one else’s. The Milacron also has a complete design line of Fluid Auto meter mixers.

Milacron is one of the best in the business of injection molding and if your company needs to replace a machine, consider this one, it is one of the best.

Injection Molds

Injection Molds

The designs of the mold are predetermined by whose company is requesting the parts. A lot of thought has to be put into making the molds, the molds have to be designed so that the molds don’t get stuck inside the mold and ruin the piece. The molds are designed that when the resin (hard plastic) is complete that the mold can be taken out and polished to be the piece that the mold was designed for.

If any air gets into the plastic molds or any kind of condensation the mold could get ruined and must be done again. This is not very productive, so the molds must be made to the exact specifications. The molds come in tow parts called the core and the cavity, the core is the middle of the mold and the cavity will encase the core when the mold is complete. Each part must be removed with care, any imperfection and the mold has to be tossed out.

There are molds that they are considered easy and then they have what they call the more complex molds. Some molds are very complex that they have different parts to them such as slides as well as a core and a cavity. Remember, you can create a car door with injection molding so you have to know that the mold for that is going to be very complex.

When you get a mold that is very heavy, the core and the cavity in conjunction with cooling hoses working together they form a molding tool. Sometimes when the tools are heavy they have to be lifted into the molding machine. When the tool needs to be cleaned or maintained they can hoist it back out again. So far, these are the basics of injection molds.

Injection Molding Companies

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?

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Injection Molding Glossary

Injection Molding Glossary

Injection Molding: this is a technique used to fabricate parts made from thermoplastic materials.

Thermoplastic materials: are materials made out of plastic that are able to melt into a liquid when heated at a high enough heat and when it freezes it will be in a glassy state when it is cooled.

Polystyrene is a polymer that is a liquid hydrocarbon that is commercially made from petroleum.

Polypropylene is a very hard plastic that is used for many different uses such as food packaging, reusable containers and textiles. It is a very durable and rugged unusually.

Resin is comes from many plants especially from the Coniferous tree that is used for its chemicals. You can use resin for adhesives and incense and some perfumes.

Solidify is to become hard or firm.

Pellet is a small compressed piece of material or a substance.

Nylon is a chemically resistant, it is also heat resistant, but it is tough and very flexible.