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.

Custom Molding Jobs

Custom Injection Molding Jobs

In the industry of injection molding, things work on a very specific scale. The molds must be right, the specifications must be right. That is true for the molds that are already designed. When a company wants and needs brand new design molds the process must be handled very delicately.

When an plastic molding company gets contracted by a new company to design and fill molds. The company needing the molds must be very accurate and very specific when it comes down to doing a custom job. One slight imperfection and the whole project could be worthless. Time is money and that is not something that either can afford to be wasted.

The injection molding process is a specific one, there are certain stages and certain things that have to be done and if your design has a flaw in it then there are going to be set backs. When a mold comes out after it hardens, it looks great a little rough around the edges, but it looks what it is supposed to.

Molding produces great products and there is a science to the skill in making the molds and producing the injection molds. If you are a company who is looking for a custom design, make sure the specs and designs are not flawed and you will get an unbelievable product.

How Injection Molding Works

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

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.