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Plastic Injection Molding Secret

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Finally, the rest of the company can secretly learn about plastic injection molding

Sometimes you just have to nod your head and pretend that you know what it is they are talking about. On the other hand, it sure would be nice to really understand how plastic injection molding works and what all those terms mean.

Often, terms like overmolding, two-shot molding, galling, hobbed-in, coined, toasted, NFG, shut-off, etc, etc, are just taken for granted. And usually, people don’t like to reveal that they just don’t know.
Really, it is in everyone’s best interest to truly have a fundamental grasp of the how and why of plastic injection molding. The explanations offered here are not technical, but rather a general idea of the concepts.

Some of the processes involved in plastics molding and mold making are easy to grasp, others are downright mysterious to an outsider. Click on any process below to learn more.

 What about EDM, or electrical discharge machining?

Of all the methods used to produce a plastic injection mold, EDM is the least understood. How can a non-technical person grasp it when you usually can’t even see what is going on? Since the workpiece is usually submerged in a tank of smelly, oily fluid, who could know what it’s all about?

The main reason to have a basic understanding of EDM is because it is the most essential process involved in plastic injection moldmaking. Before EDM, many operations were extremely difficult and time consuming.

Other names for EDM are: ram EDM, ED, spark erosion, and burner.

What about WEDM or wire electrical discharge machining? WEDM is sort of a cousin to EDM, in that it was developed quite a bit later. Wire EDM was originally thought to have a very limited application in plastic injection mold making, but it has proven to be indispensable.

Mold designers have become very creative in applying WEDM to build injection molds. In the not-so-distant-past, much of what is “wired ” was done on surface grinders. This was very tedious and difficult, requiring a high level of skill and expertise.

Much of what is done with WEDM was simply impossible otherwise. The shapes and contours attainable are sometimes only possible with this technology. go to one of the best mold manufacturer China home page to know more.

Thermoset Injection Molding

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Thermoset Injection Molding

Thermoset injection molding is an automated process transforming granular material into molded shapes that Rebling Plastics has been performing since the company’s inception. It typically is the most economical way to mold thermoset materials.
Thermosets are materials that cure through a chemical reaction activated by heat and pressure, thus forming a strong molecular bond. This molecular bonding enables thermoset materials to maintain their physical properties at elevated temperatures which is why they are used in applications such as electrical connector housings, automotive ashtrays, and cookware appliance handles and knobs.

The thermoset injection molding process begins by adding granular or pelletized material to a hopper. The material is gravity fed into a barrel and screw, which heats and moves the material toward the mold. The material is injected into a hot mold which has been clamped shut under enough force to keep the mold together while the material is forced into the cavity under high pressure. The plastic flows through a runner system in the mold to reach all the cavities. When the mold cavities are filled, the parts cure to a solid form. The mold then opens for part removal, and some parts simply drop into a box, while others are removed by hand or automated equipment.

plastic molding | Plastic molds

plastic molding | Plastic molds

Thermoset vs. Thermoplastic Injection Molding

Unlike thermoplastic injection moulding, cured thermosets cannot be reground and mixed with virgin material for reprocessing. In general, thermoset materials have a low viscosity, so when the material fills the mold cavity under pressure, some of the material will leak between the two halves of the mold typically at an area of the cavity where vents have been added to allow for gas and air escapement. This is called flash. While this problem can normally be prevented in thermoplastic injection molding by proper mold construction and processing parameters, flashing cannot be avoided in thermoset injection molding. Therefore, flash must be removed as a secondary operation. When possible, the parts are de-flashed in an automatic tumbling operation rather than hand de-flashing to save costs.

Cycle times are longer for thermoset materials than thermoplastic materials due to the chemical reaction and cure that takes place in the mold. Since thermosets are more abrasive than thermoplastics, Rebling Plastics considerable expertise in mold design (including choice of tool steels, heat treating and plating requirements), as well as mold maintenance, will ensure a long lasting productive mold life.

Thermoset injection molding equipment

Thermoset injection molding presses ranging from 80 to 200-ton clamping pressure. Having these types of presses allows to make different sized parts with the option of making multi-cavity molds. In addition to the presses, we also use a variety of auxiliary equipment to keep molding costs down. Robots and sprue pickers are used to remove parts and runners from the plastic molds. Removing flash from the parts by sandblasting or automated feeding and tumbling is only an advantage.

Rapid Injection Molding

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Rapid Injection Molding

Rapid injection molding is exactly what the name implies, but multiplied by a factor of 10! It is hard to imagine that anyone could offer a service that can guarantee a fully functioning injection mold in a day or two, but that is actually the case.

This is precisely what rapid injection molding is all about. Rapid, as in very rapid! These molds are made of high-grade aluminum and can produce anywhere from a few parts to thousands.

Personally, I have worked on many aluminum molds that produce high-quality parts even after several hundreds of thousands of cycles. At first, I was highly sceptical, but after several years of making injection molding prototypes, It became routine.

plastic molding

rapid injection molding

How does rapid injection molding work?

It works by automating as much as possible in the plastic mold making procedure. By taking the customer’s 3-D model and automating the design and manufacture of the mold, the lead times are cut down to a fraction of the conventional process.

One of the central parts of the automation process lies in the design of the plastic part. By working with knowledgeable designers, many features, such as undercuts, can be minimized or eliminated.

Some of the features that must be considered are:

  • Part draft angles and radii
  • Ejection
  • Using straight pulls whenever possible
  • Simple approaches to side actions
  • The CNC milling process
  • Part size limits

What are the advantages of rapid injection molding?

  • A way to bridge the time gap between prototype and full production. If you need a working injection mold right now, this is the answer.
  • Short run production to get your product in the marketplace immediately.
  • Gives engineers a working model to approach a full-blown design for a production tool.

What are the disadvantages of rapid injection molding?

  • The aluminium molds are low production.
  • Works best for simpler parts with minimal side action and undercuts.
  • EDM machining is eliminated, thus some detail may be sacrificed.
  • The entire core and cavity are high-speed CNC machined, often on 5-axis CNC machines, therefore the design has limitations.

Is rapid injection molding expensive?

Surprisingly, the cost is quite reasonable, though there is always a premium to pay for extremely quick turnaround. Typically though, the cost is much less than might be expected. This is due to the highly developed automation process of this type of plastic injection mould making.

Conclusion

Rapid injection molding is a niche market segment of injection mold making. It serves a highly specialized marketplace, yet is very important within the niche. The ability to get your injection molded plastic part to market in a matter of days is very valuable to the right company.

Also, the ability to bridge the gap between prototype and high production is a very useful tool for custom injection molders.

A leading plastic mold company who is professional in rapid injection molding is plasticmold.net, in China. They have just about everything you might need when it concerns rapid injection molding.