What is Plastic Injection Molding

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Injection molding is a molding procedure whereby a heat-softened plastic material is forced from a cylinder into a relatively cool cavity giving the article the desired shape. Injection molding is a manufacturing technique for making parts from the plastic material. Molten plastic is injected at high pressure into a mold, which is the inverse of the desired shape. The mold is made by a Mold Manufacturer China Company from metal, usually either steel or aluminum, and precision-machined to form the features of the desired part. Injection molding is very widely used for manufacturing a variety of parts, from the smallest component to entire body panels of cars.

The process of plastic injection molding



An injection molding machine consists of three basic parts, the mold plus the clamping and injection units. The clamping unit is what holds the mold under pressure during the injection and cooling. Basically, it holds the two halves of the injection mold together.

During the injection phase, plastic material, usually in the form of pellets, are loaded into a hopper on top of the injection unit. The pellets feed into the cylinder where they are heated until they reach molten form (think of how a hot glue gun works here). Within the heating cylinder there is a motorized screw that mixes the molten pellets and forces them to end of the cylinder. Once enough material has accumulated in front of the screw, the injection process begins. The molten plastic is inserted into the mold through a sprue, while the screw controls the pressure and speed.

The dwelling phase consists of a pause in the injection process. The molten plastic has been injected into the mold and the pressure is applied to make sure all of the mold cavities are filled.

Then the plastic is allowed to cool to its solid form within the mold. The clamping unit is then opened, which separates the two halves of the mold. An ejecting rod and plate eject the finished piece from the mold.

Extrusion

A machine used to extrude materials is very similar to the injection-moulding machine explained above. A motor turns a thread, which feeds granules of plastic through a heater. The granules melt into a liquid, which is forced through a die, forming a long ‘tube-like’ shape. The extrusion is then cooled and forms a solid shape. The shape of the die determines the shape of the tube.

Advantages of Injection Molding 



– High tolerances are repeatable 

– Wide range of materials can be used 

– Low labour costs

– Minimal scrap losses 

– Little need to finish parts after molding

Plastic Injection molding
Plastic Injection molding

Disadvantages of Injection Molding



– Expensive equipment investment 

– Running costs may be high 

– Parts must be designed with specific molding consideration.

Overview

Injection molding is a relatively new way to manufacture parts. It is a fast process and is used to produce large numbers of identical items from high precision engineering components to disposable consumer goods. Injection molding is often used in mass-production and prototyping. It produces such small products as bottle tops, sinks plugs, children’s toys, containers, model kits, disposable razors and parts of cameras. The process can even mould such large items as dingy hulls and kit car body shell parts.

What to know more about injection molding? Please go to
https://en.wikipedia.org/wiki/Injection_molding to take a look.

Precision Injection Mold Making

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Precision Measurement And Injection Mold Making

It is remarkable that it is possible to open a package from Sweden, clean up EDM tool, and install it in an engine lathe spindle made in upstate New York, and indicate the run-out with a dial indicator made in Switzerland, held by a magnetic base made in Japan. This is amazing in itself, but the truly amazing thing is that it all works, quite well!

In this example, which actually happened to me, the run-out was less than .0001in/.0025 mm, right out of the box, first try. This is what precision tool measurement is all about.

The number of precision tools used by an injection mold maker are numerous. A partial list would include:

Precision measurement tools

  • Granite surface plate
  • Surface gage
  • Dial indicator
  • Height master/Cadillac gage
  • Gage blocks
  • Pin gages
  • Sine plate
  • Magnetic squaring block
  • Vee-block
  • Precision micrometers
  • Spin fixture

One of the more challenging aspects of building a mold is to have all of the various measuring tools calibrated to the same standard. This is why the EDM chuck from Sweden fit in the American lathe spindle: the accuracy was traceable to a common standard.

It doesn’t mean much if you are accurate within .0002 in., if your micrometer is off! It just won’t work. Shops need to have a master set of gage blocks that are traceable to the NIST, or National Institute of Standards and Technology. This is not as hard as it sounds, you just need to invest in a good set of gage blocks, not some made by child labor in a developing nation.

The proper care and use of these expensive tools is critical as well. They need to be treated with respect, handled carefully, kept free from rust and grinding grit. They need to have a clean storage place, with a grit-free surface on which to sit.

There are many places that you can cut costs in Plastic mold making, precision measurement tools is not one of them. It simply makes no sense to save money by buying a cheap dial indicator, for example. It is only going to haunt you in the long run. The same holds true for gage blocks, micrometers, squaring blocks, sine plates and so on.

With large items, such as the optical comparator or coordinate measuring machine, it is especially important to obtain a reliable tool. Valuable shop time can be quickly consumed with trouble-shooting a low quality machine. Not only that, but what if the measurements are unreliable? The mistakes can become extremely expensive and will quickly erase the initial savings.

Reliable precision measurement manufacturers

 Starrett Brown-and Sharpe Interapid Girod
 Etalon Mitutoyo Suburban Mahr
 Tesa Hermann Schmidt OGP Magnets
 Harig Micro-Vu Mitutoyo Zeiss

Insert Molding

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Insert Molding Advantages

Over the years, the technical advancements have taken place and instead of step-by-step manufacturing of products, there is manufacturing through one full-fledged process called insert molding . Certain industries still manufacture components through processes that include assembling discrete parts such as soldering, connectors, adhesives or fasteners. Molding through inserts is the perfect alternative to all such things and can benefit you in the following ways:

Decreased labour cost and assembly

Simply because various components are being joined or connected through thermoplastics, you can greatly bring down the assembly as well as labour cost with the help of this process.

Decreased weight and size

This process can yield smaller as well as lighter components by eliminating the need for connectors or fasteners. It merely blends the strength of metal inserts and resin.

Increased reliability

This process helps you in avoiding problems such as misalignment, part loosening, and improper termination as well as other problems. Every single part is secured tightly with the thermoplastic.

Design flexibility

Plastic Molding

Insert Plastic Molding

Another advantage of the insert molding process is that it gives you design flexibility. Designers love the unlimited configurations which can be used in insert plastic molding.

This process can literally allow you to reduce cost and experiment with the designs apart from getting other advantages as well. Most of all, it can allow you to save time and faults that might occur in manufacturing components otherwise. In a lot of ways, this process can be used by various industries to produce high quality and efficient components for all the purposes.