Injection Molding From a Molders Point of View

  I have been in the field of Custom Plastic Injection Molding for about 21 years now as of the writing of this article. I am currently working as a Process Engineer, which I have done for about 15 of my 20+ years in the field of injection molding and I have primarily worked for molders that were involved in the automotive field.

Plastic injection molding, by definition, is the process of injecting plastic into a mold (or mould in European circles), cooling the plastic, ejecting it from the mold, and packing the finished product for sale to the customer. This sounds simple and in it's basic form it is, but the process involved with making all this happen is actually quite complicated. Plastic can be injected into the mold with low pressure, but typically is done under high pressure upwards of 30,000 PSI cavity pressure.

There are many diverse types of injection molding and as many different types of plastic injection molding machines to go with it. Formenbau-spritzguss.de Some of the more common types of plastic molding are standard mold injection, insert molding, plastic extrusion, blow molding, multi-color or material molding, stack molding, and rotary molding just to name a few. There are custom plastics as well, from common every day plastic resins to the more exotic engineering grade resins used in most automobiles today. There are even injection molding grade "metals" being experimented with and used these days.

There are many types of injection molding machines all made for specific purposes. There are the standard horizontal injection molding machines which range in size from a few tons all the way up to 9000 tons and more. You could drive car between the platens of a press that large. Vertical injection molding machines are often used for insert molding (although this can also be done horizontally) and share a common cover with two ejection halves of the mold. This allows for de-molding and loading of inserts in one half, while the other half is producing the next shot of parts. There are also two and three shot injection molding machines for producing multi-color or multi-material parts such as lenses for tail lights and gear shift knobs with hard plastic inner core and a soft vinyl out covering. The newest machines are "all electric versions" which stray from the standard hydraulic injection machines used now for years. These injection molding machines are much more efficient and repeatable then their hydraulic cousins are. Common injection molding machine manufacturers are Toshiba, Husky, Cincinnati, DeMaag, Engel, Nissei, UBE, Arburg and Boy, just to name a few.

The basic steps to producing a plastic injection molded part on a stand injection molding machine are:

Heating the plastic resin to the required range of the product being used.

Developing the shot size through use of a reciprocating screw which conveys the melted plastic to the front of the screw.

Injecting the plastic into the mold under pressure to fill the cavity of the mold.

Plastic Injection Molding: Past, Present and Future

Plastic injection molding is a process that forces liquid plastic into a mold to make custom plastic name plates, plaques, signs and product branding elements. Once the plastic cools and solidifies, it releases from the mold to form a variety of plastic parts for any industry. Popular uses of injection-molded include: appliance name plates, name plates for industrial equipment, car emblems, vehicle branding and license plate holders, as well as product identification for recreational products.

Injection-molded plastic name plates and other components are produced by a machine that consists of three basic components:

A mold which can be made to manufacture any size and shape that is needed

A clamping unit that clamps and holds the mold together throughout the whole process

An injection unit will then inject molten plastic into the mold, where it will remain until it has sufficiently cooled and released

The molten plastic used for injection-molded products is produced by melting small plastic pellets, which are fed into an injection machine heating the pellets to a molten or liquid form.

Once the now molten plastic pellets reach a predetermined temperature the semi liquid is forcefully injected into a mold. The speed and pressure of this process is controlled by a hydraulic cylinder that, once engaged, forces the liquid plastic into the mold.

In "dwell" phase of the plastic injection molding process, the plastic is left in the mold to ensure that it completely fills the mold and then allowed to cool to the point where it solidifies and the desired object is produced. It is then ready for secondary processes as decoration, sub assembly, or shipment.

The injection-molded plastic process allows manufacturers to produce custom plastic name plates and components that would be too costly to make as intricately by utilizing traditional machining methods. Injection-molded plastics also saves time and money by allowing many pieces of the same component to be made at the same time, from the same mold; each copy identical to the one before it. This process also reduces labor costs by minimizing the need for manual labor from employees. There is also nearly no wasted material, as any unused or left over plastic can be re-cycled to be reused in the process

The History of Plastic Injection Molding

Plastic injection molding originated with chemists in Europe and The United States who were experimenting with plastics. Originally it was done by hand and pressed into a mold using Parkesine but it proved to be too brittle and flammable. John Wesley Hyatt is the official inventor of plastic injection molding and the process has a rich history with brilliant minds.

John Wesley Hyatt was a creative inventor and developed the processing of celluloid plastics. This was an amazing feat for a young printer from Illinois who took on the challenge from the New York Billiards Company to replace the ivory that was used in billiard balls.

So began his career in plastics engineering as he and his brother Isaiah started making several mixtures for checkers and other objects. After some time trying various mixtures, John mixed nitrocellulose, camphor and alcohol together. He pressed these ingredients into a circular steel mold that was heated and allowed it to cool. When the material was removed from the mold, he realized that he had successfully created a billiard ball composed of plastic. Thus began the process of plastic injection molding.

John and his brother Isaiah patented this process of producing celluloid in 1870 and continued by making dentures from their new material which replaced dentures made of rubber. Thus began the manufacturing process of celluloid plastics. John was quite like the Da Vinci of industrial invention because he also was credited with the invention of the sewing machine and roller bearings all of which contributed heavily to manufacturing.

Today, Celluloid and Cellulosic plastics can be found almost anywhere including screwdriver handles, tooth brushes and utensils. Celluloid can be found in Hollywood, California today and is used for production of your favorite films.

To further the processes of plastic injection molding another great inventor came into plastics actively in New York after traveling from Belgium on a fellowship. Leo Hendrick Baekeland began working with polymers and this lead to his invention for Kodak Eastman which was Velox. Velox is a photographic paper which could be developed in gaslight instead of sunlight.

As a chemist he made several developments in this field also going on to investigate how polymers were molecularly structured. These investigations lead too many inventions and discoveries beyond what chemists had discovered thus far about coatings and adhesives.

In 1926 Eckert and Ziegler invented the plastics molding machine in Germany which was the first successful machine used in manufacturing plastics. This brought injection plastic molding on the production line successfully.

Many more creative inventors have come through the process of plastic injection molding in history and it has come through an even finer process for production in today's products such as appliances and name plates, signs and plaques.

The Injection Plastic Molding Process Today

Today's version of the plastic injection molding equipment is computer controlled and plastic raw material is injected into steel and aluminum molds to produce the custom plastic name plates, plastic components and many of the plastic products we use every day. The molding equipment injects hot plastic into the mold and cools the plastic and extracts the parts. The molding equipment of today makes mass production of plastic components easy and cost effective.

Today, plastic injection molding manufacturers use vertical and horizontal presses, injection screw presses, electric presses and hydraulic presses for whatever rate of pressure is needed to complete the product pressure to form. This process produces everything from car parts to license plates and even toothbrushes.

The Future of Plastic Injection Molding Equipment

Plastic injection molding is a very innovative process which has created many useful products that we use every single day in our households. While the history of plastic injection molding is quite full of creativity and innovation, the future is filled with even greater possibility as more creative minds add new ways to improve plastic injection molding equipment and process.

While the improvements in the plastic injection machinery continue, the future of injection molding is now turning its attention to the molds and mold components. High tech plastic molds can be made of metal, epoxy or carbon fiber and can increase output through faster cooling times and cycle times.

The invention of 3D printing gives us a glimpse of how far plastic injection molding can travel into the future. 3D printing is a process of making a three-dimensional solid object of virtually any shape from a digital model. With the integration of 3D printing in the plastic injection molding process, concepts and samples can be produced with far less expense.

Some innovative minds have even been working with corn seed producers to replace traditional petroleum based plastic into corn starch based plastic. l Biodegradable material is currently being used on a limited scale and there are many uses this material could soon have that would astound the mind. All it would take would be the mold and the material to produce a new wave of the future for plastics engineering. Scientist are still researching polymers the way they did when plastic injection molding began and their research is unbelievable at this point with many possibilities to come.