Advantages Of Injection Molding

Injection molding is one of the most widely used methods for mass manufacture of items like cars, car parts, pet bottles, etc. It is a process by which material is injected into a mould used usually to manufacture small or large parts of a larger assembly. One of the most common applications of injection molding is to produce plastic housings which are used in a variety of household appliances, consumer electronics, etc. Buckets, toothbrushes, medical devices like syringes and the valves are manufactured using injection molding.

Injection Molding
Injection Molding

The four processes involved in an injection molding process which all together take typically between two and four minutes  are:

Clamping, injection, cooling and ejection

Clamping is securing the mould before injection, typically clamping together both its halves

Injection – is injection of the material to be molded, usually melted plastic

The cooling – molten plastic begins to cool as soon as it comes in contact with the mould surface.

Ejection – after sufficient cooling, the molded part may be ejected from the molding machine.

Building the mould to utmost precision is the main task, rather than the process of molding itself. Finishing of a mould by machines can take up to 20 hours.

Benefits of Injection molding:

  • Huge range of applications – some of the common products manufactured using injection molding are bearings, cams, gears, rollers, rotors, slide guides, valves, display stands, knobs, lenses, panels, automotive consoles, eyeglass frames, air filters, safety masks, aircraft components, kitchenware, drains, gutters, bushings, seals, washers and many more
  • It is a very precise method.
  • Allows the manufacture of complicated shapes and designs that would otherwise be difficult and time consuming to make
  • Mass production of such parts is possible; high output coupled with low labor cost, easy to repeat.
  • Less workload as essentially the product is ready after injection molding
  • Helps recycling plastic as scrap and unused molding can be reused. Hence it can be termed as environmentally friendly
  • Design can be changed by changing the mould specifications.
  • The color of the product can be changed easily
  • In addition to plastic, fillers can be added while molding to make the part stronger by reducing the density of plastic. Inserts can also be made available in the final product.
  • Co-injection molding is possible when two different types of plastic can be used. This helps when there is difficulty in sourcing one type of plastic for mass production
  • Good finish
  • Has wide applications. Almost every manufactured thing around us, is manufactured through injection molding
  • Injection molding allows greater detailing than any other molding process, because of the extremely high pressure the plastic is subjected to.
  • It is a highly automated process performed by machines and robots. Just one person is sufficient to oversee the process. Hence this cuts down on manufacturing costs, as the overheads are reduced. This cost saving can be passed onto the customer. Much cheaper method of manufacture when compared to machining which can cost up to 25times more.
  • Encourages research on more and more durable thermosetting polymers which can be used in injection molding.

 Injection moulding in China is very well known the world over. They provide accurate moulding machines to specifications of mould makers in China and abroad. Mould tech in China is actually gone worldwide.

How To Make Precision Plastic Molded Parts

Precision Plastic molded parts can be made only by Plastic injection molding. This is the preferred method because injection molding has the advantages of high tolerance precision work.

precision plastic molded parts
precision plastic molded parts

The following points go into making Precision Plastic molds.

  1. Using the proper clamping force

Injection molding machine – also known as presses, consist of a material hopper, an injection ram or plunger, and a heating unit. Plastic is injected into the mold through the sprue orifice. These presses are rated by tonnage which is the calculation of the clamping force the press can exert. This force keeps the mold closed while the molding is going on. By rule of thumb, the force needed is determined by the projected surface area of the part being molded. Tonnage can vary from a few to a few thousand. The nature of the material also determines the clamping force. If the plastic is stiff, more injection pressure and more clamping force is needed to keep the mold closed.  Also, larger parts require greater clamping forces. These points should be kept in mind when molding.

  1. Using the proper material for Molds – or die refers to the tooling used to produce the plastic parts by molding. They are expensive to manufacture and were preferred to be used only in large scale production. They are typically constructed from hardened steel, beryllium-copper alloys or aluminium. Steel though expensive, is more long lasting and its high initial cost will definitely be offset by the number of times it can be used. Pre hardened steel is used for larger parts molding. The mold is heat treated after machining for longer life.

Aluminum Molds cost much less and are used for mass manufacture of small parts. Aircraft quality aluminum is used for making molds. They offer quicker turnaround times because of their high heat dissipation quality. Since they are not wear resistant, they can be coated with fiberglass reinforced material.

Beryllium Copper also is used for quick heat removal especially where the shear heat is more. Shear heat is the phenomenon of heat trapping in a viscous material like melted plastic when the mechanical energy of the plastic granules when they are injected under high pressure is converted to heat energy.

  1. Using the right Gate

The main enemy of injection molding is stress. The molecules of plastic undergo severe stresses as they are extruded out of the injector into the crevices and corners of the mold to take that shape. They are forced to take sharp corners instead of their natural flow movement. These stresses when the part is cooled get locked into the part and cause warping, cracking, sink marks etc.

Gates are provided at the point of injection to prevent warping. Depending on the shape and size of the part, different types of gates are used.

  1. State of the art Machining

Using the proper machining to achieve very tight tolerances for their clients molded products. Proper initial designing is very important and can be outsourced to experts on a turnkey project basis. State of the art CNC machining, large boring mills, Blanchard grinding capabilities, conventional EDMs all go into making that perfect precision plastic mold.

Mold manufacturers in China have incorporated these and many more features to produce high quality Chinese molds that are in demand the world over at a fraction of the cost at which they are available in western countries.