Designing plastic parts can indeed be a very challenging and intricate task. There are an end number of questions which arise when as a beginner you start researching about injection molding machines. Some of them are how to use such parts, how to assemble the fittings or how will the load be experienced and many others. Traditionally, hydraulic injection plastic machines were used for productions, but now people are using electric injection plastic molding machines. Such machines are cost effective and you do not need to use any oil in these machines. Plus, you can easily complete large scale project with electric molding machine with less downtime. It is hence recommended to be in compliances with some standard rules when it comes to designing. Dividend a large part in smaller components will also aid in minimizing complex problems.
This is a fundamental document which will help you get the basic understanding about plastic injection molding machine.
1) Basics of the machine – Plastic injection molding equipment are also summoned as presses. They comprises of a hopper material, injection ram, heating unit and a plunger like a screw. Here plastic is injected inside the mold using a sprue based orifice.
The press can be rated using tonnage. Tonnage is measured as the clamping force and you need to check the tonnage capacity of such machine before you buy. With the force of the tonnage the mold is closed when the injection molding process is conducted. The tonnage can be differentiated and ranges from 5 ton to 6000 tons. You can also use higher tonnage according to your requirements, but you need to take advices from the experts in this regard. The force of the total clamp required is determined using the project custom area which is molded. This projected area is usually multiplied using a clamp force which is 2 to 8 tons for one square inch of area projected.
There is a rule of thumb that around 4 to 5 tons for each inch can be utilized for most product development. If there is stiffness in the plastic material then it might just need more injection pressure in order to fill up this mold. Hence a higher clamp tonnage might be required for holding the mold in a closed manner. A larger size of plastic part for example, will need a clamp force which is higher as well. So for your large scale products and medical parts, you can use higher tonnage pressure.
2) The Mold-Mold in injection molding process is basically a die. It is the basic tool which helps in molding the plastic parts. Conventionally it used to be highly expensive for using injection molds in manufacturing. They were only restricted to mass volumes productions where large number of parts was required to be created.
Molds typically are constructed using hard steel, aluminum, pre harden steel or beryllium copper based alloy. Selection of the material for building mold is the main decision which needs to be wisely done from an economic perspective. Steel based mold, for example, costs higher but offer high durability and longer life span. So a large number of the part created will help get the returns much faster before it wears out. Pre-harden based steel molds are wear resistant and they can provide you more durability than other molds. Hence they are used for low volume productions. Hardened steel are treated with heat once they are used in making the machines. They have higher resistance and longer lifespan and are used widely in plastic injection molding machine.
Aluminum molds substantially cost you less. Moreover, there are different grades of aluminum which can be chosen based on the budgets and production needs. They can be coated more for being a wear resistant and can be reinforced with fiberglass materials. Beryllium based copper alloys are chosen in molds where fast removal of heat is needed.
Following are the basic features of a standard mold in an injection molding machine.
- Fixed and the moving platens- These are molds which are made from rectangle blocks from aluminimum or steel from which the part shape is cut out.
- Cavity – Cavity is the space which is created based on the cut out segments when the platens which are fixed or moving touch and this defines the final shape.
- Sprue – Sprue is basically the hole which is cut in the central point of a fixed platen. Here plastic which is molten flows for filling the cavity.
- Runner- These are channels in the platen where plastic flows from sprue to gates.
- Gates – These are tiny openings which occur in between the cavities and runners.
3) Fundamental Process- Plastic product making the machine process is simple. There is a granular form of plastic which is fed inside the machine with the help of gravity used from the hopper to a heated barrel. Since these granules are pushed slowly to the plunger and the plastic is compelled to get inserted in the heated chamber. This is known as the barrel and it is melted here. Here it enters the cavity of the mold via the gate and the runner system. This mold is kept as it is at a certain temperature so the plastic can harden.
4) The basic molding cycle- There are events running sequentially in the injection molding machine process. These are also known as injection molding cycle where the initial event start as the mold is closed. This is followed with the polymer being injected to the cavity of the mold. As this cavity is filled up with a pressure the material shrinks. The screws are turned and the next shot is fed to the screw at the front section. So as the next shot prepares the last one retracts. The part is cooled sufficiently and then the mold is opened and the part designed is ejected.
This will be a strong knowledge base about plastic product making machine. With this enormous knowledge you can now envision your entrepreneurial dream of making profitable manufacturing possible.