Knowledge Base

Plastic Moulding Simulation

The Injection Moulding Process

Plastic injection moulding is a cyclic process in which melted polymer (plasticized polymer) is poured into a mould cavity under pressure and allowed to cool off. The term plastic describe compounds of polymers with one or more additives. Polymers can be classified, based on the structural shape of polymer molecules, as linear, branched, orcross-linked. Polymers are thermoplastic, which means they can be softened and hardened reversibly by changing their temperature. Fabricating processes like injection molding, extrusion moulding, compression molding, transfer moulding and blowing take advantage of this feature to shape thermoplastic resins. Plastics are now among the most widely used materials, even more widely consumed than steel and other material the world over. The plastic moulding process essentially consists of softening the material in a heated cylinder and injecting it under pressure into themould cavity. Upon cooling, you get an object of the desired shape. The main components of an injection-molding machine are the injection unit which melts the moulding material and forces it into the mould, the clamping unit which opens and closes the mould under pressure, the control unit and the hopper from where the melted plastic is poured into the injection unit. Advanced plastic moulding machines of today also use robotic equipment to improve overall efficiency of the plant. At a very basic level, the plastic injection moulding process consists of heating the polymer in the injection unit where it is made to flow under pressure to the mould. It is then allowed to solidify, whereby it gets the shape of the mould cavity. The mould is then opened and the finished product is ejected. The process is then repeated. Small objects are created utilizing multiple patterns, so that one batch produces a number of objects in a single process cycle. The quality of the mould and the characteristics of the polymers, or blend of polymers used play a very crucial role in determining the quality of the finished product.

Plastic Injection Moulding Simulation
Plastic injection moulding products can be found everywhere, from automotive parts, aeroplane parts to household items and consumer electronics parts. Innovations in plastic material, coupled with 3D Printing technology that allows direct, additive printing, have propelled the growth of the plastics industry. Increased customer demand and stricter environmental norms have necessitated better quality control of the plastic manufacturing process. With increasing competition in the global marketplace, companies are migrating to lean manufacturing and zero-fault quota. This has forced the plastic manufacturers from India and other countries to enhance their quality as well.

The quality and performance of plastic injection moulding depends on the material, shape and function of the part design as well as on the way in which the plastic is processed during the moulding. In addition, changing the proportion of additives can have a vast impact on the properties of the raw material. Raw material is only one of the aspect of moulding process. The injection pressure, the temperature of heating and cooling the polymers, the duration of cooling, all play an important part in mould consideration. Too little pressure and the plastic component can be porous. Too much pressure and it can cause flashing, forcing the mould to open prematurely.  There are also other variables to consider, like the runner length, the speed of the feed in order to minimize defects like sink, void, warp and dimensional stability. Before computer simulation was possible, it used to be a time consuming and challenging job for engineers to research and refine the properties of the raw material used for plastic moulding, since it involved changing the variables and gauging their effect on the final product. As the number of variables increase, so does the complexity of the permutation and complexities involved in fine tuning the plastic mould injection process. By employing advanced CAE based mouldflow simulation tools (like the 3DTimon® plastic moulding simulation software), it is now possible for plastic and polymer engineers to quickly qualify final design and material selection without physically committing real material and machine time. Thus, mouldflow simulation has helped the plastic manufacturing sector to save not only on time, but also on material, thereby protecting the environment.Thanks to mouldflow simulation software, it is now possible to achieve a high quality plastic component instead of the costly and time consuming trial-and-error manufacturing process of the past. Proper use of a plastic moulding simulation like that from 3DTimon® can therefore enable a company achieve competitive edge in designing of the plastic product / component. Companies from India and other parts of the world are already benefitting from it.

The Simulation Process
Simulation analysis starts with the creation of a geometric model, which is nothing but the CAD model of the object / part. This drawing is fed to a simulation software, which then creates a mesh (a collection of vertices, edges and faces that defines the shape of a polyhedral object) that fits the demand of simulation process. The plastic injection moulding software also offers a selection of polymers that helps engineers choose the proper material. Of course, the software also allows addition of custom material. The design engineer then sets the boundary conditions of moulding process that emulate the real manufacturing process, including all the moulding parameters.

There are two main approaches in which plastic moulding simulation can be carried out. In numerical simulation, the physical process of injection mouldingis described to visualize the flow and identify potential defects in the mould like incomplete filling, weld lines and voids. This is done with the help of CAE models. Optimization, another type of simulation, helps simulate different geometrical designs, sprue and gating systems, and optimal flow paths. Today’s plastic moulding software also employ different artificial intelligence based models for optimization that increase the quality of the finished item. Thermal simulation helps in estimating the cycle time and proper formation of the end product. It is important to remember that different plastics exhibit different properties when heated. Their flow can be laminar or non-laminar, and this creates design challenges as well. In particular, simulation helps engineers understand the flow near the mould walls and the kinematics in areas where shear and extensional deformations contribute significantly to the stress.With the rapid progress in hardware capabilities, it is now possible to provide a full 3D simulation of the product or component. It works very well with thick and solid plastic parts like the dashboard of an automobile, the handles of a plastic chair, electrical connectors, etc.

The success of a moulding process is not only dependent on the choice of the right software, but also on the boundary condition used in the simulation software.  As competition intensifies, reliance on cutting edge plastic moulding simulation software is only going to increase, especially in progressive countries like India.