One can see injection moulded products everywhere ranging from small parts to large casings for equipments. Manufacturers of consumer and industrial products may choose to have their own in-house injection moulding division or better still, outsource it to specialists.
Why employ injection moulding services? The answer is that injection moulding is a sophisticated and highly precise process where a number of factors affect the product’s appearance, characteristics and also price.
There are many aspects to design in injection moulding:
Product design: This aspect needs very careful consideration to get it right on all counts. The designer must consider appearance of the product, its structural strength, the material to be used for injection moulding and the mould type that will be used for its production to make it easy for mould designers and for the process itself. This is a skill only very experienced professionals in injection moulding services possess.
Mould design: A variety of factors go into the process of mould design. The mould designer will base his mould design on the product design. Another consideration is how many cavities the mould should have, dictated by the quantity required to be produced. Longevity of the mould will dictate the material used in making moulds. Materials used for moulds can range from hardened steel to prehardened steel, aluminium and copper. Each has different thermal and dimensional characteristics as well as longevity. The material used for moulding is another important consideration. Melting point, flow rate, structural integrity of product, shrinkage, speed of production, size of the product and also the machine on which the mould will be used are all factors that must be considered with great care. The designer needs to consider the draft or ejection angle and also the size of gates through which material is injected into the cavity. Matters can become quite complicated when one considers the use of hot runner moulds where the designer has a tough challenge to design all the intricate parts, heating arrangement and placement of nozzles, manifolds, hot valves and heaters for optimal performance, especially when the mould is large and has multiple cavities.
Cost optimization: A mould designer also needs to factor in cost optimization. Just focusing on the material to be used, machine on which mould will be mounted and the mould design is not sufficient. Cost optimization is equally important especially in bulk production. Experienced designers have full knowledge about various thermoplastic materials and know just how thick or thin the walls need to be, where to place ribbing and supports to impart structural strength with minimum use of material. Reduction of waste in the final moulded product is another thing to be considered.
Plastic injection moulds are expensive and take a lot of time for manufacture especially if they are complicated and have multiple cavities in a hot runner design. It is usual to first design a sample mould to find if the design concepts work and, if not, to carry out modifications after the testing. Testing is carried out for viscosity to know fill rate and pattern. Tests on the gate seal let engineers know if they have to adjust tooling to ensure full sealing. Testing is also carried out for mould temperature, coolant flows, pressure, fill time and melt temperatures to optimise the process of moulding. Testing and quality control assures perfection in the mould manufacture and eliminates rework that can be quite expensive.
Just creating a perfect mould for the process is not sufficient. It must be matched with the injection moulding machine to ensure consistency in the moulded product. The process, of course starts with mould design and then extends to manufacturing where the machine, usually with computer control, enables operators to set various parameters.