FIM offers design engineers a number of important benefits over traditional methods of product decoration, most of which are effectively post-mould processes. By comparison with spray painting, laser etching, appliqué, Aquagraphics or pad printing, for example, FIM can significantly reduce the number of production stages and component parts, thereby cutting both production time and cost, while improving the quality, complexity and durability of finished products. Perhaps as importantly, FIM also offers greater flexibility, in terms of design and manufacturing options for shallow and deeply drawn profiles, enables original and often innovative designs to be considered and can be used to produce both short and long production runs without cost penalties.

The FIM Process

The FIM process involves four steps: printing, forming, trimming and molding. The part or component graphics are firstly screen printed onto the underside of a special hardcoated film, with the screen tooling being designed to maximize the number of parts on each sheet. The printed sheets are then transferred to a vacuum, pressure or thermoforming press, where they are formed to the exact shape of the components being made, with the upper or outer side of film effectively becoming the outer side of the finished component.

The sheet is trimmed and individual components are then cut to size before being moved to the final, injection molding stage. Each part is subsequently inserted in a female injection mold cavity, where molten polymer is injected behind the film to form a strong and create a solid and finished part ready for subsequent product assembly.

This simple but effective combination of processes delivers a number of important benefits, including the ability to realize complex high definition designs and produce durable textured parts.

In particular, as the components can be shaped extremely accurately, with print registration within ±0.2mm, high quality designs can be achieved that may not be possible with alternative production methods. In addition, for products such as appliance control panels, it is possible to integrate a decorated enclosure and clear LCD display window into a single component, reducing the materials required and therefore costs.

Furthermore, by printing the decoration or graphics onto the undersurface of the film, the hard coated substrate forms a tough protective skin over the complete outer of the finished part. This makes each component considerably more resistant to scratches and abrasions than those that have been sprayed or have had designs applied to them.

Material Choice

In many respects, the success of the FIM technique has only been made possible by the availability of a new generation of performance films and inks, that are capable of withstanding the different mechanical and thermal stresses encountered at each stage of the overall production process.

For example, the latest film substrates, such as those in the Autoflex Xtraform range from MacDermid Autotype, feature a specially developed, high gloss, hard coated surface finish and have been developed to offer a combination of properties. These include the ability to accept intricate graphics, using a range of inks; to be shaped using pressure, heat or vacuum forming systems; and to provide resistance to surface abrasion, physical wear and chemicals, greases and solvents. In addition, they have excellent resistance to ultra-violet light, so can be used for extended periods in sunlight; offer high levels of transparency, so that backlighting can easily be incorporated; and can be surface embossed or textured.

Perhaps most importantly, the films have been specially developed to offer consistent results when drawn into three dimensional shapes using FIM techniques. The range of films offer varying degrees of workability, from those capable of producing shallow formed fascia panels, to others suitable for deep drawn components such as instrument covers. Unlike conventional film substrates, these films are able to be shaped without weaknesses occurring or the mechanical properties of the film being compromised, resulting in a high quality uniform finish.

Additionally, the inks used for the FIM process should be chosen carefully, as conventional screen print inks are not generally formulated to withstand the higher temperatures and mechanical stresses imposed during thermoforming and injection molding. Many specialty inks are now available, while products such as Aquatex texturing lacquers from MacDermid Autotype have been developed to enable a variety of tactile finishes to be applied to the surface of products formed using FIM techniques.

Cutting Costs

One of the main advantages of Film Insert Molding is its ability to reduce production costs when compared with traditional techniques, with savings of up to 40% being possible in many applications, mainly through reductions in processing times and the labor required.

For example, on a product such as the outer case for a personal CD player there may be up to eleven different components, including etched metal labels, metallized buttons and molded case and display area, with around twelve separate production processes (spray painting and hard coat, pad printing, screen printing, etching etc) being involved. By switching to Film Insert Molding it is possible to reduce the number of component parts to just one, with only eight production processes being required (including printing, forming, die-cutting and injection molding), representing a considerable saving in both production costs and time.

Similarly, for parts such as instrument or control panels on business machines, medical equipment or industrial system, FIM techniques will both reduce costs, when compared with spray painting, and dramatically improve the durability of text and graphics, as they are sealed beneath the surface layers. In addition, the ability to create extremely fine print definition makes FIM an effective method of simulating wood or carbon fiber effects, while the use of special varnishes, overprinted during the first stage of production, enable textured and gloss finishes to be selectively created around or on control knobs or switches.

Production Factors

Although FIM represents a major step forward for the production of high quality components there are a number of important factors that should be considered at both the product design and production stages.

Perhaps most importantly, it is essential to recognize that FIM is essentially an integrated procedure and that it can involve a number of different suppliers and processes. Typically, these can include raw material (film, ink and resin) suppliers, screen printers, forming or injection molding companies and of course the OEM or end user.

It is important that all of these parties are consulted and that agreement is reached on the integration of each process step, with careful consideration being given to the affect that each step may have on preceding or subsequent stages. For example, film materials and inks must be formulated to match the often diverse characteristics of both screen printing and subsequent forming and injection molding processes, without suffering from problems such as ink washout, melt damage or degradation of material properties.

Additionally, the production of high volume parts, such as fascia panels for white goods, can easily be achieved at the screen print stage, as multiple images can be printed on each sheet of film or using roll-fed machines. However, a production bottleneck may subsequently occur at the forming stage, as high precision thermoforming systems are only generally capable of handling smaller numbers of units per production cycle, making careful planning of the overall process a necessity.

It should also be noted that most films used for FIM have been purpose designed and are extremely resilient, enabling both shallow and deeply drawn shapes, typically up to 3.0cm in depth, to be produced without surface cracking or affecting their mechanical or physical properties. In choosing the best films it is, however, important to consider the requirements of the final application so that, for example, chemical or abrasion resistance is incorporated.

Similar, there is a growing range of screen printing inks that have been developed specifically for FIM and these are able to withstand the high temperatures and shear stresses imposed during injection molding. Bear in mind, however, that the inks lay between the film and the molten resin so can easily be damaged by heat if they have not specifically been designed for FIM, leading to a condition known as washing out.

In particular, problems can occur around the gate area, or the point or points in each mould through which molten resin is injected and where temperatures tend to be highest. To overcome these issues special melt-resistant inks, such as thermal-cure, UV-curable or high melt-resistant polymers, are required.

Forming represents the second major stage in the FIM process, taking the printed flat sheet to create a three dimensional shape, prior to final trimming and injection molding. There are a number of methods that can be used and choosing the right process for each job is important to ensure that print registration and quality are retained.

For example, vacuum forming can be carried out at relatively low cost, produces shallow and deep drawn parts, and is capable of handling large area sheets, so higher numbers of components can be produced during each production cycle. The high temperatures used, however, can lead to distortions that adversely affect areas requiring high print registration tolerances.

By comparison, high pressure forming at lower temperatures can minimize distortion errors, and be used for shallow and deep drawn parts alike, but the high clamp forces required mean that machines tend to be smaller, so fewer parts can be produced per cycle.

A third option is Hydroforming, which produces extremely high pressures, so sheets can be molded at low or ambient temperatures, thereby eliminating heat distortion. However, although registration is generally excellent it is difficult to form anything other than shallow drawn shapes, while harder polymer films have to be used to prevent surface damage from contact with the blanket or bladder.

The final process stage is injection molding and this ideally requires mould tools that have been designed for each FIM component, to ensure that high levels of detail and graphics resolution are realized. In addition, the forming or molding tool should be formatted to maximize the number of parts produced in each production cycle, as careful part placement will minimise scrap and simplify subsequent trimming operations.

When producing the mould tool it is important to ensure that the wall thickness, especially near gates, is carefully controlled, as thin walls will cause extreme shear stress on the pre-printed inks. Detailed graphics should be kept away from deep drawn sections and gates should be positioned in areas free of ink; if this proves impossible then use a wide fan gate or a gate that produces an even melt-flow across that area of the component, to minimise turbulence, ink wash and shear effects; try also to ensure that particularly detailed graphics are not included in the gate area.

In conclusion

Film Insert Molding is an exciting and rapidly evolving process that offers considerable opportunities for designers, OEMs and end users alike in a wide range of applications. In a world where manufacturers have to respond faster and more cost effectively than ever before to retain a competitive edge, FIM looks set to become a key tool that delivers value and cost savings while cutting time to market.

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