Factors influencing microinjection molding replication quality

Abstract

In recent years, there has been increased interest in producing and providing high-precision plastic parts that can be manufactured by microinjection molding: gears, pumps, optical grating elements, and so on. For all of these applications, the replication quality is essential. This study has two goals: (1) fabrication of high-precision parts using the conventional injection molding machine; (2) identification of robust parameters that ensure production quality. Thus, different technological solutions have been used: cavity vacuuming and the use of a mold coated with DLC or CrN deposits. AFM and SEM analyses were carried out to characterize the replication profile. The replication quality was studied in terms of the process parameters, coated and uncoated molds and crystallinity of the polymer. Specific studies were processed to quantify the replicability of injection molded parts (ABS, PC and PP). Analysis of the Taguchi experimental designs permits prioritization of the impact of each parameter on the replication quality. A discussion taking into account these new parameters and the thermal and spreading properties on the coatings is proposed. It appeared that, in general, increasing the mold temperature improves the molten polymer fill in submicron features except for the steel insert (for which the presence of a vacuum is the most important factor). Moreover, the DLC coating was the best coating to increase the quality of the replication. This result could be explained by the lower thermal diffusivity of this coating. We noted that the viscosity of the polymers is not a primordial factor of the replication quality.

Synergetic effects of surface texturing and solid lubricants to tailor friction and wear – A review

“…Indirect structuring refers to a textured surface that is subsequently coated with DLC, while direct structuring refers to the texturing of the DLC coating itself [191]. LST has been the most widely used technique for DLCs, for both indirect texturing [117,[194][195][196][197][198][199][200][201][202][203][204][205][206] and direct texturing [118,124,[207][208][209][210][211].…”

“…Since DLC films tend to be rather thin, conventional laser texturing techniques have not been very successful for direct texturing, leading to severe spalling [191]. Most successful reports of direct texturing of DLCs have been carried out using femtosecond pulsed lasers (due to reduced thermal effects) [124,209,212]. One alternative is direct laser interference patterning (DLIP) allowing for a fast fabrication of periodic patterns on macroscopic areas based on the interference of two coherent laser beams [118,192,210,211,213,214].…”

“…For bulges with heights around 100 nm and above, beneficial effects of texturing were often observed [207,208,210,212]. The width of the bulges changes with the laser fluence, varying from nanometers [118,192,209,210] to a few micrometers [208,211,212]. The main effects of the spacing between bulges are the change in real contact area and the amount of graphitization inside and outside the bulges.…”

Submillimeter features on injected acrylonitrile butadiene styrene parts: Visualization of the flow and numerical simulation

“…These cumulated effects generate this difficulty in micro-texture replication on the surface of a macroscopic part and therefore will limit functionalization quality of the part surface. [7] The creation of this frozen layer is also influenced by the injection velocity, which in multiple studies is shown to be a key process parameter in the replication quality of micro-features. [8] Nowadays, an injection molding simulation allows for a relatively reliable prediction of injection problems and this is done using the commercially available software.…”

Micro-Injection Moulding In-Line Quality Assurance Based on Product and Process Fingerprints

“…In fact, as the injected melt volume is extremely small, the surface-to-volume ratio increases, and thus a very fast solidification occurs, hindering the complete filling of the cavity [ 6 ]. Therefore, in order to favour the replication capability of the process, high levels of injection speed, melt temperature and mould temperature are typically required [ 7 , 8 , 9 ]. Since the levels of these parameters are superiorly limited by the occurrence of polymer degradation, the process window of µIM becomes narrower than that of IM, making process optimization a fundamental step for manufacturing products that comply with design specifications.…”