A review of liquid silicone rubber injection molding: Process variables and process modeling

Bont, Matthew; Barry, Carol; Johnston, Stephen

doi:10.1002/pen.25618

Cited by 36 publications

(31 citation statements)

References 81 publications

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“…[19] The machine then clamps the mold together with 8-25 MPa of pressure, and precisely dispenses both components through a static mixer into the mold with pressures from 1-10 MPa. [20][21][22][23] The mold is heated typically between 120 and 160 °C to allow quick curing and fast cycle times. [22,[24][25][26][27][28] The part is then removed, and the processes is repeated.…”

Section: Industrial Liquid Silicone Injection Moldersmentioning

confidence: 99%

Injection Molding of Soft Robots

Bell

Becker

Wood

2021

Adv Materials Technologies

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tional components such as magnets or tubing, or using new production methods such as directly 3D printing soft actuators. [1] The creation of internal voids and undercuts is inherently a challenge when molding. The traditional method is to glue two parts together, [2] or dip a cured half in uncured material. [3] Soluble or wax cores can allow for complex voids which are later removed out drain holes. [4][5][6] Soft cores are flexible (usually softer than the desired molding material), and enable voids to be created while being able to be reused multiple times. [7] Using a technique from industry, rotational molding that is normally used to make large plastic products such as kayaks, can be used to create internal voids in soft actuators, but control of the wall thickness becomes difficult for features such as bellows. [8] Alternatively, dip-coating can control the internal geometry but control of the external wall thickness is difficult. [9] Strain limiting layers are the most common type of reinforcements embedded into soft actuators, such as paper or fabric sheets to prevent extension of an actuator. [10,11] In order for embedded components to adhere to the silicone, components can be dipped and stuck to a structure, [11] or molded during the casting process. [10] Small magnets or nuts can also be embedded, but require a mesh to grip enough silicone to prevent the magnet or nut from pulling out during use. [12,13] 3D printers and materials have recently become more capable of directly printing soft actuators, potentially eliminating the need for mold making and casting. [14,15] Thermoplastic polyurethane (TPU), which is widely and cheaply used in shoes and clothing, has the potential to be directly printed producing robust bellows. [16] Recently, Voxel8's ActiveLab Digital Fabrication System (Voxel8, Somerville, MA, USA) has been able to print varying stiffness TPU with large overhangs while curing on-the-fly. Another method, embedded 3D printing, allows complex microchannels to be produced using sacrificial materials to create void space after silicone is cured. [17] Injection Molding Soft RobotsWe have developed a low-cost injection molding method ($10s-$100s), as seen in Figure 1, that incorporates the high pressure and in-line mixing capabilities of industrial liquid silicone injection molding machines into a versatile machine for prototype and low volume production. Our setup allows for To date, injection molding has not been a practical manufacturing method for soft robots due to machine costs, large volumes of liquid silicones required, and the inability to change materials quickly between shots. Injection molds are typically machined from metals to allow for high pressure and clamping forces, which further limits the ability to rapidly prototype soft robots when molds could cost thousands of dollars. To circumvent these issues, a lowcost injection molding system and process are pioneered. In this article, the apparatus, design process, economics, and workflow are described using standard stereolithogra...

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Section: Industrial Liquid Silicone Injection Moldersmentioning

confidence: 99%

Injection Molding of Soft Robots

Bell

Becker

Wood

2021

Adv Materials Technologies

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“…Liquid silicone rubber (LSR) can be injection moulded with specialized equipment and cures (crosslinks) in a heated mould [ 5 , 8 ]. The most common LSRs are based on vinyl methyl silicone pre-polymers, but there are also other chemistries (with the same siloxane backbone) for certain applications.…”

Section: Introductionmentioning

confidence: 99%

“…For LSR, the crosslinking reaction is a platinum-catalysed hydrosilylation reaction between Si-H on a (short) crosslinker and a vinyl end group on a (longer) pre-polymer [ 5 ]. LSRs are sometimes post-cured [ 6 , 8 ]. The post-curing can serve a dual purpose: to finalize the crosslinking (if uncomplete) and to remove volatiles such as short chain siloxanes [ 9 ].…”

Section: Introductionmentioning

confidence: 99%

Cyclic Compression Testing of Three Elastomer Types—A Thermoplastic Vulcanizate Elastomer, a Liquid Silicone Rubber and Two Ethylene-Propylene-Diene Rubbers

Persson

Andreassen

2022

Polymers

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Thermoplastic elastomer vulcanizate (TPV) and liquid silicone rubber (LSR) are replacement candidates for ethylene-propylene-diene rubbers (EPDM), as they offer the possibility for two-component injection moulding. In this study, these material types were compared side by side in cyclic compression tests. The materials were also characterized to provide details on the formulations. Compared to the rubbers, the TPV had higher compression set (after a given cycle) and hysteresis loss, and a stronger Mullins effect. This is due to the thermoplastic matrix in the TPV. The LSR had lower compression set (after a given cycle) than the EPDM, but stronger Mullins effect and higher relative hysteresis loss. These differences between the LSR and the EPDM are likely due to differences in polymer network structure and type of filler. Methods for quantifying the Mullins effect are proposed, and correlations between a Mullins index and parameters such as compression set are discussed. The EPDMs showed a distinct trend in compression set, relative hysteresis loss and relaxed stress fraction vs. strain amplitude; these entities were almost independent of strain amplitude in the range 15–35%, while they increased in this range for the TPV and the LSR. The difference between the compression set values of the LSR and the EPDM decreased with increasing strain amplitude and increasing strain recovery time.

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“…This resin is widely used in electronic appliances, construction, chemical industry, and transportation. [1][2][3][4][5][6][7] However, traditional polysiloxane polymers have disadvantages, such as low thermal conductivity and poor mechanical properties, which limit their applications as thermal interface materials. Nanomaterials can improve the mechanical and thermal properties of silicones.…”

Section: Introductionmentioning

confidence: 99%

Study on preparation and field induction mechanism of organic silicon composites based on aligned carbon nanotubes

Liu

Zhou

et al. 2022

Polymer Engineering & Sci

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High thermal conductivity materials are an urgent need for high power, microelectronic components and equipment, but are limited by low thermal conductivity of the traditional silicone materials. 4‐Cyano‐4′‐n‐octyl biphenyl (8OCB) was synthesized to modify carbon nanotubes, and silicone was used as the matrix. In the curing process of the composite, an electric field was applied and the liquid crystal induced the orientation of carbon nanotubes in the direction of 8OCB liquid crystal. The morphology, structure and properties of modified carbon nanotubes and composites were characterized by Fourier transform infrared spectroscopy, polarized microscopy, transmission electron microscopy, thermal conductivity, and so on. The 8OCB liquid crystal can improve the dispersion of carbon nanotubes in silicone composites. When the mass fraction of multiwalled carbon nanotubes (MWCNTs) was 11 wt%, the thermal conductivity of 8OCB‐MWCNTs/silicone composite after electric field was 2.39 W/(m K), which is 6.4 times that of MWCNTs/silicone composite after electric field and 15.5 times that of pure silicone matrix. A method to obtain highly ordered filled thermal conductive materials by applying an electric field to induce the orientation of carbon nanotubes is demonstrated.

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A review of liquid silicone rubber injection molding: Process variables and process modeling

Cited by 36 publications

References 81 publications

Injection Molding of Soft Robots

Injection Molding of Soft Robots

Cyclic Compression Testing of Three Elastomer Types—A Thermoplastic Vulcanizate Elastomer, a Liquid Silicone Rubber and Two Ethylene-Propylene-Diene Rubbers

Study on preparation and field induction mechanism of organic silicon composites based on aligned carbon nanotubes

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