INNOVATION | CAPS AND CLOSURES
different additive manufacturing technologies that allow larger dimensions, smoother channels, and higher cost effectiveness compared with Powder Bed Fusion 3D printing technology.” Traditionally, cooling channels for moulds were
straight and drilled in secondary machining operations. If a mould required additional cooling, toolmakers might design an insert that provided channels with baffles or helix baffles. In more complex instances requiring highly intricate cooling channels, the mould would be split into segments. Matching half-channels were milled into the segments, which were then soldered together to produce channels that did not follow straight lines. This process is expensive and mould life shortened because the solder often deteriorated over time. Moreover, these designs are often limited geometri- cally, introduce potential leakage issues (a risk if high value controllers and hot runners, for example, are nearby), and offer unbalanced water flow on multi-cavity tools. This means that thermal perfor- mance is almost always limited with these tech- niques, often resulting in slower cycle times or warp/sink quality issues associated with hot spots or uneven cooling patterns.
Most conformally cooled components are now manufactured by PBF, which typically does not perform well with overhangs greater than 45 degrees (cooling channels will all have to close at greater angles), introducing porosities or crack initiation sites at the closure of channels that are too large. For this reason, PBF is typically limited to 3-4mm diameter channels and often using awk- ward ‘tear drop’ shapes to try and reduce overhang challenges. Rough internal surfaces result from the process and must be dealt with properly, otherwise corrosion, scale and contaminants build up much more quickly on the small rough channels. To counteract the high pressure drop from small channels, designers of PBF parts often introduce parallel flow circuits which are notoriously hard to troubleshoot for clogging. Additionally, micro- cracking, bad thermal post-processing, warping
Residence time
comparison between
conventional and iTherm hot runner manifold
and high cost are all associated issues with PBF. Material choice in PBF is limited to non-tooling steel grades, such as Maraging steel. HTS IC has developed Metal Fusion Technology (MFT) – a form of Diffusion Bonding Additive Manufacturing – to produce conformal cooled components under the iTherm brand. MFT is based on diffusion bonding of pre-machined layers of premium tool steel, with the mechanical properties of the diffusion bond being comparable to that of forged tool steel. Material selection can practically be any tool steel, although most often 1.2343 / H11, 1.2344 / H13, 420SS, High Thermal Conduc- tivity Steel (HTCS) is used. The company says that this presents many material options, including new high thermal conductivity tool steel alloys that can offer a unique thermal advantage when combined with iTherm technology, to deliver industry-best thermal performance for challenging geometries. MFT also enables complex geometry possibilities,
Steady state analysis of conventional gate insert and iTherm gate insert
Source: HTS
Source: HTS 42 INJECTION WORLD | April 2021
www.injectionworld.com
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