Tag: thermal conductivity

A Deeper Understanding Of Conformal Cooling For Injection Molds

By Bozilla
November 22, 2019

Conformal cooling has become the latest trend in the injection molding industry   As it compares to traditional gun-drilled cooling lines, it appears to be better, but is that always the case?  We will discuss the comparisons and application of both traditional cooling versus conformal cooling as it applies to heat removal of the polymer/part

When designing cooling for injection molds, several factors must be understood with regards to the properties of the tool steel such as the type of steel and its corresponding properties ie  thermal conductivity, thermal diffusivity, specific heat capacity and density   Those same properties must be considered for the coolant along with Reynolds number and flow rate

Thermal conductivity:

A measure of a materials ability to conduct heat as shown below:

Thermal Conductivity

Thermal diffusivity:

The thermal conductivity divided by the density and specific heat capacity (at constant pressure) as shown below:

Thermal diffusivity

In order to take advantage of these properties, certain guidelines should be considered such as the spacing between adjacent cooling circuits, thickness or cross section of the circuits and the spacing between cooling circuits and the cavity  The flow rate must be sufficient enough such that the coolant is turbulent (Reynolds number above 8000) in all regions of the circuits in order to have maximum heat removal

Conventional Cooling (gun-drilling):

Gun drilled cooling channels are straight holes cut through the tool steel  Because these are straight holes, it limits the regions in which holes can be cut such as in any action within the tool or small or difficult regions near the cavity of the tool  Implements can be used such as heat pipes (thermal pins), bubblers, baffles and small circuits and high heat-transfer materials  However, there are still regions within the tool that are difficult to implement cooling and these regions are typically accepted  They can cause issues within the mold such as parts sticking or controlling cycle time

Gun drilled cooling channels are very adequate when sized and spaced correctly  Basic guidelines will take advantage of the properties of both the coolant and the cooling channels:

  • The spacing of the cooling channel from center-line to center-line (pitch) should be no more than 3 times the diameter (3D)
  • The distance from the cooling channel to the cavity surfaces should be no more than 15 times the diameter (15D)

If these simple guidelines are maintained, there will be adequate

Read More