Tag: thermal diffusivity

Using Aluminum for Injection Molds?

By Bozilla
July 14, 2022

Aluminum tooling has significant benefits when compared to steel tooling because of the cost of aluminum as well as the ease of manufacturing Aluminum tools can be cut much quicker than steel saving a lot of time and money These benefits can result in shorter cycle times and price-per-part savings However, there are some drawbacks of aluminum such as being a softer metal which can cause mold deflection and also having a fatigue limit which can be catastrophic In order to better understand the advantages and disadvantages of utilizing aluminum for injection molds we will take a closer look at the properties of both aluminum and steel

Let’s compare the properties of aluminum to steel

Table of Aluminum v Steel properties

aluminum v steel table

The above table compares the properties of aluminum and steel Based on this table, we can determine the following

Density:                                  Aluminum is 279 times less dense than Steel

Hardness:                               Aluminum is much softer than steel

Thermal Conductivity:          Aluminum is 655 times more conductive than Steel

Thermal Diffusivity:              Aluminum has 79 times the thermal diffusivity than Steel

Yield Strength:                      Aluminum has almost half of the yield strength of Steel

Poissons Ratio:                      Aluminum deforms more than Steel

 Advantages of Using Aluminum for Injection Molds

 Now that we’ve compared aluminum to steel, we can take a look at the advantages of using aluminum for injection molds based on the above properties


 Aluminum is 279 times less dense than steel resulting in a lighter end product As the cost of shipping is increasing dramatically, the weight of any product will have a direct impact on shipping costs and must be kept low as possible


The softer aluminum reduces machining hours and wear and tear on machining components

Thermal Conductivity and Diffusivity:

Thermal conductivity and diffusivity is extremely important in injection molding as it directly impacts the cycle time Aluminum is 655 times more conductive and 799 times the diffusivity of steel which results in a significant reduction in cycle time, faster start-up times, reduction in response times to process temperature changes, and mold change times

The faster thermal recovery of aluminum also modulates the cyclic ‘highs-and lows’ of the tool temperature during processing As the melt is injected into the mold, the heat must be removed as quickly as possible Aluminum is able to process the heat out of the tool much faster than steel resulting in a more stable mold temperature and thus a more stable process

Disadvantages of Using Aluminum for Injection Molds

Poissons Ratio:

The Poissons Ratio of Aluminum is 033 and Steel

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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

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