Moldmax In Injection Molding

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MOLDMAX HH is a high-strength beryllium copper mould alloy made by Brush Wellman Inc. for plastics moulding applications. Its main properties include:

  • High thermal conductivity
  • Good corrosion resistance
  • Good polishability
  • Good wear resistance
  • Good resistance to galling
  • Good machinability
  •  high strength and hardness
  •  excellent weld ability

The special properties of MOLDMAX HH beryllium copper alloy make it a suitable mould/core/insert material for a wide variety of moulding situations but especially where a combination of high thermal conductivity, corrosion resistance and good polish ability are needed.

  • Blow moulds: pinch offs, neck rings and handle inserts
  • Injection mould: moulds, cores, inserts
  • Injection nozzles and manifolds for hot runner systems

Moldmax is a registered trademark name for a number of copper alloy materials that are designed for the plastic injection molding industry.  

They are available in a variety of shapes and sizes, can be machined with conventional toolmaking machinery, can be welded and coated for extra abrasive resistance but the main advantage are their high heat conductivity compared to tool steels such as P20 and H13.

It has a heat transfer rate 3 to 4 times faster than tool steels so has the potential to improve cycle times and part quality.

When used in steel molds, MoldMAX alloys cool hot spots, reducing or eliminating the need for cooling channels. By minimizing the temperature differences of mold parts, MoldMAX alloys provide tighter molded tolerances and less post-mold shrinking or warping.

Not A Substitute For Poor Part Design

Parts that have been designed with extra thick walls are difficult to cool because plastics are a natural insulator.  As plastic is injected into a mould cavity the outside layer that touches the cavity wall has already become solid and this will limit the heat transfer  between the inside of the part and the mould cavity.  Naturally, parts with thick walls will take longer to cool than parts with thinner walls no matter what mould material is used.

That’s why when designing plastic parts the thinnest wall section possible in line with the application should be used and it should be uniform.  Having thick and non-uniform wall sections will cause hot spots in a mold and set up extra stresses in the part and will likely cause part warpage or distortion and longer than necessary mold cooling times.

Similarly, part shape can also have a significant effect on cooling rates and quality.  It is easy to get even cooling in flat parts such as container and lids because they allow the use of conventional machining processes such as drilling to be used. However, when the part is a complex 3D shape then more consideration must be given to the mold cooling system.

It is often the case however, that part design can be modified to allow even cooling especially during the early stages of a project.  Part designers need to have a sound knowledge of mold cooling design in order to avoid the possibility of hot spots which inevitably lead to low productivity levels and poor quality parts.

Although mold-max might help to improve part quality and productivity levels in some cases, the best solution is to design a part that will allow proper mold cooling design in the first place.

Flexibility

Moldmax has many of the advantages of tool steels so it can be used in a wide variety of applications. It can hold nickel, chromium and ceramic coatings such as TiN. There is no one coating that is right for all applications. Each coating will provide different degrees of corrosion resistance, easier mold release of parts during ejection, scratch resistance, and wear resistance from glass reinforced materials.

It can also be polished to a mirror finish. This gives parts an attractive cosmetic finish.  Care must be taken however, during the polishing process not to apply too much pressure for too long or the polished surface will become pitted and detract from the surface finish of the part. From this point of view, tool steel is easier to polish.

Mold max can be welded.  This is a big advantage because mold building materials can be damaged in a number of ways during the molding process and welding provides a quick and effective way of repairing.

 

Additional Comments

Although the material cost is higher than that of tool steel, when used for the right application, moldmax increases productivity while maintaining quality. It is not a substitute for poor part design, poor injection mold design or incompetent die setting or processing.

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