Twenty Years of Copper Alloys in Moldmaking(1)

A look at where we are today with the integration of copper alloys in mold building.

Prior to 1987, there was very limited use of copper alloys as molding surfaces and molds using copper alloy materials were rare. It was believed by a majority at that time that copper alloys were just not strong enough, hard enough or tough enough to endure in a mold.

In 1988 there was an article published, whose first sentence read, “Every injection and blow molder who intends to stay in business must continually ask himself, ‘What must I do to run as fast and efficiently as possible and still meet the customers’ quality requirements?’” From that point, the article went on to cite the how’s and why’s for using copper alloys in mold applications and how copper alloys would contribute to mold cycle reductions and part quality improvements.

Fast forward 19 years and ask the following:

Q. How many of the molders and moldmakers—who did or did not follow that insightful and educational information—are still in business today?

A. Statistically about 50 percent of molders and moldmakers have embraced the technology and it is believed that the holdouts who chose not to have paid the price. Some are gone from the industry completely, some have lost business and others are still out there, but struggling.

Q. Are molders and moldmakers using copper alloys effectively and efficiently in their molds?

A. In most applications the usage is still quite conservative and in many cases the copper alloy that does get used, may be the wrong alloy for the specific application. The decision to use the wrong copper alloy may be driven by misinformation about specific alloy performance, product misrepresentation, pricing or availability issues. This will lead to less than optimum performance, short component life or outright failure.

Q. Are the best products for the mold application being used or is the techno-logy being obstructed by ignorance, supplier sales pitch or misinformation?

Table 1
CDA #
Hardness Elongation Conductivity
C17510 20 R/C 5-15% 145
C17200 30 R/C 3-8% 75
C17200 40 R/C 1-3% 60
C18000 20 R/C 9-13% 150
none 28-30 R/C 7% 80-90
C72700 30 R/C 4% 35-40
C72900 34 R/C Min 3-5% 22
C95400 89 R/B 12-14% 36
C95900 30 R/C 1.5% 25
none 29-32 R/C 1% 25
Hardness, elongation and conductivity. Table courtesy of Manufacturer’s Product Literature.

A. There are misapplications of copper alloys all of the time. Many times the wrong copper alloy is used because of ignorance, misinformation or misrepresentations by suppliers. What may seem as an insignificant change from one product designation or brand to another can significantly impact the mold component life and performance. For example, copper alloys with similar hardness levels can have conductivity levels (the main reason for using copper alloys) only slightly higher than steel. Another example: copper alloys with hardness levels approaching 40 Rockwell “C” have very low ductility with elongations in ranges less than 3 percent. Low ductility and elongation often leads to cracking or breakage of mold components (see Table 1).

Copper Alloy Usage
During the last 20 years, copper alloy use as molding and wear surfaces in molds has been expanding although the industry has been slow in learning how to properly and fully integrate copper alloy products into their mold designs. The growth of copper alloy use in comparison to technological advancements with machinery, process equipment and resins has been limited by market acceptance, and in some cases, lack of understanding the available products.

An informal survey of molders and moldmakers still shows a large percentage believing that copper alloy usage in their molds is of little to no benefit. The belief is that copper alloys will not really reduce their mold cycles, will not improve part quality or will not contribute to other performance improvements. There also is fear of higher maintenance costs or higher initial mold costs.

How to Choose the Right Copper Alloy

Bronze alloys or spinodal alloys are often mistakenly used as molding surfaces because they tend to be less expensive or readily available. Although for ejector sleeve, bushing and wear plate applications bronze and spinodal alloys work extremely well.

For molding details such as cores and core inserts, there are alloys that have five times the conductivity, making them a far better choice because the mold performance is not just slightly better, but drastically better.

Experience by molders has shown copper alloys actually do reduce mold cycle times, improve piece part quality and reduce mold maintenance costs. Moldmakers or molders that increase prices because of copper alloy usage are often just inexperienced with the product or just taking advantage of the situation. Typically copper alloy mold components show cost savings to the mold builder due to machining processes for those copper alloys that offset the additional cost of copper alloys over tool steels.

Beryllium Copper or Copper Nickel Alloys
Basically there are two families of alloy chemistries that yield high strength, high conductivity alloys that are the best choices for use as molding surfaces in molds. The families are either beryllium copper-based, or copper nickel-based. Both alloy families have other minor elements added for individualized purposes in each combination.

 

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