Advanced Beryllium Copper Alloys for Injection Molding

By AZoM

Table of Contents

Introduction
Key Material Properties
Fabrication of Mold
Selection of Suitable Materials
Conclusion
About IBC Advanced Alloys

Introduction

Like any manufacturing industry, the molding industry has given attention to cost reduction. The overhead cost represents a major portion of the per component cost in a molding operation when compared to material and tooling costs, as shown in Figure 1.

Figure 1. Material and tooling costs represent only a small portion of the per part cost in a molding operation. The overhead, which is directly related to the part cycle time is the driving factor

Achieving cycle time reduction can reduce the overhead cost without making any modifications to the product itself. In a typical injection molding operation, the time taken for cooling or curing can represent up to 50% or more of the total time required for part production. This curing stage of the molding cycle nearly entirely relies on the thermal conductivity of the core mold and cavity. Hence, optimizing the thermal conductivity reduces the curing time for the part, thus eventually decreasing component cost.

Key Material Properties

In addition to minimizing cycle time, high thermal conductivity also improves the thermal homogeneity of the component during cooling, thus resulting in reduced warping. Hot spots are areas where the tooling temperature is more than the surrounding material and the fabricated component’s local cooling rate is lower when compared to rest of the component. Hardness of the material is also another key property to be considered, because a hard material minimizes wear and provides better durability as it makes the mold more resistance to dents and scratches. Weldablity, machinability and corrosion resistance are other important properties. The comparison of thermal conductivity for materials typically utilized for mold cores and cavities is shown in Figure 2.

Figure 2. The ideal material for mold cores and cavities is one that has both excellent thermal conductivity and high hardness (note: the aluminum alloys have hardnesses below the effective range of the HRC scale)

From Figure 2, the C17200 beryllium copper alloy in TF01 condition demonstrates slightly decreased thermal conductivity for increased hardness, thus providing better wear resistance when compared to the TF02 temper of the C17200 beryllium copper alloy. The TF02 condition is engineered to optimize the thermal conductivity of the mold. In its both TF01 and TF02 conditions, the C17200 alloy demonstrates superior thermal conductivity and hardness when compared to any other materials.

It is necessary to consider the cost of the material to be utilized for making the core and cavity based on the hardness and thermal conductivity data provided in Table 1.

Table 1. Thermal conductivity, hardness and cost data for different alloys utilized for mold cavities and cores. Due to the variability of market prices, cost is represented as relative numbers from 1 to 10 where 1 is a higher cost material and 10 is very low cost.

Material [W/mK] [HRC] Rel. Cost
P-20 42 30 10
420 24 50 7
H-13 29 45 8
QC-7 138 80HRB 5
QC-10 159 165HRB 4
C17200 TF01 103 40 2
C17200 TF02 130 30 2

The cost of the core and cavity material typically accounts for below 15% of the total cost of the part. The limited effect of tooling cost provides the significant leeway during the process of materials selection. Point ratings for weldability, machinability and corrosion resistance for C17200 beryllium copper alloys as well as P-20, H-13 and 420 steel alloys are listed in Table 2.

Table 2. Point ratings for material properties from 1 to 10 where 10 is the highest

Mat. Therm. Cond. Corrosion Resist. Machin-ability Weld-ability
P-20 5 2 5 4
420 2 6 4 4
H-13 4 3 9 5
C17200 10 4 10 7

Fabrication of Mold

It is a challenge to specify the ease of machining of different materials. Nevertheless, the steels, especially the 420 alloy is tough to machine, while aluminum alloys are easy to machine and enable very high cutting speeds. On the other hand, the ease of machining characteristic of the C17200 beryllium copper alloy generally falls between the aluminum and steel alloys. The C17200 alloys requires a cutting speed slower than that applied for aluminum, but not as slow the speed used for the hard steels. The reasonable cutting speed for the C17200 alloys is roughly twice that used for steels.

The slower cutting speeds and increased cutting tool wear make steel and C17200 molds more expensive when compared to aluminum alloy molds. However the softer cores and cavities of aluminum alloy molds are more prone to damage and need frequent repair or replacement, negating the apparent cost savings associated with mold fabrication. Hence, aluminum alloy molds are ideal for only small production runs.

Selection of Suitable Materials

Selecting a material that is suitable for all molding applications is impossible. Part material, part geometry, and the number of parts to be fabricated are the deciding factors in materials selection. The mold fabricated from the C17200 alloy can produce components with good dimensional tolerances thanks to the material’s unique combination of superior hardness and thermal conductivity. Table 2 demonstrates that the C17200 alloy has equivalent or better scores in a number of key properties when compared to steel alloys. Although the initial investment required for the C17200 alloy is high, this cost can be rapidly recovered through sizeable savings achieved from the drastically reduced cycle times and part warpage, as shown Figure 3.

Figure 3. Selection of the wrong alloy for cores and cavities can result in significant lost profit due to the cost of inefficiency

Conclusion

Selecting the right alloy for mold tooling is a difficult task and several competing factors need to be considered. The use of C17200 alloy in mold tooling for large volume or high precision production runs can result in significant savings when compared to aluminum alloys or steels like 420, H-13 and P-20. Moreover, the use of hybrid molds of C17200 alloys and steels provides the cost advantage of steel in small production runs, while still minimizing the occurrence of warped, unusable parts.

About IBC Advanced Alloys

IBC Advanced Alloys Copper Division manufactures and distributes a wide variety of copper alloys as castings and forgings: beryllium copper, chrome copper and aluminum bronze in plate, block, bar, rings; and specialty copper alloy forgings for plastic mold tooling and resistance welding applications. We sell directly to end users and serve some markets through a network of established dealers and distributors. We source copper alloys in cast billet, slab or ingot and convert these into usable industrial products serving the industrial welding, oil and gas, plastic mold, metal melting, marine defense, electronic and industrial equipment markets. We also provide tooling components for the North American automotive industry, the European and North American consumer plastic tooling producers, the global oil and gas service industry, the prime North American submarine and aircraft carrier producers and repair facilities including the US Navy, electronics industries and general equipment manufacturers.

This information has been sourced, reviewed and adapted from materials provided by IBC Advanced Alloys.

For more information on this source, please visit IBC Advanced Alloys.

Date Added: Mar 28, 2013 | Updated: Jun 11, 2013
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