Liquidmetal Alloys in Sporting Arms

Transcription

1 Liquidmetal Alloys in Sporting Arms Industry Sporting Equipment Challenge Overcome common firearm manufacturing obstacles and trade-offs by producing more durable firearm parts

2 Demand for higher quality, lower cost equipment in the sporting arms market continues to grow, and as a result, pressure on manufacturers has significantly increased. Innovative new designs have flooded the market, making firearms and other sporting equipment lighter, more durable, customizable, and more visually appealing. This can only be seen as a benefit to the consumer, but producing all of these requirements is often difficult and costly. From recreational shooters to the military, demands are typically the same: a lighter, more consistent, accurate, durable, and customizable gun. In order to design for these improved specifications, manufacturers must make tradeoffs. Will the firearm be heavier or more expensive? Are we willing to sacrifice dimensional consistency and potential performance for lower cost components or corrosion resistance? Is scratch resistance worth the extra cost? Are engraving, knurling, surface textures, or eye-catching CNC demanding design modifications completely out of the question due to the added cost? These are questions engineers in this industry ask themselves every day, and this case study will explain why Liquidmetal alloys could provide solid answers.

3 Precision The accuracy and consistency of a firearm are critical to its performance and may be the most important value proposition from a customer s point of view. Several factors go into the performance and accuracy of a weapon, but it is impossible to attain acceptable levels without excellent part-to-part tolerances and fit. CNC machines use small cutting tools guided by computer programs to generate shapes within very close tolerances. A downside is that no two parts are exactly the same because of variations in the cutting process and continuous wear of the cutting tools. Exact tolerances and intricate geometries can often make parts very expensive to CNC machine. Many sporting arms parts are manufactured using MIM because of its significantly lower costs than machining. MIM has provided a very valuable manufacturing solution for firearms components, but in some cases, dimensional variation from the process cannot achieve requirements. Repeatability and accuracy are limited with MIM because of the multiple process steps like compounding feedstock, injection molding, debinding, and sintering. Secondary processing can help attain critical dimensions but adds significant post-processing costs to the final part. Following extraordinary documented results on a recent customer application where surface profiles were critical to the performance of the part, Liquidmetal has begun collecting additional process variation data to be reported in an upcoming white paper. The Liquidmetal team is using a Hexagon Metrology, Optiv Classic 321 tp coordinate-measuring machine (CMM) to evaluate the precision of a Liquidmetal test part. Preliminary data collected from a sample size of 32 parts have demonstrated remarkable results. No part differed from the next by more than 16μm ( ) for two different dimensions on the part, which were 28.7mm and 45.6mm. Like the recent customer experience, tight tolerances equal or better than CNC machining can be achieved by the Liquidmetal process and alloys. The chart below contains a comparison breakdown of CNC machining, MIM, and Liquidmetal dimensional variation capabilities. Part-to-part variation Tolerances CNC MACHINING MIM LIQUIDMETAL ± 13 μm (0.0005") ± 13 μm (0.0005") ± μm ( ") ± μm ( ") ± 8 μm (0.0003") ± 13 μm (0.0005") For the sake of performance and feel, minimal part-to-part variation is crucial. When parts fit together within the firearm, moving components perform better and provide a feel of precision that separates great firearms from the average. In addition, many sporting arms enthusiasts prefer to swap parts in and out, or even build their own firearm from scratch. Manufacturing parts with exact tolerances and minimal variation will allow for easy part replacement, as well as giving the user confidence in their firearm s performance. Durability As previously noted, amorphous alloys are in uncharted territory when considering their strength to weight ratio in comparison to stainless steels and low alloy steels. A few other factors to consider in firearm applications are hardness, elasticity, and corrosion. LM105 as-molded hardness is comparable to the best hardened and heat-treated stainless and low alloys steels. Heat-treating requires specialized equipment and can lead to distortion, cracking and general quality problems, even when properly managed. The Liquidmetal process produces remarkable consistency out of the mold and will be discussed more below.

4 Hardness (Vickers) It is almost impossible to discuss the effectiveness of any sporting or outdoor equipment without mentioning corrosion. Extreme environments will corrode materials rapidly. Amorphous alloys perform among the best in terms of corrosion resistance. Several tests, including the ASTM B117 salt spray, a 30-day immersion test, have been performed with Liquidmetal amorphous alloys PH Stainless Condition H Stainless LM C Stainless 420 Stainless Hardened and Stress Relieved ASTM 4605 Low Alloy Steel Heat Treated LM105 has an elastic limit of 1.80% (as a percentage of its original shape). This could be its most impressive property considering its incredible strength and lightweight. In previous prototype testing, amorphous alloys replaced a steel clamp spring design that was failing after 100 cycles to an expected failure point up to 1240 cycles. In this application, the spring clamp is cycled open and closed and is expected to return to its unstressed dimensions. This is a great example of the performance impact amorphous alloys can have on a part under high stress over long periods of time. The Liquidmetal clamp returned to its original unstressed shape at every cycle and did not fail well beyond the minimum number of cycles. A firearm is exposed to natural elements from the desert heat and sand to freezing temperatures and snow, and everything in between. Many parts endure extreme demands and are expected to perform consistently in conjunction with many other mating parts over a long lifespan. Despite the lack of post-processing or treatment, manufacturers and users will have confidence knowing that amorphous alloys perform among the best in terms of scratch/dent resistance and elastic deformation. Visual inspection after the ASTM B117 test showed no change in surface properties from 336 hours in the salt spray chamber. When measured on a Scanning Electron Microscope at 5,000x magnification, there were no visible changes in surface quality. In the 30-day immersion test, the solutions were analytically diluted to 1L and inductively coupled plasma mass spectrometry was performed to determine elemental concentrations. In comparison with stainless steel, the amorphous alloy experienced roughly 1/14th the dissolution in 1N HCl, and 1/5th the dissolution in 1N H2 SO4. Liquidmetal alloys excelled in the salt spray test, and well outperformed stainless steel in the 30-day acidic submersion test. The Liquidmetal engineering team is continuing corrosion studies going forward, to further grasp the potential of the material. Surface Finish Because amorphous alloys reflect the surface of the mold, it is typical to see parts come out of an appropriately finished mold with a surface roughness of μm (1-2μin). That surface roughness is nearly the surface quality of an optical-grade mirror and cannot be achieved by any other molding process. How this works is tied to a differentiating characteristic of amorphous alloys from that of any other metal alloy: amorphous alloys have a random atomic structure. Why is a lack of crystals important?

5 Crystalline metals go through one or more phase transformations when processed, which naturally give rise to the material properties of the final metal part. No phase transformation occurs during the molding process of amorphous alloys. After the material is heated for molding, it is frozen or solidified in the mold in the same atomic configuration as it was in its liquid state. This is the key factor that allows the material to accurately mimic the condition of the mold cavity, including dimensional precision. The final part s surface roughness ultimately depends on the manufacturers requirements, as the desired roughness will be built into the mold and no secondary operations or costs will be required to achieve the desired results. As with other metal alloys, additional processing is necessary to achieve material coloring on Liquidmetal amorphous parts. In the sporting arms industry bluing is often used on steel alloy parts. The result is a black finish, commonly seen on external firearm parts. Customization Laser etching, hand engraving, and other forms of custom design are common on metal and wood firearm parts. These markings can range from intricate designs, as seen in figure 1, to simple text, similar to that in figure 2. figure 1 figure 2 Due to the nature of the alloy used, Liquidmetal parts cannot undergo the bluing process but, physical vapor deposition (PVD), painting, and media blasting are all options for coloring. In the case of a firearm, PVD coating would be the most likely option to replicate the black appearance. In the case of complex engravings, like figure 1, most often a talented hand craftsman will spend many hours imparting extreme detail onto the firearm. This results in an original and authentic look, but at an extremely high cost to the customer.

6 With less intricate designs there is usually less labor associated with the engraving. CNC machines can often take the place of the hand craftsman, but still include machine-hours and set up costs. In the chart below, Liquidmetal alloy LM105 is compared to several commonly used metals in firearm production. Other alternative manufacturing methods to CNC machining, such as investment casting, can produce simulated engravings that attain the consistency and lowered cost of mass production. These include CNC machining, laser etching, photochemical etching, and stamping or coining. The main problem with these methods is that the result can easily be differentiated from true hand engraving and so the mimicked results are less desirable and attractive Density (g/cm 3 ) This is a major trade-off firearm buyers and manufacturers must make: should the gun have truly authentic looking engravings or a lower cost? Liquidmetal amorphous alloys have an extremely valuable asset in this situation what you mold is what you get. Due to the combination of Liquidmetal s injection molding process, its alloys, and extremely precise molds, the resulting molded components exactly duplicate the condition of the mold cavities. A hand engraved mold cavity surface, would produce exactly the same result on a molded part. This means that not only can detailed engravings, lettering, logos, and other surface details be injection molded, but part accuracy and repeatability are better than many other manufacturing methods. What is designed into the mold will be reflected onto the part. Weight No matter who you are or what the activity is, everyone can benefit from a lighter firearm. A key aattribute of amorphous alloys is its extraordinary strength to weight ratio. When discussing weight, any gun enthusiast will lobby for less of it, but never sacrifice quality, accuracy, or durability in the process PH Stainless Condition H Stainless LM C Stainless 420 Stainless Hardened and Stress Relieved ASTM 4605 Low Alloy Steel Heat Treated LM105 outperforms all of the other materials by a minimum of 13%, in density alone. When yield strength is factored in as well, only ASTM 4605 Low Alloy Steel and 440C Stainless Steel compete with LM105 s (1524 MPA) number. Both 440C and ASTM 4605 (along with most other stainless and low alloy steels) require different levels of heat treatment in order to achieve their high strength. Many heat treatment options are available for these metals, but the result is the same, added processing and cost. Additionally, heat treating can also cause distortion, which may undo efforts to produce tight toleranced part features. With amorphous alloys, final physical properties are achieved in the mold and therefore, no dimensional precision is lost as can be the case with heat treated metal alloys. LM105 s unique combination of low density and high strength results in no trade-off between weight and performance.

7 To determine which parts might work best for amorphous alloys, here are a few basic guidelines to follow for identifying and designing parts: Part weight up to 180 grams Maximum dimension of 200mm Outer draft angles of 0.5 to 3 Inner draft angles of 1 to 5 Wall thickness 0.3mm to 4.0mm Dimensional tolerance of ±0.020mm or better for critical dimensions Summary Restrictions on material properties and manufacturing processes impact the way engineers in the sporting arms industry design new products every day. Amorphous alloys present the opportunity to no longer have to make tradeoffs when manufacturing. The process offers design freedom within only a few restrictions and extraordinary material properties that come free with the part. Currently, the post-processing that is necessary for other materials to achieve many of the properties Liquidmetal alloys obtain is often economically prohibitive. Now you can produce hard, strong, corrosion resistant, elastic parts with extraordinary part-to-part precision and mirror-like surface roughness right out of the mold.

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