Возможно кому-то будет полезно в качестве ликбеза.
Firearm sales have increased exponentially over the past few years, and forecasts are continuing to rise. As manufacturers seek to meet demand while decreasing costs, reducing weight, and increasing durability, the spotlight is turning to engineering and design capabilities in the industry. Engineered metal solutions, including expertise in such technologies as precision CNC machining, metal injection molding (MIM, also known as powder injection molding, or PIM), laser welding, and stamping, are key to meeting the challenges of this growing industry.
Engineering firms are rapidly expanding to provide the engineering and design capabilities necessary to accommodate the boom in the firearms market. In guns and other projectiles, most branches of mechanical engineering are applied, including wear properties (tribology) of the moving parts, manufacturing of highly precise machining processes, and system design. A high degree of design collaboration with top gun manufacturers is imperative to meet the needs of today's firearms purchasers, whether they are for personal protection, law enforcement, hunting, or for the military.
For example, Tracy MacNeal, ATW Companies' director of business development, notes the importance of engineering expertise for helping firearms manufacturers hit tight tolerances and resolve complex issues. "Identifying prototyping needs, turning around a prototype quickly, developing the best materials for the application, and providing advice on appropriate designs and tolerances are services that are essential to supporting today's firearms industry," says MacNeal. Warwick, R.I.-based ATW Companies is a provider of highly engineered metal solutions to the metal component marketplace. ATW's metal injection-molding arm, Parmatech, specializes in small parts of complex shapes, enabling part manufacturing that can often be prohibitive or impossible to make with conventional technologies.
According to Chris Schirmer, quality control manager at STI International, a Texas-based company that manufactures complete M1911 pistols and parts for competition, duty, and self-defense, designers must pay careful attention to the application of the firearm. "What is the intent of the firearm?" Schirmer asks. "Is it concealed carry, competition, or law enforcement? Each area of firearm use will have specific requirements that need to be met, which requires decisions on size, material, weight, length, and caliber."
Since most people have very limited budgets, consumers like to buy inexpensive firearms, and most manufacturers are responding by looking for ways to reduce costs. This is why many firearm manufacturers are using molded plastics, aluminum extrusions, and die-cast zinc parts in their new designs. All of these processes can be used to make inexpensive, strong, and durable components.
High tolerances and precision function are keys to every component in gun manufacturing. For example, Metalform Magazines (one of the ATW Companies), produces firearms magazines. A magazine is a relatively simple device that feeds rounds into the pistol's chamber via a spring-loaded follower mechanism. Although standard magazines tend to cost only $15 to $75, depending on design/size, this small component can determine how well a $2,000 pistol works.
Kevin Collins, a senior design engineer at Savage Arms, a Westfield, Mass.-based manufacturer of rifles and shotguns, explains that designing weapons for today's firearms purchasers depends not only on precision, but also weight. "Lighter and stronger has been a goal for a long time, and the design mantra has been to look to polymers, aluminum, titanium, and carbon fiber to get just the right combination of durability and weight," Collins says.
Today's hunters are looking for lightweight rifles, and designers are responding to the demand by looking at aluminum frames and receivers, says Collins. This can save as much as 30 to 50 percent of the weight of the firearm and shipping of the raw material, and it also saves on machining costs.
The application of the firearms determines much of the desired weight requirements. Collins notes that in hunting applications, in which the hunter might be making only a few shots in a given day, a lighter gun is easier to carry, and the extra recoil is not much of a problem. By contrast, in a shooting-range application in which the shooter might be firing many rounds, the recoil associated with a very lightweight rifle will cause fatigue fairly quickly. Engineering design seeks to resolve these opposing requirements.
Reinforced plastic with steel ribbing is another design innovation being pursued, though Collins acknowledges the downside of polymers, especially where the weapon may be used in areas with a large temperature fluctuation, as steel components may expand when plastic does not. The variation in these temperature coefficients will eventually cause loosening of the gun's components, which is not desirable.
Metal injection molding for firearms manufacturing
Metal injection molding (MIM) is a popular choice for relatively high precision at a low cost. MIM combines powder metal with a low-melt polymer to create a feedstock that is molded using conventional injection-molding equipment and molds. After molding, the plastic, which is known as the binder, must be removed in a step called debinding. After debinding, the parts are placed into high-temperature sintering furnaces and sintered. The result is a solid metal part created from powder metal to near net shape at 96 percent density of wrought metal.
There is little waste in the MIM process compared to other competing technologies, making MIM a green technology. MIM is a low-cost, high-volume manufacturing process that produces geometrically complex metal parts that are difficult or near impossible to produce using other conventional metal fabrication technologies. This means MIM can be used to produce complex shapes that can cost 20 to 50 percent of a machined part, producing far less material waste, with high production rates.
Key major firearms manufacturers have adopted MIM widely, and new projects are likely to include MIM parts, due to the cost and consistency of the process. Depending on volume requirements and part complexity, MIM can significantly reduce the component cost and, in some instances, yield parts that could not be made using any other method. Manufacturing of metal components using MIM technology has enabled U.S. companies to stay within the United States for sourcing components, due to MIM's high manufacturing capability and competitive pricing.
John Lewinski, director of supplier management at Springfield, MA-based Smith & Wesson, notes that any of the company's new projects are likely to include MIM parts, due to the cost and consistency of the process. "MIM has allowed us to take cost out of the product while maintaining quality, and therefore pass the savings on to the consumer," says Lewinski.
Collins agrees, calling MIM the modern replacement to investment casting, especially for small parts. He says that MIM is a fairly new technology that is being used more and more for making firearm components. The parts are dimensionally consistent, fairly inexpensive, and the surface finish is smoother than machined or investment cast (IC) components. To save on costs, especially for entry-level guns, designers are achieving savings by designing guns with a less-than-smooth mirror finish on mating parts or where the parts are not super-close-fitting. The result is a utilitarian, perfectly functional firearm that is a little rough around the edges (pun intended).
In his view, Collins says the main drawback of current MIM technology is the material designation and selection. Most engineers are not familiar with the materials used for MIM parts. "Most MIM parts are not made from common AISI materials such as 4340 and 8620 alloy steels, and this is certainly a drawback for anyone wanting to make parts for existing military rifles such as the M14 and M16," says Collins. The rifles purchased by the U.S. military use lots of parts made from AISI 8620 alloy steel, and they don't have options for similar or equivalent materials. "Getting new materials approved for military use can be a hassle," Collins says.
Collins also notes that, at this point, IC still has a distinct advantage over MIM in that the cast parts can be bigger or heavier than the MIM parts. Next to stocks and barrels, receivers are the largest and most complex components for firearms. "Making a receiver with the MIM process would be a good test to validate the strength and durability of MIM components and materials," says Collins.
According to Collins, creative designs and manufacturing methods will be key, similar to the way firearm manufacturers during WWII found the most economical and least time-consuming ways of manufacturing firearms. In his view, there is no reason to make a firearm component any stronger or more complicated than it needs to be. This would only drive up its manufacturing cost, and it wouldn't necessarily improve its quality.
Chris Schirmer of pistol-maker STI International also believes that that the introduction of MIM components to the firearms industry has had a significant impact. "MIM allowed the manufacturers to create a ready-to-use, high-detail metal part in high volume at low cost," says Schirmer. "Unfortunately, the early MIM process left a lot to be desired, and the manufacturers using these parts experienced failures."
Schirmer says that, over time, the MIM process has improved to the point that it is a perfectly acceptable method of manufacture for most firearms makers, including STI. He does acknowledge that there is still concern in the public about the early failures, and its use may never be accepted by some consumers or by 100 percent of manufacturers.
According to ATW's MacNeal, designers must also pay careful attention to the identification and management of complex secondary operations that are performed on the MIM part, which may include laser marking, sub-assemblies, post-machining operations, and coating and plating requirements. Tooling design expertise and use of the latest analytical tools -- for example, SolidWorks and MoldFlow software -- are the final piece of the design puzzle. Companies with consolidated and broad capabilities are often a good solution for firearms manufacturers seeking to meet demand in today's boom, while ensuring the best balance of design and production are satisfying the market.
I have read with much interest the many comments in this [Smith and Wesson] forum pertaining to MIM, MIM Parts and the use of same in a S&W product. So far I have come away with several impressions and they are, "people in general don't like/trust MIM parts", and, "no one has said why." I will take a stab at this issue and see where it goes.
As background to our decision to use MIM in some areas of our Mfg Process we took a long hard look at our "Life Time Service Policy". It was clear to us that any change in any of our products such as the use of MIM components had to show equivalent or better performance and durability to those components that were being replaced or the "Lifetime Service" would haunt us forever. The second consideration was to determine if the change was too radical a departure from S&W mainstream design.
For the performance and durability issues we decided that if MIM could be used for the fabrication of revolver hammers and triggers successfully this would truly be an "Acid Test". There is nothing more important to a revolvers feel than the all-important Single Action that is established between the hammer and the trigger. Mechanically few places in a revolver work harder than at the point where the hammer and trigger bear against each other. If these surfaces wear or lose their edge the "feel" is lost. Initial testing was on these two critical parts.
Over time we arrived at a point where our best shooters could not tell the difference between a revolver with the old-style hammer and trigger and the new MIM components. Special attention was given to their endurance when used in our very light magnum J-frames such as the early prototype 340 & 360 Sc's. None of our revolvers work their components harder than these small magnum revolvers. Throughout this testing MIM held strong and finally we determined that this change judged on the basis of durability and feel was a good one.
The second area of concern to S&W was our customer’s reaction to this departure from the traditional. Many heated, intense discussions resulted but in the end the decision was made to move ahead with MIM. The issue of cost was only one of the considerations in making this decision. Equally as important was the issue of part-to-part uniformity and the result of this of course is revolver-to-revolver consistency. We found that revolvers that used MIM hammers and triggers required almost no fitter intervention in those areas during final assembly and final inspection and trigger-pull monitor rejection rates dropped markedly on finished guns. From an internal process point of view it appeared a "Winner".
Let's shift gears for a moment and talk about the MIM process. It is unclear to me as to the reason for many of the negative feelings on the forum concerning MIM. Typically when people complain and aren't specific in the reason why, the problem is often created by a departure from the "Traditional". Perhaps that is indeed what is bothering some people when they view MIM.
The term MIM stands for Metal Injection Molding. It holds some similarities to Plastic Injection Molding and many differences as well. To start we would take a finally divided metal powder. This could be stainless or carbon steel. Today even titanium is being used in some MIM fabrications. We would mix the metal powder and a thermoplastic binder (generally a wax) forming slurry of sorts when heated and inject this mix into a precision mold and finally form what is known as a “green part". This part is roughly 30% larger than the finished part it will become at the end of the process. Interestingly enough the green part at this stage can be snapped in two with simple finger pressure. The green parts are then placed in a sintering furnace filled with dry hydrogen gas and the temperature is brought almost to the melting point of the metal being used. Over time the wax in the green part is evaporated, the metal fuses and the part shrinks 30% to it's final correct dimensions. At this stage of the process the MIM part has developed 98 to 99%of the density of the older wrought materials and a metallurgy that is almost identical. Dimensionally it is finished and no machining is required. However the job is not yet done and the MIM parts are brought to our heat treat facility for hardening and in the case of hammers and triggers, case hardening. Depending on the particular metal alloy that was used at the start of the process we apply a heat treat process that is the same as would be used if the material were the older wrought style. Final hardness, case thickness and core hardness are for the most part identical to parts manufactured the older way.
Lets look for a moment at how we achieve dimensional precision when comparing these 2 processes. The old parts were each machined from either bar stock or a forging. Each cut and every resulting dimension was subject to machine variations, cutter wear, operator variations etc. If every operation was done exactly right each and every time and the cutter didn't let you down you would have produced a good part but sometimes this didn’t happen, resulting in a rejected gun and rework or in the worst case an unhappy customer. With MIM parts you must still machine to very high tolerances and your cutters have to be perfect and your machinist has to be highly qualified but all of this only has to come together one time. That time is when the injection mold is made. Typically a mold for this process costs S&W between $30,000.00 and $50,000.00; once it is perfect every part it makes mirrors this perfection and you have, in my view, a wonderful manufacturing process.
Hopefully this description will help us all better understand the MIM process. Please forgive the spelling errors and misplaced punctuation. I have no spell checker on this and the phone continues to ring!
Have a Great Weekend,
Project Manager, Smith & Wesson]
Currently S&W is paying about $1.20/Lb for stainless steel bar stock. Raw MIM stainless steel inject able material costs $10.00/Lb.
Investment casting is one of the oldest metal working techniques, and refers to the process in which molten metal is poured into a mold formed by using a wax pattern, which is then melted away. Metal Injection Molding (MIM) is a more recent metal working process, and uses molds and injection molding equipment to create metal parts.
Both processes result in strong, intricately shaped metal parts that are difficult to produce by traditional machining processes such as forging. However, there are certain differences between the two processes, and the suitability of one process over the other depends mainly on your business and product engineering needs.
COMMONLY USED MATERIALS
A wide range of materials such as stainless and carbon steels, and aluminum alloys can be used in in the investment casting process. Since ceramic molds are used in this process, they can be heated to a temperature above the melting point of the metal, and will not cool down when the metal is being poured. This makes investment casting the best process for high quality steel parts.
MIM uses a ‘feedstock’ that comprises finely-powdered metal mixed with a measured amount of binder material. Materials suitable for MIM are alloys with a higher melt temperature than copper; metals like zinc and aluminum that have a lower melt temperature, and alloys (like titanium) that form strong oxides are not suitable for the MIM process.
COMPLEXITY & PART SIZE
MIM allows for more design complexity – for example, thinner wall sections, sharper cutting points and tighter tolerances of up to +0.005" per linear inch – as compared to the investment casting process. In addition, MIM is better suited for the production of smaller parts that weight less than 20 grams, and that are less than 100 mm long.
MIM can achieve a surface finish of 1 µm, whereas the surface roughness of an investment cast part is usually around 3.2 µm. In other words, MIM produces a better surface finish than investment casting, and does not usually require post-production machining.
COST OF PRODUCTION
Tooling is a major cost factor in MIM, and therefore MIM is considered an ‘economy of scale’ technology, ideal mainly for large scale production of runs of millions per year. In general, for production volumes of less than 1000 parts per run, investment casting is the more economical process.
There is obviously a place for both the MIM and the investment casting processes – each has its own strengths and weaknesses. In general, however, MIM is the process of choice to produce large volumes of small, highly intricate parts made of high melt alloys, where finish and tolerance are critical. Investment casting is more suitable for smaller production runs of larger parts made of lower melt temperature alloys.
AmTech offers its customers both the above technologies, and we hope this article helps you choose the right processing solution for your part. For more information, contact the sales team at AmTech International.