If you machine brass parts through which drinking water will one day flow, you’re likely aware of the recent lead-free legislation affecting your customers. Federal law S3874, the Reduction of Lead in Drinking Water Act, went into effect nationwide on January 4, 2014. In the near future lead will be removed from virtually all ferrous and non-ferrous alloys, so free cutting brass will no longer be available for any application. Which means manufacturers face a number of challenges to machine lead-free brass rather than the brass materials you have used for many years.
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Why There Is Lead In Brass
Lead is added to brass to make the material easier to machine, because it is softer than steel, copper and zinc. Lead also acts as a lubricant within brass, because it has a lower coefficient of friction and produces less heat. This enables CNC machines to operate at high speeds that result in fast cycle times.
Removing lead from brass, therefore, increases the hardness of the material as well as the amount of friction, which creates more heat. No-lead brass alloys also produce chips that are more complex than those formed by machining traditional brass. Many unleaded brass alloys produce longer, stringier chips and bird’s nests.
Machining Unleaded Brass
Clearly, switching to no-lead brass alloys will require rethinking how to properly machine these parts in the most efficient way. The primary reason is that it simply takes longer to machine unleaded brass than 360 brass. It also requires different types of cutting tools, presents potential problems for maintaining acceptable surface finish due to chip breakage, and produces chips that may be more difficult to remove. The goal for manufacturers is to reduce the impact of these issues on cycle times, overall productivity and customer deliveries.
Machining most unleaded brass alloys is much like machining 1018 steel. This brings up a number of considerations for manufacturers who historically focused on machining 360 brass:
- Machine Tools: Machining unleaded brass requires much greater rigidity and power to cut through the harder material. Not every machine tool that successfully makes parts from 360 brass can properly machine unleaded brass. Even if your present CNC machine is capable of handling the increased demands of machining unleaded brass, you should ask yourself if it has been properly maintained and is up to the new task. If you’ve been steadily machining 360 brass on this machine, it may need a serious tune-up before taking on the new challenge. Multi-diameter step and form tools traditionally employed for part machining free cutting brass are not applicable for lead free brass. Nor are threading dies in most cases. Single pointing, multi-diameter characteristics are the best approach to vary chip loads and achieve best results.
- Tooling: Obviously machining a harder material like unleaded brass requires a change in tooling strategy. Unlike 360 brass that requires simple cutting tools, unleaded brass is not only harder to machine but creates more heat. This means using cutting tools with the right coating, such as AITiN and TiN coated carbide for some applications. Each specific type of unleaded brass material and the processes being performed will dictate the kind of cutting tool material, coating and point style to be used. Certain applications may also require higher helix angles, increased clearance angles and wider flutes. ISO insert style tools become the standard, as the brazed carbide step tool is no longer practical.
- High Pressure Coolant: The increase in friction-produced heat requires precise applications of coolant to the cutting area. Higher coolant pressure directed at the cut can also break up chips to help maintain surface finish and aid in chip disposal. In many cases this requires high-pressure coolant delivered at 40 to 75 bar. Programmable, high-pressure coolant systems that provide variable pressures are helpful when switching between various types of materials. Of course, the days of dry machining brass are over.
- Feed Rates: Assuming you’ll need to reduce cutting speeds to compensate for the increased heat build-up when machining unleaded brass, by increasing the feed rate you can maintain a removal rate that helps make up for the speed reduction.
- Using Hot Forged Parts: The best way to machine a challenging material is to machine as little of it as possible. Therefore one approach to dealing with the impact on productivity when switching to unleaded brass is to machine hot forged parts rather than working from bar stock. These parts are near net shape, machine more easily than bar stock and require less material removal. Hint: Hot forging technology that produces cored forgings provides further weight reduction.
Protecting Your Bottom Line
In addition to the machining challenges presented by no-lead brass are potential dollar-and-cents issues. Manufacturers must comply with regulations, but what about increased costs? After all:
- Material cost for lead-free is higher per pound.
- Perishable cost per pound of material removed is higher, by as much as 5 times for rough turning.
- Feed & speeds are slower, producing fewer parts per hour.
- Lead-free brass chips & scrap need to be separated from other materials.
All of which could add up to increased costs of 50% or more. Not a pretty picture, but there is a solution: Applying the right CNC machine tool technology.
Your Pittsburgh Haas Factory Outlet consultants can help you make sure you have the right CNC machines to efficiently machine no-lead brass. To learn more call (724) 778-3220, email: tom.jonas@haasfactoryoutlet.com, or visit www.hfopittsburgh.com.