Sandvik Coromant, a reference in the field of cutting tools and toolholder systems, explains in the following technical article, advances in aluminum machining processes.
There continues to be a year-on-year rise in the number of aluminium engines being produced, both for conventional and hybrid passenger cars. In fact, close to 100 million are now being manufactured every year. These engines house parts that are often complex in shape and, after casting, demand a sequence of varied but essential milling operations.
Sandvik Coromant now has a complete offer for aluminum machining in the automotive industry, from pre-machining of first stage references to roughing, semi-finishing and finishing. Each special engineering milling tool, five in total, has been designed to offer optimized quality and cost per piece. To help achieve this efficiency, certain tools in the range perform a combination of tasks such as roughing and finishing in the same operation to reduce cycle time.
An example of this is M5C90, an innovative milling cutter that combines roughing and semi-finishing in the same operation. It is a custom-made high-speed planning tool to eliminate long configuration times in the client's facilities. M5C90 operates with a reduced number of teeth compared to conventional milling cutters, mainly as a result of the exclusive radial and axial positioning of the inserts in their row of finish / inner diameter (without requiring any adjustment of the insert). This positioning guarantees a burr-free milling and an optimal surface finish on cylinder heads, braking systems and any piece of aluminum that allows to achieve a great fogging of the milling cutter (not applicable in thin wall parts).
Regarding the potential benefits offered through the use of M5C90, there is the case of a customer dedicated to the machining of valve bodies for braking systems of AlSi12Cu1. With an outer diameter of 10 hard metal inserts and an inner diameter of four inserts (plus a wiper insert), the tool is applied at a spindle speed of 8,000 rpm, a cutting speed of 4,021 m / min (13,192 ft. min) and an advance of 0.25 mm / tooth (0.009 in./ teeth). In addition, the axial depth of cut is 2 mm (0.078 in). With a radial depth of cut of 140 mm (5.51 in). Which produces a chip volume of 5,600 cm3 / min (342 in.3). / min). Although the total duration of the tool is not yet determined, it has been in the machine for 18 months.
For those requiring a cutter that can also finish thin-walled aluminium parts such as gearbox housings and casings, Sandvik Coromant has another cutter that is equally effective, the M5F90. The M5F90 is another one-shot roughing and finishing tool. Dedicated to the machining of thin wall aluminium parts and spot-facing operations, the cutter body (25-80 mm, 0.98-3.15 inch in diameter) houses brazed PCD tips. Each tip contains both a roughing edge and a finishing edge. The roughing area works as a conventional milling tool, with all cutting edges on the same diameter and height, while the finishing area consists of radial and axial stepped cutting edges. This concept enables a close pitch to deliver burr-free machining and outstanding surface finish.
Impressive time savings are possible, as seen in a customer case trial that involved the face milling of an aluminium (high Si content) cylinder head. Here, the use of M5F90 against a special PCD cutter manufactured by a competitor, not only saw a 150% cycle time saving, but eliminated burr generation. Cutting data included: 15,915 rpm spindle speed; 2000 m/min (6562 ft/min) cutting speed; a feed rate of 0.16 mm/tooth (0.006 in/tooth); and 1.5 mm (0.06 inch) depth of cut.
In a further M5F90 example, cycle time reductions of 44% were achieved on an aluminium chain case in comparison with using a competitor’s 63 mm (2.48 inch) diameter indexable cutter featuring six PCD inserts. What’s more, the solution eliminated a previously required brush deburring operation.
Another new engineered tool is the M610, which has been developed to mill the deck face/top of engine cylinder blocks with bi-metal interfaces, typically aluminium and grey cast iron (CGI).
A range of thermal and mechanical properties makes for challenging machining when it comes to bi-metal materials. Existing milling cutters for this application are complex and require adjusting, resulting in compromised throughput rates. In addition, such tools often cause chipping on the GCI portions of the component.
In contrast, M610 requires no set up and no adjustment, and results in the potential to deploy high feed rates without chipping, burring or scratching of parts. This capability is important as surface imperfections have the potential to produce leakage between the cylinder block and head, which in turn compromises power and performance. Some global automotive OEMs are already benefitting from the adoption of M610.
To reference one particular customer, enormous competitive gain has been achieved when finishing the combustion face on bi-metal engine blocks. Pitched against a competitor’s adjustable cutter with cartridges, the M610 achieved a tool life improvement of 833%, completing more than 4000 parts, in comparison with the competitor cutter’s 480. Moreover, the M610 performed at 10 times the speed. Cutting data for the 15-insert M610 included: 3000 m/min (9843 ft/min) cutting speed; a feed speed of 5720 mm/min (225 in/min); a spindle speed of 3820 rpm; a feed rate of 0.15 mm/tooth (0.006 in/tooth); and a depth of cut on aluminium of 0.5 mm (0.02 inch) and on cast iron of 0.05 mm (0.002 inch).
Other tools in the family include the M5Q90 tangential roughing cutter, which performs first-staging cubing (first machining of faces after casting) in a single operation without burring. The tool is fitted with PCD tangential inserts that provide a smooth and stable cutting action to reduce power consumption and eliminate vibration.
Aluminium cylinder heads and blocks are among the components to benefit from the M5Q90. By way of example, the cubing operation on a cast cylinder head would typically involve machining the camshaft face, inlet/outlet face and combustion face. In a customer case study, the rough face milling of cylinder heads cast from AS-9 aluminium alloy on a horizontal machining centre, produced highly impressive tool life results. At 3000 m/min (9843 in/min) cutting speed, feed per tooth of 0.2 mm (0.008 in) and 2.0 mm (0.079 in) axial depth of cut (fully engaged to 40 mm (1.57 in), more than 10,000 components were completed.
A further tool is the M5R90 for second stage roughing/semi-finishing. This standard cutter works with adjustable cartridges and supports a depth of cut of up to 8 mm (0.315 inch) with a 0.4 or 0.8 mm (0.016 or 0.031 inch) radius depending on the cartridge used. Easy-to-adjust cartridges are of benefit in many automotive applications, as could be seen in a recent customer trial involving the face milling of an engine cover. Cast from MRHB Si12 aluminium alloy, the M5R90 performed extremely favourably against the incumbent competitor cutter. Based on identical cutting data, the M5R90 extended tool life from 8000 to 10,000 workpieces. Moreover, the competitor cutter needed to be adjusted after every 1000 parts due to cartridge movement that compromised surface finish. In contrast, the M5R90 produced 8000 parts before any adjustment to the cartridge was required.
Also included in the family is the M5B90 super-finishing face mill with its unique axial and radial positioning of inserts. This configuration, together with the wiper insert, ensures burr-free cutting with excellent surface quality, as a manufacturer of cylinder heads for passenger cars recently discovered. The company was experiencing process instability and issues with burrs, while another problem was unpredictable insert life, which depended on cartridge adjustments that differed from set-up to set-up. Switching to the M5B90 cutter provided a smooth finishing operation with predictable wear and no burr. The tool produces only very thin chips, which are easily removed during the cutting process to avoid any damage to the component face. In addition, changing to M5B90 extended tool life from 30,000 to 45,000 parts on average.
CoroDrill and CoroTap family drilling and tapping tools can also be offered to customers as part of the same family of solutions for machining aluminium automotive components, as can the standard CoroMill® Century 590 face mill finishing cutter.
In all cases, the potential to reduce cycle times and cost per part, while at the same time improving tool life and quality, is very real, as can be seen by the customer case examples described. In the automotive industry, where high-volume production is prevalent, even a small saving in cycle time can equate to significant financial returns. With this thought in mind, any technology that can demonstrate the ability to deliver larger gains, is difficult to ignore.