At the fore, high speed milling of aluminium parts for the aerospace industry. By Reuven Shapir, Iscar Industry Manager for the Aerospace Marketing Division.
The milling of aluminium parts for the aerospace industry is a machining process that requires the removal of large volumes of material by rough milling.
As a result, semi and finishing operations of these parts are characterised by the creation of narrow walls and thin bases that lead to limited workpiece rigidity. In spite of aluminium being a soft material with relatively good machinability, due to the large size of many aerospace parts and their multiple pockets, milling operations normally involve the removal of over 90 percent of the original workpieces’ material, a long process that involves extended semi and finish milling times.
Going Through The Gantry
Throughout the world many parts are still produced on gantry machines that feature large horizontal tables and vertical spindles. However, this machine tool arrangement often causes chip evacuation difficulties. Also, as these machines have limited spindle power and speed capabilities, limited control results in low feeds, which leads to long production times.
The aluminium removal rate ability for the common gantry machine reaches up to 2,000 cc/min, while semi and finishing operations is also very time consuming due to control and spindle speeds limits. In order to reduce Cost Per Unit (CPU), manufac turers need to increase Metal Removal Rates (MRRs) for roughing and to achieve faster table feeds for semi and finishing operations.
To help manufacturers realise these aims, Machine Tool Builders (MTB) developed the now common 5-axis machines that have much higher spindle speeds – up to 30,000 / 33,000 rpm, combined with increased power.
Metal Removal Rates
The first generation of these power ful machines was typically rated at 60 KW, later machine power was increased to 70KW, now 80 KW – 120 KW figures are common. Today’s advanced 5-axis machine also often features coolant through spindle capability, resulting in much improved coolant and chip evacuation, a vitally important attribute when milling deep pockets.
When roughing with spindle speeds of 30,000 rpm at 60 KW power in reliable production conditions, an MRR of 4,000 cc/min aluminium is achieved, similarly an MMR of 5,000 cc/min is achieved with 80 KW of power. Machines featuring an updated reinforced spindle with 120 KW are able to remove 8,000 cc/min aluminium.
The emergence and continuing development of modern 5-axis machines with enhanced capabilities have challenged tool manufacturers to develop a range of advanced tools with the ability to function effectively in much higher, extreme cutting conditions. Rough milling tools have an indexable insert diameter of 50 mm (2.0”), whereby the number of inserts is dictated according to the machine’s spindle power; Z=2 for 60 KW, Z=3 for 80 KW and Z=4 for the reinforced spindle 120 KW.
High-Spindle Speed & Fast Controls
After rough milling operations are complete, the use of a machine capable of 30,000 rpm with fast CNC axis controls of up to 60,000 mm/min enables solid carbide endmills to be employed to significantly reduce milling times for both semi and finishing operations.
Solid carbide endmills with a 25 mm (1.0”) diameter are commonly used to complete roughing operations within contours where a tool diameter of 50 mm (2.0”) is too large. The result of the above milling figures under extreme conditions considerably increases the productivity and performance of high-speed, modern machines when compared to the previously used machines. Today, a standard, modern machine with a powerful high-spindle speed and fast controls is much more productive than any top of the range, previous generation machine.
For extreme conditions, the modern 5-axis machine operates and contributes to higher MRR results. Although, to realise the full productive potential of these machines, suitable advanced cutting tools need to be used. To ensure the development and launch of a range of highly efficient cutting tools that are ideally suited to use on modern 5-axis machines, Iscar has taken a two pronged approach.
The company’s R&D department has undertaken in-depth laboratory work and in-house machining trials to help further refine a series of advanced cutting tool prototypes. They have worked in close cooperation with several multi-national aerospace companies to test its products in the harshest of ‘real world’ aluminium milling situations.
Increased Productivity & Reduced Production Costs
Iscar’s R&D department’s brief was to design a range of cutting tools that were able to resist intense cutting and centrifugal forces, to guarantee the delivery of an ultrareliable process and to ensure perfect chip evacuation while moving large volumes of chips when milling deep pockets.
Also, in order to prevent Build-Up Edge (BUE) and to enable milling in these extreme conditions, inserts with ground sharp super positive edge geometry, combined with polished rake, must be included.
As the first cutting tool manufacturer to develop carbide inserts with helical and super positive polished cutting edges for milling aluminium, ISCAR developed the HSM90S style tools with indexable inserts, specifically for the efficient rough milling of aluminium, at for instance 33,000 rpm’s and 120 KW.
Offering performance, perfect chip evacuation, lower cutting forces and the generation of less vibration, these cutting tools provide huge time savings when used on modern, powerful machines with high spindle speeds and fast feeds.
Reduced Machining Times & Lower Costs
For semi and finishing milling, the company has developed high-performance solid carbide endmills that are suitable for extreme speed and fast feed conditions.
These tools deliver the required levels of accuracy and surface finish characteristics, and result in the highly-efficient milling of aerospace industry aluminium par ts. Reduced machining times and lower costs are made possible with its high-performance, solid-carbide endmills.
Having launched several advanced products related to efficient aluminium milling, aerospace manufacturers throughout the world are now reaping the multiple benefits of Iscar’s research and the company’s cooperation with leading aerospace manufacturers.
APMEN Metal Cutting