“Machine Designed for Aerospace.“ Just Talk or Walking the Walk?

Posted by: 16. January 2014

Makino T1 A and B Axes

Makino bills their T1, 5-Axis Horizontal Machining as a machine that’s ideal for handling industrial component and aerospace machining.  And sure enough, the T1, T2, and T4 are all found in the “aerospace” industry section on Makino’s website.  Skeptic that I am, I wondered if this machine really has features or design elements that make it any more suitable for aerospace machining than any other machine.  To find out I need to dissect-the-spex.

I start by outlining some of the unique characteristics of typical aerospace components.  

Materials:           aluminum and titanium

Shapes:               large, heavy, small, complex 3D surfaces, difficult to fixture

Accuracy:            tight dimensional and surface finish requirements

Then, I consider the key elements of the T1 to see if it addresses aerospace-specific machining and fixturing requirements.

CASTING:  The casting is the very foundation upon which every other component’s performance depends.  Stiffness and rigidity are critical for high-speed, high-feed machining in aluminum as well as heavy roughing and close tolerance machining in titanium. The T1 base casting is built with a thicker Z-axis bed for more support, a monolithic cast column which eliminates weakness that might occur between welded components, and wider slideway surfaces for increased bearing contact. To further address the need for stable, vibration-free cutting, Makino has developed a proprietary technology called “Active Damping.” Sensors detecting low-frequency vibration conditions within an axis automatically create friction along that axis to stamp out the vibration before it gets out of control.  Active Damping is like an insurance policy. More aggressive cutting can be implemented knowing that the machine will adapt if and when necessary to avoid excessive tool wear or breakage.  

SPINDLE:  The 12,000 top rpm spindle which generates 75 hp continuously from 1,000 – 12,000 rpm provides acceptable surface footage requirement for most drilling or milling operations in aluminum, certainly enough SFM for all but the smallest cutters.  Roughing aluminum at very high feed rates can be achieved due to the high continuous horse power rating.  For prolonged roughing operations, horse power output of 100 or more can be achieved in the duty cycle range.  1,000Nm (737 ft-lbs) of torque is delivered at spindle speeds from 20 – 1,000 rpm, providing the cutting power and torque needed to machine titanium.   The HSK-A100 is an exceptionally robust configuration designed to withstand extreme forces and speeds typical of higher loads generated while cutting titanium and high speeds associated with machining aluminum.   This particular 5-axis HMC incorporates the “5th” axis (the A axis) on the spindle providing -110° ~ +45° range of programmable motion.  Some 5-axis machines apply both the 4th and 5th axes to either the spindle or the table, but the T1 dedicates only one axis to the spindle and the other to the table. Just as the main spindle and the X, Y, and Z axis drives must provide sufficient torque to cut titanium, the A-axis provides 6,300 Nm torque (20,000 Nm peak).  The pivot distance of the spindle is 400mm from the HSK-A100 face to the centerline of the A-axis.   This, coupled with a long Z-axis stroke of the table, allows both long and short tools to access all sides of the part in most cases, even when the tool is at the extreme ends of the 155° A-axis range of motion.  This is an important feature because it eliminates envelope restrictions that require 2D or 3D machining on any surface of the part.  Unlike many machine tool builders, Makino builds all of its own spindles and has been especially successful in expanding the range of useful low end torque to higher and higher rpms, so as to keep pace with any developments that the cutting tool manufacturers might come up with--next year or five years from now. 

TABLE:  With a workpiece load capacity of 6,600 lbs., the T1 is obviously designed to handle large parts. Though many 5-axis HMCs integrate the 4th and 5th axes within a trunnion-style table, this model assigns one axis to the table and one to the spindle.  What’s the advantage of splitting control?  Imagine loading a 6,000 lb. part on the table then rotating its center of gravity to outside the table base.  No matter how rigidly constructed a machine might be, overhang is the enemy of accurate, stable machining.  B-axis rotary table drive torque, like torque on the A-axis drive, enables milling from less than 1 rpm up to 10 rpm (table rotation speed) while delivering 10,000 Nm of continuous torque (29,000 Nm peak).  This design does address the unique aerospace material requirements for unusually high torque when milling titanium.  Though ergonomic design isn’t any more or less important in the aerospace industry, avoiding the trunnion table design in larger machines helps operator visibility in the workpiece area.

CHIP CONTROL:  The T1 is a large machine with plenty of torque and horse power.   Typical uses of the machine are going to generate a large volume of chips.  Both titanium and aluminum chips can be difficult to control. Aluminum chips are stringy and difficult to break up. Titanium is a thermal resistant material; therefore, heat generated during cutting tends to transfer to the coolant.  Naturally, fines (dust-like chips) will collect and could interfere with flow and contaminate the clean coolant. The T1 meets these challenges head on with high volume, high pressure, through-the-tool coolant delivery, chip dispersal nozzles, a coolant temperature control system, baffling and filtration to remove swarf from the coolant, and large capacity twin tanks so that as the just-used coolant is treated for temperature and contamination, the processed coolant is sufficiently abundant to keep up with high volume coolant requirements demanded by aluminum and titanium. The coolant system is equipped with pumps that generate 1,000 psi at 26 gallons per minute flow rate through the spindle. High pressure/high volume ensures both efficient cutting and chip evacuation from the cutting zone.

CONDITION MONITORING & CNC CONTROL:  Hard and difficult to machine materials found in aerospace machining test the most rigidly constructed machine tools. Irregular cutting conditions in hard materials can introduce stress on the tool, spindle, and bearings similar to the stresses of interrupted cuts.  If it’s possible to pre-sense the onset of what can seem like sudden significant increase in tool load, then it might be possible to manage material inconsistencies without excessive tool wear or catastrophic outcomes. Makino has developed a new damping method adapted from an old technology.  Sensors constantly gather feedback from the rotary and linear axis drives to detect low frequency harmonics that presage full-blown harmonics which can wreak havoc on stable cutting. When the sensors detect such a condition, the system actively controls the gap between the stationary and moving portions of the axis way.  “Controlling the gap” means that friction is intentionally created to eliminate the vibration. As a result cutting is stabilized.  This is all accomplished within milliseconds and can be ongoing during much of the time the machine is cutting, if material conditions are particularly challenging.  

CONCLUSION:  The T1 is especially suited to handle the unique challenges that aerospace machining presents.  Makino doesn’t just talk the aerospace talk, the T1 proves they walk the walk, too.


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