SEMINAR ON HIGH SPEED MACHINING (HSM)

CONTENTS Introduction Definition of HSM Advantages Application areas Machining system Some recommended parameters Comparison Disadvantages Conclusion

DEFINITION OF HSM Carl Salomon assumes that “At a certain cutting speed which is 5-10 times higher than in conventional machining the chip removal temperature at the cutting edge will start to decrease”

DEFINITIONS High cutting speed machining High rotational speed machining High feed machining High speed and feed machining High productive machining Finally, “HSM is a powerful machining method that combines high feed rates with high spindle speeds, specific tools and specific tool motion.”

ADVANTAGES High material removal rate High surface finish Increased productivity Possibility of machining of very thin walls Reduction in lead times Low cutting force Cutting tool and work piece temperature are kept low Connection time between the cutting edge and work piece is short It eliminates the need of coolant Reduction of production process

FEATURES EFFECTS Reduced heat transfer in to the work piece Part accuracy Reduction of cutting forces Surface quality Increased cutting speed Stability of rotating cutting tool feed rate Increased material removal

APPLICATION AREAS Industry which deals with the machining of Al to produce automotive components, small computer parts or medical devices Aircraft industry involves machining of Al often with thin walls Die mould industry which requires dealing with finishing of hard materials . Used to machine such parts as die casting dies, forging dies, injection moulds and blow moulds, milling of electrodes in graphite and copper, modeling and prototyping of dies and moulds.

MACHINING SYSTEM MACHINE TOOLS 3-axis horizontal and vertical milling machines CNC 4-axis milling machine offers the option of tilting the milling cutters to improve the cutting conditions 5-axis machine with inter changeable spindle units allow to rough, semi finish and finish with a single set up.

DEMANDS ON THE MACHINE Spindle speed range <=40000 rpm Spindle power >22 KW Programmable feed rate 40-60 m/min Rapid travels <90 m/min Block processing speed 1-20 ms High thermal stability and rigidity in spindle Air blast/coolant through spindle Advanced look ahead function in the CNC

CUTTING TOOLS TiN and TiCN coated Carbide for materials with hardness less than 42 HRC TiALN coated Carbide for materials with hardness 42 HRC and above For special applications like hard turning (HRC 60-65) PCBN is used Cubic boron nitrite (CBN) and ceramic for cast iron Poly crystalline diamonds (PCD) and Cermets are used for aluminum

RECOMMENDED PARAMETERS 1.True cutting speed As the speed is dependent on both spindle speed and diameter of tools HSM should be defined as “true cutting speed” above a certain level

2.Material removal rate Material removal rate, Q = (ap* ae * vf)/1000 cm3/min where ap = vertical dist from tool tip to the reference point mm ae = step over distance mm vf = feed speed mm/min

3. Surface finish Surface finish is depends upon cutting tool geometry, coating of the cutting tool, wear status of the cutting tool etc.

COMPARISONS Conventional machine High speed machine Max speed 600 m/min Speed starts at 600 m/min Max feed ~40 ipm Feed starts at 100 ipm Require high levels coolant With coolant ,feed rate can go more than 2000 ipm No need for coolant for low feed rate Between conventional and high speed machines

Comparison between speeds used in conventional and high speed machining

The contact time between tool and work is large Contact time is short Conventional HSM The contact time between tool and work is large Contact time is short Less accurate work piece More accurate work piece Cutting force is large Cutting force is low Low surface finish High surface finish Material removal rate is low Material removal rate is high Cutting fluid is required Cutting fluid is not required Comparison between convl and HSM process

Material removal rate high Material removal rate is low HSM EDM Material removal rate high Material removal rate is low Dimensional tolerance 0.02 mm Dim tolerance 0.1- 0.2 mm There is no need of making cutting tool according to the contour to be machined Cutting tool has to be made according to the contour to be machined Comparison between HSM and EDM

DISADVANTAGES Need for expensive and special machine tools with advanced spindle and controllers Excessive tool wear Good work and process planning necessary It can be difficult to find and recruit advanced staff

CONCLUSIONS HSM is not simply high cutting speed .It should be regarded as a process where the operations are performed with very specific methods and precision equipment HSM is not necessarily high spindle speed machining. Many HSM applications are performed with moderate spindle speeds and large sized cutters HSM is performed in finishing in hardened steel with high speeds and high feeds often with 4-6 times conventional cutting speeds

HSM is high productive machining in small sized components in roughing to finishing and in finishing to super finishing in components of all sizes. Even though HSM is known for a long time, the research are still being developed for further improvement of quality and optimization of cost.

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