1. BMFS 3373 CNC TECHNOLOGY Lecture 9

2. Lecture Objectives At the end of the lecture, you will be able to:
Understand the basic elements comprising the CNC lathe
Identify the axis of motion for CNC lathes
State the different types of tooling and cutting operations performed on the CNC lathe
Explain the lathe feeds, speeds and depth of cut

3. Component of CNC Lathes
The CNC lathe is a machine tool designed to remove material from stock that is clamped and rotated around the spindle axis
Single point cutting tool is mostly used
Chucks are used to grip the work while Turrets are used to hold and index cutting tool called by the word address program.
Two types of turrets: Rear & Front
Two spindle opposed and vertical turret are other features known in CNC lathe machine.

4. Component of CNC Lathes

5. Component of CNC Lathes
Bed
Headstock
Chuck: Jaw/Faceplate – Hard/Soft – Collet
Turret
Carriage
Tailstock
Slant Bed
MCU

6. CNC Lathe Axes of Motion
Normally two basic axis motion is dealt in a CNC lathe machine: X & Z
The Z axis is in the direction of the spindle where +Z is motion away from the spindle and work while –Z is motion towards it
The X axis is in the direction of the cross-slide movements where +X is motion away from the spindle centerline and –X is the motion toward it.
In machines with programmable tailstocks, the W axis is used to designate the movement for a third axis on these machines.

7. CNC Lathe Axes of Motion

8. Basic Lathe Operations
Facing: flatting the end surface
Turning: removing the outer layer

9. Basic Lathe Operations
Chamfer: smoothing of inner or outer edge
Grooving
OD & ID Grooving Face Grooving
Parting

10. Basic Lathe Operations
Drilling; Boring
Threading

11. Basic Lathe Tooling Insert Materials Insert Shapes
Cemented Carbides: tungsten carbide sintered in a cobalt matrix
Coated Carbides: cemented carbides coated with wear resistant material-titanium carbide and aluminum oxide
Ceramics: material formed without metallic bonding
Diamonds: Single crystal natural diamond or synthetic diamond crystals
Insert Shapes

12. Basic Lathe Tooling
Advantage of indexable/insert tooling in lathe operation:
Cutting capabilities at higher speeds
Reduction in tool inventory
Elimination of regrinding time and cost
Inserts are made with a precise tool nose radius for cutting(accurately determined tool nose center

13. Cutting Speeds, Feeds & Depth of Cuts
Cutting speed is defined as the rate at which a point on the boundary of the material that is cut passes the edge of the cutting tool
For drilling, reaming and tapping, the Tool Diameter is used to calculate the spindle rpm
Spindle rpm = Cutting Speed (mpm)
π × Tool Diameter (m)
(Drilling, reaming and tapping)
The spindle rpm is input into the CNC program since the spindle maintains a constant rpm level throughout these machining operation
The spindle speed is specified by the S code. When programmed with G97, it indicates the spindle rpm
G97 Sn (General Syntax)
*n specifies the spindle speed

14. Cutting Speeds, Feeds & Depth of Cuts
For turning, boring, facing, grooving and parting, the cut diameter changes during operations.
The cutting speed is input into the CNC program where the controller automatically adjusts the spindle rpm up or down in order to maintain the cutting speed.
The relationship between Cutting Speed and the Cut Diameter and the Spindle Speed rpm for operation of this matter (turning, etc) is given approximately:
Cutting Speed (mpm) = Spindle Speed(rpm) × π × Cut Diameter(m)

15. Cutting Speeds, Feeds & Depth of Cuts
The relationship indicates that, for outside operation, constant Cutting Speed is maintained by increasing the Spindle Speed as the Cut Diameter decreases and vice versa for an inside cut.
A G96 code is used to insure constant surface speed control. The S code no longer specifies the Spindle speed but the Cutting speed.
G96 Sn (General Syntax)
*n specifies the cutting speed

16. Cutting Speeds, Feeds & Depth of Cuts
Tool feed is the rate at which the tool advance into the work per revolution of the work
Depth of cut is the thickness of the material machined from the work or is the distance from the uncut work surface to the cut surface
Cut Diameter = Uncut Diameter – 2×DOC

17. Feed Direction & Rake Angles
Right handed cutting tools have their cutting edge on the right side and are usually fed from right to left
Left handed cutting tools have their cutting edge on the left side and are usually fed from left to right
Neutral cutting tools have their cutting edge on both the right and left side and can be fed from either way

18. Feed Direction & Rake Angles

19. Feed Direction & Rake Angles
Tooling Nomencalture
Tool Nose Radius (TNR) – surface finish & longer tool life
Back Rake Angle (BR) – directing chip away and towards tool holder
Side Rake Angle (SR) – directing chip away and towards side
Side Clearance (SC) – permitting the side of the tool to enter the work
End Clearance (EC) – permitting the end of the tool to enter the work
SCEA – Improving shear cut and producing thinner chips
ECEA – Maintaining clearance between tool and work during boring or facing operations

20. End
Chapter 9