BMFS 3373 CNC TECHNOLOGY Lecture 9

1. BMFS 3373CNC TECHNOLOGYLecture 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 • 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