BMFS 3373

CNC TECHNOLOGYLecture 9

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

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.

Component of CNC Lathes

Component of CNC Lathes

Bed Headstock Chuck: Jaw/Faceplate – Hard/Soft – Collet Turret Carriage Tailstock Slant Bed MCU

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.

CNC Lathe Axes of Motion

Basic Lathe Operations

Facing: flatting the end surface

Turning: removing the outer layer

Basic Lathe Operations

Chamfer: smoothing of inner or outer edge Grooving

OD & ID Grooving Face Grooving

Parting

Basic Lathe Operations

Drilling; Boring

Threading

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

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

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 rpmSpindle 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

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)

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

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

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

Feed Direction & Rake Angles

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

EndEndChapter 9Chapter 9