Chapter 22Chapter 22

Turning and Boring Turning and Boring Processes Processes (Review) (Review)

EIN 3390 Manufacturing ProcessesEIN 3390 Manufacturing ProcessesSummer A, 2012Summer A, 2012

22.1 Introduction22.1 IntroductionTurning is the process of machining external

cylindrical and conical surfaces.

Boring is a variant of turning where the machining results in an internal cylindrical or conical surface.

Turning and Boring are performed on a lathe where a single point tool is moved across the rotating workpeice

Basic Turning OperationsBasic Turning Operations

FIGURE 22-2 Basic turning machines can rotate the work and feed the tool longitudinally for turning and can perform other operations by feeding transversely. Depending on what direction the tool is fed and on what portion of the rotating workpiece is being machined, the operations have different names. The dashed arrows indicate the tool feed motion relative to the workpiece.

22.2 Fundamentals of Turning, 22.2 Fundamentals of Turning, Boring, and Facing OperationsBoring, and Facing Operations

Turning constitutes the majoring of lathe work and is summarized in two categories.1) Roughing: Used to remove large amounts

of material using large depth of cuts and slow speeds. Requires less time to remove material, though dimensional accuracy and surface finish quality are lost.

2) Finishing: Uses light passes with speeds as fine as necessary to produce the desired finish. One to two passes are usually required to produce a smooth finish.

Turning Calculations Turning Calculations

FIGURE 22-3 Basics of theturning process normally doneon a lathe. The dashed arrowsindicate the feed motion of thetool relative to the work.

Depth of Cut

Lathe rpm

Cutting Time

Ns = (12V) / (D1)

Tm = (L + A) / (fr Ns)

Turning Calculations (Example)Turning Calculations (Example)1.78” diameter steel bar is to be turned down to 1.1”. Overall

length of the bar is 18.75”, and the region to be turned is 16.5”. The steel bar is made from cold-drawn with a Bhn of 250. Please design the manufacturing processes.

Total required DOC = (1.78-1.1)/2 = 0.34”Two cutting processes are planned: 1) rough cut: d1 = 0.3”,

and finish cut d2 = 0.04”

The toll material for rough cut: HSS for finish cut: Coated carbide tool

FIGURE 20-4 Examples of a table for selection FIGURE 20-4 Examples of a table for selection of speed and feed for turning. of speed and feed for turning. (Source: (Source: Metcut’s Metcut’s Machinability Data Handbook.Machinability Data Handbook.))

AISIfor “in”

ISOfor “mm”

(for workpiece)

FIGURE 20-4 Examples of a table for selection FIGURE 20-4 Examples of a table for selection of speed and feed for turning. of speed and feed for turning. (Source: (Source: Metcut’s Metcut’s Machinability Data Handbook.Machinability Data Handbook.))

AISIfor “in”

ISOfor “mm”

(for workpiece)

Turning Calculations (Example)Turning Calculations (Example)

1) Rough cut:from Figure 20 – 4, v = 100 fpm, and f1 = 0.02 ipr

for HSS toolThe bar is held in a chuck with a feed through the hole in a

spindle and supported on the right end with a live center. The ends of the bar have been center drilled. Allowance is 0.5”, and 1 min for resetting the tool after the first cut.

Turning Calculations (continued) Turning Calculations (continued) The spindle rpm

Ns = (12V) / (D1) = 12 x 100 / (3.14 x 1.78) = 214 rpm

But we don’t have this particular rpm, so the closest selected rpm is 200 rpm. The time for rough cutting is :

Tm = (L + Allowance) / (fr Ns) = (16.5 + 0.5) / (0.02 x 200) = 4.25 min

2) Finish cuttingIf we select a uncoated carbide tool for the second cut, the allowed cutting

speed is 925 fpm and feed is 0.007”. Ns = (12V) / (D1) = 12 x 925 / (3.14 x 1.18)

= 2,996 rpm with 3,000 rpm the closest value.Tm = (L + A) / (fr Ns) = (16.5 + 0.5) / (0.007 x 3,000)

= 0.95 min

Turning Calculations, cont.Turning Calculations, cont.

FIGURE 22-3 Basics of theturning process normally doneon a lathe. The dashed arrowsindicate the feed motion of thetool relative to the work.

Metal Removal Rate, MRR

Alternate equation for MRR

s

Turning Calculations, cont.Turning Calculations, cont.Typo on page 601 of the textbook:

Rewriting the last term:(D1

2 – D22)/(4D1) = (D1 – D2)/2 x (D1 + D2)/2

Therefore, since d = (D1 – D2)/2 and (D1 + D2)/(2D1) =~ 1 for small d

s

Boring CalculationsBoring Calculations

Cutting time

Material Removal Rate

or

FIGURE 22-4 Basic movementof boring, facing, and cutoff (orparting) process.

s

MRR =

Facing CalculationsFacing Calculations

Cutting time

Material Removal Rate

FIGURE 22-4 Basic movementof boring, facing, and cutoff (orparting) process.

s s

s

rr

Deflection in Boring, Facing, and Deflection in Boring, Facing, and Cutoff OperationsCutoff OperationsThe speed, feed and depth of cut are less

in Boring, Facing and Cutoff operations because of the large overhang of the tools. Basic deflection calculations for the tool are:

l : overhand of tool

Dimensional Accuracy in TurningDimensional Accuracy in Turning

FIGURE 22-7 Accuracy and precision in turning is a function of many factors, including tool wear and BUE.

22.3 Lathe Design and 22.3 Lathe Design and TerminologyTerminology

Lathe Engine essential components:◦ Bed

Gray cast for vibration dampening

◦ Headstock assembly Spindle Transmission Drive motor

◦ Tailstock assembly Longitudinal way

clamp Transverse way clamp Quill for cutting tools,

live centers, or dead centers

FIGURE 22-8 Schematic diagram of an engine lathe, showing basic components.

22.3 Lathe Design and 22.3 Lathe Design and TerminologyTerminology Lathe Engine essential

components:◦ Quick-change

gearbox Powers Carriage

Assembly movement with lead screw

◦ Carriage Assembly Fixed to cross slide Holds tool post at

variable orientations

Provides longitudinal and transverse movement of tooling

◦ Ways Provides precise

guidance to carriage assembly and tailstock

FIGURE 22-8 Schematic diagram of an engine lathe, showing basic components.

22.3 Lathe Design and 22.3 Lathe Design and TerminologyTerminology Lathe Engine essential

components:◦ Quick-change

gearbox Powers Carriage

Assembly movement with lead screw

◦ Carriage Assembly Fixed to cross slide Holds tool post at

variable orientations

Provides longitudinal and transverse movement of tooling

◦ Ways Provides precise

guidance to carriage assembly and tailstock

FIGURE 22-8 Schematic diagram of an engine lathe, showing basic components.

22.4 Cutting Tools for Lathes22.4 Cutting Tools for LathesTools consists of cutting surface and

support◦Cutting surfaces can be of same material as support or a separate insert

◦Supports materials must be rigid and strong enough to prevent tool deflection during cutting

◦Cutting materials are typically carbides, carbide coatings, ceramics, or high carbon steels

◦Inserts are used to decrease cost in that the insert is disposed of, and the support reused.

Typical Tool HoldersTypical Tool Holders

FIGURE 22-16 Commontypes of forged tool holders:(a) right-hand turning,(b) facing, (c) grooving cutoff,(d) boring, (e) threading.(Courtesy of Armstrong BrothersTool Company.)

Quick Change Tool HoldersQuick Change Tool Holders

Tool changing can take over 50% of manual lathe operations

Quick Change holders are used to reduce manual tool change time and increase production

22.5 Workholding Devices for 22.5 Workholding Devices for LathesLathesWork pieces can be held by various

methods◦Work piece mounted between centers◦Work piece mounted within a single chuck◦Work piece mounted within a collet◦Work piece mounted on a faceplate

Lathe ChucksLathe ChucksLathe Chucks are adjustable mechanical

vises that hold the work piece and transfer rotation motion from the drive motor to the work piece

Lathe Chucks come in two basic types◦Three-jaw self-centering chucks

Used to center round or hexagonal stock◦Four-jaw independent chucks

Each jaw moves independently to accommodate various work piece shapes

Lathe ChucksLathe Chucks

FIGURE 22-24 The jaws onchucks for lathes (four-jawindependent or three-jaw selfcentering)can be removed andreversed.

FIGURE 22-25 Hydraulicallyactuated through-hole three-jawpower chuck shown in sectionview to left and in the spindle ofthe lathe above connected tothe actuator.

SummarySummary

Lathes are used for turning, boring, drilling and facing

Lathe typically holds the work piece in a rotating chuck, with the opposite end supported by a center held in the tailstock

A wide variety of lathe types, and tool types are available depending upon the application and the rate of production

HW for Chapter 22HW for Chapter 22Review Questions:10, 17, 18, and 22 (page 625)

Problems (page 625):1, 23. (depth of cut = 0.125 in.)4. 5. a)