machines & machining issues

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Machines & Machining Issues

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Material Removal Process

Mechanical Machining

Milling

Grinding

Turning

Drilling

All hard materials

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Machining DOF (Degrees of Freedom)DOF- # of independently controllable axes of motion-- excluding spindle rotation or tool translation responsible for cutting.

1 DOF- Drill Press

2 DOF- Lathe

3 DOF- 3 independent axis motions between tool & table Can use a ball end mill w/ 3 axis machine- for smoothest

contour Following a true 3-D contour requires a minimum of 3 DOF

2 1/2 DOF- 3 independent axes, but can only move 2 at a time

> 3 DOF- Generally allows rotation of spindle wrist or table Helps keep tool normal to workpiece/ fewer separate

fixtures 5 DOF- Minimum to follow any normal at any point

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Turning Operations

Turning (Performed on lathe) Part is moving and tool is stationary.

Used to make parts of round cross section Screws, shafts, pistons....

Number of various lathe operations Turning, facing, boring, drilling, parting, threading

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Lathe Components

Machine Components (Main items)Bed: Supports all other machine parts

Carriage: Slides along the machine ways Head stock: Power train of system (spindle included) Tail Stock: Fixes piece at end opposite to the head

stock Swing: Maximum diameter of the machinable piece Lead screw: controls the feed per revolution with a

great deal of precision

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Ref: Fig. 8.52, Kalpakjian. Manufacturing Processes for Engineering Materials 2nd Ed, Addison-Wesley 1991.

LatheSpindleSpeed

Selector

Headstock

SpindleWays

Tool PostCross Slide

Carriage (saddle)Center Tailstock quill

Tailstock

FeedRod

LeadScrew

BedApronCompoundRest &

Slide (swivels)

Feed changegear box

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Lathe Tools

Lathe toolsLeft handed

Right handed

Threading

Boring

Groove

Parting (Cut-Off )

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Lathe Operations

Ref: Fig. 8.51, Kalpakjian. Manufacturing Processes for Engineering Materials 2nd Ed, Addison-Wesley 1991.

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Cutting Speeds

Typical Lathe Cutting Speeds• Nominally 30 - 800 ft./min.

• Roughing cuts

- Depth of cut greater then .02 in

- Feed speed of .008 - .08 in/rev.

• Finishing Cuts

- Lower than roughing cuts.

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Milling

Types of Milling Machines Horizontal Milling Machine Vertical Milling Machine

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Mill Cutting DirectionCutting direction- Depending on the orientation of the workpiece

feed w.r.t. the rotation of the cutting tool.

• Climb (Down) Milling- Maximum thickness of chip at start of cut.

• Conventional (Up) Milling- Maximum thickness of chip at end of cut

Ref: Figure J-48, Kibbe ,et al. Machine Tool Practices 5th Ed, Prentice Hall,1995.

Ref: Figure J-48, Kibbe ,et al. Machine Tool Practices 5th Ed, Prentice Hall,1995.

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Vertical Knee Milling MachineBase and Column- support structure

Knee- Connected to slide on column- can move up and down

Saddle- Engages slide on top of knee- can be moved in and out.

Table- Engages slide atop of saddle- moved lengthwise. Holds workpiece.

Ram- Engages swiveling slide atop column.

Toolhead- Attached to end of ram, contains motor and quill.

Quill- Non rotating, but contains rotating spindle. Can be moved up and down.

Ref: Kibbe ,et al. Machine Tool Practices 5th Ed, Prentice Hall,1995, p 550-551

Ref: Figure 8.69, Kalpakjian. Manufacturing Processes for Engineering Materials 2nd Ed, Addison-Wesley 1991.

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Vertical Milling Machine

• Flexible• Versatile• Newer machines –

more DOF

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Bed Mill

Similar to vertical knee milling machines

Less versatile than knee mill

No knee - Bed does not move up and down

Vertical motion possible in head only

Controllable range of motion of head larger than in knee mill (total range of motion less)

Bed mill stiffer than knee mill

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Vertical Milling Applications

Collet

Ref: Process Selection, KG Swift and JD Booker, p.98.

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Scallop Height w/ Ball Nosed End Mill

R

hs x

y d

Basic Equation for a circle- x2+R−y( )2=R2

Solving for y.... y=R− R2−x2 Max height for x= s

2( )

Thus h=R− R2− s2

⎛ ⎝ ⎜

⎞ ⎠ ⎟ 2⎡

⎣

⎢ ⎢ ⎢

⎤

⎦

⎥ ⎥ ⎥ (if h≤d)

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Scallop Height- Ball Nose on an Incline

hdR

s

xy

α

Edge of cutter described byx1

2 +y12 =R2

On previous pass it was

x2 +s

cos(α )⎛ ⎝ ⎜

⎞ ⎠ ⎟

2+y2

2 =R2

Set x1 =x2 =x andy1=y2 =y

x=− s2⋅cos(α )

⎛ ⎝ ⎜

⎞ ⎠ ⎟ y=− R2 − s

2⋅cos(α )⎛ ⎝ ⎜

⎞ ⎠ ⎟

2

h=R− R2 − s2⋅cos(α )

⎛ ⎝ ⎜

⎞ ⎠ ⎟

2 (if h≤d)

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Horizontal Milling Machine

COMPONENTS Base & Column Knee Saddle Table Spindle Overarm & Arbor Support

Ref: Figure 8.68, Kalpakjian. Manufacturing Processes for Engineering Materials 2nd Ed, Addison-Wesley 1991.

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Types Horizontal Milling OperationsSlab- Axis of cutter //

to workpiece surface

Face- Axis of rotation |

to workpiece surface

Side- Axis of cutter //

to workpiece surface

Figure 8.63b, Kalpakjian. Manufacturing Processes for Engineering Materials 2nd Ed, Addison-Wesley 1991.

Figure 8.67c, Kalpakjian. Manufacturing Processes for Engineering Materials 2nd Ed, Addison-Wesley 1991.

Figure 8.63a, Kalpakjian. Manufacturing Processes for Engineering Materials 2nd Ed, Addison-Wesley 1991.

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Drilling

Any component requiring cylindrical holes.

Engine Blocks, Machine Components

Ref: Process Selection, KG Swift and JD Booker, p.104.

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Grinding and Abrasive Processes

Abrasive Processes- Generally slower (more expensive) than other traditional machining processes. Used on very hard materials, and can achieve HIGH (virtually unmatched) levels of precision and finish.

• Grinding• Deburring• Honing• Polishing• Lapping• Superfinishing

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Grinding MachinesPedestal Grinder

Surface Grinder Type I- Horizontal spindle w/ reciprocating table Type II- Horizontal spindle w/ rotary table Type III- Vertical spindle, table either reciprocates or rotates (blanchard)

Cylindrical Grinder Center-type Roll-type- workpiece in bearings rather than on centers Centerless Grinder- workpiece supported on rest blade, grinding wheel on one side, regulating wheel on the other Internal Cylindrical Grinder Tool Cutting Grinders

Specialty Grinders Form Grinders and Generating Types

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Surface GrindersType I Type II

Type IIIReciprocatingTable

RotatingTable

Ref: Figures N-1, N-3,N-4, & N-5, Kibbe ,et al. Machine Tool Practices 5th Ed, Prentice Hall,1995.

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Cylindrical Grinders

Center/Roll Type

Centerless Type

Ref: Figures N-8, N-17, N-18, Kibbe ,et al. Machine Tool Practices 5th Ed, Prentice Hall,1995.

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Surface RoughnessSurface roughness is generally described with 1 of 2 methods Ra- Arithmetic Mean Value- the average of the absolute values of the deviations from the center line of the surface

Rq (formerly RMS)- Root Mean Squared-

Rq = a2 +b2 +c2 +d2 +...n

Ra= |a| + |b| + |c| + |d| + … n( )

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Roughness Units

1 Micrometer = 1m = 1 micron = 10-6 meters 1 Microinch = 1in= 10-6 inches 1in = 0.025 m 1m = 40 in Human hair ~ 40 m

Both generally given in micrometers (microns) or microinches

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Typical Arithmetic Average Roughness

Ref: Fig. 8.35, Kalpakjian. Manufacturing Processes for Engineering Materials 2nd Ed, Addison-Wesley 1991.

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Summary

Four types of mechanical removal processes Turning Milling Drilling Grinding

Finish of workpiece

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Credits This module is intended as a supplement to design classes in mechanical

engineering. It was developed at The Ohio State University under the NSF sponsored Gateway Coalition (grant EEC-9109794). Contributing members include:

Gary Kinzel …………………………………….. Project supervisor Chris Hubert and Alan Bonifas ..……………... Primary authors Phuong Pham and Matt Detrick ……….…….. Module revisions L. Pham ……………………………………..….. Audio voice

References:Kalpakjian, Manufacturing Processes for Engineering Materials 2nd Ed,

Addison-Wesley 1991Kibbe ,et al. Machine Tool Practices 5th Ed, Prentice Hall,1995 Swift, KG and JD Booker, Process Selection, Arnold/John Wiley& Sons Inc.,

New York, 1997

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Disclaimer

This information is provided “as is” for general educational purposes; it can change over time and should be interpreted with regards to this particular circumstance. While much effort is made to provide complete information, Ohio State University and Gateway do not guarantee the accuracy and reliability of any information contained or displayed in the presentation. We disclaim any warranty, expressed or implied, including the warranties of fitness for a particular purpose. We do not assume any legal liability or responsibility for the accuracy, completeness, reliability, timeliness or usefulness of any information, or processes disclosed. Nor will Ohio State University or Gateway be held liable for any improper or incorrect use of the information described and/or contain herein and assumes no responsibility for anyone’s use of the information. Reference to any specific commercial product, process, or service by trade name, trademark, manufacture, or otherwise does not necessarily constitute or imply its endorsement.