精密数控加工

Precision

CNCMachiningRepeatability

and

Tight

Tolerancesfor

Complex

Part

Geometries2What

ItDoes:What

are

some

common

11uses

for

CNC

Swiss

machining?Drilling

11Threading

(OD

&

ID)

12Slotting

13Boring

14Reaming

14Polygonmachining

15Broaching

15Deburring

16How

It’s

Used:

What

are

some

applications

18for

precision

CNC

Swiss

machining?General

industry

applications

18Benefits

in

medical

device

applications

18Conclusion:

Why

precision

CNC

machining?

21Introduction:

3What

is

precision

CNC

machining?The

role

of

“CNC”

in

precision

machining

3Materials

that

are

machined

4Some

advantages

of

precision

CNC

machining

4How

It’s

Done:

What

processes

and

equipment

5are

commonly

used

in

precisionmachining?Milling

vs.

turning

5Manual

vs.

CNC

machining

6CNC

mills

6CNC

lathes

8Unique

advantages

of

CNC

Swiss-style

machining

10TABLE

OF

CONTENTStable

of

contentsTHE

ROLE

OF

“CNC”

IN

PRECISIONMACHININGUsing

codedprogramminginstructions,

precision

CNCmachining

allows

a

workpiece

to

be

cut

and

shaped

tospecifications

without

manual

interventionbya

machineoperator.Taking

a

computer

aided

design

(CAD)

model

providedbyacustomer,

an

expert

machinist

uses

computer

aidedmanufacturingsoftware

(CAM)

to

create

the

instructions

formachining

the

part.

Basedon

the

CAD

model,

the

softwaredetermines

what

tool

paths

areneeded

and

generatestheprogramming

codethat

tells

the

machine:What

the

correct

RPMs

and

feed

rates

areWhen

and

where

to

move

the

tool

and/or

workpieceHow

deep

to

cutWhen

to

apply

coolantAny

other

factors

related

tospeed,

feed

rate,

andcoordinationA

CNC

controller

then

uses

the

programming

code

to

control,automate,

and

monitor

the

movements

of

the

machine.IntroductIon:

What

Is

precIsIon

cnc

machInIng?3Introduction:What

isprecision

CNC

machining?For

design

engineers,

R&D

teams,

and

manufacturers

thatdepend

on

part

sourcing,

precision

CNC

machining

allows

forthe

creation

of

complex

parts

without

additional

processing.In

fact,

precision

CNC

machining

often

makesit

possible

forfinished

parts

to

be

made

on

asingle

machine.Themachining

process

removes

material

and

uses

a

widerange

of

cutting

tools

to

create

the

final,

and

often

highlycomplex,

design

of

a

part.

The

level

of

precision

is

enhancedthrough

the

use

of

computer

numerical

control

(CNC),

whichis

used

to

automate

the

control

of

the

machining

tools.Today,

CNC

is

a

built-in

feature

of

a

wide

range

of

equipment,from

lathes,

mills,

and

routers

to

wire

EDM

(electricaldischarge

machining),laser,and

plasma

cutting

machines.

Inaddition

to

automating

the

machining

process

and

enhancingprecision,

CNC

eliminates

manual

tasksand

frees

machiniststo

oversee

multiple

machines

running

at

the

same

time.In

addition,

once

a

tool

path

has

been

designed

and

amachine

is

programmed,

it

can

run

a

part

any

number

of

times.

This

provides

a

high

level

of

precision

andrepeatability,

which

in

turn

makes

the

process

highlycosteffective

and

scalable.MATERIALS

THAT

ARE

MACHINEDSome

metals

thatarecommonly

machined

includealuminum,

brass,bronze,copper,steel,

titanium,

and

zinc.In

addition,

wood,

foam,

fiberglass,

and

plastics

such

aspolypropylenecanalso

be

machined.In

fact,

just

about

any

material

can

be

used

with

precision

CNC

machining

—

of

course,

depending

on

the

application

and

its

requirements.SOME

ADVANTAGES

OF

PRECISIONCNC

MACHININGFormany

of

the

small

parts

and

components

that

are

usedina

wide

rangeof

manufactured

products,

precision

CNCmachining

is

often

the

fabrication

method

of

choice.IntroductIon:

What

Is

precIsIon

cnc

machInIng?4As

is

true

of

virtually

all

cutting

and

machining

methods,different

materialsbehavedifferently,

and

the

size

and

shape

of

a

component

also

have

a

big

impact

on

the

process.However,

in

general

theprocess

of

precision

CNC

machiningoffers

advantagesover

other

machining

methods.That

isbecauseCNC

machining

is

capable

of

delivering:A

high

degree

of

part

complexityTight

tolerances,typically

ranging

from

±0.0002”

(±0.00508mm)

to

±0.0005”

(±0.0127

mm)Exceptionally

smooth

surfacefinishes,

including

customfinishesRepeatability,

even

at

high

volumesWhile

askilled

machinist

can

useamanual

lathe

to

make

aquality

part

in

quantities

of

10or

100,

what

happens

when

youneed

1,000

parts?

10,000

parts?100,000

or

a

million

parts?With

precision

CNC

machining,

you

can

get

the

scalability

andspeedneeded

for

this

type

of

high-volume

production.

Inaddition,

the

high

repeatability

of

precision

CNC

machininggives

you

parts

that

are

all

thesamefrom

start

to

finish,

nomatter

how

many

parts

you

are

producing.Get

some

machinists’

tips

on

how

tokeep

the

productionof

small,

complex

parts

cost-effective

in

our

blog

Top5

Challenges

in

CNC

Machining

Services

Explained.In

the

next

section,

we’ll

take

a

look

at

some

of

the

equipmentand

the

processes

that

are

most

frequently

usedin

precisionCNC

machining.Therearesome

very

specialized

methods

of

CNC

machining,

including

wire

EDM

(electrical

discharge

machining),additive

machining,

and

3D

laser

printing.

For

example,

wire

EDM

uses

conductive

materials

—

typically

metals

—

andelectrical

discharges

to

erodea

workpiece

into

intricate

shapes.However,

herewe

will

focus

on

the

milling

and

turning

processes

—

two

subtractive

methods

that

arewidely

available

andfrequently

used

for

precision

CNC

machining.hoW

It’s

done:What

processes

and

equIpment

are

commonly

used

In

precIsIon

machInIng?5How

It’s

Done:

What

processes

and

equipmentare

commonly

used

in

precision

machining?MILLING

VS.

TURNINGMilling

is

amachining

processthat

usesa

rotating,

cylindrical

cutting

tool

to

remove

material

and

create

shapes.Milling

equipment,

known

as

amill

or

amachining

center,accomplishes

auniverse

of

complex

part

geometries

on

someof

the

largest

objects

machined

metal.An

important

characteristic

of

milling

is

that

the

workpieceremains

stationary

while

the

cutting

tool

spins.

In

otherwords,

on

a

mill,

the

rotating

cutting

tool

moves

around

theworkpiece,

which

remains

fixed

in

place

onabed.Turning

is

the

process

of

cutting

or

shaping

a

workpieceon

equipment

called

a

lathe.

Typically,

the

lathe

spins

theworkpiece

ona

vertical

or

horizontal

axis

whilea

fixed

cuttingtool

(which

may

or

may

not

be

spinning)

movesalong

theprogrammed

axis.The

tool

cannot

physicallygo

around

the

part.

The

materialrotates,

allowing

the

tool

to

perform

the

programmedoperations.

(There

is

asubset

of

lathes

in

which

the

tools

spinaround

a

spool-fed

wire,

however,

that

is

not

covered

here.)In

turning,

unlike

milling,

the

workpiece

spins.Thepart

stockturns

on

the

lathe’s

spindle

and

the

cutting

tool

is

broughtinto

contact

with

the

workpiece.MANUAL

VS.

CNC

MACHININGWhile

both

mills

and

lathes

are

available

in

manual

models,CNC

machines

are

more

appropriate

for

purposes

of

smallparts

manufacturing

—

offering

scalability

and

repeatabilityfor

applications

requiring

high

volume

production

of

tighttolerance

parts.In

addition

to

offering

simple

2-axismachines

in

which

thetool

moves

in

the

X

and

Z

axes,

precision

CNC

equipmentinclude

multi-axis

models

in

which

the

workpiece

can

alsomove.

This

is

in

contrast

toa

lathe

where

the

workpiece

islimited

to

spinning

and

the

tools

willmovetocreate

thedesired

geometry.These

multi-axis

configurations

allow

for

the

production

of

more

complex

geometries

in

asingle

operation,

withoutrequiring

additional

work

by

the

machine

operator.

Thisnot

only

makesit

easier

to

produce

complex

parts,

but

alsoreducesor

eliminates

thechanceof

operator

error.In

addition,

the

use

of

high-pressurecoolant

with

precisionCNC

machining

ensures

that

chips

do

not

get

into

theworks,

even

when

utilizing

amachine

with

a

verticallyoriented

spindle.hoW

It’s

done:What

processes

and

equIpment

are

commonly

used

In

precIsIon

machInIng?6CNC

MILLSDifferent

milling

machines

vary

in

their

sizes,

axisconfigurations,

feed

rates,

cuttingspeed,

the

milling

feeddirection,

and

other

characteristics.However,

in

general,

CNC

mills

all

utilize

a

rotating

spindle

tocut

away

unwanted

material.

They

are

used

to

cut

hard

metalssuch

as

steel

and

titanium

but

can

also

beusedwith

materialssuch

as

plastic

and

aluminum.CNC

mills

are

built

for

repeatability

and

can

be

used

foreverything

from

prototyping

to

high

volume

production.High-end

precision

CNC

mills

are

often

used

for

tight

tolerancework

such

as

milling

fine

dies

and

molds.While

CNC

milling

can

deliver

quick

turnaround,

as-milledfinishing

creates

parts

with

visible

toolmarks.It

mayalso

produce

parts

with

some

sharp

edges

and

burrs,

soadditional

processes

may

be

required

if

edges

and

burrs

areunacceptableforthose

features.Of

course,

deburring

tools

programmed

into

thesequencewill

deburr,

althoughusually

achieving

90%

of

the

finishedrequirement

at

most,

leaving

some

features

for

finalhand

finishing.As

for

surface

finish,

there

are

tools

that

will

produce

not

onlyan

acceptable

surface

finish,

but

alsoa

mirror-like

finish

onportions

of

the

work

product.TYPES

OF

CNC

MILLSThe

two

basic

types

of

milling

machines

are

known

as

vertical

machiningcenters

and

horizontal

machiningcenters,

wherethe

primary

difference

is

in

the

orientation

of

the

machine

spindle.A

vertical

machining

center

is

a

mill

in

which

the

spindle

axis

is

aligned

ina

Z-axis

direction.

These

vertical

machines

can

befurther

divided

into

two

types:Bed

mills,

in

which

the

spindle

moves

parallel

to

its

own

axis

while

the

table

moves

perpendicular

to

the

axis

of

the

spindleTurret

mills,

in

which

the

spindle

is

stationary

and

the

table

is

moved

so

that

it

is

always

perpendicular

and

parallel

to

theaxis

of

spindle

during

the

cutting

operationInahorizontal

machining

center,

the

mill’s

spindle

axis

is

aligned

inaY-axis

direction.

The

horizontal

structuremeansthesemills

tend

to

take

up

more

space

on

the

machine

shop

floor;

they

are

also

generally

heavier

in

weight

and

more

powerful

thanvertical

machines.A

horizontal

mill

is

oftenusedwhena

better

surface

finish

is

required;

that’s

because

the

orientation

of

the

spindlemeansthecutting

chips

naturally

fall

away

and

are

easily

removed.

(As

an

added

benefit,

efficient

chip

removal

helps

to

increase

tool

life.)In

general,

vertical

machining

centers

are

more

prevalent

becausethey

can

be

as

powerful

as

horizontal

machining

centers

andcan

handle

very

small

parts.

In

addition,

verticalcentershave

a

smaller

footprint

than

horizontal

machining

centers.MULTI-AXIS

CNC

MILLSPrecision

CNC

mill

centersare

available

with

multiple

axes.

A3-axis

mill

utilizes

the

X,

Y,

and

Z

axes

for

a

wide

variety

ofwork.

With

a4-axis

mill,

the

machine

can

rotate

on

avertical

and

horizontal

axis

and

move

the

workpiece

to

allow

for

morecontinuous

machining.A

5-axis

mill

has

three

traditional

axes

and

two

additional

rotary

axes,

enabling

the

workpiece

to

be

rotated

as

the

spindle

headmoves

around

it.This

enablesfivesides

of

a

workpiece

to

be

machined

without

removing

the

workpiece

and

resetting

themachine.Learnmoreabout

precision

CNC

milling

here.hoW

It’s

done:What

processes

and

equIpment

are

commonly

used

In

precIsIon

machInIng?7CNC

LATHESA

lathe

—

also

called

a

turning

center

—

has

one

or

more

spindles,

and

X

and

Z

axes.Themachine

is

used

to

rotate

aworkpiece

on

its

axis

to

perform

various

cutting

and

shaping

operations,

applyingawide

range

of

tools

to

the

workpiece.CNC

lathes,

which

are

also

called

live

action

tooling

lathes,

are

ideal

for

creating

symmetrical

cylindrical

or

spherical

parts.Like

CNC

mills,

CNC

lathes

can

handle

smaller

operations

such

prototyping

but

can

also

be

set

up

for

high

repeatability,supporting

high

volume

production.CNC

lathes

can

also

be

set

up

for

relatively

hands-free

production,

whichmakes

them

widelyused

in

the

automotive,electronics,

aerospace,

robotics,

and

medical

device

industries.There

is

hands-free

production

—

and

then

there

is

fully

automated

“lights

out”

production.

Learn

about

the

challenges

in

our

blogBarriers

to

Lights

Out

Operation

in

Precision

Machining.HOW

A

CNC

LATHE

WORKSWith

a

CNC

lathe,

a

blank

bar

of

stock

material

is

loaded

into

the

chuck

of

the

lathe’s

spindle.

This

chuck

holds

the

workpiece

inplace

while

the

spindle

rotates.

When

the

spindlereaches

the

required

speed,

a

stationary

cutting

tool

is

brought

into

contactwith

the

workpiece

to

remove

material

and

achieve

the

correct

geometry.A

CNC

lathe

can

perform

anumber

of

operations,suchas

drilling,

threading,

boring,

reaming,

facing,

and

taper

turning.Different

operations

require

tool

changes

andcanincreasecost

and

setup

time.When

all

of

the

required

machining

operations

are

completed,

the

part

is

cut

from

the

stock

for

further

processing,

if

needed.The

CNC

lathe

is

then

ready

to

repeat

the

operation,

with

little

or

no

additional

setup

time

usually

required

in

between.CNC

lathes

can

also

accommodate

avariety

of

automatic

bar

feeders,

which

reduce

the

amount

of

manual

raw

materialhandling

and

provideadvantages

suchas

the

following:hoW

It’s

done:What

processes

and

equIpment

are

commonly

used

In

precIsIon

machInIng?8Reduce

the

time

and

effort

required

of

themachine

operatorSupport

the

barstock

toreducevibrations

that

cannegativelyaffect

precisionAllow

the

machine

tool

to

operate

at

optimumspindle

speedsMinimize

changeover

timesReduce

material

wasteTYPES

OF

CNC

LATHESThere

are

anumber

of

different

types

of

lathes,

but

the

most

common

are

2-axis

CNC

lathes

and

Swiss-style

automatic

lathes.Most

CNC

Swiss

lathes

useone

or

two

main

spindles

plus

one

or

two

back

(or

secondary)

spindles,

with

rotary

transferresponsible

for

the

former.

The

main

spindle

performs

the

primary

machining

operation,

with

the

help

ofa

guide

bushing.In

addition,

some

Swiss-style

lathescomeequipped

withasecondtool

head

that

operates

asa

CNC

mill.With

aCNC

Swiss-style

automatic

lathe,

the

stock

material

is

fed

throughasliding

head

spindle

intoaguide

bushing.

Thisallows

the

tool

to

cut

the

material

closer

to

the

point

where

the

material

is

supported,

making

the

Swiss

machine

especiallybeneficial

for

long,

slender

turned

parts

and

for

micromachining.Multi-axis

CNC

turning

centersand

Swiss-style

lathescan

accomplish

multiple

machining

operations

using

a

single

machine.Thismakes

them

a

cost-effective

option

for

complex

geometries

that

would

otherwise

require

multiple

machines

or

toolchanges

using

equipment

such

asatraditional

CNC

mill.Learn

about

5-

and

7-axis

Swiss

machining

capabilities

here.hoW

It’s

done:What

processes

and

equIpment

are

commonly

used

In

precIsIon

machInIng?9UNIQUE

ADVANTAGES

OF

CNCSWISS-STYLE

MACHININGOlder

style

lathes

werecam-driven,

making

them

relativelyprimitive.

Today’s

Swiss-style

lathe

with

CNCis

leaps

andbounds

better,

in

both

accuracy

and

efficiency.On

a

regular

chucker

lathe,

the

part

sticks

out

and

is

pushedaway

—

that

is,

deflected

—

as

you

start

removing

material.But

on

a

CNCSwiss

machine,

the

material

moves

and

thetools

are

stationary,

so

there

is

farlessdeflection.In

addition,

a

Swisslathe

has

both

a

collet

and

a

guidebushing,

to

further

reduce

deflection

and

machine

the

partsmore

precisely.

All

the

action

is

at

the

edge

of

the

guidebushing;

the

correct

length

of

material

is

fed

out,

machined,and

parted

off,

then

another

length

of

material

is

fed.hoW

It’s

done:What

processes

and

equIpment

are

commonly

used

In

precIsIon

machInIng?10So,

with

little

or

no

deflection

in

its

machining

process,

theCNC

Swiss-style

screw

machine

providesgreateraccuracy,precision,

and

consistency.

Learn

more

about

the

advantagesof

eliminating

deflection

in

our

blog

DeflectionandPrecision

in

CNC

Swiss

Machining.In

addition,

compared

with

other

precision

CNC

machiningmethods,

CNC

Swiss-style

machining:Reduces

part

handling

and

laborStreamlines

setupAccelerates

cycle

timesAllows

parts

to

be

finished

in

a

single

operationEliminates

the

risk

of

operator

errorIn

the

next

section,

we’ll

examine

some

of

the

tools

andtechniques

used

with

precision

CNC

Swiss

machining.The

Swiss

screw

machine

has,

quite

literally,

been

around

for

centuries

and

shows

no

sign

of

stopping.

You

can

read

about

theevolution

of

the

modern

Swiss

lathe

in

our

blog

The

Swiss

Machine

in

Today’s

Machine

Shop.The

modern

precision

machine

shop

leverages

CNC

Swiss-style

machining

with

a

wide

rangeof

tools

to

create

parts

with

aninterestingarrayoffeaturesand

functions,

described

below.DRILLINGWhat

It

does:

What

are

some

common

uses

for

cnc

sWIss

machInIng?11What

It

Does:

What

are

some

commonuses

for

CNC

Swiss

machining?Drilling

is

a

process

that

is

often

used

in

precision

machiningto

remove

material

before

performing

finishing

operationssuch

as

threading,

tapping,

boring,reaming,or

broaching.For

Swiss-style

machining,

almost

any

drill

can

be

attached

to

a

screw

machine

tool

holder,

within

the

size

limitations

of

the

machine.

The

drill

is

then

used

to

remove

material

and

createfeatures

such

as

through

holes,

cross

holes,

and

blind

holes

ofvarious

sizes.The

world

of

drills

issovast,

you

could

write

a

book

on

it,

andthe

availability

of

drills

hasexploded.

Today,

there

are

drills

ofremarkably

small

diameters

—

as

small

as

0.002”

(50

micronsor

0.051

mm).Of

course,

the

length

and

diameter

ratios

apply,so

there

are

limitations

to

how

deep

you

can

drill

withultra-small

diameter

drills.Drills

come

in

a

range

of

sizes

and

with

different

types

offlutes.

Here

at

Metal

Cutting

Corporation,

most

of

the

drillswe

use

for

precision

CNC

machining

are

standard,

fractional,decimal,

wire,

and

letter

sizes.Certain

drills

areusedfor

specific

processes.

For

instance,a

#7drill

is

used

to

make

a

hole

to

tap

a

quarter-twenty

threadinside

a

part.Flutes

are

grooves

that

can

vary

in

size,

shape,and

thenumber

on

the

bit.

The

purpose

of

a

drill’s

flutes

is

to

ease

theexit

of

the

chips

as

the

material

is

being

cut.The

exception

isaspadedrill,

which

doesn’t

have

flutes

because

it

isusedforshallow

hole

drilling.Drills

are

typically

made

of

hardened

steel

or

carbides,

somewithabrasive

features.

The

point

of

a

drill

is

typically

angledbetween

118°

and

135°

(sometimes

145°),

depending

on

thematerial

being

machined,

witha

118°

being

the

standardangle.

It

isused

on

all

drills

for

all

materials,

usually

followinga

spot

drill

orcenter

drill

application.THREADING

(OD

&

ID)Forthe

purposes

of

precision

CNC

Swiss

machining,

athread

is

a

symmetrical

radial

feature

that

varies

in

its

pitch.

The

pitch,

orangle,

determines

the

depth

of

the

thread.In

the

machining

of

small

parts,a

threadingprocessisused

to

create

precision

threads

on

the

outside

diameter

(OD)

or

insidediameter

(ID)

of

the

part.

There

are

four

methods

for

producing

OD

threads:Singlepoint

threading

usesatool

that

is

ground

to

the

specific

angle

needed

for

the

thread

you

want

to

create;

at

MetalCutting,

typically

we

thread

at

60°

inclusive.

The

single

point

tool

is

fed

along

the

Z

axis

until

the

desired

depth

is

met.Thread

rolling

involves

feeding

the

material

between

(usually,

three)

die

rolls,

where

the

threads

are

formed

rather

thancut

into

the

correct

shapeand

depth.

Quicker,

more

efficient,

and

more

accurate

than

the

single

point

method,

threadrolling

can

also

create

threads

all

the

way

to

the

shoulder

of

the

part

(such

as

up

to

the

headof

a

screw).Threadwhirling,

which

was

invented

for

surgical

bone

screws,

is

complicated

and

expensive.

However,

with

the

propertools

and

inserts,

it

can

be

used

to

make

virtually

any

type

of

thread

an

engineer

can

design

for

medical

and

otherproprietary

uses.

With

the

tool

spinning

at

a

set

RPM

and

the

material

also

rotating,

the

threads

come

out

with

no

burrs.Die

threading

makes

threads

using

adie

made

of

high-speed

steel

or

carbide

and

having

the

pitch

and

diameter

of

thethread

you

want

to

make.

Generally,

the

die

is

fed

over

a

rotating

diameter,

usually

along

the

Z

axis.

Alternatively,

a

die

maybe

inserted

into

the

holder

and

used

to

form

threads

rather

than

cut

them.In

Metal

Cutting’s

world

of

very

small

diameter

parts,

ID

threading

presents

adifferent

kind

of

variable.

That’sbecause

weusually

don’t

have

the

luxury

ofaperpendicular

tool,

due

to

the

extremely

small

IDs

we

are

requested

to

tap.However,

in

general

precision

CNC

Swiss

machining

uses

one

of

two

methodsusedto

produce

ID

threads:

singlepointthreading

and

tapping.

ForID

threads,

single

point

threading

is

accomplished

in

basically

thesameway

as

described

abovefor

OD

threading,

except

in

this

instance

on

the

ID

of

the

part.What

It

does:

What

are

some

common

uses

for

cnc

sWIss

machInIng?12Tapping

creates

threads

using

a

tool

called

a

tap,

which

has

a

specific

pitch

and

diam