The Increasingly Perfected Science of Machining … · The Increasingly Perfected Science of Machining Composites ... interior structure components with carbon fiber reinforced plastic

April 2015 | AdvancedManufacturing.org 89

Composites maChining

The Increasingly Perfected Science of Machining Composites

A 1965 Shelby Cobra 427

shown at the Detroit Auto Show

was additively manufactured on a

Cincinnati BAAMCI machine by

DOE’s Oak Ridge National Laboratory

(ORNL), one of seven founding members

of the Institute for Advanced Composites

Manufacturing Innovation. The Detroit IACMI

branch will get $70 million to develop a robust

supply chain to improve materials, handling, and

machining properties for automotive composites.

Jim Lorincz

Senior Editor

As use of composites matures in

aerospace, how to machine the

advanced materials grows up too,

with advanced tooling solutions

and tested approaches

Thanks to the aerospace industries and large quality-

intensive programs such as the Airbus 380 and Boeing

787, the business of machining composites has moved

into the mainstream of the manufacturing industry.

There’s a bevy of tools, specialty tools and know-how about how

to machine composites today, which helps make the complex

materials ripe for expansion into other areas of industry.

The auto industry is the next big growth area for the light-

weighting, strength, and design flexibility that composites offer.

BMW’s Vision Future Luxury concept car introduced last year

showcased how “subtractive modeling” could be used to design

interior structure components with carbon fiber reinforced plastic

(CFRP) and structural load-bearing layers of aluminum and deco-

rative and functional wood and fabric—milled down to reduce

total weight.

More car and truck components made with composites, and

a fully developed supply chain to support them, are on the way.

When the Strati 3D-printable car rolled out of IMTS 2014 last

Photo courtesy Cincinnati Inc.

90 AdvancedManufacturing.org | April 2015

September, it represented 44 hours of additive manufacturing

on Cincinnati Inc.’s BAAMCI (Big Area Additive Manufacturing

Machine) and a full day of subtractive milling by Local Motors

Inc. (Phoenix, AZ) of the ABS plastic/carbon fiber composite

on a CNC router. Local Motors says 24 hours of AM is a realiz-

able goal.

At the Detroit Auto Show, ORNL, one of seven founding

members of the Institute for Advanced Composites Manufac-

turing Innovation (IACMI), showcased

a 3D-printed 1965 Shelby Cobra 427.

$70 million of the Institute’s $259 mil-

lion public-partnership of 122 member

companies will fund IACMI’s Detroit

branch to develop a robust, risk-free

supply chain for advanced compos-

ite materials—to improve materials,

handling, and machining properties for

automotive applications.

Automotive Chases Lightweighting

Promise of Composites

According to Randy Von Moll,

technical sales director, Fives Cincinnati

(Hebron, KY), automotive manufactur-

ers are following the lead of the aero-

space industry exploring the potential

of composites to reduce weight and

increase fuel efficiency. “We may see

the main chassis of the car being built

from composites one day in the future.

The hood is a good example of a part

that weighs a lot and can benefit from

lightweighting,” said Von Moll.

“Automakers are striving to manu-

facture composite parts to net shape.

They can get pretty close to net shape,

but virtually every part that is built

from composites needs some form of

machining to finish it. There are only a

couple of parts in composites that I can

cite that can be made all the way to net

shape. Usually there’s a certain amount

of excess material, around the periph-

ery of the part in aerospace because of

the way that the composite part is built

up that it always has to have a pro-

file trim done on it and typically holes

drilled,” said Von Moll.

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re-engineered PMT [precision, mill, trim]

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traveling gantry-type machine can extend the X axis for a large single part or be set

up in multiple work zones with light-curtain dividers or physical barriers between

zones. All of the new aircraft designs are getting designed more accurately to

minimize or eliminate the hand fitting that has historically taken place during the

aircraft manufacturing process. The aircraft producers want to build airplanes more

like the car builders build cars and pull them together on a moving line and they’re

making a lot of progress toward that. Today virtually all the newer Boeing models

are built on moving lines,” said Von Moll.

“There is a wide variety of tooling for different types of material that is being

cut. Compresson-type cutters featuring both left-hand and right-hand helixes have

been developed to machine laminated stacks of material without delamination. A

lot of machining that is done of composites also involves other materials. It isn’t

unusual for us to supply a solution for a composite material that has carbon fiber,

Kevlar, usually a nonmetallic honeycomb core or foam, a copper mesh for lightning

strikes, a titanium sheet in there for additional design purposes. It would be more

unusual for us to have just a uniform material type. The sandwich structures are

getting more complex,” said Von Moll.

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At IMTS 2014, the Strati car was additively manufactured in 44 hours by Local Motors

using an ABS plastic/carbon fiber composite on a Cincinnati BAAMCI machine. A

full day of subtractive milling was performed before final assembly. Local Motors

has targeted 24 hours as 3D printing time required for the Strati in the future.

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Machining CFRPs Not Like Cutting Metal

According to Don Graham, Seco Tools Inc. (Troy,

MI), carbon fiber reinforced plastics (CFRP) are

machined by a series of brittle fractures in which the

cutting action shatters the abrasive hard carbon fibers

producing powder or brush-type chips. “Machining

optimization of composite materials in drilling has to

resolve problems of fiber pullout, uncut fibers and

delamination, especially in exiting the material by

addressing issues resulting from dull edges, improper

prep, feed rates that are too aggressive, and wrong

drill angles. For milling applications, fiber pull out,

uncut fibers, delamination, chatter/vibration, and torn

fibers benefit from some combination of replacing dull

cutters, remedying prep, reducing aggressive feed

rates, changing too high helix angles, improving cutter

angle of attack and better fixturing,” said Graham.

“Tools can fall into one of two categories,” said

Graham. “End mills with a double helix—both a left and

right-handed helix—for cutting action

use a guillotine action and are particu-

larly useful for honeycomb materials

and fiber reinforced materials as well.

The idea is that you shear the fibers,

not fray, split, or delaminate them,” said

Graham. Seco Tools’ Jabro JPD and

JC end mills were developed specifi-

cally for composite materials. The JPD

group of solid carbide end mills features

brazed polycrystalline diamond plates

with through-coolant channels for chip

and dust evacuation and are available in

square, ballnose, and compression-type

end mills. The JC group includes the

875 solid carbide router with a special

edge treatment and diamond coating.

For drilling CFRP materials, Seco

Tools offers drills with two different ge-

ometries: C1 geometry has an optimized

drill point for carbon fiber and in stacked

titanium/carbon fiber or aluminum/

carbon fiber when exit is in the carbon

fiber. The diamond-coated drill has a

double chamfer and two different angles

for exiting on the carbon fiber without

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PCD-veined series 85 geometry cutting tools are monolithic in structure

and can be ground with various geometries and features that were once

difficult to achieve in the past using conventional brazing methods.

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splintering and delamination. C2 geometry is used for stacks

entered on carbon fiber and exited on titanium or aluminum,

controlling chips so that the metal chips don’t roughen the

carbon-fiber surface. C1 and C2 drills are coated with a CVD

Dura coating.

Many Industries Are

Affected by Composites

When it comes to composites,

everybody thinks of aerospace first, ac-

cording to Adrian von Rohr, KOMET of

America Inc. (Schaumburg, IL). “That is

completely wrong. If you look around

composites are becoming more and

more interesting for applications where

a heavier material component made

from steel or cast iron can be replaced

with a composite that requires less

energy to move the object. Also, com-

posites allow extreme positive features

and physical hardness and toughness

to be designed into components. In the

automotive industry, weight reduction

of composites results in fuel efficiency.

BMW, for example, has launched a

car that is completely made out of

composites, except for the engine and

drive train. It’s not a prototype, and

BMW has a manufacturing line for that

car,” said von Rohr.

Fiber reinforced plastics (FRP) are

durable, but also lightweight, reducing

loads, drag, and energy consumption.

However, composite materials present

their own special machining challenges.

They are brittle, and the glass fibers

within them are particularly abrasive.

The glass sections of FRP require

particularly sturdy drills and tools, while

the plastic pockets need to be ma-

chined with care. “KOMET’s portfolio of

tools includes drills, mills, and routers

for opening holes up, milling slots, and

cleaning trimming and drilling to get to

the final shape. These tools are used

both on manual and CNC machine

tools. “The real challenge is to match the tooling solution

with the right coating, tool geometry and tool body for the

composite application based on the information that the

customer supplies to us,” said von Rohr.

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Full Range of Composite Machining Products

There is major growth in the use of composites in virtually

every industry, including aerospace, automotive, and medi-

cal, according to Jeffrey Stephens, OSG USA Corp. (Glendale

Heights, IL). “We have a number of tools designed specifi-

cally for aircraft production. The EXOPRO AERO BNC router

with our patented ultrafine diamond coating is designed for

trimming carbon fiber and glass cloth. It features a fine nicked

geometry for roughing as well as over-

lapping with finishing. The nick is actually

a flat portion making the tool highly ef-

ficient in producing clean cutting edges

without delamination or leaving fibers

uncut when used on CNC machines.

The CNC router is the workhorse,

capable of plunge and helical interpola-

tion,” said Stephens.

“If you look at our current composite

products, we’ve developed roughing

and finishing routers and drills for CNC

applications that are solutions tailored to

the customer’s requirements. There are

still a lot of applications in aircraft where

the parts are awkward, sometimes the

fixturing isn’t very good. They might use

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Compression-style end mills with a double

helix (left hand and right hand) like the

Jabro JC845 are particularly useful for

shearing honeycomb materials and fiber-

reinforced composites without fraying,

splitting, and delamination.

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Tool

s

See us at AERODEF Booth #233


a vacuum frame or even adhesives to hold the part down and we have to develop

cutting tools that reduce the cutting forces,” said Stephens. “The EXOPRO AERO

HBC router features a diamond-coated herringbone for high-feed CNC applications

that produces excellent surface finish. The EXOPRO AERO drill features diamond

coating for clean entry and exit from the composite material.”

Machining honeycombs is an entirely different matter. “In our original herring-

bone compression router design, we featured a 30° helix. Compression-style rout-

ers compress the laminate together with a left-hand and right-hand helix, leaving a

clean edge on both top and bottom. What we found was that the 30° didn’t work

in all cases, especially for fibers with higher strength. So we developed a 45° helix

with a higher shearing capability for more difficult fibers. For the most difficult to cut

Kevlar honeycombs, we developed a 60° helix that performs like a pair of scissors

to cut the Kevlar very cleanly,” said Stephens.

PCD Veined Drills Feature Unique Solution

Many of the most difficult challenges still originate with aircraft production

generally and with jet engine applications specifically. The latest surge in jet engine

design and production for new aircraft and for retrofit applications will ramp up

demand for machining the toughest of materials, ceramic composites, with the

hardest of materials, diamond.

Sandvik Coromant (Fair Lawn, NJ) has developed its unique solution in a series

of PCD-veined cutting tools for drills, mills, and end mills. “Series 85 geometry

cutting tools provide a real alternative to brazed diamond-tipped tools, especially

for ceramic composites that require the hardest material to drill,” according to Linn

Win, composites product specialist for Sandvik Coromant. “Our PCD-veined series

85 geometry cutting tools are monolithic in structure. That means that they can be

ground with various geometries and features that were once difficult to achieve in

the past using conventional brazing methods,” said Win.

The monolithic PCD-veined tool is formed by slitting a carbide nib in precise

location and configuration in accordance to the customer’s requirements, filling

the carbide nib with diamond powder, and then sintering the tool under high

pressure and high heat. Once the nib is extracted from the pressure and heat

vessel, the diamond has bonded with the carbide as one monolithic structure

leaving no brazing weak points and allowing more options when grinding the

cutters face

geometry. “The

monolithic struc-

ture allows cutters

to be reground

multiple times, so

that tools have

the durability of

diamond as well

as the versatility

of carbide,” said

Win. Buy online today. www.birchwoodtechnologies.com

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?Cincinnati Inc.513-367-7100 / e-ci.com

Fives Cincinnati859-534-4600 / fivesgroup.com

Komet of America Inc.847-923-8400 / komet.com

OSG USA Corp.800-837-2223 / OSGtool.com

Sandvik Coromant201-794-5000 / sandvik.coromant.com/us

Seco Tools LLC248-528-5200 / secotools.com/us

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The Increasingly Perfected Science of Machining … · The Increasingly Perfected Science of Machining Composites ... interior structure components with carbon fiber reinforced plastic