machining titanium (technical report) by global industrial fluids, cincinnati, ohio

7/27/2019 Machining Titanium (Technical Report) by Global Industrial Fluids, Cincinnati, OHIO

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Milacron Marketing Co. | Global Industrial Fluids | Cincinnati, Ohio 45209

Machining TitaniumPage 1 of 23/07

Machining Titanium

Background:

With its low mass, high strength, and excellentresistance to corrosion, titanium solves manyengineering challenges. (1) Titanium is 30%stronger than steel but is nearly 50% lighter.Titanium is 60% heavier than aluminum but twiceas strong. (2)

The aerospace industry is the single largestmarket for titanium products. Titaniumapplications are most significant in jet engineand airframe components that are subject to

temperatures up to 1100 F and for other criticalstructural parts. Titanium is alloyed withaluminum, manganese, iron, molybdenum andother metals to increase strength, to withstandhigh temperatures and to lighten the resultantalloy. Titaniums high corrosion resistance is alsoa valuable characteristic. When exposed to theatmosphere, titanium forms a tight, tenacious

oxide film that resists many corrosive materials.(3)

In the 1950s the titanium metal industry wasestablished primarily in response to theemerging aerospace industry that used it in themanufacture of airframe structural componentsand skin, aircraft hydraulic systems, air enginecomponents, rockets, missiles, and spacecraft,where these properties are invaluable. Themilitary also uses titanium in its guided missilesand in artillery. As the 1970s approached, thecost of titanium dropped making it more available

for other practical applications such asshipbuilding: primarily in submarines, in shipspropellers, shafts, rigging, and other highlycorrosive parts. Titanium is being increasinglyused for medical applications due to itslightweight, its strength, and its hypoallergenicproperties, as titanium is nickel-free. Titaniumproducts are being utilized in other industries as

well, from petrochemical applications to sportinggoods. (2)

For automotive applications, titanium is used forengine valves, connecting rods, wheel-rimscrews, exhaust systems, and suspensionsprings. Titanium engine components increasehorsepower and torque while improving fueleconomy and solving problems with noise andvibration. When used in exhaust systems,titanium reduces material weight approximately50% compared to traditional systems and

substantially increases product life. Titaniumsuspension springs give OEMs greater massreduction, up to 70%, over conventional springsperforming the same function in less space,allowing increased payload and engine orpassenger compartment space. (1)

While the material once had a reputation forbeing expensive, advances in productiontechnology and increased consumption inindustrial markets have allowed steep costreductions. (1)

General Considerations: (4)

Historically, titanium has been perceived as amaterial that is difficult to machine. Due totitaniums growing acceptance in manyindustries, along with the experience gained byfabricators, a broad base of titanium knowledgenow exists. Given the proper procedures,titanium can now be fabricated using techniquesno more difficult than those used to machine 316stainless steel.

Machining of titanium alloys requires cuttingforces only slightly higher than those needed tomachine steel, but these alloys havemetallurgical characteristics that make themsomewhat more difficult to machine than steels ofequivalent hardness.


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The fact that titanium sometimes is classified asdifficult to machine by traditional methods in partcan be explained by the physical, chemical andmechanical properties of the metal. For example:

Titanium is a poor conductor of heat. Heat,generated by the cutting action, does notdissipate quickly. Therefore, most of the heatis concentrated on the cutting edge and thetool face.

Titanium has a strong alloying tendency orchemical reactivity with materials in thecutting tools at tool operating temperatures.This causes galling, welding and smearingalong with rapid destruction of the cutting

tool.

Titanium has a low modulus of elasticity, thusit is more springy than steel. This meansthat the work-piece tends to move away fromthe cutting tool unless heavy cuts aremaintained. Slender parts tend to deflectunder tool pressure and this can causechatter, tool rubbing and hence toleranceproblems. Rigidity of the entire machiningsystem is consequently very important, as isthe use of sharp, properly shaped cutting

tools.

Titaniums work-hardening characteristics aresuch that titanium alloys demonstrate acomplete absence of built-up edge.Because of the lack of a stationary mass ofmetal (BUE) ahead of the cutting tool, a highshearing angle is formed. This causes a thinchip to contact a relatively small area on thecutting tool face and results in high loads perunit area. These high forces, coupled with thefriction developed by the chip as it passes

over the cutting area, result in a greatincrease in heat on a very localized portion ofthe cutting tool. All this heat (which thetitanium is slow to conduct away), andpressure, means that tool life can be short,especially as titanium has a tendency to galland weld to the tool surface.

Tool-life Considerations: (4)

When cutting titanium, as cutting speedincreases, tool life dramatically decreases, forreasons out-lined above.

Thus, although the basic machining properties oftitanium metal cannot be altered, their effects canbe greatly minimized by decreasing temperaturesgenerated at the tool face and cutting edge if thefollowing rules are observed:

Use low cutting speeds. Tool tiptemperatures are affected more by cuttingspeed than by any other single variable. (Achange from 20 to 150 sfpm with carbidetools results in a temperature change fromabout 800F to 1700F).

Maintain high feed rates. Temperature is notaffected by feed rate nearly so much as byspeed, thus the highest feed rates consistentwith good machining practice should be used.Note: a change from 0.002 to 0.02 perrevolution (a 10 fold increase) results in atemp increase of only about 300F. (Comparethis to the temperature increase resultingfrom only a seven and one half fold increasein cutting speed- 900F).

Use generous amounts of cutting fluid.Coolant carries away heat, washes awaychips, and reduces cutting forces.

Use sharp tools and replace them at the firstsign of wear. However, note that tool wear isnot linear when cutting titanium. Completetool failure occurs rather quickly after a smallinitial amount of wear takes place.

Never stop feeding when a tool and work-piece are in moving contact. Permitting a tool

to dwell in a moving contact causes workhardening and promotes smearing, galling,seizing and total tool breakdown.

Tooling Considerations:


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High-speed steels are widely used for machiningtitanium because of their flexibility and lower costthan cemented carbides. When it comes to truetool economy, do not equate least expensive

tooling with the most economical tooling; oftenthe tooling that costs least to buy ends up beingthe most expensive on a cost-per-cut basis. Forbest tool economy, the cutting tool should bematched to the material being machined. (3)

Metalworking fluid Considerations:

Metalworking fluids used in machining titaniumalloys require special consideration becausechloride ions have, under certain circumstances,caused stress-corrosion cracking in laboratorytesting of these alloys. Sodium ions, too, have

been implicated in the stress cracking of titaniumalloys. Many plants are unwilling to use ametalworking fluid that contains chlorine (used asan extreme pressure lubricant), though fewpeople seem to be aware that sodium might alsobe a problem.

Water-based fluids are the best choice to provideheat dissipation and good cleanliness formachining titanium. Synthetics offer low-foaming,excellent heat removal, good filterability andcleanliness. Soluble oils offer excellent lubricity.

Semisynthetics combine beneficial properties ofthe synthetics and soluble oils - such as goodoverall lubricity, cleanliness, sump life, and easeof fluid management.

The final selection of the fluid must include areview of the water quality, filter, fluid deliveryand pressure (and foam potential), and othermetals involved, tooling, fluid management, andother machine and operator requirements.

Metalworking fluid Recommendations:CIMTECH 310, a moderate to heavy-dutysynthetic metalworking fluid, has been tested forits effects on stress cracking and found to besafe for use on titanium. This product has beenused for machining titanium without problems. Itwould appear that the most importantconsideration when using the CIMTECH 310 is toensure that there is copious flow, and when

machining, and that the fluid is applied throughthe tool. Since CIMTECH 310 is non-foaming,high pressures can be used without fear of foamgeneration. The main job of the metalworking

fluid is to remove heat as quickly as possible toprevent tool damage, thus the more fluid, thebetter.

CIMTECH 410C and CIMTECH 500 would alsobe good choices to machine titanium, asmoderate to heavy-duty synthetics.

CIMSTAR QUAL STAR XL or CIMSTAR 3890would be good moderate to heavy-dutysemisynthetics for machining titanium. (bothchlorine-free)

CIMPERIAL 1060T is also recommended fortitanium machining as a moderate to heavy-dutysoluble oil. This product is chlorine and sodiumfree.

This is a partial list of products that can be usedfor machining titanium. Contact CIMCOOLTechnical Services (1-513-458-8199) foradditional information.

References:

(1) AMERICAN MACHINIST 1-1-02 issue(2) www.Aerospacemetals.com(3) www.Titanium.com(4) www.Superalloys.com Titanium: A

Technical Guide (1988). ASMInternational, Materials Park, OH 44073-0002 pgs. 75-83

machining titanium (technical report) by global industrial fluids, cincinnati, ohio

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