Cold lubricant misting device and method

A method and device for lubricating a workpiece-machine tool interface during a machining operation in which the temperature of lubricant atomized within a stream of air is substantially reduced. The preferred embodiment utilizes a vortex tube to accomplish the cooling and thereby provides an extremely simple device that greatly reduces the amount of heat generated in a machining operation. Reduced heat production decreases the temperatures to which both the workpiece and machine tool are subjected. Lower temperatures serve to extend the machine tool's service life while preserving the workpiece's metallurgy and consequently allows for increased machining rates.

BACKGROUND OF THE INVENTION 
The present invention relates to lubricant devices and methods and more 
particularly pertains to an apparatus and method for significantly 
extending machine tool service life. The apparatus and method of the 
present invention are adaptable to various machining operations including, 
but not limited to drilling, cutting, reaming, tapping, boring, routing 
and milling. 
Heat generated during the above mentioned machining operations is both 
detrimental to the workpiece as well as to the machine tool. Excessive 
heat can cause metallurgical changes within the workpiece while 
accelerating the wear and dulling of the tool. A dull tool is less 
effective, generates even more heat during use, and thereby accelerates 
its own deterioration and ultimate failure. Backing off on the machining 
rate decreases the amount of heat generated, but results in a slower and 
less efficient production throughput. 
The undesirability of excessive heat build-up associated with machining 
operations has long been recognized and efforts to reduce temperature 
generally fall into two categories. The workpiece and machine tool are 
either cooled or their interface is lubricated. Supplying a cooling fluid 
either at ambient or subambient temperatures serves to reduce temperatures 
by transporting away heat generated during the machining operation. 
Alternatively, lubricating the machining surface reduces the amount of 
heat actually generated without compromising the effect of the tool on the 
workpiece. Flooding the workpiece and machine tool with copious amounts of 
lubricant would suggest that both effects are achieved simultaneously. The 
lubricant serves to reduce friction and hence heat generation at the 
outset as well as reduce the resulting temperature by transporting away 
heat that is generated. A particularly effective variation on this basic 
theme includes finely dividing or atomizing the lubricant into a mist (see 
for example, U.S. Pat. Nos. 3,188,010 and 3,939,944) to provide more 
surface area, and hence achieve a more efficient heat exchange. 
Disadvantages associated with prior art devices are generally attributable 
to the overall effectiveness of a particular method or device. Regardless 
of the amount of coolant supplied or the amount of lubricant applied, an 
increased machining rate will ultimately be attained wherein the machine 
tool and workpiece suffers and throughput efficiency must be forfeited. In 
addition, the disposal or recycling of toxic or contaminated cooling or 
lubricating compositions can pose a problem in modern pollution-conscious 
industrial settings. 
A method and apparatus applying such a method is therefore called for that 
more efficiently reduces the production or build-up of heat during a 
machining operation and that preferably generates reduced amounts of waste 
material. 
SUMMARY OF THE INVENTION 
The present invention provides a lubricating method that significantly 
reduces the amount of heat evolved during a machining operation. 
Application of this method, or utilization of the device employing this 
method greatly extends a machine tool's service life and enables increased 
machining rates to be achieved without adversely effecting the metallurgy 
of the workpiece nor the sharpness of the tool. The present invention 
achieves this by supplying a substantially cooled mist of lubricant to the 
workpiece-machine tool interface. 
This method has proven much more effective than either cooling alone or 
lubrication alone and is actually more effective than what an arithmetic 
combination of cooling methods and lubrication methods would suggest. It 
is, therefore, theorized that only substantial cooling of the lubricant 
allows the lubricant to actually reach the workpiece-machine tool 
interface where it is then able to reduce friction, and hence, reduce heat 
evolution. At high machining rates uncooled lubricant is simply boiled off 
before it reaches the interface and the violent outgassing, as a result of 
the sudden change of state the lubricant undergoes, serves to sweep away 
incoming fresh lubricant. This phenomenon is present even when a workpiece 
and machine tool is flooded with copious amounts of lubricant at 
substantially ambient temperatures as the actual interface, when viewed on 
a microscopic level remains clear of lubricant due to the sweeping effect 
of the violently expanding lubricant as it changes into its gaseous state. 
At high machining rates, in effect, neither conventional cooling means nor 
conventional lubrication means actually serve to lubricate the 
workpiece-machine tool interface to prevent or reduce the amount of heat 
generated at the outset. In actuality, heretofore methods applied to high 
feedrate machining operations have merely served to transport heat away 
once generated. 
The method of the present invention additionally serves to reduce the total 
amount of lubricant consumed due to its more efficient exploitation 
thereof. 
In a device employing the above-described method of the present invention, 
a pressurized stream of air is cooled substantially below ambient 
temperature after which lubricant is introduced thereinto at a controlled 
rate. Upon introduction into the cold air stream, the lubricant is 
atomized and its temperature is substantially reduced. The resulting 
cooled lubricant mist is subsequently directed at the workpiece-machine 
tool interface. Provisions are included to fine-tune flow rates as well as 
the resulting temperature of the mist, and additionally adaptation of a 
programmable metering unit permits lubricant to be introduced into the 
stream only when actually needed at a rate tailored to a particular type 
of machining operation and a particular machining rate. 
Other features and advantages of the present invention will become apparent 
from the following detailed description, taken in conjunction with the 
accompanying drawing, which illustrate, by way of example, the principles 
of the invention.

DETAILED DESCRIPTION OF THE INVENTION 
Generally, the method of the present invention provides a mist of cold 
lubricant to a workpiece-machine tool interface. More specifically, this 
method comprises introducing lubricant into a fast moving stream of cooled 
air and then directing the resulting mixture at the workpiece-machine tool 
interface during a machining operation. The introduction of the lubricant 
into the fast moving cold air stream has the effect of first atomizing the 
lubricant into a fine mist and then cooling the lubricant particles down 
to a preselected subambient temperature. It has been found that only 
substantially cooled lubricant is able to actually reach a 
workpiece-machine tool interface during high rate machining operations 
where its lubricating properties can then be exploited to reduce the 
amount of heat generated. Uncooled lubricant merely boils off to its 
ineffective gaseous state and the commensurate expansion it undergoes 
during this change of state actually serves to sweep away additional 
incoming lubricant. 
The FIGURE illustrates a preferred embodiment of the invention wherein the 
illustrated apparatus employs the above described method to reduce the 
amount of heat generated by a machining operation in which a machine tool 
17 engages a workpiece 15. For the purposes of this particular 
illustration, the machine tool 17 comprises a drill bit while the 
workpiece 15 constitutes a billet. 
Pressurized air from a source (not shown) is introduced into pressure line 
20 at 19 and is initially filtered through an inline filter 21 to remove 
any potentially harmful contaminants. Valve 23 controls the amount of air 
passing through line 20, while valve 27 controls the airflow introduced 
into the cooling unit 29. In the preferred embodiment, the cooling unit 29 
takes the form of a vortex tube, more formally referred to as a Hilsch 
Tube or Ranque-Hilsch Tube, which, without the use of any moving parts, 
produces a flow of warm air from its hot air orifice 31 and a flow of 
cooled air from its cold air orifice 33. An adjustable valve 32 located at 
the hot air orifice 31 controls the ratio of hot air to cold air expelled 
from the orifice. A flexible conduit 37 conducts the cold air issuing from 
the cold air orifice 33 towards the workpiece-machine tool interface 16. 
The pressure line 20 is tapped at junction 25 to provide pressurized air to 
lubricant pump 43 which introduces a precisely metered amount of lubricant 
into outgoing line 46 at a function of the incoming air flow. A computer 
41 controlled solenoid valve 49 regulates the airflow that actually 
reaches the metering pump. 
This diverted and regulated airflow serves to both prompt the introduction 
of lubricant into line 46 and additionally transport the lubricant to its 
discharge end 47. The lubricant tube 46 is introduced into and then 
coaxially routed within the flexible conduit 37 to a point a short 
distance from its mouth 48. 
An additional airline 36 allows uncooled air to be introduced into the 
Hilsch Tube 29 near its cold end. Valve 35 controls the amount of air 
injected into the Hilsch Tube 29 at this location. 
The unexpected effects of application of the methods of the present 
invention can be achieved through the combination of the few and rather 
simple components illustrated in the FIGURE. In its operation, it is to be 
pointed out that a single source of pressurized air is employed to fulfill 
a multitude of different functions simultaneously. The pressurized air 
flowing through the Hilsch Tube 29 produces, without external power 
demand, a low temperature fraction which subsequently serves to lower the 
lubricant mist's temperature. The air stream flowing past the lubricant 
tube's 46 discharge end 47 serves to first atomize the lubricant into fine 
particles and then transport the resulting mist to the workpiece-machine 
tool interface 16. In addition, airflow routed to the lubricant pump 43 
first prompts the dispensation of lubricant into line 46 and then 
transports it to the discharge end 47. The use of a Hilsch Tube 29 
provides an extremely simple, reliable and foolproof means of providing a 
flow of cold air. The interior of the Hilsch Tube consists of a number of 
precisely oriented and dimensioned passages which induce two counter 
rotating vortices 49, 50 within the tube to interact with one another to 
ultimately produce the two emitted air flows at the high and low 
temperatures. A control valve 32 controls the ratio of the hot air to cold 
air and can be adjusted to tailor the resulting temperature and flowrate 
to a particular machining operation. A Hilsch Tube supplied with 8-15 cfm 
at 80-110 psi is capable of providing a cold fraction down to 135.degree. 
F. below ambient temperature and is capable of maintaining such 
temperature within 1.degree. F. A larger cold air fraction is obtainable 
with less temperature reduction. A Hilsch Tube properly adapted for this 
application is no longer than 8" in length, is inexpensive and utterly 
reliable. 
Lubricant introduced into line 46 is coaxially routed within conduit 37 to 
point 47, located a short distance from the conduit's mouth 48. Particular 
attention must be paid to the routing of the line 46 within conduit 37. 
Because the rheological properties of the lubricant change as a function 
of temperature and more particularly, because typically, viscosity 
increases as temperature decreases, it is important that the lubricant's 
temperature is reduced once in its mist form in conduit 37 between 47 and 
48 and beyond, as opposed to while still in bulk within conduit 46. A 
premature reduction of the lubricant's temperature can restrict flow or 
even cause a blockage within line 46. Consequently, the length of line 46 
within conduit 37 must be limited accordingly, or alternatively, 
adequately insulated. The additional airline 36 allows uncooled air to be 
introduced into conduit 37 and thereby allows the temperature to be fine 
tuned without resort to the gross adjustment available by resetting of 
valve 32. 
The introduction of the lubricant at 47 into the high velocity flow of cold 
air serves to atomize the lubricant and thereby produces a mist of 
particles of lubricant which can then easily be directed towards the 
workpiece machine tool interface. Additionally, formation of the mist 
substantially increases the lubricant's surface area thereby promoting 
accelerated heat exchange with the cold air stream. A variety of different 
types of lubricant are available and can be dispensed by the described 
apparatus. Different machining operations or materials to be machined 
require different types of lubricant. Such lubricants can consist of any 
of a variety of formulations, including, but no limited to, various oils, 
greases, water soluble hydrocarbons, synthetics, glycerols and alcohols. 
Controller 41 controls the activation of solenoid 39 which then permits 
pressurized air to enter the lubricant pump 43 at a precise rate and 
timing sequence. Controller 41 may be programmable to tailor the rate of 
dispensation of a particular type of lubricant to a particular machining 
operation and can additionally be directly linked to the machine tool so 
as to provide lubricant only when the machine tool is actually in contact 
with the workpiece. Alternatively, the controller may be controlled by a 
manual override. Lubricant pump 43 meters the amount of lubricant actually 
introduced into the air stream as a function of the flow of air by the 
solenoid valve. 
EXAMPLE 
The following empirical observations serve to demonstrate the efficacy of 
the method of the present invention. 
The machining operation comprised drilling a 0.140" hole through 1/2" thick 
hardened stainless steel (Rockwell number C36/40). The machine tool 
consisted of a high-speed Cleveland Twist drill bit, with a 135.degree. 
point angle. 
By flooding the workpiece machine tool interface with coolant (Petroleum 
based water soluble), a total of 20-40 holes were drilled at a preselected 
constant rate prior to deterioration of the drill bit. In addition to the 
early deterioration of the tool, the workpiece showed burr marks, chatter 
marks and discoloration. 
By directing a stream of cold (40.degree. F.) air at the workpiece machine 
tool interface, 50-80 holes were drilled at the identical rate prior to 
complete deterioration of the drill bit. Similar flaw marks on the 
workpiece were observed. 
Directing lubricant (Acculube or Boelube) at ambient temperatures towards 
the workpiece machine tool interface slightly extended machine tool 
service life to about 80-100 holes prior to failure. 
A cooled lubricant mist (Acculube or Boelube, 40.degree. F.) produced in 
accordance with the present invention yielded the astounding results of 
extending machine tool service life to 200-500 holes prior to failure at 
twice the feedrate. No burn marks or chatter marks were visible on the 
workpiece and no heat discolorization was observed. 
While a particular form of the invention has been illustrated and described 
it will also be apparent that various modifications can be made without 
departing from the spirit and scope of the invention. Accordingly it is 
not intended that the invention be limited, except as by the appended 
claims.