ISOTHERMAL SYSTEM FOR MACHINE TOOL

Abstract: A machine tool frame having a base (10) and column means (12), (16) extending from the base is provided with a fluid delivery system (44), (46) for flowing a fluid over interior wall elements making up the base and the column means. This provides for a heat exchange between the wall elements and the fluid to thereby maintain isothermal conditions throughout the frame.

Description: ISOTHERMAL SYSTEM FOR MACHINE TOOL "> This invention relates to the construction of machine φ. tools and, more particularly, to an improved system for - minimizing the errors introduced when significant temperature 5 variations exist simultaneously between different portions of the machine ffame. Background of the Invention Many machine tool operations, particularly those relating to the hobbing of gears, often are plagued with 10 accuracy problems resulting from the uneven warm up of drive motors, gear trains, bearings, etc. These various hot spots, along with the temperature changes which accompany the cutting activity itself, often cause major changes in the temperature of one particular portion of a machine 15 relative to more distant portions of the machine, resulting in distortion of the machine frame. For instance, a change of merely 10 degrees Centigrade in ambient room temperature can cause a machine base which is 2.5 meters long to expand or contract as much as 0.25 mm. When 20 such expansion and contraction is non-uniform, serious changes result in the alignment of machine elements, often resulting in the introduction of significant errors in the part being manufactured. Such thermal problems are well recognized, and 25 where extremely high precision is required, many different solutions have been proposed in the prior art, including all of the following: (a) encapsulation of the entire machine in its own air-conditioned environment; (b) refrigeration to reduce the temperature of lubricating 30 oils and cutting coolants; (c) use of heat exchanges, heating elements, or heat extractors within portions of a machine frame; (d) removal of all major drive elements and motors to positions remote from the machine frame; and (e) even placing the entire machine in a cocoon-like enclosure, subjecting it to a continual shower of cooled and temperature-controlled liquid which is sprayed over the top of the entire machine and permitted to flow, by gravity, down the outside of the machine. While specific temperature control (for the ambient air surrounding the machine as well as for the lubricating and cutting fluids) is the best known manner to avoid this type of distortion problem, such solutions are not practical for most machine tools. Another way of attempting to control thermal distortion is to attempt to obtain a uniform temperature in a specific part of a machine through the use of a heat exchanger, or similar device. It can be appreciated that these prior art temperature control systems are extremely expensive and, therefore, they can seldom be justified for most jobs. Nonetheless, temperature-generated distortions still create costly errors, and the reduction of such temperature problems is very desirable. Brief Summary of the Invention The invention herein greatly reduces such temperature distortion in a much simpler, more economical, and novel manner. As indicated above, refrigerants are commonly used in the prior art to lower the temperature of machine hot spots, and such cooling measures may still be used with the subject invention. However, rather than concentrating on the cooling of particular hot portions of the frame, the novel system disclosed herein spreads the heat generated by the machine drive and the cutting process evenly throughout the entire machine by heat exchange and by raising the temperature of the cooler and more remote portions of the frame. OMPI It is known in the prior art to use portions of the machine frame as reservoirs for the lubricating and cutting fluids. The invention herein utilizes such in-frame fluid storage, but expands this known feature and makes it part of a novel system for distributing at least one of these fluids throughout the interior walls of the machine frame in a manner which tends to keep the entire frame, including its column portions, at approximately the same temperature. in the preferred embodiment, the cutting fluid, which cools and lubricates the tool and workpiece and carries away the chips and heat created by the cutting process, is circulated .from a reservoir formed throughout the central section of the base of the machine frame, while the fluid which lubricates the drive mechanism, in quantities considerably larger than that normally required for such lubrication, is circulated from a second reservoir formed around the periphery of the same base portion of the frame. These two reservoirs are contiguous to each other and, preferably, include ribs or fins which facilitate heat exchange between the two separate volumes of fluid. The lubricating fluid is delivered through conventional and well-known means to the various bearings, shafts, gears, etc. of the machine drive mechanism. In addition, however, a much larger quantity of this same lubricating fluid is also delivered. through spray pipes and troughs to substantially all of the interior walls of the base and column portions of the machine frame. While the cutting fluid and the lubricating fluid are maintained in separate circulating systems, the design of their respective resevoirs facilitates a heat exchange which tries to equalize any temperature differences between these fluids. By virtue of this heat exchange in the machine base, the lubricating fluid which is continually flowed over the interior walls of the frame tends to maintain all portions of the frame at substantially the same temperature. While this temperature may vary upwardly or downwardly in accordance with the length of time the machine has been in operation and with the type of cutting that is taking place, temperature variations between different parts of the machine frame, at any given time, are markedly reduced. This isothermal system therefore tends to reduce machine inaccuracies caused by frame distortions which otherwise result from such uneven temperature changes, and it achieves this result in. a relatively simple and inexpensive manner. The detailed description of the invention which follows will be made with reference to the accompanying drawings in which: Fig. 1 is a side view, in schematic cross-section, of a machine tool having a frame modified according to the invention herein; — Fig. 2 is an end view, in schematic cross-section, of the machine tool shown in Fig. 1, the cross-section being taken generally along the line 2-2 in Fig. 1; Fig. 3 is an enlarged plan view of the machine in Fig. 1, shown in schematic cross-section taken general! along the line 3-3 in Fig. 1; Fig. 4 is an enlarged schematic view in partial cross-section of one of the pressure spray units which provide a flow of fluid to the interior walls of the column portions of the frame of the machine in Fig. 1; and Fig. 5 is an enlarged schematic representation, in partial cross-section, of one of the trough arrangements which provide a flow of fluid to the interior walls of the base portion of the machine frame. Detailed Description of the Invention The frame of a gear hobbing machine is shown in three very schematic, partial cross-section views in Figs. 1, 2 and 3 which are, respectively a side elevation, an end elevation and a plan view. The frame comprises a base portion .10, a workholding column 12 with appropriate means for holding a gear blank workpiece 14, and a tool-holding column 16 carrying a hob tool 18. As can be best seen in Fig. 3, base portion 10 includes a central reservoir 20 surrounded by two peripheral reservoirs 22 and 24 interconnected by a pipe 26. Central reservoir 20 holds cutting fluid which overflows a dam 28 into a sump 30. A pump 32. delivers the cutting fluid from sump 30 through pipe 34 to the interface between hob tool 18 and workpiece 14, the fluid being used to cool and lubricate the cut as well as to flush away chips produced during the cutting process. The cutting fluid absorbs heat from the cutting process and, carrying the flushed chips, falls into central reservoir 20 where an auger 36 moves the chips to the end of reservoir 20 where they are picked up by a magnetic chip conveyor 37 in a well known manner. The peripheral reservoirs 22 and 24 are filled with a lubricating fluid which is delivered to the various components of the machine drive mechanism. The machine's operating components are merely indicated schematically in Figure 1, and the lubricating fluid is distributed to these components by conventional means (not shown) well known in the art. However, reservoirs 22 and 24 contain considerably more lubricating fluid than would normally be necessary for conventional lubricating purposes, and this excess fluid is delivered under pressure by pump 38 through pipes 40 and 42 to the upper parts of frame columns 12 and 16 where it is directed by pressure- spray means 44 and by deflector/trough means 46 to flow over the interior of all of the wall elements of columns 12 and 16. The lubricating fluid then passes through the bottom of the column structures and is directed by further deflectors, channels and troughs, including conduits 47, to flow down the interior of substantially all of the wall elements of base 10. One of the pressure spray means 44 is illustrated in enlarged schematic form in Figure 4 in which small arrows show the direction of the lubricating fluid as it exits from a delivery pipe 48 through orifices 50 to shower against the interior walls of a section of column 16. Figure 5 illustrates in enlarged schematic form a preferred trough means comprising a plurality of troughs 52 and openings 54, as they might appear when positioned at the top of an interior section of base 10. Fluid is directed from the bottom of one of the column portions, e.g., through a conduit 47, into the troughs 52 so. that the lubricating fluid passes through the openings 54 to flow down the interior wall elements of the frame. In the preferred embodiment, a plurality of wall elements 56 extend through both central reservoir 20 and peripheral reservoirs 22 and 24, and some of the wall elements 56 may, if desired, be fabricated from aluminum or some other highly conductive material, being appropriately redesigned as fins for exchanging heat between the two fluids. In central reservoir 20, the cutting fluid is maintained at the level generally indicated by dotted line 58, and the lubricating fluid in peripheral reservoirs 22 and 24 is preferably maintained at a similar level, indicated by dotted line 60. This heat exchange arrangement tends to heat lubricating fluid in reservoirs 22 and 24 to the more elevated temperatures of the cutting fluid in reservoir 20. Distribution of this heated fluid, in the manner described above, raises the temperature of the interior of the more remote portions of columns 12 and 16 and base 10 of the frame. Ideally, this fluid delivery system maintains the entire frame at substantially the same temperature. As indicated above, while the machine may be provided with refrigerating means for lowering the temperature of these fluids, the invention herein is not directed at the lowering of these temperatures in the manner well known in the prior art. To the contrary, the isothermal system disclosed herein is directed to raising the temperature of the cooler areas of the frame to reduce differences in temperature between those otherwise cooler areas and the portions of the frame which are normally heated by the operation of the machine's drive mechanism and by the cutting process itself. That is, the invention does not try to maintain any particular level of temperature OMPI in the fluids or in the active components of the machine, but rather is intended to spread the heat of operation evenly throughout the frame to reduce the distortions which otherwise result from uneven expansion and contraction of various critical portions of the frame. OMPI

Claims: What is claimed is: 1. In a machine tool comprising a frame including a base portion and at least a first column portion extending from said base portion, said frame portions each having a plurality of wall elements;, respective means for holding a tool and a workpiece; drive means for creating relative motion between said tool and workpiece; and means for delivering fluid for lubricating said drive means and for cooling-lubricating said tool and workpiece; the improvement wherein said fluid delivery means also supplies a flow of said fluid over the interior of substantially all of the wall elements of the base and column portions of said frame for providing heat exchange between said wall elements and said fluid to maintain isothermal . conditions throughout said frame. 2. The machine tool -of claim 1 wherein said fluid delivery means further comprises trough means for distributing said fluid along substantially the entire width of a plurality of said wall elements. 3. The machine tool of claim 1 wherein said fluid delivery means further includes pressure spray means for distributing said fluid along substantially the entire width of a plurality of said wall elements. 4. The machine tool of claim 1 wherein said first column portion supports said tool-holding means, and further comprising a second column portion extending from the base portion for supporting said work-holding means, both said column portions being supplied with a constant flow of said fluid over their respective wall elements. 5. The machine tool of claim 1 wherein said fluid delivery means comprises separate means for, respectively, lubricating the drive means and cooling-lubricating the tool and workpiece, said separate means each having a respective fluid reservoir formed within said frame. 6. The machine tool of claim 5 wherein said means for lubricating the drive means also supplies said flow of fluid over the wall elements of the frame. 7. The machine tool of claim 5 wherein said two fluid reservoirs are formed in contiguous sections of said base portion. 8. The machine tool of claim 7 wherein one of said reservoirs is formed substantially by a central section of the base portion and the other of said ieservoirs is formed substantially by sections on the periphery of said base portion. 9. The machine tool of claim 7 further comprising heat exchange means interconnecting said contiguous sections of the base portion. 10. The machine tool of claim 9 wherein said heat exchange means comprises aluminum elements. OMPI

Inventors: HUNKELER ERNST J, HUNKELER, ERNST, J.
Applicants: GLEASON WORKS, THE GLEASON WORKS
Application year: 1983
Main classification: B23F5
IPC codes: B23Q11