Gear cutting – milling – or planing – Milling – Cutter spindle or spindle support
Reexamination Certificate
2001-09-17
2003-03-18
Wellington, A. L. (Department: 3722)
Gear cutting, milling, or planing
Milling
Cutter spindle or spindle support
C409S136000, C408S23900A
Reexamination Certificate
active
06533509
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to powered machine tools and equipment, and more specifically to a modification for a Haas mill vertical milling machine, permitting considerably higher coolant pressures to be used and precluding or greatly reducing damage and wear to the carbide coolant seals within the machine.
2. Description of the Related Art
In commercial machine shops and related operations, the rate at which machining can be performed on a given workpiece obviously has a significant bearing upon productivity. High rates of machining, and correspondingly high productivity, are obviously desirable in such operations. Such machines are typically configured for rapid and efficient interchange of cutting elements or tooling, in order to minimize down time and increase productivity. An example of such is the Haas overhead milling machine, with its pneumatically operated tool unclamp mechanism, which drives the drawbar downwardly to release the tool holder from its tapered chuck or receptacle at the end of the spindle.
This system utilizes a relatively large diameter, short stroke plate which is driven downwardly by pneumatic pressure within a wide and relatively short cylinder. This plate engages a piston, with the piston contacting the upper end of the drawbar to drive the drawbar downwardly through the spindle. In such mills, the piston and drawbar are separated by a pair of coolant seal inserts, with the non-rotating piston seal insert contacting the drawbar seal insert during tool change and other operations.
The rate of machining of the workpiece is limited by several factors, such as the type and hardness of the material being machined, the specific machining operation, cutting speeds, tolerances and surface finish, etc. However, another limiting factor is the delivery of coolant to the workpiece as it is being machined. Automated powered machine tools and equipment almost universally provide for some form of coolant and/or lubricant to be delivered to the cutting element as it engages the workpiece being machined. Coolant can be delivered by an external coolant delivery system, or by manufacturing the machine with internal, through spindle coolant delivery passages. Where internal coolant delivery is provided, the coolant delivery passages and orifices are of fixed size in any given machine, and cannot be practicably enlarged for greater coolant flow. Thus, the limiting factor for coolant delivery is the pressure at which the coolant is being delivered.
Heretofore, coolant delivery in a conventional overhead milling machine has been limited to about 300 pounds per square inch (psi), with this limitation often being set by the internal seal inserts noted further above between the conventional non-rotating tool change piston and the upper end of the rotating drawbar to which the tool holder is removably secured. These inserts are customarily formed of an extremely hard carbide material, with their mating faces being machined to an extremely close tolerance. The mating faces of the two seal inserts are the only sealing means provided; no other elastomer or other seals are provided between the drawbar piston and the drawbar, to contain the coolant within the concentric drawbar passage.
This system has its disadvantages, in that the two inserts also suffer from impact forces when the piston is driven downwardly to force the drawbar down for tool holder release. The impact forces can cause the extremely hard and somewhat brittle carbide inserts to crack and chip, which leads to coolant leakage during operation of the mill. In a conventionally configured Haas mill, this coolant leakage often travels into the spindle bearings and washes out the lubricants therein, thereby ruining the bearings and requiring costly repair. Also, the conventional Haas mill seal inserts are in constant contact with one another, whether coolant is passing therethrough or not. When the mill is run without coolant, the friction between these seal inserts can produce considerable heat, which can deform the end of the drawbar and lead to further cracking and/or deformation of the seal inserts.
Accordingly, a need will be seen for a tool holder unclamp mechanism for a milling machine, particularly for the Haas mill type machine, which obviates the above problems. The present invention essentially comprises the incorporation of a rotary union at the upper portion of the tooling unclamp piston above the drawbar, with the union containing the seal inserts between the lower end of the piston and the upper end of the drawbar. The union permits relatively high coolant pressures to be run therethrough, and thus throughout the machine. The union includes means for separating the two seal inserts during periods where coolant is not being run through the system, thereby precluding frictional wear and heating of the two seal inserts against one another. The present invention also obviates impact forces between the two inserts during tool holder changes, by applying all compressive forces concentrically around the union, piston, and seal inserts to a collar or coupling which attaches to the upper end of the drawbar. When coolant is run through the system, any leakage from the seal inserts is contained within the union and thence passed from the machine, thereby protecting the spindle bearings of the mill. The present invention includes further advantages as well, such as tapering the walls of the pneumatically actuated center plate to preclude binding or “cocking” of the plate within its cylinder during tool changeover operations.
A discussion of the related art of which the present inventor is aware, and its differences and distinctions from the present invention, is provided below.
U.S. Pat. No. 3,481,248 issued on Dec. 2, 1969 to Donald F. Engstrom, titled “Drawbar For Machine Tools,” describes a tool unclamp drawbar assembly for a milling machine or the like. The Engstrom assembly utilizes pneumatic pressure both to extend and to retract the drawbar for tool release, using a concentric air impact motor for extending the drawbar and a radially displaced pneumatic motor for retracting the drawbar after a tool change. No disclosure is made of any form of concentric or other coolant passages through the machine, as provided in the mill incorporating the present invention. Moreover, the Engstrom system operates directly against the upper end of the drawbar, rather than applying tool holder release forces around the upper end of the drawbar, as in the present mechanism.
U.S. Pat. No. 3,678,801 issued on Jul. 25, 1972 to Robert Z. Hague et al., titled “Quick Tool Change Mechanism For Machine Tools,” describes a system utilizing a relatively wide, flat plate disposed within a mating cylinder concentrically above the drawbar of the machine. The plate includes a central “bolt” having an open center, which fits over the upper end of the drawbar. When the plate is driven downwardly by pneumatic pressure, the “bolt” contacts the end of the drawbar to drive it downwardly to release the tool holder at the lower end thereof. As in the Engstrom assembly discussed above, Hague et al. do not disclose any form of coolant passages in the machine incorporating their invention, and thus do not require any seal inserts, as incorporated in the mill to which the present invention is applied.
U.S. Pat. No. 4,063,488 issued on Dec. 20, 1977 to Franz Kagerer, titled “Tool Chuck,” describes a clamping mechanism at the lower end of the drawbar, for clamping and unclamping the upper end of the tool holder within the lower end of the spindle. The Kagerer system has a series of radially disposed keys, which move radially from corresponding slots in the locking head to engage a flange extending from the stem at the upper end of the tool holder. This structure differs from that used with other mills, e.g. the Haas mill to which the present invention is applied, with the Haas mill having a series of ball bearings which engage cooperating receptacles in the locking head and stem of the t
Cadugan Erica
Litman Richard C.
Wellington A. L.
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