Patent Application
20170304908
The present invention relates to methods and machinery for mill-cutting materials, particularly hard ceramic materials.
The present invention relates to apparatus which includes milling machines, particularly three-axis vertical milling machines, which are familiar general purpose pieces of equipment used in machine shops and the like to shape workpieces by cutting tool action. Generally, the shank of a tool bit called a milling bit or end mill is held at the end of in a rotating vertical spindle while being moved in three orthogonal directions, familiarly referred to as the x, y and z axes. In most familiar vertical milling machines, the spindle translates up and down along the z axis relative to the work piece which is mounted on a work table that is located vertically beneath the spindle, and the table moves in the horizontal plane along the x and y axes. The table is typically moved by a combination of slides, drive screws, and drivers which are located beneath or adjacent to the table which holds the workpiece. Typically, the path of the tool bit in a modern milling machine is actuated by CNC (computer numerical control). That is, a software program acting in a micro-processor controls the movement of the actuators or drivers which move the spindle and table.
To speed production a CNC vertical milling machine may have a tool changer accessory. Typically, tools bits are held within a standardized adapter that fits the spindle. The tool bit and adapter assemblies are stowed in sockets of a tool storage device which is part of tool changer system. The storage device is spaced apart from the work table. When the time for change from one tool to another arises, because of wear or because a different machining operation is to be carried out, the tool held in the spindle is deposited in an empty socket in the tool storage device. A new tool bit assembly is removed from its place in the storage device and is captured in the lower end of the spindle. Tool bit change is commonly effected by the software with opportunity for operator intervention.
Familiar tool storage devices include a carousel or magazine type device. With such, tool bits or tool bit assemblies are typically are carried on a movable part of the storage device so that, when desired, a tool assembly (or an empty socket, as may apply) is presented at a definite location relative to the spindle. If the machine tool is contained within an enclosure, as is common, then if a subsequent process to be carried out demands a different array of tool bits, machining must be stopped and the enclosure opened to change the tool bit array, thereby slowing production. Thus there is a continuing need for improvements in tool bit changers.
For precision of machining, it is typical for the machine operator to “zero” the tool, that is to input to the machine software the precise location—relative to the work table and work piece held on the table—of the tip of each tool bit that is newly installed in a tool storage device. That not only requires a bit of skill from the operator, but takes time during which the machine is non-productive. Improvements in the process would speed production.
The predominant use of vertical milling machines is for fabricating metal components. A lesser but important use is to machine dense structural ceramic materials, such as Hot Isostatically Pressed (HIP) alumina or monolithic boron carbide. Such ceramic materials present particular problems in machining, including that they are very hard and brittle. One way of milling such workpieces is through the use of diamond coated end mills, with use of a coolant.
Heretofore, persons fabricating hard and strong structural ceramic pieces have often found that tool bit life is short and machining is slow compared to machining even low machinability metals. That means that frequent tool bit changes are needed. Heretofore, the slides of the typical vertical milling machine, which enable movement of the workpiece-holding table in the x and y directions, are prone to premature wear due to infiltration of fine abrasive ceramic particles which are carried from the workpiece location to vicinity of the slides by the coolant, notwithstanding attempts to seal the slides. When slides are worn prematurely they can be costly to rebuild or replace.
Thus, there is a persistent need for improvements in milling machine operations, particularly when such machines are used for machining ceramics.
An object of the invention is to provide apparatus particularly suited for machining ceramic materials, and other materials where fine abrasive debris is generated during machining. A further object is to provide apparatus which includes a vertical milling machine system for machining ceramics and other materials that reduces the need to stop a machining operation when there is need to replace the tool set in a tool changer magazine.
In accord with the invention, an embodiment of apparatus comprises an enclosure within which is a vertical milling machine tool. The apparatus comprises a work table for holding a workpiece and a spindle which holds and rotates a tool bit for material removal from the workpiece. A useful tool bit will be a hollow-shank end mill with an electroplated diamond coating surface. The spindle is adapted for vertical z axis motion of the tool bit and is mounted on a combination of slides which move the spindle in both the x axis and y axis horizontal directions.
Within the apparatus, coolant which flows down the spindle and through the hollow tool onto the workpiece then flows downwardly toward a sump at the bottom of the enclosure, to be recirculated to the fluid input portion of the spindle. One or more shields run horizontally within the enclosure and the lower end of the spindle which holds the tool bit, extends through a shield. The shield(s) partitions the interior of the apparatus into an upper region where the slides are located and a lower region where the tool bit and workpiece are located. An air mover flows air downwardly through small openings in, or at the edges of, the shield(s). Preferably there is a plurality of slot like openings at the side walls of the enclosure where the shields run around rollers or reels. The downward flow of air through the slot like openings inhibits coolant spray from the workpiece region from migrating upwardly to the vicinity of the slides.
Preferably, the apparatus comprises two fabric shields which have horizontal portions that extend across part or all of the cross section of the enclosure. The shields are made of sheet material that runs around rollers or reels, to enable the horizontal portions to translate laterally with lateral movement of the spindle. The rollers or reels are closely spaced to the side walls of the enclosure to define the aforementioned small slot like openings for downward air flow.
In further accord with embodiments of the invention, a tool tray having a flat surface that holds a multiplicity of tool assemblies (which comprise tool bits held in adapters) is positioned on a support surface within the lower region of the apparatus, preferably in close proximity to the work table. The tray is contained within a housing that has a movable cover which protects the tray and tools from coolant spray during machining. The cover is openable when needed to enable a change of tool assembly which is held in the spindle. An access door in the side of the enclosure enables the tool tray to be removed from with the lower region of the apparatus while machining is underway, since the housing and associated cover keeps coolant which is spraying about the lower region away from the tool tray and the support surface.
In apparatus of the invention, the slides are not prone to high wear due to infiltration of fine workpiece debris carried by coolant; and productivity is enhanced when a new array of pre-set tool bits can be positioned within the tool changer while machining takes place. The foregoing and other objects, features and advantages of the present invention will become more apparent from the following description of preferred embodiments and accompanying drawings.
The invention is described in terms of machining ceramic materials, for which it is particularly suited. However, the invention apparatus may be used for machining other materials, such as metals and plastics. The disclosure of U.S. provisional patent application 62/327,439 filed Apr. 25, 2016 is hereby incorporated by reference.
Enclosure 54 that is shaped for containing coolant spray and for guarding against inadvertent operator contact with moving parts of the machine. As described below, embodiments of the invention include one or two shields having horizontal running portions that are engaged with the spindle lower end, just above the tool bit location. For illustrative purpose, phantom shield 82P is shown in semi-schematic form in
Machine tool 20 is comprised of ball slides (also called linear motion bearings) which are moved by ball screws rotated by drivers. These are familiar commercial articles and are shown in simplified fashion in the Figures; they are referred to herein simply as slides. A vertical spindle assembly (or simply “spindle”) 40 is mounted on a beam 28 which is movable in the x horizontal direction by slide 26. Slide 26 is supported on parallel spaced apart slides 24, for movement (with the spindle) in the y horizontal direction. Generally, spindle 40 may be directly connected to or mounted on a x or y slide, or indirectly connected to a slide, as by means of another structural element. Spindle 40 comprises an internal linear bearing (not visible) which enables vertical z direction movement of the lower end telescoping portion 32 of the spindle. With reference to
With reference to
During machining of a workpiece, a coolant recirculation system 98 provides liquid coolant to the workpiece location. In the typical kind of coolant recirculating system, one of which is embodied in the apparatus of
When ceramics are being machined the tool bit 51 is preferably a commercial cutting tool having an electroplate surface that contains diamond particulate; and the tool has a hollow shank and one or more cutting surface discharge ports. Fluid flowed down the hollow shaft exits through ports in the side of the tool, to deliver coolant to cutting surface region, thereby providing good cooling and allowing higher rotational cutting tool speeds than can be attained by externally flooding the tool bit. The cutting action of such kinds of tool bits may alternatively be referred to as “cutting,” “machining,” or “grinding.”
A preferred tool bit 51 of the foregoing hollow shank type, suitable for machining ceramics, is a commercial hollow end mill sold by G. G. Shultz Tool Inc., Taveres, Florida. Such type of tool bit, and the associated coolant flow and material removal process, are described in U.S. Patent Publication 2016/0306685 of Rakes et al., dated Oct. 29, 2015; the disclosure of which is hereby incorporated by reference. Another preferred end mill is described in U.S. provisional patent application Ser. No. 62/372,774 of the present inventor, entitled “Diamond coated end mill,” filed Aug. 9, 2016, the disclosure of which is hereby incorporated by reference.
As mentioned, the preponderant flow of spent coolant from the workpiece location is downwardly from the cutting zone. That flow is away from the location of the x-y slides and the actuator for the z-axis direction-moving spindle. The foregoing slide apparatus is most often referred to simply as the “x-y moving parts” hereafter. The x-y moving parts are located higher in elevation than the work table surface and workpiece location. Nonetheless, coolant vapor and a substantial amount of spray which goes in all directions are usually generated, depending on the pressure of the coolant provided to the tool bit, the rotary speed of the tool bit, and the heat generated during machining. And in the absence of features of the invention, substantial amounts of coolant vapor and spray could move to the location of the x-y moving parts, which location is also referred to below as being upper region of the apparatus.
For cleanliness and worker safety, the spray and vapor generated during machining are contained by enclosure 54. Referring especially to
Embodiments of the present invention are configured for a particularly advantageous air flow. Generally, the air is channeled in ways which inhibit the extent to which the coolant carrying fine ceramic particulate comes in contact with the x-y moving parts. The preponderance of the flow of airborne coolant is downward, away from the upper region of the apparatus and the location of the x-y moving parts. When the preferred shielding is used, air in the upper region is in flow communication with the air in the lower region. In particular, flows downwardly, past the outer edges of one or more fabric shield portions that substantially run horizontally and through slot like openings associated with rollers or reels (described below), and into the lower region of the apparatus where the workpiece is located and where cutting takes place. Air also may be additionally flowed around the shields by means of a duct.
The present invention contrasts with a common conventional vertical milling machine where the x-y direction slides are located beneath a movable work table. The slides thus are in a region where gravity will cause spent coolant to flow, and slides—notwithstanding shielding—can be prone to infiltration of coolant which carries workpiece and tool debris, resulting in accelerated wear.
The air handling system comprises portions of enclosure 54, namely side walls 61 which are below the elevation of the x-y-moving parts. Optionally, the air handling system also comprises the portions of enclosure side walls which extend upwardly to encompass the upper region of the apparatus, as shown in the present Figures. The air handling system also comprises one or more shields which control air flow within the apparatus, one or more air movers 74 (such as a fan or blower), and a liquid-vapor separator such as cyclone separator 72, alternatively a HEPA filter.
Air which is flowed into the lower region 27 within enclosure 54 may be drawn from the shop within which the apparatus 19 is located, moving past the x-y slides and shields. Air which is discharged from the lower region 27 may flow through exit port 73, to a location exterior to the shop within which assembly 19 is located, or with adequate filtering to the shop interior. Alternatively, air mover 74 may be positioned at the exit port 73A of the separator 72. Part or all of the air handling system can be alternatively contained within the enclosure 54. Preferably, the lower region of the apparatus which is inside the enclosure is kept at negative pressure relative to the ambient environment by having the air mover pull air from it, rather than push air into it.
Enclosure 54 preferably has a roof 59 which has a plurality of openings 66 that are spaced apart around the periphery of the roof, as pictured in
Airflow, indicated by arrows 70, is downwardly from the upper region 25 of the apparatus (see
As may be more fully appreciated from the further description below, air flows downwardly around or through the shields (for example, when a shield has an opening as described in connection with
Shields 80, 82 are preferably made of flexible material such as vinyl plastic sheet. The sheet material of the shields largely blocks the movement of coolant spray in the upward direction. Air flow may move downwardly around the lengthwise edges of the shields were they run along the side walls of the enclosures. The airflow obviates the need for seals along the lengthwise edges, although such may optionally be used. Some downward migration of air can take place by flow through the horizontal space between one shield 80 and the other shield 82.
Spindle lateral movement is enabled by translation of the horizontal portion of each shield where it is engaged with the spindle. Vertical spindle part motion may be accommodated by sliding of the spindle through a bellows or slip-fit collar that secures the shield to the spindle exterior.
At the lengthwise extremities of the each shield's horizontal portion, shields 80, 82 run around rollers 84 and then generally upwardly. Movement of the sheets which comprise shields 80, 82 is indicated by double headed arrows M. The x-y motion of the spindle and the spindle engagement with a shield where it penetrates the shield can be sufficient to cause the desired movement M of a shield. Optionally, drives may be applied to the rollers or reels to help movement M.
The x-shield 82 is part of shield assembly 87, which is configured to enable lengthwise x-direction motion of a horizontal portion adjacent the spindle, as is best shown in
The y-shield 80 is part of shield assembly 97, which is configured to enable lengthwise y-direction motion M, as is best shown in
What is the desirable area for a slot like opening depends on the size of the machine and the amount of air which is moved through the machine. Generally, to save energy it is undesirable to require a large air mover. In a preferred embodiment of the invention, the area of each slot like opening is small compared to the cross section area of the machine. As an example, for a shield that spans a rectangular cross section enclosure having a width/length that is about 90 or 100 cm, each slot like opening might have a width of about 0.3 cm. Smaller and larger slot shape openings may be employed and the openings may vary from place to place within an apparatus. Preferably, the total area of slot openings for airflow, measured in the horizontal plane, is less than about 5 percent, more preferably about 1 percent of the cross section area of the enclosure. The air mover is sized both to ensure adequate flow downward velocity through all slot like openings, sufficient to prevent upward flow of coolant and particulate bearing air, and as desired, to thin out or to carry away a misty atmosphere of fine droplets in vicinity of the workpiece, so the operator can better see the workpiece, spindle and interior of the enclosure.
During use, it may be desirable to have more airflow in the workpiece area than the slots provide or to direct the air differently from that which the channeling of the slots provides. As shown in
In an alternative embodiment of the invention, the x-shield may be configured as a reel system and the y-shield may be configured as a continuous loop system. In still other embodiments, both shields may be continuous loop shields or both may be reel-configured shields. If a particular machine tool necessitated only x axis or y axis motion, then only one such shield may be used in carrying out the invention. In the generality of the embodiments of the invention presently being described, at least one shield has a horizontal plane portion through which the lower end of the spindle—or at least the tool bit—projects downwardly, and the horizontal plane portion is configured for moving in opposing shield lengthwise directions.
When shields are characterized as having lower portions which run horizontally, within the scope of invention, that means the shield lower portion is substantially horizontal. By “substantially horizontal” is meant that when running from one to another more or less same elevation locations, a shield may run along a partially or fully sloping, curved, or undulating path.
While air preferably enters the enclosure through roof openings (when there is a roof), in alternative embodiments, the air may enter elsewhere, while accomplishing the same result of protecting the x-y moving parts by downward air flow from the vicinity of such parts. For example, air may flow through openings at the upper portions of the side walls of the enclosure, when the enclosure extends upwardly from the location of the x-y slides. In another example, the enclosure in the region above the shield may be pressurized by an air mover which causes air to flow downwardly from vicinity of the x-y moving parts.
It will be appreciated that use of the foregoing apparatus comprises a method of machining, particularly for ceramics, which in short is: machining a workpiece with a tool bit while flowing liquid coolant to the workpiece location where machining takes place, and recirculating the coolant; providing apparatus with x-y slides located above one or more shields with partition the apparatus in to an upper region and a lower region where workpiece cutting takes place; and flowing air downwardly from the upper region to the lower region past one or more shields, so the air inhibits coolant spray in the lower region from moving upwardly into the upper region and contacting the x-y slides.
The following description is about a system comprising a tool tray which holds tool assemblies. The tool tray is contained within a housing within the enclosure of the apparatus. Such tool change system is useful with the apparatus 19 and is described in such relation. The tool change system of the present invention may be used in connection with other machine tools and other enclosures, including those in which there is no airflow or associated shields.
Tool tray 30 is shown in top perspective view in
Tray 30 has a multiplicity of keyhole shape slots 44, each shaped for holding a tool assembly 49 which is comprised of tool bit 51 and adapter 50. (Reference may be made again to the beginning of this description.) Tray 30 is preferably elongate; in particular it has a planar rectangular surface. Other shape tool trays, including trays having stepped or other configuration tool-assembly-receiving surfaces, are with the scope of the generality of the invention. A tray for apparatus 19 preferably holds tool assemblies so the shank of the end mill of the assembly lies along the z axis.
Each adapter 50 is shaped for being held in the telescoping end of spindle 32 during machining and for fitting into a slot 44 when stored in the tray. Each adapter 50 has a circumferential groove that engages the smaller portion of the keyhole slot 44, so a tool assembly 49 will not easily fall out of the tray during normal manual handling when the tray is outside the enclosure. For convenience of removing, inserting, and carrying about outside the machine, tray 30 comprises handles 38 at each end.
In the tool change system of the present invention, when in use for machining, tray 30 is contained within housing 64 which has a pivoting cover 42. Housing 64 is fixed relative to the support 62. Cover 42 is shown in the closed position in
When machining is being carried out, the tool changer system of the present invention enables the spindle (or when used, a robot arm) to deposit a used tool assembly and access an unused tool assembly from the tool tray. To effect a change of assembly held in the spindle, flow of coolant is momentarily ceased and cover 42 is opened. As shown by phantom cover 42P and the curved arrow in
In alternative embodiments of the invention, the cover of the housing may be configured differently than shown, for opening and closing. For instance, the cover may slide lengthwise or the cover may comprise opposing side “clam shells” which hingedly pivot from opposing sides of the housing and which meet at the centerline of the housing. In alternative embodiments, there may be more than one tool tray and associated housing.
As an example of the method of this aspect of the invention, when a tool bit is to be changed the coolant flow is ceased, cover 42 of housing 64 is opened, and the spindle holding a tool assembly moves to the location of an empty slot 44 in the tool tray. The spindle positions and releases the tool assembly so it sets securely within the chosen empty slot. The spindle then moves to the location of the next-desired tool assembly within the tray, and engages it. Engagement with and release of a tool assembly from the spindle may be carried out by a powered drawbar type mechanism internal to the spindle, of a kind which is well known in the art.
When engaging and disengaging from the tool assembly, the spindle telescoping end portion moves predominately vertically (in the z-axis direction). Thus, in the invention the part of the tool assembly which is engaged by the end of the spindle, and the tool bit, are oriented vertically. In the generality of the invention, the tool assemblies could be differently oriented and a robot arm or the like could be added to pull a selected tool assembly out of the tray and present it to, or position it within, the lower end of a spindle.
In use of a tool changer system comprising tray 30 and its housing, prior to the tool tray being placed on the support within the enclosure, each tool assembly can be measured with respect to the distance between the tip or diameter or other feature of the tool bit and a reference point on the adapter—which reference point will be always be located precisely at the same location relative to the end 32 of the spindle 40 when the adapter is being held in a spindle. Such measurements can be done by a skilled technician at a workplace removed from the machine. Data about the measurements can then be electronically communicated at an appropriate time to the control system of machine tool 20 (generally termed a CNC control system), so that when the tool tray is placed within the housing, and when any particular tool assembly is taken up by the spindle from the tray, there will be no need for further calibration or location of the end of the cutting portion of a particular tool bit, prior to commencing machining with that particular tool, in comparison to what is often the case in industry today.
In partial summary: An embodiment of tool changer system of the present invention comprises a housing having openable cover, a tray for holding a multiplicity of cutting tool assemblies oriented for engagement with the spindle by spindle z axis direction motion, a support for holding the tray in vicinity of the work table. The tool tray support and tool tray and housing are configured in a way that enables removing the tray from within the machine enclosure through a door in the side of the enclosure. The foregoing tool changer system may be used with machines other than the vertical milling machine of the type which is shown in
When using the preferred tool bits mentioned above, another enhancement facilitated by the present invention relates to the manner (speed and feed) in which the side of an end mill tool bit engages the workpiece, particularly when doing such as making a feature such as a 90 degree inside corner of a pocket. Preferably, the invention apparatus is operated with use of commercial software from SolidCAM, Inc., Newtown, Pa., U.S.A. The invention apparatus is particularly capable of carrying out with accuracy tool path, speeds and feed rates as commanded by the software.
The invention, with explicit and implicit variations and advantages, has been described and illustrated with respect to several embodiments. Those embodiments should be considered illustrative and not restrictive. Any use of words such as “preferred” and variations suggest a feature or combination which is desirable but which is not necessarily mandatory. Thus embodiments lacking any such preferred feature or combination may be within the scope of the claims which follow. Persons skilled in the art may make various changes in form and detail of the invention embodiments which are described, without departing from the spirit and scope of the claimed invention.
This application claims benefit of provisional patent application 62/327,439 filed Apr. 25, 2016, the disclosure of which is hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62327439 | Apr 2016 | US |
