4-Axis Hybrid Machining Center (VHMC01) - Radiation hardened

VHMC01 is a hybrid machining center that combines high-speed milling with micro-wire electrical discharge machining (mWEDM) in a single machine. Designed and built to machine highly radioactive materials, the machine features an extremely small footprint (900 x 900 mm = 35.4 x 35.4 in) and low machine height (1400 mm = 55 in) to allow it to be placed inside a hotcell to shield the operator from gamma radiation.

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VHMC01 is located inside a hotcell and remotely operated with master-slave manipulators

Highspeed Milling

	Toolrack for 10 HSK32E tool holders. Slot #1 is reserved for touch probe
Highspeed spindle, 5.5 kW, 24,000 rpm	Pneumatic tool lift with HSK32E tool fork is mounted to work tank

The work piece location is identified with a touchprobe that is mounted in a HSK32E toolholder and located in the tool rack in slot #1. The tool height and tool radius of all milling tools can be set with the vertical and horizontal toolsetter that consists of microswitches with a repeatability of less then 0.0005 mm (0.00002 in).

The touch probe utilizes a pogo-pin connector that establishes electrical connection as the tool holder is inserted into the spindle	The tool setter features a vertical and horizontal microswitch with 0.0005 mm repeatability that measures the tool height and tool radius

Micro-Wire Electrical Discharge Machining

The micro-wire EDM head is mounted to the rear vertical axis (W-axis) and features a unique wire guide setup that creates both a vertical and horizontal wire section. The dual sections greatly increase manufacturing flexibility and reduce the need for changes in work piece setup. Each wire guide is mounted to a flexure-based micro stage with micro adjuster to achieve perfect wire alignment of both sections. Automatic wire threading is performed with a wire gripper that threads the wire from the supply spool around each of the wire guides and pulleys to the takeup spool. Wire spools are held magnetically to facilitate operating the machine with master-slave manipulators. The dielectric fluid is a synthetic EDM oil that requires no maintenance besides filtering.

A single wire is exposed at two separate locations, thereby creating a vertical and horizontal wire section for increased manufacturing flexibility	Micro-flexure stages allow the vertical and horizontal wire sections to be aligned with the principal machine axes. The wire gripper performs wire threading through pre-programmed coordinated XYW motion.
The tensioning required for delicate micro wires is achieved through a friction-only brake system based on the Capston effect around ceramic wheels	The wire tension servo system is based on the displacement of linear springs that is measured with extreme accuracy by a LVDT
	The wire system features a standard DIN 125 wire spool that is loaded outside the hotcell into a custom spool carrier. The carrier has strategically located magnets that create a highly repeatable position of the carrier and its wire orifice during loading with a master-slave manipulator. The accurate position of the wire orifice is of critical importance to the reliability of the automatic wire threading process as it defines the pickup point of the wire with the pneumatic gripper. The spent wire is wound onto a takeup spool that is partly surrounded by an insulating cover. In the case of wire breakage, any excess wire is first pulled onto the takeup spool where the cover prevents loose ends from touching the conductive parts of the machine. The new wire, after it is threaded around all required pulleys and guides, is fixed to the spool with a toggle clamp that is closed using the manipulator. Similar to the supply spool carrier, the takeup spool carrier is located inside a carrier that is magnetically registered onto the machine.
The wire system uses custom carriers that allow a manipulator to load a standard EDM wire spool into the machine. The spent wire is pulled onto a takeup spool and disposed off together with its carrier.

Work Piece Clamping

The external setup station contains the same pneumatic connections and swing clamps as the work tank. This allows the Universal Clamp (UC) to be operated both inside the machine as well on the setup table.
	The work piece specific jaws mount to the Universal Clamp (UC) with captive screws and are registered with diamond pins. The tensile test specimen and fracture coupon test specimen jaws utilize the short-stroke front clamp while the rod/canister jaws utilize the side clamp. The clamps are designed such that the complex geometries of both the tensile test as well as the fracture test coupons can be machined in a single setup without any changes to the work piece setup.
The machine comes with 2 sets of work piece specific jaws that mount to the Universal Clamp with captive screws and diamond pins. Shown are the rod/canister jaw, the tensile test coupon jaw, and the fracture test coupon jaw.

Dielectric System

The dielectric system consists of an electric pump, a filtration unit with user replacable cartridges, manual diverter valves, flexible hoses, and a storage tank. The filtration unit features a large hex nut that pulls the filter body, which is mounted on a spring-loaded vertical slider with bottom pivot against the filter port (fixed). After the hex nut is loosened, the filter is dropped down by pushing the filter handle with the manipulator and then flipping it to the left. This creates access for the manipulator to the filter cartridge. After the cartridge is replaced, the filter housing is again pushed down and then flipped to the right. Releasing the filter handle causes the spring-loaded slider to push the filter housing upwards against the filter port. Tightening the hex nut then seals the unit.
The manual diverter valves allows the system to be operated in four distinct modes: Filling and draining of the work tank as well as circulation of fluid inside the work and the storage tank. The circulation modes are particular useful for cleaning the dielectric fluid either during or after machining since the fluid is repeatedly passing through the filter. This cleaning process ensures that the majority of radioactive material particles are trapped in the filter cartridge which can readily be disposed after machining, thereby leaving the machining center largely free of contaminated materials. The pump is protected by a pressure switch, which shuts off the pump when the pressure inside the filter reaches 35 psi.
The dielectric system except for the filter housing is mounted on a single plate and connected electrically to the rest of the machine using slip-on connections. Therefore, after loosening the 3 captive screws, the entire unit can be lifted off the storage tank and taken out of the hotcell for servicing or replacing.

The dielectric system is bolted onto the storage tank using captive screws. The electric slip-on connections allow the entire module to be lifted off the tank once the captive screws are loosened. This allows the unit to be removed from the machine and taken out of the hotcell for servicing or replacing.

Controls

The user interface (MicroPEC 5) was specifically created for touchscreens. On the left 1/3 of the screen, critical information about machine status such as axis position, EDM status, process overrides, etc. is provided. The upper portion of the right 2/3 of the screen are tabbed according to distinct operation modes. Shown in the picture is the “Tool Setup” tab, which provides controls and information that are relevant for setting up the milling tools (T1 - T10), operate the 10-tool changer, and perform the EDM wire threading process. Also provided is a permanent touchscreen keyboard for manual data entry. This is particularly useful for the creating G-Code on the machine and setting or changing of tool and work piece offsets.
Other tabs provided relate to the setup of the work piece (Work Piece Setup), allow manual data to be entered (MDI), the running of machining programs (Machining), the sampling of coordinate measurement points of work pieces using the touch probe, the EDM wire, or the external measurement station (CMM), and a live video stream that is captured by the on-machine vision system (Video).
MicroPEC 5 performs machining by executing G-Code that includes the full set of EDM parameters. The controls allows up to 3 work piece offsets (G54 - G56) to be set up with the EDM wire (for WEDM operations) and another 3 offsets (G57 - G59) to be set up with the touch probe (for milling operations). A unique feature of MicroPEC is that setting up work piece offsets is performed by automatically taking into consideration the probe size (EDM wire or touch probe) as well as the approach direction, thereby eliminating the need for manual modifications. Milling and EDM operations do not require separate G-Codes because a specific code (M-Code) can be set to define the machine mode (milling vs. EDM).

MicroPEC is optimized for a touchscreen interface and provides separate tabbed screens for uncluttered presentation of individual machine functions

The control module is mounted to the outside of the hotcell with a swing arm that allows the user to orient the module freely. It features a 19” touchscreen and a full-size keyboard with integrated trackball. Critical machine functions such as cycle start/stop, power on/off, and emergency stop are handled by hardware buttons. Not shown in the picture is a removable CNC pendant with magnetic backing and 3 m (10 ft) of coiled cabeling. The pendendant has a jog wheel to move any of the 4-axis in switch-selectable increments. Furthermore, pressing one of the two dedicated jog buttons allows for continuous jogging at a switch-selectable jog speed. For additional safety, the pendant is also equipped with an emergency stop button.
	The control module is housed in a stainless steel enclosure that is mounted on a swing arm. It features a 19” touchscreen, full keyboard, trackball, and dedicated buttons for critical machine functions. A removable CNC pendant is housed in the lower left recess.

Machine Vision System

Micromachining inside a hotcell poses a challenge for the operator. The machine is located at considerable distance and separated by thick leaded glass, which leads to greatly reduced visibility. Delicate operations such as setting up the work piece offsets or manually navigating a tool inside the work space without causing collisions can be a real challenge.
As an aid for the operator, VHMC01 is equipped with a machine vision system based on an industrial USB camera that is mounted on a movable support. Using the manipulator, the camera can be repositioned to capture any view of interest. The live video stream from the camera is displayed in the control screen on the “Video” tab. The camera is relatively inexpensive and is expected to need replacing after prolonged exposure to gamma radiation.

The on-machine camera provides a clear video stream of the work piece setup using the touch probe

Work Pieces

Tensile test specimen from Al6061 machined in a single setup using the vertical and horizontal WEDM of the VHMC01. Six samples can be machined together from a rod section of 32 mm (1.26 in) length and 16 mm (0.63 in) diameter. The samples remain attached to the work piece by small tabs in the lower left corner and can be snapped off later using the manipulator.	TEM (transmission electron microscopy) samples are machined as disks with 3 mm (0.118 in) diameter and 0.5 mm (0.02 in) thickness. 17 disks are machined together from a 12 mm (0.47 in) section in a single setup using the vertical and horizontal WEDM of the VHMC01. The disks remain attached to the work piece by small tabs at the bottom and can be snapped off later using the manipulator.
Fracture toughness test specimen cut on VHMC01 in a single setup. First, the milling spindle center drilled and then drilled two diameter 3 mm (0.118 in) holes. Next, the horizontal WEDM machined two v-grooves with 0.15 mm (0.006 in) depth into the center of the top and bottom surfaces. Finally, the vertical WEDM machined a 0.3 mm (0.012 in) wide slot from the outside to the center of the disk. The machining was programmed in a single G-Code file, combining the milling, the horizontal and the vertical WEDM instructions.	Ring compression test specimen machined from tubular Zircaloy in a single setup using the vertical WEDM of VHMC01