Processing and Quality Assurance Equipment

Transcription

1 Processing and Quality Assurance Equipment The machine tool, the wash station, and the coordinate measuring machine (CMM) are the principal processing equipment. These machines provide the essential capability to machine the workpiece, clean and dry it, and inspect it during system operation. Turning Centers Modern turning centers have advanced considerably in capability, flexibility, versatility, and reliability. Because of their increased flexibility and capability, NC lathes are classified in two types: vertical and horizontal. Vertical NC turning centers are modern adaptations of the manual vertical turret lathes (VTSs). Horizontal NC turning centers of the shaft, chucker, or universal type has not only changed relative to advanced features and technology, but in basic construction as well. Many modern horizontal NC turning centers are of the slant-bed design include easy access for loading, unloading, and measuring, allowance for chips to fall free, minimum floor space utilization, ease and quickness of tool-changes, and better strength and rigidity. Four-axis and dual-spindle turning centers have also gained considerable acceptance among manufacturers. Four-axis lathes provide considerable savings and productivity increases over conventional two-axis machines because OD and ID operations can be performed simultaneously through independently programmed slides. Dual-spindle machines have two spindles with two independent slide motions for OD and ID operations for each spindle. Machines of this type are also capable of achieving high productivity levels with considerable savings. Operations performed on NC turning centers are basically no different than those performed on older or conventional machines. These consist of the standard turning, facing, drilling, boring, tapping, and threading. These modern CNC versions can still remove metal no faster than their conventional counterparts; however, enhanced cutting tool technology, tool-changing and work-holding methodology, and new automated features have considerably shortened the non-cutting time.

2 Axes The primary axes of a turning center are Z and X. The Z axis travels parallel to the machine spindle, while the X axis travels perpendicular to the machine spindle. U and W axes are typically auxiliary axes providing additional movement and tool capacity. For both OD and ID operations, a negative Z(-Z) is a movement of the saddle toward the headstock. A positive Z(+Z) is a movement of the saddle away from the headstock. A negative X(-X) moves the cross slide toward the spindle center-line, and a positive X(+X) moves the cross slide away from the spindle center-line. Work-holding and work-changing equipment Improvements in work-holding and work-changing equipment have advanced considerable, keeping pace with the rapid technological development of modern turning centers. This equipment, consisting of automatic chuck-changing systems, counter-centrifugal chucks, automatic pallet-changing systems, and automatic chuck-jaw changing systems, enhances the productivity of rotational part cells and systems. Rotational work-holding equipment, most commonly chucks and special application face plate drivers and chucks, must safely hold the workpiece to withstand the tremendous cutting forces generated by the metal-removal process. It must also compensate for the centrifugal forces that, at high rotating speeds, counteract the clamping power provided by the work-holding equipment with a tendency to open the chuck.

3 This constant and dangerous jaw force loss at high speeds can be nearly eliminated with a centrifugal compensated chuck. A variety of other actuated chucks is available, consisting of through-bore power chucks, draw-down chucks, and retractable jaw chucks. All commonly available standard and power chucks provide radial adjustment of the jaws to clamp parts having different diameters. Modern jaw-changing systems are controlled hydraulically, but generally have an electronic stroke control to select, set, and secure the desired clamping range and position. Pallet-changing systems are increasingly being utilized for the machining of complex parts. Automated features and capabilities 1. Automatic gauging 2. Probing 3. Live spindle tooling: C-axis 4. Tool change systems 5. Tool monitoring and sensing Horsepower sensing Acoustic-emission sensing Learn-mode system Force-monitoring

4 The principal benefits of automated turning center tool-change systems are: 1. Reduction in setup time 2. Reduction in insert changing time 3. Added machine flexibility 4. Improved accuracy and reduced errors through a reduction of manual intervention 5. Increased machine tool utilization Machining Centers Known in the 1960s are ATCs, or automatic tool changers, machining centers originated out of their capability to perform a variety of machining operations on a workpiece by changing their own cutting tools. Thus began a tool change and additional feature/capability revolution among machine tool builders that continues to escalate by adding improvements and enhancements to the staggering array of machining center choices. Type, Construction, and Operations Performed Vertical machining centers continue to be widely accepted and used, primarily for flat parts and where three-axis machining is required on a single part face such as in mold and die work. Horizontal machining centers are also widely accepted and used, particularly with large boxy, and heavy parts and because they lend themselves to easy and accessible pallet shuttle transfer when used in a cell or FMS application. General advantage and disadvantages of vertical and horizontal machining centers

5 Machining center construction has improved to accommodate higher spindle speeds, feeds, and horsepower requirements, along with overall higher utilization rates and increased performance requirements. Fifth axis (and more) of movement: key to new designs are pitch and roll motions right in the spindle head Horizontal and vertical spindle: these are similar in appearance to right-angle spindle attachments that have long been available to change the spindle orientation by 90 degrees. An automatic tool changer: tool-storage mechanisms vary among the diversified machine tool supplier, as some are front, side, or top mounted. High-technology carbide-insert cutting tools are gaining wide acceptance and prominence due to their inherent accuracy and ease of maintainability. This eliminates removing the entire tool from the holder and re-sharpening. Machining center improvements: Improved flexibility and reliability Increased feeds, speeds, and overall machine construction and rigidity Reduced loading, tool-changing, and other non-cutting time Greater machine control unit (MCU) capability and compatibility with systems Reduced operator involvement Improved safety features and less noise Axes and format information The primary axes of both vertical and horizontal machining centers are X, Y and Z. On vertical machining centers, the X axis provides the longitudinal table travel, the Y axis provides in and out saddle movement, and the Z axis provides up and down movement of the head or spindle. On horizontal machining centers X-axis movement is also through the longitudinal table travel. Y-axis movement is up and down, provided through movement of the machine tool s knee or spindle carrier. Z-axis positioning is through in and out movement of the machine tool s saddle, table, or spindle carrier. Horizontal machining centers also provide B- or beta-axis movement, which greatly increases a horizontal s versatility. B axis can be used t index a workpiece for machining in the X,Y and Z plane or simultaneously with one or more other axes for a contouring cut.

6 Pallet and part loading Various types of fixturing and tombstoning are used to configure and locate prismatic parts for machining center part processing. Part may be mounted to a standard four-sided tombstone for horizontal machining center processing using three conventional schemes: 1. Single load mounting: providing access to only one surface at a time without indexing the B axis. 2. Multi-load mounting: the same surface of multiple parts is presented for machining at each B-axis index since the tombstone is loaded with parts all mounted identically. 3. Progressive load mounting: it involves progressively moving the part through different settings, exposing all sides of the workpiece and removing a completed part at the end of each programmed machining cycle. Multiple parts may be mounted to standard tombstones, thus increasing productivity and machine utilization rates Automated features and capabilities 1. Torque control machining: sometimes referred to as adaptive control, this feature was developed to speed up or slow down a cutting tool while the tool is engaged in the actual cutting operation. 2. Surface sensing probe: Check for part presence and alignment on single- to multiple-part loaded pallets Calculate the center position of a hole by averaging measured points taken around the hole or boss Computer and store offset data in the fixture offset table Detect stock variations or cored hole shifts and automatically regrind the machine 3. Automated tool delivery 4. Multiple and angled spindle heads 5. Broken tool detection

7 Torque control machining, Automated tool delivery Surface sensing probe Multiple and angled spindle heads