Accuracy - control instrumentation resolution and hardware accuracy.
Control resolution: the minimum length distinguishable by the control unit (BLU).
Hardware inaccuracies are caused by physical machine errors.
HARDWARE INACCURACIES
Component tolerances:
inaccuracies in the machine elements, machine-tool assembly errors, spindle runout, and leadscrew backlash.
Machine operation:
Tool deflection (a function of the cutting force), produces dimensional error and chatter marks on the finished part.
HARDWARE INACCURACIES
Thermal error:
heat generated by the motor operation, cutting process, friction on the ways and bearings, etc. Use cutting fluids, locating drive motors away from the center of a machine, and reducing friction from the ways and bearings
REPEATABILITY
LEADSCREWS
pitch (p): the distance between adjacent screw threads
the number of teeth per inch (n):
n = 1 / p
BLU: Basic Length Unit (machine resolution)
BLU = p (inch/rev)) / N (sensor points/rev)
Where N is normally defined as the gain from a resolver or encoder.
Example
number of teeth per inch (n) = 20
n = 1 / p (teeth/in) = 0.05 in/rev
Resolver gain - N (sensor points/rev) = 200 pulses/rev
BLU = p (inch/rev)) / N (sensor points/rev)
= 0.05 in/rev / 200 pulses/rev
= 0.00025 inch
CONTROL LOOPS
Open loop - No position feedback.
Use stepping motor.
CONTROL LOOPS
A machine has 1 BLU = 0.001".To move the
table 5" on X axis at a speed (feed rate) of
6 ipm.
pulse rate = speed/BLU = 6 ipm/0.001
ipp= 6,000 pulse/min
pulse count = distance/BLU
= 5/0.001 = 5,000 pulses
CLOSED LOOP
INTERPOLATION
Control multiple axes simultaneously to move on a line, a circle, or a curve.
INTERPOLATORS
Most common : linear and circular
Since interpolation is right above the servo level, speed is critical, and the process must not involve excessive computation.
Traditional NC interpolators: Digital Differential Analyzer (DDA)
Higher order curves, such as Bezier's curve, use off-line approximation algorithms to break the curves into linear or circular segments.
COORDINATE SYSTEMS
Right hand rule
Z axis align with the spindle - +Z moves away from the workpiece or the spindle.
X axis - Lathe: perpendicular to the spindle.
Horizontal machine: parallel to the table.
Vertical machine: +X points to the right.
MACHINE COORDINATES
PROGRAM STORAGE
Paper tape
Paper or Mylar coated paper.
Diskettes
From other computers through RS 232 or local area network (LAN)
High-Speed Spindles 30,000-rpm Spindle: The Haas 30K spindle uses BT 30-taper tooling and accepts tools up to 0.5" max diameter. Hybrid ceramic angular-contact bearings, an air/oil spot lubrication system, and a spindle chiller ensure superior accuracy and long bearing life. The 30K spindle is available on VF-1 through VF-4 models. 10,000- and 15,000-rpm Spindles: A variety of 10K spindles are available for Haas VF models – for 40- or 50-taper models, with or without a gearbox. A 15K spindle option is available for all 40-taper, direct-drive VF models.
Machining Centers Continued
High-Speed Machining The HSM option provides a powerful tool to reduce cycle times and improve accuracy. Using a motion algorithm called ”acceleration before interpolation,“ combined with full look-ahead of up to 80 blocks, HSM provides fast contouring feeds without distortion of the programmed path. The Haas HSM option accepts ISO standard G code, and is a fraction of the cost of other high-speed controls
Machining Centers
Through-Spindle Coolant Optional TSC supplies coolant at up to 300 psi to the cutting edge, for longer tool life, higher speeds, and improved deep hole drilling and blind pocket milling – as well as reduced cycle times. The exclusive Haas design includes a special seal that disengages when the system is not in use, which extends the life of the system. (Note: This system provides 300 psi at a flow rate of 1.5 gallons per minute and 250 psi at 4 gpm. The actual pressure will vary with the diameter of the coolant passages in the tool). High-Pressure (1000 psi) TSC Available on the VF Super Speed models and all 50-taper VF models, high-pressure TSC makes it easier to perform deep-hole drilling and heavy cuts, allows faster feedrates and provides better surface finishes. Max flow rate is 6 gal/min at 1000 psi; max spindle speed is 10,000 rpm with the high-pressure TSC option enabled.
Machining Centers
Linear Scales When absolute positioning accuracy is necessary, linear scales are the only way to ensure exact axis positioning under the fluctuating conditions that exist in today’s machine shops. Linear scales ensure positioning accuracy along X, Y and Z axes by compensating for the thermal variations inherent in all machine tools. With 2-micron resolution, these scales deliver high accuracy for the type of precision that mold making and other high-tolerance machining applications demand.
Machining Centers
Full 4th- and 5th-Axis Capabilities Add a fully integrated Haas rotary table to your VMC to create a supercharged machining center: Program any angle, perform circular cuts on the outside of your parts, or machine complex contours such as impellers. From the original HA5C collet indexer to the HRT series to the TR series trunnion tables, a Haas rotary is the industry benchmark. For superior accuracy, Haas cuts the worm gear while it's attached to the spindle, rather than assembling the finished worm gear to the spindle. And Haas rotary products run directly from the machine’s control, for seamless operation and uncomplicated programming.
Machining centers
Machining Centers
Auto Door With this option, the machine doors open and close automatically via the part program. This reduces operator fatigue during repetitive machining – which can increase operator productivity by up to 25% – and allows for unattended operation when used with a robotic loader.
Hard Drive & Ethernet Interface w/USB Support This option provides tremendous flexibility in program transfer and storage. The 20 GB hard drive supplies ample storage space for program files, and the USB connection supports either a customer-supplied ZIP™ drive or flash disk. The Ethernet component allows quick and easy data transmission between your Haas machine and a network or PC, and large files can be accessed by multiple machines. High-speed data transfers allow DNC of large files at up to 1000 blocks per second. The Ethernet interface works with Windows XP, ME, 2000 Pro & Server, NT 4.0, 98 and 95. IPX/SPX or TCP/IP protocol; easy setup from the control screen.
Machining Center
Haas Probing Systems ML PS 95/175 Laser Tool Monitor and Work Measure Upgrade Kit: Upgrade to Marposs - This non-contact laser system allows for automatic tool length, diameter measurement and breakage detection for tools from 0.008" to 6.8" in diameter. The laser can be programmed to check tool profiles, monitor wear on multi-insert end mills, and can update tool offsets and compensates for thermal variations. This kit features IPC, Instant Productivity Cycles for quick and easy use on both laser tool setting and work probe systems by anyone who can operate an edge finder and indicator. IPC are defaulted program cycles that do not require approximate tool offset inputs or descriptions for length and diameter measurements. IPC along with the work probe are just as easy to use for setting work offsets and measuring and finding part features by utilizing the wide range of defaulted programs. IPC features are many, fully defaulted cycles or creative and program them yourself. This upgrade kit will reduce your set-up times, while automatically updating your tool offset registers and more!
Haas Servo Bar 300 Designed to boost productivity and streamline turning operations, this servo-driven bar feeder is built by Haas exclusively for Haas CNC lathes. It runs directly from the Haas control, making it the only “smart” bar feeder on the market. Unique features make setup and operation simple, like a large access door for spindle liner change-out and a single adjustment for setting bar diameter. All bar feed parameters are set at the lathe control.
Turning Centers
Live Tooling The live tooling option for Haas lathes allows you to use standard VDI 40 axial or radial driven tools to perform secondary operations such as milling, drilling, flatting and tapping – both on the face of the part and around the diameter. This option includes a full C axis, which provides interpolated bidirectional motion at precise speeds and feeds for part positioning and repeatability. A powerful hydraulic brake locks the main spindle during secondary operations, and disengages for turning and indexing. Live tooling is not available with a standard bolt-on style tool turret. It is only available with the VDI or VB Hybrid turret.
Turning Centers
Steady Rest Provision The Haas steady rest platform provides increased support for turning and boring long shafts on SL-30 and SL-40 lathes. It features industry-standard mounting holes to accept a variety of aftermarket automatic hydraulic steady rests. Hydraulic power is provided by the lathe, and the gripper is activated by M code. *The steady rest provision does not include the gripper. Minimum and maximum part diameters are dependent on the size and style of gripper unit mounted on the platform. Minimum and maximum travel limits are measured from the spindle bulkhead, and do not include chuck dimensions or other workholding.
Turning Center
Parts Catcher For bar feed applications, or when using a bar puller, the parts catcher rotates into position to catch the finished part and direct it into a bin located on the front door. There’s no need to stop the machine and open the door to retrieve parts.
Turning Centers
Tool Presetter The manual tool-probe arm swings down for fast tool setting. Touch the tool tip to the probe and offsets are automatically entered.
Turning Centers
Turning Centers
Resources
Primary Reference:
Chang T-C., Wysk, R. A., and Wang, H-P., “Computer
Aided Manufacturing”, Prentice Hall International Series
in Industrial and Systems Engineering, 2006, Upper Saddle
Machined from a 5" x 4" x 2" workpiece. low carbon steel.
The process plan:
1. Set the lower left bottom corner of the part as the machine zero point (floating zero programming).
2. Clamp the workpiece in a vise.
3. Mill the slot with a 3/4" four flute flat end mill made of carbide. From the machinability data handbook, the recommended feed is 0.005 inch/tooth/rev, and the recommended cutting speed is 620 fpm.
4. Drill two holes with a 0.75" dia twist drill. Use 0.18 ipr feed and 100 fpm speed.
PART DRAWING
SOLUTION TO EXAMPLE
Solution:
The cutting parameters need be converted into rpm and ipm.
Milling:
Drilling:
SETUP AND CUTTER PATH
CUTTER LOCATIONS
The coordinates of each point (cutter location) are calculated below:
