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原文一
CNC machine tools
Outdate, J. and Joe, J. Configuration Synthesis of Machining Centers with Tool ，John
Wiley & sons, 2001
While the specific intention and application for CNC machines vary from one machine type to another, all forms of CNC have common benefits. Here are but a few of the more important benefits offered by CNC equipment.
The The first first first benefit benefit benefit offered offered offered by by by all all all forms forms forms of of of CNC CNC CNC machine machine machine tools tools tools is is is improved improved
automation. automation. The The The operator operator operator intervention intervention intervention related related related to to to producing producing producing work work work piece
s pieces pieces can can can be be reduced reduced or or or eliminated. eliminated. eliminated. Many Many Many CNC CNC CNC machines machines machines can can can run run run unattended unattended unattended during during during their their their entire entire machining machining cycle, cycle, cycle, freeing freeing freeing the the the operator operator operator to to to do do do other other other tasks. tasks. tasks. This This This gives gives gives the the the CNC CNC CNC ur ur veral veral side side side benefits benefits benefits including including including reduced reduced reduced operator operator operator fatigue, fatigue, fatigue, fewer fewer fewer mistakes mistakes mistakes caud caud caud by by human human error, error, error, and and and consistent consistent consistent and and and predictable predictable predictable machining machining machining time time time for for for each each each work work work piece. piece.
Since the machine will be running under program control, the skill level required of the CNC operator (related to basic machining practice) is also reduced as compared to a machinist producing work pieces with conventional machine tools.
The cond major benefit of CNC technology is consistent a nd accurate work and accurate work pieces. Today's CNC machines boast almost unbelievable accuracy and repeatability spe
cifications. This means that once a program is verified, two, ten, or one thousand identical work pieces can be easily produced with precision and consistency. 我的一次改变作文
A third benefit offered by most forms of CNC machine tools is flexibility. Since the the machines machines machines are are are run run run from from from programs, programs, programs, running running running a a a different different different workpiece workpiece workpiece is is is almost almost almost as as
easy as loading a different program. Once a program has been verified and executed for one production run, it can be easily recalled the next time the workpiece is to be run. This leads to yet another benefit, fast change over. Since the machines are very easy to t up and run, and since programs can be easily loaded, they allow very short tup time. This is imperative with today's just-in-time (JIT) product requirements.
Motion control - the heart of CNC The The most most most basic basic basic function function function of of of any any any CNC CNC CNC machine machine machine is is is automatic, automatic, automatic, preci, preci, preci, and and
consistent consistent motion motion motion control. control. control. Rather Rather Rather than
than than applying applying applying completely completely completely mechanical mechanical mechanical devices devices devices to to cau cau motion motion motion as as as is is is required required required on on on most most most conventional conventional conventional machine machine machine tools, tools, tools, CNC CNC CNC machines machines
allow motion control in a revolutionary manner2. All forms of CNC equipment have two two or or or more more more directions directions directions of of of motion, motion, motion, called called called axes. axes. axes. The The The axes axes axes can can can be be be precily precily precily and and automatically automatically positioned positioned positioned along along along their their their lengths lengths lengths of of of travel. travel. travel. The The The two two two most most most common common common axis axis
types are linear (driven along a straight path) and rotary (driven along a circular path).
Instead of causing motion by turning cranks and handwheels as is required on conventional machine tools, CNC machines allow motions to be commanded through programmed programmed commands. commands. commands. Generally Generally Generally speaking, spea
king, speaking, the the the motion motion motion type type type (rapid, (rapid, (rapid, linear, linear, linear, and and
circular), the axes to move, the amount of motion and the motion rate (federate) are programmable with almost all CNC machine tools.
A CNC command executed within the control tells the drive motor to rotate a preci number of times. The rotation of the drive motor in turn rotates the ball screw.
And the ball screw drives the linear axis (slide). A feedback device (linear scale) on the slide allows the control to confirm that the commanded number of rotations has taken place3. Refer to fig.1. 左手写爱
fig.1 typical drive system of a CNC machine tool
Though a rather crude analogy, the same basic linear motion can be found on a common table vi. As you rotate the vi crank, you rotate a lead screw that, in turn, drives the movable jaw on the vi. By comparison, a linear axis on a CNC machine tool is extremely preci. The number of revolutions of the axis drive motor precily controls the amount of linear motion along the axis.
How axis motion is commanded - understanding coordinate systems
It would be infeasible for the CNC ur to cau axis motion by trying to tell
each axis drive motor how many times to rotate in order to command a given linear motion motion amount4. amount4. amount4. (This (This (This would would would be be be like like like having having having to to to figure figure figure out out out how how how many many many turns turns turns of of of the the handle on a table vi will cau the movable jaw to move exactly one inch!) Instead, all CNC controls allow axis motion to be commanded in a much simpler and more a much simpler and more logical logical way way way by by by utilizing utilizing utilizing some some some form form form of of of coordinate coordinate coordinate system. system. system. The The The two two two most most most popular popular
coordinate coordinate systems systems systems ud ud ud with with with CNC CNC CNC machines machines machines are are are the the the rectangular rectangular rectangular coordinate coordinate coordinate system system
and and the the the polar polar polar coordinate coordinate coordinate system. system. syste
m. By By By far, far, far, the the the more more more popular popular popular of of of the the the two two two is is is the the
rectangular coordinate system.
The program zero point establishes the point of reference for motion commands in in a a a CNC CNC CNC program. program. program. This This This allows allows allows the the the programmer programmer programmer to to to specify specify specify movements movements movements from from from a a hp进bios
common common location. location. location. If If If program program program zero zero zero is is is chon chon chon wily, wily, wily, usually usually usually coordinates coordinates coordinates needed needed needed for for
the program can be taken directly from the print.
With this technique, if the programmer wishes the tool to be nt to a position one one inch inch inch to to to the the the right right of of the the the program program program zero zero zero point, point, point, X1.0 X1.0 X1.0 is is is commanded. commanded. If If the the
programmer wishes the tool to move to a position one inch above the program zero point, Y1.0 is commanded. The control will automatically determine how many times to rotate each axis drive motor and ball screw to make the axis reach the commanded destination point . This lets the programmer command axis motion in a very logical manner. Refer to fig.2, 3.
fig.2, 3.
Understanding absolute versus incremental motion
All discussions to this point assume that the absolute mode of programming is ud6. The most common CNC word ud to designate the absolute mode is G90. In the absolute mode, the end points for all motions will be specified from the program zero point. For beginners, this is usually the best and easiest method of specifying end points for motion commands. However, there is another way of specifying end points for axis motion.
In the incremental mode (commonly specified by G91), end points for motions are are specified specified specified from from from the the the tool's tool's tool's current current current position, position, position, not not not from from from program program program zero. zero. zero. With With With this this
method method of of of commanding commanding commanding motion, motion, motion, the the the programmer programmer programmer must must must always always always be be be asking asking asking "How "How "How far far
should should I I I move move move the the the tool?" tool?" tool?" While While While there there there are are are times times times when when when the the the incremental incremental incremental mode mode mode can can can be be
very helpful, generally speaking, this is the more cumbersome and difficult method of specifying motion and beginners should concentrate on using the absolute mode.
Be Be careful careful careful when when when making making making motion motion motion commands. commands. commands. Beginners Beginners Beginners have have have the the the tendency tendency tendency to to
think think incrementally. incrementally. incrementally. If If If working working working in in in the the the absolute absolute absolute mode mode mode (as (as (as beginners beginners beginners should), should), should), the the
programmer should always be asking "To what position should the tool be moved?" This position is relative to program zero, NOT from the tools current position. 消防法
Aside Aside from from from making making making it it it very very very easy easy easy to t
o to determine determine determine the the the current current current position position position for for for any any
command, another benefit of working in the absolute mode has to do with mistakes made during motion commands. In the absolute mode, if a motion mistake is made in one one command command command of of of the the the program, program, program, only only only one one one movement movement movement will will will be be be incorrect. incorrect. incorrect. On On On the the the other other
hand, if a mistake is made during incremental movements, all motions from the point of the mistake will also be incorrect.
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Assigning program zero
Keep in mind that the CNC control must be told the location of the program zero point by one means or another. How this is done varies dramatically from one CNC machine and control to another8. One (older) method is to assign program zero in the program. program. With this With this method, the programmer tells the control how far it is from from the the
program program zero point to zero point to t he starting position of the machine. This the starting position of the machine. This is is commonly done commonly done
with a G92 (or G50) command at least at the beginning of the program and possibly at the beginning of each tool.
Another, newer and better way to assign program zero is through some form of offt. Refer to fig.4. Commonly machining center control manufacturers call offts ud to assign program zero fixture offts. Turning center manufacturers commonly call offts ud to assign program zero for each tool geometry offts.
fig.4 assign program zero through G54
Flexible manufacturing cells
田单复国
A flexible manufacturing cell (FMC) can be considered as a flexible manufacturing subsystem. The following differences exist between the FMC and the FMS:
1. An FMC is not under the direct control of the
坚持下去英语central computer. Instead, instructions from the central
computer are pasd to the cell controller.
2. The cell is limited in the number of part families it
can manufacture.
The following elements are normally found in an FMC:
• Cell controller
• Programmable logic controller (PLC)
• More than one machine tool • A materials handling device (robot or pallet)
The The FMC FMC FMC executes executes executes fixed fixed fixed machining machining machining operations operations operations with with with parts parts parts flowing flowing flowing quentially quentially
between operations.
High speed machining
The term High Speed Machining (HSM) commonly refers to end milling at high rotational rotational speeds speeds speeds and and and high high high surface surface surface feeds. feeds. feeds. For For For instance, instance, instance, the the the routing routing routing of of of pockets pockets pockets in in
aluminum airframe ctions with a very high material removal rate1. Refer to fig.5 for the cutting data designations and for mulas. Over the past 60 60 years, HSM years, HSM
has been applied to a wide range of metallic and non-metallic workpiece materials, including the the production production production of of of components components components with wi
th with specific specific specific surface surface surface topography topography topography requirements requirements requirements and and machining machining of of of materials materials materials with with with hardness hardness hardness of of of 50 50 50 HRC HRC HRC and and and above. above. above. With With most most steel steel components components hardened hardened hardened to to to approximately approximately approximately 32-42 32-42 32-42 HRC, HRC, HRC, machining machining machining options options options currently currently include:
Fig.5 cutting data rough rough machining machining machining and and and mi-finishing mi-finishing mi-finishing of of of the the the material material material in in in its its its soft soft soft (annealed) (annealed)
condition heat treatment to achieve the final required hardness = 63 HRC machining of electrodes and Electrical Discharge Machining (EDM) of specific parts of dies and moulds (specifically small radii and deep cavities with limited accessibility for metal cutting cutting tools) tools) tools) finishing finishing finishing and and and super-finishing super-finishing super-finishing of of of cylindrical/flat/cavity cylindrical/flat/cavity cylindrical/flat/cavity surfaces surfaces surfaces with with appropriate cemented carbide, cermets, solid carbide, mixed ceramic or polycrystalline cubic boron nitride (PCBN)
For many components, the production process involves a combination of the options options and and and in in in the the the ca ca ca of of of dies dies dies and and and moulds moulds moulds it it it also also also includes includes includes time time time consuming consuming consuming hand hand finishing. Conquently, production costs can be high and lead times excessive.
It is typical in the die and mould industry to produce one or just a few tools of the same design. The process involves constant changes to the design, and becau of the changes there is also a corresponding need for measuring and rever engineering.
The main criteria are the quality level of the die or mould regarding dimensional, geometric and surface accuracy. If the quality level after machining is poor and if it cannot meet the requirements, there will be a varying need of manual finishing work. This work produces satisfactory surface accuracy, but it always has a negative impact on the dimensional and geometric accuracy.
One of the main aims for the die and mould industry has been, and still is, to reduce or eliminate the need for manual polishing and thus improve the quality and shorten the production costs and lead times. Main economical and technical factors for the development of HSM
Survival
The The ever ever ever increasing increasing increasing competition competition competition in in in the the the marketplace marketplace marketplace is is is continually continually continually tting tting tting new new
standards. The demands on time and cost efficiency is getting higher and higher. This has forced the development of new process and production techniques to take place. HSM prov
ides hope and Materials 思想汇报入党积极分子
The development of new, more difficult to machine materials has underlined the necessity necessity to to to find find find new new new machining machining machining solutions. solutions. solutions. The The The aerospace aerospace aerospace industry industry industry has has has its its its heat heat resistant resistant and and and stainless stainless stainless steel steel steel alloys. alloys. alloys. The The The automotive automotive automotive industry industry industry has has has different different different bimetal bimetal
compositions, Compact Graphite Iron and an ever increasing volume of aluminum3. The The die die die and and and mould mould mould industry industry industry mainly mainly mainly has has has to to to face face face the the the problem problem problem of of of machining machining machining high high hardened tool steels, from roughing to finishing.
Quality
The The demand demand demand for for for higher higher higher component component component or or or product product product quality quality quality is is is the the the result result result of of of ever ever
increasing competition. HSM, if applied correctly, offers a number of solutions in this
