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14. CNC MACHINES
? Computer Numerical Control machines use a computer to guide a process that might otherwise be done manually.
14.1 MACHINE AXES
14.2 NUMERICAL CONTROL (NC)
? The use of numerical data to drive a machine for processes such as,
- milling
- turning
- drilling
- grinding
- shot peening
- tube bending
- flame cutting
- automated knitting machines
- automatic riveting
- etc.
? Basic components of NC systems,
- program
- controller unit
- machine tool
? Most suited to,
- parts are pr ocessed frequently in small lot sizes
- complex part geometry
- close tolerances on workpart
- many oper ations on part in processing
- large amounts of metal to be removed
- engineering design will possibly change
- parts that are too expensive for mistakes
? The methods for developing NC programs include,
- manual part programming
- computer-assisted part programming
- computer gener ated programs
? The manual and computer aided methods use various NC programming languages,
- APT (Automatically Programmed Tools)
- AUTOSPOT (Automatic System for Positioning Tools)
- SPLIT (Sundstrand Processing Language Internally Translated)
- COMPACT II
- ADAPT (ADaptation of APT)
- EXAPT (Extended Subset of APT)
- UNIAPT
? These languages are used by a parts programmer to define the motion of the cutting tool.
? The languages may be preprocessed, and then used for a number of various control types,
such as,
- punched paper tape
- Computer Numerical Control (CNC)
- Direct Numerical Control (DNC)
? The automatic methods work with geometry created in a CAD program.
14.2.1 NC Tapes
? NC Progr ams are preprocessed on computers, and punched onto paper or mylar tapes.
? Simple NC machines can use a tape reader to direct the machine.
? Problems,
- required storage, transportation, and manual loading of NC tapes
- has to reread the tape for each new part
- tapes tend to wear, and become dirty, thus causing misreadings
- the mechanical parts in the readers reduced reliability
- testing had to be done on the NC machine
- no program editing abilities (increased lead time)
? The end of tapes was the result of two competing developments
- DNC used remote computers to replace tape readers, these were displaced in most cases by CNC
- CNC allowed the use of a local computer to overcome problems with tapes, and the problems with distant computers. While CNC was used to enhance tapes for a while, they eventually allowed the use of other storage media, and cur rently program transfer media are not required.
14.2.2 Computer Numerical Control (CNC)
? A computer controller is used to drive an NC machine directly.
? Characteristics are,
- controls a single machine
- located very close to machine tool
- allows storage/retrieval/entry of NC programs without preprocessing of NC code
? Advantages of CNC,
- progr am is only entered into memory once, so it is more reliable
- the programs can be tested and altered at the machine
- increased flexibility and control options on the local computer
- easy to integrate into FMS systems
? The Background,
- the problems with NC tapes were approached using DNC networks
- the communication problems with DNC systems became obvious, and local computers were added to act as tape readers which would read tapes once, and play them back to the NC machine indefinitely
- CNC controllers began using other storage media like magnetic tapes, and floppy disks
- CNC now offers features like,
- local programming,
- communication over interfaces,
- hard disk storage,
- program simulation
- etc.
? ASIDE: Direct Numerical Control is similar to CNC, except a remote computer is used to control a number of machines. This gives the advantage of more computer power. This approach is no longer popular, as the dropping cost of computers offsets any advantages.
? Some companies use proprietary NC Languages,such as the example of DYNA Mill NC code shown later
? These machines are often programmed by downloading NC code from a computer, or manually programming the controller computer.
? Future trends involve,
- adaptive feed rates to increase speeds as the metal removal rate varies
- tool wear detection
14.2.3 Direct/Distributed Numerical Control (DNC)
? Uses a few methods,
- the oldest methods used modems, and a mainframe which emulated a tape reader, to control the NC machine (no storage)
- a more recent advance used a local computer which acts as a storage buffer. Programs are downloaded from the main DNC computer, and then the local controller feeds instructions to the hardwired NC machine, as if they have been read from tape.
- the newer methods use a central computer which communicates with local CNC computers (also called Direct Numerical Control)
? DNC controllers came before CNC machines, but as computer technology impr oved it became practical to place a computer beside the NC machine, and DNC changed in form.
? Characteristics of modern DNC systems are,
- uses a server (with large storage capacity) to store a large number of part programs。
- the server will download part programs on demand to local machines
- may have abilities to,
- display and edit part programs
- transmit operator instructions and other data needed at the machines
- collect and process machine status information for management purposes
? Advantages are,
- eliminates the need for NC tapes (the advantages are obvious)
- design changes are immediate
- NC programs may be edited quickly
- can be used to support an FMS system
- increase efficiency of individual machine tools
- more shop up-time than with stand alone machines
- simplifies implementation of group technology, computer aided process planning, and other CIM concepts
-reduces peripheral costs with NC tapes
? A Brief History,
? Mid 60’s
- concept proved by Cincinnati Milacron and G.E.
- telephone links used to send instructions from large computers to hard wired NC machines. Basically replaced a tape reader.
? 1970
- several commercial DNC systems announced.
? Mid 70’s
- Aerospace companies used DNC because of the large number of distributed
-machines in their facilities.
? Initial resistance to DNC technology was (previously) based on,
- high cost of computer hardware
- the number of machines which could be controlled by one computer was limited
- computer sof tware was limited for maintenance, scheduling, control, and data collection
- a backup computer was usually required
- was hard to justify on the basis of downloading parts programs
? when downloading programs there are two popular opinions,
- a program should only be downloaded in part, this accommodates easy engineering
changes in a real-time environment.
- many programs should be downloaded to the local controller to provide protection
against system failure, and eliminating the cost of real-time response in the DNC
centr al computer.
14.3 EXAMPLES OF EQUIPMENT
? The number of NC machines available commercially will be well into the thousands.
14.3.1 EMCO PC Turn 50
? This is a small desktop lathe capable of turning parts in metal.
? The basic physical specifications are,
Cutting volume radial travel 48mm rad axial travel 228mm
Max.holding volume radial 30-65mm axial 300mm 12mm by 12mm
Max.tool size max 80mmm dia
Chuck 130-3000rpm
Spindle 0.001mm
Resolution 0-750mm/min
Feed <=600N below 500mm/min
Feed force 100/110/230VAC,0-6KVA
Power 840 by 695 by 345 mm
? The basic sequence of operations for this machine are,
1. Unpack components.
2. Connect devices to power, air supply, and attach interface cables
3. Install RS-485 card in PC.
4. Install software.
5. Test basic system (Done initial setup here).
6. Start and initialize lathe and PC with software.
7. Setup tools for new job. Find zero positions/offsets, and enter values for turret.
8. Load NC code.
9. Simulate program.
10.Load stock and close automatic chuck.
11.Close door.
12.Run program on Lathe.
13.Open door and open chuck.
14.If cutting a similar part go to step 8, if doing a new setup go to step 7.
14.3.2 Light Machines Corp. proLIGHT Mill
? This is a small desktop lathe capable of turning parts in metal.
? The basic physical specifications are
Cutting Volume
Max. Holding Volume
Max. Tool Size
Spindle 200-5000rpm
Resolution
Feed 50ipm x,y and 40ipm z
Feed Force
Power
Dimensions
Weight
Controller IBM compatible computer
Control Interface IBM compatible computer
Programming G-Codes and Dos softwar
Spindle 1 H.P.
? The basic sequence of operations for this machine are,
1. Unpack components.
2. Connect devices to power, air supply, and attach interface cables.
3. Install software.
4. Test basic system (Done initial setup here).
5. Start and initialize mill and PC with software.
6. Setup tool for new job. Find zero position/offset.
7. Load NC code.
8. Simulate program.
9. Run pr ogram on Mill.
10. If cutting a similar part go to step 7, if doing a new setup go to step
14.4 PRACTICE PROBLEMS14.5 TUTORIAL - EMCO MAIER PCTURN 50 LATHE (OLD) ? The lathe is shipped with software that is meant to emulate shop floor interfaces. We donnot have the standard keyboard, so we need to use special key stroke sequences on the PC keyboard.
? Procedure:
1. Connect the air supply to the lathe and make sure that the regulator on the lathe is between 25 and 75 psi - 50 psi is good. Ensure that the lath is connected to the PC with the DNC cable. The computer card must also have a terminator on the second connector - this is an empty connector. Turn on the lathe, and the PC.
2. Once the PC is booted, run the emco control software. The screen may come up with warnings. If these warnings don’t disappear when you hit ‘ESC’ call the instructor.
3. First we must zero the lathe. To do this first hit ‘F1’ and then ‘F7?-ZRN’. A small label
‘ZRN’ should appear near the bottom of the screen. Press ‘4’ on the number pad of the keyboard - the lathe should move in the ‘x’ dir ection. Next, press ‘8’ on the keyboard, the lathe should move in the ‘z’ direction. After all motion has stopped the lathe is calibrated, and it will be put in jog mode.
4. You can move the lathe with the keys on the number pad as well as perform other function.
4 - move carriage left
6 - move carriage right
2 - cross slide out
8 - move cross slide in
7 - turn spindle on
6 - turn spindle off
2 - turn on/off chip blower
1 - turn tool turret
+/- - increase/decrease feed
5. You can now put the mill in MDI mode by pressing ‘F1’ then ‘F6?-MDI’. Push the door open and hold it for a second, it will then stay open. Clear the error on the screen with ‘ESC’ and press ~ the chuck should open and close. Mount a work piece and then close the door.
6. Put the computer in program mode ---------------
14.6 TUTORIAL - PC TURN 50 LATHE DOCUMENTATION: (By Jonathan DeBoer)
? SETUP:
The lathe is controlled by a computer through an RS485 port. RS485 is a serial data bus that can be chained from one device to another and must be terminated.The controlling computer must be running Windows 3.1 or 3.11 and must have the RS485 card installed. Windows 95 will not get along with the interface card, and the software refuses to use an RS232 port with an RS485 adapter. The machine should have as few peripherals as possible; if one device happens to use any of the IRQs/
DMAs/IO ports as the RS485 card, there will be problems. So remove sound cards, extra interface cards, etc. The RS485 card has two DB9F connectors on the back, plug the cable from the lathe in one and a terminator in the other.Install WinNC (the control software) under Windows 3.1. There are two disks; the installer and a machine data disk.The lathe needs to be plugged in to the computer, to a power outlet (of course), and to an air supply at 50-75 psi (less than 50 and there isn't enough pressure to open the door). A pressure gauge is on the left side of the machine, all plugs/etc are on the right.
? POWER ON/OFF:
To Turn On:
Turn on the computer and machine. To turn on the machine, turn the key on the right side. On the computer, launch Windows if neccisary. Once windows is running, launch WinNC. Make sure NumLock is on befo re launching WinNC. WinNC will then establish communication with the machine.
To Turn Off:
To just shut off the lathe but not the computer, just turn the key on the lathe. An error will co me up in WinNC indicating it lo st RS485 communication. Not to worry; when the lathe is turned back on later, hit ESC and the error will go away.To turn off both, exit WinNC by hitting Alt-F4 and then exit Windows. Then Simply switch off both the machine and the computer.
? OPERATION:
Some notes:
The EMCO software is distinguished by having the most counter-intuitive, unnatu-ral, information-withholding, and ornery interface known to man. Most technical references available are in German。The software periodically pops up error messages for minor and major errors. Errors can be dismissed by pressing ESC. If they don't go away, there is a problem that needs to be looked into.At the bottom of the screen is a menu of options you can select with the F3-F7 keys. This is called the "softkey list" by the Emco documentation, and will henceforth be referred to as the "menu".
A note on coordinates:
The X axis is into/out of the material. X = 0 should be the center of rotation. As long as X is a positive value, moving along X in the positive is moving the tool out of the material and away from center. Moving along X in the negative is moving into the material and toward center.
The Z axis is along the length of the part (along the axis of rotation). Moving along Z in the negative direction is moving toward the spindle head (to the left, facing the machine). Moving along Z in the positive direction is moving away from the spindle head (to the right, facing the machine)。
Modes:
The software is ruled by mo des. What mode the software is in determines what it can do and what it displays. I f something doesn't work or doesn't look right, check what mode the software is in. Remember operational modes are set independently of display modes. The operational mode can be EDIT but programs cannot be edited until the view mode is set to PRGRM, and vice versa.
Hit F1 to get a menu of operational modes:
ZRN mode is used for zeroing the tool position. This should be done the first thing afterthe machine is turned on.
JOG is used for manual control of the lathe.
MDI is used for changing tools, opening chuck, etc. (actually, you can do all this with JOG)
EDIT is used for editing, loading, and exporting programs.
AUTO is used for running programs.
Hit F12 to get display modes:
Note: when you switch view modes, the menu changes.The default is ALARM mode, which displays operator messages and alarms. Hit F3 to display alarms, F5 to display operator messages.POS mode displays positions.Hit F3 to display the current absolute position, F4 for the current relative position, and F5 for a variety of details.
PRGRM mode displays the program. Hit F3 to display the program code, hit F4 for a list of all the programs available. If the operational mode is EDIT, you can also edit the code when you hit F3 。
OFFSET is used for displaying and changing offset values. Hit F3 for wear adjustment and F4 for geometry. These are both parameters for tools.Data for up to 16 tools can be stored at once. Hit F5 for work shift. This is how the working reference point is set. See below.
PARAM is used for changing setup parameters and viewing system information. Hit F3 for setup see below for details. Hit F4 for diagnostics on the RJ485 por t and the software version。
GRAPH is used to simulate output with a graph
The fact that all these modes must share the menu can cause confusion.Remember that if you should be seeing a menu and you aren't, the menu you are looking for may be "behind" the one you are seeing. For example, when you switch to a display mode, you should see the menu f or that display mode. If you hit F1, that menu is "covered up" by the menu to select an operational mode. Once you select something from that menu, you will see the view mode's menu again.
Keyboard control:
Note on keyboard control: Many of the keys outlined in the manual are for German keyboards only and are mapped differently on US keyboards. Use this as reference, NOT the manual:
Alt-F4 - Exit
ESC - Dismiss error message
F1 - mode menu
F3 thru F7 - select item from current menu
F11 - scroll through menus when they are too wide to fit on the screen (like the MORE key on a Ti-85 calculator)
F12 - function key menu
Ctrl-\ - open/close chuck (must not be in EDIT mode, door must be open)
Ctrl-] - open/close door (spindle must be off)
Ctrl-1 - change tool (must not be in EDIT or ZRN mode, door must be closed)
Ctrl-2 - Turn on/off blower
Ctrl-6 - Turn off spindle (JOG mode)
Ctrl-7 - Turn on spindle (JOG mode, door must be shut)
arrows - move cursor in the editor
on the numeric keypad:
4 - move -Z in JOG mode, or zero Z axis in ZRF mode
6 - move +Z in JOG mode, or zero Z axis in ZRF mode
2 - move -X in JOG mode, or zero X axis in ZRF mode
8 - move +X in JOG mode, or zero X axis in ZRF mode
5 - zero both axis in ZRF mode
From：《Integration and Automation of Manufacturing Systems》by Hugh Jack
14.數(shù)控機床
計算機數(shù)控機床使用一臺計算機引導一個可能需要手工完成的過程
14.1機床坐標軸
14.2 數(shù)字化控制
?使用數(shù)字數(shù)據(jù)驅(qū)動機器進行的加工過程如下
-銑削
-車削
-鉆削
-磨削
-噴丸加工
- 折彎
-火焰切割
-自動化編制機
-自動鉚接
-等
?數(shù)控系統(tǒng)的基本組成部分
-程序
-控制器單元
-機床設備
?最適合于
-頻繁加工的小批量零件
-復雜的部分幾何體
-工件上的緊公差部分
-加工過程中操作量大的部分
-大量的金屬切削
-工程設計可能變化時
-價值昂貴不允許報廢的零件
?開發(fā)數(shù)控程序的方法包括
-手工零件編程
-計算機輔助編程
-計算機編程
? 手工和計算機輔助方法采用各種數(shù)控編程語言
-自動編程工具
-用于工具定位的自動化系統(tǒng)
-桑斯川特內(nèi)部轉(zhuǎn)換處理語言
-緊湊型 2
- APT改編語言
- APT 的擴展子集
- UNIAPT
?這些語言是通過一部分編程人員定義切削刀具的動作來使用的
?這些語言可以進行預處理，然后為一系列不同的控制類型所使用，例如
-穿孔紙帶
-計算機數(shù)字控制（CNC）
-直接數(shù)字控制（DNC）
? 自動化方法與CAD程序中創(chuàng)建的幾何體一起工作
14.2.1數(shù)控條帶
?數(shù)控程序在計算機上進行預處理，并在紙條或膠帶上打孔
?簡單的數(shù)控機床可以使用條帶帶閱讀器來指揮機器
?相關(guān)問題
-數(shù)控條帶所必需的存儲，傳輸，手動裝載
-必須為每個新零件重讀條帶
-磁帶往往磨損，變臟，從而導致誤讀
-閱讀器很慢，并且可能在復雜零件上產(chǎn)生滯留標記
-閱讀器里的機械零件降低了可靠性
-測試必須在數(shù)控機床上完成
-沒有程序編輯能力（增加了所需的時間）
?條帶的結(jié)束是兩種發(fā)展相互競爭的結(jié)果
-分布式數(shù)控使用遠程計算機來代替條帶閱讀器，但這些在大多數(shù)情況下被計算機數(shù)控所取代
-計算機數(shù)控還允許在本地計算機上使用以克服條帶和遠程計算機的問題。雖然一段時間內(nèi)計算機數(shù)控被用來加強條帶性能，但計算機數(shù)控最終被允許使用其他存儲介質(zhì)，并且目前不需要程序傳輸介質(zhì)
14.2.2計算機數(shù)字控制
?一個電腦控制器是用來直接驅(qū)動數(shù)控機床的
?特點是
-控制一臺機器
-位于非常接近機床的地方
-允許沒有預處理的數(shù)控代碼進行數(shù)控程序存儲/輸入/檢索
?數(shù)控的優(yōu)勢，
- 程序只輸入到內(nèi)存中一次，所以它更可靠
- 該程序可以在機器測試和修改
- 在本地計算機上增加了控制選項增強了靈活性
- 易于集成到柔性制造系統(tǒng)
? 相關(guān)背景
-使用DNC網(wǎng)絡處理與數(shù)控條帶有關(guān)的問題
-使用DNC系統(tǒng)的通訊問題變得顯著，并且本地計算機被添做能讀取條帶一次并可以讓數(shù)控機床無限回放的的條帶閱讀器
-數(shù)控控制器開始使用其他像磁帶，軟盤之類的存儲器
-數(shù)控現(xiàn)在提供的功能如下
-本地程序
-接口通信
-硬盤存儲
-程序仿真
-等
?旁白：除了一臺遠程計算機用來控制許多機器之外，直接數(shù)控與計算機數(shù)控很相似。這給出了更強大的計算機功能的優(yōu)勢。由于電腦成本下降抵消了任何優(yōu)勢，這種方法不再流行。
?有些公司使用專用的數(shù)控語言，例如最近展示的德納銑削數(shù)控代碼
?這些機器經(jīng)常沖電腦上下載數(shù)控代碼編程，或手工對控制器電腦進行編程。
? 未來走向涉及
- 根據(jù)不同的金屬切削速率自動調(diào)整進給速度以提高加工速度
- 刀具磨損檢測
14.2.3直接/分布式數(shù)控（DNC）
? 使用了以下幾種方法
-最古老的是使用調(diào)制解調(diào)器和一臺仿效條帶閱讀器的主機來控制數(shù)控機床（不能存儲）
-一個新近的方法是使用一臺用作存儲緩沖的本地電腦。從主計算機數(shù)控主機上下載程序，然后本地控制器像從紙帶上讀取程序一樣把程序提供給數(shù)控機床
-較新的方法是使用一臺能與本地數(shù)控電腦交互的核心電腦（也稱作直接數(shù)字控制）
? DNC控制器產(chǎn)生于CNC機床之前，但由于計算機技術(shù)的發(fā)展DNC變的比在數(shù)控機床旁放置計算機實用并且DNC在形式上產(chǎn)生了變革
?現(xiàn)代的DNC系統(tǒng)的特點是
-使用服務器（有很大的存儲容量）來存儲大量的零件程序
-服務器將根據(jù)需要把零件程序下載到本地機床上
有能力
- 顯示和編輯零件程序
- 傳送機床上需要的操作指令和其他數(shù)據(jù)
- 收集和處理用來操縱機床的狀態(tài)信息
? 優(yōu)點
- 不再需要數(shù)控條帶（優(yōu)點是顯而易見的）
- 即時的設計變更
- 數(shù)控程序編輯快速
- 可以用來支持FMS系統(tǒng)
- 提高了單個機床的效率
- 比單個機床有更多的工廠運行時間
- 簡化成組技術(shù)，計算機輔助工藝規(guī)劃和其他計算機集成制造內(nèi)容的實施
- 減少使用數(shù)控紙帶的額外花費
? 歷史概述,
?60年代中期
- 辛辛那提米拉克龍概念和GE證明
- 電話鏈接用來從大型計算機向硬件連接的數(shù)控機床發(fā)送指令，這從根本上取代了讀帶器
? 1970
- 幾個商業(yè)的DNC系統(tǒng)公布
? 70年代中期
- 航天公司因為他們工廠里有大量的分布式機床而使用DNC
? DNC技術(shù)最初的阻礙是（以前）基于
-計算機硬件的高額成本
-一臺計算機能控制的機器數(shù)量是有限的
- 計算機軟件因為維護調(diào)度控制和數(shù)據(jù)收集而受限制
- 通常需要一臺備份計算機
- 在下載部分程序的基礎上很難調(diào)整
?下載程序時，有兩種流行的觀點
- 一個程序只能被部分下載, 這在現(xiàn)實環(huán)境中很容易改變