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絞盤和轉(zhuǎn)塔機床
中心機床是通用機床,加工中心的一些限制是：
(i) 加工前的設(shè)置時間是很長的。
(ii) 正常的加工過程中只能選用一把刀具。有時候有四把刀具的正方形刀架取代了傳統(tǒng)刀架。
(iii) 設(shè)置過程中的閑置時間和兩切削間隔中刀具的運動是大的。
(iv) 如果操作者不適當(dāng)?shù)年P(guān)注，那么到指定地點的刀具精確運動是很難達(dá)到的。
所有的這些困難意味著中心機床將不會在生產(chǎn)中使用以消除低的生產(chǎn)率。因
此為了提高生產(chǎn)率中心機床必須加以調(diào)整改進(jìn)。各種各樣改進(jìn)后的機床有絞盤和轉(zhuǎn)塔車床，半自動機床和全自動機床。
在以下方面的改進(jìn)基本上已經(jīng)達(dá)到了：
(a) 有效的加工方法
(b) 多個有效的刀具
(c) 全自動刀具進(jìn)給
(d) 在精確位置刀具的自動停止
(e) 按照正確的操作次序自動控制
絞盤和轉(zhuǎn)塔機床的主要特征是六個方（六角）塊裝在床尾的一端取代正常尾座。這使得六個安裝刀具座中每一個都可以根據(jù)需要包含一個或多個刀具。另外兩個刀架固定在十字滑臺上，一個在前面，另一個在后面。它們中的每一個每次可容納多達(dá)四個刀具。因此，總的可以最高達(dá)到14個刀具，一個刀具安裝在一個位置。
轉(zhuǎn)塔車床包含了全直齒齒輪，具有一系列心軸轉(zhuǎn)速的重負(fù)荷軸承。轉(zhuǎn)頭安裝在滑動座架上，滑動座架可以在床身上依次滑動。在回?fù)羝陂g當(dāng)座架在床身上滑動時，它會自動檢索下一個刀具的位置，從而減少機器的閑置時間。
轉(zhuǎn)塔車床刀具在進(jìn)料桿上設(shè)有停行系統(tǒng),可精確的控制刀具移動的實際距離.因此有可能確定和控制零件所需的刀具單獨運動。
支承裝置工作型式可以在轉(zhuǎn)塔車床中使用類似于普通車床，但是由于生產(chǎn)力要求較高和可重復(fù)性要求更大，一般的自動裝置，例如夾頭，自定心夾緊或氣動夾緊均被使用。
襯套有各種不同的設(shè)計。實際夾緊是由襯套沿著軸線方向推或拉的運動來完成的。有時襯套閉合期間棒料不是推前就是后拉。這可以防止因外管鎖住停止使軸向運動被阻止。
常常由多種轉(zhuǎn)塔車床零件是從未加工的棒料加工出來的。連續(xù)進(jìn)給棒料，特殊的棒料進(jìn)給安排是可行的，通過確切數(shù)據(jù)越過在一轉(zhuǎn)開始六角轉(zhuǎn)臺表面提供的障礙推進(jìn)棒料。
十字滑臺刀架用的大部分刀具都非常類似于加工中心。成型刀具也通常用在十字滑臺中。為提供更大的生產(chǎn)力轉(zhuǎn)塔中使用了種類繁多的專用刀具。一箱工具通常用于車削工藝，因為刀具切割時也支持這個工作。它們有一把切削刀還有滾齒刀以提供對工作部件必要的支承。這有助于對桿的加工，但加工操作方面沒有很好的支承。盒裝刀具中也可能有至少一把切斷刀，那樣在提供工件支承的同時可以重復(fù)切削。
組合刀具讓很多復(fù)合切割刀具按規(guī)定調(diào)整以適應(yīng)加工形勢。它們可以同時執(zhí)行一個以上的切削操作，從而減少實際操作加工所需的時間。在一個刀架上有內(nèi)外切削刀具，那樣工件可以達(dá)到更高的精度。
許多轉(zhuǎn)塔車床將裝有與加工中心很相似的錐形轉(zhuǎn)向裝置來加工錐形物。小的錐形物可以用成型刀具生產(chǎn)，而內(nèi)部錐形可以用錐形鉸刀來加工。
因此可以發(fā)現(xiàn)絞盤和轉(zhuǎn)塔與通用機床之間的很多不同點：
(一) 軸承有越來越多的各級轉(zhuǎn)速允許更高的生產(chǎn)速率。
(二) 刀架是可轉(zhuǎn)位的（四把刀具）。任何一個工具都可以進(jìn)入切削位置。
(三) 一個有六把刀具位置的刀架取代了刀柄尾部。
(四) 可以通過進(jìn)給停止器來調(diào)節(jié)每一個刀具的進(jìn)給。
(五) 安裝在同一個刀架表面的兩個或以上的刀具可以同時進(jìn)行切削。
(六) 半熟練的操作要求。
(七) 以上是用于涉及更好重復(fù)性的生產(chǎn)經(jīng)營。
轉(zhuǎn)塔車床的變化是絞盤車床，其中轉(zhuǎn)臺可以在滑動座架上移動，滑動座架視工件的長度可以固定在床身的任何位置。因此刀具的行程局限于滑動座架的長度。這種類型通常用于小規(guī)模的機器。
Numerical control
Numerical control of machine tools may be defined as a method of automation in which various functions of machine tools are controlled by letters, numbers and symbols. Basically a NC machine runs on a program fed to it. The program consists of precise instructions about the manufacturing methodology as well as the movements. Fox example, what tool is to be used, at what speed, at what feed and to move from which point to which point in what path, all these instructions are given. Since the program is the controlling point for product manufacture, the machine becomes versatile and can be used for any part. All the functions of an NC machine tool are therefore controlled electronically, hydraulically or pneumatically.
In NC machine tools one or more of the following functions may be automatic:
(i) Starting and stopping of the machine tool spindle.
(ii) Controlling the spindle speed.
(iii) Positioning the tool tip at desired locations and guiding it along. Desired paths by automatic control of the motion of slides.
(iv) Controlling the rate of movement of tool tip.
(v) Changing of tools in the spindle.
Initially the need of NC machines was felt for machining complex shaped small batch components as those belonging to an aircraft. However, this spectrum currently encompasses practically all activities of manufacturing, in particular capital goods and white goods. Thus the range covered is very wide. Besides machining with which we are concerned, NC has been used in a variety of manufacturing situations. The majority of applications of NC are in metal cutting machine tools such as milling machines, lathes, drilling machines, grinding machines and gear generating machines. Besides a number of metal forming machine tools such as presses, flame cutting machines, pipe bending and forming machines, folding and shearing machines also use NC for their program control. The inspection machines called Co-ordinate Measuring (CMM) are also based on NC. Lastly the robots basically may be material handling units, but their control principles are very close to the NC. Besides these applications listed for manufacturing, other applications such as filament winding or assembly machines based on the NC principles can also be seen in the industry.
NC machines have been found suitable for the following:
(i) Parts having complex contours, that cannot be manufactured by conventional machine tools.
(ii) Small lot production, often for even single (one off) job production, such as for prototyping, tool manufacturing, etc.
(iii) Jobs requiring very high accuracy and repeatability.
(iv) Jobs requiring many set-ups and/or when the set-ups are expensive.
(v) Parts that are subjected to frequent design changes and consequently require more expensive manufacturing methods.
(vi) The inspection cost, which is a significant portion of the total manufacturing cost.
One or more of the above considerations would justify the processing of a part by an NC machine tool.
Numerical Control is superior to conventional manufacturing in a number of ways. The superiority comes because of the programmability. These are as follows:
(i) Parts can be produced in less time and therefore are likely to be less expensive. The idle (non-cutting) time is reduced to minimum. This of course depends on the way the part program for the part is written. The endeavour of the machine tool builder is to provide a facility whereby the non-cutting time can be brought to the minimum. It is possible to reduce the non-productive time in NC machine tools in the following ways:
(a) by reducing the number of set-ups
(b) by reducing set-up time
(c) by reducing workpiece-handling time
(d) by reducing tool-changing time.
These make machines highly productive.
(ii) Parts can be produced more accurately even for smaller batches. In conventional machine tools, precision is largely determined by human skill, NC machines, because of automation and the absence of interrelated human factors, provide much higher precision and thereby promise a product of consistent quality for the entire batch.
(iii) The operator involvement in part manufacture is reduced to a minimum and as a result less scrap is generated due to operator errors. No operator skill is needed, except in setting up of the tools and the work. Even here, the set-up has been simplified to a great extent.
(iv) Since the part program takes care of the geometry generated, the need for expensive jigs and fixtures is reduced or eliminated, depending upon the part geometry. Even when a fixture is to be used, it is very simple compared to a conventional machine tool. It is far easier to make and store part program (tapes).
(v) Inspection time is reduced, since all the parts in a batch are identical, provided proper care is taken about tool compensations and tool wear in part program preparation and operation. With the use of inspection probes in the case of some advanced CNC controllers, the measurement function also becomes part of the program.
(vi) The need for certain types of form tools is completely eliminated in NC machines. This is because the profile generated can be programmed, even if it involves three dimensions.
(vii) Lead times needed before the job can be put on the machine tool are reduced to a great extent, depending upon the complexity of the job. More complex jobs may require fixtures or templates if they are to be machined in conventional machine tools, which can be reduced to a large extent.
(viii) CNC machining centers can perform a variety of machining operations that have to be carried out on several conventional machine tools, thus reducing the number of the machine tools on the shop floor. This would save floor space and result in less lead-time in manufacture. This would also result in an overall reduction in production costs.
(ix) The set-up times are reduced, since the set-up involves simple location of the datum surface and position. Further, the number of the set-ups needed can also be reduced. All this translates into lower processing times. A component can be fully machined in a single machining center or turning center, each of which having wider machining capabilities. In conventional manufacture if the part has to be processed through a number of machine tools which are located in different departments, the time involved in completion and the resultant in process inventory would be large. This would be greatly eliminated by the use of NC machine tools.
Capstan And Turret Lathes
The center lathe is a general purpose machine tool,it has a number of limitations of center lathes are:
(i) The setting time for the job in terms of holding the job is large.
(ii) Only one tool can be used in the normal course. Sometimes the conventional tool post can be replaced by a square tool post with four tools.
(iii) The idle times involved in the setting and movement of tools between the cuts is large.
(iv) Precise movement of the tools to destined places is difficult to achieve if proper care is not taken by the operator.
All these difficulties mean that the center lathe cannot be used for production work in view of the low production rate. The center lathe is thus modified to improve the production rate. The various modified lathes are turret and capstan lathes, semi-automatics and automatics.
Improvements are achieved basically in the following areas:
(a) work holding methods
(b) multiple tool availability
(c) automatic feeding of the tools
(d) automatic stopping of the tools at precise locations
(e) automatic control of the proper sequence of operations.
The main characteristic feature of the capstan and turret lathes is the six sides (hexagonal) block mounted on one end of the bed replacing the normal tailstock. This allows for mounting six tool blocks, each one of which can contain one or more tools depending upon the requirement. Further on the cross slide, two tool posts are mounted, one in the front and the other in the rear. Each one of them can hold up to four tools each. Thus the total carrying capacity is a maximum of 14 tools when only one tool is mounted in each of the locations.
The turret lathe consists of an all gear, heavy duty headstock with a greater range of spindle speeds. The turret is mounted on a saddle which in turn is sliding on the bed. When the saddle moves on the bed during the return stroke it would automatically be indexed to the next tool position, thus reducing the idle time of the machine.
The tools in the turret lathe are provided with a system of stops and trips on the feed rod which can precisely control the actual distance moved by the tool. Thus it is possible to set and control the individual movements of the tools as required by the component.
The type of work holding devices that can be used with turret lathe is similar to the conventional lathes, but in view of the higher productivity demanded and greater repeatability required, generally automatic fixtures such as collets, self centering chucks or pneumatic chucks are used.
The collet chucks come in a variety of designs. The actual clamping is done by the movement of the collet tube along the axis of the spindle by either pushing or pulling .Sometimes the bar material is either pushed or pulled back during the closing of the collet. This can be prevented by having an external tubular locking stop so that the axial movement is prevented.
Often a large variety of components on a turret lathe are machined from raw material which is in a bar from. For continuous feeding of the bar special bar feeding arrangements are available which pushes the bar by a precise amount against a stop provided on the face of the hexagonal turret at the beginning of the cycle.
Most of the tools used in the cross slide tool post are very similar to those used in the center lathe. Form tools are generally used in the cross slide. A large variety of special tool holders are available for use in the turret for providing greater productivity. A box tool is generally used for long turning jobs since the tool while cutting also supports the job. They have a cutting tool and also support rollers for providing the necessary support to the workpiece. This helps in machining of bars which are not well supported during the machining operation .It is also possible to have more than one cutting tool held in a box tool such that there is an overlap of the cuts while providing support for the workpiece.
Combination tool holders allow for mounting multiple cutting tools with provisions for their adjustment to suit the machining situation. They have the ability to perform more than one cutting operation at the same time, thereby reducing the actual machining time required for the operation. They can be have both the internal and external cutting tools in a single tool holder such that the workpiece support can be taken care of so that higher accuracy can be achieved.
Many turret lathes would be fitted with taper turning attachments very similar to that used in center-lathes, for machining tapers. Small tapers can be produced by form tools from the cross slide, while internal tapers are produced by taper reamers.
Thus the various differences that can be found between capstan and turret with that of a general purpose center lathe are:
(i) The headstock has more and heavier range of speeds and to allow for higher rate of production.
(ii) The tool post is indexable (four tools). Any one tool can be brought into the cutting position.
(iii) The tail stock is replaced by a tool turret with six tool positions.
(iv) Feed of each tool can be regulated by means of feed stops.
(v) Two or more tools mounted on a single tool face can cut simultaneously.
(vi) Semi-skilled operators are required.
(vii) These are used for production operations involving better repeatability.
A variation of the turret lathe is the capstan lathe, in which the turret moves on the saddle while the saddle can itself be fixed at any position on the bed depending upon the length of the job. Thus the tool travel length is limited to the length of the saddle. This type of arrangement is normally used for small size machines.
箱體類零件鉆、鏜組合機床夾具CAD系統(tǒng)
摘 要:針對箱體類零件鉆、鏜組合機床夾具設(shè)計中存在的大量標(biāo)準(zhǔn)件和典型結(jié)構(gòu)提出基于被加工件三維模型的箱體類組合機床夾具設(shè)計方法,研究了夾具的定位設(shè)計、夾緊設(shè)計和導(dǎo)向設(shè)計。
關(guān)鍵詞:組合機床, 鉆鏜加工, 夾具設(shè)計, CAD 系統(tǒng)
CAD System of Fixture in Combined Machine of Turning and Drilling
Abstract : Based on the large amount of standard units and prototypes in fixture design of combined machine of drilling and turning , the fixture design method based on 3D model of work-pieces is presented , and the design methods of positioning , clamping , and guiding device are researched.
Keywords: combined machine, drilling and turning ,fixture design, CAD system
1 引言
箱體類零件是機械、汽車、家電、航空、紡織、石化等領(lǐng)域產(chǎn)品結(jié)構(gòu)的主體,其加工分為外表面銑削和孔系鉆、鏜加工。在用組合機床進(jìn)行箱體類零件的大批量加工時,其孔系加工質(zhì)量主要由夾具保證,因此夾具設(shè)計是保證加工精度的重要環(huán)節(jié)。
本文研究和分析了箱體類零件鉆鏜加工用組合機床夾具的結(jié)構(gòu)及功能,并提出基于被加工件三維模型的箱體類組合機床夾具設(shè)計方法。
2 箱體類鉆鏜組合機床夾具設(shè)計分析
2-1 夾具結(jié)構(gòu)
圖1 為三面鉆鏜組合機床上所使用的加工某柴油機機體夾具的爆炸視圖。工件導(dǎo)入裝置1 由導(dǎo)軌、導(dǎo)輪和支撐裝置組成;定位裝置2 由處于工件底面的兩行支承塊、后面的側(cè)支承塊和輔助定位裝置組成;3 為工件;4 為刀具導(dǎo)向裝置(圖中僅指出左面的導(dǎo)向裝置,實際上右面、后面也有導(dǎo)向裝置,根據(jù)工件的具體情況而定) ;5 為液壓夾緊裝置(亦可根據(jù)要求的不同,選用氣動夾緊裝置) 。
1.工件導(dǎo)入裝置 2.定位裝置 3.工件 4.導(dǎo)向裝置 5.夾緊裝置
圖1 某柴油機機體夾具
2-2 夾具設(shè)計分析
夾具結(jié)構(gòu)設(shè)計過程為: ①確定加工設(shè)備(立式或臥式)；②根據(jù)給定工序圖確定的定位方案進(jìn)行定位設(shè)計,包括選擇定位件,并設(shè)計相應(yīng)結(jié)構(gòu)；③導(dǎo)向設(shè)計,具體內(nèi)容為確定導(dǎo)向裝置與被加工件間的位置關(guān)系、選擇或設(shè)計導(dǎo)向部件、設(shè)計導(dǎo)向板等； ④根據(jù)工序圖確定的夾緊方案,確定夾具力作用位置,并選擇夾緊件、設(shè)計相應(yīng)夾緊機構(gòu)、選擇匹配動力裝置；⑤據(jù)加工中工件的受力特點,合理地確定輔助支承裝置； ⑥設(shè)計夾具體； ⑦設(shè)計工件的導(dǎo)入裝置； ⑧其它結(jié)構(gòu)的設(shè)計。
不同箱體類零件的加工對應(yīng)不同的夾具,但其中存在大量的典型結(jié)構(gòu)和通用件、標(biāo)準(zhǔn)件。典型結(jié)構(gòu)是指一組零件組合在一起、完成特定功能的子裝配體,如鉆削中用到的快換鉆套與襯套及鉆套固定螺釘?shù)慕M合、鏜削中臥軸鏜孔用滑動導(dǎo)套的組合等。又如箱體零件在夾具中的定位方式一般為一面兩銷或三個平面(六點定位) ,箱體類零件組合夾具的夾具體一般都采用支架式、為提高工件效率并夾緊工件一般采用液壓夾緊等。這些結(jié)構(gòu)都可采用標(biāo)準(zhǔn)化處理,將這些結(jié)構(gòu)做成參數(shù)化的典型結(jié)構(gòu)庫,在設(shè)計中進(jìn)行調(diào)用,避免重復(fù)勞動,提高設(shè)計效率。
由于工件形狀、尺寸不同,夾具結(jié)構(gòu)會發(fā)生相應(yīng)變化,如何有效地快速響應(yīng)工
件變化是箱體類零件組合機床夾具CAD 的一個難題。本文針對不同的結(jié)構(gòu)組成采用不同的設(shè)計方法予以處理。
3 箱體類零件組合機床夾具設(shè)計系統(tǒng)研究
3-1 定位方案設(shè)計
箱體類零件組合機床的定位方案一般有一面兩銷定位和三平面定位兩種。
一面兩銷定位:其中一面為支承面,由于加工孔系是決定箱體類零件精度的關(guān)鍵加工工序,之前對其所用定位面已進(jìn)行過精加工,故支承件一般選取與工件接觸面較大的支承板;如考慮工件的導(dǎo)入,則支承板與導(dǎo)向板配合使用,或合二為一。支承板與導(dǎo)向板在夾具體中的布局有其典型格式,可針對工件定位面的大小,總結(jié)支承件的選擇條件,利用條件語句實現(xiàn)支承件的選擇。而兩銷的選擇則完全由工件中定位孔的尺寸來確定。由于組合機床是高效的加工設(shè)備,故對一般工件的裝卸速度要求較高,在一面兩銷定位方式中一般采用插拔銷機構(gòu),以適應(yīng)快速裝卸要求。采用三平面定位時,支承件的選擇方法與一面兩銷定位相同。而其它定位件及相應(yīng)機構(gòu)的選擇則有所不同:一般用側(cè)導(dǎo)板來限制兩個自由度,用后定
位板(或圓柱銷) 來限制剩下的一個自由度。
3-2 夾緊方案設(shè)計
鉆、鏜組合機床夾具中,夾緊機構(gòu)一般為氣動或液壓機構(gòu),易于實現(xiàn)自動控制,且形式比較簡單,易于設(shè)計。在組合機床夾具CAD 系統(tǒng)中,不僅要考慮把使用液壓夾緊、氣動夾緊的典型結(jié)構(gòu)納入其中,使其能被方便地調(diào)用,并針對不同的工件根據(jù)設(shè)計需要進(jìn)行定位、定向。還應(yīng)考慮把相關(guān)的液壓氣動裝置的設(shè)計計算、相關(guān)標(biāo)準(zhǔn)件的選用、與夾具體的聯(lián)接及其它相關(guān)驗算納入其中,根據(jù)加工工藝的要求,輔助進(jìn)行相關(guān)的設(shè)計估算。
3-3 導(dǎo)向機構(gòu)設(shè)計
孔對于基準(zhǔn)的定位精度由定位方案來保證,而孔系中孔間位置關(guān)系則由導(dǎo)向機構(gòu)來保證,其設(shè)計隨被加工孔系的變化而變化。具體的導(dǎo)向結(jié)構(gòu)是一塊包容了針對不同孔加工用的導(dǎo)向套或鏜套的模板(其中導(dǎo)向套或鏜套應(yīng)可更換) 。在夾具CAD 系統(tǒng)中,應(yīng)能針對工件的孔系自動生成這樣的裝置和相應(yīng)的模板,同時能盡量自動從標(biāo)準(zhǔn)件庫中選擇標(biāo)準(zhǔn)的導(dǎo)向套和襯套、避免過多的人工調(diào)整。
3-4 工件導(dǎo)入、導(dǎo)出機構(gòu)設(shè)計
工件的導(dǎo)入、導(dǎo)出機構(gòu)是為了便于工件的裝入、粗限位、取出以及大臥式組合機床中承載過重、過大的工件質(zhì)量而設(shè)計的。工件的導(dǎo)入、導(dǎo)出機構(gòu)的設(shè)計要根據(jù)工件質(zhì)量、生產(chǎn)率要求、加工自動化程度和工件具體形態(tài)確定。如工件較輕、生產(chǎn)率要求較低、加工自動化程度要求不高,也可采用人工方式裝卸工件,只需簡易的導(dǎo)入、導(dǎo)出機構(gòu)。
3-5 夾具體設(shè)計
夾具體是夾具的主體,直接或間接地把夾具中定位裝置、夾緊裝置、導(dǎo)向裝置等連成一個能使工件在其中導(dǎo)入、定位、夾緊、取出、使夾具具備對刀能力并能在機床中進(jìn)行定位和固定的整體?；谌SCAD 技術(shù)進(jìn)行設(shè)計,可充分運用其幾何鏈接工具,把直接與夾具體關(guān)聯(lián)的定位件、夾緊件、導(dǎo)向件的與夾具體的定位面、聯(lián)接面直接或間接相關(guān)的面鏈接到夾具體部件中,使之成為夾具體設(shè)計的鏈接特征。這樣夾具體的設(shè)計始終與相關(guān)的定位件、夾緊件、導(dǎo)向件等關(guān)聯(lián),當(dāng)這些結(jié)構(gòu)的形式、規(guī)格、方位在設(shè)計中需調(diào)整時,則夾具體的設(shè)計隨之變更。當(dāng)工件結(jié)構(gòu)有所調(diào)整時,夾具相關(guān)結(jié)構(gòu)也會隨之調(diào)整,以避免大量的重復(fù)勞動。
3-6 標(biāo)準(zhǔn)件、通用件及合成組件庫的設(shè)計
標(biāo)準(zhǔn)件、通用件及合成組件的應(yīng)用使夾具設(shè)計變得更為快捷、有效。在夾具CAD 系統(tǒng)中,使用這些結(jié)構(gòu)應(yīng)遵循夾具設(shè)計的內(nèi)在規(guī)律,即系統(tǒng)中要支持用戶選擇標(biāo)準(zhǔn)件、通用件、組合件在工件上的作用面,能在作用面上確定作用位置,能定義其相對于工件的方向和位置。
在夾具CAD 系統(tǒng)設(shè)計中,要充分運用三維CAD軟件的功能和二次開發(fā)工具,使得設(shè)計過程中的每個環(huán)節(jié)設(shè)置合理、便于用戶操作和拓展功能。
參考文獻(xiàn)
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2 楊黎明. 機床夾具設(shè)計手冊. 北京:國防工業(yè)出版社,1996
3 孫大涌. 先進(jìn)制造技術(shù). 北京: 機械工業(yè)出版社, 1999(12) :31～44
4 肖人彬, 周 濟, 查建中. 智能設(shè)計:概念、發(fā)展與實踐.中國機械工程,1997 ,8(2) :74～76