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Computer-Aided Process Planning
According to the Tool & Manufacturing Engineers Handbook, process planning is the systematic determination of the methods by which a product is to be manufactured economically and competitively. It essentially involves selection, calculation, and documentation. Processes, machines, tools, operations, and sequences must be selected. Such factors as feeds, speeds, tolerances, dimensions, and costs must be calculated. Finally, documents in the form of illustrated process sheets, operation sheets, and process routes must be prepared. Process planning is an intermediate stage between designing and manufacturing the product. But how well does it bridge design and manufacturing?
Most manufacturing engineers would agree that, if ten different planners were asked to develop a process plan for the same part, they would probably come up with ten different plans. Obviously, all these plans cannot reflect the most efficient manufacturing methods, and, in fact, there is no guarantee that any one of them will constitute the optimum method for manufacturing the part.
What may be even more disturbing is that a process plan developed for a part during a current manufacturing program may be quite different from the plan developed for the same or similar part during a previous manufacturing program and it may never be used again for the same or similar part. That represents a lot of wasted effort and produces a great many inconsistencies in routing, tooling, labor requirements, costing, and possibly even purchase requirements.
Of course, process plans should not necessarily remain static. As lot sizes change and new technology, equipment, and processes become available, the most effective way to manufacture a particular part also changes, and those changes should be reflected in current process plans released to the shop.
A planner must manage and retrieve a great deal of data and many documents，including established standards，mach inability data，machine specifications，tooling inventories，stock availability，and existing process plans．This is primarily an information—handling job，and the computer is an ideal companion．
There is another advantage to using computers to help with process planning．Because the task involves many interrelated activities，determining the optimum plan requires many iterations. Since computers can readily perform vast numbers of comparisons，many more alternative plans can be explored than would be possible manually．
A third advantage in the use of computer-aided process planning is uniformity. Several specific benefits Can be expected from the adoption of computer-aided process—planning techniques：
1．Reduced clerical effort in preparation of instructions．
2．Fewer calculation errors due to human error．
3. Fewer oversights in logic or instructions because of the prompting capability available with interactive computer programs．
4．Immediate access to up—to—date information from a central database．
5．Consistent information，because every planner accesses the same database．
6. Faster response to changes requested by engineers of other operating departments．
7．Automatic Use of the latest revision of a part drawing．
8. More—detailed，more—uniform process-plan statements produced by word—processing techniques.
9．More—effective use of inventories of tools，gages，and fixtures and a concomitant reduction in the variety of those items.
10. Better communication with shop personnel because plans can be more specifically tailored to a particular task and presented in unambiguous，proven language.
11. Better information for production planning, including cutter-life, forecasting, materials-requirements planning, scheduling, and inventory control.
Most important for CIM, computer-aided process planning produces machine-readable data instead of handwritten plans. Such data can readily be transferred to other systems within the C1M hierarchy for use in planning.
There are basically two approaches to computer-aided process planning: variant and generative.
In the variant approach, a set of standard process plans is established for all the parts families that have been identified through group technology. The standard plans are stored in computer memory and retrieved for new parts according to their family identification. Again, GT helps to place the new part in an appropriate family. The standard plan is then edited to suit the specific requirements of a particular job.
In the generative approach, an attempt is made to synthesize each individual plan using appropriate algorithms that define the various technological decisions that must be made in the course of manufacturing. In a truly generative process-planning system, the sequence of operations, as well as all the manufacturing-process parameters, would be automatically established without reference to prior plans. In its ultimate realization, such an approach would be universally applicable: present any plan to the system, and the computer produces the optimum process plan.
No such system exists, however. So called generative process-planning systems--and probably for the foreseeable future---are still specialized systems developed for a specific operation or a particular type of manufacturing process. The logic is based on a combination of past practice and basic technology.
計(jì)算機(jī)輔助工藝過(guò)程設(shè)計(jì)
根據(jù)《工具與制造工程師手冊(cè)》，工藝過(guò)程是能夠經(jīng)濟(jì)地和有競(jìng)爭(zhēng)力地將產(chǎn)品制造出來(lái)的一整套方法。它主要由選擇、計(jì)算和建立工藝文件組成。對(duì)加工方法、機(jī)床、刀具、工序和順序必須進(jìn)行選擇。對(duì)于一些參數(shù)如進(jìn)給量、速度、公差、尺寸和成本等應(yīng)該進(jìn)行計(jì)算。最后，應(yīng)該制訂帶工序簡(jiǎn)圖的工藝過(guò)程卡片，工序卡片和工藝路線等方面的工藝文件。工藝過(guò)程是產(chǎn)品設(shè)計(jì)和制造的中間環(huán)節(jié)。那么，它是如何將設(shè)計(jì)與制造聯(lián)接起來(lái)的呢?
大部分制造工程師都會(huì)同意這個(gè)看法，即如果10個(gè)不同的工藝人員編制同一個(gè)零件的工藝規(guī)程，他們很可能得出10種不同的方案。顯然，并不是所有這些方案都能反映最適當(dāng)?shù)闹圃旆椒?，而且，事?shí)上也不能保證它們中的任何一個(gè)方案是由加工這個(gè)零件的最好的方法組成的。
在目前的制造過(guò)程中的一個(gè)更為混亂的事情是，對(duì)于一個(gè)零件來(lái)說(shuō)，現(xiàn)在所
編制的工藝規(guī)程可能與以前在制造過(guò)程中所編制的同一個(gè)零件或者相似零件的工藝規(guī)程相差很多，而且這個(gè)工藝規(guī)程可能再也不會(huì)應(yīng)用于同一個(gè)零件或者相似
零件。這說(shuō)明很多工作成果都被浪費(fèi)了，而且在工藝路線、工藝裝備、對(duì)工人的要求和成本等方面都不一致，甚至對(duì)外購(gòu)件的要求都不一樣。
當(dāng)然工藝規(guī)程不應(yīng)該是一成不變的。隨著產(chǎn)品批量的變化和新技術(shù)、新設(shè)
備、新的加工方法的出現(xiàn)，加工制造某一特定零件最適當(dāng)?shù)姆椒ㄒ矔?huì)發(fā)生變化，而且這些變化應(yīng)該在車間目前使用的加工工藝規(guī)程中反映出來(lái)。
工藝人員應(yīng)該管理和檢索大量的數(shù)據(jù)和很多文件，其中包括：已經(jīng)建立了的
標(biāo)準(zhǔn)、可加工性數(shù)據(jù)、機(jī)器的規(guī)格、工藝裝備的清單、原材料庫(kù)存量和一些目前正在應(yīng)用的工藝文件。這主要是一些信息處理工作，而計(jì)算機(jī)是完成這項(xiàng)工作的一個(gè)理想助手。
在設(shè)計(jì)工藝過(guò)程時(shí)應(yīng)用計(jì)算機(jī)還有一個(gè)優(yōu)點(diǎn)。因?yàn)檫@項(xiàng)工作涉及到許多相
互關(guān)聯(lián)的事情，在確定最優(yōu)的方案時(shí)，需要進(jìn)行許多次迭代。由于計(jì)算機(jī)可以很
容易地進(jìn)行大量的比較工作，它比人工所能夠分析的可供選擇的方案要多得多。
采用計(jì)算機(jī)輔助工藝過(guò)程設(shè)計(jì)的第三個(gè)優(yōu)點(diǎn)是所設(shè)計(jì)的工藝過(guò)程具有一致性。
采用計(jì)算機(jī)輔助工藝過(guò)程設(shè)計(jì)可以獲得以下幾點(diǎn)好處：
1.在準(zhǔn)備工藝文件時(shí)，減少了書寫工作量。
2. 減少了在進(jìn)行人工計(jì)算時(shí)所產(chǎn)生的錯(cuò)誤。
3. 由于交互式計(jì)算機(jī)程序的提示功能而減少了在邏輯和說(shuō)明方面的疏漏
4. 通過(guò)中央數(shù)據(jù)庫(kù)可以直接利用最新的信息.
5. 由于每一個(gè)工藝人員都利用相同的數(shù)據(jù)庫(kù)，因此，可以保證信息的一致性。
6. 對(duì)由其他業(yè)務(wù)部門的工程技術(shù)人員所提出的修改意見作出快速反應(yīng)。
7. 自動(dòng)地利用最新版本的零件圖紙。
8. 采用文字處理技術(shù)，產(chǎn)生更詳細(xì)、更一致的工藝文件。
9. 更有效地利用庫(kù)存的刀具、量具和夾具，減少這些物品的種類。
10. 由于能夠使工藝規(guī)程適合于某一項(xiàng)特定的工作，而且用清楚的、有理有據(jù)的語(yǔ)言表達(dá)出來(lái)，因此，可以與車間的人員進(jìn)行更好的交流。
11. 可以更好地獲得編制生產(chǎn)計(jì)劃所需的信息，其中包括：刀具壽命、預(yù)測(cè)、材料需求計(jì)劃、進(jìn)度和庫(kù)存控制。
對(duì)計(jì)算機(jī)集成制造最為重要的是，計(jì)算機(jī)輔助工藝過(guò)程設(shè)計(jì)可以生成機(jī)器可以閱讀的數(shù)據(jù)，而不是手寫的規(guī)程。這種數(shù)據(jù)可以傳遞到計(jì)算機(jī)集成制造體系中的另一個(gè)系統(tǒng)中，用以進(jìn)行工藝過(guò)程設(shè)計(jì)。
計(jì)算機(jī)輔助工藝過(guò)程設(shè)計(jì)通常有兩種類型：派生式和創(chuàng)成式。
在派生式中，對(duì)采用成組技術(shù)確定的一個(gè)零件族中的所有零件編制一套典型
的加工工藝規(guī)程。這個(gè)典型工藝規(guī)程存貯在計(jì)算機(jī)的存儲(chǔ)器中，根據(jù)新零件的零
件族編碼進(jìn)行檢索。成組技術(shù)可以幫助把新零件歸類于適當(dāng)?shù)牧慵逯?。通過(guò)
對(duì)典型工藝規(guī)程的編輯，可以滿足特定工作的專門要求。
在創(chuàng)成式中，通過(guò)采用確定加工制造過(guò)程中各種工藝決策的適當(dāng)算法，將各
個(gè)單獨(dú)的工藝規(guī)程綜合起來(lái)。在一個(gè)真正的創(chuàng)成式計(jì)算機(jī)輔助工藝過(guò)程設(shè)計(jì)系統(tǒng)中，工序的排列和所有的制造過(guò)程參數(shù)都可以在不必參考以前的工藝規(guī)程的情況下自動(dòng)生成。在它最終實(shí)現(xiàn)之后，這種方式將會(huì)是普遍適用的：將任何一個(gè)計(jì)劃提交給這個(gè)系統(tǒng)，計(jì)算機(jī)都會(huì)產(chǎn)生最優(yōu)的工藝規(guī)程。
然而，這種系統(tǒng)目前還不存在。所謂的創(chuàng)成式計(jì)算機(jī)輔助工藝過(guò)程設(shè)計(jì)系統(tǒng)
——大概在可以預(yù)料到的將來(lái)——仍然是應(yīng)用于一個(gè)特定的工序或者特定的加工過(guò)程的專用系統(tǒng)。其邏輯原理是以過(guò)去的經(jīng)驗(yàn)與基本理論的組合為基礎(chǔ)的。