機加工外文翻譯-工藝規(guī)程制訂與并行工程【中英文WORD】【中文5160字】
機加工外文翻譯-工藝規(guī)程制訂與并行工程【中英文WORD】【中文5160字】,中英文WORD,中文5160字,加工,外文,翻譯,工藝,規(guī)程,制訂,并行,工程,中英文,WORD,中文,5160
【中文5160字】
工藝規(guī)程制訂與并行工程
T. Ramayah and Noraini Ismail
摘要
產(chǎn)品設(shè)計是用于產(chǎn)品，及它的部件裝配的計劃。為了把產(chǎn)品設(shè)計轉(zhuǎn)換成一個實際物體，這需要一個制造計劃。而制訂一個這樣的計劃的行動就叫做工藝規(guī)程制訂。它是產(chǎn)品設(shè)計和制造之間的連接，工藝規(guī)程制訂包括決定加工順序和制造產(chǎn)品所必須完成的裝配步驟。在以下文章中,我們將解釋工藝規(guī)程制訂和他的一些相關(guān)主題文章開始，我們應(yīng)該區(qū)別在下列文章中被反復(fù)提到的工藝規(guī)程制訂和生產(chǎn)計劃。工藝規(guī)程制訂與如何制造產(chǎn)品和它的零件等工程技術(shù)問題有關(guān)，制造零件和裝配產(chǎn)品需要什么樣的設(shè)備和工具？工藝規(guī)程制訂與產(chǎn)品制造物流管理有關(guān)系。它在工藝規(guī)程制訂后面與原料分類及獲得滿足制造充分數(shù)量產(chǎn)品要求的資源有關(guān)。
工藝規(guī)程制訂
工藝規(guī)程制訂包括決定最適當(dāng)?shù)闹圃旒把b配步驟和順序，在這些順序和步驟中他們必須根據(jù)所提出的詳細的設(shè)計說明書規(guī)范完成給定零件或產(chǎn)品制造。 能夠被計劃的工藝范圍和多樣性通常由于公司車間可用設(shè)備和技術(shù)能力而受到限制。在公司內(nèi)部不能夠制造的零件必須到外部市場購買，工藝規(guī)程制訂所提及的工藝選擇同樣也受到詳細設(shè)計資料的限制，我們稍后將會回到這一點。
工藝規(guī)程制訂通常是由制造工程師完成的，工藝制訂者必須熟悉工廠中詳細可用的制造流程并且能夠說明工程圖?；谥朴喺叩闹R、技術(shù)和經(jīng)驗，用于制造每個零件的工藝步驟以最合乎邏輯的順序被發(fā)展制訂。下列各項是在工藝規(guī)程制訂范圍里的許多決定和詳細資料：
? .設(shè)計圖的說明.? 在工藝規(guī)程制訂的開始，產(chǎn)品設(shè)計的這一部分( 材料、尺寸、公差、表面處理等等)必須進行分析。
? .工藝和順序.? 工藝制訂者必須選擇哪一個工藝是必需的及必需工藝的序列。此外還必須準(zhǔn)備好一個簡短的工藝步驟描述。
? .設(shè)備選擇.? 大體上，工藝制訂者必須逐步展開利用工廠現(xiàn)有機器的計劃。另外，組件必須被購買或在新設(shè)備上的投資必須被制定。
? .工具、沖模、鑄模、夾具、量具.? 工藝必須決定每個工序需要什么工具，這些工具的實際設(shè)計和制造通常通過委派工具設(shè)計部門和工具庫或者聯(lián)系專攻那種工具制造的外面廠商來完成。
? .方法分析.? 車間規(guī)劃，小工具，提升重物的提升間。甚至在一些人工操作情景中的肢體動作也被指定。
? .操作步驟.? 工作測量技術(shù)被用來為每個操作設(shè)定時間標(biāo)準(zhǔn)。
? .切削工具和切削條件.? 這些必須對加工操作通過推薦標(biāo)準(zhǔn)手冊來進行詳細說明。
零件工藝規(guī)程制訂
對于單個零件，加工順序通過一種被稱為進路表的表格來進行文件證明備份。就如工程圖被用于詳細說明設(shè)計產(chǎn)品一樣，進路表被用于詳細說明工藝計劃。他們是類似的，一個用于產(chǎn)品設(shè)計，另一個用于制造。
制造單個零件的典型加工順序包括：(1) 一個基本工序 (2) 二級工序 (3) 提高物質(zhì)特性工序和(4) 最后工序。一個基本工序決定了工件的起始造型。金屬鑄件、塑料成型、金屬精煉是基本工序中的實例。起始造型常常必須通過改變起始造型操作(或者接近于最終造型)的二級工序來精制。二級工序習(xí)慣于和基本工序一起提供起始造型，當(dāng)砂型鑄造是基本工序，車加工通常是二級工序。當(dāng)軋鋼廠制造金屬片是基本工序，沖壓操作像沖裁和彎曲通常是二級工序。當(dāng)塑料注入成型是基本工序時，二級工序通常是不必要的，因為他的大多數(shù)幾何特征制造通過別的方式如成型制造來完成。塑料成型和其他操作的二級工序被稱為凈成型工序的并發(fā)二級工序，需要一些但并不多的二級工序的操作就是所提到的近似成型工序。許多有印象的摸鍛件就是這一類，這類零件能夠經(jīng)常在鍛造(初級工序)階段被成型，因此減少了必要的加工(二級工序)。
一旦模型被建立，許多零件的下一步是改良它們的機械物理性能。提高特性工序并不改變零件模型，然而，它卻能改變零件的物理特性。金屬零件的熱處理操作就是最普通的實例。類似的如玻璃通過熱處理來制造鋼化玻璃，對于大多數(shù)零件的制造來說，這些特性加強工序在加工工序中并不需要。
最后工序通常對零件(或裝配體)的表面提供一個涂層。例如電鍍、薄膜沉積技術(shù)、涂漆。表面處理的目的是改善外觀，改變顏色或者表面保護防止腐蝕和磨損等等。在很多零件中最后工序是并不需要的。例如：塑料成型就很少需要最后程序。當(dāng)必須需要最后程序，他通常是加工順序的最后一步。
裝配工藝規(guī)程制訂
一個既定產(chǎn)品的典型裝配方法由以下因素決定的：(1)預(yù)期產(chǎn)品數(shù)量(2)裝配產(chǎn)品的復(fù)雜性。例如：不同組件的數(shù)量和(3)常用裝配工藝。例如：機械定位焊接、對于小數(shù)量產(chǎn)品，通常在人工裝配線上進行裝配。對于大量制造的一打或這樣組件的簡單零件，要采用適當(dāng)?shù)淖詣踊b配線。無論如何這里有一個工作必須被完成的優(yōu)先順序，這個優(yōu)先需求經(jīng)常用一個優(yōu)先表來進行圖表描繪。
裝配工藝規(guī)程制訂包括裝配指令的發(fā)展，但是更詳細地對于小批量生產(chǎn)。在一個崗位完成整個裝配，對于一個裝配線上的大批量生產(chǎn)，工藝規(guī)程制訂由一種分配工作條件到裝配線個別工位并被叫做人工投入線性平衡法的程序組成。這種裝配線按照裝配線平衡解決方案決定的順序發(fā)送工作單元到個別工位，在個別組成，任意工具或夾具的工藝規(guī)程制訂時，一條裝配線的決定、設(shè)計和制造必須被完成，并且工作站的必須被列出來。
制造或購買決定
在工藝制定過程中出現(xiàn)的一個重大問題是一個特定零件應(yīng)該在公司內(nèi)部的工廠內(nèi)生產(chǎn)還是從外部銷售商處購買，并且這個問題的答案被認為是制造或購買決定。如果公司沒有技術(shù)設(shè)備或制造零件所必須的詳細制造工藝中的專門技術(shù)，那么答案就很明顯了。因為沒有其他選擇零件必須購買。然而，在很多例子中零件既可以在利用現(xiàn)有設(shè)備在內(nèi)部制造或者可以從外部擁有相似制造能力的生產(chǎn)銷售商處購買。
在我們的關(guān)于制造或購買的決定的討論中，他應(yīng)該認識到在開始幾乎所有的制造者從供應(yīng)商那里購買原料。一個機械加工廠從一個金屬經(jīng)銷商購買他的起動柄原料或從一個鑄造廠購買他的砂型鑄件。一個塑料成型廠從一個化工廠購買他的模塑料。一個沖壓廠可以去經(jīng)銷商或直接從軋鋼廠購買金屬片。很少的公司能夠在操作中從原料一直進行垂直整合，這看來至少購買一些也許在他的工廠可以另外制造的零件是合理的。也有可能為公司使用的每一個組成要求制造或購買決定。
這里有許多影響制造或購買決定的因素，一個人可能認為成本是決定是購買還是制造零件的最重要的因素。如果一個外部經(jīng)銷商比公司工廠更精通于制造零件的工藝，因而公司內(nèi)部生產(chǎn)成本可能比經(jīng)銷商賺取成本后的價格還要高?？墒?，如果購買決定導(dǎo)致公司工廠設(shè)備和勞動的閑置，購買零件的表面優(yōu)勢就會喪失。考慮以下例子制造或購買決定。
為一個特定零件被引述的價格是100個單位的每單位$20.00。制造零件的成分如下所示：
單位原料成本=每單位$8.00
直接勞動成本=每單位$6.00
勞動加班150%=每單位$9.00
設(shè)備修理成本=每單位$5.00
___________________
總計=每單位$28.00
這個組成應(yīng)該被購買還是在內(nèi)部制造 ？
解決方案：盡管經(jīng)銷商的引證似乎支持購買決定，讓我們來考慮如果引證被接受可能在生產(chǎn)操作中的沖突。$5.00設(shè)備維修成本是已經(jīng)被制定的投資成本，如果設(shè)備設(shè)計因為購買零件的決定而變的沒有利用價值，那么這個固定成本仍然繼續(xù)盡管設(shè)備閑置著。同樣，如果零件被購買由工廠空間，效用和勞動成本組成的$9.00的勞動間接成本仍然繼續(xù)。通過這種推理，如果應(yīng)該已用于生產(chǎn)零件的設(shè)備閑置的購買決定并不是一個好決定因為他可能花費公司將近$20.00+$5.0+$9.00=$34.0每單元。另一方面，如果正在討論的設(shè)備可以被用于生產(chǎn)其他零件并且內(nèi)部生產(chǎn)成本低于外部聯(lián)系報價，那么一個購買決定就是一個好決定。
制造或購買決定并不像這個例子中的那樣直接。這幾年的一個趨勢，尤其在汽車工業(yè)，公司和零件供應(yīng)者建立緊密關(guān)系。由此我們將引出并行工程。
在計劃操作方面制造公司有很大興趣利用計算機輔助工藝（CAPP）系統(tǒng)來完成。
那些熟悉加工詳細資料和其他工藝的工廠培訓(xùn)的工人逐漸退休，并且這些人在將來工藝制訂的過程中是非常有用的。一種可選擇的用于完成這種功能的方式是必需的，CAPP 提供了這種選擇。CAPP經(jīng)常被看作是計算機輔助制造（CAM）的一部分。然而這種趨向意味著CAM是一系列系統(tǒng)。事實上，當(dāng)CAD和計算機輔助設(shè)計協(xié)同作用創(chuàng)造了一個CAD/CAM系統(tǒng)。在這樣一個系統(tǒng)中，CAPP成為設(shè)計和制造之間的直接聯(lián)結(jié)。來自計算機輔助工藝的優(yōu)點包括以下幾點：
.工藝合理化和標(biāo)準(zhǔn)化.? 自動工藝規(guī)程制訂比完全用手工編制工藝產(chǎn)生的更合理化和一致化。標(biāo)準(zhǔn)設(shè)計趨向產(chǎn)生低成本和高生產(chǎn)質(zhì)量。
? .增強工藝制訂者的生產(chǎn)力.? 在數(shù)據(jù)文件中的系統(tǒng)方法和標(biāo)準(zhǔn)加工設(shè)計的實用性使工藝制訂者可完成更多的工作。
? .減少工藝規(guī)程的制訂時間.? 與手工準(zhǔn)備相比，利用CAPP系統(tǒng)的工藝制訂者可以在較短的時間內(nèi)準(zhǔn)備好進路表。
? .改良異讀性.? 計算機準(zhǔn)備的進路表比手工準(zhǔn)備的進路表更容易簡潔。
? .結(jié)合其他應(yīng)用軟件.? CAPP 系統(tǒng)可以在界面上與其它應(yīng)用軟件結(jié)合，象成本估計和工作標(biāo)準(zhǔn)。
計算機輔助工藝圍繞著兩個路徑來設(shè)計，這兩個路徑被叫做：（1）CAPP檢索系統(tǒng)和（2）CAPP生成系統(tǒng)。許多CAPP系統(tǒng)結(jié)合這兩種路徑而被稱為生成檢索CAPP系統(tǒng)。
制造業(yè)的并行工程和設(shè)計
并行工程引用一種常用于產(chǎn)品發(fā)展的路徑，通過它使工程設(shè)計功能、工程制造功能和其他功能綜合起來以減少一種新產(chǎn)品投放市場所需要的共用時間，也被稱為并發(fā)工程，他可能被認為是CAD/CAM技術(shù)的類似組織版本，按照傳統(tǒng)路徑來使一件產(chǎn)品投放市場。如圖(1)a所示，工程設(shè)計功能和工程制造功能這兩種功能是分開并且連續(xù)的，產(chǎn)品設(shè)計部門開展一項新的設(shè)計有時很少考慮到公司的制造能力，也很少有機會能夠讓制造工程師來提供如何使設(shè)計更容易制造的一些建議。他好像消除了在設(shè)計和制造之間的一堵墻，當(dāng)設(shè)計部門完成設(shè)計，他投擲工程圖和說明書越過這面墻，并且那時工藝規(guī)程制訂也開始了。
圖（1）? 比較 : (a) 傳統(tǒng)產(chǎn)品發(fā)展周期和 (b) 并行產(chǎn)品的發(fā)展周期
通過比較，實行并行工程的公司，工程制造部門在早期就參與到產(chǎn)品發(fā)展周期。為如何使產(chǎn)品和他的組成能夠被設(shè)計的更適于制造提供建議。他同樣為產(chǎn)品提供制造計劃繼續(xù)進行的早期準(zhǔn)備，這種并行工程的路徑在圖(1)b中被描繪出。除了工程制造以外其他功能同樣被包括在產(chǎn)品發(fā)展周期中，如質(zhì)量工程、制造部門、后勤服務(wù)、市場供應(yīng)評定組成和一些情況下將使用這些產(chǎn)品的消費者。在產(chǎn)品發(fā)展階段的所有這些功能不僅能改善新產(chǎn)品的功能和性能，同時也能改善他的可造性、自檢性、易測性、服務(wù)能力和可維護性。通過早期功能改善，因為在最終產(chǎn)品設(shè)計之后的回顧太晚以至于不能對設(shè)計進行便利的修改的不利因素的消除，使產(chǎn)品發(fā)展周期的持續(xù)期大大減少。
并行設(shè)計包含以下因素：(1)一些制造和裝配設(shè)計(2)質(zhì)量設(shè)計(3)成本設(shè)計和(4)生命周期設(shè)計。另外，像快速成型、虛擬制造、和組織轉(zhuǎn)變等輔助技術(shù)需要被用來促進公司的并行工程。
制造和裝配設(shè)計
據(jù)估計一件產(chǎn)品的70%的生命周期成本是由在產(chǎn)品設(shè)計時所做的基本決定所決定的，這些設(shè)計決定包括每個零件的材料、零件模型、公差、表面處理、零件是如何被組織裝配的和常用裝配方法。一旦這些決定被指定，減少產(chǎn)品制造成本的能力就會被限制。例如，如果產(chǎn)品設(shè)計者決定用鋁砂型鑄造法制造一個分開零件，但是這個零件的工藝特性只能通過加工來完成(如螺紋孔和配合公差)，制造工程師沒有選擇的余地，只能按照先砂型鑄造在加工的方法來達到既定要求。在這個例子中，用一個在單獨步驟所需要的塑料模制品也許是一個較好的決定。因此，當(dāng)產(chǎn)品設(shè)計展開時給制造工程師一個忠告設(shè)計者的機會對產(chǎn)品的順利可造性是非常重要的。
這種被用于嘗試描述順利改變一件新產(chǎn)品的可造性的條件是制造設(shè)計(DFM)和裝配設(shè)計(DFA)。當(dāng)然，DFM和DFA是緊密相連的，因此讓我們用制造和裝配設(shè)計(DFM/A)的形式來表達。制造和裝配設(shè)計包括在一件新產(chǎn)品中的可造性和可裝配性的綜合考慮，這包括： (1)組織變化和(2)設(shè)計原理和指導(dǎo)方針。
.在DFM/A中的組織變化.? DFM/A的有效執(zhí)行包括公司組織機構(gòu)的正式或非正式的變化，因此設(shè)計職工和制造職工之間有很好的交流和交互作用。這可以通過以下方法來完成：(1)通過成立由產(chǎn)品設(shè)計者制造工程師和其他員工(例如：質(zhì)量工程師、材料專家)組成的攻關(guān)小組來進行產(chǎn)品開發(fā)；(2)通過要求設(shè)計工程師用一些事業(yè)時間在制造上，以能夠掌握第一手可造性和可裝配性是如何通過產(chǎn)品設(shè)計聯(lián)系在一起的；(3)通過指派制造工程師到產(chǎn)品設(shè)計部門在一個臨時的或?qū)Ｈ蔚幕A(chǔ)上做一個還原性顧問。
.設(shè)計說明和指導(dǎo)方針.? DFM/A為了理解如何設(shè)計一個既定產(chǎn)品來使可造性和可裝配性最大化也依賴于設(shè)計說明和指導(dǎo)方針的使用，這些通用設(shè)計指導(dǎo)方針中的一些幾乎適用于任何產(chǎn)品設(shè)計。在其他方面，一些設(shè)計原理只適用于特定工序，例如：軸或錐度在階梯中的使用和利用模制品來切除模內(nèi)零件，在制造過程中我們只把這些具體過程指導(dǎo)方針放在書本上。
指導(dǎo)方針有時互相矛盾，一條指導(dǎo)方針是“簡化零件模型，避免不必要的特征”。但是在同一表格里的另一指導(dǎo)方針為了裝配安全而規(guī)定在設(shè)計產(chǎn)品時“特殊幾何特征必須不時加上他的組成”。而且他也許值得來結(jié)合個別裝配件的特征來減少產(chǎn)品中零件的數(shù)量。在這些示例中零件制造設(shè)計與裝配設(shè)計相沖突，在這個矛盾沖突的兩邊，一個適當(dāng)解決方法必須被發(fā)現(xiàn)。
Process Planning and Concurrent Engineering
T. Ramayah and Noraini Ismail
ABSTRACT
The product design is the plan for the product and its components and subassemblies. To convert the product design into a physical entity, a manufacturing plan is needed. The activity of developing such a plan is called process planning. It is the link between product design and manufacturing. Process planning involves determining the sequence of processing and assembly steps that must be accomplished to make the product. In the present chapter, we examine processing planning and several related topics.
Process Planning
Process planning involves determining the most appropriate manufacturing and assembly processes and the sequence in which they should be accomplished to produce a given part or product according to specifications set forth in the product design documentation. The scope and variety of processes that can be planned are generally limited by the available processing equipment and technological capabilities of the company of plant. Parts that cannot be made internally must be purchased from outside vendors. It should be mentioned that the choice of processes is also limited by the details of the product design. This is a point we will return to later.
Process planning is usually accomplished by manufacturing engineers. The process planner must be familiar with the particular manufacturing processes available in the factory and be able to interpret engineering drawings. Based on the planner’s knowledge, skill, and experience, the processing steps are developed in the most logical sequence to make each part. Following is a list of the many decisions and details usually include within the scope of process planning.
? .Interpretation of design drawings.? The part of product design must be analyzed (materials, dimensions, tolerances, surface finished, etc.) at the start of the process planning procedure.
? .Process and sequence.? The process planner must select which processes are required and their sequence. A brief description of processing steps must be prepared.
? .Equipment selection. ?In general, process planners must develop plans that utilize existing equipment in the plant. Otherwise, the component must be purchased, or an investment must be made in new equipment.
? .Tools, dies, molds, fixtures, and gages.? The process must decide what tooling is required for each processing step. The actual design and fabrication of these tools is usually delegated to a tool design department and tool room, or an outside vendor specializing in that type of tool is contacted.
??.Methods analysis.? Workplace layout, small tools, hoists for lifting heavy parts, even in some cases hand and body motions must be specified for manual operations. The industrial engineering department is usually responsible for this area.
??.Work standards.? Work measurement techniques are used to set time standards for each operation.
.Cutting tools and cutting conditions.? These must be specified for machining operations, often with reference to standard handbook recommendations.
Process planning for parts
For individual parts, the processing sequence is documented on a form called a route sheet. Just as engineering drawings are used to specify the product design, route sheets are used to specify the process plan. They are counterparts, one for product design, the other for manufacturing.
A typical processing sequence to fabricate an individual part consists of: (1) a basic process, (2) secondary processes, (3) operations to enhance physical properties, and (4) finishing operations. A basic process determines the starting geometry of the work parts. Metal casting, plastic molding, and rolling of sheet metal are examples of basic processes. The starting geometry must often be refined by secondary processes, operations that transform the starting geometry (or close to final geometry). The secondary geometry processes that might be used are closely correlated to the basic process that provides the starting geometry. When sand casting is the basic processes, machining operations are generally the second processes. When a rolling mill produces sheet metal, stamping operations such as punching and bending are the secondary processes. When plastic injection molding is the basic process, secondary operations are often unnecessary, because most of the geometric features that would otherwise require machining can be created by the molding operation. Plastic molding and other operation that require no subsequent secondary processing are called net shape processes. Operations that require some but not much secondary processing (usually machining) are referred to as near net shape processes. Some impression die forgings are in this category. These parts can often be shaped in the forging operation (basic processes) so that minimal machining (secondary processing) is required.
Once the geometry has been established, the next step for some parts is to improve their mechanical and physical properties. Operations to enhance properties do not alter the geometry of the part; instead, they alter physical properties. Heat treating operations on metal parts are the most common examples. Similar heating treatments are performed on glass to produce tempered glass. For most manufactured parts, these property-enhancing operations are not required in the processing sequence.
Finally finish operations usually provide a coat on the work parts (or assembly) surface. Examples included electroplating, thin film deposition techniques, and painting. The purpose of the coating is to enhance appearance, change color, or protect the surface from corrosion, abrasion, and so forth. Finishing operations are not required on many parts; for example, plastic molding rarely require finishing. When finishing is required, it is usually the final step in the processing sequence.
Processing Planning for Assemblies
The type of assembly method used for a given product depends on factors such as: (1) the anticipated production quantities; (2) complexity of the assembled product, for example, the number of distinct components; and (3) assembly processes used, for example, mechanical assembly versus welding. For a product that is to be made in relatively small quantities, assembly is usually performed on manual assembly lines. For simple products of a dozen or so components, to be made in large quantities, automated assembly systems are appropriate. In any case, there is a precedence order in which the work must be accomplished. The precedence requirements are sometimes portrayed graphically on a precedence diagram.
Process planning for assembly involves development of assembly instructions, but in more detail .For low production quantities, the entire assembly is completed at a single station. For high production on an assembly line, process planning consists of allocating work elements to the individual stations of the line, a procedure called line balancing. The assembly line routes the work unit to individual stations in the proper order as determined by the line balance solution. As in process planning for individual components, any tools and fixtures required to accomplish an assembly task must be determined, designed, built, and the workstation arrangement must be laid out.
Make or Buy Decision
An important question that arises in process planning is whether a given part should be produced in the company’s own factory or purchased from an outside vendor, and the answer to this question is known as the make or buy decision. If the company does not possess the technological equipment or expertise in the particular manufacturing processes required to make the part, then the answer is obvious: The part must be purchased because there is no internal alternative. However, in many cases, the part could either be made internally using existing equipment, or it could be purchased externally from a vendor that process similar manufacturing capability.
In our discussion of the make or buy decision, it should be recognized at the outset that nearly all manufactures buy their raw materials from supplies. A machine shop purchases its starting bar stock from a metals distributor and its sand castings from a foundry. A plastic molding plant buys its molding compound from a chemical company. A stamping press factory purchases sheet metal either fro a distributor or direct from a rolling mill. Very few companies are vertically integrated in their production operations all the way from raw materials, it seems reasonable to consider purchasing at least some of the parts that would otherwise be produced in its own plant. It is probably appropriate to ask the make or buy question for every component that is used by the company.
There are a number of factors that enter into the make or buy decision. One would think that cost is the most important factor in determining whether to produce the part or purchase it. If an outside vendor is more proficient than the company’s own plant in the manufacturing processes used to make the part, then the internal production cost is likely to be greater than the purchase price even after the vendor has included a profit. However, if the decision to purchase results in idle equipment and labor in the company’s own plant, then the apparent advantage of purchasing the part may be lost.
Consider the following example make or Buy Decision.
The quoted price for a certain part is $20.00 per unit for 100 units. The part can be produced in the company’s own plant for $28.00. The components of making the part are as follows:
??????????????????? Unit raw material cost = $8.00 per unit
??????????????????? Direct labor cost =6.00 per unit
??????????????????? Labor overhead at 150%=9.00 per unit
??????????????????? Equipment fixed cost =5.00 per unit
????????????????? ________________________________
?????? ??????????????????????Total =28.00 per unit
Should the component by bought or made in-house ?
Solution: Although the vendor’s quote seems to favor a buy decision, let us consider the possible impact on plant operations if the quote is accepted. Equipment fixed cost of $5.00 is an allocated cost based on investment that was already made. If the equipment designed for this job becomes unutilized because of a decision to purchase the part, then the fixed cost continues even if the equipment stands idle. In the same way, the labor overhead cost of $9.00 consists of factory space, utility, and labor costs that remain even if the part is purchased. By this reasoning, a buy decision is not a good decision because it might be cost the company as much as $20.00+$5.0+$9.00=$34.00 per unit if it results in idle time on the machine that would have been used to produce the part. On the other hand, if the equipment in question can be used for the production of other parts for which the in-house costs are less than the corresponding outside quotes, then a buy decision is a good decision.
Make or buy decision are not often as straightforward as in this example. A trend in recent years, especially in the automobile industry, is for companies to stress the importance of building close relationships with parts suppliers. We turn to this issue in our later discussion of concurrent engineering.
Computer-aided Process Planning
There is much interest by manufacturing firms in automating the task of process planning using computer-aided process planning (CAPP) systems. The shop-trained people who are familiar with the details of machining and other processes are gradually retiring, and these people will be available in the future to do process planning. An alternative way of accomplishing this function is needed, and CAPP systems are providing this alternative. CAPP is usually considered to be part of computer-aided manufacturing (CAM). However, this tends to imply that CAM is a stand-along system. In fact, a synergy results when CAM is combined with computer-aided design to create a CAD/CAM system. In such a system, CAPP becomes the direct connection between design and manufacturing. The benefits derived from computer-automated process planning include the following:
??.Process rationalization and standardization.? Automated process planning leads to more logical and consistent process plans than when process is done completely manually. Standard plans tend to result in lower manufacturing costs and higher product quality.
? .Increased productivity of process planner. ?The systematic approach and the availability of standard process plans in the data files permit more work to be accomplished by the process planners.
??.Reduced lead time for process planning. ?Process planner working with a CAPP system can provide route sheets in a shorter lead time compared to manual preparation.
? .Improved legibility. ?Computer-prepared rout sheets are neater and easier to read than manually prepared route sheets.
? .Incorporation of other application programs. ?The CAPP program can be interfaced with other application programs, such as cost estimating and work standards.
Computer-aided process planning systems are designed around two approaches. These approaches are called: (1) retrieval CAPP systems and (2) generative CAPP systems .Some CAPP systems combine the two approaches in what is known as semi-generative CAPP.
Concurrent Engineering and Design for Manufacturing
Concurrent engineering refers to an approach used in product development in which the functions of design engineering, manufacturing engineering, and other functions are integrated to reduce the elapsed time required to bring a new product to market. Also called simultaneous engineering, it might be thought of as the organizational counterpart to CAD/CAM technology. In the traditional approach to launching a new product, the two functions of design engineering and manufacturing engineering tend to be separated and sequential, as illustrated in Fig.(1).(a).The product design department develops the new design, sometimes without much consideration given to the manufacturing capabilities of the company, There is little opportunity for manufacturing engineers to offer advice on how the design might be alerted to make it more manufacturability. It is as if a wall exits between design and manufacturing. When the design engineering department completes the design, it tosses the drawings and specifications over the wall, and only then does process planning begin.
Fig.(1). Comparison: (a) traditional product development cycle and (b) product development using concurrent engineering
By contrast, in a company that practices concurrent engineering, the manufacturing engineering department becomes involved in the product development cycle early on, providing advice on how the product and its components can be designed to facilitate manufacture and assembly. It also proceeds with early stages of manufacturing planning for the product. This concurrent engineering approach is pictured in Fig.(1).(b). In addition to manufacturing engineering, other function are also involved in the product development cycle, such as quality engineering, the manufacturing departments, field service, vendors supplying critical components, and in some cases the customer who will use the product. All if these functions can make contributions during product development to improve not only the new product’s function and performance, but also its produceability, inspectability, testability, serviceability, and maintainability. Through early involvement, as opposed to reviewing the final product design after it is too late to conveniently make any changes in the design, the duration of the product development cycle is substantially reduced.
Concurrent engineering includes several elements: (1) design for several manufacturing and assembly, (2) design for quality, (3) design for cost, and (4) design for life cycle. In addition, certain enabling technologies such as rapid prototyping, virtual prototyping, and organizational changes are required to facilitate the concurrent engineering approach in a company.
Design for Manufacturing and Assembly
It has been estimated that about 70% of the life cycle cost of a product is determined by basic decisions made during product design. These design decisions include the material of each part, part geometry, tolerances, surface finish, how parts are organized into subassemblies, and the assembly methods to be used. Once these decisions are made, the ability to reduce the manufacturing cost of the product is limited. For example, if the product designer decides that apart is to be made of an aluminum sand casting but which processes features that can be achieved only by machining(such as threaded holes and close tolerances), the manufacturing engineer has no alternative expect to plan a process sequence that starts with sand casting followed by the sequence of machining operations needed to achieve the specified features .In this example, a better decision might be to use a plastic molded part that can be made in a single step. It is important for the manufacturing engineer to be given the opportunity to advice the design engineer as the product design is evolving, to favorably influence the manufacturability of the product.
Term used to describe such attempts to favorably influence the manufacturability of a new product are design for manufacturing (DFM) and design for assembly(DFA). Of course, DFM and DFA are inextricably linked, so let us use the term design for manufacturing and assembly (DFM/A). Design for manufacturing and assembly involves the systematic consideration of manufacturability and assimilability in the development of a new product design. This includes: (1) organizational changes and (2) design principle and guidelines.
.Organizational Changes in DFM/A. ?Effective implementation of DFM/A involves making changes in a company’s organization structure, either formally or informally, so that closer interaction and better communication occurs between design and manufacturing personnel. This can be accomplished in several ways: (1)by creating project teams consisting of product designers, manufacturing engineers, and other specialties (e.g. quality engineers, material scientists) to develop the new product design; (2) by requiring design engineers to spend some career time in manufacturing to witness first-hand how manufacturability and assembility are impacted by a product’s design; and (3)by assigning manufacturing engineers to the product design department on either a temporary or full-time basis to serve as reducibility consultants.
.Design Principles and Guidelines. ?DFM/A also relies on the use of design principles and guidelines for how to design a given product to maximize manucturability and assembility. Some of these are universal design guidelines that can be applied to nearly any product design situation. There are design principles that apply to specific processes, and for example, the use of drafts or tapers in casted and molded parts to facilitate removal of the part from the mold. We leave these more process-specific guidelines to texts on manufacturing processes.
The guidelines sometimes conflict with one another. One of the guidelines is to “simplify part geometry, avoid unnecessary features”. But another guideline in the same table states that “special geometric features must sometimes be added to components” to design the product for foolproof assembly. And it may also be desirable to combine features of several assembled parts into one component to minimize the number of parts in the product. In these instances, design for part manufacture is in conflict with design for assembly, and a suitable compromise must be found between the opposing sides of the conflict.
工藝規(guī)程制訂與并行工程
T. Ramayah and Noraini Ismail
摘要
產(chǎn)品設(shè)計是用于產(chǎn)品，及它的部件裝配的計劃。為了把產(chǎn)品設(shè)計轉(zhuǎn)換成一個實際物體，這需要一個制造計劃。而制訂一個這樣的計劃的行
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