2351 車床變速用撥叉加工工藝及關(guān)鍵工序工裝設(shè)計(jì)

2351 車床變速用撥叉加工工藝及關(guān)鍵工序工裝設(shè)計(jì),車床,變速,用撥叉,加工,工藝,關(guān)鍵,癥結(jié),樞紐,工序,工裝,設(shè)計(jì) 南京理工大學(xué)泰州科技學(xué)院畢業(yè)設(shè)計(jì)(論文)外文資料翻譯系　　部： 機(jī)械工程系 專 業(yè)： 機(jī)械工程及自動(dòng)化 姓 名： 劉劍超 學(xué) 號(hào)： 05010125 外文出處： Process Planning and Concurrent Engineering 附 件： 1.外文資料翻譯譯文；2.外文原文。 指導(dǎo)教師評(píng)語(yǔ)：簽名： 年 月 日附件 1：外文資料翻譯譯文工序制訂與并行工程產(chǎn)品設(shè)計(jì)是用于產(chǎn)品，及它的部件裝配的計(jì)劃。為了把產(chǎn)品設(shè)計(jì)轉(zhuǎn)化成一個(gè)實(shí)際存在的物體，這需要一個(gè)制造計(jì)劃。而制訂一個(gè)這樣的計(jì)劃的行動(dòng)就叫做工序制訂。它是產(chǎn)品設(shè)計(jì)和制造之間的連接。工序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。在這篇文章中，我們將對(duì)工序制訂和他的一些相關(guān)的主題進(jìn)行解釋。首先，我們應(yīng)該區(qū)別在這篇文章中被反復(fù)提到的工序制訂和生產(chǎn)計(jì)劃。工序制訂與如何制造產(chǎn)品和它的零件等工程技術(shù)問(wèn)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？工序制訂與產(chǎn)品制造物流管理有關(guān)系。它在工序制訂后面與原料分類及獲得滿足制造充分?jǐn)?shù)量產(chǎn)品要求的資源有關(guān)。工序制訂工序制訂包括決定最適當(dāng)?shù)闹圃旒把b配步驟和順序，可計(jì)劃的工序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(chǎng)購(gòu)買。工序制訂所提及的工序選擇同樣也受到詳細(xì)設(shè)計(jì)資料的限制。我們稍后將會(huì)回到這一點(diǎn)。工序制訂通常是由制造工程師完成的。（工業(yè)工程師擁有其他權(quán)利。）工序制訂者必須熟悉工廠中詳細(xì)可用的制造流程并且能夠說(shuō)明工程圖?；谥朴喺叩闹R(shí)，技術(shù)和經(jīng)驗(yàn)，用于制造每個(gè)零件的工序步驟以最合乎邏輯的順序被發(fā)展制訂。下列各項(xiàng)是在工序制訂范圍里的許多決定和詳細(xì)資料：.設(shè)計(jì)圖的說(shuō)明. 在工序制訂的開始，產(chǎn)品設(shè)計(jì)的這一部分（材料、尺寸、公差、表面處理、等等）必須進(jìn)行分析。.工序和順序. 工序制訂者必須選擇哪一個(gè)工序是必需的及必需工序的序列。此外還必須準(zhǔn)備好一個(gè)簡(jiǎn)短的工序步驟描述。.設(shè)備選擇. 大體上，工序制訂者必須逐步展開利用工廠現(xiàn)有機(jī)器的計(jì)劃。另外，組件必須被購(gòu)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. 工序必須決定每個(gè)工序需要什么工具。這些工具的實(shí)際設(shè)計(jì)和制造通常通過(guò)委派工具設(shè)計(jì)部門和工具庫(kù)或者聯(lián)系專攻那種工具制造的外面廠商來(lái)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(dòng)作也被指定。.操作步驟. 工作測(cè)量技術(shù)被用來(lái)為每個(gè)操作設(shè)定時(shí)間標(biāo)準(zhǔn)。.切削工具和切削條件. 這些必須對(duì)加工操作通過(guò)推薦標(biāo)準(zhǔn)手冊(cè)來(lái)進(jìn)行詳細(xì)說(shuō)明。零件工序制訂對(duì)于單個(gè)零件，加工順序通過(guò)一種被稱為進(jìn)路表的表格來(lái)進(jìn)行文件證明備份。（不是所有的公司使用進(jìn)路表這個(gè)名字；另外的一個(gè)名字是“操作說(shuō)明書?！?）就如工程圖被用于詳細(xì)說(shuō)明產(chǎn)品設(shè)計(jì)一樣，進(jìn)路表被用于詳細(xì)說(shuō)明工序計(jì)劃。他們是類似的，一個(gè)用于產(chǎn)品設(shè)計(jì)，另一個(gè)用于制造。典型的進(jìn)路表，如圖21.1 中舉例，包括下列信息：（1）所有工作部分要執(zhí)行的操作都按照他們應(yīng)當(dāng)被執(zhí)行的順序列出來(lái)；（2）一個(gè)指出關(guān)于零件圖尺寸公差必須完成加工的每個(gè)操作的簡(jiǎn)短描述；（3）用于完成這個(gè)操作的特定設(shè)備；（4）象沖模，鉆模，切削刀具，鉆夾具或夾具，和量具這樣的特定工具。一些公司還包括時(shí)間設(shè)置，周期標(biāo)準(zhǔn)和其他數(shù)據(jù)。他被稱為進(jìn)路表是因?yàn)楣ば蝽樞蛞?guī)定了零件在工廠中必須遵循的路線。如表21-1中，列出了在準(zhǔn)備一個(gè)進(jìn)路表時(shí)所需要的一些指導(dǎo)方針。進(jìn)路表 包含 XYZ 在內(nèi)的機(jī)械工廠零件號(hào)081099材料 1050 H18 A1序號(hào)零件名稱發(fā)電機(jī)軸 產(chǎn)品尺寸 60mm diam,206mm length操作內(nèi)容面向末端(0.003mm). 粗車直徑至52.00mm.在 50.00mm 處結(jié)束車削面向并車削長(zhǎng) 15.00mm 直徑為 42.00mm的軸肩退刀結(jié)束.表面加工至 200.00mm 長(zhǎng).粗車直徑到 52.0mm.至 50.mm 車削結(jié)束.鉆 4 個(gè)直徑為 7.5mm 的孔銑 6.5mm 深 x 方向 5.00mm 寬的槽在對(duì)面銑寬 10.00mm 的槽制訂者M(jìn)PGroover校核: N.Needed日期08/12/xx頁(yè)數(shù) 1/1注釋加工方法 設(shè)備 裝備 時(shí)間設(shè)置 操作時(shí)間1020304050latheL45DrillMillMillL45G0810D09M32F630G08100.7hrJ555F6621.5hr1.0hr3.0min.0.5hr0.7hr4.8min5.2min3.2min6.2min圖 21.1 詳細(xì)說(shuō)明工序計(jì)劃的典型進(jìn)路表表 21-1 準(zhǔn)備一個(gè)進(jìn)路表的典型指導(dǎo)方針連續(xù)操作步驟的操作序號(hào)應(yīng)該以 10，20，30，等形式列出。如果必要的話這允許插入新的操作。當(dāng)一個(gè)工件從一個(gè)工作站到另一個(gè)工作站， 新的操作和序號(hào)必須進(jìn)行詳細(xì)說(shuō)明。當(dāng)一個(gè)工件從一個(gè)夾具到另一個(gè)夾具，盡管有可能在同一設(shè)備上，新的操作和序號(hào)也必須進(jìn)行詳細(xì)說(shuō)明。當(dāng)在一條生產(chǎn)線上如果一個(gè)工件從一個(gè)工人到另一個(gè)工人，新的操作和序號(hào)也必須進(jìn)行詳細(xì)說(shuō)明。開始原料基礎(chǔ)工序二級(jí)工序 特性加強(qiáng)工序 最后工序 完成零件特性加強(qiáng)工序不一定是必須的在特性加強(qiáng)之后,有時(shí)需要一些二級(jí)工序圖 21.2 在零件制造中的典型工序順序制造單個(gè)零件的典型加工順序包括：（1）一個(gè)基本工序， （2）二級(jí)工序，（3） 提高物質(zhì)特性工序，和（3）最后工序。在圖 21.2 中顯示了這種序列。一個(gè)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(shí)例。 起始造型常常必須通過(guò)改變起始造型操作（或者接近于最終造型）的二級(jí)工序來(lái)精制。二級(jí)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(jí)工序。當(dāng)軋鋼廠制造金屬片是基本工序，沖壓操作象沖裁和彎曲通常是二級(jí)工序。當(dāng)塑料注入成型是基本工序時(shí)，二級(jí)工序通常是不必要的，因?yàn)樗拇蠖鄶?shù)幾何特征制造通過(guò)別的方式如成型制造來(lái)完成。塑料成型和其他操作的二級(jí)工序被稱為凈成型工序的并發(fā)二級(jí)工序。需要一些但并不多的二級(jí)工序的操作就是所提到的近似凈成型工序。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(jí)工序）階段被成型，因此減少了必要的加工（二級(jí)工序）。一旦模型被建立，許多零件的下一步是改良它們的機(jī)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(shí)例。類似的如玻璃通過(guò)熱處理來(lái)制造鋼化玻璃。對(duì)于大多數(shù)零件的制造來(lái)說(shuō)，這些特性加強(qiáng)工序如在圖 21.2 指出的可選擇路徑那樣在加工工序中并不需要。 最后工序通常對(duì)零件（或裝配體）的表面提供一個(gè)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(hù)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。表 21-2 列出了一些普通原料加工的典型加工順序：表 21-2 一些典型加工順序基本工序 開始原料 二級(jí)工序 最后成型 加強(qiáng)工序 最后工序砂型鑄造 砂型鑄件 加工 車加工零件 （可選擇） 涂漆拉摸鑄造 拉摸鑄件 （凈成型） 拉摸鑄造 （可選擇） 涂漆玻璃鑄造 玻璃錠 擠壓 ，吹塑法玻璃器皿 熱處理 （無(wú)）注塑成型 模型制品 （凈成型） 成型塑料 （無(wú)） （無(wú)）軋?jiān)?金屬片 l 切割模彎曲模沖壓 （無(wú)） 電鍍 噴漆軋?jiān)?金屬片 l 深沖壓 沖壓 （無(wú)） 電鍍 噴漆鍛造 鍛件 （凈成型） 加工機(jī)加工件 （無(wú)） 電鍍 噴漆軋?jiān)?棒材拉拔 棒料 磨削加工 機(jī)加工件 熱處理 電鍍 噴漆擠壓鋁 壓出型材 切削 擠壓零件 （無(wú)） 陽(yáng)極電鍍 噴漆霧化 金屬粉末 擠壓 PM 零件 燒結(jié) 噴漆粉碎 陶器粉末 擠壓 陶器 燒結(jié) 上釉錠拉拔 矽塊 鋸和碾磨 硅片 清洗鋸 和 磨削 矽塊 氧化，CVD，PVD蝕化IC 芯片 表面處理裝配工序制訂一個(gè)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）常用裝配工序，例如，機(jī)械定位焊接。對(duì)于小數(shù)量產(chǎn)品，通常在人工裝配線上進(jìn)行裝配。對(duì)于大量制造的一打或這樣組件的簡(jiǎn)單零件，要采用適當(dāng)?shù)淖詣?dòng)化裝配線。無(wú)論如何，這里有一個(gè)工作必須被完成的優(yōu)先順序。這個(gè)優(yōu)先需求經(jīng)常用一個(gè)優(yōu)先表來(lái)進(jìn)行圖表描繪。裝配工序制訂包括裝配指令的發(fā)展，但是更詳細(xì)地，對(duì)于小批量生產(chǎn)，在一個(gè)崗位完成整個(gè)裝配。對(duì)于一個(gè)裝配線上的大批量生產(chǎn)，工序制訂由一種分配工作條件到裝配線個(gè)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(gè)別工位。在個(gè)別組成，任意工具或夾具的工序制訂時(shí)，一條裝配線的決定，設(shè)計(jì)，和制造必須被完成,并且工作站的必須被列出來(lái)。制造或購(gòu)買決定在工序制定過(guò)程中出現(xiàn)的一個(gè)重大問(wèn)題是一個(gè)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(gòu)買，并且這個(gè)問(wèn)題的答案被認(rèn)為是制造或購(gòu)買決定。如果公司沒(méi)有技術(shù)設(shè)備或制造零件所必須的詳細(xì)制造工序中的專門技術(shù)，那么答案就很明顯了：因?yàn)闆](méi)有其他選擇零件必須購(gòu)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(gòu)買。在我們的關(guān)于制造或購(gòu)買的決定的討論中，他應(yīng)該認(rèn)識(shí)到在開始幾乎所有的制造者從供應(yīng)商那里購(gòu)買原料。一個(gè)機(jī)械加工廠從一個(gè)金屬經(jīng)銷商購(gòu)買他的起動(dòng)柄原料或從一個(gè)鑄造廠購(gòu)買他的砂型鑄件。一個(gè)塑料成型廠從一個(gè)化工廠購(gòu)買他的模塑料。一個(gè)沖壓廠可以去經(jīng)銷商或直接從軋鋼廠購(gòu)買金屬片。很少的公司能夠在操作中從原料一直進(jìn)行垂直整合，這看來(lái)至少購(gòu)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(gè)組成要求制造或購(gòu)買決定。這里有許多影響制造或購(gòu)買決定的因素。在表 21-3 中列出一列影響決定的因素和結(jié)果。一個(gè)人可能認(rèn)為成本是決定是購(gòu)買還是制造零件的最重要的因素。如果一個(gè)外部經(jīng)銷商比公司工廠更精通于制造零件的工序，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(jià)格還要高?？墒牵绻?gòu)買決定導(dǎo)致公司工廠設(shè)備和勞動(dòng)的閑置，可是購(gòu)買零件的表面優(yōu)勢(shì)就會(huì)喪失。考慮以下例子，例 21.1 制造或購(gòu)買決定為一個(gè)特定零件被引述的價(jià)格是 100 個(gè)單位的每單位$20.00。制造零件的成分如下所示：?jiǎn)挝辉铣杀?每單位$8.00直接勞動(dòng)成本=每單位 6.00勞動(dòng)加班 150%=每單位 9.00設(shè)備修理成本=每單位 5.00總計(jì)=每單位 28.00表 21-3 制造或購(gòu)買決定因素因素 在制造或購(gòu)買決定的說(shuō)明和效果零件成本是如何比較的？ 這也許被看作是在制造或購(gòu)買決定的最重要的因素。然而，成本比較并不明顯，如例21.1這種加工可以在內(nèi)部使用嗎？ 如果一個(gè)給定工序的設(shè)備和專門技術(shù)在內(nèi)部不能用，那么購(gòu)買是顯而易見(jiàn)的決定。經(jīng)銷商經(jīng)常適合精通特定工序，這使得他們?cè)趦?nèi)外比較中有較強(qiáng)的成本競(jìng)爭(zhēng)力。然而，如果公司不發(fā)展在對(duì)于制造該類型產(chǎn)品的重要特定工序的專門技術(shù)，這將影響公司的長(zhǎng)期成本運(yùn)算。什么是產(chǎn)品總產(chǎn)量？ 必需的單位總數(shù)在產(chǎn)品的生命上是主要因數(shù)。如果總生產(chǎn)量增大，這用意支持制造決定。較低的生產(chǎn)量支持購(gòu)買決定。什么是產(chǎn)品預(yù)期壽命？ 較長(zhǎng)的產(chǎn)品壽命趨向于支持這種決定組成是不是一個(gè)標(biāo)準(zhǔn)項(xiàng)目？ 標(biāo)準(zhǔn)目錄項(xiàng)目（舉例來(lái)說(shuō)，硬件項(xiàng)目如螺栓，螺釘，螺母，和其他標(biāo)準(zhǔn)件）由那些專門制造這種產(chǎn)品的廠商以低成本制造。在標(biāo)準(zhǔn)件上，成本比較幾乎一直支持一個(gè)購(gòu)買決定供應(yīng)商是否值得信賴？ 一個(gè)經(jīng)銷商在關(guān)鍵零件的交貨延誤將導(dǎo)致公司總裝配廠的停工。擁有保證交貨期和質(zhì)量報(bào)告的供應(yīng)商比那些有較少報(bào)告的供應(yīng)商要受到優(yōu)先考慮的。公司工廠是不是已經(jīng)全能力操作？ 在最高要求周期中，公司也許被迫從外部經(jīng)銷商購(gòu)買一部分必需的產(chǎn)品來(lái)增大列出工廠設(shè)備能力。公司需要一個(gè)其它可能的供給來(lái)源嗎？ 公司有時(shí)為他們的生產(chǎn)工廠從外部經(jīng)銷商購(gòu)買的零件來(lái)維持可選擇的貨源。附件 2：外文原文Process Planning and Concurrent EngineeringThe 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.At the outset ,we should distinguish between process planning and production planning ,which is covered in the following chapter. Process planning is concerned with the engineering and technological issues of how to make the products and its parts. What types of equipment and tooling are required to fabricate the parts and assemble the product ? Production planning is concerned with the logistics of making the product .After process planning is concerned with ordering the materials and obtaining the resources required to make the product in sufficient quantities to satisfy demand for it.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 .（Other titles include in industrial engineer.) 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 partsFor individual parts,the processing sequence is documented on a form called a route sheet .(Not all companies use the name route sheet ;another name is “operation 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 route sheet ,illustrated in Fig.21.1,includes the following information: (1) all operations to be performed on the work part ,listed in the order in which they should be performed ; (2) a brief description of each operation indicating the processing to be accomplished,with references to dimensions and tolerances on the part drawing; (3) the specific machines on which the work to be done; and (4) special tooling such as dies molds ,cutting tools,jigs or fixtures ,and gages.Some companies also include setup times ,cycle time standards,and other data.It is called a route sheet because the processing sequence defines the route that the part must follow in the factory .Some of the guidelines in preparing a route sheet are listed in Table 21-1.Decisions on process to be used to fabricate a given part are based largely on the starting material for the part .This starting material is selected by the product designer.Once the material has been specified ,the range of the possible processing operation is reduced considerably .The product designer’s decisions on starting material are based primarily on functional requirements ,although economics and manufacturability a role in the selection.Route Sheet XYZ Machine Shop,Inc.Part no.081099Material 1050 H18 A1No.Part name Shaft ,generatorStock size 60mm diam,206mm lengthOperation descriptionFace end (approacx.3 mm).Rough turn to 52.00 mm diam Finish turn to 50.00 mm diam.Face and turn shoulder to 42.00 mm diam.and 15.00 mm lenghthReverse end.Face end to 200.00mm length.Rough turn to 52.00mm diam.Finish turn to 50.00mm diam Drill 4radial holes 7.50mm diamMill 6.5 mm deep X 5.00 mm wide slotMill 10.00 mm wide flat ,opposite side.PlannerMPGrooverCheck by: N.NeededDate 08/12/xxPage 1/1CommentsDept Machine Tooling Setup Sdt1020304050latheL45DrillMillMillL45G0810D09M32F630G08100.7hrJ555F6621.5hr1.0hr3.0min.0.5hr0.7hr4.8min5.2min3.2min6.2minFig.21.1 Typical routes sheet for specifying the process plan Table 21-1 Typical Guidelines in Preparing a Route Sheet.Operation numbers for consecutive processing steps should be listed as 10,20,30,etcThis allows new operations to be inserted if necessary..A new operation and number shouled be specified when a work part leaves one workstation and is transferred to another station..A new operation and number should be specified if a part is transferred to another workholder(e.g...,jig or fixture),even if it is on the same machine tool..A new operation and number should be specified if the work part is transferred from one worker to another ,as on a production line.Starting raw materialBasic processSecondary process Property-enhancing processesFinishing operations Finished partProperty-enhancing processes not always required Additionary secondary processes sometimes required following property enhancementFig.21.2 Typical sequence of processes required in part fabricationA 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.The sequence is shown in Fig.21.2. A basic process determines the starting geometry of the workpart.Metal casting ,plastic molding ,and roling 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 ,as indicated by the alternative arrow path in Fig.21.2.Finally finish operations usually provide a coat on the work parts (or assembly )surface. Examples inclued 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 .Table 21-2 presents some typical processing sequences for common materials used in manufacturing .In most cases,parts and materials arriving at the factory have complete their basic process.Thus ,the first operation in the process plan follows the basic process that has provided the starting geometry of the part ..For example ,machined parts begain as bar stock or castings or forgings,which are purchased from outide vendors.The process plan begains with the machining operations in the company’s own plant .Stempings begin as sheet metal coils or strips that are bought from the rolling mill.These raw materials are supplied outside sources so that the secondary processes,property-enhancing operations ,and finishing operatios can be performed in the company’s own factory.In addition to the route sheet ,a more detailed description of eac operation is usually prepared. This is filed in the particular production department office where the operation is performed.It lists specific details of the operation ,such as cutting conditionsand toolings(if the operation is machining )and other instructions that may be useful to the amchine operator.The desciptions often include sketches of the machine setup.Table 21-2 Some Typical Process SequenceBasic Process Starting MaterialSecondary processes Final shape Enhancing ProcessesFinishing ProcessesSand casting Sand casting Machining Machined part(optional) PaintingDie casting Die casting (Net shape) Die casting (optional) PaintingCasting of glassGlass ingot Pressing ,blow moldingGlass ware Heat treatment(None)Injection modeling Molded part (Net shape) Plastic Molding(None) (None)Rolling Sheet metal Blanking punching bending formingStamping (None) Plating paintingRolling Sheet metal Deep drawing Drawing (None) Plating paintingForging Forging (near net shape) MachiningMachined part (None) Plating paintingRolling and bar drawing Bar stock Machining grinding Machined partHeat treatmentPlating paintingExtrusion of aluminum Extrudate Cutoff Extruded part(None) Painting anodizingAtomize Metal powdersPress PM part Sinter PaintComminution Ceramic powderspress Ceramic wareSinter GlazeIngot pulling Silicon boule Sawing and grinding Silicon wafer CleaningSawing and grindingSilicon boule Oxidation,CVD,PVDetchingIC chip CoatingProcessing Planning for AssembliesThe 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,and 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 .We have complied a list of the factors and issues that affect the decision in Table 21-3 .One would think that cost is the most i