【機(jī)械類畢業(yè)論文中英文對(duì)照文獻(xiàn)翻譯】利用三坐標(biāo)測(cè)量?jī)x確定聚苯乙烯材料表面形態(tài)

【機(jī)械類畢業(yè)論文中英文對(duì)照文獻(xiàn)翻譯】利用三坐標(biāo)測(cè)量?jī)x確定聚苯乙烯材料表面形態(tài),機(jī)械類畢業(yè)論文中英文對(duì)照文獻(xiàn)翻譯,機(jī)械類,畢業(yè)論文,中英文,對(duì)照,對(duì)比,比照,文獻(xiàn),翻譯,利用,應(yīng)用,坐標(biāo),測(cè)量?jī)x,確定,肯定,聚苯乙烯,材料,表面,形態(tài) 附錄1 利用三坐標(biāo)測(cè)量?jī)x確定聚苯乙烯材料表面形態(tài) D·艾奇遜 R·蘇萊曼 新西蘭克賴斯特徹奇坎特伯雷大學(xué)機(jī)械工程學(xué)院 【摘要】由于泡沫材料的用途廣泛，全世界材料市場(chǎng)對(duì)它的需求量迅速上升。泡沫材料被廣泛應(yīng)用與汽車工業(yè)、食品包裝工業(yè)、醫(yī)療衛(wèi)生、運(yùn)動(dòng)器械、家庭用具、海岸浮標(biāo)及救生圈,和小型船只等。因?yàn)榕菽牧系氖褂么蟠箨P(guān)系到人們的日常生活，所以有必要通過(guò)改變切割和加工的速度使它形成各種不同的形狀。這種利用計(jì)算機(jī)輔助切割機(jī)床或全自動(dòng)切割機(jī)才能達(dá)到。但是，切割的速度將會(huì)影響到材料加工后的表面粗糙度。所以，為達(dá)到優(yōu)質(zhì)的表面加工質(zhì)量，有必要確定聚苯乙烯的表面形態(tài)。當(dāng)前，人們正在研究制造一臺(tái)用于這種泡沫材料的快速原型制造設(shè)備，研究的第一階段就是在不同種類的金屬切割絲在不同的溫度下用不同的進(jìn)給量切削后利用坐標(biāo)測(cè)量?jī)x確定聚苯乙烯表面形態(tài)。 【關(guān)鍵字】 聚苯乙烯 表面形態(tài) 熱切割絲 1． 簡(jiǎn)介 當(dāng)今世界材料市場(chǎng)對(duì)泡沫材料的需求量正迅速上升。泡沫材料可分成兩大類，即柔性泡沫和剛性泡沫。柔性泡沫材料主要用于家具，運(yùn)輸工具、床墊、地毯、包裝、玩具、運(yùn)動(dòng)器材和鞋子等，同時(shí)也被用于實(shí)現(xiàn)共振和吸音。剛性泡沫材料經(jīng)常被用于建筑行業(yè)、絕緣隔離裝置、管道、罐子、浮漂和裝食物和飲料的容器等。⑴泡沫材料被如此廣泛地應(yīng)用，總的來(lái)說(shuō)可以概括為以下幾點(diǎn)原因： ① 泡沫材料經(jīng)濟(jì)實(shí)用； ② 泡沫材料適合于室內(nèi)和戶外使用； ③ 泡沫材料能被涂上一層各種不同的材料以達(dá)到任何設(shè)計(jì)的光潔度； ④ 泡沫材料質(zhì)量輕，運(yùn)輸安裝方便。 泡沫材料的是生產(chǎn)可以用各種不同的技術(shù)方法得以實(shí)現(xiàn)。生產(chǎn)連續(xù)泡沫板材的最常用方法是通過(guò)注入包括二甲苯異氰酸鹽、聚醚多元醇等石油化工藥劑和水的混合原料，這些原料可以被用來(lái)進(jìn)行再生和再加工。不同的添加劑混合在一起以達(dá)到專門的特性。如顏色、活化吸收功能、作用于紫外線及其它一些特性。 這種方法生產(chǎn)的泡沫此時(shí)仍然處于原始狀態(tài)，接下的工作就是要把這些混合物加工成不同的形狀和尺寸的材料。通常有切削的方法就能達(dá)到。切削泡沫材料有兩種主要的方法，即發(fā)熱切割絲切割和振動(dòng)式切片法。兩者分別適合于生產(chǎn)不同特性的泡沫材料。振動(dòng)式切片法主要用于生產(chǎn)具有簡(jiǎn)單幾何形狀的剛性泡沫，而發(fā)熱切割絲切割法適用于加工復(fù)雜幾何形體的柔性泡沫材料。當(dāng)前，著兩種加工技術(shù)只作為人工的或半自動(dòng)生產(chǎn)生產(chǎn)方式。⑵ 2. 三坐標(biāo)測(cè)量?jī)x（CMM） 在做進(jìn)一步討論之前,有必要對(duì)作為一種工具被用于確定聚苯乙烯表面形態(tài)這項(xiàng)研究的坐標(biāo)測(cè)量?jī)x進(jìn)行一些說(shuō)明。一臺(tái)三坐標(biāo)測(cè)量?jī)x(以下簡(jiǎn)寫為CMM)具有一個(gè)測(cè)量工件上各點(diǎn)的探針。這就像用手指去丈量地圖上的坐標(biāo)，探針就相當(dāng)于手指，在工件表面觸碰或觸摸一定的區(qū)域。工件上的每一個(gè)點(diǎn)對(duì)于儀器的坐標(biāo)系都是對(duì)立的，而這個(gè)坐標(biāo)系描述了測(cè)量?jī)x的運(yùn)動(dòng)情況。 通常有兩種類型的坐標(biāo)系，第一個(gè)叫做機(jī)器坐標(biāo)系，它的X，Y，Z軸分別表示CMM探針的移動(dòng)方向，第二個(gè)叫做工件坐標(biāo)系，它上面的三軸對(duì)應(yīng)于工件的基準(zhǔn)。一個(gè)基準(zhǔn)確定工件上的一個(gè)特定部位的位置。這個(gè)部位可以是一個(gè)孔，一個(gè)面或是一個(gè)槽。CMM通過(guò)測(cè)量一個(gè)工件坐標(biāo)來(lái)確定兩個(gè)特定部位的距離。它也能被用來(lái)確定質(zhì)地較軟的物體的表面形態(tài)或表面粗糙度，比如聚苯乙烯。 以下實(shí)驗(yàn)中使用的CMM是Discovery系列坐標(biāo)測(cè)量?jī)xModel D-12(如圖1a)。機(jī)器利用一個(gè)固體探針或電子探測(cè)頭觸摸被測(cè)試件的表面來(lái)收集數(shù)據(jù)。這個(gè)實(shí)驗(yàn)使用了電子探測(cè)頭。由于該探測(cè)頭在工作時(shí)頭部的微小側(cè)滑將會(huì)影響到數(shù)據(jù)的正確讀取，所以它工作時(shí)必須與被測(cè)工件表面保持垂直正交以獲得最準(zhǔn)確的數(shù)據(jù)信息。在筆者的實(shí)驗(yàn)室里可使用的探測(cè)頭頭部接觸信號(hào)傳輸元件直徑有1.0、2.0、3.0、4.0和5.0mm五種。由于聚苯乙烯比較軟，更小尺寸的接觸信號(hào)傳輸元件在觸摸工件表面時(shí)可能會(huì)導(dǎo)致新的斜面或坑洞的產(chǎn)生，因此在這個(gè)實(shí)驗(yàn)中使用了一個(gè)直徑為3.0mm的紅寶石傳輸元件。（如圖b1）。較大尺寸的元件相對(duì)就會(huì)減少導(dǎo)致聚苯乙烯表面產(chǎn)生斜面或坑洞的可能性。所以用直徑用3.0mm的傳輸元件可以避免上述現(xiàn)象的發(fā)生而減少數(shù)據(jù)讀取誤差。（如圖c1 和d） 3.表面形態(tài) 表面形態(tài)或者表面粗糙度包括表面刮擦痕跡和碎片痕跡，這種認(rèn)識(shí)被普遍接受。這些痕跡彼此分開但相對(duì)緊密地排列，這使得他們很難被測(cè)量到。究竟為什么工程師們要不怕麻煩地去測(cè)量表面粗糙度呢？主要原因是被測(cè)的表面經(jīng)常與其它表面相關(guān)。通過(guò)了解工件表面的形態(tài)，接觸位置的狀態(tài)和相接觸的各種部件的表現(xiàn)都被控制了。 (d) 圖1 (a)本次實(shí)驗(yàn)使用的CMM；(b)在顯微鏡下觀測(cè)到的聚苯乙烯表 (c)典型探針直徑；(d)本次實(shí)驗(yàn)中用的探針 區(qū)分表面形態(tài)和表面粗糙度的不同是很有必要的。表面形態(tài)是柔性材料表面的幾何屬性，如聚苯乙烯或海綿。要測(cè)量柔性材料表面粗糙度是一項(xiàng)非常困難和具有挑戰(zhàn)性的工作，但最終也能做到。[3]。表面粗糙度更多地被認(rèn)為是一種無(wú)規(guī)則或者凹凸不平的表面狀態(tài)，通常是在堅(jiān)硬的材料表面進(jìn)行測(cè)量[4]。這樣定義它們有利于開發(fā)和鑒定測(cè)量工件硬度的技術(shù)和等級(jí)。 假如表面粗糙度需要遵循一個(gè)書面的標(biāo)準(zhǔn)，那很少有這樣的書面標(biāo)準(zhǔn)可以參考。最常用的就是1961年英國(guó)標(biāo)準(zhǔn)學(xué)會(huì)BS1134出版的Centre-line A verage Height Method for Assessment of Surface Texture。當(dāng)前機(jī)械工業(yè)中常用的另一個(gè)標(biāo)準(zhǔn)就是1984年頒布的國(guó)際標(biāo)準(zhǔn)體系第一版第12—15頁(yè)中的Surface Roughness-Terminology-Part 1-surface and Its Parameters。測(cè)量標(biāo)準(zhǔn)基于掃描一機(jī)械實(shí)體表面后得到的外形輪廓。要得到一個(gè)經(jīng)仔細(xì)評(píng)價(jià)的粗糙度標(biāo)準(zhǔn)，就要涉及到ISO組織出版的國(guó)家標(biāo)準(zhǔn)。后者可以與國(guó)家參考實(shí)驗(yàn)室聯(lián)系查閱到。這些實(shí)驗(yàn)室有英聯(lián)邦國(guó)家物理實(shí)驗(yàn)室，德國(guó)Physikalishe Technishe Bundesabstalt，美國(guó)國(guó)家標(biāo)準(zhǔn)與技術(shù)研究所和法國(guó)d’Essais國(guó)家實(shí)驗(yàn)室。 4.柔性材料表面形態(tài) 涉及到測(cè)量柔性材料諸如聚苯乙烯及其它泡沫材料的表面粗糙度時(shí)往往問題就會(huì)產(chǎn)生。有一種恰當(dāng)?shù)臏y(cè)量方法就是運(yùn)用光學(xué)技術(shù)，然而由于運(yùn)用光學(xué)技術(shù)只仔細(xì)關(guān)注局部位置，如試樣表面那些比較陡的斜坡，就像動(dòng)力學(xué)只關(guān)注結(jié)構(gòu)一樣，會(huì)使反饋失真。其它一些光學(xué)技術(shù)遇到的問題是當(dāng)掃描到較陡的斜破時(shí)沒有足夠的光反射回探測(cè)系統(tǒng)。 這就是此項(xiàng)研究要使用CMM的原因。CMM之所以能測(cè)量聚苯乙烯表面形態(tài)是因?yàn)榫郾揭蚁┍砻嬗卸傅男逼?。用顯微鏡觀測(cè)后發(fā)現(xiàn)這些陡坡的形狀非常有規(guī)律。測(cè)試的結(jié)果如圖2所示。我們可以注意到，坡越陡CMM讀取數(shù)據(jù)后繪制的線越長(zhǎng)。 5.實(shí)驗(yàn)技術(shù) 在這項(xiàng)研究中，設(shè)計(jì)了一臺(tái)用線切割技術(shù)切割聚苯乙烯的簡(jiǎn)單機(jī)器。這臺(tái)機(jī)器在一維空間上切割聚苯乙烯材料，即水平方向向工件輸送熱切割絲。用熱絲切割泡沫材料尤其是聚苯乙烯的方法很常用。熱切割絲的兩端與一個(gè)電源相連，當(dāng)切割絲兩端的溫度不一致時(shí)熱量就會(huì)沿著切割絲傳遞。熱量按照一定的溫度梯度沿切割絲從溫度高的部位傳遞到溫度低的部位，這樣來(lái)實(shí)現(xiàn)熱的傳導(dǎo)。熱切割絲的一頭與一個(gè)熱電偶相連，用來(lái)讀取切割絲的溫度。我們通過(guò)控制熱切割絲兩端的電壓和流過(guò)切割絲上的電流就能夠控制切割絲的溫度了。是實(shí)驗(yàn)中用到的溫度為100、200和300℃。 這個(gè)實(shí)驗(yàn)的目的就是要通過(guò)用CMM測(cè)量用不同材料的切割絲，不同的溫度和不同的切割絲給進(jìn)速度來(lái)呈現(xiàn)聚苯乙烯的各種表面形態(tài)。它的表面形態(tài)的變化取決于熱線切割機(jī)的切割絲材料、溫度和切割絲的給進(jìn)速度。 被測(cè)試的材料工件是長(zhǎng)度為300mm，寬300mm，厚50mm的聚苯乙烯。之所以選擇這樣的尺寸是因?yàn)樵谶M(jìn)行檢測(cè)時(shí)方便抓握。用于切割的切割線有鎳鉻合金切割絲、Inconel和鎳鉻鐵彈簧絲[5]。選擇使用Inconel和鎳鉻鐵彈簧絲是由于它們?cè)诒挥糜诟邷厍懈詈笥斜３中螤畹哪芰6][7]。而選擇鎳鉻合金切割絲是因?yàn)樗乔懈罹郾揭蚁r(shí)最常用的切割絲。 聚苯乙烯在不同的溫度下，不同的切割絲給進(jìn)速度和不同類型的切割絲被切割。切割時(shí)的給進(jìn)速度范圍從100到500mm/min。在每次切割后，聚苯乙烯工件的表面就用CMM測(cè)量上面的20個(gè)測(cè)點(diǎn)。在這個(gè)實(shí)驗(yàn)開始之前，我們測(cè)試了大量的測(cè)量用接觸點(diǎn)。用CMM進(jìn)行10到200次測(cè)量試驗(yàn)以調(diào)整測(cè)量用的測(cè)點(diǎn)。調(diào)整測(cè)點(diǎn)的測(cè)試次數(shù)越多，本次測(cè)量時(shí)間就越長(zhǎng)。試驗(yàn)結(jié)果表明，測(cè)試次數(shù)為20和200次的情況非常相似，所以在本次測(cè)量中選擇了20個(gè)測(cè)點(diǎn)。 6.結(jié)果 實(shí)驗(yàn)中聚苯乙烯的表面形態(tài)用CMM直接計(jì)算和記錄下來(lái)。用不同的切割線，溫度和切割給進(jìn)速度，聚苯乙烯材料被切割成厚度為10mm的小塊，然后，CMM就分別在這些小塊表面檢測(cè)20個(gè)點(diǎn)。圖3顯示了用鎳鉻合金切割絲在100℃，給進(jìn)速度為100mm/min進(jìn)行切割，材料形成的表面形態(tài)數(shù)值為0.551個(gè)單位。最好的表面形態(tài)值應(yīng)該接近0。圖3同時(shí)顯示出用鎳鉻合金切割絲切割聚苯乙烯材料時(shí)最適合的切割溫度為200℃，最適合的給進(jìn)速度為200mm/min。當(dāng)給進(jìn)速度大于200mm/min時(shí)，切割絲容易滑動(dòng)和彎曲，這會(huì)影響到切割的質(zhì)量，進(jìn)而影響到聚苯乙烯的表面形態(tài)。圖4比較了三種材料切割絲在100℃時(shí)切割表現(xiàn)。 圖2 用CMM測(cè)量結(jié)果輸出樣本 最好的表面形態(tài)質(zhì)量是用英科耐爾合金材料(Inconel)切割絲在100℃和200mm/min給進(jìn)速度是形成的。這時(shí)的表面形態(tài)值僅為0.14個(gè)單位。我們注意到，英科耐爾合金材料(Inconel)切割絲在給進(jìn)速度為500mm/min時(shí)仍然可以進(jìn)行工作，但這時(shí)形成的工件表面形態(tài)質(zhì)量是很差的。 圖3 直徑為1.0mm的鎳鉻合金切割絲在不同給進(jìn)速度下切割后的表面形態(tài)比較 圖4在100℃下不同給進(jìn)速度切割后的表面形態(tài)比較 圖5顯示了三種切割絲在200℃時(shí)的切割表現(xiàn)。在這個(gè)溫度下，英科耐爾合金材(Inconel)切割絲和鎳鉻鐵彈簧絲在給進(jìn)速度為500mm/min時(shí)也仍然可以繼續(xù)工作。最好的表面形態(tài)質(zhì)量是Inconel在給進(jìn)速度為300mm/min時(shí)形成的。但是，只有鎳鉻鐵彈簧絲在各種不同給進(jìn)速度下進(jìn)行切割時(shí)所形成的表面形態(tài)值保持在1.0個(gè)單位以下。 圖5在200℃下不同給進(jìn)速度切割后的表面形態(tài)比較 7.討論 前面已經(jīng)提到，之所以選擇英科耐爾合金材(Inconel)和鎳鉻鐵彈簧絲是由于它們?cè)?00、200和300℃溫度下進(jìn)行切割作業(yè)后仍能保持原來(lái)的形狀。選擇鎳鉻合金切割絲是因?yàn)樗乔懈罹郾揭蚁┎牧献畛Ｓ玫那懈罱z。保持切割絲的形狀不變是一個(gè)非常重要的性能指標(biāo)，因?yàn)榍懈罱z的彎曲變形直接影響到切割聚苯乙烯后形成的表面形態(tài)質(zhì)量。 圖6比較了實(shí)驗(yàn)中用到的三種切割絲對(duì)應(yīng)的彈性率。假設(shè)檢測(cè)前切割絲被做成環(huán)狀，就像一個(gè)彈簧，彈性率的計(jì)算公式如下： 其中 R—彈性率 G—剪切模數(shù) d—切割絲直徑 n—線圈數(shù) D—線圈直徑平均值 它的單位是力每偏差單位（或力每毫米）。彈性率實(shí)際上分散了偏差所要求產(chǎn)生的力[8]。下面這個(gè)圖表比較了三種材料切割絲的彈性率。我們從圖中不難看出，彈性率越高，恢復(fù)形狀的能力越大。圖6表明，選擇鎳鉻合金切割絲彈性率最大，因此這種切割絲能夠保持自己原來(lái)的形狀。 圖6 直徑為1毫米切割絲在不同線圈直徑下的彈性率比較 然而，基于這些實(shí)驗(yàn)，切割工件后產(chǎn)生的最好表面形態(tài)的是用英科耐爾合金材料(Inconel)切割絲在200℃下用300mm/min的給進(jìn)速度切割時(shí)形成的。英科耐爾合金材料(Inconel)切割絲能夠在500mm/min的給進(jìn)速度切割工件，但產(chǎn)生的工件表面形態(tài)質(zhì)量很糟糕。 一個(gè)更加連續(xù)的表面形態(tài)可以有鎳鉻鐵彈簧絲切切割后形成。用鎳鉻鐵彈簧絲在200℃下用200mm/min的給進(jìn)速度進(jìn)行切割所形成的表面形態(tài)質(zhì)量最好。鎳鉻鐵彈簧絲也能在接近500mm/min給進(jìn)速度下工作，而且可以得到一個(gè)有趣的結(jié)果，就是用鎳鉻鐵彈簧絲切割工件時(shí)，在所有不同的給進(jìn)速度下產(chǎn)生的表面形態(tài)值都在1.0個(gè)單位以下。用不同給進(jìn)速度進(jìn)行切割能夠形成連續(xù)的表面是它的一個(gè)優(yōu)點(diǎn)，因?yàn)檫@樣就提供了一個(gè)安全切割環(huán)境，同時(shí)能夠避免產(chǎn)生切割錯(cuò)誤的發(fā)生。所有以上材料的切割絲均能在300℃的溫度下工作并表現(xiàn)出良好的切割性能。 8.結(jié)論 像聚苯乙烯這樣的柔性材料的表面形態(tài)能夠用CMM在設(shè)置20個(gè)檢測(cè)點(diǎn)的條件下確定。最好的連續(xù)表面形態(tài)能夠用鎳鉻鐵彈簧絲切割工件達(dá)到，其次是英科耐爾合金材料(Inconel)切割絲。最適合的切割條件是在200℃溫度下，用200mm/min的給進(jìn)速度。如之前提到的，沒有現(xiàn)行的研究來(lái)制造用于切割泡沫材料工件的快速成型機(jī)。這項(xiàng)研究的第一步就是在不同的溫度和給進(jìn)速度條件下，被不同材料的切割絲切割后再通過(guò)CMM確定聚苯乙烯的表面形態(tài)。根據(jù)實(shí)驗(yàn)第一步的結(jié)果，切割聚苯乙烯快速成型機(jī)應(yīng)該用鎳鉻鐵彈簧絲作為刀具。 附錄2 Determining the surface form of polystyrene through the coordinate measurement machine D Aitchison and R Sulaiman* Department of Mechanical Engineering, University of Canterbury, Christchurch, New Zealand Abstract: The market for foam materials has been growing rapidly throughout the world as they have a variety of uses. Some examples are in the automotives industries, food packaging industries, medical application, sports gears, home insulations and floatation in offshore drilling rigs, buoys and small boats. Since the uses of foam affects greatly the daily lives of humans, the need to have foams in different shapes requires speed in cutting and manufacture. This can only be done through computer aided cutting machines or automated cutting of foams. However, the speed of cutting will affect the surface . finish of the cut. Therefore, it is necessary to determine the surface form of the polystyrene to achieve quality results. This is an on-going research to produce a rapid-prototyping machine that cuts foam models. The . first phase of this research is to determine the surface form of polystyrene through the use of a coordinate measuring machine (CMM), after being cut with different types of wires, at different temperatures and cutting feed-rates. Keywords: polystyrene, surface form, hot-wire cutting 1 INTRODUCTION The market for foam material has been growing rapidly throughout the world. Foams can be categorized into two major types, namely flexible foams and rigid foams. The flexible foams are mainly used in furniture, transportation, bedding, carpet underlay, packaging, toys, sports application and shoes, as well as for vibration and sound attenuation. The rigid foams are usually used in building appliances, insulation agents, pipes, tanks, floatation and food and drink containers [1]. The reason why foams are used everywhere can be summarized as follows: 1. Foam is very inexpensive. 2. Foam is suitable for use indoors or outdoors. 3. Foam can be coated with many different products to achieve any desired . finish. 4. Foam is lightweight for easy handling and installation. The production of foams can take place using many different techniques. The most common method to produce continuous foam slab is by pouring mixed ingredients of petrochemical agents that include toluene di-isocyanate, polyol and water. These ingredients are left to rise and cure. Additives are blended in for specific. characteristics such as colors, absorbing capacity, effects on ultra violet and others. This method produces foam in its ‘raw’ state, which must then be formed into different shapes and sizes. This is usually done by cutting the foams. There are two ways to cut foam materials, which are by using hot-wire techniques and the oscillating blade method. Both produce different features to the foams. The oscillating blade produces simple geometrical shapes and is suitable for rigid foams. The hot-wire technique is capable of producing complicated geometrical shapes and is suitable for flexible foams. Presently, both techniques are performed either manually or in a semi-automated manner [2]. 2 COORDINATE MEASUREMENT MACHINE (CMM) Before further discussion, it is necessary to describe the features of a coordinate measurement machine (CMM) as a tool used in this research for determining the surface form of polystyrene. A CMM consists of a probe to measure points on a work-piece. This is similar to using a . finger to trace a map coordinate. The probe acts as a . finger that points or touches a certain location on the work-piece. Each point on the work-piece is unique to the machine’s coordinate system. The coordinate system describes the movement of the measurement machine. There are two types of coordinate system. The . first is called the machine coordinate system. Here, the X, Y and Z axes refer to the machine’ s motion. The second coordinate system is called the part coordinate system, where the three axes relate to the datum of the work-piece. A datum is a location of a feature on a work-piece. It can be a hole, a surface or a slot. A CMM measures a work-piece to determine the distance from one feature to another. It can also be used to determine the form or roughness on a surface of a soft object, such as polystyrene. The CMM used in the present experiment is the Discovery Series coordinate measuring machine Model D-12 (Fig. 1a).Data are gathered by touching the test piece with either a solid probe or an electronic touch trigger probe. This experiment uses the electronic touch trigger probe. The probe measurement was taken perpendicular to the test piece to obtain the optimal result because probe tip ‘skidding’ will affect the reading of data. The stylus sizes that are available in the authors’ laboratory are 1.0, 2.0, 3.0, 4.0 and 5.0mm in diameter. The stylus used in this experiment was ruby with a size of 3.0mm in diameter. As polystyrene is soft, a smaller stylus size may create new slopes or holes when touching the polystyrene (Fig. 1b). A larger stylus size may not detect the existing slopes and holes on the surface of the polystyrene. Therefore, the stylus 3.0mm in diameter was used to avoid the above reading errors (Figs 1c and d). 3 SURFACE FORM It is generally agreed that surface form or roughness consists of scratch marks and fragmentation marks within them. These marks are relatively closely spaced together. This makes them dif. cult to measure. Why do engineers trouble to measure surface roughness at all? The main reason is that the surface being measured will be in contact with some other surfaces. By understanding its surface, the nature of the contact and the performance of the contacted components can be controlled. （d） Fig. 1 (a) The CMM used in this experiment; (b) the surface of polystyrene as seen through a microscope; (c) typical diagram of the probe; (d) the probe used in this experiment It is necessary to state that surface form and surface roughness are not the same. Surface form is a geometrical pro. le of a surface on soft materials, such as polystyrene or sponge. Measuring surface roughness on soft material is challenging and complicated, but can be done [3]. Surface roughness is more commonly recognized as an irregular or uneven surface, usually on hard materials [4]. The definitions tend to refer to the technique or scale of measuring its hardness. If surface roughness needs to comply with a written standard, there are a few to choose from. The most common is the British Standards Institution BS 1134, Centre-line Average Height Method for Assessment of Surface Texture, 1961. There is also another one being used in the mechanical engineering industry to date, which is the International Standard ISO 4287, Surface Roughness—Terminology—Part 1—Surface and Its Parameters, 1st edition, 1984, pp. 12–15. The measurement standards are based on a line pro. le obtained by scanning a mechanical stylus across the surface. For a thorough assessment of the roughness standards, refer to ISO 4287 and the published national standards based on this ISO documents. The latter can be traced by contacting national reference laboratories, e.g..National Physical Laboratory in the United Kingdom, Physikalishe Technishe Bundesanstalt in Germany, National Institute of Standards and Technology in the United States and Laboratoire National d’Essais in France. 4 SURFACE FORM FOR SOFT MATERIALS Questions are often raised concerning the possibility of measuring surface roughness of soft materials such as polystyrene or other foam materials. A suitable method of measuring is by using the optical technique. However, with the optical technique careful attention must be focused on local, steep slopes in the surface of the test piece, as the dynamic focusing instruments tend to produce corrupt feedback at these points. Other optical techniques encounter problems with steep local slopes by not reflecting enough light back into the detector system. This is the main reason why this research uses the CMM machine. The CMM machine can measure the surface form of polystyrene because polystyrene usually does not have steep slopes. When examined through a microscope, these slopes appear to be sperical in shape. Results of the tests are produced as shown in Fig. 2. Notice that the deeper the slope, the longer the line produced by CMM readings. 5 EXPERIMENTAL TECHNIQUE In this research, a simple machine is designed to cut polystyrene using the hot-wire technique. The machine will cut the polystyrene in a one-dimensional movement, i.e. feeding the hot wire horizontally towards the polystyrene. Hot-wire foam cutters are very common when working with polystyrene. The two ends of the hot wire are connected to a power source. Heat will flow when there is a difference in temperature across the wire. Heat flows from warm to cold areas at a rate proportional to the temperature gradient and the thermal conductivity of the wire it is ? owing through. A thermocouple is connected to the hot wire to give a reading of the wire temperature. Manipulating the current and voltage of the wire can control the temperature. The temperatures considered in this experiment are 100, 200 and 300 8C The objective of this experiment is to reveal the surface form of polystyrene through the use of a CMM with different types of wires, temperatures and cutting feed-rates. The surface form is affected by the federate and temperature of the hot-wire cutter. The test material was polystyrene with width of 300mm, length of 300mm and thickness of 50mm. These sizes were selected because they can be easily handled when performing the test. The wires used as the cutting tool were nickel–chromium alloy (Nichrome), Inconel and nickel–chromium–iron (NiCr-C) spring wire [5]. The reasons for selecting Inconel and NiCr-C spring wires are due to their ability to maintain their shape after being applied to the operating cutting temperatures [6, 7]. Nichrome wire was chosen as it is the most commonly used wire for cutting polystyrene materials.The polystyrene was cut using different types of wires at different temperatures and feed-rates. The feed-rate ranged from 100 to 500mm/min. After each cut, the surface of the polystyrene was measured using the CMM with 20 touch points. A test was done prior to this experiment on the number of touch points. Touch points from 10 to 200 touches were investigated using the CMM. The higher the number of touches, the longer the time required in order to perform the test. Results show that the surface form from 20 and 200 touches were very similar. Therefore, in this experiment 20 touch points were chosen. 6 RESULTS The surface form of the polystyrene was calculated and recorded directly from the CMM. Using different types of wires, temperatures and cutting feed-rates, the polystyrenes were cut into small pieces of 10mm thickness. Then, the CMM ran the 20 touch points D AITCHISON AND R SULAIMA842 N test on the cut pieces of polystyrene. Figure 3 shows that a Nichrome wire at a temperature of 100℃ and a feed-rate of 100mm/min produces a surface form of 0.551 units. The best surface form should be the one nearest to 0.Figure 3 also shows that the most suitable cutting temperature and feed-rate for Nichrome wire were 200℃ and 200mm/min respectively. Cutting can only be done up to a feed-rate of 300mm/min. At a feed-rate higher than this, the wire tends to slip and bend. This affects Fig. 3 Surface form against feed-rate for Nichrome wire of 1.0mm diameter Fig. 4 Surface form against feed-rate at a temperature of 100℃ the cutting quality and, hence, the surface form of the polystyrene. Figure 4 illustrates the comparison of all three types of wire used in this experiment at a cutting temperature of 100 8C. The best surface form was made by Inconel wire at a temperature of 100 8C and a feed-rate of 200mm/min. The surface form was 0.14 units. Notice also that Inconel was able to perform the cutting at feed-rates up to 500mm/min. However, at this cutting speed the surface form was poor. Figure 5 shows the cutting performance of all three wires at a temperature of 200 8C. At this temperature, two wires were able to cut up to a feed-rate of 500mm/min, namely Inconel and NiCr-C spring wires. The best surface form was made from Inconel at a feed-rate of 300mm/min. However, NiCr-C produces a consistent surface form of below 1.0 unit at different feed-rates. 7 DISCUSSION As mentioned earlier, the reason for selecting Inconel and NiCr-C spring wires was due to their ability to maintain their shape after being applied at temperatures of 100, 200 and 300 8C. Nichrome wire was chosen as it is the most commonly used wire for cutting polystyrene materials. Maintaining their shape was a main concern because a bent wire will affect the quality of the cut polystyrene. Figure 6 shows the comparison of the three types of wire selected in this experiment against their spring rate. Assuming that the wires are shaped into a loop, similar to a spring, the spring rate was calculated as Gd4 R= ———— 8nd3 where R =spring rate G = shear modulus d =wire diameter n =number of coils D =mean coil diameter Its unit is force per unit of deflection (or force per millimetre). The spring rate actually divides the force by the deflection required to produce that force [8]. A graph comparing the spring rates of the three wires was plotted. The lower the spring rate, the more recoverable the shape will be. Figure 5 shows that the lowest spring rate was made by the NiCr-C wire. Thus, this wire is able to maintain its shape. Fig. 5 Surface form against feed-rate at a temperature of 200℃ Fig. 6 Comparing the spring rate R and the loop diameter for wires of 1mm diameter However, based on the experiments, the best surface form was made using Inconel wire at a cutting temperature of 200 8C and a cutting feed-rate of 300mm/min. Inconel was able to perform cutting at a feed-rate up to 500mm/min but the surface form was very poor. A more consistent surface form was produced by NiCr-C spring wire. The best surface form made from NiCr-C was at a cutting temperature of 200 8C and a feed-ate of 200mm/min. NiCr-C was also able to cut at a feed-rate up to 500mm/min. An interesting outcome was that, at all the different feed-rates, the surface form produced by NiCr-C was be