喜歡這套資料就充值下載吧。資源目錄里展示的都可在線預(yù)覽哦。下載后都有，請放心下載，文件全都包含在內(nèi)，圖紙為CAD格式可編輯，有疑問咨詢QQ:414951605 或 1304139763p 中文譯文 一個激光束加工（LBM方法）數(shù)據(jù)庫的切割瓷磚 摘要 本文介紹了使用CO2laser切割機市售瓷磚切割，以期產(chǎn)生的激光束加工（LBM方法）數(shù)據(jù)庫，其中包含其成功的關(guān)鍵參數(shù)信息對象處理。各種激光切割參數(shù)進行了研究，將產(chǎn)生一個瓷磚切割這需要最小的后處理。各種屏蔽氣體多通切割和水下切割。 關(guān)鍵詞：二氧化碳，激光切割，陶瓷材料，先進制造工藝 1.介紹和背景 瓷磚切割手工方法非常類似于玻璃，即劃線用鎢硬質(zhì)合金刀具材料的傾斜，由一個彎矩沿劃線應(yīng)用控制破裂之后開始。然而，手工技術(shù)僅限于直線切割和較大半徑的削減。內(nèi)部和削弱型材生產(chǎn)幾乎是不可能單獨與得分（與內(nèi)部圈子可能例外），更復(fù)雜的方法將適用于有實現(xiàn)這些配置文件。傳統(tǒng)上，金剛石鋸片，流體力學(xué)（水射流）或超聲波加工用于制造形狀復(fù)雜的陶瓷磚，但這些過程是非常耗時和昂貴。例如，典型的鉆石鋸切割速度在20 mm每分最小 [1]的順序，而氧化鋁超聲波鉆孔每孔30 s需要[2]。 最關(guān)鍵的因子是二氧化碳激光切割瓷磚的使用所產(chǎn)生的裂縫損傷，基本上是在陶瓷基片內(nèi)造成一個高溫度梯度在切割過程。這些裂縫的強度，并減少對臨界裂紋增長，這可能會導(dǎo)致部分或完全的瓷磚基板[3]故障源。因此,一個過程,減少誘發(fā)裂紋的形成是為現(xiàn)實的商業(yè)利用激光切割瓷磚最重要的。 2 激光切割參數(shù) 任何材料激光加工都是是一個復(fù)雜的過程，涉及許多不同的參數(shù)，這都需要在配偶工作，生產(chǎn)優(yōu)質(zhì)的加工操作[4]，參數(shù)，如：（一）激光電源輸入;（二）的重點設(shè)置;（三）協(xié)助氣體種類和壓力;（四）噴頭配置;（五）工件厚度;（六）運動物理屬性。在作者的部門此前的研究[1,5,6]也證明了在有效的激光切割上述參數(shù)臨界。 2.1激光功率 激光功率取決于激光的類型。對于本文的工作報告，一費倫蒂數(shù)控激光切割機MF400受雇于，在400瓦特額定輸出功率，但由于升級，束功率達到最大520和530間W的連續(xù)波（CW）切割模式。激光也有工作能力，在脈沖模式（PM）和超脈沖模式（SPM的，圖1。）。為了確定在操作等效功率脈沖輸出，脈沖功率圖是在配合使用的下列基本方程： 圖1 切割方法 雖然激光切割機可經(jīng)營50間和5000赫茲，500赫茲的頻率被推薦的價值在以往的工作[1,5]。由于此設(shè)置被證明是成功的，只有到其他頻率進行了有限度的調(diào)查（250赫茲，750和100赫茲）。 2.2 切割速度 工作上用的數(shù)控激光切割機的費倫蒂MF400使用了10000mm每分鐘最大進給速度。以前的工作[6]如上所述，飼料率6000mm每分鐘一被證明是不穩(wěn)定的標(biāo)準(zhǔn)化測試。最佳切割速度與功率設(shè)置，更重要的變化，隨著工件的厚度。 2.3 保護氣體種類和壓力 壓縮空氣，氬氣，氮氣和氧氣被用來作為擋箭牌氣體切割過程中，與P最大約等于4條。不同的屏蔽氣體被用來檢測處理后其對切割質(zhì)量的影響，因為不僅保護氣體冷卻和切割邊緣并移除熔融材料，但也產(chǎn)生與基體材料的化學(xué)反應(yīng)[7]。這個化學(xué)反應(yīng)的結(jié)果不同的保護氣體為每個使用的類型。對于不同的測試目的磷含量在0.5至2.5巴的步驟，然后在步驟由2.6至0.2巴最大達到氣體的壓力。 2.4 噴嘴配置 噴嘴直徑直接有助于達到的最大氣體壓力，從而對氣體的質(zhì)量流速為切割經(jīng)濟學(xué)的重要，特別是使用氬氣和氮氣鋼瓶。噴嘴出口的只有圓形剖面可用（0.6 毫米≤Ns≤20毫米），但這個統(tǒng)一的噴管的幾何形狀允許在任何方向切割。 2.5 噴嘴高度和重點定位 在成立該噴嘴高度應(yīng)依該聯(lián)絡(luò)點的地位激光切割機的費倫蒂MF400僅擁有（升級前原本是一個短46毫米焦距可）一個110毫米長焦距的長度，這可能是由正負5毫米改變。如果噴嘴高度被錯誤地設(shè)置梁將'夾'的噴嘴，減少功率輸出相當(dāng)于工件。對于大部分的檢驗重點高度設(shè)置，以便重點是'在工作'，即工件的頂面。這種情況顯然管轄上述工件噴嘴的位置。 3 實驗過程 六硅類型：氧化鋁基陶瓷磚進行了研究（表1），從不同的countries.Note的是，各種瓷磚組成，厚度一樣起源，但都具有一個表面釉在7.5的情況下，8.6和9.2毫米西班牙瓷磚的釉層雙層。 3.1 設(shè)置程序 由于是一個標(biāo)準(zhǔn)的測試條件的需要，實施下列程序測試開始前的：（一）驗證，束功率為規(guī)范，即520-530 W于滿功率（連續(xù)）開發(fā)的，雖然這下降到50瓦約1小時的測試;（二）噴嘴和焦鏡頭被檢查，以確保其處于良好狀態(tài)的，即清潔，完好;（三）保護氣體的壓力調(diào)節(jié)器和保護氣體坦克被打開為了防止損壞的焦點鏡頭;（四）激光束中心內(nèi)使用的噴嘴下午一'廣場測試'，以較低的能源投入被用于切割低碳鋼上，閃著火花的密度，從一個正方形切割產(chǎn)生被檢查，看它是否是同樣關(guān)注的淘汰線分布;及（五）的焦點是確定其所需的定位，即'在工作'。 表1 使用瓷磚的類型 3.2 測試 直線測試（SLT）的被用于評估全面通過切割（FTC）的激光參數(shù)的變量。角切割配置為探討如何在緊張的幾何材料切割反應(yīng)。圓方檢定測試和設(shè)計，確定了從切割各種幾何形狀的影響造成的。為兩個獨立的參數(shù)對一試件允許這個工作隊的聯(lián)合試驗完成后，結(jié)果在場自動在'切割矩陣'中所形成的削減形式。 P和V是最重要的激光參數(shù)，因為它們決定了每單位的能源投入量的切割長度，因此他們對這個工作隊配對，因為是P和Ns的管轄之盾氣體的質(zhì)量流量。 對于光伏測試運行時，功率保持不變，而切削速度增加沿切割恒定的切削長度切割速度，必須有足夠的規(guī)模，以適應(yīng)加速或減速的變化之間的數(shù)控表減速：以前的工作[6]指出，50毫米是足夠的。解釋結(jié)果是比較容易，因為它們表格形式，與'切割矩陣'清楚顯示任何趨勢或模式發(fā)生由于參數(shù)設(shè)置的變化。這個工作隊還允許大量的削減進行了很短的時間框架了。這證明有利，因為激光往往隨時間的漂移，從它的初始設(shè)置。必須采取預(yù)防措施，避免定位于從連續(xù)加熱接近切割瓷磚作為一個瓦體溫度的變化，由此產(chǎn)生的任何數(shù)據(jù)將無效。最初，削減20毫米之間，采用分離，這足以證明。為了研究如何關(guān)閉削減可能作出相互之間的切割分離，減少了2毫米遞增，從最初的20毫米間距。在這個工作隊的其他激光參數(shù)都必須保持不變[6]。對于P與五，f被500赫茲舉行與NS1.2毫米和P三欄。光束焦點仍然在工作。從P結(jié)果：第V切割矩陣確定了切割速度固定值為后續(xù)SLT和脈沖設(shè)置。對于Ns：切割矩陣，沿噴嘴尺寸保持不變在X軸（參考圖。2（一）），而P的增加0.2桿2桿的步驟，在Y軸（切分離常數(shù)保持在20毫米）。新矩陣其后創(chuàng)建每個噴嘴的大小。角測試（圖2（b））被用來研究如何切料反應(yīng)持續(xù)曝光從期間的'緊'加工的激光束幾何（即有幾個削減在接近接近的除外）。測試中提到的接近為普通話機決定如何關(guān)閉平行線可切割給對方，而角測試是用來確定效果如何切割銳角切割質(zhì)量。從一個角度切工件減少從45°?10°，對應(yīng)的表面光潔度質(zhì)量（SFQ）指出。 有兩個原因進行平方和循環(huán)測試（圖2（c）和（d））：第一，確定對激光束引入優(yōu)化方法內(nèi)部切割型材;其次，以確定是否有是任何維度的大小限制方形或孔切。如果不能正確介紹，激光光束會導(dǎo)致內(nèi)部切剖面在失敗點介紹，由于短暫的，但過度從切削熱梯度（即熱誘導(dǎo)休克）。因此，利用光束介紹的方法，如穿孔，復(fù)雜到一個配置文件中啟用幾何形狀進行調(diào)查。什么也成為明顯的是在測試過程中的重要性梁位置提取輪廓和切割梁出發(fā)點的相對位置幾何，即無論是在一個角落里或在直邊。 圖2 測試配置 ：（a）；直線測試（b）；角測試（c）；循環(huán)測試（d）; 方檢定 3.3 多通和水下切割 多道切割是一個低功率（P=100瓦）的激光束開始。在第一階段產(chǎn)生了良好的基體中定義的盲縫，接著由第二通過削減更深，等等。這個過程重復(fù)直到切口約20毫米深，然后激光功率為500瓦和切換到做最后的聯(lián)邦貿(mào)易委員會。多通采伐的目的是要減少能源使用的投入少，每單位長度的熱過載。在這個測試中使用的參數(shù)列于表2。 表2 多道切削參數(shù) 水下切割與目標(biāo)進行降低周圍地區(qū)的熱切割的影響并還審議了關(guān)于通過切割質(zhì)量的影響加快散熱使用水[8]。陶瓷瓦劃歸水和噴嘴還浸在水中，防止保護氣體壓力任何進入水射流噴嘴室。 4 切割質(zhì)量 材料特性，激光參數(shù)和工件幾何均對最終結(jié)果產(chǎn)生重大影響激光切割工藝。本質(zhì)特征是切割質(zhì)量表面粗糙度和糟粕的高度，而裂紋長度決定了強度降低襯底（圖3）。在整體SFQ釉表面被列為按規(guī)模分級列于表3。因此，對切割質(zhì)量表面和邊緣進行測量與尊重的：（一）表面粗糙度;（二）表面光潔度和;（三）糟粕堅持。 圖3 用于激光切割瓷磚的質(zhì)量標(biāo)準(zhǔn) 圖4 Ra的測量切面 4.1 表面粗糙度 重要的是要測量表面粗糙度為這使切割質(zhì)量的同時要衡量從以往的工作中獲取的值[1]和價值觀其他錄得制造工藝。由于大量的削減正使得有必要減少裁員數(shù)量進行分析。因此，與SFQ小于2沒有測量被削減。 砍掉了邊緣表面粗糙度的特點由條紋線形成的左側(cè)切削過程Ra值測定從中心線的切緣（圖4）。測量結(jié)果接管了12.5毫米的手寫筆與導(dǎo)線截止2.5毫米，即價值采取了五種讀在穿越，這保證了手寫筆走超過合理數(shù)量的紋線。 4.2 殘渣 堅持渣直接影響了Ra值削減和能力，消除內(nèi)部切割的幾何形狀。一微米是用來衡量在其糟粕高度三沿切節(jié)間隔。糟粕高度一直相當(dāng)穩(wěn)定（約1毫米）與所有類型的切割。由于此值被認為是沒有實際意義，它不是記錄在數(shù)據(jù)庫。 5 結(jié)果 表4包含目前雷射加工切割數(shù)據(jù)庫這是從結(jié)果匯編瓷磚工作本文報道。第一部分表包含襯底參數(shù)和結(jié)果大氣中削減，而水下的結(jié)果切列在第二部分。 5.1 參數(shù)影響 5.1.1 切割速度 對于較薄的磚（ts<7毫米）的P：第V切割矩陣顯示與SFQ一聯(lián)邦貿(mào)易委員會廣泛的地區(qū)。在巴西的瓷磚案（3.7毫米的TS）聯(lián)邦貿(mào)易委員會是獲得的切割高達2200毫米的速度1分鐠上下0.5（與減少的速度）在f500赫茲。這個地區(qū)在減少與增加瓷磚厚度，并與身體的顏色發(fā)紅（一般的厚磚體顏色較深）。圖5顯示了最大切割速度為聯(lián)邦貿(mào)易委員會隨徘徊。在'指數(shù)'的關(guān)系得到同意與以前的工作[6]不同材料如鋼材，木材和有機玻璃。切割矩陣還表明，一旦切割速度超過價值觀為達到美國聯(lián)邦貿(mào)易委員會，劃線或盲目切割效果。 圖5 Vmax隨Ts的變化 5.1.2 脈沖 脈沖為所有，但厚厚的西班牙瓷磚的激光是不是必須的，因為連續(xù)設(shè)置產(chǎn)生切斷與一個良好的SFQ分級。在成功獲得美國聯(lián)邦貿(mào)易委員會公關(guān)]巴西0.4瓦，但是如此之低的，在實際意義上，設(shè)置是不可行的。論梁厚脈沖西班牙瓷磚是必需的，連續(xù)引起了釉裂。這可能是由于輸入的能量單位的切割長度超過熱膨脹引起的熱沖擊率不同的釉料充分從父項瓦。由于激光脈沖的能量輸入的減少約25瓦，每下降0.1在箴在f500赫茲，表面釉裂幾乎消失在公關(guān)0.6和最佳的切割速度，雖然微小在切邊仍然裂縫（的0.5毫米寬的順序排列）仍然存在。 5.1.3 氣體壓力 此參數(shù)對質(zhì)量有很大影響，削減的速度，可以作出成功。以前的工作[2]已經(jīng)表明，高瓦斯壓力被要求實現(xiàn)厚基板（聯(lián)邦貿(mào)易委員會的TS\7毫米）。這證明了取得的成果在P：南北切割矩陣。高品質(zhì)被削減在薄磚（tsB6毫米）實現(xiàn)在氣體壓力2個酒吧，但在雙層玻璃，厚磚值SFQB3沒有實現(xiàn)，除非p\ 3吧。在低壓力（pB2.5欄），最大切割速度為聯(lián)邦貿(mào)易委員會的大幅下降，當(dāng)氣體中的角色失敗糟粕清晰。在連續(xù)下跌巴西瓷磚的Vmax從2200 mm最小的酒吧在P1到3.8分鐘一1500毫米在P3條。在表面釉裂也增加成為在低氣壓明顯。導(dǎo)致這結(jié)論是，保護氣體為冷卻劑的作用從而有助于最大限度地減少大熱梯度創(chuàng)建的光束。 5.1.4 氣體種類 壓縮空氣為前面的推薦工作[1]證明了在適當(dāng)?shù)娜廴诓牧先コ浞艧嵝阅懿皇苋魏尾焕挠绊懸陨系拇纱u厚度齊全。切割使用惰性氣體氬氣和氮氣產(chǎn)生更好的結(jié)果，尤其是后者，因為它充當(dāng)高效冷卻劑[9]。與SFQ1高品質(zhì)的削減生產(chǎn)了較厚的瓷磚在最佳的360毫米分鐘1切削速度在CW模式。然而，當(dāng)使用所需的高瓦斯壓力，一缸氮氣或氬氣是用來迅速。 5.1.5 噴嘴尺寸 這個參數(shù)直接關(guān)系到P（即噴嘴尺寸越小越高的索取壓力）。表5顯示了最大的實現(xiàn)盾與相應(yīng)的噴嘴氣體壓力的大小當(dāng)使用壓縮空氣。噴嘴直徑大于1.5 mm的漠視Pmax的不足。直徑較小的噴嘴產(chǎn)生更好削減較高的切削速度。 5.1.6 聯(lián)絡(luò)點定位 在測試過程中梁的焦點仍在工作中，即表面上。切斷與充足SFQ分級取得了與此設(shè)置。調(diào)查顯示，通過降低進入的焦點工作的'殘渣'殘留降低，在提高焦點距離為失去工作的美國聯(lián)邦貿(mào)易委員會梁德為重點。因此，基于實際理由，焦點仍然在工作。 5.1.7 多道切割 厚瓦片被切斷成功的多通法無切割質(zhì)量退化。由于低功率激光束，溫度梯度在瓦大大減少，從而物質(zhì)損失減少到最低限度。這種方法也可以用來處理有任何骨折較厚的陶瓷。然而，多道切割已成為一個明顯的劣勢非常耗時的過程，并會證明不符合經(jīng)濟原則在商業(yè)基礎(chǔ)上。 5.2 實質(zhì)影響 較深的體密度和瓷磚的重，他們保留在切割時比白人身體更熱瓷磚。分析如何實施的切割是不可能的，因為瓷磚的厚度也增加身體的顏色變暗，在厚度增加掩蓋對材料的成分任何效果。在瓷磚的材料組成部分并不相同。這是否是由于特定的瓷磚制造工藝是未知的，但結(jié)果削減聯(lián)邦貿(mào)易委員會是一個損失的，即使在最佳切削速度。 釉損害是在評估減少的重要因素質(zhì)量。在所有，但厚釉磚損傷即使在最小的貧困參數(shù)設(shè)置。例如，用7.5毫米為最西班牙瓷磚SFQ53用壓縮空氣削減，雖然氮生產(chǎn)更好的價值。與此問題是后一種類型瓷磚有雙層釉。沒有出現(xiàn)開裂在較低的白色釉（類似于其他瓦），但上明確釉分裂和片狀如在瓦能量輸入或保暖性太高，巴貝羅，考夫曼和Idelsohn[10]所示釉的表面通常擁有不同的線性膨脹率到基礎(chǔ)基板。因此，大溫度梯度引起的激光光束會導(dǎo)致較低的基材，以擴大在不同的率，導(dǎo)致釉開裂。 表3 最大壓力（壓縮空氣）的不同噴嘴尺寸 另一個重要的因素是數(shù)量控制能量輸入，并從削減散熱。該參數(shù)設(shè)置效果不佳要么損失ofFTC（這是很容易地更正），或熱休克瓷磚或表面釉（即在釉裂）。激光切割過程中容易推廣熱在切割沖擊，因此這是至關(guān)重要的控制效應(yīng)參數(shù)的正確選擇。該瓷磚的熱性質(zhì)主要是造成這個問題的，一般有一個貧窮的瓦導(dǎo)熱系數(shù)（0.9 W mk的15k51 W馬可福音1）和相對較低的共同擴張效率（2 10 6K表15a5510 6 K表1）。 玻薄膜（或渣），涵蓋的切緣增厚，在增加和減少瓷磚基板在切割速度。在糟粕增加，因為瓦厚度是顯而易見的：更多的瓷磚融化，因此更糟粕的結(jié)果。該影片還厚度的糟粕通過多種多樣的削減。有兩個明顯的原因這一點。 首先，梁寬分道揚鑣后聯(lián)絡(luò)點（即在工作了），造成了外的平坦度的削減而導(dǎo)致在一個更大的縫寬度在底部。因此，更多的家長瓦降低材料熔化切割下來。根據(jù)對激光焦距和焦點定位點，切縫寬度不等的焦點尺寸（約0.1毫米）到2毫米。 第二，有能力或屏蔽氣無力繼續(xù)通過削減集中噴射也出于對切緣的糟粕格局。在頂削減那里的氣體壓力仍高，氣還是針對流動，很少或沒有糟粕的黏附顯而易見，但由于切削深度增加氣流變得更加動蕩，減少壓力，因此允許更多殘渣切緣。 Journal of Materials Processing Technology 84 (1998) 4755A laser beam machining (LBM) database for the cutting ofceramic tileI. Black *, S.A.J. Livingstone, K.L. ChuaDepartment of Mechanical and Chemical Engineering, Heriot-Watt Uni6ersity, Riccarton, Edinburgh EH14 4AS, UKReceived 13 December 1997AbstractThis paper covers the cutting of commercially-available ceramic tiles using a CO2laser cutting machine, with the object ofproducing a laser beam machining (LBM) database that contains the essential parameter information for their successfulprocessing. Various laser cutting parameters were investigated that would generate a cut in ceramic tile which required minimalpost-treatment. The effects of various shield gases, of multi-pass cutting and of underwater cutting were also examined. 1998Elsevier Science S.A. All rights reserved.Keywords:CO2; Laser cutting; Ceramic materials; Advanced manufacturing processes1. Introduction and backgroundManual methods of cutting ceramic tiles are verysimilar to that for glass, i.e. scribing the materials withtungsten-carbide tipped cutter, followed by the applica-tion of a bending moment along the scribed line toinitiate controlled fracture. However, manual tech-niques are limited to straight-line cutting and relativelylarge-radius cuts. Internal and undercut profiles arenearly impossible to produce with scoring alone (withthe possible exception of internal circles); more sophis-ticated methods having to be applied to achieve theseprofiles.Traditionally,diamond-saw,hydrodynamic(water jet) or ultrasonic machining are used to createcomplex geometries in ceramic tiles, but these processesare very time consuming and expensive. For example,typical diamond-saw cutting speeds are in the order of20 mm min11, while ultrasonic drilling of Al2O3takes over 30 s per hole 2.The most critical factor arising from use of a CO2laser to cut ceramic tiles is crack damage, which isessentially caused by a high temperature gradientwithin the ceramic substrate during the cutting process.These cracks reduce the strength and are sources forcritical crack growth, which may result in partial orcomplete failure of the tile substrate 3. Thus a reduc-tion of process-induced crack formation is paramountfor the realistic commercial use of lasers to cut ceramictiles.2. Laser cutting parametersLaser machining of any material is a complex processinvolving many different parameters that which all needto work in consort to produce a quality machiningoperation 4, parameters such as: (i) laser power input;(ii) focal setting; (iii) assist gas type and pressure;(iv) nozzle configuration; (v) workpiece thickness; and(vi) optophysical properties.Previous research within the authors department1,5,6 has also demonstrated the criticality of the aboveparameters in efficient laser cutting.2.1.Laser powerLaser power depends on the type of laser used. Forthe work reported in this paper, a Ferranti MF400CNC laser cutter was employed, rated at a poweroutput of 400 W. However, due to upgrading, themaximum beam power achievable was between 520 and* Correspondingauthor.Fax:+441314513129;e-mail:i.blackhw.ac.uk0924-0136/98/$ - see front matter 1998 Elsevier Science S.A. All rights reserved.PIIS0924-0136(98)00078-8I. Black et al./Journal of Materials Processing Technology84 (1998) 475548530 W in continuous wave (CW) cutting mode. Thelaser also had the ability to work in pulse mode (PM)and super-pulse mode (SPM; Fig. 1). To determine theequivalent power output during pulsing operation, apower verses pulsing chart was used in conjunctionwith the following basic equation 9:Pr=Pl/Psf=1/(Pl+Pr)Although the laser cutter could operate between fre-quencies of 50 and 5000 Hz, a value of 500 Hz wasrecommended in previous work 1,5. Since this settingproved to be successful, only limited investigation intoother frequencies was carried out (at 250 Hz, 750 and100 Hz).2.2.Cutting speedThe CNC table used with the Ferranti MF400 lasercutter had a maximum feed rate of 10000 mm min1.Previous work 6 indicated that feed rates above 6000mm min1proved to be unstable for any standardisedtesting. The optimum cutting speed varied with thepower setting and, more importantly, with the thicknessof the workpiece.2.3.Shield gas type and pressureCompressed air, argon, nitrogen and oxygen wereused as shield gases during cutting, with pmax:4 bar.Different shield gases were used to examined their effecton cut quality after processing, since the shield gas notonly cools and cut edges and removes molten material,but also generates a chemical reaction with the sub-strate material 7. The results of this chemical reactiondiffer for each type of shield gas used. For test purposesp was varied in steps of 0.5 bar from 1 to 2.5 bar, thenin steps of 0.2 bar from 2.6 bar to the maximumattainable gas pressure.2.4.Nozzle configurationThe nozzle diameter contributes directly to the maxi-mum achievable gas pressure and hence to the massflow rate of the gas was important for the economics ofcutting, especially when using cylinders of argon andnitrogen. Only circular profiles for the nozzle exits wereavailable (0.6 mm5Ns520 mm), but this uniformnozzle exit geometry allowed cutting in any direction.2.5.Nozzle height and focal positioningThe height at which the nozzle was set was governedby the position of the focal point. The Ferranti MF400laser cutter only possessed a long focal length of 110Fig. 1. Cutting modes.mm (originally a short focal length of 46 mm wasavailable before upgrading) and this length could bealtered by 95 mm. If the nozzle height was incorrectlyset the beam would clip the nozzle and reduce theequivalent power output to the workpiece 6. For thebulk of the testing the focal height was set so the focalpoint was on the job, i.e. on the top surface of theworkpiece. This condition obviously governed the posi-tion of the nozzle above the workpiece.3. Experimental procedureSix types of Si/Al2O3-based ceramic tiles were exam-ined (Table 1), originating from different countries.Note that the composition of the tiles varied, as did thethickness, but all possessed a surface glaze and in thecase of the 7.5, 8.6 and 9.2 mm Spanish tiles the glazewas double layered.3.1.Set-up procedureSince there was a need for standard testing condi-tions, the following procedure was implemented beforethe start of testing: (i) the beam power was validated tospecification, i.e. 520530 W developed at full power(CW), although this dropped to around 50 W afterTable 1Types of ceramic tile usedts(mm)Tile typeBody colour3.7BrazilianWhite4.7WhitePeruvianLight redItalian5.2SpanishRed5.74Spanish7.5RedRedSpanish8.69.2RedSpanishI. Black et al./Journal of Materials Processing Technology84 (1998) 475549about 1 h of testing; (ii) the nozzle and the focal lenswere checked to ensure that they were in good condi-tion, i.e. clean and undamaged; (iii) the shield gaspressure regulator and shield gas tanks were turned onto prevent damage to the focal lens; (iv) the laser beamwas centred within the nozzle using a square test, alower energy input in PM being used to cut a square ona mild steel, the sparking density that resulted fromcutting being checked to see if it was equally distributedabout the cut line; and (v) the focal point was set for itsdesired positioning, i.e. on the job.3.2.TestingA straight-line test (SLT) was used to evaluate thevariablelaserparametersforfullthrough-cutting(FTC). Angular cutting was configured to investigatehow the material reacted during cutting of tight geome-try. Circular testing and square testing were devised todetermine the effects resulting from cutting variousgeometries.The SLT allowed for the combined testing of twoseparate parameters on one testpiece, upon completionthe results being present automatically in a cuttingmatrix in the form of the resulting cuts. P and V arethe most important laser parameters, as they dictate theamount of energy input per unit length of cut, thereforethey were paired for the SLT, as were p and NSwhichgovern the mass flow rate of the shield gas.For the P/V test runs, the power was held constantwhile the cutting speed was increased along the cut(Fig. 2(a). The length of cut at constant cutting speedhad to be of sufficient magnitude to accommodate theacceleration or deceleration of the CNC table betweenfeed changes: previous work 6 indicated that 50 mmwas adequate. Interpreting the results was made easierdue to their tabular format, with the cutting matrixshowing clearly any trends or patterns occurring due tothe changes in parameter settings. The SLT also al-lowed a large number of cuts to be carried out over ashort time-frame. This proved advantageous, as thelaser tended to drift from its initial settings with time.Precautions had to taken to avoid localised heating inthe tile from continuous close proximity cutting, as achange in tile body temperature would invalidate anyresulting data. Initially, a 20 mm separation betweencuts was used and this proved sufficient. In order tostudy how close the cuts could be made to each other,the separation between cuts was reduced by incrementsof 2 mm from an initial 20 mm spacing.During the SLT the other laser parameters had to beheld constant 6. For P versus V, f was held at 500 Hzwith NS=1.2 mm and p=3 bar. The beam focal pointremained on the job. The results from the P/V cuttingmatrix determined the fixed values for the cutting speedand pulse settings for the succeeding SLT. For the NS/pFig. 2. Testing configuration: (a) straight-line testing; (b) angulartesting; (c) circular testing; (d) square testing.cutting matrix, the nozzle size remained constant alongthe x-axis (refer to Fig. 2(a) while p was increased insteps of 0.2 bar from 2 bar in the y-axis (the cutseparation remained constant at 20 mm). A new matrixwas created subsequently for each nozzle size.Angular testing (Fig. 2(b) was used to investigatehow the cut material reacted to sustained exposurefrom the laser beam during the machining of tightgeometries (i.e. where several cuts are made in closeproximity to each other). The proximity test mentionedfor SLT determines how close parallel lines can be cutto each other, whereas angular testing is used to deter-mine how the cutting of acute angles effects the cutquality. The angles cut from a workpiece were reducedfrom 45 to 10 and the corresponding surface finishquality (SFQ) was noted.I. Black et al./Journal of Materials Processing Technology84 (1998) 475550Table 2Multi-pass cutting parametersPlCutting modePsNo. of passesLast cutCW60FTC9000100SPMFTC100Table 3Grading of SFQGrading1No cracking in surface glaze, solid sharp cut edgeMinimal glaze cracking (WcB2 mm) with slight2loss of sharpness in cut edgeMedium cracking (2 mmBWcB4 mm) and slight3damage to unglazed tile substrateSignificant damage to glaze coating (Wc6 mm),4heavy damage to unglazed substrate causing flakingin the glazed surface5Same as 4 but with the formation of cracks in thetiles main body leading to structural failure in apart of the tile (usually at the end of a cut orwithin 8 mm of the tile edge).There are two reasons for conducting square andcircular testing (Fig. 2(c) and (d): first, to determinethe optimum method of laser-beam introduction tointernal cut profiles; and secondly, to determine if therewas any limitation in the dimension of the size ofsquare or hole cut. If not correctly introduced, the laserbeam would cause an internally-cut profile to fail at thepoint of introduction, due to the brief but excessivethermal gradient induced from cutting (i.e. thermalshock). Therefore, utilising methods of beam introduc-tion, such as trepanning, onto a profile enabled com-plex geometries to be investigated. What also becameapparent during testing was the importance of theposition of beam extraction from the cut profile and theposition of the beam starting point relative to thegeometry, i.e. whether it was at a corner or on astraight edge.3.3.Multi-pass and underwater cuttingMulti-pass cutting was begun with a low power(P=100 W) laser beam. The first pass produced a welldefined blind kerf in the substrate, followed by a secondpass to cut deeper and so on. The process was repeateduntil the kerf was about 20 mm deep and then the laserpower was switched to 500 W and do the final FTC.The objective of multi-pass cutting was to reduce ther-mal overload by use of less input energy per unitlength. The parameters used in this test are given inTable 2.Underwater cutting was conducted with the objectiveof reducing the influence of heat around the cut areaand also to examined the effect on cut quality throughaccelerated heat dissipation using water 8. The ce-ramic tile was placed under water and the nozzle wasalso dipped in water, the shield gas pressure preventingany water from entering the nozzle jet chamber.4. Cut qualityMaterial properties, laser parameters and workpiecegeometry have a significant effect on the final result ofthe laser cutting process. Cut quality is essentially char-acterisedbysurfaceroughnessanddrossheight,whereas crack length dictates the strength reduction inthe substrate (Fig. 3). The overall SFQ at the glazesurface was classified according to the grading scalegiven in Table 3. Therefore, the quality of the cutsurface and edge were measured with respected to:(i) surface roughness; (ii) surface finish and; (iii) drossadherence.Fig. 3. Quality criteria for the laser cutting of ceramic tiles.I. Black et al./Journal of Materials Processing Technology84 (1998) 475551Fig. 4. Measurement of Rafor the cut surface.4.1.Surface roughnessIt was important to measure surface roughness asthis allowed the cut quality to be gauged alongsidevalues obtained from previous work 1 and valuesrecorded for other manufacturing processes. Due to thelarge number of cuts being made it was necessary toreduce the number of cuts to be analysed. Thereforecuts with SFQB2 were not measured.The surface roughness of the cut edge was character-ised by the formation of striation lines left by thecutting process Ravalues were measured from thecentre-line of the cut edge (Fig. 4). Measurements weretaken over a 12.5 mm traverse of the stylus with acut-off value of 2.5 mm, i.e. five readings were takenover the traverse, which ensured that the stylus trav-elled over a reasonable number of striation lines.4.2.Dross adherenceDross adherence directly effected the Ravalue of thecut and the ability to remove internally-cut geometries.A micrometer was used to measure the dross height atthree intervals along the cut section. The dross heightremained fairly constant (approximately 1 mm) with alltypes of cutting. Since this value was deemed to be ofno practical importance, it was not recorded in thedatabase.5. ResultsTable 4 contains the current LBM database for cut-ting ceramic tiles that was compiled from the results ofthe work reported in this paper. The first part of thetable contains the parameters and results for substratescut in atmosphere, while the results for underwatercutting are shown in the second part.5.1.Parameter effects5.1.1.Cutting speedFor the thinner tiles (tsB7 mm) the P/V cuttingmatrix showed a wide region of FTC with SFQ=1. Inthe case of the Brazilian tile (ts=3.7 mm) FTC wasobtained with cutting speeds of up to 2200 mm min1and down to Pr=0.5 (with reduced speeds) at f=500Hz. This region diminished with the increase in tilethickness and also with the redness of the body colour(generally the thicker tiles are darker in body colour).Fig. 5 shows how the maximum cutting speed for FTCvaries with ts. The exponential relationship obtainedconcurs with previous work 6 for different materialssuch as steel, wood and perspex. The cutting matrixalso showed that once the cutting speed exceeded valuesfor attainable FTC, scribing or blind cutting results.5.1.2.PulsingPulsing the laser for all but the thick Spanish tileswas not required, as the CW setting produced cuts witha good SFQ grading. Successful FTC was obtained atPr0.4 in the Brazilian tile, but Vmaxwas so low that,in a practical sense, the settings were not viable. On thethick Spanish tiles pulsing of the beam was required, asCW caused cracking in the glaze. This was probablydue to an excess of energy input per unit length of cutcausing thermal shock as the thermal expansion rate ofthe glaze differed sufficiently from that of the parenttile. Since pulsing the laser reduced the energy input byapproximately 25 W for every 0.1 drop in Pr at f=500Hz, the surface glaze cracking virtually disappeared atPr=0.6 and optimum cutting speed, although tinycracks (of the order of 0.5 mm wide) at the cut edge stillremained.5.1.3.Gas pressureThis parameter has a great effect on the quality andthe rate at which cuts could be made successfully.Previous work 2 had shown that high gas pressureswere required to achieve FTC on thick substrates (ts7 mm). This was borne out by the results obtained fromthep/Nscuttingmatrix.Highqualitycutswereachieved in the thinner tiles (tsB6 mm) at gas pressuresof 2 bar but in the double-glazed, thicker tiles values ofSFQB3 were not achieved unless p3 bar. At lowpressures (pB2.5 bar), the maximum cutting speeds forFTC dropped drastically, as the gas failed in its role ofdross clearer. Vmaxfor Brazilian tile in CW droppedfrom 2200 mm min1at p=3.8 bar to 1500 mm min1at p=3 bar. An increase in surface-glaze cracking alsobecame apparent at low gas pressures. This led to theconclusion that the shield gas was acting as a coolantand thus helping to minimise the large thermal gradientcreated by the beam.I. Black et al./Journal of Materials Processing Technology84 (1998) 475552Table 44 LBM database for ceramic tilesAtmospheric cuttingRa(mm)V (mm/min)Tile typets(mm)BodyShield gasSFQGlaze typeNs(mm)Geometricp (bar)Pl-Pscutcolour1.21.51Brazilian3.7WhiteWhiteStraightCW5001000C. air32535253511.21.53180205001000C. air31.21.51253516040500900C. air253511.21.53Internal18020400600C. air1.21.515Angular16040300500C. air32535253511.21.53Radial18020300500C. air31.21.51Peruvian4.72535WhiteWhiteStraightCW500700C. air125351.21.5318020500700C. air31.21.51253516040500700C. air253511.21.53Internal18020300500C. air31.21.5152535Angular16040250450C. air125351.21.53Radial18020250450C. air31.21.51Italian5.21725Light redWhiteStraightCW500700C. air1.21.5118020500700C. air3172511.21.51725316040500700C. air1.21.51Internal18020300500C. air317251725151.21.53Angular16040200400C. air31.21.511725Radial18020200400C. air203011.21.5Spanish5.74Red3WhiteStraightCW300550C. air1.21.5118020300400C. air32030203011.21.5316040300450C. air31.21.512030Internal18020200350C. air2520301.21.53Angular16040200300C. air31.21.512030Radial18020200350C. air163721.21.5Spanish7.5Red3Clear/whiteStraightCW200370C. air31.21.52163718020200350C. air1637121.21.5316040200350C. air31.21.52163714060200350C. air1.21.512Internal14060200300C. air31637351.21.516373Angular14060200250C. air1.21.513Radial16040200300C. air3163791211.2Spanish8.5Red2.8WhiteStraight1002503070Argon2.81.219111002003080Argon121311.22.81003003040Argon1.211502503080Argon2.8101411.22.8Internal1002007080Argon2.81.211502505070Argon31.21.52.2StraightCW150250Argon2.21.21.534618020150250Argon48241.21.52.218030150250Argon2.21.21.5246918040150250Argon247111.21.52.218050150250Argon2.21.21.5391116020150250Argon1.21.5316030150250Argon2.2101131.21.511132.216040150250Argon1.21.5214020150200Argon2.21012101431.21.52.214040150200Argon2.21.21.53101414060150200Argon7911.2Spanish8.5Red3.5WhiteStraight15025050C. air3.51.21100250783050C. air101211.23.51002005070C. air3.51.212Angular1002006080C. air315181.23.5StraightCW70160Nitrogen3.51.219121502504060Nitrogen81011.23.51002503050NitrogenNitrogen3.51.219111002002050I. Black et al./Journal of Materials Processing Technology84 (1998) 475553Table 4 (continued).Atmospheric cuttingts(mm)Tile typeBodyGlaze typeGeometricRa(mm)Pl-PsV (mm/min)Shield gasp (bar)Ns(mm)SFQcutcolourAngular1502504060Nitrogen3.51.2341002503040Nitrogen3.51.234StraightCW80100Oxygen3.51.231002005060Oxygen3.51.211011100