手機外殼的注塑模具設計與加工
手機外殼的注塑模具設計與加工,手機外殼,注塑,模具設計,加工
編號
無錫太湖學院
畢業(yè)設計（論文）
相關資料
題目：手機外殼的注塑模具設計與加工
信機 系 機械工程及其自動化 專業(yè)
學 號： 0923275
學生姓名： 陳 兵
指導教師： 王士同（職稱：教 授 ）
（職稱： ）
2013年5月25日
目 錄
一、畢業(yè)設計（論文）開題報告
二、畢業(yè)設計（論文）外文資料翻譯及原文
三、學生“畢業(yè)論文（論文）計劃、進度、檢查及落實表”
四、實習鑒定表
無錫太湖學院
畢業(yè)設計（論文）
開題報告
題目：手機外殼的注塑模具設計與加工
信機系 機械工程及其自動化 專業(yè)
學 號： 0923275
學生姓名： 陳 兵
指導教師： 王士同 （職稱：教 授 ）
（職稱： ）
2012年11月12日
課題來源
某模具公司提供，該產(chǎn)品為手機背面外殼，要求設計一套模具來生產(chǎn)它，預估產(chǎn)量比較大，所以設計為一模兩腔。
科學依據(jù)（包括課題的科學意義；國內(nèi)外研究概況、水平和發(fā)展趨勢；應用前景等）
（1）課題科學意義
眾所周知中國很早就開始制作模具和使用模具，但長期未形成產(chǎn)業(yè)。不過從上個世紀80年代開始，在國家產(chǎn)業(yè)政策和與之配套的一系列國家經(jīng)濟政策的支持和引導下，我國模具工業(yè)發(fā)展迅速，年均增速均為21%，至2005年我國模具總產(chǎn)值約為610億元，其中塑料模具約30%左右。在未來的模具市場中，塑料模在模具總量中的比例還將逐步提高。模具技術的進步極大地促進了工業(yè)產(chǎn)品的生產(chǎn)發(fā)展，模具是“效益放大器”，用模具生產(chǎn)最終產(chǎn)品的價值將超過自身價格的幾十倍乃至百倍及上千倍。據(jù)各國報導，模具工業(yè)在歐美等工業(yè)發(fā)達國家被稱之“點鐵成金”的“磁力工業(yè)”，雖然我國模具行業(yè)已經(jīng)駛?cè)氚l(fā)展快車道，但由于在精度、壽命、制造周期及能力等方面，與國際水平和工業(yè)先進國家相比尚有較大差距，所以還不能滿足我國制造業(yè)發(fā)展的需求。特別是在精密、大型、復雜、長壽命模具方面，中國與國際平均水平和發(fā)達國家仍有較大差距，因此，每年尚需大量進口。
不過當前全球制造業(yè)轉(zhuǎn)移的規(guī)模不斷加大，中國已成為世界上最大的制造業(yè)之地，并正向深度和廣度延伸，而我國的模具制造業(yè)正是承接轉(zhuǎn)移的較為理想之地。目前國家正在大力支持具工業(yè)的發(fā)展，在多重有利條件下，我國模具行業(yè)的未來將展現(xiàn)出一派美好景色。
研究內(nèi)容
① 調(diào)查、研究、查閱文獻和搜集資料；
② 閱讀和翻譯與研究內(nèi)容有關的外文資料；
③ 撰寫開題報告
④ 掌握CAD,UG等模具設計方面的軟件；
⑤ 詳細設計內(nèi)容（澆注系統(tǒng)，冷卻系統(tǒng)，頂出系統(tǒng)，機構系統(tǒng)等）或研究方法 ；
⑥ 設計或有關計算；
⑦ 撰寫畢業(yè)設計（論文）。
擬采取的研究方法、技術路線、實驗方案及可行性分析
（1）實驗方案
模具課題的研究很難用準確的數(shù)學模型來描述。他很大一部分靠設計人員的經(jīng)驗。所以我們從傳統(tǒng)的將其分為四部分。
1 設計前準備工作：明確設計的要求以及必要的設計資料，研究材料的工藝成型性。
2．方案設計：確定模具結(jié)構包括結(jié)構類型，型腔數(shù)目，分型面，澆注系統(tǒng)，排氣方式，冷卻系統(tǒng)等
3．零部件的設計：排氣結(jié)構設計，成型零件設計，溫度調(diào)控系統(tǒng)設計，模架選擇，頂出機構設計，模具材料選擇等
4．后期階段：繪制零件圖以及總裝配圖，使用說明書。
（2）研究方法
本課題的主要通過AUTOCAD，UG等軟件的輔助設計將模具各個零件繪制出來以構成各個系統(tǒng)與結(jié)構，在通過對結(jié)構的分析修改以達到可以加工產(chǎn)品要求。
研究計劃及預期成果
研究計劃：
2012年12月12日-2012年12月25日：按照任務書要求查閱論文相關參考資料，填寫畢業(yè)設計開題報告書。
2013年1月11日-2013年3月5日：填寫畢業(yè)實習報告。
2013年3月8日-2013年3月14日：按照要求修改畢業(yè)設計開題報告。
2013年3月15日-2013年3月21日：學習并翻譯一篇與畢業(yè)設計相關的英文材料。
2013年3月22日-2013年4月11日：模具分模以及模具結(jié)構設計。
2013年4月12日-2013年4月25日：模具相關2D圖面繪制。
2013年4月26日-2013年5月21日： 畢業(yè)論文撰寫和修改工作。
預期成果：
利用設計出來的模具將產(chǎn)品生產(chǎn)出來，并達到預期效果
特色或創(chuàng)新之處
① 可以代替機床將產(chǎn)品生產(chǎn)出來，并實現(xiàn)自動化。
② 實現(xiàn)了對產(chǎn)品的大批量復制性生產(chǎn)。
已具備的條件和尚需解決的問題
① 提高了生產(chǎn)效率。
② 該模具結(jié)構還需要改善，精度還有待提高。
指導教師意見
指導教師簽名：
年 月 日
教研室（學科組、研究所）意見
教研室主任簽名：
年 月 日
系意見
主管領導簽名：
年 月 日
英文原文
Automated surface finishing of plastic injection mold steel with spherical grinding and ball burnishing processes
Abstract
This study investigates the possibilities of automated spherical grinding and ball burnishing surface finishing processes in a freeform surface plastic injection mold steel PDS5 on a CNC machining center. The design and manufacture of a grinding tool holder has been accomplished in this study. The optimal surface grinding parameters were determined using Taguchi’s orthogonal array method for plastic injection molding steel PDS5 on a machining center. The optimal surface grinding parameters for the plastic injection mold steel PDS5 were the combination of an abrasive material of PA Al2O3, a grinding speed of 18 000 rpm, a grinding depth of 20 μm, and a feed of 50 mm/min. The surface roughness Ra of the specimen can be improved from about 1.60 μm to 0.35 μm by using the optimal parameters for surface grinding. Surface roughness Ra can be further improved from about 0.343 μm to 0.06 μm by using the ball burnishing process with the optimal burnishing parameters. Applying the optimal surface grinding and burnishing parameters sequentially to a fine-milled freeform surface mold insert, the surface roughness Ra of freeform surface region on the tested part can be improved from about 2.15 μm to 0.07 μm.
Keywords Automated surface finishing · Ball burnishing process · Grinding process · Surface roughness · Taguchi’s method
1 Introduction
Plastics are important engineering materials due to their specific characteristics, such as corrosion resistance, resistance to chemicals, low density, and ease of manufacture, and have increasingly replaced metallic components in industrial applications. Injection molding is one of the important forming processes for plastic products. The surface finish quality of the plastic injection mold is an essential requirement due to its direct effects on the appearance of the plastic product. Finishing processes such as grinding, polishing and lapping are commonly used to improve the surface finish.
The mounted grinding tools (wheels) have been widely used in conventional mold and die finishing industries. The geometric model of mounted grinding tools for automated surface finishing processes was introduced in. A finishing process mode of spherical grinding tools for automated surface finishing systems was developed in. Grinding speed, depth of cut, feed rate, and wheel properties such as abrasive material and abrasive grain size, are the dominant parameters for the spherical grinding process, as shown in Fig. 1. The optimal spherical grinding parameters for the injection mold steel have not yet been investigated based in the literature.
Fig.1. Schematic diagram of the spherical grinding process
In recent years, some research has been carried out in determining the optimal parameters of the ball burnishing process (Fig. 2). For instance, it has been found that plastic deformation on the workpiece surface can be reduced by using a tungsten carbide ball or a roller, thus improving the surface roughness, surface hardness, and fatigue resistance. The burnishing process is accomplished by machining centers and lathes. The main burnishing parameters having significant effects on the surface roughness are ball or roller material, burnishing force, feed rate, burnishing speed, lubrication, and number of burnishing passes, among others. The optimal surface burnishing parameters for the plastic injection mold steel PDS5 were a combination of grease lubricant, the tungsten carbide ball, a burnishing speed of 200 mm/min, a burnishing force of 300 N, and a feed of 40 μm. The depth of penetration of the burnished surface using the optimal ball burnishing parameters was about 2.5 microns. The improvement of the surface roughness through burnishing process generally ranged between 40% and 90%.
Fig. 2. Schematic diagram of the ball-burnishing process
The aim of this study was to develop spherical grinding and ball burnishing surface finish processes of a freeform surface plastic injection mold on a machining center. The flowchart of automated surface finish using spherical grinding and ball burnishing processes is shown in Fig. 3. We began by designing and manufacturing the spherical grinding tool and its alignment device for use on a machining center. The optimal surface spherical grinding parameters were determined by utilizing a Taguchi’s orthogonal array method. Four factors and three corresponding levels were then chosen for the Taguchi’s L18 matrix experiment. The optimal mounted spherical grinding parameters for surface grinding were then applied to the surface finish of a freeform surface carrier. To improve the surface roughness, the ground surface was further burnished, using the optimal ball burnishing parameters.
Fig. 3. Flow chart of automated surface finish using spherical grinding and ball burnishing processes
2 Design of the spherical grinding tool and its alignment device
To carry out the possible spherical grinding process of a freeform surface, the center of the ball grinder should coincide with the z-axis of the machining center. The mounted spherical grinding tool and its adjustment device was designed, as shown in Fig. 4. The electric grinder was mounted in a tool holder with two adjustable pivot screws. The center of the grinder ball was well aligned with the help of the conic groove of the alignment components. Having aligned the grinder ball, two adjustable pivot screws were tightened; after which, the alignment components could be removed. The deviation between the center coordinates of the ball grinder and that of the shank was about 5 μm, which was measured by a CNC coordinate measuring machine. The force induced by the vibration of the machine bed is absorbed by a helical spring. The manufactured spherical grinding tool and ball-burnishing tool were mounted, as shown in Fig. 5. The spindle was locked for both the spherical grinding process and the ball burnishing process by a spindle-locking mechanism.
Fig.4. Schematic illustration of the spherical grinding tool and its adjustment device
Fig.5. (a) Photo of the spherical grinding tool (b) Photo of the ball burnishing tool
3 Planning of the matrix experiment
3.1 Configuration of Taguchi’s orthogonal array
The effects of several parameters can be determined efficiently by conducting matrix experiments using Taguchi’s orthogonal array. To match the aforementioned spherical grinding parameters, the abrasive material of the grinder ball (with the diameter of 10 mm), the feed rate, the depth of grinding, and the revolution of the electric grinder were selected as the four experimental factors (parameters) and designated as factor A to D (see Table 1) in this research. Three levels (settings) for each factor were configured to cover the range of interest, and were identified by the digits 1, 2, and 3. Three types of abrasive materials, namely silicon carbide (SiC), white aluminum oxide (Al2O3, WA), and pink aluminum oxide (Al2O3, PA), were selected and studied. Three numerical values of each factor were determined based on the pre-study results. The L18 orthogonal array was selected to conduct the matrix experiment for four 3-level factors of the spherical grinding process.
Table1. The experimental factors and their levels
3.2 Definition of the data analysis
Engineering design problems can be divided into smaller-the better types, nominal-the-best types, larger-the-better types, signed-target types, among others [8]. The signal-to-noise (S/N) ratio is used as the objective function for optimizing a product or process design. The surface roughness value of the ground surface via an adequate combination of grinding parameters should be smaller than that of the original surface. Consequently, the spherical grinding process is an example of a smaller-the-better type problem. The S/N ratio, η, is defined by the following equation:
η =?10 log10(mean square quality characteristic)
=?10 log10
where:
yi : observations of the quality characteristic under different noise conditions
n: number of experiment
After the S/N ratio from the experimental data of each L18 orthogonal array is calculated, the main effect of each factor was determined by using an analysis of variance (ANOVA) technique and an F-ratio test. The optimization strategy of the smaller-the better problem is to maximize η, as defined by Eq. 1. Levels that maximize η will be selected for the factors that have a significant effect on η. The optimal conditions for spherical grinding can then be determined.
4 Experimental work and results
The material used in this study was PDS5 tool steel (equivalent to AISI P20), which is commonly used for the molds of large plastic injection products in the field of automobile components and domestic appliances. The hardness of this material is about HRC33 (HS46). One specific advantage of this material is that after machining, the mold can be directly used for further finishing processes without heat treatment due to its special pre-treatment. The specimens were designed and manufactured so that they could be mounted on a dynamometer to measure the reaction force. The PDS5 specimen was roughly machined and then mounted on the dynamometer to carry out the fine milling on a three-axis machining center made by Yang-Iron Company (type MV-3A), equipped with a FUNUC Company NC-controller (type 0M). The pre-machined surface roughness was measured, using Hommelwerke T4000 equipment, to be about 1.6 μm. Figure 6 shows the experimental set-up of the spherical grinding process. A MP10 touch-trigger probe made by the Renishaw Company was also integrated with the machining center tool magazine to measure and determine the coordinated origin of the specimen to be ground. The NC codes needed for the ball-burnishing path were generated by PowerMILL CAM software. These codes can be transmitted to the CNC controller of the machining center via RS232 serial interface.
Fig.6. Experimental set-up to determine the optimal spherical grinding parameters
Table 2 summarizes the measured ground surface roughness alue Ra and the calculated S/N ratio of each L18 orthogonal array sing Eq. 1, after having executed the 18 matrix experiments. The average S/N ratio for each level of the four actors is shown graphically in Fig. 7.
Table2. Ground surface roughness of PDS5 specimen
Exp.
Inner array
(control factors)
Measured surface
roughness value (Ra)
Response
no
A
B
C
D
S/N(η(dB))
Mean
1
1
1
1
1
0.35
0.35
0.35
9.119
0.350
2
1
2
2
2
0.37
0.36
0.38
8.634
0.370
3
1
3
3
3
0.41
0.44
0.40
7.597
0.417
4
2
1
2
3
0.63
0.65
0.64
3.876
0.640
5
2
2
3
1
0.73
0.77
0.78
2.380
0.760
6
2
3
1
2
0.45
0.42
0.39
7.530
0.420
7
3
1
3
2
0.34
0.31
0.32
9.801
0.323
8
3
2
1
3
0.27
0.25
0.28
11.471
0.267
9
3
3
2
1
0.32
0.32
0.32
9.897
0.320
10
1
1
2
2
0.35
0.39
0.40
8.390
0.380
11
1
2
3
3
0.41
0.50
0.43
6.968
0.447
12
1
3
1
1
0.40
0.39
0.42
7.883
0.403
13
2
1
1
3
0.33
0.34
0.31
9.712
0.327
14
2
2
2
1
0.48
0.50
0.47
6.312
0.483
15
2
3
3
2
0.57
0.61
0.53
4.868
0.570
16
3
1
3
1
0.59
0.55
0.54
5.030
0.560
17
3
2
1
2
0.36
0.36
0.35
8.954
0.357
18
3
3
2
3
0.57
0.53
0.53
5.293
0.543
Fig.7. Plots of control factor effects
The goal in the spherical grinding process is to minimize the surface roughness value of the ground specimen by determining the optimal level of each factor. Since ?log is a monotone decreasing function, we should maximize the S/N ratio. Consequently, we can determine the optimal level for each factor as being the level that has the highest value of η. Therefore, based on the matrix experiment, the optimal abrasive material was pink aluminum oxide; the optimal feed was 50 mm/min; the optimal depth of grinding was 20 μm; and the optimal revolution was 18 000 rpm, as shown in Table 3.
The optimal parameters for surface spherical grinding obtained from the Taguchi’s matrix experiments were applied to the surface finish of the freeform surface mold insert to evaluate the surface roughness improvement. A perfume bottle was selected as the tested carrier. The CNC machining of the mold insert for the tested object was simulated with Power MILL CAM software. After fine milling, the mold insert was further ground with the optimal spherical grinding parameters obtained from the Taguchi’s matrix experiment. Shortly afterwards, the ground surface was burnished with the optimal ball burnishing parameters to further improve the surface roughness of the tested object (see Fig. 8). The surface roughness of the mold insert was measured with Hommelwerke T4000 equipment. The average surface roughness value Ra on a fine-milled surface of the mold insert was 2.15 μm on average; that on the ground surface was 0.45 μm on average; and that on burnished surface was 0.07 μm on average. The surface roughness improvement of the tested object on ground surface was about (2.15?0.45)/2.15 = 79.1%, and that on the burnished surface was about (2.15?0.07)/2.15 = 96.7%.
Fig.8. Fine-milled, ground and burnished mold insert of a perfume bottle
5 Conclusion
In this work, the optimal parameters of automated spherical grinding and ball-burnishing surface finishing processes in a freeform surface plastic injection mold were developed successfully on a machining center. The mounted spherical grinding tool (and its alignment components) was designed and manufactured. The optimal spherical grinding parameters for surface grinding were determined by conducting a Taguchi L18 matrix experiments. The optimal spherical grinding parameters for the plastic injection mold steel PDS5 were the combination of the abrasive material of pink aluminum oxide (Al2O3, PA), a feed of 50 mm/min, a depth of grinding 20 μm, and a revolution of 18 000 rpm. The surface roughness Ra of the specimen can be improved from about 1.6 μm to 0.35 μm by using the optimal spherical grinding conditions for surface grinding. By applying the optimal surface grinding and burnishing parameters to the surface finish of the freeform surface mold insert, the surface roughness improvements were measured to be ground surface was about 79.1% in terms of ground surfaces, and about 96.7% in terms of burnished surfaces.
中文譯文
基于注塑模具鋼研磨和拋光工序的自動化表面處理
摘要
這篇文章研究了注塑模具鋼自動研磨與球面拋光加工工序的可能性，它可以在數(shù)控加工中心完成注塑模具鋼PDS5的塑性曲面。這項研究已經(jīng)完成了磨削刀架的設計與制造。 最佳表面研磨參數(shù)是在鋼鐵PDS5 的加工中心測定的。對于PDS5注塑模具鋼的最佳球面研磨參數(shù)是以下一系列的組合：研磨材料的磨料為粉紅氧化鋁，進給量50毫米/分鐘，磨削深度20微米，磨削轉(zhuǎn)速為18000RPM。表面粗糙度Ra值可由大約1.60微米改善至0.35微米，通過用優(yōu)化的參數(shù)進行表面研磨。 如果用球拋光工藝和參數(shù)優(yōu)化拋光，還可以進一步改善表面粗糙度Ra值，一般從0.343微米至0.06微米左右。而在模具內(nèi)部曲面的測試部分，用最佳參數(shù)的表面研磨、拋光，曲面表面粗糙度就可以提高約2.15微米至0.07微米。
關鍵詞: 自動化表面處理 拋光 磨削過程 表面粗糙度 田口方法
一、引言
步距
研磨高度
球磨研磨
進給速度
工作臺
由于塑膠工程材料的重要特點,比如耐化學腐蝕性、低密度、易于制造,并且已經(jīng)日漸取代了金屬部件在工業(yè)中廣泛應用。 在注塑成型領域，其對于塑料制品是一個重要工藝。設計的本質(zhì)要求是注塑模具的表面質(zhì)量,因為它直接影響了塑膠產(chǎn)品的外觀和性能。 加工工藝如球面研磨、拋光常用于改善表面光潔度。
圖1 球面研磨過程示意圖
研磨工具(輪子) 的安裝的磨削工具（車輪）已被廣泛地用在常規(guī)的模具和模具精加工產(chǎn)業(yè)。安裝的幾何模型的整理工序引入英寸甲球面磨削工具自動化表面精加工處理模式的狀態(tài)下，完成系統(tǒng)開發(fā)英寸磨削速度，切削深度，進給速率，如研磨材料和車輪屬性自動化表面的磨削工具。和磨料顆粒的大小，是用于球形研磨過程的主要參數(shù)，如在圖所示。1。的最佳的球形研磨參數(shù)用于注射模具鋼中尚未調(diào)查是根據(jù)在文獻中。
在最近幾年中，已經(jīng)進行了一些研究，在確定球拋光過程（圖2）的最優(yōu)參數(shù)。比如，已發(fā)現(xiàn)，可以減少使用的鎢硬質(zhì)合金球或輥在工件表面上的塑性變形，從而改善表面粗糙度，表面硬度和耐疲勞性。拋光過程是通過加工中心和車床。主要的拋光參數(shù)，具有顯著的表面粗糙度的影響的滾珠或滾子材料，拋光力，進給速率，拋光速度快，潤滑和拋光通行證的數(shù)量，等等。最佳的表面的塑料注射模具鋼PDS5擠光參數(shù)的組合的潤滑脂，碳化鎢球的拋光速度為200毫米/分鐘，拋光力，300 N，和一個飼料為40μm。使用的最佳球拋光參數(shù)的磨光表面的滲透深度為約2.5微米。通過拋光過程中的改進的表面粗糙度一般介于40％和90％之間。
圖2 球面拋光過程概略圖
本文研究的目的是開發(fā)球面磨削球拋光表面處理工藝的自由曲面，塑料注塑模具加工中心。自動化表面精加工的流程圖中，使用球面磨削和球拋光過程示于圖3中。我們開始設計和制造的球面磨削加工中心上使用的工具，其定位裝置。最佳的表面球面磨削參數(shù)進行了測定，利用田口正交陣列的方法。四個因素，三個相應的級別，然后選擇為田口L18矩陣實驗。的最佳安裝球面磨削參數(shù)，然后將其應用于自由曲面載體的表面光潔度的表面研磨。為了改善表面粗糙度，地面進一步打磨，使用的最佳球擠光參數(shù)。
PDS試樣的設計與制造
選擇最佳矩陣實驗因子
確定最佳參數(shù)
實施實驗
分析并確定最佳因子
進行表面拋光
應用最佳參數(shù)加工曲面
測量試樣的表面粗糙度
球研磨和拋光裝置的設計與制造
圖3 自動球面研磨與拋光工序的流程圖
二、球研磨的設計和對準裝置
要進行可能的球形研磨過程中的自由曲面，球研磨機的中心應與z-軸的加工中心重合。的安裝的球形研磨工具和其調(diào)整裝置的設計，如在圖所示。4。電動研磨機中，安裝在工具保持架有兩個可調(diào)的樞軸螺釘。以及研磨機球的中心對準的圓錐槽的取向組分的幫助。對準的粉碎機球，兩個可調(diào)節(jié)的支點螺絲擰緊后，對齊組件可以被刪除。中心之間的偏差的坐標球研磨機的柄部的時間是約5微米，這是由一個數(shù)控三坐標測量機測量。由振動引起的力的機床吸收由一個螺旋彈簧。所制造的球形研磨工具和球磨光工具被安裝，如圖所示 5。主軸被鎖定的球面研磨過程和球拋光由主軸鎖定機構的方法。
模柄
彈簧
工具可調(diào)支撐
緊固螺釘
磨球
自動研磨
磨球組件
圖4 球面研磨工具及其調(diào)整裝置
圖5 a 球面研磨工具的圖片. b.球拋光工具的圖片
三、矩陣實驗的規(guī)劃
3.1田口正交表
幾個參數(shù)的影響，可以有效地進行矩陣實驗田口直交。要與上述球形研磨參數(shù)相匹配，研磨機的球（直徑為10毫米），進給速度，磨削深度，和革命的電動研磨機的研磨材料被選定為四個實驗因素（參數(shù)）并指定為因子A到D（見表1），在本研究中。每個因子的三個層次（設置）被配置為覆蓋感興趣的范圍內(nèi)，并確定了數(shù)字1，2，和3。三種類型的研磨材料，即，白色氧化鋁（Al2O3，WA），碳化硅（SiC）和粉紅色的氧化鋁（Al2O3，賓夕法尼亞州），選擇和研究。每個因子的三個數(shù)值的預研究結(jié)果的基礎上確定的。 L18直交被選中的4個3級因素的球面磨削過程中進行矩陣實驗。
表1 實驗因素和水平
因素
水平
1
2
3
A.
碳化硅
白色氧化鋁
粉紅氧化鋁
B.
50
100
200
C.研磨深度（μm）
20
50
80
D.
12000
18000
24000
3.2數(shù)據(jù)分析的界定
工程設計問題,可以分為較小而好的類型,象征性最好類型,大而好類型，目標取向類型等。 信噪比(S/N)的比值，常作為目標函數(shù)來優(yōu)化產(chǎn)品或者工藝設計。 被加工面的表面粗糙度值經(jīng)過適當?shù)亟M合磨削參數(shù)，應小于原來的未加工表面。 因此,球面研磨過程屬于工程問題中的小而好類型。這里的信噪比（S/N）,η,按下列公式定義:
η =?10 log 平方等于質(zhì)量特性
=?10 log （1）
這里，
y——不同噪聲條件下所觀察的質(zhì)量特性
n——實驗次數(shù)
從每個L18型正交實驗得到的信噪比（S/N）數(shù)據(jù)，經(jīng)計算后，運用差異分析技術(變異)和殲比檢驗來測定每一個主要的因素。 優(yōu)化小而好類型的工程問題問題更是盡量使η最大而定。各級η選擇的最大化將對最終的η因素有重大影響。 最優(yōu)條件可視研磨球而待定。
四、實驗工作和結(jié)果
本研究中所使用的材料是PDS5工具鋼（相當于AISI P20），這種材料通常用于大型塑料注塑產(chǎn)品，汽車部件和國內(nèi)家電領域中的模具。這種材料的硬度是HRC33（HS46）。這種材料的一個具體的優(yōu)點是，加工后，模具可直接用于進一步的精加工過程中未經(jīng)加熱處理的，由于其特殊的前處理。試樣被設計和制造，使他們能夠被安裝在測力計來測量的反作用力。 PDS5標本粗略加工，然后安裝在底盤測功機上進行精銑陽鋼鐵公司（MV-3A型），配備一個FUNUC公司的NC-控制器（0M
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