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學(xué)士學(xué)位畢業(yè)設(shè)計
軸蓋復(fù)合模的設(shè)計與制造
學(xué)生姓名：吳乃明
學(xué) 號：20054024134
指導(dǎo)教師：代洪慶
所在學(xué)院：工程學(xué)院
專 業(yè)：機械設(shè)計制造及其自動化
中國·大慶
2009 年 6 月
黑龍江八一農(nóng)墾大學(xué)
畢業(yè)設(shè)計(論文)開題報告
學(xué)生姓名： 吳乃明 學(xué) 號： 20054024134
專 業(yè)： 機械設(shè)計制造及其自動化
設(shè)計(論文)題目：軸蓋復(fù)合模的設(shè)計與制造
指導(dǎo)教師： 代洪慶
2009 年 3 月 17 日
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1．結(jié)合畢業(yè)設(shè)計（論文）課題情況，根據(jù)所查閱的文獻資料，每人撰寫
2000字左右的文獻綜述：
文 獻 綜 述
?隨著工業(yè)產(chǎn)品質(zhì)量的不斷提高，沖壓產(chǎn)品生產(chǎn)正呈現(xiàn)多品種、少批量，復(fù)雜、大型、精密，更新?lián)Q代速度快的變化特點，沖壓模具正向高效、精密、長壽命、大型化方向發(fā)展。為適應(yīng)市場變化，隨著計算機技術(shù)和制造技術(shù)的迅速發(fā)展，沖壓模具設(shè)計與制造技術(shù)正由手工設(shè)計、依靠人工經(jīng)驗和常規(guī)機械加工技術(shù)向以計算機輔助設(shè)計（CAD）、數(shù)控切削加工、數(shù)控電加工為核心的計算機輔助設(shè)計與制造（CAD/CAM）技術(shù)轉(zhuǎn)變。
????（一）沖壓成形理論及沖壓工藝
????加強冷沖壓變形基礎(chǔ)理論的研究，以提供更加準(zhǔn)確、實用、方便的計算方法，正確地確定沖壓工藝參數(shù)和模具工作部分的幾何形狀與尺寸，解決冷沖壓變形中出現(xiàn)的各種實際問題，進一步提高沖壓件的質(zhì)量。
????研究和推廣采用新工藝，如精沖工藝、軟模成形工藝、高能高速成形工藝、超塑性成形工藝以及其它高效率、經(jīng)濟成形工藝等，進一步提高冷沖壓技術(shù)水平。
????值得特別指出的是，隨著計算機技術(shù)的飛躍發(fā)展和塑性變形理論的進一步完善，近年來國內(nèi)外已開始應(yīng)用塑性成形過程的計算機模擬技術(shù)，即利用有限元等數(shù)值分析方法模擬金屬的塑性成形過程，通過分析數(shù)值技術(shù)結(jié)果，幫助設(shè)計人員實現(xiàn)優(yōu)化設(shè)計。
?????(二)模具先進制造工藝及設(shè)備
?????模具制造技術(shù)現(xiàn)代化是模具工業(yè)發(fā)展的基礎(chǔ)。隨著科學(xué)技術(shù)的發(fā)展，計算機技術(shù)、信息技術(shù)、自動化技術(shù)等先進技術(shù)正不斷向傳統(tǒng)制造技術(shù)滲透、交叉、融合，對其實施改造，形成先進制造技術(shù)。模具先進制造技術(shù)的發(fā)展主要體現(xiàn)在如下方面：
1． 高速銑削加工
普通銑削加工采用低的進給速度和大的切削參數(shù)，而高速銑削加工則采用高的進給速度和小的切削參數(shù)，高速銑削加工相對于普通銑削加工具有如下特點：
?????（1）高效 高速銑削的主軸轉(zhuǎn)速一般為15000r/min～40000r/min，最高可達100000r/min。在切削鋼時，其切削速度約為400m/min，比傳統(tǒng)的銑削加工高5～10倍；在加工模具型腔時與傳統(tǒng)的加工方法(傳統(tǒng)銑削、電火花成形加工等)相比其效率提高4～5倍。
?????（2）高精度 高速銑削加工精度一般為10μm，有的精度還要高。
?????（3）高的表面質(zhì)量 由于高速銑削時工件溫升?。s為3°C），故表面沒有變質(zhì)層及微裂紋，熱變形也小。最好的表面粗糙度Ra小于1μm，減少了后續(xù)磨削及拋光工作量。
2． 磨削及拋光加工技術(shù)
磨削及拋光加工由于精度高、表面質(zhì)量好、表面粗糙度值低等特點，在精密模具加工中廣泛應(yīng)用。目前，精密模具制造廣泛使用數(shù)控成形磨床、數(shù)控光學(xué)曲線磨床、數(shù)控連續(xù)軌跡座標(biāo)磨床及自動拋光機等先進設(shè)備和技術(shù)。
3． 數(shù)控測量
產(chǎn)品結(jié)構(gòu)的復(fù)雜，必然導(dǎo)致模具零件形狀的復(fù)雜。傳統(tǒng)的幾何檢測手段已無法適應(yīng)模具的生產(chǎn)。現(xiàn)代模具制造已廣泛使用三坐標(biāo)數(shù)控測量機進行模具零件的幾何量的測量，模具加工過程的檢測手段也取得了很大進展。三坐標(biāo)數(shù)控測量機除了能高精度地測量復(fù)雜曲面的數(shù)據(jù)外，其良好的溫度補償裝置、可靠的抗振保護能力、嚴密的除塵措施以及簡便的操作步驟，使得現(xiàn)場自動化檢測成為可能。
?????模具先進制造技術(shù)的應(yīng)用改變了傳統(tǒng)制模技術(shù)模具質(zhì)量依賴于人為因素，不易控制的狀況，使得模具質(zhì)量依賴于物化因素，整體水平容易控制，模具再現(xiàn)能力強。
?????(三)模具新材料及熱、表處理
?????隨著產(chǎn)品質(zhì)量的提高，對模具質(zhì)量和壽命要求越來越高。而提高模具質(zhì)量和壽命最有效的辦法就是開發(fā)和應(yīng)用模具新材料及熱、表處理新工藝,不斷提高使用性能,改善加工性能。??
1． 模具新材料
沖壓模具使用的材料屬于冷作模具鋼，是應(yīng)用量大、使用面廣、種類最多的模具鋼。主要性能要求為強度、韌性、耐磨性。目前冷作模具鋼的發(fā)展趨勢是在高合金鋼性能基礎(chǔ)上，分為兩大分支：一種是降低含碳量和合金元素量，提高鋼中碳化物分布均勻度，突出提高模具的韌性。另一種是以提高耐磨性為主要目的，以適應(yīng)高速、自動化、大批量生產(chǎn)而開發(fā)的粉末高速鋼。??
??
2． 熱處理、表處理新工藝
?為了提高模具工作表面的耐磨性、硬度和耐蝕性，必須采用熱、表處理新技術(shù)，尤其是表面處理新技術(shù)。除人們熟悉的鍍硬鉻、氮化等表面硬化處理方法外，近年來模具表面性能強化技術(shù)發(fā)展很快，實際應(yīng)用效果很好。其中，化學(xué)氣相沉積（CVD）、物理氣相沉積（PVD）以及鹽浴滲金屬（TD）的方法是幾種發(fā)展較快，應(yīng)用最廣的表面涂覆硬化處理的新技術(shù)。它們對提高模具壽命和減少模具昂貴材料的消耗，有著十分重要的意義。
?????(四)模具CAD/CAM技術(shù)
?????計算機技術(shù)、機械設(shè)計與制造技術(shù)的迅速發(fā)展和有機結(jié)合，形成了計算機輔助設(shè)計與計算機輔助制造（CAD/CAM）這一新型技術(shù)。
?????CAD/CAM是改造傳統(tǒng)模具生產(chǎn)方式的關(guān)鍵技術(shù)，是一項高科技、高效益的系統(tǒng)工程，它以計算機軟件的形式為用戶提供一種有效的輔助工具，使工程技術(shù)人員能借助計算機對產(chǎn)品、模具結(jié)構(gòu)、成形工藝、數(shù)控加工及成本等進行設(shè)計和優(yōu)化。模具CAD/CAM能顯著縮短模具設(shè)計及制造周期、降低生產(chǎn)成本、提高產(chǎn)品質(zhì)量已成為人們的共識。
隨著功能強大的專業(yè)軟件和高效集成制造設(shè)備的出現(xiàn)，以三維造型為基礎(chǔ)、基于并行工程（CE）的模具CAD/CAM技術(shù)正成為發(fā)展方向，它能實現(xiàn)面向制造和裝配的設(shè)計，實現(xiàn)成形過程的模擬和數(shù)控加工過程的仿真，使設(shè)計、制造一體化。
?????(五)快速經(jīng)濟制模技術(shù)
?????為了適應(yīng)工業(yè)生產(chǎn)中多品種、小批量生產(chǎn)的需要，加快模具的制造速度，降低模具生產(chǎn)成本，開發(fā)和應(yīng)用快速經(jīng)濟制模技術(shù)越來越受到人們的重視。目前，快速經(jīng)濟制模技術(shù)主要有低熔點合金制模技術(shù)、鋅基合金制模技術(shù)、環(huán)氧樹脂制模技術(shù)、噴涂成形制模技術(shù)、疊層鋼板制模技術(shù)等。應(yīng)用快速經(jīng)濟制模技術(shù)制造模具，能簡化模具制造工藝、縮短制造周期（比普通鋼模制造周期縮短70%～90%）、降低模具生產(chǎn)成本（比普通鋼模制造成本降低60%～80%），在工業(yè)生產(chǎn)中取得了顯著的經(jīng)濟效益。對提高新產(chǎn)品的開發(fā)速度，促進生產(chǎn)的發(fā)展有著非常重要的作用。
參考文獻
[1] 李大鑫,張秀棉. 模具技術(shù)現(xiàn)狀與發(fā)展趨勢綜述[J]模具制造, 2005,(02).
[2] 趙昌盛 ,朱邦全. 我國模具材料的應(yīng)用發(fā)展[J]模具制造, 2004,(11).
[3]?付宏生.冷沖壓成形工藝與模具設(shè)計制造[M].北京：化學(xué)工業(yè)出版社，2004
[4] 趙昌盛.實用模具材料應(yīng)用手冊[M]. 北京：機械工業(yè)出版社，2005，6
[5] 張六玲. 國內(nèi)外模具工業(yè)的基本現(xiàn)狀與市場預(yù)測[J]. 模具制造 , 2002,(01)
[6] 胡興軍. 我國模具業(yè)的發(fā)展及改進措施[J]. 世界制造技術(shù)與裝備市場 , 2005,(01)
[7] 洪慎章. 現(xiàn)代模具工業(yè)的發(fā)展趨勢及企業(yè)特征[J]. 航空制造技術(shù) , 2003,(06)
[8] 周永泰. 模具設(shè)計和加工技術(shù)的發(fā)展方向[J]. 制造技術(shù)與機床 , 2003,(05)
[9] 李雙義.冷沖模具設(shè)計[M].清華大學(xué)出版社[J]
[10] 薛啓翔.冷沖壓實用技術(shù). 北京：機械工業(yè)出版社，2006,1
[11]沖模設(shè)計手冊編寫組. 沖模設(shè)計手冊[J].北京：機械工業(yè)出版社，2006
[12]曾霞文，徐正坤.冷沖壓模具及模具設(shè)計[M].長沙：中南大學(xué)出版社，2006
[13].駱志濱.模具工實用手冊[J].南京：江蘇科學(xué)技術(shù)出版社，2000
[14].肖景榮，姜奎華.沖壓工藝學(xué)[M].北京：機械工業(yè)出版社，2006
[15].胡世光，陳鶴崢.板料冷壓成形的工程分析[M].北京：北京航空航天大學(xué)出版社，2004
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２．本課題要研究或解決的問題和擬采用的研究手段（途徑）：
主要在原有基礎(chǔ)上通過模具的設(shè)計合理，改進加工方法，加工精度和工序來提高模具質(zhì)量。研究的手段是通過CAD/CAXA來進行圖紙的繪制。在研究過程中的缺點和不足望老師提出并指正。
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e pos 模具工業(yè)現(xiàn)狀Process simulation in stamping – recent
applications for product and process design
Abstract
Process simulation for product and process design is currently being practiced in industry. However, a number of input variables have a significant effect on the accuracy and reliability of computer predictions. A study was conducted to evaluate the capability of FE-simulations for predicting part characteristics and process conditions in forming complex-shaped, industrial parts.
In industrial applications, there are two objectives for conducting FE-simulations of the stamping process; (1) to optimize the product design by analyzing formability at the product design stage and (2) to reduce the tryout time and cost in process design by predicting the deformation process in advance during the die design stage. For each of these objectives, two kinds of FE-simulations are applied. Pam-Stamp, an incremental dynamic-explicit FEM code released by Engineering Systems Int'l, matches the second objective well because it can deal with most of the practical stamping parameters. FAST_FORM3D, a one-step FEM code released by Forming Technologies, matches the first objective because it only requires the part geometry and not the complex process information.
In a previous study, these two FE codes were applied to complex-shaped parts used in manufacturing automobiles and construction machinery. Their capabilities in predicting formability issues in stamping were evaluated. This paper reviews the results of this study and summarizes the recommended procedures for obtaining accurate and reliable results from FE simulations.
In another study, the effect of controlling the blank holder force (BHF) during the deep drawing of hemispherical, dome-bottomed cups was investigated. The standard automotive aluminum-killed, drawing-quality (AKDQ) steel was used as well as high performance materials such as high strength steel, bake hard steel, and aluminum 6111. It was determined that varying the BHF as a function of stroke improved the strain distributions in the domed cups.
Keywords: Stamping; Process ;stimulation; Process design
1. Introduction
The design process of complex shaped sheet metal stampings such as automotive panels, consists of many stages of decision making and is a very expensive and time consuming process. Currently in industry, many engineering decisions are made based on the knowledge of experienced personnel and these decisions are typically validated during the soft tooling and prototyping stage and during hard die tryouts. Very often the soft and hard tools must be reworked or even redesigned and remanufactured to provide parts with acceptable levels of quality.
The best case scenario would consist of the process outlined in Fig. 1. In this design process, the experienced product designer would have immediate feedback using a specially design software called one-step FEM to estimate the formability of their design. This would allow the product designer to make necessary changes up front as opposed to down the line after expensive tooling has been manufactured. One-step FEM is particularly suited for product analysis since it does not require binder, addendum, or even most process conditions. Typically this information is not available during the product design phase. One-step FEM is also easy to use and computationally fast, which allows the designer to play “what if” without much time investment.
Fig. 1. Proposed design process for sheet metal stampings.
Once the product has been designed and validated, the development project would enter the “time zero” phase and be passed onto the die designer. The die designer would validate his/her design with an incremental FEM code and make necessary design changes and perhaps even optimize the process parameters to ensure not just minimum acceptability of part quality, but maximum achievable quality. This increases product quality but also increase process robustness. Incremental FEM is particularly suited for die design analysis since it does require binder, addendum, and process conditions which are either known during die design or desired to be known.
The validated die design would then be manufactured directly into the hard production tooling and be validated with physical tryouts during which the prototype parts would be made. Tryout time should be decreased due to the earlier numerical validations. Redesign and remanufacturing of the tooling due to unforeseen forming problems should be a thing of the past. The decrease in tryout time and elimination of redesign/remanufacturing should more than make up for the time used to numerically validate the part, die, and process.
Optimization of the stamping process is also of great importance to producers of sheet stampings. By modestly increasing one's investment in presses, equipment, and tooling used in sheet forming, one may increase one's control over the stamping process tremendously. It has been well documented that blank holder force is one of the most sensitive process parameters in sheet forming and therefore can be used to precisely control the deformation process.
By controlling the blank holder force as a function of press stroke AND position around the binder periphery, one can improve the strain distribution of the panel providing increased panel strength and stiffness, reduced springback and residual stresses, increased product quality and process robustness. An inexpensive, but industrial quality system is currently being developed at the ERC/NSM using a combination of hydraulics and nitrogen and is shown in Fig. 2. Using BHF control can also allow engineers to design more aggressive panels to take advantage the increased formability window provided by BHF control.
Fig. 2. Blank holder force control system and tooling being developed at the ERC/NSM labs.
Three separate studies were undertaken to study the various stages of the design process. The next section describes a study of the product design phase in which the one-step FEM code FAST_FORM3D (Forming Technologies) was validated with a laboratory and industrial part and used to predict optimal blank shapes. Section 4 summarizes a study of the die design stage in which an actual industrial panel was used to validate the incremental FEM code Pam-Stamp (Engineering Systems Int'l). Section 5 covers a laboratory study of the effect of blank holder force control on the strain distributions in deep drawn, hemispherical, dome-bottomed cups.
2. Product simulation – applications
The objective of this investigation was to validate FAST_FORM3D, to determine FAST_FORM3D's blank shape prediction capability, and to determine how one-step FEM can be implemented into the product design process. Forming Technologies has provided their one-step FEM code FAST_FORM3D and training to the ERC/NSM for the purpose of benchmarking and research. FAST_FORM3D does not simulate the deformation history. Instead it projects the final part geometry onto a flat plane or developable surface and repositions the nodes and elements until a minimum energy state is reached. This process is computationally faster than incremental simulations like Pam-Stamp, but also makes more assumptions. FAST_FORM3D can evaluate formability and estimate optimal blank geometries and is a strong tool for product designers due to its speed and ease of use particularly during the stage when the die geometry is not available.
In order to validate FAST_FORM3D, we compared its blank shape prediction with analytical blank shape prediction methods. The part geometry used was a 5?in. deep 12?in. by 15?in. rectangular pan with a 1?in. flange as shown in Fig. 3. Table 1 lists the process conditions used. Romanovski's empirical blank shape method and the slip line field method was used to predict blank shapes for this part which are shown in Fig. 4.
Fig. 3. Rectangular pan geometry used for FAST_FORM3D validation.
Table 1. Process parameters used for FAST_FORM3D rectangular pan validation
Fig. 4. Blank shape design for rectangular pans using hand calculations.
(a) Romanovski's empirical method; (b) slip line field analytical method.
Fig. 5(a) shows the predicted blank geometries from the Romanovski method, slip line field method, and FAST_FORM3D. The blank shapes agree in the corner area, but differ greatly in the side regions. Fig. 5(b)–(c) show the draw-in pattern after the drawing process of the rectangular pan as simulated by Pam-Stamp for each of the predicted blank shapes. The draw-in patterns for all three rectangular pans matched in the corners regions quite well. The slip line field method, though, did not achieve the objective 1?in. flange in the side region, while the Romanovski and FAST_FORM3D methods achieved the 1?in. flange in the side regions relatively well. Further, only the FAST_FORM3D blank agrees in the corner/side transition regions. Moreover, the FAST_FORM3D blank has a better strain distribution and lower peak strain than Romanovski as can be seen in Fig. 6.
Fig. 5. Various blank shape predictions and Pam-Stamp simulation results for the rectangular pan.
(a) Three predicted blank shapes; (b) deformed slip line field blank; (c) deformed Romanovski blank; (d) deformed FAST_FORM3D blank.
Fig. 6. Comparison of strain distribution of various blank shapes using Pam-Stamp for the rectangular pan.
(a) Deformed Romanovski blank; (b) deformed FAST_FORM3D blank.
To continue this validation study, an industrial part from the Komatsu Ltd. was chosen and is shown in Fig. 7(a). We predicted an optimal blank geometry with FAST_FORM3D and compared it with the experimentally developed blank shape as shown in Fig. 7(b). As seen, the blanks are similar but have some differences.
Fig. 7. FAST_FORM3D simulation results for instrument cover validation.
(a) FAST_FORM3D's formability evaluation; (b) comparison of predicted and experimental blank geometries.
Next we simulated the stamping of the FAST_FORM3D blank and the experimental blank using Pam-Stamp. We compared both predicted geometries to the nominal CAD geometry (Fig. 8) and found that the FAST_FORM3D geometry was much more accurate. A nice feature of FAST_FORM3D is that it can show a “failure” contour plot of the part with respect to a failure limit curve which is shown in Fig. 7(a). In conclusion, FAST_FORM3D was successful at predicting optimal blank shapes for a laboratory and industrial parts. This indicates that FAST_FORM3D can be successfully used to assess formability issues of product designs. In the case of the instrument cover, many hours of trial and error experimentation could have been eliminated by using FAST_FORM3D and a better blank shape could have been developed.
Fig. 8. Comparison of FAST_FORM3D and experimental blank shapes for the instrument cover.
(a) Experimentally developed blank shape and the nominal CAD geometry; (b) FAST_FORM3D optimal blank shape and the nominal CAD geometry.
3. Die and process simulation – applications
In order to study the die design process closely, a cooperative study was conducted by Komatsu Ltd. of Japan and the ERC/NSM. A production panel with forming problems was chosen by Komatsu. This panel was the excavator's cabin, left-hand inner panel shown in Fig. 9. The geometry was simplified into an experimental laboratory die, while maintaining the main features of the panel. Experiments were conducted at Komatsu using the process conditions shown in Table 2. A forming limit diagram (FLD) was developed for the drawing-quality steel using dome tests and a vision strain measurement system and is shown in Fig. 10. Three blank holder forces (10, 30, and 50?ton) were used in the experiments to determine its effect. Incremental simulations of each experimental condition was conducted at the ERC/NSM using Pam-Stamp.
Fig. 9. Actual product – cabin inner panel.
Table 2. Process conditions for the cabin inner investigation
Fig. 10. Forming limit diagram for the drawing-quality steel used in the cabin inner investigation.
At 10?ton, wrinkling occurred in the experimental parts as shown in Fig. 11. At 30?ton, the wrinkling was eliminated as shown in Fig. 12. These experimental observations were predicted with Pam-stamp simulations as shown in Fig. 13. The 30?ton panel was measured to determine the material draw-in pattern. These measurements are compared with the predicted material draw-in in Fig. 14. Agreement was very good, with a maximum error of only 10?mm. A slight neck was observed in the 30?ton panel as shown in Fig. 13. At 50?ton, an obvious fracture occurred in the panel.
Fig. 11. Wrinkling in laboratory cabin inner panel, BHF=10?ton.
Fig. 12. Deformation stages of the laboratory cabin inner and necking, BHF=30?ton.
(a) Experimental blank; (b) experimental panel, 60% formed; (c) experimental panel, fully formed; (d) experimental panel, necking detail.
Fig. 13. Predication and elimination of wrinkling in the laboratory cabin inner.
(a) Predicted geometry, BHF=10?ton; (b) predicted geometry, BHF=30?ton.
Fig. 14. Comparison of predicted and measured material draw-in for lab cabin inner, BHF=30?ton.
Strains were measured with the vision strain measurement system for each panel, and the results are shown in Fig. 15. The predicted strains from FEM simulations for each panel are shown in Fig. 16. The predictions and measurements agree well regarding the strain distributions, but differ slightly on the effect of BHF. Although the trends are represented, the BHF tends to effect the strains in a more localized manner in the simulations when compared to the measurements. Nevertheless, these strain prediction show that Pam-Stamp correctly predicted the necking and fracture which occurs at 30 and 50?ton. The effect of friction on strain distribution was also investigated with simulations and is shown in Fig. 17.
Fig. 15. Experimental strain measurements for the laboratory cabin inner.
(a) measured strain, BHF=10?ton (panel wrinkled); (b) measured strain, BHF=30?ton (panel necked); (c) measured strain, BHF =50?ton (panel fractured).
Fig. 16. FEM strain predictions for the laboratory cabin inner.
(a) Predicted strain, BHF=10?ton; (b) predicted strain, BHF=30?ton; (c) predicted strain, BHF=50?ton.
Fig. 17. Predicted effect of friction for the laboratory cabin inner, BHF=30?ton.
(a) Predicted strain, μ=0.06; (b) predicted strain, μ=0.10.
A summary of the results of the comparisons is included in Table 3. This table shows that the simulations predicted the experimental observations at least as well as the strain measurement system at each of the experimental conditions. This indicates that Pam-Stamp can be used to assess formability issues associated with the die design.
Table 3. Summary results of cabin inner study
4. Blank holder force control – applications
The objective of this investigation was to determine the drawability of various, high performance materials using a hemispherical, dome-bottomed, deep drawn cup (see Fig. 18) and to investigate various time variable blank holder force profiles. The materials that were investigated included AKDQ steel, high strength steel, bake hard steel, and aluminum 6111 (see Table 4). Tensile tests were performed on these materials to determine flow stress and anisotropy characteristics for analysis and for input into the simulations (see Fig. 19 and Table 5).
Fig. 18. Dome cup tooling geometry.
Table 4. Material used for the dome cup study
Fig. 19. Results of tensile tests of aluminum 6111, AKDQ, high strength, and bake hard steels.
(a) Fractured tensile specimens; (b) Stress/strain curves.
Table 5. Tensile test data for aluminum 6111, AKDQ, high strength, and bake hard steels
It is interesting to note that the flow stress curves for bake hard steel and AKDQ steel were very similar except for a 5% reduction in elongation for bake hard. Although, the elongations for high strength steel and aluminum 6111 were similar, the n-value for aluminum 6111 was twice as large. Also, the r-value for AKDQ was much bigger than 1, while bake hard was nearly 1, and aluminum 6111 was much less than 1.
The time variable BHF profiles used in this investigation included constant, linearly decreasing, and pulsating (see Fig. 20). The experimental conditions for AKDQ steel were simulated using the incremental code Pam-Stamp. Examples of wrinkled, fractured, and good laboratory cups are shown in Fig. 21 as well as an image of a simulated wrinkled cup.
Fig. 20. BHF time-profiles used for the dome cup study.
(a) Constant BHF; (b) ramp BHF; (c) pulsating BHF.
Fig. 21. Experimental and simulated dome cups.
(a) Experimental good cup; (b) experimental fractured cup; (c) experimental wrinkled cup; (d) simulated wrinkled cup.
Limits of drawability were experimentally investigated using constant BHF. The results of this study are shown in Table 6. This table indicates that AKDQ had the largest drawability window while aluminum had the smallest and bake hard and high strength steels were in the middle. The strain distributions for constant, ramp, and pulsating BHF are compared experimentally in Fig. 22 and are compared with simulations in Fig. 23 for AKDQ. In both simulations and experiments, it was found that the ramp BHF trajectory improved the strain distribution the best. Not only were peak strains reduced by up to 5% thereby reducing the possibility of fracture, but low strain regions were increased. This improvement in strain distribution can increase product stiffness and strength, decrease springback and residual stresses, increase product quality and process robustness.
Table 6. Limits of drawability for dome cup with constant BHF
Fig. 22. Experimental effect of time variable BHF on engineering strain in an AKDQ steel dome cup.
Fig. 23. Simulated effect of time variable BHF on true strain in an AKDQ steel dome cup.
Pulsating BHF, at the frequency range investigated, was not found to have an effect on strain distribution. This was likely due to the fact the frequency of pulsation that was tested was only 1?Hz. It is known from previous experiments of other researchers that proper frequencies range from 5 to 25?Hz [3]. A comparison of load-stroke curves from simulation and experiments are shown in Fig. 24 for AKDQ. Good agreement was found for the case where μ=0.08. This indicates that FEM simulations can be used to assess the formability improvements that can be obtained by using BHF control techniques.
Fig. 24. Comparison of experimental and simulated load-stroke curves for an AKDQ steel dome cup.
5 Conclusions and future work
In this paper, we evaluated an improved design process for complex stampings which involved eliminating the soft tooling phase and incorporated the validation of product and process using one-step and incremental FEM simulations. Also, process improvements were proposed consisting of the implementation of blank holder force control to increase product quality and process robustness.
Three separate investigations were summarized which analyzed various stages in the design process. First, the product design phase was investigated with a laboratory and industrial validation of the one-step FEM code FAST_FORM3D and its ability to assess formability issues involved in product design. FAST_FORM3D was successful at predicting optimal blank shapes for a rectangular pan and an industrial instrument cover. In the case of the instrument cover, many hours of trial and error experimentation could have been eliminated by using FAST_FORM3D and a better blank shape could have been developed.
Second, the die design