ZL50裝載機總體及工作裝置設計
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摘 要
隨著社會生產力的提高與發(fā)展，現如今模具制造中的沖壓加工已經是一種非常成熟的金屬加工方法。它具有操作簡單、精度高、產品一致性好、生產效率高、材料利用率高和用于大批量生產等特點。本次畢業(yè)設計根據已經確定的沖載件即雙耳止動墊片的尺寸進行沖載工藝的分析及設計，從而得到沖載工藝。根據已經確定好的沖載工藝進行凸凹模結構參數的計算與設計，并根據文獻資料最終確定級進模的凸凹模結構。根據設計好的凸凹模結構選擇標準零件和模架，從而完成模具的設計并校核。完成模具設計后，用UG軟件完成模具的三維模型并采用AutoCAD軟件完成模具裝配圖的制圖。本次畢業(yè)設計還獨立完成與專業(yè)相關且不少于4萬字符的指定英文資料翻譯。通過本次畢業(yè)設計，我系統(tǒng)的學習和掌握了模具設計的知識和制造加工工藝的編制技術。我采用了較好的設計思想和設計方法，成功的完成了雙耳止動墊片沖孔落料級進模的畢業(yè)設計。
關鍵詞：設計；工藝分析；沖壓模具；結構計算；級進模。
Abstract
With the improvement and development of social productive forces, the stamping of Mold Manufacturing now is already a very advanced metal processing methods. It has the feature of simple operation, high accuracy, product consistency, high production efficiency, high utilization of materials and for mass production and so on. The graduation project bases on the pieces（binaural washer）of punch set that have been identified in binaural washer dimensions for analysis and design of the craft of punch set resulting in getting the craft of punch. I will do the job of calculation and design of structural parameters punch basing on the craft of punch set that has been determined，and ultimately determine the progressive of punch structure of Progressive Die according to the literature. I select the standard parts and the mold according to the designed structure of punch structure .Thus completing the mold design. After the completion of mold design, I use UG software to complete three-dimensional model and use AutoCAD software to complete the graphics of mold assembly drawing. The graduation project is independently complete not less than40,000 characters of the specified English translation associated with professional. Through this graduation design, I learn systematically and mastered the preparation of technical of manufacturing process and knowledge of mold design. I used the advanced design concepts and design methods, and I successfully complete the graduate design of Binaural Washer Punching and Blanking Progressive Die Design.
Key words : design; process analysis; stamping die; progressive die; structural calculations.
目 錄
引言 1
1 沖載件的工藝性分析 2
1.1 沖載件 2
1.1.1沖載件材料的選擇 2
1.1.2沖載件結構分析 2
1.1.3沖載件尺寸精度 2
1.2 沖載模的選擇 3
1.2.1方案一 — 單工序模生產 3
1.2.3方案二 — 復合模生產 3
1.2.3方案三 — 級進模生產 3
2 沖載工藝設計 4
2.1 排樣方式的確定及計算 4
2.1.1搭邊值的確定 4
2.1.2確定排料方向 4
2.1.3計算送料步距A 5
2.1.4計算料條寬度B 5
2.1.5排樣圖 5
2.1.6計算材料的利用率 6
2.2 級進模壓力中心的建立 7
2.3 沖載力的計算 9
2.3.1 沖孔力 10
2.3.2 落料力 10
2.3.3 沖載力 10
2.3.4 卸料力、推件力和頂件力 10
2.3.5 壓力機的選擇 11
3級進模設計 12
3.1 凸、凹刃口尺寸計算 12
3.1.1 沖孔時凸、凹模刃口尺寸的計算 12
3.1.2對于落料時凸、凹模刃口尺寸的計算 12
3.2 凸、凹模外形尺寸計算及確定 14
3.2.1沖孔及落料凸模外形尺寸計算及確定 14
3.2.1沖孔及落料凸模外形尺寸計算及確定 16
4 級進模主要零件設計 17
4.1 級進模模架的設計 17
4.2級進模模柄的設計 18
4.3 級進模墊板的設計 19
4.4 凸模固定板的設計 20
4.5 彈性卸料板設計 21
4.6 導料板的設計 23
4.7 標準圓柱銷和內六角圓柱螺釘的選擇 23
4.8 級進模導柱和導套的選擇 25
4.9 級進模校核 26
5 級進模零件材料的選擇 27
5.1 級進模凸模選材 27
5.2 級進模凹模選材 28
5.3 級進模上、下模座選材 28
5.4 級進模導柱和導套選材 28
5.5 級進模其他零件的選材 29
5.5.1級進模墊板、導料板和卸料板選材 29
5.5.2 級進模凸模固定板選材 29
6 級進模主要零部件的加工工藝 30
6.1 凸模加工工藝 30
6.1.1圓形凸模加工工藝 30
6.1.2非圓形凸模加工工藝 30
7 級進模的UG建模和autoCAD制圖 31
總結 33
謝 辭 34
參考文獻 35
附 表 36
2
引言
隨著我國經濟快速發(fā)展的拉動和我國產業(yè)政策的正確引導下，模具行業(yè)得到了快速的發(fā)展。近年來，隨著模具行業(yè)的結構調整，我國模具行業(yè)的模具產品向著更大型、更精密、更復雜和更經濟快速方向發(fā)展。我國模具行業(yè)的發(fā)展不僅為我國經濟快速發(fā)展做出貢獻還為世界制造業(yè)做出貢獻。
現在，模具制造中的冷沖壓加工已經是一種成熟的金屬加工方法。因此，冷沖壓模具的設計就很有必要。但是，冷沖壓模具的設計尤其是對于相對復雜的冷沖壓模具來說，設計時需要很強的想象力和創(chuàng)造力。對于模具設計者和制造者來說，模具設計理論、模具設計經驗和模具設計創(chuàng)新是不可或缺的。為了設計出擁有自主知識產權、適合我國國情、具有較高水平的模具，設計者和制造者必須不斷學習模具設計與制造的最新知識并且要敢于不斷創(chuàng)新。我國現在已經擁有了大量的模具標準件，包括模具、導向件，推桿等標準件，這為實現我國模具行業(yè)快速健康發(fā)展提供可能。同時，因為有較大產量模具標準件的存在，使得我們的模具設計的周期縮短并為設計出更精密更大型的模具提供可能。
結合我大學期間所學知識以及實踐所得經驗，本次設計就是在這樣的背景下進行的。本次設計在為期十六周的時間里順利完成。
1 沖載件的工藝性分析
1.1 沖載件
1.1.1沖載件材料的選擇
由于此次設計的沖載件是雙耳止動墊片，根據《機械設計手冊》[1]中冷沖壓零件推薦用鋼和鋼鐵材料的分類及技術條件的綜合比較，可以選擇本次畢業(yè)設計的雙耳止動墊片的原材料為A2，即304不銹鋼。
根據《機械設計手冊》[1]可知，A2的抗拉強度范圍為340~520MPa。根據設計經驗，對塑性材料：剪切應力極限 =(0.6一0.8)*抗拉極限；對脆性材料：剪切應力極限 =(0.8～1.0)*抗拉極限。所以可以取材料的抗剪切值為。
編號：
畢業(yè)設計(論文)外文翻譯
（原文）
學 院： 機電工程學院
專 業(yè)： 機械設計制造及其自動化
學生姓名： 韋良華
學 號： 1000110129
指導教師單位： 機電工程學院
姓 名： 陳虎城
職 稱： 助教
2014年 5 月 26 日
a r t i c l e i n f o
Article history:
Received 25 October 2010
Received in revised form
12 January 2011
Accepted 14 January 2011
Available online 21 January 2011
Keywords:
Microcellular injection molding
Plastic foaming
Swirl-free surface
a b s t r a c t
Microcellular injection molding is the manufacturing method used for producing foamed plastic parts.Microcellular injection molding has many advantages including material, energy, and cost savings as well as enhanced dimensional stability. In spite of these advantages, this technique has been limited by its propensity to create parts with surface defects such as a rough surface or gas flow marks. Methods for improving the surface quality of microcellular plastic parts have been investigated by several researchers. This paper describes a novel method for achieving swirl-free foamed plastic parts using the microcellular injection molding process. By controlling the cell nucleation rate of the polymer/gas solution through material formulation and gas concentration, microcellular injection molded parts free of surface defects were achieved. This paper presents the theoretical background of this approach as well as the experimental results in terms of surface roughness and profile, microstructures, mechanical properties, and dimensional stability.
l Introduction
The commercially available microcellular injection molding process (a.k.a. the MuCell Process) consists of four distinctive steps, namely, gas dissolution, nucleation, cell growth, and shaping [1]. In the gas dissolution stage, polymer in the injection barrel is mixed with supercritical fluid (SCF) nitrogen, carbon dioxide, or another type of gas using a special screw which is designed to maximize the mixing and dissolving of the gas in the polymer melt. During injection, a large number of nucleation sites (orders of magnitude higher than conventional foaming processes) are formed by a rapid and substantial pressure drop as the polymer/gas solution is injected into the mold cavity, thus causing the formation of cells (bubbles). During the rest of the injection molding cycle, cells continue to grow to fill and pack out the mold and subsequently compensate for the polymer shrinkage as the material cools inside the mold. The cell growth is driven by the amount and spatial distribution of the dissolved gas. The cell growth is also controlled by processing conditions such as melt pressure and temperature as well as material properties such as melt strength and gas solubility. Finally, the shaping of the part takes place inside the mold until the mold opens allowing the part to be ejected.
Since the microcellular injection molding process was invented, there have been numerous studies on process, material, and technical developments aimed at materializing the full process potential. According to previous studies [1-5], microcellular injection molding offers a number of advantages such as cost savings, weight reduction, ease in processing due to low viscosity, and outstanding dimensional accuracy. Due to these advantages, the microcellular injection molding process has been used in many industries such as automotive, electrical goods, and home appliances using a broad range of thermoplastics. Despite these advantages, however, the surface imperfections associated with microcellular injection molded partsdsuch as unique gas flow marks, referred to as swirl marks throughout this paper, and a lack of smoothnessdstill remain one of the main drawbacks surrounding microcellular injection molding. In order to eliminate or reduce these surface imperfections there have been several studies attempted, as reported in Refs. [6-14]. Some researchers have focused on temperature modification of the mold surface to improve the surface quality of microcellular injection molded parts [6-8]. With polymeric foam, it was found that bubbles forming at the advancing melt front are first stretched by the fountain flow behavior toward the mold surface and subsequently dragged against the mold wall causing swirl marks [9]. During the filling stage of polymer melts, keeping the mold wall temperature high enough for bubbles at the mold surface to beeliminated improves the surface quality of microcellular injection molded parts. By controlling the mold temperature rapidly and precisely using mold temperature control units or other kinds of thermal or surface heating devices, microcellular foamed plastics with glossy and swirl-free surfaces can be produced.
There have also been efforts to eliminate the swirl marks on microcellular injection molded parts without any mold temperature controller. In particular, it was proposed that inserting an insulator onto the mold wall might help keeping the interface temperature between the mold and the polymer melt high. This technique basically yields the same result as temperature modification of the mold [10]. Thermal analysis and experimental results prove that the addition of an insulator layer on the mold can improve the surface quality of microcellular injection parts [11].
Another method of producing parts with an improved surface quality leads to a microcellular co-injection molding process [12]. In this technique, a proper amount of solid skin material is injected prior to the injection of a foaming core material. This can yield a sandwiched (solid skinefoamed coreesolid skin) structure with a surface finish similar to a conventionally molded component while partially maintaining the advantages of microcellular injection molding.
Another approach for improving the surface quality of microcellular
injection molded parts is the gas counter pressure process [13,14]. In this process, a high-pressure gas is injected into the mold prior to the polymer/gas solution to suppress cell nucleation and bubble growth while the polymer/gas solution is being injected into the mold cavity. Toward the end of injection, counter gas pressure is released and bubbles begin to form within the cavity. Since a majority of the part surface is already solidified, gas flow marks are eliminated.
In spite of these efforts to improve the surface quality, there have been difficulties in applying the microcellular injection molding process in industries requiring parts with high surface qualities because these techniques entail additional equipment which results in high costs or maintenance. There have been no reported studies on improving the surface quality of microcellular injection molded parts without any additional equipment or modification to existing equipment.
This paper proposes a novel approach to improve the surface quality of microcellular injection molded parts by controlling the cell nucleation rate. In this study, the cell nucleation rate was dramatically lowered or delayed by controlling the degree of supersaturation so that cell nucleation was delayed during the filling stage. After the polymer/gas solution volumetrically filled the mold cavity, intentionally delayed nucleation occurred and bubbles formed in the polymer matrix, except on the surface where the material had already solidified upon touching the mold surface. Theoretical background and experimental results are described in this paper. Microstructure, surface profile, surface roughness,mechanical properties, and dimensional stability are also investigated in this study.
2. Theoretical
2.1. Nucleation theory for polymeric foams
In polymeric foams, nucleation refers to the initial stage of the formation of gas bubbles in the polymeregas solution. For nucleation,
gas bubbles must overcome the free energy barrier before they can survive and grow to macroscopic size [15]. According to classical nucleation theories [16-18], the nucleation rate is controlled by the macroscopic properties and states of the polymer and gas such as solubility, diffusivity, surface tension, gas concentration, temperature, and the degree of super saturation.
One representative equation for the nucleation rate of polymeric foams was reported by Colton and Suh [19,20]. In addition to the mathematical representation, they also verified their nucleation theory experimentally for a batch foaming process using a high pressure vessel. The nucleation equation for microcellular foams dominated by the classical nucleation theory [16e18] can be expressed as
N=fCex(-?G**/kT)
where N is the nucleation rate, f is the frequency of atomic molecular lattice vibration, C is the concentration of gas molecules, k is the Boltzmann’s constant, T is the absolute temperature, and ?G**is the activation energy barrier for nucleation.
According to previous studies [19,20], the nucleation rate of polymeric foams is composed of two components: a homogeneous term and a heterogeneous term. The activation energy for homogeneous nucleation is given by
?Ghom**?16πr33?P2
where g is the surface energy of the bubble interface and ?P.is
assumed to be the gas saturation pressure. More precisely,
?P=|Pr'-Pr| where Pr` is the pressure that is exerted in a high
pressure vessel and Pr is the pressure of the supersaturated vapor in
the sample [16]. That is, DP is the pressure difference between the
pressure that is applied to the sample and the pressure of the supersaturated vapor in the sample. When the pressure that saturates
the gas in a high pressure vessel is suddenly released to trigger the so-called thermodynamic instability by rendering the sample into the supersaturated state, Pr` becomes 1 bardso low compared to Pr that DP can be approximated as Pr.
On the other hand, the activation energy for heterogeneous nucleation is affected by a geometric factor that depends on the contact (wetting) angle between the polymer and the particle and can be expressed as
?Ghet**=?Ghom**×f(θ) (3a)
fθ=12-34cosθ+14cosθ3 (3b)
where f(q) is a geometric factor that is dependent upon the contact
angle, θ, of the interface between the polymer and a second phase,
and has values of less than or equal to 1. For a typical wetting angle
of around 200 on the interface between a solid particle and the polymer melt, the geometric factor is 2.7X10-3, suggesting that the energy barrier for heterogeneous nucleation can be reduced by three orders of magnitude with the presence of an interface [20,21].
l 2.2. Nucleation theory for microcellular injection molding
In the batch foaming process, the theory of Colton and Suh was verified by their experiments. Due to the large difference between the pressure exerted in a high pressure vessel and the pressure of the supersaturated vapor in the sample, the gas pressure dissolved in the polymer, the?P in the Gibbs free energy equation, can be approximately assumed to be the saturation gas pressure. The assumption that ?P is the gas saturation pressure is fairly reasonable in a batch foaming process although the ?Pcan still have an error of about 30-40% due to overestimation as reported in a previous study [15].
The nucleation theory by Colton and Suh is a simplified form derived and modified from classic nucleation theories [16-18] and is generally adequate for the batch foaming process. However, there is a need for this theory to be modified in cases of microcellular injection molding and extrusion systems because ?P cannot be directly controlled and measured. To predict nucleation in microcellular injection molding and extrusion processes more precisely, this paper proposes a cell nucleation theory of a different form, which includes a term for the degree of supersaturation because it is a directly controllable factor.
To avoid misestimating ?P, and to consider the degree of supersaturation, a more proper activation energy equation for nucleation can be derived from the following equation [16,17]
?P=|Pr'-Pr|=2rrc （4）
where rc is the radius of a characteristic droplet, and the W.
Thomson equation
RTlnPrP∞=2r?Mr?p （5）
where P∞ is the pressure of the saturated vapor (i.e., the equilibrium
pressure), R is the universal gas constant, M is the molar mass, and p is the density. These equations yield
?P=RTρlnPrP∞M （6）
which can be alternatively expressed as
?P=ktρ1lnS (7)
whereρ1is the molecular density of the bulk liquid, and S(=PrP∞)
is defined as the degree of supersaturation.
Thus, the activation energy equation (cf. Equation (2)) for nucleation in the microcellular injection molding process can be given by
?G**=16πr33(kTρ1lnS)2 （8）
Hence it can be stated that the activation energy for nucleation is inversely proportional to the square of the natural logarithm of the supersaturation degree.
In the microcellular injection molding process, the polymer/gas
solution becomes a metastable supersaturation solution when it is
injected into the mold cavity. This is because the amount of gas able to be dissolved in the polymer in the presence of a rapid pressure drop is less than the gas amount originally dissolved in polymer melts. In particular, assuming the air in the cavity is properly vented, the pressure at the advancing melt front is at the atmospheric pressure. The solubility of a gas in a polymer at atmospheric pressure and processing temperature can be obtained by an Arrhenius-type expression with regard to temperature [22]
S@1 atm; melt temperature=S@STPexp?(-?HsR(1Tmelt-1298)) (9)
where S@STP is the solubility of the gas in the polymer at standard
temperature and pressure conditions (298 K and 1 atm). The parameter DHs is the molar heat of sorption, and Tmelt is the polymer melt temperature.
Thus, the degree of supersaturation is given by
S=mgS@STPexp?(-?HsR(1Tmelt-1298)) (10)
where mg is the gas dosage which can be controlled by the supercritical
fluid (SCF) supply system.
The heat of sorption, ?HsRg, of various polymer/gas systems at standard temperature has been studied and summarized in many previously published studies. In order to obtain the degree of supersaturation for a polymer/gas solution in the microcellular injection molding process, one has to either measure the solubility of the gas in the polymer at standard temperature and pressure or consult published data on the solubility of the gas in the polymer. Then, the activation energy barrier for nucleation in Equation (8), ?G**, can be obtained based on the calculated degree of supersaturation and the surface energy of the bubble interface, γ. Given the activation energy barrier and the frequency factor, f, the nucleation rate (expressed in Equation (1)) can then be calculated.The estimate of the surface energy of the bubble interface and the frequency factor is discussed below.
In microcellular injection molding, the polymer/gas solution can
be treated as a liquid mixture. Thus, the surface energy of the
bubble interface, g, can be expressed as [23,24]
γmix=γpolymerρmixρpolymer4(1-wgas) （11）
where γpolymer is the surface energy of the polymer, P′S are the
densities, and wgas is the weight fraction of gas.
In addition, a frequency factor for a gas molecule, f, in Eq. (1) can
be expressed as [24-26]
f=Zβ(4πrc2) (12)
where z is the Zeldovich factor, which accounts for the many clusters that have reached the critical size, rc., but are still unable to grow to sustainable bubbles. The parameter b is the impingement rate at which gas molecules collide with the wall of a cluster. The parameter Zβcan be used as a correction factor and is determined experimentally.
Once the nucleation rate as a function of the degree of supersaturation
is obtained, one can control the gas (SCF) content in the polymer melt to control or delay the onset of cell nucleation so that no bubble will form at the advancing melt front during the injection filling stage, thus, allowing microcellular parts with solid, swirl-free surface to be injection molded.
3. Experimental
3.1. Materials
The material used in this study was an injection molding grade
low density polyethylene, LDPE (Chevron Phillips Chemical Company, Texas, USA). It has a melt index of 25 g/10 min and a density of 0.925 g/cm3.
To confirm the theory for improving surface quality by controlling
the degree of supersaturation, a random copolymer polypropylene (PP)was also used in this study. The PP used in this study was Titanpro SM668 (Titan Chemicals Corp., Malaysia), with a melt flow index of 20 g/10 min and a density of 0.9 g/cm3. Both materials were used as received without any colorant, fillers, or additives.
Commercial grade nitrogen was used as a physical blowing agent for the microcellular injection molding trials.
3.2. Microcellular injection molding
In this study, an Arburg 320S injection molding machine (Arburg,Germany) was used for both the solid conventional and microcellular injection molding experiments. The supercritical fluid (SCF) supply system used in this study was the S11-TR3 model (Trexel, Woburn,MA, USA). The total gas dosagewas controlled by adjusting the gas injection time, t, and the gas injection flowrate,m_ g. A tensile test mold, which produces tensile test specimens that meet the ASTM D638 Type I standards, was used for this experiment.
For injectionmolding of both LDPE and PP tensile test specimens,
nozzle and mold temperatures were set at 221 。C and 25 。C, respectively. The cycle time was 40 s. An injection speed of 80 cm3/s was employed. In this study, six different gas dosages (concentrations) were used for injection molding of LDPE as shown in Table 1. Also, four different gas dosages were employed for microcellular injection molding of PP. The supercritical fluid was injected into the injection barrel at 140 bar pressure to be mixed with the polymer melts in this experiment. The weight reduction of foamed versus solid plastic partswas targeted at 8 _ 0.5% for each specimen. For the conventional injectionmolding experiment, the shot size of 20.2 cm3 and a packing pressure of 800 bars were employed for 6 s. For the microcellular injection molding experiments, the shot size of the polymer melt was 19.2 cm3 and the packing stage was eliminated.
3.3. Analysis methods
To analyze the surface roughness of the molded tensile bar specimens, a Federal Surfanalyzer 4000 (Federal Product Corporation, RI, USA)was used. The surface roughnesses of conventional and microcellular injection molded parts were evaluated at three locations shown in Fig. 1 and the averaged surface roughness based on measurementsdone at all three locationswas recordedandreported. The cutoff, drive speed, and drive length for the test were 0.75 mm, 2.5 mm/s, and 25 mm, respectively. For each process condition, ten specimens and three points on each specimen were tested.
In addition to the surface roughness, swirl marks commonly observed in microcellular injection molded samples can also be clearly revealed by a 3-D surface profiler. Zygo NewView (Zygo Corporation, CT, USA), a non-contact 3-D surface profiler, was employed to examine the surface profile of injection molded parts in this study using a scan distance of ±10 mm.
A JEOL JSM-6100 scanning electron microscope with an accelerating
voltage of 15 kV was employed for observing the microstructures of the foamed parts. To observe the cross section of the microcellular injection molded parts, test specimens were frozen by liquid nitrogen and subsequently fractured. Representative images of each process condition were selected and cell sizes and densities were analyzed. A UTHSCSA Image Tool was employed as the ima