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第三章
In the previous chapters, we defined what a successful design is and then moved on to determining the placement of the objects that will be in the design. We’ll now take up the structural considerations of the design. Why consider the structural considerations at this juncture, and why not the thermal aspects, or the user interfaces? It’s probably only because I have a mechanical engineering ba
在前面的章節中,我們定義了什麼是成功的設計,然後繼續進行確定將要在設計中放置的對象的位置。現在好了據設計的結構考慮。為什麼在此時考慮結構性考慮,為什麼不考慮散熱方面或用戶界面呢?可能僅是因為我擁有機械工程背景,所以我“自然地”首先了解設計必須如何“具有結構性”。我覺得我們必須建立以“堅實的基礎”為基礎,以便其餘設計可以以此為基礎。的電子外殼(本身)當然是必須足夠堅固的結構在客戶(用戶)將使用產品的各種環境中工作因此,讓我們開始討論提供此功能的主要注意事項“堅實的基礎。”本章將重點介紹:
- Using strength of material concepts to propose structural solutions
- Defining a generic process for considering the structural design of our electronic enclosure
- Look at some examples that specifically illustrate the general concepts We'll close this chapter with a section titled "Bonus Section". This last section is meant to add some complications to our problems on strength of materials and also to show how other considerations besides strength will be important to our design choices.
- 利用材料概念的強度提出結構解決方案
- 定義考慮我們電子產品結構設計的通用流程外殼
- 看一些具體說明一般概念的示例
用標題為“獎金部分”的部分結束本章。最後一部分的意思是給我們的材料強度問題增加了一些複雜性,並且展示除強度之外的其他考慮因素對我們的設計如何重要選擇。
3.1 Introduction: Strength of Materials
3.1簡介:材料強度
This chapter is not an attempt to review all of the principles of strength of materials
or of mechanical engineering. Entire texts have been devoted to stress, strain, and
strength alone; therefore, we will just “scratch the surface” of knowledge and emphasize how some basic equations help our job to design electronic enclosures. However, in the course of design of these electronic enclosures, an exacting knowledge of the structural considerations will be essential to the overall success of the design.
本章並非試圖回顧材料強度的所有原理或機械工程。整個文本都致力於強調,緊張和僅憑力量因此,我們將只是“刮擦知識”,並強調一些基本方程式如何幫助我們設計電子外殼。但是,在設計這些電子外殼的過程中,對結構上的考慮對於設計的整體成功至關重要。
The reader does not need a mechanical engineering degree or be an expert in strength of materials to benefit from this chapter. I’m hoping that some of the basic principles are touched-upon, enough to give the EPE Designers some value no matter where they are in their career. It was my belief that the more that designer understands basic strength of materials, the better the enclosure design would be.
讀者不需要機械工程學位也不需要成為專家材料強度可從本章中受益。我希望一些基本的修改原則,足以使EPE設計師無論在職業中身在何處都具有一定的價值。我認為,設計師對材料的基本強度了解得越多,外殼設計就越好。
For example, the EPE Designer can design an enclosure using 1/8-inch-thick aluminum for the enclosure material. Testing may prove that 1/8-inch-thick aluminum does indeed pass the shock and vibration testing. However, here are some questions to ask about this choice of thickness and material for the design:
例如,EPE設計人員可以使用1/8英寸厚的外殼設計外殼外殼材料為鋁。測試可以證明1/8英寸厚的鋁確實通過了衝擊和振動測試。但是,對於設計的厚度和材料選擇,這裡有一些問題要問:
- Could we have used 1/16-inch-thick aluminum instead, which would have saved weight and possibly been easier to fabricate?
- Could we have used 1/8-inch-thick plastic instead, which would again have saved weight and possibly been easier to fabricate?
- 可以改用1/16英寸厚的鋁材嗎?重量,可能更容易製造?
- 我們可以使用1/8英寸厚的塑料代替嗎,減輕重量並可能更容易製造?
So, as you can see from the above questions, it is not enough to just solve the problem, we need to solve the problem in the most cost-efficient manner possible. We’ll get into the detail of “the most cost-efficient manner” at the beginning of Chap. 4. But for now, we’ll concentrate on determining suitable designs that are at least structurally successful.
因此,正如您從上述問題中看到的那樣,僅解決問題還不夠問題,我們需要以盡可能最具成本效益的方式解決問題。在開始時,我們將詳細介紹“最具成本效益的方式”小伙子4.但目前,我們將專注於確定適合的設計在結構上最不成功。
One of the biggest contributions that a designer will make to the design of the electronic enclosure is data to prove that the design will hold up “structurally” to the rigors of the customer product environment. I’m hopeful that whatever the reader’s background is, they will be able to propose a design for an electronic enclosure that will be strong enough to pass the rigors of testing. I’ll introduce some of the basic equations and concepts involved to help even the beginning EPE Designer, and hopefully it will also help the veteran EPE Designer.
設計師對設計的最大貢獻之一電子外殼是用來證明設計將“結構性地”支撐到設計的數據。嚴格的客戶產品環境。我希望無論讀者如何背景是,他們將能夠為電子外殼提出一個設計方案,足夠強大,可以通過嚴格的測試。我將介紹一些基本的等式和概念甚至可以幫助初學者EPE Designer,以及希望它將對資深的EPE設計師有所幫助。
The fundamental approaches for designing a suitable structure for an electronic enclosure break down into four basic approaches:
設計適用於電子設備的結構的基本方法
機箱分為四個基本方法:
1.Take a look at similar products that already exist, and use the solution already designed as a quick starting point for the design at hand. Pluses for this kind of approach are speed, but the downside is that your design may suffer due to lack of creativity toward solving a unique problem that your specific product should solve.
1.看一下已經存在的類似產品,並使用該解決方案可以作為手頭設計的快速起點。加上這種方法是速度,但缺點是您的設計可能會因缺乏而遭受損失解決特定產品應解決的獨特問題的創造力解決。
2.Quick, “back-of-the-envelope” design. This approach uses some rudimentary design equations on simplified structural elements. We’ll explore some examples of these design approaches with some example problems later on in this chapter.
2.快速的“信封背面”設計。這種方法使用一些基本的方法簡化結構元素的設計方程。我們將探索一些例子這些設計方法中的一些示例性問題章節。
3.More complex analysis. This is explored a bit more in Sect. 3.3 on “Analysis Required.” Again, this text will not cover much ground for designs requiring complex analysis. What I would like to emphasize in this chapter is a feel for the structural elements of the design and what some “quick fixes” would be for improved designs.
3.更複雜的分析。在Sect中對此進行了更多探討。 3.3關於“分析需要。”同樣,對於需要設計的內容,本文不會涵蓋太多內容複雜的分析。我想在本章中強調的是設計的結構要素以及一些“快速修復”的目的改進的設計。
4.Overdesign – Of course, overdesign is not the correct answer for all of the designs. I’ve already touched upon this above in the example on the solution using 1/8 inch aluminum. I’ll go into another example of overdesign below. In a competitive product market, where customers make buying decisions mainly on price, overdesign will likely lead to increased product cost (or, certainly, increased weight and size). Structural overdesign is basically starting with a design that has a very good likelihood of success of passing structural testing, that is, surviving the customer usage environment for shock and vibration.
4.過度設計–當然,過度設計並不是所有解決方案的正確答案設計。我已經在上面的解決方案示例中談到了這一點使用1/8英寸鋁。我將在下面討論另一個過度設計的示例。在一個競爭激烈的產品市場,客戶主要根據價格,過度設計可能會導致產品成本增加(或者,當然,增加重量和尺寸)。結構性過度設計基本上是從設計很可能成功通過結構測試,也就是說,要在客戶使用環境中倖免於衝擊和振動。
A lot can be said for overdesign. The EPE Designer could determine that a bracket that is 18 gauge (0.048) thick metal would “do the job” but, instead, choose 16 gauge (0.060) thick metal. Increasing the thickness of the bracket gives one some comfort for a couple of reasons:
過度設計可以說很多。 EPE設計者可以確定18規格(0.048)厚的金屬支架將“完成任務”,但選擇16號(0.060)厚金屬。增加支架的厚度會增加一些舒適的原因有兩個:
- That the design will stand up to some of the forces that are not known to a high degree of precision. This will be further explored in Sect. 3.2 on “Design Process.”
- 該設計將經受住一些未知的力量精確度。這將在Sect中進一步探討。關於“設計3.2處理。”
- That there is just a “factor of safety” greater than 1.0 in the design. A factor of safety equal to 1.0 means that your design just meets the design criteria. A discussion on the considerations of designing with increased factor of safety is covered in Sect. 3.2 of this chapter.
- 在設計中只有一個大於1.0的“安全係數”。一個因素等於1.0的安全性意味著您的設計僅符合設計標準。本節涵蓋了有關提高安全性的設計考慮因素的討論。本章3.2。
Also, it is possible that there may be some economical reason for placing 0.060 thick metals in the design. For example, if the majority of the design is 0.060 thick already, and if the bracket can be made out of a piece of “scrap,” a savings might result.
此外,放置0.060可能有一些經濟原因設計中使用厚金屬。例如,如果大多數設計為0.060厚如果已經可以用一塊“廢料”製成支架,則可能會節省成本
It is very possible (in the above example) that using 0.048 thick metals with the addition of some simple “ribs” or bends would make the design much stronger than 0.060 thick metals. This is what I would like to spend some time on, and this issue of adding ribs to a design is explored in the problem shown in Sect. 3.4.2.
在上面的示例中,很有可能使用0.048厚的金屬添加一些簡單的“肋骨”或彎頭將使設計比0.060厚金屬。這就是我想花一些時間的問題本節探討了在設計中添加肋骨的方法。 3.4.2。
3.2 Design Process for Structures
3.2結構設計過程
I’d like to give the reader a generic process for designing the electronic enclosure (or, an individual part in the enclosure) that will satisfy the structural considerations of the design. By going through these six steps, the designer should be ready to propose a material and cross section that will work. I’ll individually break out the six steps as subsections.
我想給讀者一個設計電子外殼的通用流程(或外殼中的單個零件),將滿足結構上的考慮設計。通過這六個步驟,設計人員應該準備好提出一個可行的材料和橫截面。我將單獨介紹六個步驟作為小節。
3.2.1 Similar Designs
3.2.1類似設計
How have other designs in the industry handled similar situations? The other designs could be from examples within your own company (past products) or from competitive products outside of your own company.
業內其他設計如何處理類似情況?其他設計可能來自您自己公司內部的示例(過去的產品),也可能來自您自己公司外部的競爭產品。
3.2.2 Forces on Part
3.2.2分力
Determine the forces (static and dynamic) on the object – amplitude and direction of those forces. The part’s own weight generally doesn’t come into consideration in electronic enclosures for static forces but does get considered for dynamic forces. In this text, I refer to “objects,” “parts,” and “members,” but they should all be considered being one-in-the-same.
確定物體上的力(靜態和動態)–振幅和方向這些力量。通常不考慮零件的自重電子外殼可承受靜態力,但可以考慮使用動態力。在在本文中,我指的是“對象”,“零件”和“成員”,但它們都應視為同一對象。
3.2.3 Existing End Conditions
3.2.3現有結束條件
Determine the “end conditions” of the object, that is, its degrees of freedom of movement, and how the member will be supported. Common end conditions are “fixed” (not allowed to move) or “free” (allowed to rotate). End conditions have an effect on determining the amount of stress that loads will create.
確定對象的“最終條件”,即對象的自由度運動,以及如何支持該成員。常見的最終條件是“固定”(不允許移動)或“自由”(允許旋轉)。結束條件有一個影響確定負載將產生的應力大小。
3.2.4 Propose Material and Cross Section
3.2.4提出材料和橫截面
Determine the material and cross-sectional combination needed to support those forces (from Sect. 3.2.2), keeping in mind that “strength” is an inherent aspect that belongs to materials (so, the higher the yield strength of the material, the more loadbearing ability that material contains), and forces produce stresses in those materials. All materials have limits for maximum stress where we either have the start of deformation (yield strength) or complete failure point (ultimate strength).
確定支撐這些材料所需的材料和橫截面組合力(來自第3.2.2節),請牢記“力量”是屬於材料(因此,材料的屈服強度越高,材料包含的承載能力越強),並且力會在這些材料中產生應力。所有材料都有最大應力極限,我們要么開始變形(屈服強度)或完全破壞點(最終強度)。
Maximum stress in the member is generally known by the “common equation” of
構件中的最大應力通常由
σ = Mc / I
where:
哪裡:
σ is the maximum stress in the member.
σ是構件中的最大應力。
c is the distance of extreme “fiber” from bending axis.
c是“纖維”到彎曲軸的距離。
I is the moment of inertia. This is a property of the cross-sectional area of the object.
I是慣性的時刻。這是物體的橫截面積的特性。
M is the maximum moment in the cross section furthest from where the force is applied. It is that force times its distance from an end-point condition to where the force is applied.
M是距離力最遠的橫截面中的最大力矩應用。就是力乘以它從端點條件到施加力。
Basically, only two choices initially exist to design higher load-bearing members (as the terms “c/I” are both related to cross-sectional area and that area’s “dispersal” away from the “neutral plane” of bending).
基本上,最初只有兩個選擇來設計更高的承重構件(因為術語“ c / I”既與橫截面積相關,也與該區域的“分散”遠離彎曲的“中性面”。
Change the material, which allows a change to the stress limits. So, choosing a material with higher stress limits allows more loading to be placed on that member.
更換材料,從而可以更改應力極限。因此,選擇一個應力極限較高的材料允許在其上施加更多的載荷會員。
Change the material’s cross-sectional property, basically the member’s second moment of area (also known as the moment of inertia, I) and the amount of area that can be concentrated away from the member’s “neutral axis” or centroid. Increasing area will essentially increase a member’s ability to carry more loads. Increasing that area away from the member’s “neutral axis” will also help the member carry more load (which is why “I-beams,” which have a lot of the member’s cross-sectional area very far from the “neutral axis,” are excellent loadcarrying members).
更改材料的橫截面屬性,基本上是成員的第二個面積矩(也稱為慣性矩I)和麵積量可以遠離會員的“中性軸”或質心。面積的增加從根本上提高了成員承載更多貨物的能力。將該區域擴大到成員的“中性軸”之外,也將有助於成員承擔更多的負載(這就是為什麼“工字梁”(它的橫截面面積很大,離“中性軸”很遠)是出色的承載成員)。
I’ve illustrated the interrelation between changing both material and cross section in Fig. 3.1. Here, we have a very common load situation, one where a force is acting on the end of the member, and the member has a fixed end condition. We will be showing how various changes in (either or both) material and cross section can solve a problem. The basic problem is finding a member strong enough to survive this load, a 2000 pound force. The EPE Designer is tasked with determining both the material and cross section of the member so that the maximum stress in the member will be under the maximum stress (let’s say yield stress) allowed by the particular material. So, we can utilize the equation from above as a starting point in the design:
我已經在圖3.1中說明了更改材料和橫截面之間的相互關係。在這裡,我們有一種非常常見的負載情況,一種力是作用在構件的末端上,並且構件具有固定的末端條件。我們會展示材料和橫截面(或兩者)的各種變化如何解決問題。基本問題是找到足夠強大的成員以生存此負載為2000磅力。 EPE設計者的任務是確定兩者構件的材料和橫截面,以使構件中的最大應力成員將承受最大應力(例如屈服應力)特殊材料。因此,我們可以從上方利用方程式作為起點
該設計:
σ = Mc / I
We can calculate the maximum moment, M, as being equal to 48 inch × 2000 pounds, which we’ll then say is 96,000 in-lb (this will be the same value for any material and cross section that we choose). Let’s put forth two candidate materials:
我們可以計算出最大力矩M等於48英寸×2000磅,那麼我們將說它是96,000磅-磅(對於任何我們選擇的材料和橫截面)。讓我們提出兩個候選材料:
Pine wood, which has a yield stress of 1200 pounds/in3 (psi) Aluminum, CR H-18, which has a yield stress of 22,000 psi
松木,屈服應力為1200磅/英寸3(磅/平方英寸)鋁,CR H-18,屈服應力為22,000 psi
Let’s keep to simple rectangular shapes, which have the moment of inertia value of (for either material):
讓我們保持簡單的矩形,其具有慣性矩值的(對於任何一種材料):
I b = h3 /12
Where
b is the width of the member and h is the height of the member in cross section.
b是構件的寬度,h是構件的截面高度。
In this example, c, which is the distance from the extreme fiber to the bending axis, will be h/2.
在此示例中,c是從極端光纖到彎曲的距離軸為h / 2。
Thus, our equation for stress becomes:
因此,我們的應力方程變為:
σ = = Mc / / I h ( ) 96000×( ) 2 1 / / bh 2 = 576, / 000 bh 3 2
(Note that the stress in this member is dependent on the height of the member squared, which underscores the need for high “aspect ratio” (the ratio of height to width) cross sections.)
(請注意,該構件中的應力取決於構件的高度平方,強調了高“長寬比”(高度與寬度)。
Fig. 3.1 Material & cross-section choices
圖3.1材料和橫截面選擇
3.2.4.1 Pine Wood Solution
3.2.4.1松木溶液
Let’s try to design the member that will be made of pine wood. By putting in:
讓我們嘗試設計由松木製成的成員。通過輸入:
b = 4 inch and h = 12 inch, we see that the maximum stress will be 1000 psi. This member (pine wood, with a cross section of 4 × 12) has a “stress limit” of 1200 psi, and the load on it is only 1000 psi. Nice, we have “overdesigned” the member (with a factor of safety of 120%).
b = 4英寸,h = 12英寸,我們看到最大應力將為1000 psi。這個成員(松木,橫截面為4×12)的“應力極限”為1200 psi,它的負載僅為1000 psi。好的,我們已經“過度設計”了成員(安全係數為120%)。
Now, the EPE Designer needs to look at “other” design constraints (like weight or cost) to make a decision to see if this pine wood beam will be a good candidate for our electronic enclosure.
現在,EPE設計人員需要研究“其他”設計約束(例如重量)或費用)以決定是否可以使用此松木樑用於我們的電子外殼。
Spoiler alert: We’ll discuss the 15 considerations for determining material selection for any part in Chap. 4, but for now, just look at weight as another consideration for the “final choice” of material and cross section.
劇透警告:我們將討論確定第1章中任何零件的材料選擇的15個注意事項。 4,但目前,僅考慮體重是另一個考慮因素用於材料和橫截面的“最終選擇”。
Let’s look at the weight of this pine wood beam. At 30 pounds/ft3 , the beam will be 40 pounds. Fine (for now).
讓我們看一下松木樑的重量。 30磅/英尺3,光束會是40磅。很好(暫時)。
3.2.4.2 Aluminum Solution
3.2.4.2鋁溶液
Design is all about presenting some logical choices, so let’s look at an aluminum beam.
設計就是要提出一些合理的選擇,所以讓我們看一下鋁光束。
We can choose,
我們可以選擇,
b = 4 inch and h = 2.5 inch. We can see that the maximum stress will be 23,100 psi. This is above the maximum yield stress for the aluminum, so this will not be structurally satisfactory in our design.
b = 4英寸,h = 2.5英寸。我們可以看到最大應力為23,100 psi。
這高於鋁的最大屈服應力,因此在我們的設計中這在結構上不能令人滿意。
But what about remembering that the height of the beam is the larger “factor” in our calculations for moment of inertia,
但是要記住光束的高度是我們對慣性矩的計算
b = 2.5 inch and h = 4 inch? This will be the same cross-sectional area as the previous example for the aluminum beam. Now, the maximum stress will be 14,400 psi, well within the maximum of 22,000 psi for this aluminum. Thus, “rotating” the same cross section, where the thicker aspect is in the direction of the load force, allowed this choice of material and cross section to be structurally successful.
b = 2.5英寸和h = 4英寸?這將是與鋁樑的先前示例。現在,最大壓力將是
14,400 psi,完全在該鋁的最大22,000 psi之內。因此,“旋轉”相同的橫截面,其中較厚的方向是在載荷方向上力,使這種材料選擇和橫截面在結構上
成功。
Let’s look at the weight of this aluminum beam. At 169 pounds/ft3 , the beam will be 47 pounds. This compares to 40 pounds for the pine wood.
讓我們看一下鋁樑的重量。 169磅/英尺3,光束會是47磅。相比之下,松木為40磅。
In summary, we have looked at how two different materials (pine wood and aluminum) could be used to solve the structural problem. We can develop crosssectional areas for each material that solves the structural problem.
總之,我們研究瞭如何使用兩種不同的材料(松木和鋁)來解決結構問題。我們可以為每種材料開發解決結構問題的橫截面。
In design, deformation often shares an equal importance with strength. A load member may have sufficient strength to withstand a particular load, but it may deflect an unacceptable amount beyond the elasticity of the engineering material. Problems, where deflection (and thus the material’s modulus of elasticity, E) is also under consideration, are shown in some examples further on in this chapter.
在設計中,變形通常與強度同等重要。負載構件可能具有足夠的強度以承受特定的載荷,但是它可能偏轉超出工程材料彈性的不可接受的量。撓度(以及材料的彈性模量E)也存在問題正在考慮中的內容將在本章中的一些示例中顯示。
The economics of the above choices (change material or change material cross section) pose an interesting problem to EPE Designers. Many combinations of material and cross-sectional area will work, but a choice must be made that fits the overall goals of the project. Besides functioning, it must meet project goals of cost, manufacturability, risk, weight, time to market, etc. These choices will be further investigated at the beginning of Chap. 4. It is possible that alternative solutions would need to be reviewed, tested, and prototyped. One of the biggest assets a designer can bring to the design would be to quickly find the logical choices to be made among the viable candidates for material/cross-sectional choice that will solve the problem at hand.
上述選擇的經濟性(更換物料或更換物料交叉部分)給EPE設計師帶來了一個有趣的問題。的許多組合材料和橫截面積可以使用,但必鬚根據實際情況進行選擇項目的總體目標。除了運作外,它還必須滿足項目的成本目標,可製造性,風險,重量,上市時間等。這些選擇將是進一步的在第一章開始進行調查。 4.可能有替代解決方案需要進行審查,測試和製作原型。最大的資產之一設計師可以帶入設計中,以便快速找到要選擇的邏輯在可行的材料/橫截面選擇候選材料中做出解決眼前的問題。
3.2.5 Combine Function
3.2.5合併功能
Can the part being designed be combined with another part in the assembly which is adjacent to this part? Basically, can two separate parts (being envisioned) be combined into a single part? This is illustrated in Fig. 3.2.
可以將正在設計的零件與裝配中的另一個零件組合嗎在這部分附近嗎?基本上,兩個單獨的部分(可以設想)可以合併成一個部分?這在圖3.2中示出。
The “alternative thinking” aspect of looking at the part being combined is to actually look to create two separate parts from a (envisioned) single part. This could result in a lower overall cost reduced solution to the combined design.
查看被合併部分的“另類思維”方面是實際上希望從一個(設想的)單個零件創建兩個單獨的零件。這可能從而降低了總體成本,降低了組合設計的解決方案。
One of the main choices (for a candidate material/cross-section solution) will be determining how to fabricate this solution in production. For example, some of the choices involved here are:
主要選擇之一(針對候選材料/橫截面解決方案)將是確定如何在生產中製造該解決方案。例如,一些這裡涉及的選擇是:
What is the tooling budget for the project? Can the project “afford” spending an amount of capital needed for casting, injection molding, extruding, or other fabrication techniques that may be under consideration? Is there existing tooling that can be utilized? A determination must be made to find the “payback period” of a tooled solution. For example, knowing:
該項目的工具預算是多少?該項目可以“負擔”開支嗎?可能正在考慮的鑄造,注模,擠壓或其他製造技術所需的資金量?是否有現有工具可以利用?必須確定找到“投資回收期”解決方案。例如,了解:
- How much tooling will cost
- How many parts will be needed (over the product “lifetime”)
- How much un-tooled part will cost
- How much the tooled part will cost
1.加工費用
2.需要多少個零件(在產品“使用壽命”內)
3.未加工零件將花費多少
4.工具零件將花費多少
will determine when the “payback period” of the tooled solution. For example, if tooling will cost 50,000,andtheun−tooledpartcostis50,000,andtheun−tooledpartcostis10, while the tooled part cost is 1,thiswouldresultinasavingsof1,thiswouldresultinasavingsof9 per part needed. Thus, the tooled part pays for the tooling in 50,000/9 = approx. 5500 parts. If 5500 parts are expected to be sold in a year, then the “payback period” will be approx. 1 year. See previous discussion on tooling “breakeven” in Sect. 1.7.
將確定工具解決方案的“投資回收期”。例如,如果工具成本為50,000美元,非工具成本為10美元,而工具成本為成本為1美元,則每件零件可節省9美元。因此,工具零件支付工具費用50,000 / 9 =大約5500個零件。如果預計5500個零件如果一年內售出,那麼“投資回收期”將約為1年。見前有關在“節”中使用工具“收支平衡”的討論。 1.7。
Are there “off-the-shelf” or “previously designed” solutions that could be used in the design? This could save the tooling cost, and the increased volumes of this “new” usage (when combined with the “old” usage) will lower the individual piece cost.
是否有可用的“現成的”或“先前設計的”解決方案?該設計?這樣可以節省工具成本,並節省更多的“新”使用量(與“舊”用法結合使用)將降低單件成本。
3.2 Design Process for Structures
3.2結構設計過程
- Can the fabrication technology be phased-in over the course of the project? That is, can we use one fabrication technique in the prototype/first production stage (e.g., CNC milling) and then switch over to a tooled solution (e.g., casting) after first production? With this scenario, cost reductions are phased-in, and the savings doesn’t occur near term (but, rather, in a longer time period).
- 在整個項目過程中能否逐步採用製造技術?那是,我們可以在原型/第一生產階段使用一種製造技術嗎?(例如CNC銑削),然後在之後切換到工具解決方案(例如鑄造)第一次生產?在這種情況下,將逐步降低成本,並且不會在短期內(而是在更長的時間內)節省費用。
3.2.6 Determine Factor of Safety Needed
3.2.6確定所需的安全因素
A determination of “factor of safety” must be reviewed at this time. That is, answers
to the following questions must be known:
此時必須審查“安全因素”的確定。也就是說,答案必須知道以下問題:
- If the part fails, does anyone get injured? What is the cost of an unpredictable failure in lives, in dollars, and in time?
- 如果零件失效,是否有人受傷?不可預測的代價是什麼
生活,金錢和時間上的失敗?
- How critical is this particular part in the overall function of the product? If this part fails, does the entire product fail?
- 該特定部分在產品整體功能中的重要性如何?如果這
部分失效,整個產品是否失效?
- How well are the forces known (from Sect. 3.2.2 above)? Do we know the “error bars,” that is, how much the forces can deviate from the assumed nominal value?
- 對力的了解程度如何(根據以上3.2.2節)?我們知道“錯誤”,也就是說,力可以偏離假定的標稱值多少?
- Determine the “critical aspects” of the chosen design (material or geometry), and how in-production will they be specified, certified, and inspected? Make notes to assure these steps (certification/inspection) will be done. Determine the testing required in the various stages of the design that will be required to assure that the final design will be adequate for shipment to the customer in production.
- 確定所選設計的“關鍵方面”(材料或幾何形狀),並如何在生產中指定,認證和檢查它們?做筆記確保將執行這些步驟(認證/檢查)。確定測試在設計的各個階段所需要的,以確保最終設計將足以在生產中運送給客戶。
- There will be an optimized solution which generally can be found by analyzing the major components of the design and determining where the “weak links” in the design exist. This can be found by utilizing some testing methodologies that induce failures by testing beyond the environmental limits (such as highly accelerated life testing, HALT). By first identifying where failures might occur, then by testing design prototypes, data can be generated to determine whether certain segments are near their design limits.
- 將有一個優化的解決方案,通常可以通過分析找到設計的主要組成部分,並確定“弱鏈接”在哪裡設計存在。這可以通過使用一些測試方法來找到通過超出環境限制的測試來誘發故障(例如高度加速的壽命測試,HALT)。首先確定可能發生故障的位置,然後通過測試設計原型,可以生成數據以確定是否一定
段接近其設計極限。
If any of the above six steps in the design process do not have answers known to some degree of confidence, the designer is faced with:
如果設計過程中上述六個步驟中的任何一個都沒有已知的答案在一定程度上,設計師面臨著:
- Making further inquiries to get better information.
- 進行進一步查詢以獲得更好的信息。
- Going forward with the design. It would be rare for designers to know about all of the forces and interrelation of parts at the very beginning of the design process. Certainly, the designer can list the assumptions made and the additional information that would be essential. It is certainly possible to design parts, prototype the parts, and test them under the conditions that they will need to function in. Several approaches to this dilemma of “going forward with the design without knowing all of the information” can be taken; let’s explore an example where:
- 進行設計。設計師幾乎不了解所有情況在設計過程的最開始就考慮零件的力和相互關係。當然,設計人員可以列出所做的假設以及其他必不可少的信息。當然,可以設計零件,對零件進行原型設計並在它們需要發揮作用的條件下對其進行測試。解決這種“前進設計”難題的幾種方法知道所有信息就可以採取”;我們來看一個例子
哪裡:
Design 1 has a weight that is 110% of target weight but has a 95% chance of being structurally successful. Design 2 is 100% of target weight but has a 75% chance of being structurally successful. So Design 1 is 10% over the target weight,but with a much lower risk of failing to meet the design goal of working from a structural point of view.
設計1的重量為目標重量的110%,但有95%的機會在結構上取得成功。設計2是目標重量的100%,但在結構上成功的可能性為75%。因此,設計1超出了目標重量的10%,但是無法達到通過設計工作的設計目標的風險要低得多結構的觀點。
So, what is being “traded-off” is the time needed to optimize the design. Certainly, the product must work from a structural basis. It will be difficult to determine the “margin” in the design at the very beginning of the program. Going forward with the design without knowing all of the information has value in that the “basic design” can be tested. It is hoped that the “basic design” can be modified in a quick time frame that allows the program to continue as the rest of the information is attained. We can move forward quickly by “overdesigning” the parts or invest more time to “marginally” meet all of the requirements. These two paths are investigated a bit more below:
因此,“折衷”是優化設計所需的時間。當然,產品必須從結構的角度進行工作。很難確定在程序開始時就在設計中“預留空間”。繼續前進在不知道所有信息的情況下進行設計的價值在於“基本設計”可以測試。希望可以迅速修改“基本設計”框架,使程序可以在獲得其餘信息時繼續運行。我們可以通過“過度設計”零件來快速前進,或者投入更多時間來“勉強”滿足所有要求。仔細研究了這兩個路徑以下更多:
- “Overdesign” the parts – this approach probably guarantees that the parts will structurally function under testing. The idea here would be to iterate back to a less conservative design as testing reveals where material and weight savings are appropriate. This approach at least maximizes the chances of the design meeting the structural functionality requirements very early in the test phases of the project. However, weight changes to the design to bring these parts closer to “marginal” structural success will require time (and money) to retest the design to validate the changes. Most projects have limited time for iterative approaches to attain parts that are “perfectly” designed.
A.“過度設計”零件–這種方法可能保證零件會在測試中的結構功能。這裡的想法是迭代回到測試顯示出節省材料和減輕重量的地方,從而減少了保守的設計適當。這種方法至少使設計會議的機會最大化在項目測試階段的早期就需要結構功能。但是,為了使這些零件更接近“極限”結構成功而進行的設計重量更改,將需要時間(和金錢)來重新測試設計以達到驗證更改。大多數項目在迭代方法上的時間有限獲得“完全”設計的零件。
- Design parts with the more time-consuming path of “just marginally” meeting both the weight and strength requirements. So, this stratagem is different than overdesign (above) in that the parts are designed that have a chance of (just barely) working. For example, if space and weight reduction are highest on the list of product requirements, a design that is “marginally” acceptable from a structural strength factor, but has a greater material and weight savings, may be what is needed. This approach attempts to balance both “risk and reward” and should have the agreement of the design team to go forward. With this design, the material and weight goal would be met. However, risk of this design not structurally working goes from 5% to 25%. So, the “B” design path shows higher risk of not meeting the product requirements for structural strength but will meet the product requirements for weight.
B.設計零件時使用“僅少量”會議會花費更多時間兼顧重量和強度要求。因此,這種策略與過度設計(以上),因為零件的設計有可能(只是勉強)工作。例如,如果空間和重量減少量最大產品要求列表,該設計在“基本”上可以接受結構強度因子,但具有更大的材料和重量節省,可能是需要什麼。這種方法試圖平衡“風險和回報”與應該徵得設計團隊的同意才能前進。有了這個設計可以達到材料和重量的目標。但是,這種設計的風險不大從結構上講,工作率從5%上升到25%。因此,“ B”設計路徑顯示不滿足產品結構強度要求的較高風險,但將滿足產品的重量要求。
- Blends of the above two approaches may be appropriate. That is, some parts of the design would be conservative, while other parts of the design would be more risky. This perhaps allows an “overall risk tolerance” to be a part of the overall design. Experienced design teams will know the best places in the design to “push the envelope” of acceptability.
C.上述兩種方法的混合可能是合適的。也就是說,設計會比較保守,而設計的其他部分會更多有風險。這也許使“整體風險承受能力”成為整體風險的一部分。設計。經驗豐富的設計團隊將了解設計中的最佳位置“推翻接受度”。
3.3 Analysis Required
3.3需要分析
There are certainly many designs that warrant the most exacting analysis in the design of electronic packaging. In any highly competitive product design area, it will be the company that does the most productive job with a given technology that 3 Structural Considerations 45 will maximize its chances for success. The very highest degree of analysis will be needed if the product has:
當然,有許多設計可以保證在分析中進行最嚴格的分析電子包裝設計。在任何競爭激烈的產品設計領域,將是在給定技術的基礎上做得最多的公司3結構考量將最大限度地提高成功機會。最高程度的分析將是如果產品具有:
- A “high” production quantity. If hundreds of thousands of a particular unit are to be produced, then the savings of a dollar per unit could result in substantial total savings. An analysis that saves even a small amount of cost will result in a lot of overall profit due to the larger production quantities. If, however, only a few units are to be produced, the potential for savings is greatly reduced, and, once a design is deemed to be functional, a large investment in cost reduction will not bring substantial savings.
- 產量高。如果成千上萬的特定單位要生產,那麼每單位節省一美元可能會導致可觀的總和儲蓄。節省少量成本的分析會導致很多整體利潤歸因於更大的產量。但是,如果只有幾個單位被生產出來,節省的潛力就大大減少了,一旦設計被認為是可行的,減少成本的大量投資不會帶來可觀的節省。
- A high degree of safety as a requirement due to the environment that the product will be placed into. Examples of this are products that are in the transportation, utilities, medical, or educational industries. All customers need to have a safely operating product.
- 由於產品所處的環境,要求高度安全將被放入。例如運輸中的產品,公用事業,醫療或教育行業。所有客戶都需要安全經營產品。
- A “mission” that is critical to the customer. This would include products needed for military, space agency, or government in general.
- 對客戶至關重要的“任務”。這將包括所需的產品一般用於軍事,航天局或政府。
Note here that there can be no excuse for a design that is so overdesigned that it lowers the profitability of the company. Designers and engineers should be ever vigilant to the possibility of cost reduction. The elimination of parts, the design for manufacturability, and the overall elegance of design lead to product leadership. It is in the first stages of design that present the most cost reduction possibilities. As the design progresses to even the prototype stages, the cost of redesigning for cost reduction starts to rise exponentially. More on this aspect will be presented in Chap. 6 on “Assembly and Serviceability.”
請注意,過分設計以致降低公司的盈利能力是沒有任何藉口的。設計師和工程師應該時刻警惕降低成本的可能性。零件的減少,可製造性的設計以及整體設計的優雅,導致了產品的領導地位。只有在設計的第一階段才能最大程度地降低成本。隨著設計甚至進入原型階段,為降低成本而重新設計的成本開始呈指數級增長。這方面的更多內容將在第一章中介紹。關於“組裝和維修性”的第6條。
More on this aspect will be presented in Chap. 10, “Safety by Design.”
這方面的更多內容將在第一章中介紹。 10,“設計安全”。
The number one design consideration is still and will always be functionality. That is, the part must function as it is intended. It doesn’t matter how well it looks or how elegantly it can be produced, IF the part will fail under load. This is a major reason why the loads must be understood by the designer.
首要的設計考慮因素仍然是並且永遠是功能。即,零件必須按預期發揮作用。有多好都沒關係如果零件在負載下會失效,那麼它的外觀或生產的優雅程度。這是一個設計人員必須了解載荷的主要原因。
Modern analysis software solutions using finite element analysis (FEA) are very ubiquitous. A search on Google reveals introductory material such as:
使用有限元分析(FEA)的現代分析軟件解決方案非常實用無處不在。在Google上進行的搜索顯示了一些入門資料,例如:
- Finite Element Analysis, by David Roylance, MIT. Describes the three principal steps as:
- 有限元分析,麻省理工學院的David Roylance。描述三個主體步驟為:
- Preprocessing, where a model of the part to be analyzed in which the geometry is divided into a number of discrete subregions, or “elements,” connected at discrete points called “nodes”
- 預處理,將要分析的零件模型(其中的幾何形狀劃分為多個離散的子區域或“元素”)進行連接在離散點稱為“節點”
- Analysis, where the dataset prepared by the preprocessor is used as input to the system of linear or nonlinear algebraic equations that calculate the stresses and displacements
- 分析,將預處理器準備的數據集用作輸入線性或非線性代數方程組,用於計算應力和位移
- Postprocessing, where the results are graphically displayed to assist in visualizing the results
- 後處理,以圖形方式顯示結果,以幫助可視化結果
- Linear Analysis, by Professor K. J. Bathe, from the MIT open courseware, MIT. This video series is a comprehensive course of study that presents effective finite element procedures for the linear analysis of solids and structures.
B.線性分析,來自MIT開放式課件中的K. J. Bathe教授,麻省理工學院。該視頻系列是全面的學習課程,介紹了有效的實體和結構線性分析的有限元程序。
C.Finite Element Analysis, Dr H. J. Qi. Describes the FEA process as:
C.有限元分析,H。J. Qi博士。將FEA流程描述為:
- Formulating the physical model, that is, describing (perhaps, simplifying) a real engineering problem into a problem that can be solved by FEA
- 制定物理模型,即描述(也許簡化)將實際工程問題轉化為FEA可以解決的問題
- Using the FEA model by discretizing the solid, defining material properties, and applying boundary conditions
- 通過離散化實體,定義材料屬性來使用FEA模型,並應用邊界條件
- Choosing proper approximate functions, formulate linear equations, and solving these equations
- 選擇適當的近似函數,制定線性方程,並解決這些方程
- Obtaining results in both numerical and visual formats
- 以數字和視覺格式獲得結果
There is no doubt that using FEA can provide much useful information about engineering problems involving structural analysis (along with solid mechanics, dynamics, and thermal analysis). Any answers coming out of this analysis should be first tested by using simplified models and forces to see if the answers make some sense. Testing should be used to verify the assumptions made and the resulting answers. Another attribute of using FEA analysis is that small changes in the design can also be inputted into the analysis to see how the results vary. In this manner, it can be shown very quickly how to make the design better.
毫無疑問,使用FEA可以提供有關以下內容的許多有用信息涉及結構分析的工程問題(以及固體力學,動力學和熱分析)。分析得出的任何答案應該是首先使用簡化模型進行測試,然後用力來查看答案是否有幫助感。應該使用測試來驗證所做的假設和結果答案。使用FEA分析的另一個屬性是設計中的細微變化也可以將其輸入到分析中以查看結果如何變化。這樣,它可以很快顯示出如何使設計更好。
Some companies are large enough to have an entire department devoted to FEA analysis, while others operate with the expectation that the designer will be analyzing the structures using FEA on their own.
一些公司規模足夠大,可以將整個部門專門用於FEA分析,而其他人則希望設計人員自己使用FEA分析結構。
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