Modelling, analysis, and acceleration of a printed circuit board fabrication process
Abstract: Product design and fabrication constitute an important business activity in any manufacturing ﬁrm. Designing an optimized product fabrication process is an important problem in itself and is of signiﬁcant practical and research interest. In this paper, we look into a printed circuit board (PCB) fabrication process and investigate ways in which the fabrication cycle time can be minimized. Single class queueing networks constitute the modelling framework for our study. The model developed in this paper and the analysis experiments carried out are based on extensive data collected on a PCB fabrication company located in Bangalore, India. This is a representative PCB fabrication company involving multiple, concurrent fabrication works with contention for human/technical resources. Our model seeks to capture faithfully the ﬂow of the fabrication process in this company and such other organisations, using queueing networks. Using the model developed, we explore how the cycle times can be reduced using input control, load balancing, and variability reduction. The model presented is sufﬁciently generic and conceptual; its scope extends beyond that of a PCB fabrication organization.
While manufacturing ﬁrms have been developing new products since the industrial revolution, the importance of designing and developing high quality new products has increased dramatically in recent years. The main forces driving the importance of product design and development are competition – internal and external to the company, changing customer needs, and changes in technology. These driving forces have created a competitive imperative for speed, efﬁciency, and high quality in the design and development process. This creates substantial pressure on engineering teams to develop better products and at the same time to develop them faster. It is also observed from various studies that product life cycles are continuously becomingshorter, which has forced companies to reduce the product design and development leadtime. At the same time, the effects of shorter lead times can be considered beneﬁcialonly if they can be achieved without undue sacriﬁces in other areas such as quality.Recent literature on lead time modelling of product design and development has revealedmany techniques for faster development of new products . Thesetechniques are based on some generic approaches, which focus on the reduction of leadtime. Companies follow one or a combination of these approaches to accelerate theproduct design and development cycle. However, these approaches can be applied onlywhen the entire process is clearly understood, which is achieved through faithful modellingof the process.
Our objective in this paper is to model and analyse a typical industrial fabricationprocess and to investigate the methods to reduce fabrication cycle time. We speciﬁcallyconsider the PCB fabrication process. We apply queueing theory to model this process,and, using the model developed, we explore the improvement in fabrication cycle timeusing input control, load balancing, and variability control.
1.1 Review of relevant work
Considerable amount of research has been carried out in the past decade in the important areas of lead time modelling and lead time reduction in a manufacturing ﬁrm. For example, Hopp et al (1990) in their paper have explored the causes of excessive lead time and suggest practical, inexpensive strategies for reducing lead time. Their suggestions are based on a detailed study of six manufacturing companies and a survey of literature in the related area. Hopp & Spearman (1996) have listed several techniques (based on queueing principles) for compressing manufacturing lead times. Some of the techniques for lead-time reduction discussed by them, such as variability reduction, have been explored in our work in the current paper. Quick response manufacturing (QRM), presented by Suri et al (1995) and Suri (1998) is an important collection of techniques to compress process lead times in manufacturing ﬁrms. QRM principles include intelligent scheduling of bottleneck resources, product-oriented cellular organization, use of a judicious mix of push and pull control policies etc. It is argued that substantial improvement in lead time, of the order of 75%, in new product introduction, and 90% to ﬁll orders for existing products can be achieved by using QRM techniques. Apart from reductions in lead times, when properly implemented, a QRM strategy also results in quality improvement and cost reductions.
Lead time reduction techniques have been popular in the context of the product design process and in new product development processes also. Millson et al (1992) present a survey of major approaches for accelerating new product development. They suggest a general set of techniques for reducing the development cycle time of new products, and classify these techniques into ﬁve basic categories. These are: (a) Simplify the process; (b) eliminate the delays; (c) eliminate steps; (d) speed up operations; and (e) make processes parallel. There are several books that have appeared in recent years, which focus on improving the product development process. In their book, Clark & Wheelwright (1993) discuss lead time reduction in a qualitative way with illustrative case studies. Krishnan et al (1995) in their study, have discussed a method of reducing product development lead time by overlapping development activities through the exchange of preliminary design information. In their approach, downstream development activities begin with unﬁnalized upstream design information, and new design changes are incorporated in the subsequent iteration of development. Adler et al (1995, 1996) have analysed product development lead time in organizations that involve multiple, concurrent, non-unique projects, with shared resources, using single-class queueing network models. In fact, many of the techniques explored by us in the current paper, such as input control, process control, and load balancing, are suggested by these two papers. More recently, Narahari et al (1999) in their study have come up with lead-time models of product design and development processes using both single-class and multi-class queueing network models, and explored lead-time reduction using various lead-time reduction techniques. These techniques (Narahari et al 1999) have also inspired the current-work. Similar modelling and optimizing techniques are investigated for software product development by Nagaraju (1997).
Process models offer a systematic, well deﬁned way of representing the structure of process. They record activities that are performed in the process with the inter-dependencies among activities. Lyons et al (1995), in their report, have explained key requirements, industry practices, and research questions that should drive new methods and computer tools for process modeling of the product realization.
1.2 Queueing networks
A queueing network is a collection of stations (or service facilities) arranged in such a way that the customers proceed from one station to another in order to fulﬁll their service requirements. Each station has an associated queue in which jobs may wait prior to receiving service. The stations are characterized by service rate and the queueing discipline. The service rate is the number of jobs departing from the station per unit time, and queueing discipline is the order in which arriving jobs receive service.
2. PCB fabrication process: An outline
There are three types of printed circuit boards available today. They are
- Single sided boards: Where the entire circuit is laid on one side of the board and there may or may not be holes on the board for mounting of components, or for interconnection of component
- Double sided boards: With the circuit on both sides of the board and electrical connection is established by drilling holes through the board and plating copper through the holes.
- Multilayer boards: Two or more pieces of dielectric materials with circuitry formed upon them and are stacked up and bonded together. Electrical connections are established from one side to the other, and to the inner layer circuitry by drilled holes which are subsequently plated through with copper.
The various stages in the PCB fabrication process:
2.1 Photo ﬁlm inspection
2.2 Panel cutting.
2.3 Drilling holes
Once the panel is cut, the next stage is the drilling of holes. Either CNC drilling or manual drilling is used for this purpose. It is observed from past data that 98.92% of the jobs are drilled on CNC drilling machine and only 1.08% of the jobs are drilled on optical drilling (manual). Manual drilling is only used in one or more of the following situations: (1) very low order quantities, (2) non-availability of drill data, and (3) number of holes on the PCB is too low for using the CNC drilling machine. The panels are pinned together in stacks from one to four high, depending on panel thickness. These are loaded onto the drilling machine. NC part program is loaded into the CNC drilling machine and all required holes are drilled at proper locations, with corre simultaneously multiple stacks of panels can be drilled. Once all the holes are drilled, ct drill size. Latest CNC drilling machines are equipped with automatic tool changer which will automatically change drill bits when the hole size changes. Some CNC drilling machines are also equipped with multiple spindle, so that the panel is cleaned and deburred.
Sdudy and Application of some Key Techniques of High Accuracy and High Speed PCB NC Driling Machine
The technology of PCB manufacturing is the important foundation and composing of electronic information manufacturing industry. The PCB NC drilling machine is key technology equipment in the PCB’s precise hole site processing. It brings higher demands to PCB NC drilling machine that the electronic products become smaller,lighter and thinner such as communication computer and audiovisual equipments. The high accuracy,high speed, smaller hole and short runs have become obstacles of new PCB NC drilling machine developing and increasing. Nowadays, the high accuracy and speed PCB NC drilling machine has become a confined factor of level of electronic manufacturing industry and embodiment between our electronic manufacturing industry and advanced level in world margin. It is important and realistic meaning for increasing the level of our electronic manufacturing technology equipments and self-supporting ability of electronic manufacturing industry to develop the key technique of the high accuracy and speed PCB NC drilling machine and improve its performance.
Be dead against the demands and characteristics (namely the high accuracy,high speed,short runs,hole more but smaller) of hole site processing of PCB NC drilling machine,some methods that can completely improve keys technique index of the machine will be proposed in this paper.First,based on the PCB technology demand,the developing tendency and the hole processing state,the main direction and aiming of drilling machine system performance increasing was proposed,which achieve high accuracy,high speed and the ability of processing micro-hole.Judging standards and accuracy influence factor of micro-hole process quality will be established.The effect factors of drilling will be analyzed.Next,propose the concept and token method of the 3D-stabilization.Simulate the PCB NC drilling machine dynamic characteristic with the 3D-stabilization basing on the multi-body dynamic numerical model.Look for a feasible method and technology parameters to increase the process micro-hole ability.The third,be dead against the effect of acceleration variety in the high-speed process continuous short distance weld disk,a kind of self-adapted algorithm according to three times smooth curvilinear is proposed in order to ensure the accuracy of position fix when high speed feeding.At the same time,apply a kind of trail controller using self-adapted controller to induce the effect arisen by the torque vibration because of load,frication and so on.Finally,be dead against efficiency of route optimizing and data processing,Greed algorithm(GA) is put forward.The coding rule,joining and aberrance method basing on the GA are introduced.Obtain good engineering application result.
Research on the Machining Method and the Equipment of Drilling-tapping Once Shaping
Mechanism manufacturing is the important foundation of industry，and the forerunner department of county economy.Historic practice has proved again and again that it is somuch important of the advanced equipment and manufacturing technology to countyeconomy.As a result of the swift and violent development of the modern technology，especially micro-electronics and computer technology，mechanism manufacturing hasalready changed profundity and will continue to change.In addition to，because mechanismtechnology is integrated with micro-electronics technology tightly，especially the computertechnology，the traditional mechanism manufacturing technology has changed with eachpassing day and thoroughly remould itself，this paper wants to set about studying due to theabove result.
As we all know,the traditional operation of screwed hole includes two processes:at first drill a bottom hole which is less than the screwed hole(example:want to operate a screwed hole of M6x1 and at the beginning of drilling a bottom hole of?5),and operate the thread of the hole with the screw tap at last.If we use this operation method,it is a very low production obviously and it can hardly satisfy the modern production requirement,especially with regard to mass production.After NC(numerical control)machines appear,the efficiency of operating the screwed hole increases very rapidly because of taking advantage of the automatic tool-changing capability.However,this method still includes two processes like before,namely drilling the hole at first and tapping at last.Moreover,the cost of this NC machine is very expensive.
This paper wants to use the modern mature NC technology and combine one new type tool.And merge the tradition two processes of the operating the screwed hole into one process.It can improve the production efficiency very much.
In the paper the main task is accomplished as following:
1)Put forward the clew of screwed hole once shaping.We assume that the foreside of the multiple new type tool is the aiguille and the rear end is the screw tap.First drill a bottom hole of the screwed hole with the portion of aiguille.Second measure the rotary speed of the tool.The MCU outputs the right frequency pulse into the power amplifier according tothe rotary speed and the standard of the screw.The power amplifier drives the stepping motor and makes the tool go down.The multiple movement can shape the screwed hole inthe bottom hole.We have applied for a patent of this method and this multiple tool.The name of this patent is the special usage device of operating the screwed hole.The patentnumber is ZL0402111013.8.
2)According to the above clew,we design and make the three-helix-groove multiple tool.The standard of screw is M 6×1and the angle of helix is30°.The three cutting edges are directed at the center.The multiple tool is made up of the high-speed steel.
3)According to the above clew and the multiple tool,we design and make the MCU control system of the screwed hole once shaping.And we program the procedure of measure and control and alternation between the people and the computer.
4)In order to pledge the control system to fulfill the task,we adapt the hardware anti-jamming measure to prevent the outside-jamming signals into the control system.In addition to,we adapt the software anti-jamming measure to eliminate the mistake signals which are made by the twitter of machining framework.
5)We set up the mathematic model of the drive system of machinery and work out the inherent frequency of the system to avoid producing resonance which may destroy the precision of the screwed hole.We work out the transfer function of the system and the jumping respond function.We make sure that the overtake quantity of the system does not go beyond the tolerance of the screw.And apply the PID to adjust the control system.Under the Matlab/Simulink circumstances we operate the computer to simulate it.As a result,the effect of using PID system is more better than not using it.
6)For the sake of examining the reliability of the printed board and the multiple new type tool,we have process test some times.According to the result of workpiece,we can believe that the design of the printed board and the multiple new type tool can achieve the expected goal.
7)We establish the experiment flat roof and use the control electric circuit and the multiple new type tool which are designed by ourselves to operate the screwed hole of M 6×1 at first.Through the measure of the screwed hole,we believe that the result of the screwed hole’s size achieves the country criterion.
Study on Some Key Technological Problems
of High Speed Machine Tool
High speed and high precision is one of the main developing tendencies of modern machine tool. Along with the demand of high speed and high precision NC machining of manufacturing, the high speed and high precision machine tools are studied more and more deeply, and some scientific research results of great value have been obtained. High speed and high precision machinery should have not only high spindle speed and high feeding speed, but also high spindle and feeding system acceleration. As for the high speed and high precise machine tools, the final performances and the final manufacturing quality of the machine tools will be affected directly by the characteristics of spindle system. In order to improve the quality of products, it is very important that studying the performance of spindle system, and building the dynamic models of that, and evaluating the performance in the process of design.
The research and development of CHH6125 high speed machine tool is the national 863 and the tenth five years item which is undertaken by Shenyang No. 1 Plant of Machine Tool. Some theoretic calculation, FEA and system dynamic imitation in the key technological problems of high acceleration moving performance of machine tools’ feeding system and dynamic characteristic of bed system and etc. are done in order to increase the performances of the machine tool.
The thesis’s research is based on summing the research outcome and further research.The dynamic characteristics and thermal performances of spindle assembly of CHH6125 machine tool’s spindle assemblies are studied mainly in the paper by using the method of theoretic models and Finite Element Analysis. After that, some necessary experiments of the machine tool are done, based on it some necessary recommendations to the theoretic model and FEA model can be done. The Work is also a foundation for further improving the dynamic characteristic of high speed machine tool’s spindle system. The details are in the ensuing paragraphs.
(1) On the basis of the materials at home and overseas, the concept, origin and developing tendency of high speed cutting and manufacturing and the current ondition and developing tendency of high speed and high precise machine tools are studied. Both the development and application of the foreign high speed machine tool technique and current condition, and developing tendency of ours are studied. Additionally, the key technological problems which influence the development of high speed and high precise machine tools, and the problems which need to be solved urgently so that the machine tools can develop quickly in high speed high precise manufacture are studied.
(2) Although different mechanical structures should be used in those high speed and high precise machine tools which have different requirements, there are some common key technological problems in the high speed machine tool structure designing. The content of second part mainly analyses and illustrates the key technology problems of the structure design of high speed machine tool and investigates the rationality and key technological problems of the key structural parts of high speed machine tools.
(3) The performance of machine tool is influenced by the dynamic characteristic of machine tool’s spindle assemblies mainly. Firstly, all kinds of model methods which are suitable for the dynamic characteristic of the spindle system are investigated and analyzed the both sides. Secondly mainly dynamic characteristic of spindle system which is based on the method of transfer matrix and the dynamic model method of spindle system which is suitable for the high speed high precise machine tool are investigated. Finally, some research on the accuracy of model method through imitation and experiment are done,and some necessary recommendations are attempted.
(4) During the process of dynamic characteristic analysis of spindle assemblies, the bearing rigidity of high speed machine tools’ spindle system play much more important role to the system performance. 3D model using for FEA is built and translated into the FEA software ANSYS after discussing the bearing rigidity of CHH6125 machine tool.Then, the modal analysis and harmonic of spindle and spindle assembly are done, valid for structural degrees of freedom are obtained.
(5) As for the high speed machine tool, the characteristic of machine tools are greatly influenced by thermodynamics performance of spindle system. Firstly, the Heat Transfer characteristics of motorized spindle are investigated, every thermodynamic parameters of spindle assembly are determined. Then, the thermodynamics models of spindle assembly are built by using Finite Element Analysis method, and the thermal analysis of the motorized spindle system is performed to make sure the thermodynamics characteristic of it.
(6) In order to study the previous result, some experiments on the machine tool are done. From the results of the experiment of machine tool, we can know that the results of analysis and calculation are rational.
By through the research work of the paper, the result of the paper not only provide the theorical fondation and support, but also offer essential references and experiences to the high machine tool’s design and analysis.
研发时间缩短技术在产品设计过程和新产品研发过程中已经普及。Millson等人在1992年对加速新产品研发的主要方法做了一项调查。他们建立了一个缩短新产品研发周期的技术集合，并把这些技术分为5个基本类别。这些类别为：（a）简化过程，（b）排除迟滞，（c）排除步骤，（d）加速操作和（e）并行加工。近几年出版了几本关注改进产品研发过程的书籍。在1993年，Clark 和 Wheelwright在他们的书中，通过用定性方法对就有说明性的个案的研究，讨论了研发时间的缩减。Krishman等人在他们1995年的研究中，曾论述了一种减少产品研发时间的方法，它通过交流初步设计资料利用搭接研发来减少产品研发时间。在他们的方法中，下游的研发活动以前面未完成的设计信息开始，而新的设计变革又融入其后的重复发展中。Adler等人在1995年和1996年利用单级排队网络模型，就涉及拥有共享资源的多重、并行和普通项目的机构中的研发时间做了分析。。事实上，我们在这篇文章中探讨的很多技术是这两篇文章提出来的，如输入控制、过程控制和负载平衡。最近，Narahari等人于1999年在他们的研究中，同时运用单级和多级排队网络模型，提出了产品设计和开发过程的研发时间模型，并综合运用多种减少研发时间的技术研究研发时间缩减。这些技术（Narahari等人，1999年）也刺激了当前的工作。Nagaraju等人于1997年在研究类似的模拟和优化技术软件产品的开发。过程模型为过程结构的表达提供了一种系统的、完全定义的方式。他们记录了在过程中表现为相互依赖的活动。Lyons等人（1995年）在他们的报告中解释了将要推动产品实现过程建模的新方法和计算机工具的关键要求、工业实践和研究问题。
印制电路板( P C B ) 制造技术是电子信息制造业的重要基础和组成部分。 印制电路板 ( P C B ) 数控钻床是印制电路板精密孔位加工关键的工艺装备。 伴随着以通信、计算机、视听设备等为代表的电子产品“ 小、轻、薄”的发展趋势和特点，给印制电路板数控钻床提出了 更高的要求。 精度高、速度快、孔小而多、行程短己成为新一代P C B数控钻床发展和提高面临的主要难题。目 前，高精度高速微孔印制电路板数控钻床是制约和影响我国电子制造业水平和电子信息产业基础配套能力的重要因素，是我国电子制造业与世界先进水平差距体现的重要环节之一。因此，开展高精度高速微孔印制电路板数控钻床关键技术的研究与应用，改善和提高P C B数控钻床的整体性能，对于提高我国电子制造工艺装备水平和电子信息制造业自我配套能力具有重要的现实意义。
本论文针对印制板数控钻床孔位加工的具体特点和要求 ( 即精度高，速度快，行程短，孔多而小) ，提出了全面改善和提高机床若千关键技术指标实现方法和途径。首先，根据印制电路板的技术要求和发展趋势以及其孔位加工技术现状，提出了机床系统性能提升的主攻方向和主攻目 标，即实现高精、高速、微小孔加工能力的提高;建立了微孔加工质量评价标准和主要性能影响因素体系，对钻孔质量的影响因素作了较为具体的分析。其次，提出了钻床三维稳定性的概念和表征方法，并运用三维稳定性，在钻床多体系统动力学数值模型的基础上，对钻床的机械动态特性进行仿真测量，寻找到一条切实可行的提高微孔加工能力的设计和工艺参数的控制手段和方法，明显改善了钻床机械加工性能。第三，针对高速加工连续短距离焊盘过程中加速度的连续变化带来的精度影响，提出并应用了一种基于分段参数三次曲线的平滑运动加速度控制算法，以保证快速加工时的定位精度。同时，应用了一种基于自 适应控制器的跟踪控制结构，以解决由于负载、摩擦等因素的变化带来的力矩波动对加工精度的不利影响。最后，针对海量孔位加工存在的路径优化和数据处理速度带来的加工效率问题，提出了一种面向工程应用的带遗传 ( G A )功能的贪婪算法，详细介绍了基于路径的G A编码策略、交叉和变异的方法。取得了良好的工程应用效果。