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六西格玛到底是什么?What is Six Sigma?
作为一名职场人士,尤其是制造行业从业者,你一定有意或无意中听到过很多次“六西格玛”这个词。有时候这个词甚至变得有些烦人,因为有些机构会把它鼓吹成一种包治百病的万灵药,听起来太不靠谱了。那么,六西格玛到底指的是什么?什么问题适合用它来解决?它的优势,当然,还有局限性有哪些?
As a professional, especially a professional in manufacturing industry, you may have heard, intentionally or unintentionally, a lot about Six Sigma. Sometimes it even gets annoying as it is over promoted by some organizations as a catholicon to any problems, which sounds suspicious. So what does Six Sigma mean exactly? Which kind of problems can be solved by it? What are the strengths and, of course, limitations of it?
最初,六西格玛,也就是6σ,是摩托罗拉公司在19世纪80年代提出的一个统计学概念,指的是平均值左右各6倍标准差的宽度,总共12倍标准差的宽度,刚好完美地落在规格上下限以内。这种状态代表了一种质量水平,也就是从长期来看3.4 PPM。顺便说一句,σ是统计学中表示总体标准差的符号,μ是表示总体平均值的符号。
Originally, Six Sigma, which equals to 6 σ, was a statistical concept initiated by Motorola in 1980s. It means the width of 6 times of standard deviations on both sides of the mean value, which is the width of 12 times of standard deviations in total, perfectly fits in the specification limits. This also means a quality level, which is 3.4 PPM in a long term. By the way, in statistics σ is the notation for standard deviation of the population and μ is for mean value.
为了更通俗易懂,我们来举个例子:假设你想要知道一台车削设备在加工一种圆柱产品外径时的表现,你从这台设备加工出的工件中随机取了100件作为样本。该产品外径的规格上下限是在图纸上规定好的,那么,这台设备越稳定,你取的样本的标准差就越小,可以挤进规格上下限间空间的标准差的个数就越多。这就是说,会有更多件产品的外径尺寸落在在公差之内,也就意味着更少的报废。
To make it more sensible, let’s look at an example. Say, you would like to know the performance of a turning machine processing the outer diameter of a cylinder, so you take a random sample of 100 outputs from that machine. We know that the LSL (lower specification limit) and USL (upper specification limit) of outer diameter are fixed according to the drawing, so the more stable the process is, the smaller the standard deviation of the sample is, thus the more standard deviations can fit in the space between LSL and USL, and then the outer diameter of more parts will fall within specification, which means less defectives.
在实践中,六西格玛也意味着一种流程优化的方法论,这个方法论是19世纪90年代由通用电气公司发展出来的,也是现在六西格玛最广为人知的含义。这个方法论中主要涉及到两个系统地解决问题的途径,分别是 DMAIC 和 DMADV, 二者各自包含了五个按照严密的逻辑顺序排列的不同阶段。DMAIC指的是定义,测量,分析,改进,控制,主要用来解决现有流程存在的问题,而DMADV指的则是定义,测量,分析,设计,验证,主要用来杜绝新产品或流程可能出现的问题。
Practically, Six Sigma also means a methodology for process optimization, which was developed by General Electric in 1990s and more widely referred to in practice nowadays. Two major approaches involved in this methodology are DMAIC and DMADV, each of which stand for a systematic approach of problem solving with 5 different phases in a logical sequence. DMAIC, namely, stands for define, measure, analyze, improve, and control, aiming at solving problems on an existing process. DMADV, on the other hand, stands for define, measure, analyze, design, and verify, aiming at avoiding potential problems for a new product or a now process.
尽管这两个途径听上去逻辑清楚通俗易懂,它们的每个阶段其实都分别包含了大量的专业工具,对应着比一个个简单的动词大得多的工作量。所谓的六西格玛项目,指的就是遵循这两个途径的其中一种来解决现有问题或避免潜在问题的项目。这些项目的项目经理就是我们常听到的六西格玛各种“带”,这些“带”的级别以颜色来区分(通常分为黄带,绿带,黑带),是由专业机构按照知识层级、技能水平、项目专业度等几个方面来认证的。
Although both approaches sound logical and easy to understand, each single phase has its own work package including a sufficient number of professional tools, which link to much more workload than a simple word sounds like. Six sigma projects, therefore, are projects that follow either of these two approaches to solve or avoid problems, and the project leaders are so called “belts”. The level these belts, usually distinguished by different colors (white, yellow, green, black), are certified by professional organizations according to one’s knowledge level, skillset, projects’ professional degree, and so on.
另外,当六西格玛在集团层面被提及时,无论是在运营领域还是商业领域,它还可以表示一种持续改进的企业文化,或者至少是这种文化的一部分。在这一点上,六西格玛往往会被看作是和Kaizen, Lean 之类并列的持续改善工具。
Additionally, when Six Sigma is mentioned at a corporate level, either in operational areas or commercial areas, it is always also referred as a corporate culture of continuous improvement, or at least part of that culture. For that matter, Six Sigma is usually considered as a tool for continuous improvement, which is pretty much similar with Kaizen, lean, and so on.
企业通过建立相应的组织架构,开展培训,和提供项目辅导来推广这些工具,从而创造一种文化氛围,使员工们由足够的意识和能力来发现问题,找到正确的方法,从而最终成功地解决问题。而黑带大师,则往往是负责在集团层面推广六西格玛文化的那个人。
Companies promote these tools by building up relevant organizations, deploying trainings, providing coaching, and tracking projects, to create such a culture, where employees have the awareness and capability to identify problems, to find the right method for each problem, and to solve them with success eventually. And Master Black Belt, is the person who is responsible to promote Six Sigma at a corporate level.