All 8 entries tagged Piuss
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December 05, 2010
six sigma is the right approach to build defect-free processes.
integrating the tools and techniques of six sigma within the larger framework of Lean production,
one can make the deliver high-quality, low-cost, custmer-specified products on a sustained, continuously improveingbasis
this is true whether the product is an automobile or a transaction at an automatic teller machine.
tools can be used as follows
small-batch or single-piece continuous-flow process
reliable process through total productive maintenance
other tools such as kaizen, visual control ,5s's single minute exchange of dies and mistake proofing
December 01, 2010
six sigma in some book always comes up with lean manufacturing together,but they are not the some phylosiophy, do they should be combined? but have to understand what is lean manufacturing first.
lean manufacturing known as lean production, it is a business philosophy. Toyota Motor Company developed it first,where it was called Toyota production system(TPS).
The objective of of Lean produciton is to eliminate all forms of waste in the production process.
six sigma is aim at creating a stable process, reduce the waste at the design stage. they have very similar objective.
wastes in lean produciton are overproduction, waiting for machines or operators, transportation waste, process waste resulting from inefficient and poorly designed processes, excessive inventory wasted motions through operators leaving work stations to fetch required suppliers or through continuous reaching, searching, or carrying goods. waste of rework through producing defects.
when all these waste is eliminated, the order production life cycle time is compressed. short cycle and delivery time, higher quality, and lower costs are all positive resluts.
there are many techniques to deal with waste work result in a whole that is greater than the sum of the individual techniques. if the manufacturing process is changed, lean manufacturing will produce high-quality products built to customer requirements at lower costs than traditional manufacturing.
November 30, 2010
Cp or Cpk stands for process capability index.
it means in a specific period, what's the capability of the process to produce products at a stable ,controable level.
operator ,machinery , materials,envrionment and technology this five main factors effect the process consistently, and the final production is effected by this five major factors.
during the production process, variation always exists. Cp compares the process spread to the width of the tolerances, tolertances should be at least as wide as the process is or more wider.
but Cp is not enough, may the tolerance of two process is same but one of them not lacated into the limits, Cpk is needed.
it measures the likehood of producing non-conforming product of the process. Cp compares the distance from the process centre to either tolerance, Cpk measurs the distance from top/bottom to the centre.
the process best situation is that Cp equals to Cpk. Cpk will never exceed Cp.Cpk can be negative if centre is outside of the control limits.
November 29, 2010
Roger's presentation provide a great experimental understanding to taguchi method.
he showed the sample of a warhead and how to use taguchi method to make the lip match the filling.
pointed out what control factors are, like header too design, pot design, bitumen height, cooling in cone,
and then carry out experimental results like the day we did helicopter exercise.
different consequences give different answers, this way provides all possible situation to find out what the best results and the resluts fall in to the limitation.
the noise ratio measure the robustness of the system. noise factors are those variables which infulence the system but cant be controlled by designer. customer usage conditions, wear states or manufacturing process variation may be too expensive or impossible to control, but we have to consider them when make a product.
maybe in theory ,taguchi method is not special, means just gather the other management theroy,
but in practice, it's really usefull, as least it can find out unstable factors correctly and ananlyse the noise factors.
November 26, 2010
Taguchi—value starts with design
after have an overwiew about taguchi method, an economic way to increase the quality comes up.
some industry always focus on final checking process rather than reduce costs by designed process.
robustness is the key concept. it provides an innovation concept to the industy about increasing quality,reducing loss.
not in production stage but in design stage.
creat great value using cheap and basic materials, ensure the process is stable and minimise the effect of these environmental noise.
using this concept, enterprise can creat value not only depending on purchasing newest machinery or materials.
after 3 times design,products are usually capable,great quality.
becasue Taguchi method reduce loss at initial process, use cheap materials can still produce good quality, it is really beneficial to the industry.
November 24, 2010
six sigma exercise——making model planes
yesterday we did a great exercise lecture from Graeme to make model planes within time required.
although team2 is faster than us,i think we still did an excellent job.
after trial, we redesigned our layout to improve the process, operation process is well splitted,and only 4 operators and 1 supplier,labour cost saving. finally,8 out of 11 planes was deliveried whin the target time. around 2 sigma we reached.
but one important thing comes to my mind is listening.
During our discussion, some members have a lot of ideas, it is good,but I think we need to listen to others idea not only think about yourselves. Team means cooperation, we spent too much time on theory thinking, chatting rather than doing practice.
although Define is important, but theory never make sense without exercise. If each of us can listen to each other, lot of ideas can be gathered, and then discuss which is best, we can try it, thats criteria base ,not interput others make them to agree with your own ideas. This problem reduce our efficiency and even the passion of the group.
I think from the other side of view, leadership is required. running a team based operation without a leader is terrible!
November 10, 2010
common or special?
Deming's basic quality philosophy is that" productivity improves as variability decreases"
there are 2 types variation:chance and assignable. but the most difficulty problem is how to comprehend them.
Common cause variability is a source of variation caused by unknown factors that result in a steady but random distribution of output around the average of the data. Common cause variation is a measure of the process's potential, or how well the process can perform when special cause variation is removed. Therefore, it is a measure of the process technology. Common cause variation is also called random variation, noise, noncontrollable variation, within-group variation, or inherent variation. Example: Many X's with a small impact.
Unlike common cause variability, special cause variation is caused by known factors that result in a non-random distribution of output. Also referred to as "exceptional" or "assignable" variation. Example: Few X's with big impact. Special cause variation is a shift in output caused by a specific factor such as environmental conditions or process input parameters. It can be accounted for directly and potentially removed and is a measure of process control.
one of the most effective quality tool to distingguish them is control chart.
but as we know there are two types of mistakes exist in statistics:error of the first kind and error of the second kind.
firsrt one is objective right but we think its wrong after we analyse the data, think there's special causes exists.(right ¡úwrong)
second one is that special causes exist but we think it is common, cannot find the problem.(wrong ¡úright)
so, problems always exist. when data appear out of 6sigma,we have to know it's only a phenomena not the nature of this situation.
after initial analysis,take action to the assumed special causes to test whether it's special or not. if it is not, the first error comes up,our aim is to minimize the happening probability of these two errors.when quality level reaches 3 sigma this probability is lowest. so this is why +-3sigma in the control chat as nature limits.
if data locates out of the up and down limits, special causes may exist.
if data not distributes radomly within limilts,special causses may exist.
some industry will use 2sigma as nature limits will increase the probability of the first kind of error.this will waste some time but make sure more special causes can be found.
some industry use 4 sigma as nature limits increase the probability of the second error decrease the first one. sepcial causes will be ignored.
if the process is not stable , a lot of sepcial cause exists means the system is out of control ,we need to improve the process.
before i only heard about the SIX SIGMA as a managment method after had lacture I start know deeper about it.
From my understanding, six sigma is a quality mgt which uses statistical methods to seek perfect manufacturing,minizing costs,increasing productivity and put customer satisfaction at first place.
when sigma figure goes up, variation goes down.
traditional quality managment always focus on results, they ensure the quality by emphasizing on final product checking and customer service whlist six sigma emphasize on actual causes of these variation. Quality is maintained by improving the process saving original cost rather than checking the final product strictly.Because during the production process these waste products already make a loss, after service will make another amout of costs.