SPC process ability is evaluated improve manufacturing riding quality continuously

In producing the automobile manufacturing industry that is a feature with batch, SPC (statistical programme controll) application is overwhelm, process ability analysis already became contemporary company to carry out quality pilot in fact a kind of strong step. The article elaborated following viewpoints: What what sample collects when carrying out SPC is actual the graph of only cost process of distributinging circumstance and example, in executive process the effect in instant monitoring is very main. Contemporary quality concept from go up at all changed the traditional pattern that with examining product objective quality gives priority to, shift quality pilot emphasis to the manufacturing process that fashions a product. Practice makes clear, to the instant monitoring of the process, matter to the quality of the quality-related cost of the riding quality that produces a course, product and end item directly. And statistical programme controll (SPC) it is a kind of such technologies, it aims to carry out precautionary principle, application counts manage statistic opposite to Cheng Jin is monitored all right and be analysed, those who make the process is in Wu Ke to accept and stable level, make sure the product accords with formulary requirement thereby. The purpose of the traditional method SPC that ability of the process when executive SPC evaluates is to make produce a process to be in what Wu Ke accepts and stable level, and process ability is to show the condition of the process satisfies technical standard (product standards, public errand) ability, it is worth the dispersive limits of normal wave motion to express with quality character, and with the capability index, degree that will reflect contented technology level. In fact, process ability analysis has become contemporary company to carry out quality pilot a kind of strong step. (- R) the graph is the application when heretofore enterprise carries out SPC most, also be thought a the most effective kind metric model control graph. Build and analyse - the foundation that R control pursues is to collect the size of group of notebook of appearance of data, logical choice and example group, include namely child the amount of the group. If N is the example number of every stature inter block, the capacity that M takes sample for place, be included namely child the amount of the group, can calculate from this piece, the interconnected system such as R is metric. In beg a control that all is worth graph and extreme difference graph to be restricted then after, but scale gives control to pursue, the condition that distributings according to graph midpoint, use sentence firm criterion has corresponding analysis, judgement with the criterion that sentence different. If discover to need to search an account when unusual situation, adopt in time correct measure. - R shows when the graph the process is in Wu Tong plan when controlled condition, can evaluate process capability, when like quality character the value is two-way public errand, capability index Cp, Cpk presses type calculates: In type, USL measures the upper limit of characteristic value to produce quality, LSL is the floor level that quality character is worth, and in example all child group average is: , standard deviation is decided by formula, the Dn in type is constant, be decided by the size N at appearance notebook group, can get through checking a watch. When quality character cost is one-way public errand, process capability index takes Cpk only commonly, right now, to sheet up the circumstance that tolerancepublic errand or sheet are down tolerancepublic errand presses type respectively (2) computation: Ability of the process when executive SPC evaluates a method optimize You Wujian Yi Ke travel, moving cost is low (right at, labour of computational choose and employ persons also can be finished) , afore-mentioned methods get applied extensively in business circles. A few manufacturers still developed special software accordingly, the part already was configured go up in relevant product. However, the hypothesis of the normal school of obedience of sampling observation example that is worth with quality character just about is premise, make this kind of method is put in a few limitation. Graph the example in 1 process analysis distributings actual condition makes clear model example, in phyletic and numerous quality character cost, even if successive and draw-out random sample, the minority such as the torque in also only geometry measures medium length, physical quantity a few kinds follow normal school pattern basically, include all sorts of form tolerancepublic errand inside great majority is measured disobedient. And, when assess process ability, besides need to make an on-the-spot investigation successive and draw-out child outside group example, return the influence that the time response that must consider a course brings, right now, the proportion that collects example to follow normal distribution is smaller. These influences are passed child 2 statistic of constituent cloth model are measured, the position (T) and S(t) disperse sex will describe, graph 1 it is a few typical case that come from actual production. Apparent, state a form traditionally the circumstance of 1a of only applicable Wu Tu, namely all child the example of the group all is subject to normal school, and distributinging center position and disperse sex are stabler. But in fact, according to the information that Q-DAS company provides, when contemporary automobile manufacturing industry is undertaking instant monitoring to producing a course, in the sampling observation example that place decides with Wu Ping, follow normal school pattern occupy only 2% the left and right sides, and " mix distributing " (include " without distributing " ) what hold proportion very big however, see give a demonstration of 1c of graph 1b, graph. Come to be formed at example mix the reason that distributing a lot of, in graph 1b, right now child although the example of the group is obedient normal school, but the central position that distributing presents those who accompany the doubtful change that decide the ground to change systematically mixture mode. And in graph 1c, child group example is disobedient before normal school. The catholicity principle that evaluates process capability (also say " per cent law " ) roll out below this kind of circumstance just about. Below normal school condition, of random sample all was worth estimation and standard deviation to be mirrorred respectively distributing actually the position of the model and disperse sex, and by at example medium individual appear in ± the probability beyond 3 limits is occupied only 0.

027% , can ignor, because this thinks the disperse sex limits of normal school, distributing namely width is ± 3, the bounds of distributinging width (also say " quantile " ) for χ 0.

135% with χ 99.

865% . The catholicity principle that defines as the capability index Cp of process ability token, Cpk is: The public errand of the parameter that be measured (USL, LSL) of the statistical model with example all be worth estimation distributings with its width end worth, ratio χ 0.

135% with χ 99.

865% . Press the catholicity principle that above place narrates, cp of process capability index, Cpk can state for: When the parameter that be measured is two-way public errand, when the parameter that be measured is one-way public errand, process capability index takes Cpk only commonly, right now, to sheet up the circumstance that tolerancepublic errand or sheet are down tolerancepublic errand presses type respectively (4) computation: Difficulty is in at, the distributinging dividing line of model of cloth of different type devoir is complete be decided by the probability density function at them, although be in theoretic can choose the formula related the show accordingly (although very complex) , repass computation or the corresponding curve that make will beg the capability index Cp that takes different distributinging model, Cpk, but very troublesome. Tell from technical angle, develop the mathematical operation ability of contemporary computer adequately only, use count analysis and best draft economical law, just undertake fast, accurate ability assess likely. Also realise adequately already just about, the place of traditional assess method with old continue to use puts the limitation that be in, ability was in group of on international a few old cars to roll out updated relative standard in recent years. These standards affirmed quality character cost is shown be not normal school this one common phenomenon, made to ability assess general state. Company of well-known statistical analysis software, (heart) Q-DAS company catered to this one objective need, rolled out the relevant software product with a variety of powerful functions, qs-STAT of its core package included each relevant criterion for evaluation of big Motor Corporation, for high-end user, especially contemporary automobile manufacturing industry, offerred advantage. Example: Ability of two kinds of processes evaluates methodological comparison to be worth the histogram that the random sample of sampling observation generates by quality character, although show the state that nots agree with badly with normal school rule, but the amount of 2 features statistic that still still can acquire according to data processing in fact is: All be worth estimation and standard deviation, traditional ability assess method is narrated before carrying out, of course, the data that is an example right now is analysed as normal school. If use a few software, still can form corresponding normal school model. Graph 2a place is shown it is a typical give typical examples namely. Graph 2 through best draft those who obtain to close distributinging model the introduction of the face is foregone once upon a time, alleged ability, those who point to is quality character the disperse sex limits that is worth normal wave motion, distributing namely width, when rule of normal school of random sample obedience, its distributing width is ± 3. Undoubted, present the parameter that be measured the ability analysis when be not normal school is pressed build the method on foundation of normal school model to undertake assess, can bring an error. Graph 2a place shows an example that produces the spot oneself to come, right now the quality character of sampling observation example is worth is an axis kind of the spare parts jumpy, see from what can be clear about in the graph, of the example below this kind of circumstance distributing actually the normal school difference with hypothesis is very big, and as the distributinging bounds that measures disperse sex, if still press ± 3 will evaluate, error will very big, what affect capability index directly thereby is accurate seek the true opinion that take and runs state to producing a course. It is the example data that graph 2a place shows quality character to be worth likewise, if applied Q-DAS statistic to analyse software after, form, the distributinging model that if graph 2b place is shown,built. By at it is to pass to accord with afore-mentioned catholicity assess principles, through best the maths that plan to close and obtains analyses a model to describe this sample book, the normal school that the distributinging model that reason earnings goes to gives out than traditional assess method more suit is actual. On maths, the distributinging model in graph 2b is belonged to at lognormal distribution, decide its distributing the X103 of dot of 2 dividing line that width bounds is worth and XUP3 are worth estimation to show asymmetry to distributing relative to Wu Jun, but level of its equivalence probability still considers the ± at normal school 3. Two kinds of when show according to graph 2a and graph 2b distributinging models, use formula respectively (2) with formula (4) computation capability index, cpk beats because of the parameter that be measured for one-way public errand: This shows, have the diversity that realises random sample distributings actually only, develop the analysis of the computer and operation function adequately, ability is able to find out the distributinging model of the most adjacent and true condition, serve as the basis that has ability assess with this. Otherwise, probable meeting reachs by the method at tradition of continue to use opposite conclusion. Go up in the exemple, beg the Cpk=2 of process capability index that go out by normal school.

36, think apparently eligible, but accurate result is Cpk=1 however.

07, cannot be satisfied to ask actually by the process of assess. The improvement in quality that specific aim ground carries out manufacturing process is alleged because different basically is the unusual wave motion that in pointing to production process, appears, it basically is by exists systematization the problem is caused. As a component of quality management, quality control is to make product quality or manufacturing process riding quality maintain inside formulary level limits, and improvement in quality is through removing systematization issue, be in to existing quality standard " control " try to rise on the foundation, make its reach a new level. Although control graph is a kind of effective tool, but generally speaking, it can have caution effect only, and by what unusual element causes cannot inform this kind of caution, want to find out unusual reason, return so that rely on production and the skill that run a side and experience to solve. In fact, the simplest but what contain more information however is the figure of only cost process that collects sample, and the histogram that uses one of quality government tools, can know the distributinging position of example, so that be opposite,overall distributinging character undertakes analyse and concluding. Because of,search different again at this moment, the improvement in quality that specific aim ground carries out manufacturing process, the sense is very great. And software of Qs-STAT statistic analysis is among this produced quite positive effect. Case 1: The special fixture that by the small-sized work plan that private plane machines 3 case use body of a kind of a powerful person kind small-sized workpiece is machined by special device, private plane contains circumgyrate type double clamping apparatus, every clamping apparatus can hold clip 6 workpiece (see a picture 3) . By Wu Jia labour and fluctuation makings are undertaken at the same time, efficiency is very accordingly tall. When the enterprise is carrying out SPC, the means that collects sample is every too identical time-interval draw-out group of an appearance notebook, every groups are private plane namely 6 workpiece on a clamping apparatus. In this exemple, every other 1 hour of sampling observation a group of example, collected 19 groups continuously, undertake monitoring and analysis to machining a process accordingly. The sample book that the basis gets and data processing after are attainable - R quality dominates a picture. Sentence according to what occupy a tradition mix firmly the criterion that sentence different, after pursues to R and control a graph to undertake an analysis first, the unusual situation that whether malcontent sufficient criterion appears in pursueing to control undertakes judging. If have unusual, explain to systematization error exists in producing a course, the process is in Wu Fei controlled condition, should find out a reason in time to give eliminate. The computational method that presses above paragraphs introduction undertakes to this process ability is evaluated, cp of gotten process capability index, Cpk is respectively: Cp=7.

60, cpk=7.

28, recycle Qs-STAT software undertakes an analysis to afore-mentioned processes. When be being operated actually, no matter the user chooses which kind of assessment, analytic standard: Of Q-DAS, VW (popular) still be BOSCH (rich world) , the first pace always undertakes differentiate to collecting the distributinging condition of example first, the foundation that the after with regarding as analyses. Qs-STAT function is stronger, the example computation that collects except the basis gives a series of statistic quantities and scale to give deference control chart, be like - S graph, all be worth namely, outside graph of standard deviation control, still can provide the information related a large number of as instant as the process monitoring, the person that use can be chosen according to different need, call. From the only cost of case example at the same time the process pursues medium can see clearly, by the production that collects example institute report the process occurs apparent unusual wave motion, behave those who be appearance notebook group to become poor very small, and child group mutual between become poor very big. For instance from the histogram that collects sample, reach the distributinging model that forms from this, the mixture that its present contains systematization mutation element in the manufacturing process that distributinging condition can announce to be analysed. This one element is private plane on two Fu Ga is provided located condition is abhorrent, and to eliminate, at least is the effect that reduces this unusual factor, should adopt correcting measure is careful ground undertakes adjustment to clamping apparatus. Most after, verify the result that uses Qs-STAT software to press ability of Cheng of opposite of principle of assess of capability index catholicity to evaluate again, cp, Cpk is respectively: Cp=1.

23, cpk=1.

20. To it before the kind that carries a tradition, namely by formula (1) , (2) the numeric look that computation gets is very bigger than the difference, even conclusion also is widely divergent, former it is ability rich, and latter is " loath " (with 1.

33 as bounds, should be not worth as ability) . Investigate because process ability evaluates the accuracy of the result,its reason is, the validity that the sample book that describes with place directly distributings is concerned, and formula of traditional Cp, Cpk, computation just is in the ability when random sample is close to normal school gets more accurate result. Actually, the computational method that in wanting pair of preamble only, introduces tries to analyse after to be able to discover, law of this one party collects the inter block in appearance notebook group to become poor again only, and ignored child the across block deviation of the group. Graph the example of this with head case collects 4 workpiece, clamping apparatus the unusual wave motion with apparent existence of as it happens, reflect the systematization error that becomes poor for across block namely, very big deviate appears to also can understand in causing process ability to evaluate. Case 2: The case of lid of large work crock that makes by machining center is some model an important part, what comprise by machining center is flexible product line is made. In the working station of the machine tool, two workpiece be gone up to show 180 ° to carry two groups of clamping apparatus to the setting on the back at a revolving stage by outfit clip at the same time, by a head first after undertakes machining to them (see a picture 4) . The sampling means when executive SPC, it is the work that processes alternately from two clamping apparatus continuously in draw-out, every other gathers an example group 1 hour, the capacity is 5. Below, the sample that uses Qs-STAT software to be collected with some week undertakes as the foundation the process is analysed. If press,sentence firm criterion is opposite with the criterion that sentence different - S control graph undertakes judging, or it is the observation that pursues through be worth a process to example sheet, analysis, can reach treatment process is in the conclusion at controlled steady state. The capability index that gets according to principle of process ability catholicity is Cp=1.

34, cpk=1.

The 19 requirements that also basically can satisfy workpiece batch to make constrainedly. But the conclusion that differs through was being obtained however to the analysis of histogram, unusual wave motion is included actually in normal manufacturing procedure namely, and origin is two groups of clamping apparatus on machine tool revolving stage had not adjusted relatively consistent position. For test and verify this, throw the batch production that builds case to the crock again via adjusting after carefully to two groups of clamping apparatus of machining center. Like that after presses same sampling way, undertake through running Qs-STAT software the process is analysed, from only cost process graph can see clearly, right now quality character is worth fluctuant limits to narrow greatly, again accordingly scale gives corresponding histogram. Can discover, before appearance devoir cloth already changed " double center " mix distributing, be close to normal school quite, its are dispersive the gender decreases greatly. Undertake to right now production process ability is evaluated again, gotten process capability index is Cp=3.

33, cpk=3.

01. Before knowable photograph is adjusted than undertaking to machining center, process ability gets very big rise. The statistical process of conclusion · tradition is controlled (SPC) reach its commonly used - R dominates a picture, as a kind of effective yield character measures monitoring although mode is very mature already, but the method that its evaluate process capability still needs to optimize, in order to raise an accuracy that achieves a result. · makes full use of to control the tool of other improvement in quality beyond the graph except quality only, if sheet is worth process graph, histogram to wait, ability promotes the instant monitoring of SPC the standard truly, improve the riding quality that produces a course. Software of analysis of · Qs-STAT statistic is an enterprise not only / the user provided a kind of convenient, practical measure, and cogent improve, optimized instant to producing a course monitoring carry out. CNC Milling