Cmk calculation

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Cmk calculation

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Author	Topic: Cmk calculation
Marcin Lurker (<10 Posts) Posts: 3 From:Gdansk, Poland Registered: Dec 1999	posted 28 December 1999 09:59 AM Hi, We manufacture small plastic parts using injection-moulding machine. There are quite big batches of production (average 50 000 parts per lot). Please advise me how we should calculate Cmk factor: 1. When it should be calculated (once a year or may be after each new connection of injection-moulding machine with the tool (mould))? 2. How many samples must be taken (I assume that 1 sample always consists of 5 parts)? 3. How frequently samples must be taken? Thanks in advance. IP: Logged
Don Winton Forum Contributor Posts: 498 From:Tullahoma, TN Registered:	posted 28 December 1999 11:03 AM I do not a lot of experience in Machine Capability studies, but I took this from *Dead Link Removed* Capability - Machine Capability A Machine Capability Study is not, strictly speaking, part of Statistical Process Control, as it does not detect the presence or absence of special causes. Instead, it provides a "snapshot" of one particular component of a process, often a machine (hence the title). This could well be of use in the context of, for example, carrying out a trial run on a machine before agreeing to buy it (like test driving a car). A Machine Capability Study is essentially a way of establishing the capability of the component/machine by assessing how it operates: over a very short period of time in an ideal environment By an ideal environment, we mean one in which: the machine is set as close as possible to its optimum values it is being operated by an experienced member of staff it is isolated from the normal working environment (and thus unlikely to be affected by special cause variation) the study takes place over a very short period of time Typically, about 50 outputs of the process would provide data for a Machine Capability Study. This may vary depending on the outputs. For example, an hour's output of nails might be more than enough, whereas producing 50 back axles might not be practical. IP: Logged
Marc Smith Cheech Wizard Posts: 4119 From:West Chester, OH, USA Registered:	posted 28 December 1999 11:35 AM You can use 50 pieces. A typical capability study in automotive is 300 pieces. Sub-lot size is typicaly 5. For frequency - depends upon run rate. Calculate after 'significant' change to the process. I haven't heard of Cmk before, however. Hope this, along with Don's input, helps to get the thread started. IP: Logged
Roger Eastin Forum Wizard Posts: 345 From:Greenville, SC Registered:	posted 04 January 2000 09:59 AM I'm not sure what a "Cmk" is, either. Does "m" stand for machine? If it does, then Don probably has the right conditions listed. However, if it is a standard process capability study, you must establish that special causes have been eliminated before you calculate the capability index. Otherwise, you get into questions of things like normality and its impact on percent of product out of spec. Perhaps could describe what you are trying to do in a little more detail. IP: Logged

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