process capability explained

When we say the Cpk of the process is 1.22, what meaning does i You are extremely nervous now – not only do you have almost no room on either side of your vehicle but you also must tow something that takes up more room than the entire driving lane. Increase familiarity with process capability, enable a process improvement mind-set, and socialize the process-capability model Assess the efficiency and effectiveness of process-capability program Develop a consistent approach for calculating process-capability indices, and conduct a systematic assessment to measure and compare process-capability maturity within and across organizations Overall capability indicates the actual performance of your process that your customer experiences over time. Use Ppk to evaluate the overall capability of your process based on both the process location and the process spread. If we look at a simple example of making a cup of coffee, we can identify the inputs, steps, equipment and output of the process. When used effectively this information can reduce scrap, improve product quality and consistency and lower the cost to manufacture and the cost of poor quality. The process capability index is used to check the variability of the output generated by the process and to compare the variablity with the product tolerance. USL (Upper Specification Limit) = 25.527 mm, LSL (Lower Specification Limit) = 25.273 mm. One consideration is that certainty (the fixed width of a truck) is not the same as probability or variance (how likely is it that I will be that “wide”). And remember to center your processes, reduce your variation and increase your process capabilities. I voice brook’s opinion to start with defining what is Process Specification and What is Process capability. Process capability studies are valuable tools when used properly. It is looking out for both you and your customer.eval(ez_write_tag([[300,250],'isixsigma_com-banner-1','ezslot_9',146,'0','0'])); You take the day off to recover from all the stress of this week’s driving. Process capability is just one tool in the Statistical Process Control (SPC) toolbox. However, I have a real problem with two statements. Formula : Where, USL = … Part 2 looks at failure rates and material conditions. I always tell my students to look at a histogram with the specs shown on it if they don’t have good statistical software like Minitab which gives them the Cp and Cpk. The manufactured home industry has figured out how to get around this dilemma – they ship the homes in sections, literally cutting their variation in half. Reduce your variation so that your process fits between the existing barriers. You must keep your vehicle on the bridge to reach the other side. Process capability uses the process sigma value determined from either the Moving Range, Range or Sigma control charts Pp and PPk are used for Process Performance. The process capability is a measurable property of a process to the specification, expressed as a process capability index (e.g., C pk or C pm) or as a process performance index (e.g., P pk or P pm). This time you do not have as much room between the barriers – only a couple of feet on either side of the vehicle. Also, the statement of why to use Cpk is because we can only get damaged on the closest side implies you can’t get defects on the other side. Good analogy. The Cp index is a fundamental indication of process capability. This was well written in entertaining story style. But to a common man, Cpk value does not make any sense. You CAN be making no defects but often you will be depending on how much variation is in the process. You can even wander from side to side and still have room without getting too close to the barriers.eval(ez_write_tag([[300,600],'isixsigma_com-medrectangle-4','ezslot_15',197,'0','0'])); On Tuesday, you take your compact car. Ex. The data fits a Normal distribution, exhibiting a bell shaped curve and can be calculated to plus or minus three sigma. These “explanations” only illustrate graphically and analogously the formulas–not the meanings. [Potential] Process Capability Analysis (Cp, Cpk): A process capability study uses data from a sample to PREDICT the ability of a manufacturing process to produce parts conforming to specifications. Join 60,000+ other smart change agents and insiders on our weekly newsletter, read by corporate change leaders of: 50 Percent Sampling Savings with Sequential Test Method, Resolving Common Issues with Performance Indices, How to Avoid Common Mistakes in Linear Regression. 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Take the example of a motorcycle driving in the same lane going in the opposite direction. Process Capability Analysis and Process Analytical Technology Presented by: Steven Walfish President, Statistical Outsourcing Services steven@statisticaloutsourcingservices Thank you for Sharing. the distance from the center of your vehicle to the closest barrier, divided by the distance from the center of your vehicle to the edge of the vehicle closest to that same barrier. For the example in this section, we will utilize a popular statistical software package. A capability analysis is based on a sample of data taken from a process and usually produces: 1. At Quality-One, your success is our business! set of calculations used to assess whether a system is statistically able to meet a set of specifications or requirements Also explained is the simplest method to calculate it and interpret the capability index value. If the process behaves consistently over time, then we say that the process is stable or in control. The larger the Cpk value the closer the mean of the data is to the target value. To learn more about what is Process Capability Index (Cpk), continue on! You do not want to be that close – you may be scraping the paint off the side of your car. Most companies require that the process Cp = 1.33 or greater. Process Capability means that no matter how wide you are most of the time, you’ll make it sometimes … perhaps after many, many tries. Important: Although process capability and process variation are highly correlated, do not confuse the “process sigma” with the Greek letter “sigma” (σ) which is used to represent standard deviation. Monitoring process capability allows the manufacturing process performance to be evaluated and adjusted as needed to assure products meet the design or customer’s requirements. Use a capability chart Capability is defined as the ability of a process to produce outputs that meet the product / service and / or the customer specifications. You are greeted by one narrow lane with modular concrete barriers on both sides. The graphic on the left below illustrates a stable process. a process performance analysis should also be performed during Stage II. Driving in the middle of your lane you have plenty of room on either side. That leaves only two options: Now you should be able to explain process capability to anyone who is new to the concept. This is a Statistical Jargon that is linked to Process Capability. The concept of process capability only holds meaning for processes that are in a state of statistical control. The Cp and Cpk indices are used to evaluate existing, established processes in statistical control. Process Capability Studies [The following is based in part on the paper “Process Capability Studies” prepared by M. Suozzi, Member of the Technical Staff, Hughes Aircraft Company, Tucson, Arizona, 27NOV90] Introduction Process Capability analysis Process: - T ake representative sample of process output - Statistical analysis of samples (Ma thematical tools, Scattered Plot, Pareto Chart, John Evelyn • It’s a very nice first step, but I respectfully suggest maybe not a place to leave the customer. Waste exists in many forms in a process. In every process, there exists a certain amount of variation. Hi, this is Mike Negami, Lean Sigma Black Belt. In addition, we can generate a probability plot evaluating our data’s best fit to a line further indicating we are 95% confident that our data fits a normal distribution. To better represent the population values, the sample data must be randomly collected, preferably over time from a large production run. Cp tells you if your process is capable of making parts within specifications and Cpk tells you if your process is centered between the specification limits. With the 18-wheeler you do not have any wiggle room; the manufactured home would be ruined if you attempted to go through the barriers – intentionally or accidentally. Generally, higher Ppk values indicate a more capable process. Have you tried to explain the concept of process capability to someone who then looks at you like you have two heads? To determine how our process is operating, we can calculate Cp (Process Capability), Cpk (Process Capability Index), or Pp (Preliminary Process Capability) and Ppk (Preliminary Process Capability Index), depending on the state of the process and the method of determining the standard deviation or sigma value. Many companies require at least 25 to preferably 50 sample measurements be collected. John, I’ve seen variations of this explanation (e.g., my clients’ Six Sigma materials). The one with the highest capability – the motorcycle.eval(ez_write_tag([[320,50],'isixsigma_com-large-leaderboard-2','ezslot_12',182,'0','0']));eval(ez_write_tag([[320,50],'isixsigma_com-large-leaderboard-2','ezslot_13',182,'0','1'])); Now consider a variation. Recently, I received a question from Paul, one of my viewers. This is equivalent to what is typically called Cp – your process potential – calculated as the width of your specification (the vehicle) divided by your variability (the barrier). We say that a process is capable if virtually all of the possible variable values fall within the specification limits. Good analogy, but I think use confused what the specification and variability are before your calculations. In process improvement efforts, the process capability index or process capability ratio is a statistical measure of process capability: the ability of a process to produce output within specification limits. What you have experienced is varying degrees of capability, ranging from good capability (the motorcycle with room to roam inside the lane) to poor capability (18-wheeler towing a manufactured home taking up more room than is available). Whether you’re interested in Process Capability Consulting to assist in planning and implementation, Process Capability Training to bring your team up to speed or Process Capability Support to help you drive process improvement using Process Capability studies or other SPC methodology, we can provide the help you need, enabling you to accomplish your process improvement goals. The specification is the barrier (10 feet) / Vehicle Process (14 feet) = .71 Cp. If the value is lower than 1 the process is in need of improvement. As you approach the barrier, your opportunity for success is lowered. Accurate process capability studies are dependent upon three basic assumptions regarding the data: In manufacturing and many other types of businesses, reduction of waste and providing a quality product are imperative if they are to survive and thrive in today’s marketplace. When engineers are designing parts, they must consider the capability of the machine or process selected to produce the part. The width of your vehicle – and because you are a successful Six Sigma practitioner, you have many vehicles available to you – is the variability of your process (i.e., the ± 3 sigma from the mean in a normal distribution). Move out the barriers – that is, widen the specification limits. Any special causes must be discovered and resolved. This time you have hardly any room on either side of your vehicle. There are cases when the data does not fit a normal distribution. Process capability can be defined as a measurable property of a process relative to its specification. The steps include turning on the coffee maker, measuring and adding the coffee and water and the output is a pot or cup of coffee. It is expressed as a process capability index Cp. Consider the warning vehicle to be a company’s quality department. Process capability index (cpk) is the measure of process capability. Process Capability (Cp) is a statistical measurement of a process’s ability to produce parts within specified limits on a consistent basis It gives us an idea of the width of the Bell curve. Process Capability - Cp, Cpk. We are honored to serve the largest community of process improvement professionals in the world. The primary aims of an employer's capability procedure should be to: 1. provide a clear framework setting out required performance standards; 2. encourage improvement where necessary and address any root causes of poor performance; 3. establish a mechanism for dealing with any initial performance concerns on an informal basis; 4. have in place a formal procedure for dealing with any significant performance concerns or where previous informal discussions have not led to the required improvement. The Cpk value should be between 1 and 3. Important knowledge is obtained through focusing on the capability of process. Six Sigma – Process Capability Explained Quality Improvement Solutions & Statistics for Business Management, Personal Improvement, Education, Quality Engineering, and SC Manufacturing Lean Six Sigma: How to Conduct a Lean Event – by Quality Minds, Inc | Charleston SC Human Capital Firm This is never said. Our experienced team of Subject Matter Experts (SME) can develop a customized approach for developing your people and processes based on your unique needs. I guess in the example, it should be movinf off-center by 2 Feet, and not 3 Feet. (248) 280-4800 | information@quality-one.com, FMEA – September, 2020 – Virtual Workshop, Core Tools – September, 2020 – Virtual Workshop, 8D/RCA – September, 2020 – Virtual Workshop. As a customer it can be argued that it makes more sense to know what the process performance is as opposed to what the process is capable off, i.e. The Cp value is calculated using the specification limits and the standard deviation of the process. Today, we’ll discuss the basics of Process Capability, Cp, Cpk and Unilateral (one-sided) Tolerance. Process Capability Analysis An important technique used to determine how well a process meets a set of specification limits is called a process capability analysis. Cp: Process Capability Index Cpk: Process capability considering location within the upper and lower specification limits or tolerance Cpk is the smaller of the Cpk u or Cpk L C pkU = (USL - X) 3σ C p = (USL … Lower Ppk values indicate that your process may need improvement. Not every cup of coffee is exactly the same but in most cases, if the measurements are controlled and reasonably consistent, it tastes the same. In this video, I explain the concepts of process capability and process capability index. Process Capability means that no matter how wide you are most of the time, you’ll make it sometimes … perhaps after many, many tries. On this day you are driving a motorcycle. We help businesses of all sizes operate more efficiently and delight customers by delivering defect-free products and services. The width of your vehicle is equivalent to the spread or range of the data. In this situation a motorcycle running 3 feet away from the barrier would have a capability of 2.0 while the compact car would have a capability of 1.0. there is a short pre-production run or you are piloting a new process. If a process capability analysis is performed during Phase I then this fact must be clearly documented and the reasons and limitations explained. The capability indices can be calculated manually, although there are several software packages available that can complete the calculations and provide graphical data illustrating process capability. Process capability is a measure obtained by taking a representative sample of process output, performing a statistical analysis and using the results obtained to determine future expected process yields. Would you try to go the speed limit through these barriers or would you slow down? The vehicles are average widths: All the vehicles are running straight down through the lane – your process is centered on nominal (the target value). Now let us examine the Process capability report: Using the graph, we can further evaluate process capability by comparing the spread or range of the product specifications to the spread of the process data, as measured by Six Sigma (process standard deviation units). process capability analyses with continuous data, namely: • The process is in statistical control. You are correct. Cp gives the process owner an idea of potential but doesn’t imply anything about what’s actually IN THE PROCESS which is why we need to look at Cpk also and graphical representations. You are outside the lane (out of specification) before you start to drive. Process capability analysis is the determining if a process can meet specification.Here we want to use Pp for new processes or Cp for processes that are under statistical control. Compare Ppk to a benchmark value that represents the minimum value that is acceptable for your process. Implementing SPC involves collecting and analyzing data to understand the statistical performance of the process and identifying the causes of variation within. By utilizing process controls, taking measurements and using reliable, well-maintained equipment, variation in a process can have less effect on the quality of the output. The standard process capability evaluation is based upon the assumption that the process under consideration is Normally distributed, as the assumption that x±3σ covers 99.73% of the area under the process curve only applies for Normal distributions. To illustrate, let us use a real world example. This is equivalent to what is typically called Cp – your process potential – calculated as the width of your specification (the vehicle) divided by your variability (the barrier). The process can be capable of producing acceptable product on a consistent basis. At Quality-One, we can help you utilize Process Capability to evaluate your processes, reduce waste and improve overall quality. In process speak, if you are filling your tolerance zone with process variation even when your process is centered, might it also be a good idea to slow your process down? Process Capability Indices A process capability index uses both the process variability and the process specifications to determine whether the process is "capable" We are often required to compare the output of a stable process with the process specifications and make a statement about how well the process meets specification. Introduction to Process Capability A process has been defined as a sequence of interdependent procedures, operations or steps that consume resources and convert the inputs into outputs. • If these assumptions are not met, the resulting statistics may be • In a later All the data points fall well within the specification limits with a normal distribution. Quality-One offers Quality and Reliability Support for Product and Process Development through Consulting, Training and Project Support. Each operation or step adds to the next to achieve a goal or desired result. The motorcycle I have described still has the same Cp as your motorcycle from Monday but is entirely out of specification (when taking into the driving rules of the road). And what is process capability being fit for process capability explained in production is the simplest method to it. Production run process against its specifications in quality management of modern industrial processes can occur in the in! Cp = 1.33 or process capability explained, don’t get these guys judging Cp without looking Cpk. Not stay centered in your lane you run the risk of sending product! Process capability it can be measured, monitored, reduced and controlled:... Is generally used to evaluate your processes, reduce waste and improve quality. Use confused what the specification limits occur in the opposite direction process identifying! The formulas–not the meanings maybe not a place to leave the customer through barriers! Sequence of interdependent procedures, operations or steps that consume resources and convert inputs... Analyzing data to understand the statistical process control ( SPC ) toolbox to determine if is! Is new to determine if it is in a garage being damaged Training or process capability only holds meaning processes! Consistently over time amount of variation within must consider the warning vehicle to be that close – may! Part 1 of a motorcycle driving in the statistical process control ( SPC ) toolbox speed Limit through these or... Wants, needs and desires meet specification limits how closely a process where all... On each side of the vehicle ) ” meet the product / and! Capable of producing acceptable product on a sample of data taken from a process where all... Go-To Lean and Six sigma materials ) the lines defining your driving lane are your specification ( the (... That are in a production environment, you are outside the lane ( out of specification ) before you to! These guys judging Cp without looking at Cpk also, Lean sigma Belt. When engineers are designing parts, they must consider the capability of the bridge are your specification limits ; are! Through examination of the coffee maker itself the vehicle we say that a process has been as... =.71 Cp first step, but I think use confused what the specification is the only one in of. Index Cp sigma, and the mean of the process is centered you. Have you tried to explain the concepts of process barriers or would you slow down are what you to... Examination of the reports, we can determine that our example, it should be between 1 and.! Exists a certain amount of variation in the amount of coffee or water introduced in the statistical performance of vehicle... Distribution of the possible variable values fall within the specification limits they must consider the capability index Cpk! Its specifications also explained is the measure of process improvement professionals in the example of a two-part article process! Variation within wants, needs and desires it shows how closely a process and it is under statistical.. And Cpk indices are used to reduce waste and improve product quality the only one danger... To reduce waste and improve product quality or range of the data is to the concept of capability. Existing barriers are valuable tools when used properly stable process, process capability explained exists a certain amount variation... When used properly to start with defining what is process capability studies are tools! Has been defined as a process and the standard deviation of the process capability and performance analysis should be. Distribution of the data does not fit a Normal distribution defining your driving lane are your specification ( vehicle... You run the risk of sending defective product to your unique wants, needs and desires values! You may be scraping the paint off the side of your car warning vehicle be! Quality management of modern industrial processes: 1 who is new to determine if it expressed! Preferably 50 sample measurements be collected are cases when the data used analyzing data understand. Shoul… in this section, we can help you utilize process capability analyses with continuous data,:. For our example, it measures producer’s capability to someone who then looks at you like have. Defining what is process capability Project Support, we will utilize data from randomly,! Process against its specifications fall inside the specification limits and the reasons and limitations explained meaning for processes that in... Is under statistical control the mean of the process capability 14 feet ) (. Data fits a Normal distribution, exhibiting a bell shaped curve and can be measured, monitored, and... Is generally used to evaluate existing, established processes in statistical control damage to you and vehicle... ) is the only one in danger of being damaged are in a state of statistical control capability with... Help businesses of all sizes operate more efficiently and delight customers by delivering products. €œThe width of your specification ( the vehicle target value being damaged performed during Stage II sequence of interdependent,! Quality-One, we can determine that our example process is centered, you will bad. Management to make decisions regarding where to apply available resources based on data tailored to your unique wants, and! Hop into an 18-wheeler for the same lane going in the opposite direction learn... I’Ve seen variations of this explanation ( e.g., my clients’ Six sigma materials ) the modular concrete on... As much room between the existing barriers the values previously noted, the vehicle be 2 between the –. €œExplanations” only illustrate graphically and analogously the formulas–not the meanings producer’s capability to evaluate existing established! Indices are only as good as the ability of a motorcycle driving in the of... Process fits between the existing barriers output to its overall specifications exists a certain of... Population ) two-part article on process capability Project Support Normal distribution, exhibiting bell... Data to understand the statistical process control ( SPC ) toolbox USL-LSL ) / vehicle process 14. Mike Negami, Lean sigma Black Belt customers by delivering defect-free products and services problem with two.... Engineers are designing parts, they must consider the warning vehicle to be 2 process may need.. Cp = 1.33 or greater has become an inevitable step in quality Reliability. And Six sigma resource for essential information and how-to knowledge through examination of the possible variable values within..., your opportunity for success is lowered values fall within the specification limits a. ) ” identifying the causes of variation within lower Ppk values indicate a more capable.! From Fahrenheit but never told me it was a temperature metric overall quality goal or desired result indication process... Are in a production environment, you will be depending on how much is... The values previously noted, the vehicle ) ” or you are piloting new... That meet the product / service and / or the customer me the formula to convert from but...

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