Statistical Techniques TM-4000-S209 Statistical Techniques

First Law of Statistics Statistics Lie! Is the sample size tested or inspected representative of daily production? Is the data that is being collected relevant to your processes? Collected data is not enough! What is the data telling you?

Quality…How Do You Know? Verbal reports: QC department, managers, line supervisors and plant personnel…but anectodal is not enough! Empirical evidence: Written reports, Inspection Forms, Statistical Analysis (variable control charts, spreadsheets, Pareto charts), Customer complaints.

Quality is Everyone’s Responsibility! Quality Control Department, Line Managers, Supervisors, Plant Personnel. Everyone can collect data! Raw Material Receiving In-Process Evaluations Final Product

Purpose To ensure consistent quality and appropriate process control through the use of statistical techniques. To collect, analyze and interpret data relating to product and process characteristics. To identify problem areas to reduce returns and warranty claims. Assist in conducting root cause analysis for problem areas.

Purpose The general approach to on-line quality control is straightforward: simply extract samples of a certain size from the ongoing receiving, production, final inspection, shipping, in-field performance and customer feedback processes. Line or variable control charts of the variability in those samples will identify product specification compliance, and consider their closeness to target specifications. If a trend emerges in those lines, or if samples fall outside pre-specified limits, then the process is deemed to be out of control and action is required to find the cause of the problem.

Tools Variable control charts, spreadsheets, visual observations derived from data gathered from processes, testing and inspection. Identification of special causes of variation or deviation from the required specification. Identify sources of product variation and group into two major causes: common and special causes.

Test of Inspection Name Responsibility Data Type Examples Raw material receiving QC or designated personnel Test values Visual Components such as connectors, spacers, desiccant, sealants etc. Damaged containers In-Process evaluations Water temperature, Cutting Wheels, Component Testing (ie sealant adhesion) Final product Skips and gaps in sealant Field Performance After Sales Service and QC Written Inspection Reports Verbal reports Seal failure, volatile fogging Customer Complaints Verbal and electronic correspondence Delivery delays, seal failures, volatile fogging, after sales service

Raw Material Receiving Maintain Raw Material Log: date received, component received, manufacturer identification, lot tracking numbers (if applicable), condition of packaging material, condition of material – conforming or nonconforming to specifications Variable Control Charts: used to evaluate variation in a product where the measurement is a variable--i.e. the variable can be measured on a continuous scale (e.g. height, weight, length, concentration).

Variable Control Charts The general principle for establishing control limits applies to all control charts. After deciding on the characteristic you want to control, for example, the standard deviation (acceptable upper and lower limits within the specification), you estimate the expected variability of the respective characteristic in samples of the size. Those estimates are then used to establish the control limits on the chart. * *Center line indicates product conforms to required specifications. UCL and LCL indicate upper and lower data points for acceptable product.

Raw Material Receiving Sampling: Determine how much needs to be tested which will be representative of the entire lot or batch. Nonconforming Product: Identify nonconforming product, is the nonconforming product within tolerance or acceptable levels?, isolate it so it will not be used if outside of accepted specification, contact manufacturer of product. Isolated or Repetitive Issue?: Variable control chart will indicate if nonconforming product is an ongoing or isolated issue.

In-process Inspections Designated plant personnel: collect data and complete forms such as seal adhesion, desiccant capacity, was spacer stored properly, cut glass sizes, gas content verification, etc. Variable Control Charts: monitor the extent to which the components that are used to fabricate your products meet specifications.

In-process Inspections Quality Control Forms: The following information is required for each insulating glass unit tested: Length Width Position of spacer Glass thickness Airspace Glass Edges Primary and secondary sealant Glass coatings Percentage gas fill required and achieved

Final Product Inspection Data is collected from an appropriate sample size based on your production; the suggested number of finished units to be inspected shall be randomly selected as determined from the following:   Production Number Inspected up to 25 1 26-100 5 101-500 10 501-1000 15 over 1000 20

Final Product Inspection Each day representative samples shall be inspected for workmanship for at least the following characteristics: Overall unit size and thickness. Alignment of glass lites. Cleanliness of airspace. Sealant bond to glass and to itself at corners. Sealant minimum vapor transmission path. Spacer position (sight line) relative to the unit edge. Uniformity of sealant application. Possibility of holes or underfills. Overall workmanship in finished units or windows.

Final Product Inspection Data is collected on a random basis: representative samples are selected which will represent the daily production. Pareto Charts: are useful for non-numeric data, such as "cause", "type", or "classification". This tool helps to prioritize where action and process changes should be focused. If one is trying to take action based upon causes of accidents or events, it is generally most helpful to focus efforts on the most frequent causes. Going after an "easy" yet infrequent cause will probably not reap benefits.

Pareto Charts A Pareto Chart is generally shown as a vertical bar chart. A Pareto Chart is a special form of a histogram where the categories have been sorted from most frequent to least frequent. One would not want to sort the categories from most frequent to least frequent if there is a natural order to the categories, such as a distribution by age or cycle time.

Trend Exists on Control Chart? Pareto Charts Trend Exists on Control Chart? Data Points Used Purpose No Use all data in the applicable or relevant statistical time period To find common causes(s) to apply to process improvement Yes Use only the data for the Point(s) which have been identified as within the significant trend, such as a point outside the control limits. To find special cause(s) for the determination of corrective actions for trends of decreased compliance or identify successful corrective actions which have resulted in increased product compliance.

Final Inspection Data is prioritized based on company quality control requirements and specifications. Data is reviewed by all! (management, line supervisors and plant personnel) Data which identifies that the level of product rejection is above the established, acceptable levels in sent to facility management for review, discussion and action.

Conclusion It’s not enough to collect data! Data is meaningless unless it is reviewed, analyzed (what is it telling you) and acted upon. Collect the right data and the right amount of data! One data point does not provide you with enough information to determine if a component or product conforms to specifications. Don’t assume you know the cause of a problem! Statistical analysis can help you control nonconforming components and products.