In nearly all industry sectors quality control is part of the developing, engineering or manufacturing process in order to ensure that the designed and fabricated products meet the customers’ expectations or stay within previously defined tolerances. QC is a part of Total Quality Management (TQM). (1.)
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Quality starts at the design stage. A TQM (Total Quality Management) system will quantify, by means of precise measurement, the production capability (including measurement capability) of the organisation. This will facilitate improved tolerancing for functionality of the product, the identification of areas of capability associated with specific tolerance (customer) demands. Simply put – measurement is the tool that is used to quantify the capabilities of the people, the processes, the tools, the machines and therefore the organization. The correct application of the above will greatly facilitate right-first-time manufacturing. (1.)
y= f(X1,……..,Xn)
The enemy is variation:
y is a function of the variables (x….) within the process. When the variables x1 through xN are not under control and acting in an unknown way then y will always be at risk of failure. The systematic control of process variables through good measurement, analysis and actions will result in y (the product) being within specification. Control of the variables is achieved with good measurement to reduce variation.
Good management acts on accurate and timely information, but how does one get one’s hands on good information? In measurement it is really quite simple.
We select validated products and systems for process, product and business improvement based on our knowledge and beliefs. We are quite happy to measure a product to evaluate it as OK or not OK, so shouldn’t we be validating our measurement methods and procedures to see if they too are OK or not OK?
Having validated your measurement system you can now confidently capture your product and process performance data. This data is then the key to process improvement; the control of the variables.
Once you have identified your measurement and process capability you can plan and schedule work according to performance capabilities and, humans aside, you are on the road to right-first-time production.
Good production processes exhibit only small amounts of variation, good measurement processes exhibit much less variation. (1.)
A Coordinate Measuring Machine (CMM) captures 3D data from objects to give the position in XYZ, vectors etc. of the object under investigation. CMMs are used by manufacturing companies to ensure that parts or components are within defined tolerance levels for quality, and to capture statistical process capability data.
There are many types of CMMs. Traditional CMMs include the bridge type, cantilever type, gantry type, etc. These are floor-mounted machines that require you to bring the parts to the CMM, they are generally kept in a controlled environment and are used only by very skilled personnel. The portable CMM (generally known as measurement arm,
laser tracker or laser scanner) is designed to be fully portable and therefore can be used anywhere the measurement is needed – the machine goes to the part. Portable measuring arm can find in picture 1. (1.)
Picture 1. Faro Platinium portable CMM
http://www.faro.com/
http://www.nikonmetrology.com/home.php
http://www.leica-geosystems.com/en/index.htm
http://www.ndigital.com/industrial/
http://www.zeiss.com/imt
http://centria.cou.fi/Koulutuskalenteri.aspx#Averko, Central Ostrobothnia University of Applied Sciences WEB-courses
http://www.control-messe.com/en/control , Stuttgart Exhibition Centre in Germany from the 8th through the 11th of May, 2012
http://www.tradefairdates.com/ , Search engine for Trade fairs
http://www.tekes.fi/en/community/Home/351/Home/473 , Finnish national financier
Good QAQC is critical!
If you don’t get it right, you have wasted all your drilling and sampling… So, what is good QAQC? It comes in two parts, Quality Assurance (underappreciated) and Quality Control. Quality Control is what you probably expect, standards, blanks, duplicates etc. we’ll get to that, but first Quality Assurace.
What is the Quality Assurance part? And is it an important part of the process? Of course it’s important, it’s all about assuring that the process’ you expect are being followed.
You should have procedures written for all your sampling processes, Quality Control sample placement and requirements, sample submissions, etc. You should also have a way to observe and check that the procedures are being followed and complete the checks routinely, and document that you are checking.
You should also check and inspect the Laboratory, and make sure they are following their own processes and procedures, equipment is in good order and the place is clean and tidy. And again, record record record.
It is important to check, and show you are checking that good quality processes are undertaken, and performed in a good quality way, and this can be easily overlooked. Assure you are doing good work.
Quality Control
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Control samples inserted into sampling to check the precision and accuracy of the assay results surrounding samples. Generally control samples fall into 2 categories, Company and Lab checks.
Company checks are any check samples submitted by you, the company, such as Standards, Field Duplicates and Blanks with Lab checks, standards, duplicates and repeats that the Laboratory complete themselves. Each check sample is designed to test an aspect of the assaying process.
Company Check samples:
Standards
Standards check the Labs ability to get the right answer. Standard samples have an expected grade, and a standard deviation (SD) grade that can be used to statistically check how close to the expected grade the lab has got. Standard deviation is a measure of how dispersed the data is in relation to the mean, and based on the statistical normal distribution of populations. Each company will have an acceptable level of difference between the lab result and the expected standard result, usually 2 or 3 SD’s from the mean. Statistically, ~68% of your standards should fall within 1 SD, ~95% should fall within 2 SD, and 99.8% should fall within 3SD’s.
Selecting the standards to use is also important. You should use standards close to the grades that are important for your decision making, and likely grades that you will see in your mineralisation. For example, if you have a mining cut-off grade of 4 grams per tonne gold, you want to make sure the lab is accurate around that grade, so select a standard at around 4.
What do standards mean? As I said at the start of the section, check the ability of the lab to get a result that is statistically valid, and close to the actual result as possible.
Blanks.
Blanks are used to check for contamination between samples during sample preparation. Samples are crushed and pulverised in machines which should be cleaned between samples to minimise cross contamination between samples. This is particularly important when you are dealing with very high grades. Blank samples inserted can test for contamination between samples by passing through the sample preparation process and being subject to any contamination which will show up with elevated grades during the final assay process.
Keep in mind, most labs use multiple machines to prep samples, so a blank sample wont necessarily be testing contamination from the previous sample. What I mean is, if a lab has 3 pulverises, sample 1 goes through pulveriser 1, 2 through 2, 3 through 3, sample 4 goes through pulveriser 1 following sample 1. So, if you have a very high grade sample, followed by a blank, there is a high likelihood that it wont follow the high grade sample, unless you specify, or you are very tricky and have a blank sample 4 samples later…
Field Duplicates
Interestingly, field duplicates are not a check on laboratories performance! They are a check on the appropriateness of your sampling. I.E. is half core NQ2 appropriate way to sample, or is your RC sampling and splitting appropriate. If your grades are consistent across your field duplicate samples, your sampling is ok, if there is a discrepancy, you should investigate why? And decide if your sampling is acceptable…
Laboratory Checks
Lab standards
Lab Standards do the same job as company standards. The lab uses them to ensure they are getting results as they expect.
Lab Duplicates
Lab Duplicates test whether the lab can get an acceptably similar result from the same sample in the same firing. The Lab will take a second subsample of the pulverised sample material and process it the same as the primary sample at the same time. This checks the homogenisation of the sample during the pulverisation, and the appropriateness of the subsampling for assaying.
Lab Repeats
Lab Repeats test whether the lab can get an acceptably similar result from the same sample in a different firing. The lab will take a second subsample of the pulverised sample material and process it during a later firing. This checks the lab is consistent over time and different firings.
The acceptable level of performance of any Lab and their ability to duplicate and repeat assay results varies according to what you are trying to test for. But, keeping an eye on the lab performance is critical to make sure that they are reporting both precise and accurate results. If you want to go down a rabbit hole, look up the difference between precise and accurate….
At the end of the day, Labs are trying to get the answer right, and help you. It would be very strange for someone to deliberately try and get the answer wrong….
The best practice to getting good results, is a good and open relationship with your Lab. Be honest and open and discuss performance regularly and talk through any issues you might see. Issues will be fixed, everyone will learn and get better!
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