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Is Your Measurement Method Creating Quality Issues
Is Your Measurement Method Creating Quality Issues By: Jim Szumera - MACOR Published on: 02/21/2014
Quality is job one. But often times I find myself in a constant battle with quality engineers, the customer and the production floor about the same issue. Many times I have had good product rejected and bad product shipped. The devil lies in the details.
Throughout my career I have been battling the issue of quality, whether it be manpower, method, material, or machine. The methods between the tooling guys, the production floor, quality and the customer should all be consistent and if possible, the same. The machines or gauges must fit the criteria or part specifications to be checked. For example, if I am checking an outside diameter with a specification of +/- .002, I would not choose calipers as my method. The variation in the calipers is too great that I can use up a good portion of my part tolerance, good or bad. The following Wikipedia explanation on ANOVA Gauge R&R may be helpful in dealing with shop floor dilemmas.

Gauge R&R (gauge repeatability and reproducibility) is a measurement systems analysis technique that uses analysis of variance (ANOVA) random effects model to assess a measurement system.
The evaluation of a measurement system is not limited to gauges but to all types of measuring instruments, test methods, and other measurement systems.
The Purpose of Gauge R&R is to measure the amount of variability induced in measurements by the measurement system itself, and compares it to the total variability observed to determine the viability of the measurement system. There are several factors affecting a measurement system, including:
• Measuring instruments, the gauge or instrument itself and all mounting blocks, supports, fixtures, load cells, etc. The machine's ease of use, sloppiness among mating parts, and, "zero" blocks are examples of sources of variation in the measurement system. In systems making electrical measurements, sources of variation include electrical noise and analog-to-digital converter resolution.
• Operators (people), the ability and/or discipline of a person to follow the written or verbal instructions.
• Test methods, how the devices are set up, the test fixtures, how the data is recorded, etc.
• Specification, the measurement is reported against a specification or a reference value. The range or the engineering tolerance does not affect the measurement, but is an important factor in evaluating the viability of the measurement system.
• Parts or specimens (what is being measured), some items are easier to be measured than others. A measurement system may be good for measuring steel block length but not for measuring rubber pieces, for example.
There are two important aspects of a Gauge R&R:
• Repeatability: The variation in measurements taken by a single person or instrument on the same or replicate item and under the same conditions.
• Reproducibility: the variation induced when different operators, instruments, or laboratories measure the same or replicate specimen.
It is important to understand the difference between accuracy and precision to understand the purpose of Gauge R&R. Gauge R&R addresses only the precision of a measurement system. It is common to examine the PIT ratio which is the ratio of the precision of a measurement system to the (total) tolerance of the manufacturing process of which it is a part. If the PIT ratio is low, the impact on product quality of variation due to the measurement system is small. If the PIT ratio is larger, it means the measurement system is "eating up" a large fraction of the tolerance, in that the parts that do not have sufficient tolerance may be measured as acceptable by the measurement system. Generally, a P/T ratio less than 0.1 indicates that the measurement system can reliably determine whether any given part meets the tolerance specification. A P/T ratio greater than 0.3 suggests that unacceptable parts will be measured as acceptable (or vice-versa) by the measurement system, making the system inappropriate for the process for which it is being used.
Gauge R&R is an important tool within the Six Sigma methodology, and it is also a requirement for a Production Part Approval Process (PPAP) documentation package.
There is not a universal criterion of minimum sample requirements for the GRR matrix, it being a matter for the Quality Engineer to assess risks depending on how critical the measurement is and how costly they are. The "10x2x2" (ten parts, two operators, two repetitions) is an acceptable sampling for some studies, although it has very few degrees of freedom for the operator component. Several methods of determining the sample size and degree of replication are used.

All gauging techniques and systems should be defined at the design review stage between customer, quality, production and tooling. And of course, all systems should be calibrated regularly.
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Mick LongFeb 25, 2014 - 12:03 pm
In a strategic Value Engineering initiative, a CPG manufacturer determined many of the tolerances reflected on part drawings actually conflicted with process capability.

The benefit of a closed loop Supplier Quality Assurance Program is to educate designers on process variability and options. While progressive metal stamping dies may be more expensive that lower cost pick & place, Statistical process Control has proven beyond a reasonable doubt that tooled attributes are more reliable than human intervention.
Dona VincentFeb 27, 2014 - 11:56 am
For contract stamping , customer defined critical characteristics may not reflect production. It is your process criticals that need to define tool performance and quality output. Gage R&R assures consistency. Excellent article, good comment.
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Three Things to Eliminate Screw Failure Forever
Three Things to Eliminate Screw Failure Forever By: Jim Szumera - MACOR Published on: 01/24/2014
Three Simple Things to Eliminate Screw Failure Forever.
We have all experienced screw and bolt failure in our careers to varying degrees. In some instances we were lucky. The damage was minimal. In other cases, not so lucky. The die crashed and resulted in broken details, strippers and punches. All things considered and assuming we have executed best practices in utilizing correct tap drill sizes, proper torgue and application, the screws still fail. Three vital, less known criteria to eliminate screw failure is as follows:

1. Only use quality name brand fasteners certified to meet or exceed specification, such as Unbrako, Holo-Krome and others. Do not purchase counterfeit screws and bolts. By counterfeit, I mean sub-standard material, heat treatment and machining. This problem proliferated from cost and resulted in poor quality imports from Asia, and Europe. It became widespread and was used in everything from bridge building and construction to high speed stamping dies. It became such a systemic problem that Congress passed the Fastener Quality Act of 1999.

2. In die applications the class of fit is critical. Many die builders go oversize on the tap drill size to facilitate CNC, tap life, and expedience in screw removal. While this may be good for die building economics, it spells disaster when trying to run these dies. Screws come loose and cause all kinds of havoc. Using a slightly smaller tap drill, or preferably fine thread usually works well. This is especially critical when fastening upper dynamic components, such as punches into hardened retainers and back up plates. Many die shops engineer punch removal in the press.

3. The last little known item is proper through hole preparation. Here we are referencing the inside clearance hole. It must have a chamfer to allow for the radius at the screw head. Often this step is overlooked in the die building process because it may not be called out on the prints or due to bad practice or negligence. This causes the screw to fail at the head. This may not develop into a failure mode if the counter bored hole is in soft steel. The screw will actually form the soft steel slightly when tightened. Check out the Parameters for Eliminating Screw Failure file in the Technical Data Tab.
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Rakesh Kumar shrivastavaJan 28, 2014 - 11:00 pm
Good!!! Useful points.To be conveyed to as many die shop manager as possible.
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The Last Die Shop Standing
The Last Die Shop Standing By: Jim Szumera - MACOR Published on: 09/30/2013
The Last Die Shop Standing
We have been downsized, upside downsized, sold out, bankrupt and left for dead. The world as we know it has changed. The Industrial Revolution is over. Every man for himself! Survival and expansion seem diametrically opposite but it need not be. In todays manufacturing world, especially the smaller shops, survival means working lean. By lean, I am not necessarily advocating cutting costs to the point it jeopardizes productivity or basic human essentials. Survival means rethinking and executing on a new plan. Manpower needs to be reassigned and tasked differently. Do you really need tool and die makers performing redundant tasks, such as die maintenance? Can you cross train press room personnel and machine operators to fill the role of tooling technician and take on the various maintenance tasks as well? How can technology streamline production and front office tasks to help improve your competitive position? Have you fully leveraged or utilized software such as Word, Excel, Outlook and CAD or are you just useful at it? How can you restructure your purchasing, accounts receivable, payable, HR, IT, production, maintenance and tool room departments and activities going forward? On the surface these questions can seem daunting and complex to deal with. We need to look at simplification first. For example, can purchasing utilize Amazon and Ebay as a competitive choice for shop tools and supplies? I was amazed at both the offerings and prices on these sites. Establish price lists for all common tooling supplies, materials, punches, dies and components. Develop new sources for supplies. Leverage the internet as much as possible for all departmental tasks such as Payroll, HR, Engineering, Shipping and Receiving, Accounts Receivable and Payable, Marketing, Production and Quality.

Kaizen events can play a significant role in reducing costs and increasing productivity for all departments, from purchasing to production and die maintenance. Reconfiguration is the new expansion. Cross training, out sourcing, and resourcing will lead to a new robust manufacturing process whereby skilled craftsman don’t have to be relied upon at every turn, especially for redundant tasks. Production work cells can become reliable self sufficient business units. The last shop standing is the first in line for new opportunity and success.
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Dona VOct 7, 2013 - 10:12 am
Well structured data systems to collect qualitative & quantitave date over time provides continual improvement for any type of work. Great comments on cross-training as well.
StephenOct 10, 2013 - 9:00 am
"so true, this is happening a lot now
"last shops standing" first to take new opportunities"
JoeOct 11, 2013 - 12:27 pm
"I had some thoughts about this very topic throughout time over my last 15 years working for Plastic Injection Moldmaking shops. What is more advantageous.....hiring a manager with a degree or experience in management"
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