Movip was an initiative to develop a methodology of predicting the product quality during the design phase. For this project a number of OEM's (ASML, Philips Healthcare, Fei, Assembleon), Knowledge Institutes (IMEC, TNO) and a number of common suppliers (Prodrive, TBP/Technolution, Neways, Variass, KMWE, NTS, CCM, Sioux, MI-Partners, Fibreworks and Bicore) deliverd the backbone of the product Quality prediction model (MoViP).
When manufacturing products its evident that the risk of a failure increases with increasing the number of parts. This number of failures is the Zero Hour Defect Rate (ZHDR) of a product. Zero Hour Defect Rate (ZHDR) reflects the number of products which failed at the customer, with respect to the number of products delivered to the customer during an agreed period of time.
A “failure” is the unplanned occurrence that prevents the product from meeting its functional requirements under the specified operating conditions.
The time period in which a product fails can be as short as on receipt of the product (consumer) or as long as the build and test time when this product (industrial) is used in a larger system.
After this agreed period the failure mechanism is life time related (reliability).
When designing a product its evident that the risk of a failure increases with increasing the number of parts and/or design complexity.
Risk increases with #PartsTo determine the quality of the product the traditional methods such as design or process FMEA's, early design involvement of manufacturing, building prototypes, ... works well for products manufactured in large quantities and not having the pressure of fast market introduction. When manufacturing low quantities these methods helps but are costly and time consuming and doesn't help in cost price or market introduction. For industries in this category a methodology is developed to identify the manufacturing, part and the design risks during the design phase.
When designing a product there are only three failure modes (Parts, Processes and the Design) which contributes to the "Non" Quality of a product.
Parts are either vendor parts which are bought or manufactured parts which started with a material and ends up as a part manufactured according a drawing.
Processes are either the manufacturing processes (material -> part) or the assembly processes where vendor and manufactured parts put together lead to sub assembly(s) with in the end a product.
A design is the combination of parts when put together correctly deliver the required functionality.
The three failure modes are:
Possibly as fourth failure mode handling and transport is mentioned. This can be easely seen as a part which is packed and handled, stored or transported (process).
Processes are always coupled to either a material or a part (vendor, manufactured or (sub)assembly). Based on this the Bill of Materials (BoM) contains everything to identify the part or material risks and based on the coupling of processes to either a material or a part also all processes. Each part or material and the coupled processes based on the BoM result in an Zero Hour Defect Rate (ZHDR) when added statistical correct.
Vendor parts - Material & Processes
The risks of a failure per part or process is based on the history of that part or process. To identify the risk of failure for the part of processes a number of defect opportunities are used.
Part related risk described for vendor parts.
What's the risk on not working at all (defect) or not physical accpording specification (physical out of spec) or not functioning accpording specification (functional out of spec).
A part is defect when the part is not functioning at all.
Example: Hard disk is not functioning at all
Part is not conform the physical specifications. This can be a large number of physical defects.
Example: Hard disk is either dented, scratched, has no threaded holes for mounting, connect broken,...
Part Physical out of Spec
Part functions not conform specification but is still working.
Example: Hard disk turn slower than specified rpm, access time slower,...
Assembly Defect Opportunities
First step in the assembly process is placement of the parts.
Risks of placing the part in the (sub)assembly in the wrong way, forget or damage the part.
The risk that a part is not placed in the assembly.
Another part is placed in the assembly than specified in the Bill of material (BoM)Examples:
Part is placed with the wrong orientation in the assembly.Examples:
The part is not mounted on the specified position.
Part is damaged during placement. How bigger the part how easier the damage occurs. This is also true if a part is fragile.Examples:
Risks of connecting the part in the (sub)assembly not according specification. (screw not tigtening according torque, glue step not resulting in required strenght,...
Risk of not connecting at all.Examples:
Risk of connecting at the wrong place.Examples:
Risk of connecting in the wrong orientation.Examples:
Risk of not correct connecting.Examples:
Part is Misconnected
Theses processes even if they influences the (sub)assembly can be treated as the part processes with as difference they occur on (sub)assembly or product level only once.
Manufacturing Defect Opportunities
Material is not conform the physical specifications. This can be a large number of physical defects.
Example: material is of wrong material, is bended, scratched, to short,..
Manufacturing is a flow (workflow) of processes. Each manufacturing process contributes to the risk of not meeting the required manafuctured part. Where in assembly DPMO's are used as measure of the risk in manufacturing the Cpk, Ppk, sigma's are more used. When for each manufacturing step the Cpk, Ppk or sigma's are known these can be easely translated to DPMO's. Processes are:
The manufactred part risk is noting more than the material riks and the 'added' process risks.
Functionality risks are normal determined after building the part. To be able to predict the design Risks only a few methodologies are available.
The traditional design FMEA is a methodology to determine the risk based on a design review where experts give a score of 1 to 5 if a risk can occur. This mostly leads to an list of risks based on the expert level of the team. This is brought in the design review and must lead to a solution to prevent the risk.
An other approach to start with the Bill of Material (BoM) and for each part on the BoM determine the maximum load per part and based on the safety margin set a risk of failing in a scale between 0 and 100%.
Next step is the take the specification of the product and determine per specification the risk of not meeting the requirement. Again this risk is between the 0 and 100% of occurence not meeting the spec.
The other risk is a worst case design where based on the design even when it is assembled and manufactured perfect still can lead to a not functioning product. This can be derived from the design and is used to determine the product risk.
ZHDR CalculationsThis calculation result in a product ZHDR. Based on this also a list of Part Risk and process risks can be created.
ZHDR Specified/CalculatedDesign change is the first step in mitigation. Based on the list of part or process risks a design change must be made which avoids those risks. When not possible the second best option is to improve the processes which contribute most to the high ZHDr of the product. Last resort is to test the remaining risks which could not be solved with a design change or process improvement. Realize that a test when its detected a Not Ok lead to scrap and as such increasing the cost price.
Select out of the list of risks those parts and/or processes which contribute to the not meeting the product ZHDR. For parts a replacement or avoidance is the only way to improve. For processes is take an other design which avoids those processes.
Design MitigationAs a result of the design change the BoM is also changed. The ZHDR has to calculated again.
When a design change is not sufficient to meet the product ZHDR process improvemnt is the next option.
ZHDR Specified/CalculatedIn an assembly process, even with skilled/trained operators, perfect workinstructions, sign off lists, ideal environment or ... incidents happen. To avoid these process incidents the process must be controlled in itself. The most easy way is automating the process, or put in other words avoid manual labour. Worldwide is manual labour a risk. To get a feeling for the contribution of manual labour an average incident rate is 1000ppm (1 of the 1000).
Process ImprovementImproving processes has no influence on the part or design risk.
Even when the design changes and process improvements are not sufficient to meet the product ZHDR the last resort is testing.
Each part or process which is tested and is Not Ok results in scrapping the product. When testing not on product level but on part or (sub)assembly level the consequences are the same but the cost involved is lower. For design risks this will always lead to scrap.
Process & Test resulting in OK/FOK/NOKCalculation of the Zero Hour Defect rate (ZHDR) includes now the test coupled to the defect opportunity.For the test the slip is defined as:
0 > No slip (no process failure slips through)
1 > No test (all process failures slips through to next stage)
ZHDR Calculations including test
When testing identifies a Not Ok this mabey can be reworked. When reworked this can solve the NoK but also can introduce new risks. Testing the reworked product is mostly done on another test fixture than the test used for production.
ZHDR Calculations including test & reworkTesting results in a lower risk at the customer.
Products are handled to go to a storage area or packaging area.
Based on the changes in the handling and transport process the Zero Hour Defect Rate (ZHDR) must be calculated.
The Zero Hour Defect Rate (ZHDR) handling and transport risks are multiplied with the corresponding slip.
This results in a new Zero Hour Defect Rate (ZHDR) which must be checked if the Zero Hour Defect Rate (ZHDR) is within specification.
Litirature on Quality
George, Michael l., ''What is Lean Six Sigma'', 2003, McGraw Hill, ISBN-10: 007142668X
George, Michael l., ''The Lean Six Sigma Pocket Toolbook'', 2004, McGraw Hill, ISBN-10: 0071441190
Morgan, John, ''Lean Six Sigma For Dummies'', 2012, Wiley Publishing, Inc., ISBN-10: 1119953707
Gygi, Craig, ''Six Sigma for Dummies'', 2005, Wiley Publishing, Inc., ISBN: 0-7645-6798-5
Webber, Larry, ''Quality Control for Dummies'', 2012, Wiley Publishing, Inc., ISBN-10: 0470069090
Kemp, Sid, ''Quality Management Dymistifeid'', 2006, McGraw Hill Education, ISBN: 0-07-144908-6