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Prior to use of the RASSP Manufacturing Interface, inaccurate placement
of surface-mount components caused significant recurring production difficulty.
The manual data exchange process employed did not assure accuracy of placement
information to within 1/1000th of an inch. Without this level of accuracy,
it was common for small discrete surface-mount components to move during
the solder reflow process, a difficulty referred to as component drift.
For some components, this movement caused them to make poor or no contact
with their designated connection points on the PCB. Attempts to counter
this effect centered around modifying "offset" values in the automatic
surface-mount placement equipment. Failures observed during the manufacture
of a batch of PCAs would be analyzed by a manufacturing engineer, who would
then use the analysis results to modify placement equipment "offset" values
in an attempt to correct the component misplacement problem. This approach
improved yields, but was never able to eliminate PCA failures, even over
several years of production of the same design.
Despite the ingenuity and tenacity of the engineers and technicians
supporting the facility, the inaccurate data utilized for production exacted
a heavy toll. For one program examined, 100% of 80,000 manufactured PCAs
had defects caused by inaccurate placement of surface-mount components.
These defects required manual repair. To make matters worse, on average
approximately 30% of components per PCA would require repair. Remarkably,
it was determined that the cost required to overcome these difficulties,
given the over-the-wall product data exchange paradigm the facility
was obligated to operate within, exceeded the cost of performing the repairs.
The PCA designs processed thus far using the RASSP-MI are comparable
in complexity to the design previously discussed. The metrics collected
regarding the success of these designs has been impressive. The amount
of rework required has been reduced by at least 80%, and the amount of
time required to perform manufacturing setup once the design data has been
delivered has been reduced by a factor of 10[Gad97].
Where:
Therefore, using the RASSP-MI results, Ct-RASSP is negligible.
Prior to use of the RASSP-MI, Ct-Pre_RASSP was significantly
higher. Equation 2 presents the production costs, Ct-Pre_RASSP,
associated with the program previously described in which a total of 80,000
PCAs were produced.
These results highlight the value of virtual concurrent engineering
and the importance of an agile manufacturing interface and explain why
the Lockheed Martin PCA manufacturing facility was identified for a Best
Practice award [Best95]. With further refinements, it is expected that
first-pass manufacturing success of PCAs will be consistently achieved,
primarily due to the capabilities provided and enabled by the RASSP agile
manufacturing interface.
4.0 LMC Installation
The RASSP-MI has been integrated into the RASSP enterprise system and is
being utilized by an LMC manufacturing facility. Over 100 PCA designs have
been processed by the RASSP-MI at this facility. Results indicate a significant
reduction in manufacturing errors and time required to go from design to
manufacturing setup since the RASSP-MI was integrated into the process.
4.1 Process Improvements
Because this facility had traditionally not been part of the product
design process, manufacturability issues were often present in data received
from the design organization. These issues had to be resolved before production could begin.
Resolution might require a re-design effort by the team originating the
design. Because the cost of design modification late in the design cycle
is high, manufacturability issues that were not insurmountable were often
allowed to remain, even though they increased recurring manufacturing costs.
These problems not only contributed to difficulty in achieving first-pass
manufacturing success, but unnecessarily increased production difficulties
and the cost of each PCA produced. The RASSP-MI corrected this by enabling
virtual partnering between design and manufacturing organizations.
4.2 Payback Analysis
Equation 1 below defines Ct to be the cost associated with the
time required to correct surface-mount component placement errors introduced
by the manual data conversion process previously employed by the manufacturing
facility.
Using the RASSP-MI, NC code for component placement machines is derived
automatically from the original CAD data representation of the design.
Therefore, the placement information in the NC code is as accurate as that
present in the CAD system. Due to the increased quality of the placement
data, it was determined that all of the "offset" values that had been programmed
into the surface-mount placement equipment at the manufacturing facility
could be reset to 0, which resulted in a simplification of the programming
procedures required for this equipment. The more accurate information has
also resulted in a near 0% component misplacement rate.
Based upon nominal labor cost values, the above result indicates a
cost of $20/PCA attributable to the absence of an effective and efficient
manufacturing interface capability. Given the production rate of the manufacturing
facility, the development costs of the RASSP-MI will be paid back after
approximately 5 months of use. This result highlights the tremendous savings
enabled by the RASSP-MI.
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