Assembly
conveyor, while offering flexibility and systems to gather this information, with
asynchronous operation have inherent the more sophisticated systems
disadvantages of increased work in including a means of reading the pallet
process and the need for fairly complex number so the system can track
control systems that become especially information on a particular pallet, in
burdensome in test intensive addition to identifying the status of the
operations. pallet contents.
For better efficiency in test centric Test centric assemblies not only
assembly, testing applications engineers have the means to test and track parts
designed a standardized heavy duty in but to handle rejected pallets. One
line chassis that provides for a flexible method for doing so is to have rejected
workstation setup and retooling, pallets continue down the line but
including double dwell time at selected ignored by succeeding operations until
Test centric assemblies automatic stations without slowing cycle times unloaded at an intermediate reject
defective parts removal throughout the machine. These are position or immediately after testing.
typically small footprint machines, e.g. Rejects can then be sent to a parallel
40 inches (1016 mm) x 90 inches (2286 repair line. Whatever method is used,
Some examples of how costs for mm) long for 18 stations or 61 inches its objective is to avoid any further work
rework and scrap can be avoided by in (1549.4 mm) long for 10 stations. on a rejected or defective part, which is
process testing are as follows: Assemblies can be made of multiple the overriding advantage of in process
ring6 Functional testing to verify standard testing chassis, combining testing.
electrical, pneumatic and standard units end to end, side by side,
mechanical part characteristics or end to side for assembly and test Defective parts or tests?
32
before further assembly steps. operations requiring additional stations. The inability to differentiate good parts
ring6 Automatic resistance Servo drives allow one to optimize the from defective parts may be due to
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measurements in stations that transfer rate depending on part inertia faulty testing methods, which in turn are
.eur follow the addition of coils, (weight) without requiring any machine usually the result of inadequate
oasiasemiconductor
heaters or resistors. component replacements or mechanical understanding of real testing
ring6 Leak test following ultrasonic adjustments. requirements. An example is found in
welding of two plastic housings. Individual station baseplates are test results with insufficient signal to
ring6 Leak testing following spin used to simplify adding, removing or noise ratios. In leak testing there are
riveting of a cover to a pump retooling any station without disturbing often problems with seal creep.
housing. the others. These standardised chasses Another example is in process gauging
.com
ring6 Leak testing after the insertion for test intensive operations accept a stations that are insufficiently rigid or do
of an “O” ring or other seal. wide range of standardized tooling and not have the correct reference.
ring6 Machine vision systems or robotics or customized equipment Thus, the first considerations in test
square4
Issue III 2009
probes used to ensure that needed for other parts of the assembly centric assembly are developing a
parts are positioned properly. process. What differentiates these test thorough and detailed understanding of
ring6 Dimensional gauging stations, intensive assembly chasses from power required testing accuracies, the best
especially after a crimping or and free systems is twofold; 1) the use methods to achieve the required
staking operation. of quick change fixturing and 2) the
ring6 Electrical testing of continuity, ability to double up stations for greater
voltage, current and contact flexibility and to reduce work in process
bounce. (fewer pallets).
Test centric assemblies also always
When in process testing becomes a have the ability to track the contents of
centrepiece of an assembly and test each pallet and report to control
operation, a re-design of the chassis systems on conditions of parts. In this
used in the assembly is recommended. way the control system can identify the
The ease with which one can relocate or presence or absence of parts on a
remove work stations and pallet, whether or not the part has
accommodate test operations with passed or failed a test and in some
different times in each test station is key applications, also will identify if the part 18 station assembly chassis optimised
to the outcome. A power and free was tested yet. Different signalling for test centric assembly
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