Assemblies: rework

Placement tools range from completely manual to fully automatic. All have some form of graphical feedback to the designer that assesses the quality of the placement in terms of its ability to be routed or connected in the desired number of signal layers. Most have spacing rules that ensure that the components have enough room between them for successful assembly, rework, and testing. 

Production cost Process selection Machine tools Operator skill Tooling, fixtures inspection precision Assemblability Scrap and rework... 

The benefits are many, though the basic cost justification is more elusive. The first benefit is that assembly is easier as the variations between parts is lower and less selective fitting is required. It inherently makes for better part interchangability. For the maintenance people, parts should iir without rework or hand fitting. 

When deciding on repair or rework action, you may need to consider whether the result will be visible to the customer on the exterior of the product. Rework or repairs that may not be visible when a part is fitted into the final assembly might be visible when these same parts are sold as service spares. To prevent on-the-spot decisions being at variance each time, you could ... 

As a rule, batches that are rejected or reworked are not suitable for inclusion in a retrospective validation study [7]. Indeed, a processing failure that is not fully explainable should be cause to rethink the application of retrospective validation. Nonconformance to specification that is attributable to a unique event-operator error, for example, may be justifiably disregarded. In such cases, the batch is not considered when the historical data are assembled. 

Another megatrend in this competitive business environment is that all production processes need to be world-class and lean. This means that processes must be automated lead times shortened rework, scrap, and waste minimized or eliminated and less product must appear in inventory. This places a burden on the adhesive formulator in that the products not only must perform in service (e.g., creep resistance, peel strength) but also must perform in the assembly process (e.g., fast cure time, minimal scrap, low energy cure). 

Note If rod binds, reapply rearward pressure on tube and heat up the spot weid area. Bend tube into proper alignment and reweid. If misaJiffnment is too grreat to correct hy this methodj. drill out spot weld, disassemble the entire unit and reeheok until problem area is discovered. Rework pieces as needed and start over with assembly step h. 

Materials mix-ups are serious problems in process plants, and occur when the wrong component, part, or material of construction is substituted during the fabrication or assembly of equipment, delivered to the site, or installed in process. Materials mix-ups have led to catastrophic incidents. Additionally, premature failures of improperly substituted parts from materials mix-ups have led to significant production losses and costly equipment rework. 

Polyurethane adhesives are used primarily in the assembly of printed-wiring boards to attach large components such as capacitors, magnetics, heat sinks, and connectors. Their key benefits include flexibility, absorption of stresses, vibration damping, and thermal transfer. Being thermoplastic, polyurethanes are also easier to rework than epoxies. 

The decision to rework electronic devices or assemblies depends on the cost of reworking versus the value of the part. Consumer electronics, due to their low cost, are considered throwaways and seldom reworked. For some, such as plastic-encapsulated microcircuits (PEMs) that are produced in high volumes, rework is impractical because of the difficulty in removing the plastic encapsulant without destroying the components. However, for high-value assemblies, such as densely populated PWBs and MCMs, where the final value may be as high as 10,000 or more, the ability to rework is essential. In such cases, rework may be necessary to meet schedules when small numbers of assemblies are produced. 

It is axiomatic that manufacturing productivity is increased and per unit cost is decreased by making assembly and automation processes more efficient. High-quality parts further lower costs by reducing rework and replacement liability costs. Environmental consciousness and regulatory compliance have become a permanent and increasing component... 

The new aircraft had been modified to accommodate the special bombs they would carry and the added crew. The cylindrical tunnel that connected the pressurized forward and waist sections of the plane had to be partly cut away and reworked so that the larger bomb, Fat Man, would fit in the forward bomb bay. Guide rails were installed to prevent the tail assemblies from hanging up during fallout. An extra table, chair, oxygen outlet and interphone station for the weaponeers responsible for monitor-... 

Production Cost Process Selection Machine Tools Operator Skills Tooling, Fixtures Inspection Precision Assemblability Scrap and Rework... 

Rework generally consists of removal and replacement of a failed electronic component that has been detected after initial electrical testing or testing after bum-in. The actual rework procedure is more of an art than a science. Since each component or assembly is different, considerable experience and care are required to selectively remove one device without damaging adjacent ones. 

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