*2.2.2 Design guidelines*

Design guidelines provide indications on how to deliver a *design for manufacturing* solution, rather than giving rules and consequently a PASS/FAIL decision. They can be seen as indications that the Design team has to follow in order to design a producible part.

While rules provide a PASS/FAIL criteria, often regarding geometrical or mechanical properties, guidelines provide assort of "sensible" indications so that the design has a higher probability of success. In other words, if the guidelines are followed, very limited manufacturing issues are expected later on. On the contrary, if the design team decides not to follow the guidelines, plenty manufacturing issues during the production stage should be expected.

A typical design guideline could be to avoid overcomplicating the electrical schematic, eliminating unnecessary components. Every component placed inside the schematic should answer to at least one design goal (typically performance, testability or reliability). If a component does not contribute to at least one of these "high-level" design goals, the engineering team should substantiate the reason for which it has inserted. Boothroyd and Dewhurst [6] suggests, among other topics, that unnecessary parts are those that answer "NO" to the following questions:


If the answer to all questions is "NO", the part is unnecessary and can be integrated with other parts.

Another guideline could be to design parts so that final performance can be obtained after tuning or programming performed in reasonable time and most of all avoid using components (or electrical schematic) so that the overall module performance resides on a specific component of the module. In this case any shortcoming of the component will affect one-to-one the module' behavior.

**13**

*Design for Manufacturing of Electro-Mechanical Assemblies in the Aerospace Industry*

Design engineering team, during the initial design stages, would like to have an initial prototype to test the idea and verify in-lab any limitations that commercial

Basically, there two types of prototyping techniques: virtual or real (fast). Virtual prototyping relies on very accurate model-based CAD simulations. The models are often validated through a previous trial-error-correct cycle. The method is relatively inexpensive, can be very fast and deliver accurate results providing the

Additive manufacturing technologies (metal and plastic) provide fast turnaround time to realize real and fast breadboards. In this case, the prototype is real, the time constraints are guaranteed but the exercise can be expensive, compared to

The choice between real or virtual prototyping can be performed by analyzing

If parameters 1 and 2 have higher weight then virtual prototyping appears to be the appropriate solution. On the contrary, if design uncertainties are high and risk

The objective of a preferred part list (PPL) is to direct the user toward a limited number of component types, covering all design applications. The aim is to avoid duplication and achieve cost reduction and procurement effectiveness [7].

Consequently, you should identify a subset of typically used components to generate your custom PPL. Components belonging to the PPL should be employed "by default", and any derogation from the list should be clearly explained and

Definition, creation and sustainment of a PPL should be a company-funded activity and the client-related programs receive the benefit. Like any other engineering effort, the more work put in the initial stages, the less work is required on

gained over the lifetime of the product (procurement, production and maintenance). Since the cost of introducing d sustaining a PPL in a company is rather relevant at the beginning such choice must be willingly enforced and sponsored by the company's top management (director general end director of engineering). Moreover, the director of the purchasing department has to be actively involved, since he might be tempted, over a short-term period, to prefer cheaper or readily-

available parts as an alternative to the parts in PPL.

Initial cost is only one consideration for the PPL and is compensated by the value

Components shall be introduced in PPL after analyzing the criteria listed in the

Performance history: actual field experience or extensive relevant testing.

*DOI: http://dx.doi.org/10.5772/intechopen.90098*

CAD simulations or analysis are unable to predict.

*2.2.3 Prototyping, virtual or real (fast)?*

model itself is accurate.

the following parameters:

**2.3 Preferred part list**

technically justified.

final stage.

following.

1.Virtual model accuracy

3.Associated Risk mitigation

2.Available time and budget constraints

mitigation is necessary, then real prototyping becomes useful.

virtual.

*Design for Manufacturing of Electro-Mechanical Assemblies in the Aerospace Industry DOI: http://dx.doi.org/10.5772/intechopen.90098*

#### *2.2.3 Prototyping, virtual or real (fast)?*

*Design and Manufacturing*

given in the following:

*2.2.2 Design guidelines*

producible part.

product?

assemble the products?

grated with other parts.

applicable to hybrid microwave modules or hybrid microwave integrated circuit is

• Package dimension not to exceed a certain value so that the part can be manu-

• Minimum distance between adjacent components, so the part can be assem-

• Maximum dimension of materials and substrates to avoid cracking due to

• Geometrical rules regarding thickness, angles, corner radius, shapes, etc.

While rules provide a PASS/FAIL criteria, often regarding geometrical or mechanical properties, guidelines provide assort of "sensible" indications so that the design has a higher probability of success. In other words, if the guidelines are followed, very limited manufacturing issues are expected later on. On the contrary, if the design team decides not to follow the guidelines, plenty manufacturing issues

A typical design guideline could be to avoid overcomplicating the electrical schematic, eliminating unnecessary components. Every component placed inside the schematic should answer to at least one design goal (typically performance, testability or reliability). If a component does not contribute to at least one of these "high-level" design goals, the engineering team should substantiate the reason for which it has inserted. Boothroyd and Dewhurst [6] suggests, among other topics, that unnecessary parts are those that answer "NO" to the following questions:

1.Does the part move relative to other parts in normal operating condition of

2.Is it necessary that the part is made of different materials or isolated from other parts such as electrical insulation, heat insulation, or vibration reduction?

3.Does the part have to be isolated from other parts otherwise it is impossible to

If the answer to all questions is "NO", the part is unnecessary and can be inte-

Another guideline could be to design parts so that final performance can be obtained after tuning or programming performed in reasonable time and most of all avoid using components (or electrical schematic) so that the overall module performance resides on a specific component of the module. In this case any shortcom-

ing of the component will affect one-to-one the module' behavior.

Design guidelines provide indications on how to deliver a *design for manufacturing* solution, rather than giving rules and consequently a PASS/FAIL decision. They can be seen as indications that the Design team has to follow in order to design a

factured using automatic assembly machines

bled using automatic *pick'n'place* machinery.

thermal expansion/compression

• Metallisation and finishing of surfaces

during the production stage should be expected.

**12**

Design engineering team, during the initial design stages, would like to have an initial prototype to test the idea and verify in-lab any limitations that commercial CAD simulations or analysis are unable to predict.

Basically, there two types of prototyping techniques: virtual or real (fast).

Virtual prototyping relies on very accurate model-based CAD simulations. The models are often validated through a previous trial-error-correct cycle. The method is relatively inexpensive, can be very fast and deliver accurate results providing the model itself is accurate.

Additive manufacturing technologies (metal and plastic) provide fast turnaround time to realize real and fast breadboards. In this case, the prototype is real, the time constraints are guaranteed but the exercise can be expensive, compared to virtual.

The choice between real or virtual prototyping can be performed by analyzing the following parameters:


If parameters 1 and 2 have higher weight then virtual prototyping appears to be the appropriate solution. On the contrary, if design uncertainties are high and risk mitigation is necessary, then real prototyping becomes useful.

#### **2.3 Preferred part list**

The objective of a preferred part list (PPL) is to direct the user toward a limited number of component types, covering all design applications. The aim is to avoid duplication and achieve cost reduction and procurement effectiveness [7].

Consequently, you should identify a subset of typically used components to generate your custom PPL. Components belonging to the PPL should be employed "by default", and any derogation from the list should be clearly explained and technically justified.

Definition, creation and sustainment of a PPL should be a company-funded activity and the client-related programs receive the benefit. Like any other engineering effort, the more work put in the initial stages, the less work is required on final stage.

Initial cost is only one consideration for the PPL and is compensated by the value gained over the lifetime of the product (procurement, production and maintenance). Since the cost of introducing d sustaining a PPL in a company is rather relevant at the beginning such choice must be willingly enforced and sponsored by the company's top management (director general end director of engineering). Moreover, the director of the purchasing department has to be actively involved, since he might be tempted, over a short-term period, to prefer cheaper or readilyavailable parts as an alternative to the parts in PPL.

Components shall be introduced in PPL after analyzing the criteria listed in the following.

Performance history: actual field experience or extensive relevant testing.


Considering the main stages in the product's life-cycle (from concept to maintenance), the possible savings in each phase are examined:


The design engineer who selects the components must choose as many parts as possible from the PPL. Ideally >80% of the bill-of-materials (BOM). By selecting even a majority of the parts from the PPL, the benefits realized from the arguments presented above should be sufficient to encourage the company to validate and enforce the practice of using a PPL.

Finally, it is obvious that the PPL should be created and managed by the Industrial engineering people who are the stakeholders of the activity. In fact, PPL has a n impact on all phases of the product life-cycle. The size of PPL depends on the complexity of the typical system the company develops. For an aerospace

**15**

*Design for Manufacturing of Electro-Mechanical Assemblies in the Aerospace Industry*

satellite payloads) the size of PPL could be around 2000–3000 components.

As stated many times previously, aerospace products feature high system complexity, and must provide high-performance to be delivered over time and in harsh environment and operating conditions. Consequently, the design team must take into account these aspects when designing the product. Design for Reliability, Maintenance and Test (RMT) is often referred to as design for RMT as if it were a single topic. However, different strategies are employed as clarified in the following

Design for test is a crucial aspect to guarantee the part can be efficiently produced during its life-cycle- The part must be designed so that it's key features and characteristics are accessible and verifiable during production test. Keep in mind that in the aerospace industry, practically 100% of the realized parts are fully tested, often over temperature and in mechanically stressful condition (vibration or similar), to verify they are fully compliant to specification and free from manufacturing defects. Moreover, the test is functional and not merely structural. Manufacturing functional tests are carried out to verify that the part is working and function as expected and not just assembled correctly. Functional test on 100% realized HW parts is typical of the aerospace industry to guarantee performance and reliability of manufactured parts and is less applicable to consumer products due to the very high time and cost involved in these kind of test. Finally, aerospace modules that fail the first manufacturing test need to be analyzed and tuned so the part meets the technical specification. Given the time and cost involved in the assembly process, it is illogical that the part should be discarded if the first production test fails. Consequently, designing parts for testability greatly aids the troubleshooting phase, ensuring production people can speedily identify the shortcoming

Given this scenario, it is mandatory that the design team keeps into account these aspects when designing the part. The principle is to add components and interfaces to make it easier to develop and apply manufacturing tests to the designed hardware. At the same time, test engineering department should be consulted in the design phase, so they can bring provide advice and most of all start designing the Automated Test Equipment (ATE) that will be used in production phase but could also be used by the engineering team for product verification and validation. The idea underlying design for test is: Pay less now and pay more later

Design for reliability is crucial aspect in the aerospace industry, where reliability is a must considering the mission criticality of these systems [8]. Reliability somewhat depends on the assembly process employed. One indication is to avoid those

Design for maintenance shared some requirements with design for test, since any maintenance activity starts with identifying the part in failure within the system. Other aspects consist in the designing the parts in a modular way so any failed item can be easily replaced without having replace the entire system or sub-system,

manufacturing processes that are less repeatable or controllable.

company that designs and manufacture avionic systems (radars, electronic warfare,

*DOI: http://dx.doi.org/10.5772/intechopen.90098*

to separately guarantee the three topics.

*2.4.1 Design for test*

and restore the part.

without DFT.

*2.4.2 Design for reliability and maintenance*

**2.4 Design for reliability, maintenance and test**

company that designs and manufacture avionic systems (radars, electronic warfare, satellite payloads) the size of PPL could be around 2000–3000 components.
