Product Development Stage Gate Methodology for a Composite Shroud - C119

 

Product Development Stage Gate Methodology for a Composite Shroud
Case study
Document Type	Case study
Document Identifier	119
Objective functions	Cost Maintain Rate Maintain Quality Maintain
MSTE workflow	Development
Prerequisites	Development

Summary

A utilities company was developing a composite shroud to protect a telecommunications tower from extreme icing conditions. The project presented several risks including the size of the structure, extreme environmental loads, potential signal strength degradation, and the remote installation site. Due to the high development costs and potential risks, a Stage Gate methodology was utilized to reduce these risks in a systematic way with defined stages and review gates that provided go/no-go points. This approach addressed higher risk levels early in the project schedule with lower investment, ultimately reducing the timeline and cost of the project.

Challenge

The client owned a telecommunications tower that was located on a mountain. The tower experienced high icing and wind loads that had the potential to damage the structure. The client wanted to construct a shroud to protect the telecommunications tower. Metal panels were not an option due to potential interference with the telecommunications signals so they wanted to construct the tower using composite materials (see How Composites Differ From Metals).

There were a number of challenges that the project needed to overcome:

1. The composite shroud needed to survive the same high icing and wind loads experienced by the tower.
2. The telecommunications equipment operated at four different wavelengths. When a signal travels through a composite material it loses strength. It was critical that the signal for all wavelengths met a minimum strength level.
3. The structure was large making manufacturing more challenging.
4. The installation site was remote leading to high installation costs. If the design did not perform as planned anticipated rework and repair costs were high.
5. The installation site was only accessible for a short period each year meaning that if the design failed the tower could be inoperable for a long time period.

Approach

Stage Gate Methodology

The Stage Gate concept, also known as phase-gate process, is a project management methodology used to guide product development from initial idea through to market launch and in service support. It divides the product development process into distinct stages (also known as phases) separated by decision points (gates). In each stage a specific work scope is completed that advances the product’s development a predefined step, while focusing on addressing the most significant risks to the product’s success. At each gate the development progress is evaluated based on predefined criteria by a cross-functional review team. Each stage involves specific deliverables, such as market research, feasibility studies, coupon/assembly/prototype level testing, test launch market feedback, etc. The Stage Gate methodology combines well with the building block approach to composite component development.

Gate reviews involve a cross-functional team to ensure the product’s development risks, opportunities, and barriers are considered from all angles (i.e. marketing, sales, engineering, production, distribution, and in service support). At each gate the review team decides whether to proceed with, pivot, or halt the project. This structured approach helps foster innovation while systematically de-risking products and advancing product development with the lowest cost and fastest speed, while increasing the odds of commercial product success.

The Stage Gate approach as it applies to composite component development is described in Composites design and is described as having 4 stages: Conceptual Design, Preliminary Design (Trade Study), Detail Design, and Production . There are two additional stages beyond the Production stage described in Composites design. They are Product Launch and Marketing, where the product is released into the market in a structured way and market feedback secured, and Field Support, where the product is supported in service over its lifetime. Field Support helps to ensure customer satisfaction and gathers intelligence that guides the development of future product iterations or new products driven by market needs.

Conceptual Design

A design concept was developed at the start of the project that included constructing composite beams into a support structure that surrounded the telecommunications tower. The beam structure was used to support flat composite sandwich panels. The size of each panel was determined based on the height and location of the telecommunication equipment mounted onto the tower. The desire was to minimize signal loss by centring a sandwich panel with the telecommunication equipment.

A preliminary finite element analysis (FEA) was performed that modelled the beams using 1D beam elements and the panels using 2D shell elements. The weight of potential ice buildup was added to the model, along with wind loads that were provided by Environment Canada. The preliminary FEA defined the required panel thicknesses and the maximum panel sizes. This data showed that it was feasible to design a composite structure that could withstand the environmental loading conditions.

Calculations to estimate the signal loss were also performed during the conceptual design stage. Glass, carbon, and aramid fibres were considered for the panels (see Material Selection). Polyurethane and phenolic cores were also assessed (see Cores & inserts). The dielectric constant and loss factor of each material was obtained and used in the calculations. The analysis showed that it was feasible to have all four signal frequencies pass through a composite panel and maintain a sufficiently strong signal. The aramid fibres produced the lowest signal loss, but were more expensive and difficult to manufacture. Glass fibres resulted in a higher signal loss but still met the requirements and provided a less expensive alternative.

A gate review meeting was held that included project managers, structural engineers, signal engineers, and financial controllers to review the results. With the structural and signal strength feasibility of the design confirmed it was decided to move the project forward into the Preliminary Design stage. It was also decided to pursue the fibreglass option rather than aramid fibres.

Preliminary Design

Fourteen small fibreglass test panels were manufactured for signal attenuation testing. The type and thickness of core was adjusted, along with the ply thickness and fibre content. The test thicknesses were decided using the data from the signal calculations and structural analysis performed during the conceptual design stage. Testing was performed by bouncing signals between the desired frequencies off a reflector and measuring the received decibel level as shown in the figure below. During the test the receiver was rotated from -120 degrees through +120 degrees. First, the test was performed without any composite panels attached to the receiver to measure a baseline value. The test was then repeated fourteen times with one of the composite panels attached to the receiver each time. The measured signal from each of the trials was then compared to the reference measurement to calculate the signal loss. The testing confirmed that all the panels met the signal loss requirement, but some of the panels performed significantly better than others and were selected for further structural analysis.

Signal Attenuation Testing Setup - A&S Composites Engineering

The preliminary FEA was updated with the new panel thicknesses and the model was rerun. The results confirmed that the new panel sizes could withstand the environmental loading conditions.

An initial manufacturing cost estimate was developed during this stage. This included tooling, materials, labour, and overhead costs. Based on the panel sizes and thicknesses it was determined that the panel manufacturing fell within the acceptable budget range for the project.

A gate review meeting was held that included project managers, structural engineers, signal engineers, and financial controllers to review the results. The signal attenuation testing had shown that the composite panels could meet the signal loss requirements, the preliminary FEA confirmed that panels were sufficiently stiff and strong, and the cost estimate indicated the panels were within budget. It was decided that the project should move forward to the Detailed Design stage.

Detailed Design

The detailed design stage started by designing each of the attachment methods. This included attaching the support beams to each other and to the central support pole. It also included attaching the panels to the support beams.

A detailed finite element model was then created. The support beams and attachment brackets were modelled using 3D hexahedral elements. The cores of the sandwich panels were modelled using 3D hexahedral elements with the laminate plies modelled using 2D shell elements. Bolts were modelled using 1D beam elements. Ice, wind, and snow loads were applied based on climatic data for the installation location from Environment Canada.

The maximum deflections and minimum strength safety factors of the sandwich panels were assessed and compared to the defined allowable values. An example of the safety factor results for one of the sandwich panels is shown in the figure below. The stresses in the support beams and attachment brackets were also examined and compared to their strength values. The tensile, shear, bearing, and shear out stresses in the bolts and their connecting structures were investigated and led to updates in the number and size of bolts (see Introduction to Bolted Joints in Composites).

FEA of Composite Panel safety Factor - A&S Composites Engineering

An updated cost estimate was created as the design was finalized. This included updated manufacturing costs for the sandwich panels, as well as preliminary supplier costs for the support structure beams and the attachment brackets. It was found that due to the complexity of the attachment brackets the estimated cost exceeded the original manufacturing budget.

A gate review meeting was held that included project managers, structural engineers, financial controllers, and the installation team to review the final design. The estimated manufacturing cost overrun was discussed and it was decided that it was an acceptable increase in price to achieve the project goals. Therefore, the review team decided that the project should proceed to the next stage.

Production

Drawings were created for each of the sandwich panels and a request for quote was issued to multiple manufacturers. Once the vendor was selected, they designed the required moulds for production. This involved input from the design team to ensure that all important features were included. After the moulds were completed, initial prototypes of the panels were built and sent for testing. This included measuring the thickness and fibre content of the fibre plies and comparing the results to the original design parameters. The panels were also sent for signal attenuation testing to ensure that the signal loss remained within the acceptable range. Manufacturing tolerance values and quality assurance checks were updated based on the test results to ensure the performance of all the panels.

A gate review meeting was held after the testing, but before the full-scale manufacturing. The meeting included project managers, structural design engineers, signal engineers, financial controllers, the installation team, and team members from the manufacturer to review the test results and approve the full-scale manufacturing. The signal loss was within the approved range and the thicknesses of the panels matched the design parameters. This confirmed the technical suitability of the panels and validated the manufacturing budget. Based on this information full-scale manufacturing was approved. A second meeting was held once the panels were fabricated. The measurements recorded during the panel fabrication quality assurance process met the requirements leading to installation approval from the team.

Product Launch and Field Support

The first step in the Product Launch stage was to erect the beam support structure on-site. This was followed by installation of the panels. During this process the installation team stayed in contact with the design engineers to verify some details of the design. Once the shroud was fully installed, signal testing was performed using the actual telecommunications equipment mounted on the tower to verify that the signal strength loss remained within design parameters.

A gate review meeting was held with the project managers, design engineers, signal engineers, and the installation team. With the installation complete and tested, the telecommunications equipment was approved to return to service. This moved the project to the Field Support stage. The client took responsibility for the Field Support stage and the design team was no longer involved in the project.

Outcome

At the conclusion of the project the protective shroud had been successfully installed and the signal strength loss was confirmed to be within allowable levels, clearing the installation for long term service. Due to the complexity of the tower and panel attachment brackets the final budget was higher than the original budget at the start of the project. One of the benefits of the Stage Gate approach used in this project is that these cost overruns were identified before production commenced, were reviewed, and approved by the entire team. This led to greater customer satisfaction with the project results.

Additionally, the Stage Gate approach reduced the risk of potential costly redesigns. For example, if the structural analysis had been performed before the signal loss requirements were defined and tested, the panels would have been too thick and resulted in signal strength loss values that were too high. This would have required redoing the entire structural analysis. Similarly, had signal strength testing not been completed in a systematic manner (i.e. small-scale panel testing, prototype panel testing, installed tower testing), an extremely costly rework of the tower shroud may have been required had the signal strength only been tested once in the field.

The Stage Gate approach added administrative costs to the project, but this was made up for in cost savings realized by avoiding expensive redesigns. For small simple projects the additional administrative costs may not be recovered. The approach may also increase the length of the project for small simple projects, but typically results in shorter delivery times for more complex projects such as this one.

References

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Engineered materials (designed to have specific properties) made from two or more constituent materials with different physical or chemical properties. The constituents remain separate and distinct on a macroscopic level within the finished structure.

With regards to manufacturing, risk is the combination of the probability and consequences of undesirable manufacturing outcomes. Manufacturing risk can lead to technical issues, program/schedule delays, and cost overruns.