Cost Comparison Study of a GFRP Leisure Boat Hull Manufacturing Method; Spray Up vs Resin Infusion - C115

 

Cost Comparison Study of a GFRP Leisure Boat Hull Manufacturing Method; Spray Up vs Resin Infusion
Case study
Document Type	Case study
Document Identifier	115
Themes	Materials deposition and consolidation management
Tags	Deposition Cost Resin flow Costing
Objective functions	Cost Reduce Rate Maintain Quality Maintain
MSTE workflow	Development
Prerequisites	Optimization

Summary

This case study examines the feasibility of transitioning from traditional open molding wet layup to a vacuum assisted resin infusion (VARI) in the manufacturing of glass fibre reinforced polymer (GFRP) leisure boat hulls. It highlights the potential for significant cost reductions, estimating about 23% savings per unit with resin infusion compared to a wet layup. The study utilizes the Ashby cost model to demonstrate that the savings become apparent after the initial setup costs are amortized 0ver a certain number of units produced. However, the transition carries risks, especially concerning the need for new skills and adaptations by the workforce. The company is advised to plan carefully, focusing on training and strategic implementation to mitigate risks associated with the new manufacturing technology.

Introduction

A key aspect of manufacturing engineering is the reduction of risk in order to increase the likelihood of success. Given that the majority of manufacturing scenarios are a commercial venture, risk associated with profitability is of significance and is often the centerpiece of such a discussion. It is necessary to capture and understand risk associated with profitability and general cost-driven topics for manufacturing engineers. This is especially the case when a company is moving into less familiar territory, such as when there is a desire to innovate and keep ahead of the market curves for new trends in the adoption of new materials or process technologies .

Composites processing is an area of manufacturing that is subject to many opportunities for growth, as the material and process technologies available are highly tailorable with many potential configurations, which can provide significant cost effectiveness and advantage over other more traditional materials and processes. For example, being able to consolidate thermosetting polymer composites into their final shape, while also developing material properties, can save on significant secondary, tertiary and post-processing requirements, leading to overall cost effective products . However, given that this process is not sequential in nature, rather there are many actions occurring in “one shot”, it is also much easier for one out-of-spec variable to have a cascading effect and in turn cause the overall failure of the manufacturing process . This is an inherent risk with composite parts, such as glass-fibre reinforce polymer (GFRP) boat hulls, depicted in the figure below.

Historically, due to the technically simple nature of the materials, a Wet layup process using glass-fibre and polyester resin composites have been used to manufacture composite boat hulls. However, there are many issues that arise from this process, including lower specific performance, uncontrollable environmental factors affecting each manufacturing run (to which these materials are highly sensitive), the highly manual nature of the process, plus others. There has been a desire to shift towards some closed-mould processes to reduce these sources of risk. Vacuum Assisted Resin Infusion (VARI) has been adopted by some manufacturers in the leisure boat industry and working with a local industrial partner, it has been possible to capture the financial risk associated with such a process change by using cost modeling tools. The figure below, shows a boat hull being manufactured by the infusion process, where a dry reinforcement preform is infiltrated by a resin under vacuum, given a specific window of time to fill before thermosetting cure takes place and the process comes to an end.

The approach taken is to use cost modeling of both the historical and proposed future process, then compare the results. The potential savings by using the new materials and process will be weighed against the expert opinion-derived risk of workshop employees migrating to a new and unfamiliar technology.

Approach

In this case study, a 21-foot GFRP leisure boat was considered as the manufactured part at the centre of this analysis. Initially, it is important to select an appropriate cost model to perform the work required. For this case study, the Ashby cost model was used , for its simplicity and ability to capture production scaling by increasing overhead costs associated with space and labour. The equation describing per-unit costs for manufacture is shown below. \[C_S=\frac{m C_m}{(1-f)}+\frac{C_t}{n}\left\{\operatorname{Int}\left(\frac{n}{n_t}+0.51\right)\right\}+\frac{1}{\dot{n}}\left(\frac{C_c}{L t_{wo}}+\dot{C}_{oh}\right)\]

Where \(m\) is the mass of the part, \(C_m\) is the cost per unit mass of the materials, \(f\) is the scrap fraction, \(C_t\) is the cost of tooling, \(n\) is the number of parts being made over the life of the project/contract, \(Int\) is the integer function, \(n_t\) is the lifespan of the tool (number of parts a tool can produce), \(\dot{n}\) is the production rate, \(C_c\) is the capital cost for equipment and infrastructure, \(L\) is the load factor of the infrastructure (the relative amount of time it is being used on this project/contract), \(t_{wo}\) is the lifespan of the project/contract and \(\dot{C}_{oh}\) is the overhead cost (labour, site lease, power etc.).

In order to gather the necessary data to populate the model and explore cost factors, the manufacturer has been extensively involved in this process and has provided a wide variety of information about material costs, scrap rates, labour intensities for current processes, amongst other details. The result is shown in the graph below, which parametrically shows the cost per GFRP boat hull unit, for work orders of sizes between 1 – 500 units in total. It can be seen that by approximately the tenth unit produced, the cost per unit begins to asymptote at approximately $12,600. This means that by this point, the price of all equipment, tooling and other non-recurring costs have been effectively amortized into the cost and only recurring costs, such as overhead and materials remain. This cost is in-line with the manufacturer’s real costs, illustrating the potential robustness of this highly simple cost model.

Similarly, the same process was used for the same boat made by the infusion process. A trade study was performed on this case, where it was recognized that not only would the cost of materials differ from the previous case, but the amount of material would be less, due to the higher mechanical properties obtained. This was fed into the costing analysis to scale mass. Additionally, the differences in sequential manufacturing steps and labour units needed were also incorporated. The results below show that there is a similar point of asymptotic behaviour starting around 10 units, at $9,700 per GFRP boat hull unit made by resin infusion.

Cost prediction per unit for a vacuum assisted resin infusion (VARI) procedure compared to an open mould wet layup procedure.

Outcome

Subject	Pro	Con
Cost	Resin infusion shows lower long-term costs due to material savings and efficient labor usage.	Initial setup and transition costs are high, with significant investment in equipment and training required.
Manufacturing Risk	Resin infusion reduces material waste and environmental impact.	High dependency on precise process control, with significant risk of production failure due to errors.
Employee Transition	Potential for skill development and advancement in more modern, efficient techniques.	Need for extensive training and adjustment period for employees, possibly affecting morale and productivity.

The comparison between the cost models indicates that the resin infused GFRP boat hull is cheaper to manufacture than the open moulded GFRP boat hull, by approximately 23%. However, this is only the first stage of the decision-making process, which is to ultimately move to the new material and process technology, given the potential risks apparent in the transition. In the context of this topic specifically, the company has expressed that the new technology is worth pursuing, but not without extra planning and preparation. It is believed that without it, the increased cost associated with scrap rates under the new process will exceed the baseline cost of the historic process. This has helped the company form a strategic plan for technician training ahead of the migration to the new technology.

Related pages

• See webinar on costing composite parts
• See webinar on liquid composite moulding
• See page on Materials deposition and consolidation management

Related pages

Page type	Links
Introduction to Composites Articles
Foundational Knowledge Articles
Foundational Knowledge Method Documents	How to measure gel time - M101 How to measure reinforcement content (and corresponding matrix content) - M109
Foundational Knowledge Worked Examples
Systems Knowledge Articles
Systems Knowledge Method Documents
Systems Knowledge Worked Examples
Systems Catalogue Articles
Systems Catalogue Objects – Material
Systems Catalogue Objects – Shape
Systems Catalogue Objects – Tooling and consumables
Systems Catalogue Objects – Equipment
Practice Documents	Practice for Developing a Deposition Step - P157
Case Studies	Cost Comparison Study of a GFRP Leisure Boat Hull Manufacturing Method; Spray Up vs Resin Infusion - C115 Optimizing Cost vs Weight for Low Production Volume Parts - C112
Perspectives Articles	Composite materials engineering webinar session 5 - Manufacturing processes - Introduction - A124 Composite materials engineering webinar session 6 - Manufacturing processes - Prepreg processing - A125 Composite materials engineering webinar session 7 - Manufacturing processes - Liquid composite moulding - A126 Fabric Forming: how it affects design and processing, and how simulation can address this - A310 Fibre Architecture: Availability, pros and cons, and selection for my application - A309 Pultrusion of Thermoplastic Composites - A334

References

About	Help

For polymer matrix composites (PMCs), resin refers to the matrix; the continuous material phase that binds the reinforcement together, maintains shape, and transfers load. Resins are divided into two main groups: thermosets and thermoplastics.

Vacuum assisted resin infusion (VARI) - also known as vacuum assisted resin transfer moulding (VARTM), vacuum infusion process (VIP) or often just resin infusion. VARI is a liquid composite moulding (LCM) closed mould process with a single side tool and vacuum bag where the resin is drawn through the preform using vacuum.

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.

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.

‘Preform’ is the term for the fibre reinforcement. This is the stage between the raw material form after it is processed into an architecture (fabric, mat, etc.) and becoming a composite.