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Managing Porosity Is All Part of the Business

April 1, 2022
Fixing casting defects is all part of the process for metalcasters and their most valuable customers, meaning they have decisions to make in order to identify the most efficient, cost-effective approach to sealing castings.

It is widely accepted that porosity is almost impossible to prevent during the metalcasting production process. Variables such as molten material volume, flow, pressure, trapped gases and the presence of die-release agents all contribute to the creation of porosities at varying times throughout the cycle. Usually invisible to the naked eye, the tiny holes that are micro-porosities can undermine the quality of cast components to a critical degree by providing a path for liquids or gases to leak through the finished part.

In any precision-manufacturing setting – including automotive design and manufacturing – this presents significant problems. When these imperfections are identified on site, the result is scrap and waste as well as the attendant implications for cost and productivity.

Sealing castings is the accepted resolution to the problem of porosity, and there are different methods to accomplish that. With the vacuum impregnation process the components are placed in an autoclave. A vacuum is applied to remove the air from the chamber, and then after a period of time the components are immersed into the sealant. The vacuum is used to draw the sealant into the micro-porosities and leak paths. Then, the components are washed and finally sealed in a hot cure process, which turns the liquid into a chemically and thermally resistant polymer.

The process helps eliminate casting waste and scrap, and it improves the performance and reliability of parts. Therefore, for many casting manufacturers and casting buyers there is no question of whether to adopt impregnation. However, they must decide which impregnation process is the best for their business.

Routes to sealing porosity

Essentially, there are three routes to sealing porosity, each with its own advantages: outsourcing the work to a vendor, investing in sealing process equipment, or engaging an on-site managed service.

With outsourcing, components are shipped to a sub-contract service center and then returned after impregnation. This means there are logistics costs and potential delays as parts are processed off site – even when the centers are located nearby. Add to this the potential for damage during transit, along with the administrative burden of tracking parts.

There’s also a potential need to keep in stock a higher volume of work-in-progress. And, when the sealed castings are returned, the onus of inspection remains with the manufacturer. For many larger operations, this overall lack of control over the impregnation process is an issue, and so outsourcing tends to be the preferred option for either smaller volume manufacturers or their casting suppliers.

Organizations with high-volume requirements generally opt for an in-house or on-site managed service. But which is best? As vacuum impregnation demands specialized equipment, chemicals, and expertise, it’s a question that demands careful consideration.

In-house impregnation services

The benefits of an in-house impregnation service are clear. It gives manufacturers their own dedicated service plus total control over the process. Over time, they will achieve return on investment, helping lower the total cost of ownership.

On the other hand, in-house impregnation capability involves a significant upfront capital investment, together with maintenance. Impregnation equipment needs ongoing attention, including daily machine and chemical checks, and regular servicing of filters, pumps, and gearboxes. Even the best qualified teams may not have sufficient knowledge to tackle such specialized equipment, while the added work can detract from core activities.

The same issues apply to the in-house impregnation team. However well-trained they may be, they’re still likely to be faced with new challenges they might not be immediately equipped to handle, such as dealing with unusual casting geometries, modifying cycles, and even trouble-shooting or optimizing equipment efficiency. None of these are insurmountable, but they can complicate the process.

There’s also the question of space and the storage of chemicals, which again need special attention. Essentially, impregnation is a chemical function, not a mechanical one, and so it sits outside the core of most diecasters’ or automotive manufacturers’ capabilities. Even with total commitment to the facility, there’s likely to be a huge learning curve.

Finally, the question of inspection again lies with the manufacturer, and it brings with it a degree of uncertainty and risk.

A new way forward

Considerations such as these mean that many manufacturers are turning toward a ‘managed service’ approach, which combines the benefits of in-house and outsourced impregnation without the upfront costs, ongoing commitment, or responsibility for inspection. Over recent years, Ultraseal has seen a steady global rise in demand for managed services from both manufacturers and their suppliers.

In Portugal for example, a manufacturer of air-conditioning compressors commissioned a managed service with the express objective of being able to focus exclusively on core business activities. Impregnation was vital to them, but also an unnecessary distraction. Ultraseal established a dedicated porosity sealing facility on-site, built around their exact component requirements and deploying state-of-the-art technology. Staffed with Ultraseal employees who are fully responsible for managing the operation, this ensured high-quality service and peace of mind, without ‘hands-on’ involvement.

While there is no upfront investment, commissioning a managed service is nonetheless a significant commitment, and before deciding on whether it’s the right choice it is worth considering the key points in some detail.

Equipment and maintenance. Impregnation equipment is specialized – and evolving. With a managed service, there are no upfront capital costs and no need to continuously update technology. All costs associated with these activities are eliminated, freeing working capital for core activities.

Moreover, with Ultraseal’s managed service, all repairs and maintenance are undertaken by Ultraseal’s own trained and fully qualified experts, ensuring a professional, right-the-first-time approach to minimize disruption and downtime caused by breakdown. The manufacturer is relieved of all responsibility for the equipment, freeing up their own valuable in-house maintenance teams.

Labor and inventory. With a managed service, there are no labor costs or associated overheads – including training – for the manufacturer to worry about. Fully employed by Ultraseal, the team is familiar with how to pack and load parts into the system and machine parameters to optimize performance and quality. They are led by a manager with responsibility for integrating the service seamlessly within the plant’s operations.

A managed service also assumes responsibility for purchasing and storing chemicals, eliminating risk. In Ultraseal’s model, no charge is made for chemical usage. Instead, a fee is charged as a ‘job shop’ expense according to either the weight or number of components that are processed. This provides transparency, as well as simplifying transactions.

Logistics. A managed service, based on-site or nearby, minimizes logistics costs and the potential for damage during transit, while also improving lead-times and productivity. The net result is greater supply chain control.

Along with this, with better lead times, businesses need not hold on to additional stock or work-in-progress inventory while waiting for components to return from processing. This is a traditional challenge, and accepted risk, with outsourcing.

Safety and sustainability. Sustainability is a key focus for automotive manufacturers. In addition to a pioneering range of recycling chemicals, Ultraseal also introduced the world’s first closed-loop vacuum impregnation system, capable of recycling 95% of chemicals – which ordinarily would be flushed away with wastewater. Research is ongoing, and a managed service ensures that best practice and innovation are continuously available to ensure compliance and protect investments and people.

Inspection. With in-house and outsourced services, responsibility for quality control and inspection ultimately sits with the manufacturer, who might not necessarily have the depth of technical experience required. With quality, it’s the detail that matters, so while it’s always important to remain invested in this aspect, it can help to devolve responsibility to an expert. This is what’s provided by Ultraseal through the managed service, helping eliminate risk and increasing confidence in component quality.

Benefits versus service costs

With gains in quality, confidence and component performance, and incremental cost-savings in terms of lead-times, logistics and staff, it’s clear that there are very real benefits to investing in a managed service.

While these benefits are compelling and are becoming more widely appreciated by the automotive sector, the advantages must be carefully weighed against the actual costs of the service.

Managed services are governed by KPIs and contracts, typically involving agreed order levels. If these are not reached, there can be financial implications. So, it’s a model that is best suited to manufacturers with predictable (generally daily) volumes. Where there is infrequent or variable demand, other approaches may be more suitable.

Whatever your requirement, Ultraseal is committed to delivering a responsive service focused on high-quality porosity solutions and lower total cost of ownership, helping automotive manufacturers drive efficiency and performance improvements.

John Holmes is the Applications Sales Director – Impregnation for ‎Ultraseal International.