As technology advances it is critical that the design, manufacture and testing of parts and components is undertaken in an increasingly meticulous manner. For example, in such high-cost and mission-critical sectors as aerospace it is important that the equipment functions efficiently during long cycles of operation often under extremely high pressures. It is therefore imperative that this equipment offers the highest levels of reliability and efficiency. After all, if a part or component fails in an aircraft there is a chain of potentially serious repercussions to consider; not least of which being the safety of people on-board.
The importance of quality, efficiency and accuracy may seem obvious; however as someone who has worked in the product testing industry for many years I still see what are in essence very fundamental mistakes being made, which have potentially serious, even hazardous, consequences further down the line. These mistakes often occur in the early stages of development during product design.
Paying attention to the fine detail at this stage is vital; because the prototyping, manufacturing and testing procedures that follow can be seriously jeopardized if an error is made ‘on the drawing board’. This can be a particularly serious issue when equipment designed to work under high pressures is involved and has to go through a series of cyclic fatigue tests before the equipment can be supplied to the customer.
Designers may be very able in terms of preparing a highly detailed design of a product or component as 3D model in a computer design package factoring-in the right materials and coatings to provide the appropriate stress rates and other material properties such as dimensions and weight. However, what needs to be constantly borne in mind is that every detail drawn in those designs will need to be carried through to manufacture. It only requires the slightest error or oversight related to a small part or component for serious problems to occur further down the line.
For example, a thread may not have been fully finished off or placed precisely in the right position; an O-ring may have been placed without careful thought to where the groove is positioned in relation to the rest of the thickness of the material. And it only requires a bolt to be put in the wrong place on the flange or for a radius to be not quite right. When these errors occur serious performance or lifecycle issues can arise.
Of course, design isn’t the only area of product development that can be at fault. The performance of equipment will also rely very heavily on the quality and suitability of the material that is used to make it. The required performance or resilience levels cannot always be guaranteed, which again could introduce safety or operational concerns. These concerns may mean that secondary finishing operations are required to enhance the surface strength of the material that is used for the manufacture of the outer casing of the equipment processes such as laser peening or anodizing to increase the thickness of the oxide layer on the metallic surface.
This material has to work and has to be proven to work. However, if the manufacturer totally relies on these types of secondary finishing processes and the material doesn’t function to efficiency levels required, then the customer is going to be let down in terms of service. This is when efficiency and safety factors can appear. Therefore, it is always advisable that materials and coatings used in such high-cost and high-performance sectors as aerospace are subjected to thorough cyclic fatigue tests.
Another thing to bear in mind is when product and material tests are carried out, dangerous assumptions can sometimes be made. For example, it might be assumed that a standard type of, say, aerospace oil could be used for certain types of equipment. However, there only needs to be a slight change in chemical composition before the equipment could not only experience a cyclic fatigue attack affect but could also seriously affect the efficiency and lifecycle of the product.
The good news is that there are proven test houses that specialize in providing these types of services. Also, the British Fluid Power Association (BFPA) and British Standards Institution (BSI) among other established industry bodies are keen champions of best practice with regard to the fatigue testing of pressure-containing envelopes etc. Further guidance for designers, manufacturers and product testers is also available in the form of the standard ISO 10771, which specifies a method of fatigue testing the pressure-containing envelopes of components made from metals which are used in hydraulic fluid power systems under sustained steady cyclic internal pressure loads. Additional requirements or more specific methods that can be required for particular components are contained in other standards.
We all live in an increasingly virtual world, where computerization is playing an ever greater role within design and manufacturing disciplines. We only have to consider cutting-edge concepts such as Industry 4.0, the Internet of Things and the Smart Factory to realize this is the way forward. However the end result of product design and material specification is still a physical product that has to meet the exacting requirements of its intended use. This is a quality issue that has to be taken very seriously.
We will always continue to push back the technological frontiers, but alongside this pace of change design and manufacturing procedures, as well as industry standards, have to be revised when necessary in order to accurately reflect the changes in products and how they are used under increasingly challenging conditions for example, products that encounter ever-larger levels of cyclic fatigue. Also, new product tests need to be established that are more representative of what is on the market today, and with an eye to what is likely to be launched to market in the future. In this regard, companies such as BHR Group, and industry bodies such as the BFPA and the BSI, must continue to bang the drum of high standards regarding design, manufacture and testing quality and integrity.
The devil really is in the detail of converting designs successfully into the manufactured product, and cutting corners is never an option even though, as commercial concerns, companies may be driven by margins and profit goals. However, with a thorough and accurate design and materials testing regime in place, equipment can be made fit for purpose; functioning efficiently and safely over many years of use.
About the author
Mark Fairhurst is the technical director at BHR Group. He is presently the vice-chairman the product testing committee of the BFPA/BSI, and the chairman of the Technical Advisory committee of the Water Jet Technology Conference.