Hydraulic block manifold redesign for additive manufacturing

Renishaw recently collaborated with a customer to redesign a hydraulic block manifold with additive manufacturing in mind. The main goal of the project was to reduce the mass of the existing component while retaining its robustness. Due to the increased design freedom associated with additive manufacturing, an opportunity to increase the efficiency of the flow paths was also identified.

A hydraulic block manifold directs the flow of fluid in a hydraulic system, linking valves, pumps and actuators. It enables the design engineer to manage the operation of a hydraulic circuit while combining the components in a compact unit. Traditionally, hydraulic block manifolds are manufactured from an aluminium alloy or stainless steel billet which has been cut and machined to size, followed by drilling to create the flow pathways. Specialised tooling is often needed due to the complex drilling that is required. Passages require blanking plugs to properly direct flow through the system.

The nature of the manufacturing process results in abrupt angled junctions between flow paths, which can cause flow separation and/or stagnation – a major contributor to efficiency loss. Aluminium alloy manifolds are generally less costly due to lower material costs and ease of machining, but they can be less abrasion-resistant, and so any loose particles in the flow will abrade the surface and increase wear. For this reason, stainless steel manifolds are sometimes more desirable. However, due to the higher density and hardness of stainless steel compared to aluminium alloy, these come with a significant weight increase and added cost of machining.

Benefits of additive manufacturing

• Optimised flow paths for a more efficient component functionality.
• Ability to fully utilise computational fluid dynamics (CFD) to aid the design process.
• Reduction in the requirement for fixturing.
• Minimal requirement for removable support structures.
• Significant weight reduction is achievable.
• No requirement for block extraction passages.
• With full design freedom, a manifold can be designed to pack into a significantly smaller volume.

Direct benefits to customer

• Mass reduction of up to 79%.
• Single piece construction, fewer opportunities for defects.
• Rapid design and development iterations.
• Compatibility with existing design.
• Improved flow efficiency of up to 60%.

Design scope

Additive manufacturing allows a higher level of design freedom, so the component geometry could be adapted to reduce material mass and improved functionality, within the same space. Renishaw was given certain design and function guidelines by the customer, which had to be considered when redesigning the component:

Geometry

• Defined connection ports.
• Inner diameters of flow passages.
• Wall thicknesses of the flow passages.
• Fixture points and interfaces.

Function

The customer’s main requirement was weight reduction, while still maintaining its rigidity and functionality. Renishaw design engineers also recognised scope in the redesign for additive manufacturing to improve the efficiency of the flow paths within the system.

First design iteration

The first step was to de-construct the part into just the essential passageways that provide the functionality of the hydraulic block manifold. The flow paths of the original cross-drilled design were extracted using computer-aided design (CAD) software, and any drilled areas that are not required for the flow path were removed, leaving the essential pipe network. Each hydraulic circuit was then reduced and simplified in preparation for piece-wise computational fluid dynamics (CFD) analysis, using SolidWorks Flow Simulation.

Next, the flow paths were optimised after identifying areas of flow separation and stagnation gained via CFD analysis.

Wall thickness was then generated, in this case based on the customer specification, but alternatively this could be done by using finite element analysis (FEA) stress modelling based on pressure readings taken during CFD analysis.

Finally, permanent support structures were designed and added in to the CAD geometry, creating a self-supporting, efficient structure. Generally support structures are added to a final geometry in post processing of the component design in order to anchor the object to the baseplate and dissipate heat. However, making the supports part of the component design reduces the potential waste material associated with removable support structures or anchors.

The first design iteration resulted in a reduction in volume of 52% compared to the original block manifold, as well as an improvement in flow efficiency of up to 60%. CFD analysis informs the designer on the theoretical efficiency of the fluid flow of a system based on the interaction of liquids and gases.

Second design iteration

The first iteration was built at Renishaw and evaluated by the customer, who assessed the new geometry in the context of its function as a hydraulic manifold; the original manifold is designed to be used modularly, with multiple units installed in series. Individual hydraulic block manifolds will occasionally need to be extracted from the line-up for servicing; making it necessary to include threaded ‘block extraction’ passages. The first iteration for additive manufacturing geometry has features that an engineer can use to extract the manifold manually without the use of tools, negating the requirement for the block extraction passages.

While the removal of these block extraction passages from the CAD model immediately disrupted the intricate network of self-supporting structures, this was seen as an opportunity to redevelop the design. It had been suggested that iteration 1 might be subjected to flexure, torsional distortion and/or chatter during machining due to the now reduced volume of material relative to a solid block. While simultaneously increasing its stiffness, the redesign resulted in a final manifold that was just 21% of the volume of the original.

This significant reduction in volume now opened up the option of producing iteration 2 in the more desirable stainless steel 316L. This resulted in a net reduction in weight of 37% even in a material with higher density (8 grams per cubic centimetre for stainless steel, and < 3 grams per cubic centimetre for aluminium alloy).

To get the best possible components from an additive manufacturing process, the user needs to understand that designing for additive manufacturing has a higher level of freedom compared to traditional manufacturing techniques such as subtractive machining and casting. Renishaw provides training and design for process support even after the purchase of an additive manufacturing system. For companies who are considering integrating additive manufacturing into their production processes, Renishaw’s global Solutions Centres act as a gateway to entry. Renishaw Solutions Centres provide secure development environments in which customers can expand their knowledge and confidence using additive manufacturing technology. They will be equipped with the latest additive manufacturing systems and staffed by knowledgeable engineers to allow fast access to deploying the technology, all at fixed predictable costs.

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