Superplastic Forming (SPF) Hydraulic Presses: Producing High-Strength, Lightweight Components With Complex Geometries

October 30, 2020 - "White Papers"

SPFHydPress

 

 

Introduction

At Macrodyne, we manufacture custom hydraulic presses and ancillary automation equipment of the highest quality for our customers who are leaders in more than 45 industries. We leverage our vast knowledge of hydraulic press technology to develop custom solutions based on our customers’ unique processes and needs, attributes that have been key to our high growth rate and customer retention.

One of our unique disciplines is superplastic forming (SPF) and below we highlight the process, materials and tooling used, and provide an overview of hydraulic SPF presses in the production of high-strength, lightweight components with complex geometries.

 

What is superplastic forming (SPF)?

Superplasticity is a trait that is characteristic of metals or metal alloys, which become more malleable at high temperatures, and because of this characteristic, alloys can be stretched to much larger sizes. In the SPF process, metal sheets are exposed to inert gases like argon (extremely pure) within a vacuum system.

In SPF, gas is applied uniformly to the sheet over the cavity of the die. The material is shaped over moulds to produce the required parts, including three dimensional structures like hollow or honeycomb structures. Variable gas pressures are used to ensure desired thickness is achieved.

 

Materials and applications

Certain metals like aluminum and titanium are superplastic in nature; aluminum is superplastic at temperatures greater than 500 degrees Celsius and titanium at temperatures exceeding 900 degrees Celsius. New alloys are also emerging in the market which exhibit superplasticity even at lower temperatures.

Materials like these allow for the use of thinner sheets, thereby improving both the life of the moulds and the parts, in addition to reducing component weight and cost. When compared to traditional forming methods, SPF offers material savings (>10%), reduced tooling costs (>20%), shorter lead times, and improved part strength.

One of SPF’s greatest advantages is the capacity to produce larger, stronger, and lighter parts than a traditional hydraulic press, with fewer joints and welds. This is also due, in part, to very specific (and secret) laminate material that is used in the process, like that used in the manufacture of jet engines, for example.  

The high strength-to-weight ratio and corrosion resistance of SPF components make them ideally suited to applications in the aerospace industry. Macrodyne has supplied SPF presses that produce components for some of the world’s largest commercial aircraft programs, including wing parts, engine casings, blades, and rudders. SPF is also used to produce automotive components, medical devices, architectural panels and even golf club heads.  

A great example of SPF in action in the aerospace industry is the work that has taken place at Rockwell International. There, Ti-6AI-4V alloy was used to manufacture a nacelle center-beam frame in a single component, a welcome alternative to the eight components and 96 fasteners previously required. This simplification, using both SPF and diffusion bonding, resulted in a cost savings of 55 percent and a weight savings of 33 percent.

Diffusion bonding is another more environmentally friendly process that is used in the nuclear and aerospace industries to bond multiple sheets together in a vacuum or an inert gas environment. The solid-state diffusion process allows the molecules of the sheets to integrate at high temperatures and pressure, while retaining most of the inherent properties of the individual metals or alloys.

 

Establishing Process Parameters

The SPF process is very distinct and requires long cycle times at extremely high temperatures. The average time it takes to make one part at temperatures ranging between 930 and 970 degrees Celsius is about 7 hours.

A slow forming rate makes the process ideal for low volume production applications, though it is one of the major disadvantages associated with SPF. Luckily, advances in process technology have made way for faster throughput and improved cycles times making SPF more competitive for high volume applications like those used in automotive applications.

The chart below generalizes some of the process parameters of SPF:

 

Parameter

Range

Typical tonnage

50 – 800 tons

Typical bed size

60” x 40” to 120” to 80”

Typical pressing pressure

500 – 1000 psi

 

Example:

The tonnage specifications of SPF presses depend upon the size of the die and the component. The presses are practically clamping mechanisms, and the speeds are not the same as in normal press operation. Apart from 500 psi pressure required to open the press, the tonnage must be higher to provide proper clamping effect.

If the part is 50 inches by 30 inches in size, the part area will be 1,500 square inches. Take that 1500 square inches and multiply it by the pressure: 500 psi would equate to 750,000 pounds of pressure, or the equivalent of 375 tons. Ideally, we would design the tonnage of the press for 450 to 500 tons, with a fast closing speed of around 50 inches per minute, fast return 50 inches per minute and pressing 1 to 5 inches per minute.

It is important to ensure that the materials are of uniform thickness across the entirety of the area of the sheet to ensure uniform tensile strength is retained. The process must also accommodate for the effects of spring back which tends to occur once the pressure is released during the production process.

Likewise, galling can occur when friction and adhesion are present, which causes localized roughness and other surface defects. This is particularly true of aluminum when it is heated to a superplastic state and is subject to compressive forces. To prevent the intermediate material from adhering to the mould, which causes variations in the material flow as it is stretched, use a high-temperature lubrication to limit the friction and mitigate the risk of galling.

 

Hydraulic SPF Press Design

A hydraulic press specifically designed for an SPF application is at the core of any SPF operation. There are several key SPF press features that will have implications on the process outcomes:

  • Accurate and repeatable argon gas pressures and multi-zone temperature control. These are critical elements of a successful SPF operation. To maximize effectiveness of these systems, flexible and repeatable press control systems are required. Precision gas management systems include heat exchangers for hot gas cooling during exhaust and provide accurate and repeatable argon gas pressures.
  • Innovative hydraulic and control features allow press tonnage to be increased proportional to the argon pressure rise and vice versa to minimize loading of the die seals. 
  • Highly efficient heat shields and ceramic insulation are standard on Macrodyne SPF presses and provide optimal insulation of high temperatures resulting from the process while ensuring long component life and operator safety.
  • Specialized plunger guide arrangements comprised of central plunger type guide assembly and temperature compensated guide bar/anti-rotate arrangement located in the crosshead provide enhanced guiding of the moving platen.
  • Advanced control systems easily manage process variables including multi-zone temperature control ensure successful superplastic forming operations.
  • High speed data acquisition systems provide increased access to process variable information and optimize integration of data between the press and the Buyer’s internal networks.
  • Rolling bolsters are available for rapid and safe changing of dies. They are customizable and are available in single- and double-die configurations for single direction or T-type travel.

Presses are available in standard configurations or can be customized to suit the Buyer’s specific requirements, regardless of the size or complexity.

 

Conclusion

Whether you are new to the SPF process or represent a company with extensive experience with the application, we encourage you to contact us today to learn how we can work with you to optimize your production environment and help you achieve best-in-class part quality at higher volumes and lower costs.

To learn more, visit our website at https://www.macrodynepress.com/hydraulic-presses/super-plastic-forming-presses  

Featured Industries
Move to Top