Case Study: DART – automated residual stress measurement

Our latest case study highlights the many benefits of the DART™ automated measurement system, a tool we at Hill Engineering developed specifically to improve near-surface residual stress measurement techniques such as hole drilling and TRUEslot®.

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DART – automated residual stress measurement

Near-surface residual stress data is critical when assessing material performance, optimizing design, validating models, evaluating field failures, and executing quality assurance programs. Hill Engineering’s DART™ is an industry-leading tool for efficient, precise, and reliable near-surface residual stress measurements. The DART™ overcomes limitations of existing residual stress measurement equipment and includes everything required to perform state-of-the-art measurements in accordance with industry specifications.


Hill Engineering’s DART™

A single DART™ can perform near-surface residual stress measurements using multiple techniques including hole drilling
and TRUEslot® methods. This flexibility is helpful when requirements change or new applications arise. The DART™ executes hole-drilling residual stress profile measurements in accordance with ASTM E837, providing a depth profile of the three in-plane residual stress components in a single measurement. TRUEslot® is a novel technique, like hole-drilling, but simpler and more precise. TRUEslot® provides a depth profile of one stress component per measurement.


Hole drilling measurement example


Hole drilling results example

Intuitive
Residual stress measurements with the DART™ are easy to complete. A user interface guides you through set-up, then takes over for automated measurement execution and residual stress calculation.

Efficient
With measurements completing in less than 60 minutes, the DART™ excels in the production quality management environment. Automated data capture, processing, and archiving provide you with residual stress results instantly.

Reliable
Featuring advanced cutting strategies and real-time quality checks, the DART™ gives you confidence in your residual stress data.

Features
• Hole drilling residual stress measurements according to ASTM E837
• TRUEslot® residual stress measurements
• Positional accuracy: ± 0.001 in.
• Works on most materials including: aluminum, titanium, steel, stainless steel, and nickel alloys
• Custom fixtures can be integrated to meet the needs of individual applications
• NFPA 79 compliant

Software

Each DART™ includes a complete software package that enables efficient and repeatable residual stress measurements for high-volume or single-use applications. DART™ software is designed for ease-of-use, while maintaining flexibility to meet your measurement needs and providing controls to maximize reliability. An operator defines the measurement location, the type of measurement (TRUEslot® or hole-drilling), and inputs the key measurement details. Following set-up, the software automatically controls the incremental material removal process, acquires the experimental data, computes residual stress, and outputs a test report. The entire process is significantly more efficient than other available tools.

DART™ produces the highest-quality residual stress data available
Precise engineering and extensive use of automation within the DART™ provides a demonstrated 50%+ improvement in measurement repeatability relative to other hole drilling test equipment. Hole drilling and TRUEslot® measurements performed using a DART™ have been shown to be 60%+ more repeatable than X-ray diffraction measurements.


DART™ outperforms its competitors in RS measurement repeatability

The DART™ has proven to meet our high internal standards for data quality and is currently in use in multiple facilities throughout the world. It could be in your facility soon.

To place an order for DART™ related goods or services, please contact us.

Download a DART™ brochure here

DART™ and TRUEslot® are protected by US Patent 10,900,768 and are patent pending for other international jurisdictions.

Hill Engineering awarded patent for innovative DART system

Hill Engineering was recently awarded US Patent 10,900,768 for residual stress measurement technology. Granted on January 26, 2021, the title of the patent is “Systems and Methods for Analysis of Material Properties of Components and Structures Using Machining Processes to Enable Stress Relief in the Material Under Test..” The patent abstract is available below. There is a link at the end to download and read it in full.

Continue reading Hill Engineering awarded patent for innovative DART system

Rapid Forge Design brochure

Hill Engineering’s Rapid Forge Design is an automated tool for the fast and reliable design of 2-piece, closed-die impression forgings. The brochure below provides a rundown of the highlights from this powerful software, which can drastically reduce the time needed to design a forging to industry-accepted standards.

Continue reading Rapid Forge Design brochure

Mechanical stress relief of aluminum alloys

As we discuss in a related case study, aluminum alloy heat treatment is a three-step process designed to achieve the desired properties. The process involves: 1) solution heat treatment (SHT) at an elevated temperature below the melting point, 2) quenching in a tank of fluid (e.g., 140-180°F water), and 3) age hardening. While providing good properties, the heat treatment has the negative side effect of creating bulk residual stress and distortion. These side-effects are a direct result of non-uniform cooling during the rapid quench. One approach to mitigate this problem is the application of a post-heat treatment mechanical stress relief process. In addition to modeling the heat treatment process, our analysis tools can support evaluation and optimization of mechanical stress relief processes.

Mechanical stress relief is practical for many aluminum alloy products as a means of reducing bulk residual stress. For products with a uniform cross section, such as most extrusions, plate, and bar stock, the material can be stretched on the order of 1% to 5% using special equipment. The figure below shows an example extrusion section with bulk residual stress (top) along with the remaining residual stress after mechanical stress relief (bottom). Note, the use of different color scales because the residual stress magnitude changes so significantly. This figure illustrates our capability to model post-quench and post-stretch residual stress.


Illustration of predicted post-quench (top) and post-mechanical-stress-relief-stretch (bottom) in the long direction of an example aluminum extrusion

For other products such as forgings, an alternative stress-relief process using a compressive cold work stress relief can be employed. For a hand forging this is usually achieved using open-dies comprised of mostly flat surfaces. Post-quench, the hand forging is subjected to 1% to 5% compression often in an overlapping fashion.

On the other hand, an impression-die forging usually requires a more complex process that involves a cold-work die set. Such die sets are designed to impress 1% to 5% cold-work. Typically, the compression is on the order of 1% in thinner web sections and 3% in thicker rib sections. Since the forging will be at room temperature for the compression (therefore the term – cold-work) it does require higher press loads than one sees in the hot forging operation. The following figure illustrates the elements of a cold-work die set.


Illustration of a typical cold-work die set for mechanical stress relief of an aluminum forging

In a previous case study, we demonstrated our capability to predict post-quench residual stress and distortion for an example forging. The effect of mechanical stress relief using compression dies on that same example forging is shown below. The post-quench residual stress (left) reaches as high as 20.0 ksi in this aluminum 7075 simulation. The post-cold-work residual stress (right) is significantly reduced. The reduced residual stress level in the stress-relieved state has significant advantages in terms of ease of machining (reduced distortion) and improved part performance.


Predicted residual stress post-quench (left) and post-cold-work-stress-relief (right) for an example aluminum forging

If this example relates to your production challenges, or if you have any questions about how these results might affect your projects, please do not hesitate to contact us. We would also be happy to answer any questions that you may have.

Case Study: Aluminum forging cold-work stress relief

As we discuss in a related case study, aluminum alloy heat treatment is a three-step process designed to achieve the desired properties. The process involves: 1) solution heat treatment (SHT) at an elevated temperature below the melting point, 2) quenching in a tank of fluid (e.g., 140-180°F water), and 3) age hardening. While providing good properties, the heat treatment has the negative side effect of creating bulk residual stress and distortion. One approach to mitigate this problem is the application of a post-heat treatment mechanical stress relief process.

Continue reading Case Study: Aluminum forging cold-work stress relief

Rapid Forge Design

Hill Engineering’s Rapid Forge Design™ software is an automated tool for fast and reliable design of 2-piece, closed-die impression forgings. Rapid Forge Design™ reads the final part geometry and automatically designs a forging according to accepted industry guidelines and user inputs. Rapid Forge Design™ is intended for use by forging suppliers and forging consumers/OEMs.

The Rapid Forge Design™ software comes with a user-friendly, graphical interface that allows for forging designs using a simple, 3-step, menu guided approach.

Download a fully-functional demo version of Rapid Forge Design™.

 

Illustration of Rapid Forge Design™ user interface

The inputs to Rapid Forge Design™ are the 3D geometry of the machined part (to be manufactured from the forging) and critical, user-defined parameters that allow for customization of the resulting forging design (e.g., minimum thickness and minimum radius values).

The forging design is generated by Rapid Forge Design™ according to a set of prescribed, industry-accepted design rules. After the user inputs are provided, the automated forging design process is completed by Rapid Forge Design™ in minutes without any further user intervention. With this approach, Rapid Forge Design™ enables the design of forgings with significantly less effort than existing manual processes.

Rapid Forge Design™ outputs the 3D geometry of the forging and a host of useful forging statistics and properties including volume, plan view area, periphery length, heat treatment section thickness, and other dimensional information. These metrics are essential to support the quoting process (material producers) and planning and costing activities (OEMs).

The preliminary forging designs produced by Rapid Forge Design™ can be used as the starting point for the finished forging’s more detailed design and tooling CAD files.

The Rapid Forge Design™ process is outlined in the flowchart below. The operator can input and customize important design parameters including: web thickness, draft wall cover, draft wall angle, plan view radius, fillet radius, and corner radius. Default values are provided based on alloy dependent industry standards. Help menus provide additional support and guidance, where necessary.

 

 

 

Summary of Rapid Forge Design™ workflow

Numerous examples taken from publicly available CAD files come with the software. The following are a few illustrations showing the ability of Rapid Forge Design™ to effectively produce forging designs for a wide variety of supplied final part geometry.

 

Illustration of forging designs produced by Rapid Forge Design™ (gold) along with the final machined part geometry that was used as the input for design (grey)

Download a fully-functional demo version of Rapid Forge Design™.

To place an order for Rapid Forge Design™ related goods and services, please contact us.