Engineers designing heavy machinery such as excavators, loaders, and mining equipment must consider if the strength of the structure being designed is strong enough to meet the demands of how it’s being used in the field. Any potential of structural failure is a serious liability. In my experience, most engineering teams have developed methods to help them get by with enough margin. Their solution is often a combination of tribal knowledge, several conservative static FEA load-cases, and crossed fingers. A common solution I often heard with a customer prior to implementing improved strategies to avoid the uncertainties in a set of cooked-up load-cases was to “build it beefy”.
Nowadays simply overbuilding is an unacceptable and costly mistake and you risk your competition outsmarting your product design by better utilizing CAE technology. Many companies use Multibody Dynamics Simulation (MBD) software such as MSC Adams to predict full system dynamic performance and loads, though I find it’s very uncommon to find teams who are taking full advantage of the durability predictions that can be performed in parallel and efficiently within MBD software. The rare engineer applying durability tools within Adams may be due to the unawareness of software capabilities or lack of training. Although for seasoned experts analyzing material handling equipment, the culprit is the inherent difficulties of modeling and applying trusted loads of bulk materials within MBD software. Take a moment to consider how loads induced by bulk materials propagate through the system affecting downstream structural interactions – the requirement of an accurate bulk material load model is obvious.
A poor representation of the material loads acting on the system = not having confidence in the component loads = not having confidence in the structural durability = not having confidence in the design = build it beefy.
Adding accurate physics-based bulk material loads in CAE simulation models is now possible and straightforward with tools provided by EDEM. EDEM for Adams is a specialized product designed specifically for MBD users to quickly incorporate realistic bulk material loads in an Adams model without requiring material modeling expertise. Several workflow conveniences are included in the EDEM for Adams product, including access to a large database of bulk material model parameters, typically a challenging unknown to get started. With the streamlined modeling process and the GEMM material model database, EDEM for Adams provides engineers improved results and frees up time to focus on the core tasks of advancing product designs.
EDEM for Adams was recently used successfully on a Grab Bucket simulation project where durability predictions of several structural components were required. Grab Buckets are commonly used to transfer loose materials within a local proximity. The complexity of its linkages and clam shell bucket interactions with loose bulk material is a bit more complex than a single excavator or loader bucket. In addition, Grab Bucket linkages can produce very high internal structural loads and by including flexible parts in the MBD model Adams we can help verify if the parts are strong enough to withstand the loads produced in digging operations.
Let’s consider the digging mechanics and physics of the material handling of a Grab Bucket operation. Initially with jaws open, a pair of clam shell buckets drop onto the surface of loose bulk material. After a momentary sinking of the bucket teeth into loose bulk material a hydraulic piston is actuated and forces the two bucket halves to bite down into the material and begin to close. As the two halves of the clam shell buckets close, the motion is resisted due to friction between equipment surfaces and material, breaking bonds of non-loose cohesive material, and compressing material within the bucket volume. A Grab Bucket is unique as it is pulled downward while the bucket halves take a bite into the material. Peak loads occur as the buckets are forced to fully close. Finally, material applies an inertial load onto the system as it is hoisted and the bucket swings between positions prior to dumping.
Imagine the impossible nature of properly capturing the physics via traditional methods of functions or test acquired lookup tables. The ability to perform design iterations is severely crippled with the former standard techniques and the increased modeling time is costly. The credibility of the resulting simulation results spoils any opportunity to fully utilize a complete CAE process, including jeopardizing trust in the efficient durability analysis as direct output from the MBD software.
By letting EDEM for Adams provide the realistic material behaviors and associated loads, engineers do not need to worry about how they will capture these complex behaviors, and instead focus on optimizing their design with such loads included easier than traditional methods.
The video shows a cycle of the Grab Bucket system picking up a load of loose bulk material and transporting it prior to unloading. The structural components highlighted in blue were modelled as flexible parts in MSC Adams to increase the fidelity of the simulation results and allowed for a durability analysis within the MBD software.
To find out more about EDEM for Adams, visit this page.