Caterpillar Inc., Peoria, Ill., cut waste and weld fumes associated with creating "in-iron" prototypes using advanced 3-D graphic welding process simulation software.

VFT software is used routinely for product and process design on new structures at Caterpillar.

VFT reduced the design cycle of this 160H motor grader drawbar from six months to one month.

A new design for this wheel skidder frame was based on a VFT simulation.

For years, Caterpillar Inc., Peoria, Ill., relied on the old trial-and-error method to establish fabrication and manufacturing processes. However, the tried-and-true approach required significant material, energy and labor. In addition, the firm had to test numerous "in-iron" prototypes that produced waste and weld fumes before creating a successful new fabrication process.

Recently, Caterpiller engineers created Virtual Fabrication Technology (VFT), as an alternative. "VFT was developed for the simulation of welding-induced distortion in a program sponsored by the National Institute of Standards and Technology, which dealt with advanced structures using intelligent and synergistic materials processing," explains Zhishang Yang, an engineer in Caterpillar's Technology and Solutions Division. It allows engineers to develop optimal designs without resorting to "in-iron" prototypes.

"It has been extended for simulation of other thermalmechanical processes such as thermal cutting and forming," he adds. The software is available to other companies through a license agreement with Battelle Memorial Institute.

Here is how VFT works
Developed by Caterpillar and Battelle Memorial Institute,(BMI) Columbus, Ohio, for prediction of weld distortion in large and complex structures, the simulation is accomplished by sequentially coupling thermal and mechanical analysis.

The thermal analysis is conducted using a Comprehensive Thermal Solution Package (CTSP) developed by Caterpillar and BMI, while the mechanical analysis is conducted using Finite Element Analysis software from ABAQUS Inc., Providence, R.I.

Two essential elements of VFT include CTSP and a customized User Material Subroutine in ABAQUS for weld-structure analysis.

According to Yang, Caterpillar conducted extensive validations and refinements using both simple welded plates and complex welded structures.

Using VFT, Caterpillar simulation engineers manipulate weld models on-screen. They define weld passes and sequences, and automatically generate relevant input decks for the CTSP for thermal problem solvers and ABAQUS for structural problem solvers.

VFT uses commercial software (CUBIT for meshing and ABAQUS for thermal and mechanical analysis), as

well as in-house codes (CTSP for quick thermal analysis and customized UMAT for structural analysis). The solid model is prepared with Pro Engineer software from PTC Needham, Mass.

Caterpillar's application
Caterpillar primarily uses VFT in welding distortion prediction and control in large fabricated structures for their construction equipment products.

The simulation predicts welding distortion in large and complex fabricated structures, helping to keep welds within design tolerances by optimizing weld sequence, clamping, fixturing, weld direction and sizes, and eliminating the post-welding machining process.

"That is a significant cost savings for large welded structures that would otherwise need machining in a large and expensive machining center," says Yang.

The novel becomes routine
The VFT software worked so well for large structures it soon became a routine procedure in concurrent product and process design for smaller components as well.

For example, a new frame design for a Caterpillar Log Wheel Skidder was proposed based on a VFT simulation. "In the case of the Wheel Skidder, a stiffer frame was chosen based on the welding distortion simulation," recalls Yang. A stiffer frame improves maneuverability and product durability in rough logging terrain.

"The design tolerance for the welding distortion in the vertical plate was 3 mm," said Yang. "If that design had been used, the welding distortion would be more than 15 mm, preventing product assembly during manufacturing. After redesigning the shape of the vertical plates, the weldinginduced distortion was controlled to less than 3 mm, enabling the manufacturing assembly goals to be achieved."

Ironing out the wrinkles
VFT provides a virtual design environment so that tests previously conducted "in iron" at the fabrication shop no longer require multiple prototypes. VFT also enables engineers to study many "what if" scenarios to identify unforeseen flaws and optimize processes prior to fabrication.

Caterpillar used VFT on more than 15 fabricated components over the past six years. VFT optimized welding, thermal cutting and bending processes, while boosting product performance. In all, the firm saved 200,000 pounds of steel and 13,000 pounds of welding consumables, eliminated 28 pounds of weld fume from 30 applications, and reduced the need for re-work and saved on scrap during the production phase of manufacturing. Eliminating "in-iron" shop tests also improved worker safety by reducing exposure to welding fumes, particulates and waste.

The 160H Motor Grader drawbar
VFT boosted Caterpillar's design cycle of its 160H Motor Grader drawbar. The drawbar is a critical component enabling the motor grade to break up hard soil with the ribber attachment. The design cycle for the component was reduced from six months to one month, dramatically improving productivity while reducing labor, operation and material costs, and speeding Caterpillar's 160H Motor Grader to market.

VFT also fosters more innovative design, as was done in Caterpillar's Backhoe boom side plate.

The economic benefits of VFT include the reduction in material use, as well as a savings in energy, labor and capital investment. For example, energy savings could be realized by only applying as much weld as needed with the electric arc weld machines to achieve the desired results and avoid a "trial and error" approach to identify what works. Up-front VFT analysis can reduce or eliminate costly and time consuming mock-up builds to evaluate the weld process and flame straightening sequences.

For the 30 projects that have used VFT to date, the cost savings are estimated at $3.5 million, of which $1.1 million, or 35 percent, is attributable to energy efficiencies.

VFT is now routinely used for new process and product design at Caterpillar and has been identified as one of the "core competencies" of Caterpillar's manufacturing technologies. In addition, VFT has been introduced into various Caterpillar facilities including plants in France, England, Mexico and Japan.

VFT can work in any industry in which metal fabrication plays a key role, such as shipbuilding, automobile manufacturing, nuclear piping, aerospace applications, and railway and bridge construction.

An up-close look at VFT’s features VFT has a rich set of graphic user interface components including pull-down menus, toolbar buttons, drop-down lists, pop-up menus and dialog windows. In addition, all components are integrated with a graphics window for 3-D rendering and manipulation, making the welding simulation process easier. The major features of VFT Version 1.0 include: Platform-independence. VFT will run on all platforms Windows 95/98/NT/2000, Sun/Solaris, HP, Linux) where Java Virtual Machine can run. 3-D graphics rendering and manipulation capabilities. VFT renders 3-D finite element solid models. It also provides a set of graphics handlers to allow such functionality as graphics rotation, translation and zooming, including target zooming quickly enlarge a specific area of interest. FE model importing functionality. VFT can import any D finite element solid model with the node coordinate and element connectivity definitions. Neutral VFT file. VFT saves the weld model and other data in the form of serialized Java objects. Object drop-down list. For the convenience of viewing each individual object created during the session, VFT provides a drop-down list of the names of all objects created in the session. Contents of the drop-down list are dynamically expanded or shrunk according to the user’s activity when either creating or deleting objects. Element picking capability. VFT provides the capability of picking elements from the mesh. When the picking toggle is on, the user can pick any visible elements from the mesh using mouse point-and-click selection. Display of neighboring elements. VFT displays all connecting neighbor elements associated with a picked element. This functionality can be used to make a hidden (inside) element visible when picking of such hidden elements is needed. Refresh capability. VFT provides the refresh capability to update the graphics display on the screen. Weld-pass definition function. VFT uses a pop-up dialog window for the user to define weld pass. This dialog window contains a tabbed pane with input fields for all necessary weld attributes. These attribute fields include welding start/stop positions, welding direction, plate thickness and normal, and welding parameters such as current, voltage and speed. The dialog window also includes other CTSP-specific attributes such as joint type, heat source and edge effects. Weld-element searching mechanism. A weld element searching mechanism is built into VFT to define weld elements for a specific pass. To define a weld pass, the user is only required to provide start section elements and one stop section element in the weld creation dialog window. With the information of weld start/stop ends and welding direction, VFT automatically searches and finds all other elements within this weld pass, whether linear or nonlinear. Weld-pass edition and sequence. VFT provides the functionality to edit and sequence the defined weld passes. A pop-up dialog window shows a list of the weld pass names in a scrolled pane. The user can use the editing and sequencing buttons in the dialog window (e.g., Update, Delete, Edit, Sequence, Move-Up and Move-Down) to edit weld attributes and sequence weld passes. Weld-pass sequencing preview. VFT allows the user to preview the weld-pass deposition sequence in the main graphics window. A small pop-up control window guides the user to deposit the next pass or remove the previous pass in the display. Material and welding parameter definition/edition. VFT defines and edits weld material properties and welding parameters. The functions are defined in pop-up dialog windows. CTSP and ABAQUS exporting functionality. VFT provides the functionality to export the defined weld model to CTSP and ABAQUS for welding heat flow and residual stress/distortion analyses. It generates CTSP and ABAQUS input decks automatically. On-line help. VFT provides on-line help documents for the GUI program as well as CTSP and ABAQUS UMAT documents. Additional features. VFT also offers background color change, FE model node and element ID displays.

Information for this article was provided by Caterpillar Technology Licensing; Phone: (309) 675-4306; E-mail: corporate_licensing@cat.com, Web: catlic.com