Remmele Engineering, Inc., a builder of automation ~ systems in St. Paul, Minnesota, is using a computerized engineering handbook to calculate geometric and material properties of structures. This approach allows users with various levels of training to quickly and accurately obtain answers to questions which might be very difficult with a conventional paper handbook.

Since its founding in 1949 Remmele has done business in two areas. The first is a job-shop machining business that manufactures some of the biggest and most complex tooling and parts in the country. The other business is the design and fabrication of special machines. Most of the machines built by Remmele are one-time, one-of-a-kind machines. There are, however, some areas where we have acquired a specialty, including the area of appliance foam fixtures.

During the manufacture of refrigerators or freezers, polyurethane foam is injected between the outer steel shell and the liner steel or plastic liner of the appliance. This foam expands to fill the void and provides support and insulation for the final product. During this process, a pressure of up to 20 psi can be developed. The shell and liner must be supported to withstand this pressure. A foam fixture is an automated device that provides this support. Remmele has been in the foam fixture business since the early 1960's.

Many of the innovations and ideas standard on fixtures made by present-day vendors originated with Remmele. The recent market has demanded fixtures that can be changed quickly between products and are capable of running product lot sizes as small as 50. Remmele has responded with a quick-change fixture design capable of being changed in one minute or less. This fixture has two sections, upper and lower. The lower section has adjustable surfaces to support the exterior of the appliance during foaming. Internal support is provided by a plug that has tooling to adapt it to a variety of internal geometries. This plug is usually unique to a given product. The upper part of the fixture is a large tool changer containing a number of plugs that can be rotated into a working position when its associated product is being produced.

Remmele received a contract in 1987 to produce 16 fixtures and tooling for a plant being built to produce refrigerators in Anderson, South Carolina, by White Consolidated Industries, a division of Sweden-based Electrolux. The design of the fixtures fits with other equipment in the plant to minimize changeover downtime and maximize flexibility, and to provide the capability to quickly prototype and produce new products.

A fixture is basically a support structure and would normally be overbuilt to assure adequate strength and stability. However, with the plugs and- changing equipment mounted on the upper section of the fixture, it is necessary to minimize the weight of this equipment, as well as predict and control the forces and deflection resulting from this weight and from the foaming process itself.

There are a number of ways to calculate stresses and deflection. Classical stress and strain formulas could be used. However, their use is error prone, slow and very difficult in many of the statically indeterminate problems that are often encountered. Finite element analysis is more accurate. With the limited numbers of parts to be produced, however, its use could cost more than the fabrication of the resulting parts. We needed a quick, easy, and reliable method of doing analysis and optimization without the time required to implement finite element analysis.

We found this in a software package called "The Desktop Engineer" (computer-aided analytical solutions for engineers), marketed by the Desktop Engineering Division of DVSE Inc., Woodcliff Lake, New Jersey. The Desktop Engineer is basically a computerized handbook of solutions to structural/ mechanical engineering equations. It uses these equations to calculate stresses and strains in loaded structures. It is divided into areas such as beams, plates, columns, frames, etc. In each area, the program prompts the user to provide information needed to solve the problem. The information relates to the geometry, material, support, and loading conditions—the same information that would be needed to do the problem by hand.

Self-prompting modules are also included to help the user find or calculate things like material properties, inertial, etc. Once the problem is thus defined, the program will do the necessary calculations to provide the necessary output. In most cases it will do the equation substitutions, integration and boundary condition analysis. In some of the more complicated analyses, the program uses finite elements to get a solution (even though the input and output format remains the same and the user is not required to know finite element techniques). Once a problem is accurately set up and modeled, it can be quickly changed and rerun to allow the designer to look at various design options or modifications.

Several utility modules are included to assist the designer with complex problems. A superposition module allows the designer to look at the effects of several concurrent loads on the same structure. A module is included to produce Mohr's Circle analysis for multi-axial states of stress and strain. Modules are also included to assist the user with calculating section properties. The program also has a convenient material database and several modules that look at complex geometries and dynamic conditions. However, most of our work involves simple static conditions. so we did not use some of the dynamic modules.

There are several specific examples of places where we used the program in the fixture design. The entire frame of the fixture was modeled using Module Cob: General 0-D Frames. Although the module is limited, for the sake of simplicity, to 15 nodes and 15 members a little creativity allowed us to get accurate and useful output within the confines of the program. The resulting output helped us size frame members and confirm safe stresses and deflection. The general output details maximum deflections, moments, loads, and reactions. It also provides shear, moment, and deflection diagrams. Additional data can be recalled to show output data for each node and member. The output also helps the designer create free-body diagrams, which in turn will lead to greater understanding of the problem.

In another use of the C-5 module, we modeled a vertically-moving, pneumatically-actuated ram with an associated double rack-and-pinion system. This rack-and-pinion system, with the ram, is a typical design used to assure that the ram stays horizontal and doesn't bend during actuation. The model helped us prove that the actuating cylinder would be protected from hazardous side loads that could be encountered in certain jam conditions. The solution produced was counter intuitive, but the free-body diagrams provided helped explain the problem and led to a better understanding of the overall problem.

We also made considerable use of Module B-3: Multi-Span Beams Under Transverse Loading. The uniform loading of support structures was shrunk into a beam model and analyzed on this module. We often wanted to look at structures with more than four spans (the limit of the module). However, by accurately modeling one end of the structure and varying boundary conditions at the end of the fourth span, we were usually able to get an accurate and usable range of reactions, moments, etc., on the first two spans.

In conclusion, The Desktop Engineer turned out to be a considerable time-saver on this project. The ability of the program to provide the user with geometric or material properties of a given problem saved considerable time that would otherwise be spent leafing through handbooks. The ability of the program to present the users with menus that direct them to the correct model for the problem was also a considerable time-saver. Once the correct model was defined, the user had the ability to change the model parameters to quickly find optimum conditions.

However, I feel that the biggest advantage of The Desktop Engineer was that it allowed users with various levels of training in the analysis of structures to quickly and accurately obtain answers to questions which otherwise may have been very difficult to get. For example, the beam analysis module allows a user with minimal training to get meaningful stress and deflection data for simple beam models. The2-D frame model allows a user with more training to do an analysis of problems that would be extremely difficult to do manually. It also saves the user from having to learn and use the more complicated analysis techniques such as finite element analysis. The Desktop Engineer has a quick learning curve, with easy-to-understand prompting, and help messages available at critical points. We have greatly benefited from its use and intend to make considerable use of it in the future.