DFM software gets cost-specific

When it comes to consumer products at the OEM level, designers and manufacturing engineers have no special affinity for injection molded plastics - they are simply another material-and-process combination within the engineering palette. Estimating the costs of tools, materials, and processing at an early stage in the design can be difficult. If the IM option doesn't look as though it will meet cost and performance specs, according to Peter Dewhurst of Boothroyd Dewhurst Inc., it is likely to be disregarded. "There is great pressure to move forward in design and get the product prototyped," Dewhurst told IMM in a recent phone interview. "That can be an obstacle to the use of injection molding. You've got to wait until designs are fairly detailed before getting quotes from moldmakers, which makes it difficult to get an accurate cost estimate in the concept design stage."

To give designers an upfront, more accurate picture of the opportunities and costs for an injection molded part, BDI recently updated the newest module within its Design for Manufacture suite of software. Early Cost Estimating for Injection Molding (version 2.0) breaks total cost down into four areas: tooling, processing, material, and such secondary operations as printing, painting, or labeling.

In addition, the package offers estimates on the optimum number of cavities, setup time, setup cost, and cycle times. Designers can vary material choice, wall thickness, tolerances, and other parameters to quickly compare costs for candidate designs before tooling has been finalized. Users can select from aluminum, kirksite, and tool steel as potential tooling materials.

A Geometry Calculator entirely new to this version captures part volume, projected area, and complexity without the need for CAD drawings or models. Selecting various shape and feature icons prompts the program to build a volume estimate, then determines part complexity for use in calculating tooling costs. Also, projected area is calculated to determine clamping force requirements. Final results can be viewed several ways, from a single cost figure to detailed breakdowns of cost and time factors that can also be exported to spreadsheet and word processing applications.

Running an analysis is relatively simple. In the "Describe Part" window, users enter the part name, number, and production volume, then select a neat, filled, or reinforced resin from the material library. Finally, the program will ask for envelope dimensions of the part as well as average and maximum wall thickness. By choosing "optimum selection," the program automatically chooses the number of cavities for lowest part cost. "Manual" allows users to determine the number of cavities.

An "Operations" window captures details of mold type, runner systems, parting line complexity, and cavity life as well as core pulls and part tolerances. Also, additional costs such as inserts and packaging for shipment can be included.

Motivation to develop this and four other modules within the DFM family - diecasting, powder metal forming, sheet metal forming, and machining - came from observing the evolution in elegance for consumer product design. Comments Dewhurst, "Contours and sweeping geometries are possible only with net-shape processes. We wanted to let designers explore the benefits of using these processes to see if tooling investments were justified."

Currently in beta testing, the Windows-based IM module will be commercially available by late June. New for this version is a tie-in with BDI's Design for Assembly package, so that estimates from the DFM module can be imported into a total assembly analysis.