One of Wawaka, Indiana-based B&J Specialty Inc.’s automotive supply customers was having problems with injection molds. In-mold temperatures were fluctuating by 132°C throughout the process, a much higher range than is acceptable.

Large temperature variations in an injection molding cooling cycle can dramatically increase the risk of warping and sink marks, leading to part rejections and higher scrap rates. So, B&J Specialty, a mold, die, and tool shop that specializes in repairs and high-level engineering challenges, recommended metal additive manufacturing (AM) – 3D-printed mold inserts to provide conformal cooling and minimize temperature variation.

Direct 3D printing is rare-to-nonexistent in most automotive production, but the industry has been reaping the rewards of rapidly advancing AM technology. In the design studio, designers and engineers rapidly prototype more parts in assembly plants; in manufacturing plants, industrial engineers fashion custom jigs and fixtures; and with plastic parts, mold makers embrace the geometric freedom offered by the technology to improve cooling and offer more complex mold shapes.

Jarod Rauch, information technology and 3D printing manager at B&J Specialty, says adding conformal cooling inserts to its customers existing molds “made it possible to reduce the cycle time and increase productivity throughput by 30%. The life of the mold is also expected to be substantially longer since the cycle time reductions from conformal cooling make it possible to reduce the injection pressure, which in turn reduces wear on the parting line and intricate details of the mold.”

Design phase

Rauch credits hardware and software from additive manufacturing solutions provider 3D Systems for enabling the improvements. B&J Specialty engineers took CAD files of the original automotive duct part geometry from the manufacturing and processed it with 3D Systems’ Cimatron Mold Design software.

“Cimatron is pretty much a one-stop-shop software that allows us to have full CAD functionality for designing and gives us the option to roll right into build preparation from the same package,” Rauch says. He adds that B&J Specialty discovered Cimatron while researching metal 3D printers. “We saw that 3D Systems provides a complete end-to-end solution including mold design software, build-preparation software, and 3D printers, and that’s what got me excited about this solution.”

With cooling mold inserts designed, B&J engineers exported the mold file to Moldex3D, a module of the Cimatron software system. Moldex3D, a computer-aided engineering (CAE) and simulation package simulates integration cooling in injected molding. Rauch says the tight integration of the software packages allowed engineers “to simulate the complete injection-molding cycle and map temperatures across the mold and part to identify hot and cold spots, and to simulate the effect of different cooling times.”

Simulation also highlights areas where redesign may improve cooling strategies before investing in a physical part.

Once engineers finalized designs, they used 3D Systems’ 3DXpert metal additive manufacturing software to prepare for production – importing part data, optimizing geometry, calculating scan-paths, and arranging the build platform. The finalized build file then facilitated production on a 3D Systems ProX DMP 300 metal 3D printer.

Solving old problems

Many injection-molded parts have curved surfaces, but drills used to create cooling channels only produce straight lines. Often, this means it is impossible to match cooling lines to part geometry. Conventionally-produced straight cooling lines must run beyond the outermost features of the part to avoid interfering with the cavity, so features closer to the part’s center are typically far from the nearest cooling line. This often results in significant temperature variations at the start of the cooling process.

Mold-flow simulation using Moldex3D and Cimatron software predicts coolant flows for conformal channels.

The original automotive duct design featured multiple irregular and curved surfaces. Straight cooling lines drilled through a hub and stator block adjusted the mold geometry to account for warpage. Several key features of the duct were distanced from the cooling lines due to straight-channel limitations – leading to varying residual stresses that tended to bend the part as it cooled. Before the cooling channel inserts solved the problem, the only cure to warpage was extending the cooling cycle to ensure the part was fully solidified before removing it from the mold, adding time and cost to production.

B&J engineers redesigned the part, removing the original straight cooling lines and replacing them with conformal channels that maintained a consistent distance from the part’s surface, using 3D Systems’ design software and printers. The features help ensure turbulent flow, increasing the amount of heat transferred from the mold to the coolant.

The conformally-cooled mold inserts reduced temperature variation throughout cooling to 18°C, an 86% decline, and they shrank cycle time to 40 seconds from 1 minute.

B&J Specialty Inc.
http://www.bjspecialtyinc.com

3D Systems
http://www.3dsystems.com