Designing for Moldability

The goal is to design and produce a pair of mating connectors for a handheld scanning device that can withstand 100,000 mating cycles without performance degradation … and the challenging environment a postal carrier will encounter.  The project team has three months to produce customer-approved, mating pair connector assemblies.

That’s the situation that Amphenol engineers (www.amphenol-aerospace.com) found themselves in last September.  Complete the product design, review material specifications, line-up testing and collaborate with an injection molding house on moving the design from 3D models to approved, precision molded parts by December 15th.

“The project required completing the design in a few weeks and parts within a couple months,” says Jeremy Ruff, a design engineer at Amphenol.  “We were looking for a mold house to produce molds very rapidly, manufacture parts to our print first-shot and complete the project in five weeks.”

Concurrent Design & Engineering
To jumpstart the project, Amphenol relied on an ongoing relationship with Genesee Precision (www.genprec.com) and reserved a spot in its manufacturing capacity to build parts as the design team worked to complete both the mating connector and mold designs.

Amphenol utilizes Pro-Engineer from PTC for CAD design, while Genesee Precision operates with Unigraphics from UG Solutions.  Although these CAD platforms differ, file translation allowed for immediate sharing of 3D models of the mating pair connector design rather than waiting for final drawings.  Matt Schiavi, a program engineer at Genesee Precision, began to interrogate the design and evaluate it for manufacturability. 

Concurrent Design

Mating connector pair achieves 100,000 mating cycles, critical for handheld devices frequently connecting to a docking station, by maintaining accuracy of injection molded housings.

Amphenol relied on Genesee Precision to make design recommendations and provide feedback on gate locations and any gate vestige on the part from the mold since the product tolerances were so tight.

“We didn’t know exactly how they would mold the part,” says Ruff, “so we specified general areas where we would like features to be and surfaces where we couldn’t have any marks from the molding process.  We documented those requirements in our drawings and sent it with the 3D model.”

Since the diameter on the core holes for the connector pins has a feature tolerance of +.001 inch and a true position tolerance of .001 inch, the design team altered the original 3D model to create uniform wall thicknesses throughout the part.  Genesee Precision conducted a preliminary design review with Basilio Sosa, a process engineer at Amphenol, to ensure proper mold function and part fill.

The team determined that extending the connector pin configuration even though some locations wouldn’t be used, would help control the shrink of the part and produce a higher tolerance molded part by maintaining uniform wall thicknesses.  “The true position tolerance of .001 inch for the hole location means you can only be off less than .0004 inch in both the X and Y directions,” says Schiavi.  “You can fabricate the steel for the mold to be within .001 inch true position but if you get abnormal shrink, the steel can be correct but shrink can pull the part out of tolerance.”

Precision Mold Design
By week four of the project, Genesee Precision had molded preliminary parts for internal review with a “steel safe” factor built into the mold design.  This approach guarantees the accuracy of critical dimensions in building the mold since it’s always easier to tweak the mold by removing steel in the mold rather than adding it.

Using this approach, the mold designers identify critical dimensions that are high tolerance.  A CAD file incorporating the revised 3D model, produced 100% to scale, was used to transfer every detail of the mold assembly to manufacturing personnel.  First-shot parts are measured to determine how much more steel needs to be removed from the mold to achieve the mean of a tolerance that may be +.001 inch using high precision machining or EDM operations.

CAD file released for production incorporates 3D model produced 100% to scale, and shows design of completed mold assembly.

Achieving the Goal
By week five in the project, Genesee Precision worked through final tweaks to the mold and produced 200 first article parts for inspection and review.  Later that week after gaining approval, Genesee Precision delivered 5,000 parts and Amphenol started building connectors for the handheld devices.

Gordon Collins, program manager for Amphenol says that the new connector design is particularly well suited to hand held devices which are frequently mated to an electrical docking station.  He says the connector uses patented Amphenol BrushTM contacts which have low engaging forces while achieving high durability exceeding the 100,000 mating cycles.