When it comes to toolmaking, there are many tricks to the trade. For Midwest Patterns, Quincy, IL, a favorite trick for fitting mold cores to their cavities involved masking tape. To make sure the cores had the needed 0.010 clearance, Midwest toolmakers would wrap a double layer of masking tape around the cavity. They would then rub the tape with orange wax. The core would be carefully placed inside the cavity and removed. Wherever wax was present, metal was removed. These steps were repeated many times for each core and cavity.

This manual fitting process was accurate but time-consuming, especially when the part was a large one, such as the molds used to make foam energy absorbers for inside automotive bumpers. The company replaced its masking tape with a portable measuring arm.

Modeling the data identifies where the core has to be machined to achieve precise clearance from the female half of the mold.

Midwest Pattern builds aluminum tools used in the manufacturing of EPS (expandable polystyrene), thermoforming, vacuum forming, and other manufacturing processes. Midwest's facilities include engineering and design, CNC, pattern shop, machine shop, foundry, and a test facility.

Rob Stull, quality supervisor, took the lead in linking the arm into the company's CAD system for the bi-directional exchange of dimensional data. Stull teamed with 13-year veteran pattern maker Mark Schutte, who would become the primary arm operator.

During the next two months, Schutte became comfortable using the machine and Stull learned programming techniques. When the bumper mold project arrived, Schutte and Stull were ready. Using the portable arm to collect 3D surface data from the mold halves and then fitting the halves together electronically within the CAD modeler, the team reduced the overall fitting process time by 33%.

Telescoping secondary cores.
Attached to the primary core of the bumper mold are a number of secondary cores designed to telescope into cavities within the female mold half. These were traditionally manufactured separately and fit manually to their respective cavities. The measuring arm made it possible to eliminate this hand-fitting operation. It was no longer necessary to manufacture secondary cores separately and bolt them to the primary. Primary and secondary cores now have single-piece construction, which simplifies manufacturing.

More accurate castings.
The critical dimensions for the bumper energy absorbers are locating pockets. In-process checks with the portable CMM make it possible to learn more about manufacturing processes and to tighten up the tolerance bands on castings. Now they consistently meet customer specifications without rework.

Faster validation.
To validate molds before shipping to the customers, engineers were required to hand-measure various points along the cavity that would indicate the required foam thickness. This job used to take about a day-and-a-half per cavity. This has been reduced to 1.5 hours per cavity using the portable measuring arm. The arm uses a variety of specialty probes - which can be switched on-the-fly when verifying patterns.

Wooden pattern sections are typically cut according to Mylar cross sections, then assembled and blended. Since automotive jobs come into the shop electronically, the pattern makers have no prints by which to verify the surfaces they are making. The arm is now being used to check patterns and evaluate their deviation from the electronic model of the part.

Reverse engineering.
Midwest recently used the articulating arm to reverse engineer a large vacuum tool for manufacturing side-by-side refrigerator door bodies.