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October 1, 2001

4 Min Read
Scientific molding, Part 3: The real world

In the first installment of this series on scientific molding we told you about a test of process portability conducted at injection molder Hobbs Corp. in Springfield, IL. In that test a mold was optimized on one press and then moved to another, on which settings were made to correlate with process data gathered from the first press. The goal, which was met, was to achieve good parts on the first shot in the second press, thereby proving that a good part is possible, regardless of the press it's in. 

The second part of this series focused more on the implementation of scientific molding and described how Hobbs discovered this molding method, applied it, and made it standard operating procedure. 

Although a test like the one documented in the first article is enlightening, interesting, and fun, it lacks some of the real-world panache and utility that an actual application holds. That leads us, this month, to the third and final story in the 2001 scientific molding miniseries: a look at a part molded in multiple presses in multiple locations under defined, consistent processing conditions. 

The players here are different as well. On the supplier side is RJG Inc., the Traverse City, MI firm that developed and teaches Decoupled Molding techniques and the concept of systematic (scientific) molding. It also manufactures a variety of hardware and software products designed to monitor and control hydraulic, plastic, and cavity pressures, among other parameters. The molder is DJ/Nypro, (Louisville, KY), a joint venture of Nypro (Clinton, MA) and DJ Inc. 

1001i82a.gif

Parametric data derived from scientific molding principles was used to run the same mold in three different presses. SPC data from each shows good part consistency.

The Premise and Process 
As OEMs lead suppliers to other countries in search of new markets and less expensive labor, molders are forced to devise methods of producing parts of consistent quality, no matter where they're molded. That is, a mold that produces a computer bezel in Illinois should produce a bezel with the same dimensions and specs in Ireland. One way to meet this goal is to use careful, high-quality moldmaking to produce cavity interchangeability. But a mold, once in a machine, still must be optimized and profiled. 

The goal of the case study performed by RJG and DJ/Nypro was to use parametric data derived from pressure transducers inside the cavities of a selected mold, and to replicate the process on multiple machines in multiple locations using this data. The part used for the study is a component supplied to Honda by DJ/Nypro. The mold contained two pressure sensors in the cavity, one near the gate and the other at the last point to fill. 

Producing a good part, regardless of location, is critical to molding success.

The mold was optimized and original data was recorded during a qualification run at the Louisville, KY DJ/Nypro facility. A 90-ton Toshiba was used. RJG, from its Traverse City offices, monitored the process via a modem connection. As dictated by the Decoupled Molding concept, all process data associated with the part is independent of the machine itself. An electronic template of processing data from the mold was retained for application on other machines. 

The mold was then shipped to another DJ/Nypro plant, this one in El Paso, TX. Here the mold was placed in another machine, a 150-ton Toshiba with a shot capacity different from the Kentucky Toshiba. Resin of the same type but from a different lot was used. These variables were introduced to prove the concept that a process can be established that adjusts for these variables to produce a part that still meets spec. Results of the El Paso run were recorded and compiled. 

Next, the mold went to the RJG facility in Traverse City, MI where it was dropped into a 45-ton Milacron Roboshot all-electric. Again, the screw and barrel size was different from those on the Toshibas already used. Parts were molded on the Milacron using the established electronic template. 

Results 
Parts from all three runs were sent to DJ/Nypro in El Paso for inspection and measurement to validate critical dimensions. Data from these measurements were plotted and are shown in the charts on p. 82. As the graphs show, results from each machine show virtually the same process capability from each location. 

This is impressive from a processing perspective, but more importantly, from a QC perspective, this application of mold-based parametric data can speed, if not eliminate, the startup and approval process when a tool is moved to a new machine. 

Table 1. DJ/Nypro tool transfer costs before and after machine-independent implementation

 

Setup

Press ($50/hr)

Process engineer ($50/hr)

Packer ($15/hr)

QE ($65/hr)

Resin

QA ($20/hr)

Total



In the wake of this study, DJ/Nypro compared its tool transfer costs using the old system in which re-approval was required, vs. the machine-independent system in which processing parameters are based on mold cavity data. Those costs are compared in Table 1. 

Contact information
RJG Inc.
Traverse City, MI
Mike Axford
(231) 947-3111
www.rjginc.com

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