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LOW-PROFILE, EXTENDED-CANTILEVER, FLEXIBLE SNAP DESIGN FOR ELIMINATION OF TOOLED UNDERCUTS

IP.com Disclosure Number: IPCOM000007002D
Original Publication Date: 1993-Oct-01
Included in the Prior Art Database: 2002-Feb-15
Document File: 6 page(s) / 266K

Publishing Venue

Motorola

Related People

Todd W. Roshitsh: AUTHOR [+3]

Abstract

In certain manufacturing processes, such as mold- ing of polymers or metal casting, it is often desira- ble to produce multiple parts during each mold cycle by using a multi-cavity tool. The advantage is typi- cally due to increased production capacity per shot, which in turn allows a more economical manufac- turing process.

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INC. Technical Developments Volume 20 October 1993

LOW-PROFILE, EXTENDED-CANTILRIER, FLEXIBLE SNAP DESIGN FOR ELIMINATION OF TOOLED UNDERCUTS

by Todd W. Roshitsh, David I. Blatt and Scott M. Engstrom

BACKGROUND AND PROBLEM STATEMENT

  In certain manufacturing processes, such as mold- ing of polymers or metal casting, it is often desira- ble to produce multiple parts during each mold cycle by using a multi-cavity tool. The advantage is typi- cally due to increased production capacity per shot, which in turn allows a more economical manufac- turing process.

  Another benefit ofmulti-cavity molding or cast- ing may be realized in cost savings during material handling or secondary processing of the parts. Mul- tiple parts can remain interconnected by the runner system upon completion of the mold cycle, thereby remaining essentially as one piece for handling pur- poses or secondary processing.

  However, disadvantages of multicavity molding may be increased tooling cost, tool complexity, or difftculty in filling the mold.

  In practice, some functional part designs require features with "undercuts" that can not be molded without using a tool that has movable inserts or "slides? While this may be acceptable for a single- cavity tool, it may be technically or financially impractical to construct a multi-cavity tool in this case, since it would require moving tool mechanisms at each cavity site in order to produce the required feature on each part. Slides generally cause increased tool fabrication cost, maintenance, cycle time and material flash.

  For background purposes, Figure 1 shows a can- tilever snap feature with "undercut" snap ledge, which requires tooling with a slide mechanism to produce the feature. This may be acceptable for a single-cavity mold used in conjunction with an~eas- ily molded material, assuming that geometric and material design constraints can be met to design the snap for proper performance.

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  Figure 2 shows a similar design which incorpo- rates an opening in the part design so that a "tele- scopic" tool feature can, be used to form the snap ledge. This eliminates the need for a slide and the tool can remain a simple "open/close" design.

  Now, consider the following constraints that may be encountered in a specific application: (1) the snap's "cantilever beam length" and geometry are limited due to space constraints (2) the choice of material and inherent properties is limited by design consid- erations for the part as a whole, ofwhich the snap is only one element (3) the application requires snap performance within a specified range of force-vs- deflection, while maintaining the mechanical integ- rity of the snap. With these multiple constraints, it should be obvious that in some situations it may be

impossible to develop an acceptable snap with the basic geometric approaches shown in Figures 1 and 2, particularly if the snap needs to be more flexible but the "beam length" as denoted in the figures is not allo...