Akron, Ohio-based Desenco Inc. has
been producing rubber molds for injection and transfer molding of precision
parts for over 20 years. Until recently, most of these molds were manufactured
using CNC vertical machining centers.Laser Toolsetter Solves Moldmaker's Quality and Productivity Challenges
Akron, Ohio-based Desenco Inc. has
been producing rubber molds for injection and transfer molding of precision
parts for over 20 years. Until recently, most of these molds were manufactured
using CNC vertical machining centers.
When a new horizontal machining center did not yield the expected results, Desenco installed a Marposs Laser Toolsetter to optimize performance.
Prior to toolsetter installation, Desenco personnel report that it was "almost impossible" to attain accurate "Z" depths and repeatability in the "Z" axis. Setting tool lengths was extremely difficult, and the machine did not cut to required depths, with shallow or deep variances as high as .0025 in.
According to Craig Jorstad, CNC Coordinator at Desenco, these problems were caused by the machining center's high-speed (15,000 rpm) spindle and Cat shank. When the machine was run at high speeds, centrifugal force opened the spindle up and the tool physically drew back into the taper, resulting in unpredictable variations in depth-of-cut.
Despite the machine builder's involvement, there were no easy solutions. Desenco employees attempted to manage the problem by measuring tools in the static condition with a conventional contact-type toolsetter. But in reality, depth accuracy depended on operator intervention with the tool rotating.
Operators were making shallow trial cuts, and then making adjustments to attain required depths. This made setup time-consuming, and the results unpredictable. Operators
were never certain of the depths they would achieve, nor could they count on a repeatable pattern. Depending on the properties of various tools, variances ranged between +.0005 in. and, -.0025 in. States Craig Jorstad: "You were never certain of what you were going to get in the trial cut from the first tool to the last. And it takes time to dial those things down and bring yourself to where your depths are all the same."
The resulting step variances were unacceptable, as Desenco adheres to strict tolerances of plus or minus .0005 in. for most of the features cut for their molds.
For example, accurate core pin orientation is particularly critical to successful mold production. Core pins are used to create holes in parts, and during the machining process, core pin height is maintained by a counterbore. Craig Jorstad explains: "The core pin comes up from underneath the cavity and its orientation in that cavity in terms of its height is established by a counterbore on the bottom plate. That counterbore has to be held to a very tight tolerance in terms of its depth if we are going to be able to maintain pin height. We try to hold counterbores at plus or minus .0005 in."
The Marposs laser compensates for the dynamic errors of the machine tool, spindle, and tool holder, greatly improving the performance of the machine. Other benefits include faster setup, improved part quality, and greater consistency between operators. These advantages also apply when using a broad range of tool sizes, from .024 in. up to an inch in diameter.
When asked if he would use the Marposs Laser Toolsetter on other machines, Craig Jorstad can't stress his point enough. "I would certainly be willing to recommend the Marposs Laser Toolsetter" he responds, "because it is the best thing we have seen."
Marposs Corporation is part of worldwide Marposs S.p.A. (Bentivoglio, Bologna, Italy), a global leader in the design and manufacture of inspection, measurement and process control technologies.
For more information contact:
Marposs Corporation
3300 Cross Creek Parkway
Auburn Hills, MI 48326
248--370-0400
Fax: 248-370-0621
E-mail: marposs@us.marposs.com