S.M.E. on going Modular

Society of Mechanical Engineering

Modular Fixturing Assessment

S.M.E. on going Modular. The following is an assessment of Modular fixturing systems written by Robert L. Coope, President of the Society of Mechanical Engineers. It is entitled “Modular Fixturing VS. Dedicated Tooling The Pros and Cons” SME Technical Paper #TE93-388.

While it was written in reference to large job shops and production facilities, it really applies to us. We all want to be able to do the short run faster and cheaper, without it taking all day.

INTRODUCTION

The introduction of the modular fixturing concept for machine tool applications has met with varying degrees of acceptance on the part of decision makers in this country. On one hand, managers with a strong bias in favor of traditional workholding techniques are reluctant to embrace new approaches. This reluctance translates into lost opportunities for important gains in productivity. The opposite extreme is the manager who is totally enamored with the modular concept and is wrongly advised by an over-zealous salesman to dispose of all of his permanent dedicated tooling. This extreme can have unfavorable consequences of a different nature. The purpose of the following is to suggest a way of analyzing the pluses and minuses of continued use of dedicated fixtures versus the all-modular approach of creating temporary holding fixtures using modular accessories. A measured case-by-case consideration of each approach and how it fits in with specific product mixes and production requirements can yield good results.

SMALL-LOT PRODUCTION

In discussing the relative merits of dedicated fixtures and modular fixtures, it is assumed that the reader is involved in small-lot production runs and is consequently interested in reducing 1) setup time, 2) tooling expense, and 3) tooling lead time. Whether dedicated tooling or the all-modular approach is used, a proven way to reduce machine setup time is to use an accurate grid pattern for locating fixtures, vises, and other accessories. The ability to pin fixtures and components into an accurate grid pattern eliminates the need to indicate or probe for alignment and position. While an accurate grid pattern greatly reduces machine setup time, the decision must be made whether and when to go one step further in utilizing this same grid pattern to address the other factors in small-lot production: tooling expense and tooling lead time. When should a custom dedicated fixture be designed and built? When should the all-modular approach be used?

ADVANTAGES OF DEDICATED TOOLING

When given a clean sheet of paper, an adequate budget, and sufficient lead time, a skilled tool designer can design a custom workholding fixture that is ideally suited to the application. Not limited to standard hardware, the designer may create custom details that offer the strength and rigidity to withstand aggressive cutting forces without sacrificing compactness or workpiece loading ease. Locators and clamps may be sized and shaped specifically for the part they are being used to hold. Tapped and bored holes may be incorporated into the fixture at any location. The all-modular approach generally makes some sacrifices in terms of 1) rigidity and strength, 2) ease and speed in loading the workpiece, or 3) overall compactness of the fixture. Modular accessories are designed for maximum versatility in a wide range of applications. At times, a clamp or locator made from all-modular components may consist of more than one component coupled together with some possible overall loss in rigidity versus a one-piece custom detail used in a dedicated fixture. Rigidity in an all-modular setup often comes at the expense of overall compactness. As a result, a larger working envelope may be required to accommodate a modular fixture. A custom fixture can be optimized for the ergonomic convenience of the operator, making loading of the workpiece easy. Careful planning of the all-modular fixture can minimize inconveniences but not always eliminate them.

ADVANTAGES OF THE ALL-MODULAR APPROACH

CONCLUSIONS

It has been well established that significant gains in manufacturing productivity can and have been made through use of modular tooling in manufacturing operations. This is particularly true in factories and shops where small batch quantities and continually changing production requirements necessitate frequent setup changes and reduced response time. A thorough understanding of the variety of ways that modular tooling may be applied to a broad range of manufacturing conditions will help users to apply it properly and profitably.

This paper used with permission of the Society of Manufacturing Engineers, Dearborn, Michigan