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How Tight of a Tolerance Do You Need for Your Metal Stamping?

Posted by Tim Lynch | 11/4/14 10:00 AM

How tight of a tolerance do you need for your metal stamping? That’s a good question. The answer isn’t complex, nor is it simple and straightforward. 

Tolerance, which can be defined as the permissible limit or limits of variation in the manufacturing process, is applied throughout the development of a metal stamping.  Specifications for tolerance are often tweaked at each step of the design stage, sometimes leading to an excessively tight tolerance which prohibits the execution and completion of the primary goal - the manufacturing of a product.  How wide can a tolerance be and still produce a product that meets necessary specifications for form, fit, function, safety, certification, and other regulations?  The answer to that question lies in the insight and knowledge of an experienced manufacturing professional.

Metal stamping tolerance - how tight is too tight?

Tolerance is impacted by several factors – SPC guidelines, government/ industry regulations, engineering design, and customer demands to name a few.  An idea, when brought to life on the drawing board, may not have a tolerance level applied to it.  When that concept graphic is presented to an engineer, he/she may tighten tolerances based upon engineering principles. Internally, other tolerance specifications may be applied based upon company practice. Regulations, especially for medical or automotive industry products, will tighten the tolerance even more.  Finally, a customer’s preference for form or appearance may tighten the tolerance again. 

In the end, the product could be deemed “unmanufacturable.”  Yes, unmanufacturable - it’s not actually a word or an industry term, but maybe it should be.  In other words, a tolerance can be so tight that it prohibits the manufacturing of the stamping. Just as there can be too many cooks in the kitchen, in the manufacturing world there can be too many experts adjusting and tightening tolerance to a point that manufacturing is impeded.  And even if production is possible, tight tolerances, just like the manufacturing elements of time, material and scrap/waste, translate to increased production costs or additional costly controls in the manufacturing process,

How does an experienced metal stamping manufacturer deal with tolerance?

Dealing with tolerance is like a dance.  If you hold your partner too tightly, he/she can’t move, but if you don’t lead, the dance falls apart. In manufacturing, if specifications are too tight, production is stunted, but without proper tolerance, a product may be unusable. There needs to be a balance between the necessary specifications and a reasonable variance of tolerance.

Some tolerance specifications can be negotiated. For example, a customer can be persuaded to “give” on a form element that doesn’t affect the overall function of the product.  Unnecessary as well is a tolerance based upon a sharp, ninety-degree angle or some other design idea that does not translate to “real world” stamping.

So, how tight of a tolerance do you need for your metal stamping?

We’re back to our original question, and as the content of this article suggests, the answer depends on a multiple of variables.  The goal of the manufacturer is to work with and within the limits of tolerance while simultaneously negotiating away unnecessarily tight tolerance levels.  Tolerance specifications are vital, but an overly-tight tolerance impedes the manufacturing process, increases costs, and causes headaches for manufacturers and customers alike. Once safety, industry, governmental, form and functional requirements are met, the manufacturer can work toward loosening tolerance. How tight of a tolerance do you need for your metal stamping?  It should only be as tight as it needs to be. 

A must-read for OEMs that use metal stampings in their products
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Topics: Manufacturing