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Tolerances in Custom Metal Fabrication

The word “tolerance” is thrown about often in the metal fabrication world and it stands as the most scrutinized factor for evaluating manufacturing quality. As tolerance expectations become increasingly tighter, the more challenging the manufacturing process becomes for a given part. Even with newly emerging technologies in cutting, welding, machining and other departments, especially tight tolerances are not universally achievable by any given shop.

Tolerances are so crucial to the manufacturing process as they determine how well a part will fit in final production and, in turn, how stable the final product will be. Tolerances can refer to mechanical fit, fit up (i.e. proper alignment of holes for assembly), deviations from perfect straightness or accuracy of assembly. This will be among the most important considerations for decision makers in their search for a contract metal fabricator.

More Fabrication Processes Means More Opportunity for Error

Tolerances In Metal FabricationBecause of the number of processes a specific part must go through in a given manufacturing cycle, achieving perfect or near-perfect tolerances requires meticulous work. Provided differences in materials, varied tolerance capabilities of different outsourced manufacturers, quality of assembly, among other factors, the number of hands or machines touching a part inherently creates more room for error. For this reason, outsourcing a part or finished assembly to multiple vendors can lead to tolerance issues.

It’s better, then, to have as many processes as possible consolidated in one space where there is more understanding of how each service interacts in the making of a part. “Cradle-to-grave” manufacturing will always be more conducive to producing tighter tolerances since the manufacturing process is evaluated and refined as a whole entity. Better still if the metal fabricator has in-house engineering and can properly design an entire manufacturing process to meet required tolerances.

On the subject of engineering, geometric dimensioning and tolerancing (GD&T) is an established method for communicating engineering tolerances. This methodology allows engineers and other specialists to foresee tolerance constraints in the manufacturing process before production starts. Though GD&T is rising in popularity among manufacturers, its current (and proper) usage is found among only a few metal fabricators around the country. GD&T is a powerful tool which, if used well, can greatly enhance part manufacturing.   

Optimize your custom Metal fabrication tolerances

One of the most important aspects of tolerancing is understanding when tolerances are so tight that they do nothing but drive up the cost of production and slow the manufacturing process. Tolerances are used to ensure proper fit and functionality. If the same fit and functionality can be achieved with looser tolerances, the less intensive tolerances should be chosen even if tighter tolerances are possible. The added insurance of having tighter tolerances does not make up for the loss of productivity and increased cost. It's useful to consult with your contract manufacturer on their experiences with similar parts. Since the contract manufacturer will know its own equipment and has likely seen a part with similar tolerances, they can make the best recommendations for where to sacrifice on tolerance tightness. 

Tolerances in Welding, Cutting, Machining and Forming for Custom Metal Fabrication

Depending on the manufacturing equipment available on the floor at a given time, tolerances can vary. Tolerances for precision work such as laser cutting, machining and forming will have little room for error. A metal fabricator is, therefore, incredibly dependent on the technology available (in addition to correctly moving a part from process to process). For contract manufacturer seekers, research the equipment available to check if the quoted tolerances can be reasonably met on a consistent basis.

As for welding, the presence of certified weld inspectors (CWIs) can help ensure that proper welding tolerances are hit. Since most parts touch the welding department in some form, having CWIs on staff is a sure sign that best welding practices will be followed. 

Importance of Risk Management

Checking for correct tolerances is among risk management’s most pressing duties. A well-trained risk management team will not only mitigate the risk associated with poor tolerances, but also dramatically reduce the quantity of faulty parts in a production cycle. Risk management gives metal fabricators the ability to reflect on their processes with objective data to assess how improvements can be made. By optimizing tolerances, risk management can run through parts faster. The tighter the tolerance requirements, the more time risk management must take to ensure quality. 

Appeal of Custom Metal Fabrication

Custom metal fabrication is lucrative since many or all steps of the manufacturing process can be included. This results in cleaner parts with tighter tolerances as metal fabricators will be more accustomed to the capabilities of the equipment and personnel on the plant floor. When considering tolerance targets, trusting fewer partners is better than many.

A Comprehensive Guide to Choosing The Right Metal Fabrication Partner

This blog post was previously published on 06/21/16. It has since been updated with latest information.