Tolerances in Sheet Metal Fabrication

Tolerance can be defined as a deviation from original dimensions which may have important results on the performance of the end product. Over-toleration of particular dimensions may cause the produced part to fail in complying with design and performance needs later in its operation life cycle. In such cases, it certainly takes a serious amount of money and time for correction and repairing efforts in this regard usually end up clutching in straws. Moreover, production costs will be drastically increased with the increasing degree of toleration which results in absurdly high product prices. The manufacturers are usually aware of this reality. Thus, choosing the tolerances as wide as possible without a trade-off with the operational functionality of produced part is the key solution to overcome above mentioned problems. Occasionally, decision makers of production miss the reality that tolerances should be chosen according to design requirements. Tolerances depend on the design parameters, meaning that a design can work on tight tolerances whereas another one need wider tolerances to perform its function. Latter mentioned design usually less expensive to produce and usually more resilient. So, it is crucial to decide on the tolerances at the initial steps of design process.

Classification of tolerance

Locations of tolerances are peculiar to the bandwidth of different process methods. There are mainly two classes of tolerance, and the producer should be well acquainted with both for separating them according to machining operations. One of these classes is known as “usual tolerance” in which occurrence of tolerance is not purposefully and the other one is “most applicable tolerance” which covers precise tolerances occurred on purpose. The usual one is standardized for nearly all of machining methods. In these standards, requirements for different processing methods are explained. It is due to type of processing method if something definite can be decided about the most applicable tolerance. For instance, it is easier to decide on max tolerances in cutting operation but in case of laser, autogenous and plasma cutting, it is on the contrary. As mentioned earlier in this post, the amount of increase in tolerances is directly proportional with the cost due to the risk of rejection for the produced part and machine calibration endeavors. Moreover, the existing processing methods may not be adequate and applicable for producing the desired product.

Since every operation seeks for different tolerance principles, these are listed according to each operation. Please visit our specific sheet processing page to gain further info.


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