Measuring Punch Accuracy in Metal Fabrication

July 11, 2018

It’s true, punch quality and features are important. However, even if the tools exceed all expectations, they’re not doing the job right if the punch tip isn’t accurately hitting its mark. To make sure that’s the case every single time, alignment issues need to be addressed. In a nutshell, we need to determine the dimensional tolerances of the equipment. Subsequently, punch accuracy is honed and the clients’ demands are met.

Laying Out the Witness Marks 

Initially, when a project begins, the hole centres are marked out on the sheet metal. The information is transferred manually or by machine, from a technical drawing, and the scribed crosshairs are established. A variety of steel rules enters the process at this point, for there’s no point worrying about punch accuracy measurements if the initial witness marks aren’t meticulously situated. Of course, it can be difficult to place these markings on polished steel, which is why the process calls upon white paper overlays and/or copper sulphate marking solutions.

Measuring Punch Accuracy 

A test sheet has gone through the equipment station. Just like the test sheets that calibrate office printers, this trial run was carried out to make sure the business end of each tool was properly aligned. By the way, the tolerances referenced here are incredibly fine. A punch offset of less than 1-mm might be acceptable, but certainly no more. In all likelihood, the allowable dimensional errors will be set at plus or minus a fraction of a millimetre. To ensure those limits are being met, ultra-precise micrometres and steel callipers are used to measure the distance between the punch zone and the intended strike site. Again, this distance will be slight, perhaps imperceptible, but it must be measured so that the punch turret can be certified as a project-ready asset.

A Highlighted Punch Machine Feature 

Punching equipment, the real deal, as it were, tends to incorporate tight tolerance dimensional limits. Imagine a machine that’ll vary its strike by no more than 0.12-mm. Properly calibrated, that high-end metal fabrication station will consistently observe this punch-to-punch or punch-to edge margin. However, certain mechanical factors can jeopardise equipment tolerances. For example, the closely applied punch strikes on a thin and malleable steel panel will cause that material to deform slightly. If that’s the case, a harder anvil or stronger clamping system will be used to minimize the deformation.

Laser measurements and complex scanning systems are taking over from micrometres, but the older mark-validating tools are still popular, perhaps even necessary. After all, electronic machines also require calibration. A sharp human eye and a set of steel tools, micrometres and rules among them, doesn’t require a lab-approved calibration service.

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