The whole process of punching may be straightforward. However, a successful punching can be difficult to achieve if some of the required elements are not optimised for the said process. And so, fabricators that maximise punching should know the basic principles to achieve satisfactory results. Knowing these principles can also help the fabricators become more productive and efficient in the long run.
Some of the principles that you should know to achieve successful punching are the following:
The basic tooling design for punching is comprised of four components: punch, stripper, die, and toolholder system. Knowing the features and functions of these components is pivotal to the success or failure of the punching process.
During the punching process, the punch must deal with both compressive and tensile forces. In some instances, these forces can cause damage to the workpiece and other tools. And so, the materials used for the whole punching process must be made from high-quality tool steels to effectively withstand chipping, cracking, and edge wear. A small back taper can also be used to reduce the pressure on the punch flank once the punch retracts.
The stripper, on the other hand, must be able to hold the workpiece against the die as the punch performs its function. It should also hold the punch tip rigid so that the punching process can commence properly. Die is likewise crucial to a successful punching. Once it is precisely aligned with the punch, then one can expect a great punching process. Ultimately, the toolholder system intends to perform various functions. It supports the punch tip to the centre of the die while laying the workpiece flat against the top surface of the die. It also provides the interface between the punch press machine and the punch, as long as it is in great and pristine condition and is used optimally.
Another principle that must be considered to achieve a successful punching is the die clearance. Knowing the basic tooling design is essential so that the fabricator will know the importance of each part. Knowing the correct die clearance, on the other hand, can significantly contribute to the success of punching.
A clearance that is too large can cause huge burrs and poor part quality. Too tight clearance, alternatively, can cause poor edge quality, reduce tool longevity, and lead to more replacement for tool components. An optimal die clearance can hugely improve both the edge quality and tool service life. It can also reduce the cost per hit and improve overall regrind interval.
Understanding the punching process can help in achieving the correct die clearance. A lot of punch press tooling has a crystalline structure with a fracture plane or a line of weakness. This crystalline structure helps identify the correct and accurate angle of the said plane. If the die has a correct clearance, then both the upper and lower fractures will instantly connect. This connection subsequently lets go of the slug, releases the punching force, and eradicates the slug effectively.
Inspecting the slug can determine the efficiency of the whole punching operation. It can specifically assess if the clearance is suitable for the application or not.
The burnished land is a shiny or polished surface that is generated when the punch penetrates the material. If the clearance is correct, the burnished land will be around one-third of the material thickness. Additionally, a correct clearance and proper machine alignment can result in a consistent burnished land and fracture plane around the periphery of the slug. An uneven burnished land, alternatively, means that the tool is misaligned. A rough burnished land likewise means that the die clearance is tight.