CASE STUDIES OF DEFECTS/FAILURES IN PRESSING – HOW TO PREVENT PUNCH BREAKAGES AND CONTAMINATION

Do you find any similarities with these experiences?

“Finding defects and other issues quickly is not easy. Especially visual inspection of punch breakages during the Pressing processes on-site is challenging.”

“Having experiences of producing large amounts of defective products. We did not even notice scraps like burrs and slugs were held in the dies in advance…”

In this article, we will introduce two examples of using Bolt Piezoelectric Load Sensors to detect defects and issues through the Pressing Processes.

WHAT IS PRESS WORKING?

Press Working is a processing method in which the metal material is placed between metal dies and pressurized by a press machine to deform it into the desired shape. Products produced by Press Working include bodies and doors for automobiles, exterior components for home appliances, and substrates and cases for electronic devices.

PRESS WORKING METHODS

Common Press Working methods are as follows:

• SHEARING
• BENDING
• DRAWING
• PRESS-FORMING
• PRESS-FORGING

COMMON DEFECTS IN PRESS WORKING

Pressing is the most common method in “Plastic forming” and is suitable for mass production because it can be done in a short time and can be done continuously. However, some of you may have had troubles caused by the following defects and failures:

• Rollover
• Burr
• Spring Back
• Crack
• Wrinkle
• Galling
• Slug Pulling
• Bow/Distortion/Twisting

Today, we will introduce examples of defects detected in “Drilling (Piercing),” which is classified into the Shearing process, as well as defects in the Drawing Process.

CASE STUDY 1: DETECTION OF TOOL DEFECTS/ FAILURES (PUNCHING/PIERCING PROCESS)

The 1st case is the detection of punch failures/ breakages that occur during Punching Processes in Press Working.
Punch failure frequently occurs in the process of producing multiple holes simultaneously through the sheet metals. However, it was challenging for customers to inspect products visually during machining operations, even when operators were nearby; the sounds of punch failures were too small. The fact that they could not detect defects was their main issue.

SOLUTION WITH THE BOLT LOAD SENSOR

So, to make finding punch failures/ breakages easier, we suggested a solution with Bolt Piezoelectric Load Sensor, in short, “PiezoBolt.” We asked them to mount PiezoBolts on the place shown in the picture below to check the signals.

MONITORING REPORT

The data analysis of the measured signal revealed that the signal obtained when the punch was broken differed from the normal signal as shown in the figure below. In addition, a peak that appeared to be the impact load at when the breakage happened was captured.

Gathering and analyzing the data repeatedly in this method allowed clients to visualize punch defects and failures. In addition, by defining threshold values and setting alerts for abnormal situations, it was possible to reduce the production of defective products and mitigate damage to dies, machinery, and equipment.

CASE STUDY2: DETECTION OF DEFECTS CAUSED BY  SCRAPS

The 2nd example is the detection of defects caused by scraps, such as burrs and slugs. The clients had an issue in this forming process. Because they did not notice scraps, some defective products were produced among good products without being detected.

SOLUTION WITH THE BOLT LOAD SENSOR

Two of the Bolt Load Sensors, PiezoBolts were tightened on the left and right sides (I and II) of the upper part of the die set of a plate forming press to monitor the forming load.

MONITORING REPORT

The PiezoBolt is an extremely sensitive sensor that can evaluate even the slightest differences in load when scraps are caught in the dies. In this case, we were able to monitor the eccentric load on the dies.

Based on this monitoring report, the system was set to alert operators when the load balances changed. This enabled clients to take immediate action in case of defects or failures, and they could increase production efficiency.

CONCLUSION

Thank you for taking time to read this article.
By monitoring with the Bolt Load Sensors, it is possible to visualize abnormalities that cannot be noticed by human skills alone, such as visual inspection or sound checks. In this article, we focused on Press Working and introduced some examples, but PiezoBolt can be applied to all kinds of problems at production sites, such as Cutting and Casting.
Please feel free to contact us if you have any questions or concerns.