Re-design progressive metal stamping die project
Vortool worked on a project where a new progressive sheet metal stamping tool and die design needed to replace an existing metal stamping die. The old tool and die produced metal stamped parts that were not quite up to specifications and varied within even the same run. By knowing the shortcomings of the old progressive tool and die a new, better progressive metal stamping die was designed.
Vortool Manufacturing successfully re-designed and manufactured a new sheet metal stamping die with 11 progressions to produce consistent sheet metal stamped parts.
Issues found with the old progressive metal stamping tool and die
The coil is not guided well enough in the tool, resulting the finished part off centered with different bent leg lengths at each side. The lack of sufficient pilot punches make things even worst. The strip guide wears out after about 20 thousand parts stamped, make this variation even greater. The stamped cut edges within the strip have considerable burr, make the coil stuck and buckle rather often. As a side-affect, the coil doesn’t not always completely jams but enough to disrupt the proper progression, so parts from this point on are partially cut. Another issue is that the “U” shaped form is not as parallel as it should be.
Based on this information that was experienced during production, a list of expectations were added to the new tool and die design with solutions to overcome and eliminate the problems found with the old metal stamping die.
The strip must be well guided, with no chance of axial movement inside the tool.
Solution: Permanently attach air feeder
Improvement was made by mounting the air feeder on the tool, instead of mounting it independently. The in tool mount allows perfect axial alignment, locked in position with dowel pins. When the sheet metal stamping die is completely taken apart, then put back together again, there is no guess work for aligning the feeder.
Improper feeder set up alignment is one of the causes for production problems.
To correct the strip guide issues, the new tool and die design’s guide has called slide guide pins (hardened) at the rear edge of the strip. The front of the guide has about 0.020 clearance, so the strip will never gets stuck. To ensure that the strip is pushed against the rear slide guide pins, there is an automatic stock pusher. As the tool closes, goes down, the spring-loaded stock pusher forces the strip toward the back tight, against the slide guide pins. The stock pusher can be adjusted, so it activates with full spring force around the same time as the pilots pick up the pilot holes but before the cutting punches will start cutting. In upstroke, the spring pressure is released allowing the strip with no tension.
The punches and die plate made of M2 and Vanadis 4 Extra tool steel to ensure extended tool life, so the cutting edges stay sharp a lot longer then e.g. D2, A2 or other generally used tool steel were used. In conjunction with the better tool steel, the absolute optimum die clearance is added that ensures the longest possible tool life with no premature wear that create burrs much too soon.
There were side CAMs to push the already bent “U” shape a little further in, compensating for the spring back that generally occurs from wipe forming.
To ensure that the bent “U” shape is symmetrical and even at both sides, there is an in tool adjustment to move the lower form dies to either direction to find the sweet spot and have the equal leg lengths at every time. Additionally an upper pressure plate holds the strip down while the legs being bent down, keeping the formed part flat at the top with no distortion.
The progressive die tooling has a stock oiler between the feeder and the strip guide (entry) that produce an even and light coating at both sides of the coil being fed into the tool. As the lubrication is necessary for most stamping applications, the punches may accumulate excess oil that can make the small parts stick to the top after being cut off from the coil. To prevent such events and possible double hit and tool crash, a small spring plunger is installed at the upper part of the cut off station, that can prevent the part sticking to the top.
There were several spring plungers also installed in the die plate, to lift the coil by about 0.005 from the surface.
The round and the octagon punches have ejector pins, preventing slug pulling that may be one of the reasons for coil buckling and tool crash.
The feeder has a mechanical style activation, when to feed. This simple device is triggered by a trigger arm that is mounted on the tool.
Designing sheet metal stamping dies with built in expectations, best practices and attention to detail can make a huge difference from one tool and die design to another.
You would expect the progressive sheet metal stamping die or any stamping tool to work flawlessly with no issues whatsoever. It is easier to say than done. Metal stamping dies are custom made, not like production produced parts or complex devices. There is one chance to make it right, with no improvements while in the process of tool and die design and manufacturing.
Most tool and die designers, tool and die makers cover the basics well, but may neglect seem unimportant factors. When the progressive metal stamping tool is done and ready for production, they call it “tweaking”. That includes initial metal stamping tool and die set up, corrections for proper mounting, then small modifications to make the tooling work the best possible way. This tweaking time is a waste and could be avoided rather easily, by paying attention to every detail. The progressive metal stamping tool and die tweaking times are usually a day or so additions that could have been left out altogether.
There are four pilot punches employed that ensure proper progression and strip alignment.
Just in case, these pilot punches have heavy springs behind them, in case there is a progression error, so the pilots will not try poking holes into the strip with no holes to locate
Punch press mock up for metal stamping dies
The progressive metal stamping tool and die designer could spend e.g. only an hour to come up with a press mock up, with its basic mounting dimensions, stroke, etc. and design die tooling to ensure that it fits in every way, so when the tool if finished, it is truly ready to produce parts from the moment it was mounted.
The best way is to start a progressive tool design is start designing around the finished part, the product that needs to be stamped.
Strip layout for progressive metal stamping die
Produce the proper strip layout for progressive metal stamping dies - the progressions that could provide the necessary steps with each progression. Then use the available punch press or presses with all specifications of it and design the die set that would be suitable for both the part, the strip layout with all of its progressions. Use the requirements toward the part, the tool and general or specific guidelines. Also keep in mind how the parts will be manufactured and try minimizing the time would be spent producing the components properly.
