Important features to design and build precision progressive metal stamping dies
Different metal stamped parts require different metal stamping dies that suit the application. Even that the metal stamping tooling is different, there are common features that can be used for the precision tool and die design and implement in manufacturing.
Precision custom progressive sheet metal stamping dies usually required when the number of the stamped parts are higher.
A progressive metal stamping die is a combination of many tools and dies with different features, built into one single unit.
This makes the precision custom progressive metals stamping die more complex than using several tools with single operations. The single tool can be used to stamp certain features only of the same part. The part production is slower, but the tools generally are more cost effective.
Customized progressive metal stamping dies are great to save production time and increase repeatable quality, time after time. E.g. a strip or coil (stock) enters at one end of the tool and the finished parts exit after each stroke. It sounds straight forward, but the complex features make the tool more difficult to design and build with success. Minor things could be overlooked that would cost valuable time to correct after the tool trial. Precision progressive metal stamping die manufacturers usually build the tool, test it, and then make several called tweaking to get the tool work properly and make the parts right. There is a better way when the tool likely does not need tweaking. That means once the tool is built, mounted on the designated press, it fits for the first time with no alternations and parts can be produced from the moment the punch press was turned on. The tool then should produce the correct parts for a long time without any down time, wear, breakage, etc.
When a progressive metal stamping die was made right at the first time, it becomes a good value to the user. This is what was expected in the first place. However, there are tools that require more maintenance than suppose to, have more frequent sharpening or issues with burr or even constant adjustments to be performed to maintain the expected quality of the stamped parts. Tools with too much TLC are less productive, therefore more expensive.
The examples below are some of the features that could be used to design and build progressive metal stamping tooling that can lead to longer tool life and to better parts. Made in Canada.
The finished metal stamped part
Knowing what the parts is and what required can guide you to choose the correct way to build the metal stamping die, select material, etc.. You must know the part’s its material specifications, dimensional tolerances, and the number of parts to be produced e.g per run month, year or for the lifetime of the tool. E.g. the stamped parts made of high tensile spring steel would require different tool steel than parts made of mild steel.
This basic information will dictate what type of tool is required. The die set for the tool could be two or four post guided. Depending of the punch press, maybe a high speed stamping is required, so ball bearing guided die set is necessary. E.g. there will be millions of parts to be produce per year, so the cutting components should be carbide. This material is very brittle and can easily chip if not guided well enough or the tool’s structure is not as rigid as should be.
In this example, the part is made of ½ hard 301 Stainless Steel. Generally used A2 or D2 tool steel would not be quite suitable for this application. Vanadis 4 Extra tool steel was selected for this application.
Strip layout for custom progressive sheet metal stamping dies
A proper strip layout must be designed before start designing the sheet metal stamping tool. You basically design the tool around the part and the progressive stamping strip layout, with the necessary features to produce the required, holes, notches, dimples, bends, etc.. In this example a four post guided die set was selected, using bronze plated demountable standard die bushings and guide pins. This die set is well suited for the tool steel and ridged enough to minimize flexing, rocking, etc. to protect the tool steel. As a result the cutting edges will last as long as intended, and about a million parts stamped between sharpening.
Precision progressive metal stamping tool and die features
The parallels are necessary for clearing the slugs and scraps that pass through the bottom die shoe. It can also elevate the tool to better fit the punch press. Choosing the direction of the parallels are rather important. Front the back orientation can ensure that the slugs are visible for the operator, therefore is more likely cleared from clogging up the space under the tool, than if they were placed along the tool’s length, where the scrap is not visible. Slug build up is one of the many reasons that tools jam and break.
Limit stops are for setting the tool’s shut height properly at the beginning of the production.
While the punch press is going up and down, the limit stops should not be physically contact to the top die shoe. When the tool bottoms out on the limit stops, that means the press is going to be stopped. If this happens, that means the press and the tool is jammed. This could be a serious matter. As an alternative solution, Vortool developed a battery-operated device, an electronic shut height finder. This can prevent set up errors or accidental RAM lowering.
When the finished parts are separated form the strip or coil, they need to exit the tool properly, giving room for the next parts to exit. A chute was employed in this tool and die design. When the metal stamping die made the last feature of the part, it also cuts it off from the coil. The coil then moves forward and pushes the cut part out of the tool. To ensure that the parts will not pile up, a chute was designed as the cut part is being pushed by the strip, it slides down un the chute, giving ample space for the next stamped part.
This simple solution can help the tool running free of obstructions that is a key for a successful stamping process.
There are some other features of nearly any custom progressive tool design that can increase the reliability of the tool. The incoming strip or coil enters the tool and guided between guide bars as move forward with each progression steps. The strip or coil width could vary, and the guides need some clearance as well in order to freely advance. As a result, the strip’s axial position changes. To overcome this problem, the strip or coils should be sliding against e.g. a datum face.
An automatic stock pusher can just do that. It is a spring-loaded device that pushes the strop’s front edge as the tool goes down, just about the time when the pilots enter the pilot holes. This helps the pilots to work more effectively, without yanking the strip into position with every hit. Controlling the progression is a crucial step in progressive metal stamping. The pre-set progression could change or vary that could be beyond your control. It could be due to feeder issues or strip obstruction that prevents the strip moving forward properly and freely. It may never happen during millions of hits, but if it does, it could be a mayor tool crash. When the strip or coil is obstructed what ever the reason is, the feeder will not stop advancing the stock. Since it can not move forward a before, it buckles upward. The punch press will not stop either, and will go down as same as before. At this point the strip or coil is buckled and not properly lined up for the next cut. It is nearly unavoidable that the tool will crash. In the process most of the affected tooling components, punches and die section could break. When hardened brittle punches break, they could cause serious accidents by busting away and out from the tool.
Die springs are standard purchase able components that are widely used in metal stamping. They come in different diameters, lengths and strengths. However, in high volume production they will fail much too early. When standard springs are used, you want to pre-load the springs in order to produce enough force for stripping or for hold down. Because of that, the available amount of compression shortened, and the spring life is unproportionally reduced. Pressure plates are held by shoulder bolts, controlling the springs as well, keeping them at a certain preload. All the preload pressure is held by the threads of the shoulder bolts. It could be just a matter of time before the threads are damaged or stripped. A far better solution is to use Nitrogen filled gas springs. They are many times more powerful. Their pressure can be easily adjusted. They designed to have a long service life, superseding conventional die springs.
They are also safe or the shoulder bolts. No preload is required, no stress on the thread. G springs produce the necessary force from the beginning of compression.
Custom progressive metal stamping tool and die manufacturing
The precision of the manufactured components is the key to have a well working progressive metal stamping die. Machining components to the highest possible quality is critical. Milling, grinding, etc. to the specified tolerances are extremely important.
The unsuppressed workmanship, the dedicated aim to perfect leads to building the highest quality tools that last longer work better than others.
Another good feature to use is to make in tool adjustments or maintenance as easy as possible.
Some punches could be side mounted therefore removed relatively easy while the tool rest of the tool is together or the tool is still in the press.