Dies are specialized tools used to punch, cut, bend, press, and otherwise shape metal with a press. They are used in a variety of metalworking processes, including stamping, progressive stamping, drawing, forging, press braking, and injection molding.
Most dies are custom-built for a specific part or part family. In order to achieve the desired part profiles and features with precision and within critical tolerances, it’s important that all of the components in a die set be designed and built to specifications.
Here we’ll look at the primary components in a die set, some of the important considerations for design, and things to watch out for.
Material Selection Tips
Most die components and tooling are made from hardened tool steel, which is durable and can hold a sharp edge for cutting operations. Depending on the duration and volume of part production, different grades of steel or different metals may also be suitable.
The size, shape, and other features of the die tooling, plates, and guiding elements need to correspond to the desired part features and their dimensions, within acceptable tolerances. Computer-aided drafting (CAD) software is often used along with detailed part prints and renderings to develop and model die designs. While the specific parts that go into each die will vary based on the application at hand, these are the most common:
- Die Plates, Shoes, and Die Sets. These upper and lower plates have corresponding tooling that comes together when the press ram directs the upper plate downward. The springs, guide pins, bushings, and other tools are mounted to these.
- Punches and Dies. These are the tools that do the cutting, bending, flattening, shaping, and forming of the material.
- Stripper Plates. These keep sheet metal in place as the die plates separate. They also smooth the removal of punches, buttons, and tools from the material.
- Pilot Punches. These tools are often used in progressive stamping, where they help position and locate the material inside the press for accuracy.
- Guide Pins and Bushings. Also called guiding elements, guide pins and bushings are positioned opposite each other on the upper and lower die plates and keep them aligned correctly. Bushings contain a lubricant or graphite to help the pins move smoothly.
- Springs. Die springs are heavy-duty compression springs that hold workpieces down during stamping and assist with opening the die plates. Both coiled mechanical and nitrogen gas springs are available.
In addition to these foundational components, many die sets also incorporate various fixtures, pressure pads, cams, and other components. These help position the sheet metal or other raw material and hold it securely in place during stamping or other operations. These can be blocks, vertical stops, rotating components, and other mechanical devices that limit and control the movement of the workpiece.
Tolerances & Efficiency
Most manufactured parts include a tolerance range for certain features, like hole placement relative to a bend or edge, hole diameters, bend angles, or even surface finishes. If part features fall outside the acceptable tolerance range, they may compromise how components fit together in an assembly or how they perform in an application. As a result, it’s critical that dies and tools are designed and built so that features are accurate and have minimal variation from cycle to cycle.
In modern manufacturing, tolerances have become tighter and tighter, which means there is a very small window for error in the size or location of a feature, often a tiny fraction of an inch. In terms of die design, this means it is important to anticipate how tools will change over time. For example, punches experience wear that will eventually alter the size of the hole they make. It’s necessary to figure out the best starting punch size to accommodate wear without going out of tolerance quickly during production.
It’s also important to consider material properties when designing tooling. This may include things like material hardness relative to the tool’s hardness, or how much springback a material will have and how that affects bend angles. Material behavior during stamping, forging, drawing, and other operations can have an impact on how to achieve particular tolerances.
Efficiency and Manufacturability
Efficient manufacturing relates to saving effort, time, manual labor, and material wherever possible. This reduces cycle time, saves production costs, and shortens turnaround times. Die sets should be designed and built so they can be used efficiently with minimal confusion or extra setup steps. There are several ways to do this, including:
- Ensuring all tooling and fixtures can only be inserted in a single direction to avoid errors.
- Noting any special instructions for shimming, fixturing, or tool changeover procedures.
- Indicating the type and frequency of lubrication for guiding elements.
- Noting the maximum number of cycles between preventive maintenance or inspection.
Another key to efficient production is part manufacturability. This is the ability of a part to be made without excessive errors, damage, or other problems. It’s important that the part itself be designed for manufacturability, but die design also has a role to play. For example, while a feature can be made by stamping, such as a large hole, if the punching operation ends up deforming the rest of the part, it may be better to machine the hole after stamping is complete. Changes to the steps and operations that result in fewer damaged or rejected parts are a way to increase manufacturability and make production efficient.
Common Pitfalls to Avoid
No two custom parts are the same, so it’s important to avoid common problems in die design.
In most cases, the person designing the die is not the same person who designed the part or the assembly or product it goes into. It’s important, therefore, to understand the part’s design intent, or how it will be used and how it needs to function in the real world. This can provide insight into the reasons for certain part features. It can also lead to opportunities to optimize part design for easier manufacturing.
It’s also important to review part prints carefully and clarify that all details are included, such as measurements, tolerances, angles, and other important design requirements. Avoid assumptions, and if information is missing, ask questions instead of proceeding based on a guess.
Try to keep the bigger manufacturing picture in mind as well. One way to achieve this is to make sure that you have a clear objective before you start the design process, and make sure that you find a balance between overall tool cost, stability, part quality, hits per service, and upkeep. Try to think beyond just the task of designing the die, and anticipate potential obstacles during setup, changeover, or maintenance.
Some more specific things to keep in mind include:
- Avoiding sharp corners that can concentrate stress on the material.
- Using an adequate radius for highly loaded areas.
- Taking note of the radius at the junction of two surfaces, which can impact joint strength.
- Using constant fillets and radii throughout the design for strength and smoothness.
- Adding draft angles to the surfaces aligned with the mold opening direction; otherwise, removing the component from the mold could cause damage to its surface.
Dramco for Expertise in Die Design
Custom die sets and tooling that achieve dimensions and tolerances with minimal error or scrap are always the goal for stamping, forging, casting, drawing, and similar operations. Die design is a complex process with many variables for which to account. Partnering with an expert is the best way to ensure you get the tools required for the application.
Dramco is a full-service manufacturing company that specializes in custom die design, machining, and building services for metal stamping, progressive stamping, injection molds, forgings, castings, and more. Additional capabilities include prototyping, laser cutting, water jet cutting, and custom machine design and building. Contact us today to learn more about our services or to request a quote.