Many of us can glance at a part and know its function. There is immediate recognition and you can see how it works. This comes from experience, training, or an innate talent upon which designers rely as they approach their drawings.
Drawings are the tool used to communicate information to end-users, those who manufacture the parts and those who approve them for release into service. For these reasons, drawings must be clear and complete, so anyone, no matter their level of understanding, can benefit from them.
Deep drawing is a part forming process using a progressive, shaped die which forms the outside dimensions of the product, free from burrs and sharp edges, often found on other processes such as stamping or extrusion.
Points to Consider in Designing Deep Drawn Parts
Determine the shape and size of the part
The shape and size of a part determine the metal clay to be used. This choice affects the distribution of strains in the metal, formability and ease of manufacture. The size of the part dictates how much material is needed, which can affect the cost of the part. Part size also contributes to strain distribution and formability.
Determine the metal clay required
When determining what type of metal clay to use for a specific application, considerations such as the shape and size of the part, its intended function, If any die-forming is involved with making it and if so, what kind, other internal forces that may be present during manufacture should all be considered when choosing a metal clay to use for parts like this one. Bending stresses induced in typical deep drawn applications are low. Typically, flat or gently curved surfaces with sharp corners are ideal for sheet metals with higher bending strengths, such as aluminum alloys. Parts with high bending stresses can be manufactured using different metal clays, but care must be taken to avoid cracking or failure during forming.
Choose a method
There are three methods available for deep drawing: open die, impression die and closed die. Open-die forming is used when the part has symmetry along its centerline, or the material thickness exceeds 0.25 inches (6 mm). If there isn’t any symmetry or if the material’s thickness is less than 0.2 inches (5 mm), impression die or closed-die forming must be used instead to produce uniform results in parts with complex shapes.
Select conditions for deep drawing
The following conditions must be met to successfully deep draw a part: the blank should be twice as thick as the desired finished thickness, the blank must be annealed to soften it, and the drawing die must have clearance on either side of the punch. The depth of drawing is also limited by the length of the punch and the size of the die opening.
Design the part
The designer must consider all the constraints imposed by the manufacturing process when designing a deep drawn part. The shape should be symmetrical and straightforward, and the thickness should be evenly distributed throughout the part. Corners and sharp edges should be avoided, and any holes or indentations should be located away from the edges of the part. Thick sections should also be avoided, as they are challenging to draw out and may damage the die.
Fire the metal clay
Metal clays must be fired to fuse the metal particles and create a durable object. Silver clay must be fired in a kiln at 1260 degrees Celsius (2140 degrees Fahrenheit) for an hour, while bronze clay can be fired in a kiln at 1370 degrees Celsius (2498 degrees Fahrenheit) for two hours.
Punch the part
The punched blank is then ready to be deep drawn. The punch is inserted into the die, and the part is drawn out by exerting pressure on the blank. The punch is then removed, and the part is ejected from the die. The part can be further processed by filing or sanding to remove any sharp edges or burrs. It may need to undergo further steps depending on its intended use.
Form the part
Insert the blank into the die and clamped it firmly in place. The punch, which has been lubricated with light oil, is then pressed down onto the metal. There are three ways in which a blank can be removed from a deep drawn part: ejection through a die that is larger than the opening of the drawing die; ejection when pressure from within expands to an opening from within the metal, pushing it out of both sides simultaneously; or when pressure from within cracks one side before expanding enough to escape through a door on both sides. For deep drawing to work correctly, there must be “drawing clearance” around all the moving parts of the press machine, and the punch must be in good condition.
Polish and finish the part
The part is then removed from the die, and the excess metal is trimmed away. It is usually necessary to sand the piece down to its final shape and polish it to a high sheen. Polishing can be done with various materials, such as tripoli, also known as brown rouge, or white diamond.
Finalize the drawing
After all these steps have been completed, you can now finalize the drawing by adding borders, title blocks, and other design features to make it look more presentable. I suggest using a professional drafting program like AutoCAD to complete your deep drawn part drawings, so they are ready for manufacture.
Additional points to consider in producing high quality deep drawn components.
Geometry
A part’s geometry is the foundation of its form and function. It is essential to understand how the region will deform during the deep drawing process. It is often helpful to break the part down into simpler shapes, drawn and analyzed separately. Sometimes, it may be necessary to model the part in a computer-aided design (CAD) software program.
Material
The material’s properties also play a significant role in deep drawing. For example, if the material is too complicated or brittle, it may crack or shatter during the forming process. Conversely, if the material is too soft, it may not hold its shape or it may deform excessively.
Process
The process parameters also affect the part’s geometry and material properties. It is essential to establish these parameters carefully so that the part can be successfully deep drawn with no damage to the tooling or the part itself.
Tooling
The tooling must withstand the enormous forces and deformations associated with deep drawing. In addition, the tooling must be accurately machined so that the part’s dimensions are within specifications.
Operator skill
A good operator is essential for producing quality parts. The operator must understand the process and the tooling to set up the equipment correctly and adjust it as necessary during the drawing process. The operator also needs to detect any problems with the material, tooling, or process early enough to avoid excessive wear and damage.
Quality Control
It is essential to have a robust quality control (QC) program to ensure consistent quality. This program should include inspection procedures for both the parts and the tooling. A properly functioning QC program helps identify and correct any problems before they cause excessive wear or damage to the part or tooling.
Blank design
The design of the metal sheet stock (or blank) is critical to achieving high-quality results when drawing thin-walled parts with complex geometries. If the blank is too thick, it may buckle during deformation and create voids in the wall. If the blank is too thin, it may not support the applied load, resulting in a wrinkled or crumpled part. Besides providing adequate stiffness, the material selection for the blank must also allow it to be successfully deep drawn without causing damage to either the tooling or part geometry.
Punch design
The shape and size of the punch affect how well a metal sheet stock can be formed by deep drawing. The choice of stamping method (i.e., impression die, extrusion die) depends on shape complexity and minimum hole diameter constraints. Impressions dies are most suitable for producing simple shapes with larger minimum hole sizes, whereas extrusion dies to make complex shapes with smaller minimum hole sizes.
Die design
The die geometry must be carefully matched to the punch shape to achieve the desired results. If the die is too large, it will cause excessive material deformation and reduce the part’s dimensional accuracy. If the die is too small, it will not form the part correctly and may damage the tooling.
Process control
To produce high-quality, deep drawn parts, it is essential to have a strong process control system in place. This system should include the proper sensors and controls to monitor the key variables that affect part quality, such as punch force and blank diameter. The data collected by these sensors can adjust the process parameters as necessary to achieve consistent results.
Conclusion
Deep drawn parts are a critical component of many products, yet few people understand how they are made. In this article, we have attempted to demystify the process by discussing the key factors that affect the quality and dimensional accuracy of deep drawn parts. We have also outlined some of the best practices for designing these parts, so you can ensure your next project is a success.
