Working on your next build to print drawing project? We can help! Below is a list of cost saving tips for designing and procuring a drawn part.
If you have an application you would like to source and want to drive cost down, we would be happy to answer any questions on these tips. You can fill out the form to the right, fill out the RFQ or contact forms, or call with your question. If you are on a tablet or desktop, you can “Live Chat” M-F 8a-5p.
1. Calculate the blank size and optimize.
One of the most common hidden costs for drawing parts is the hidden cost from engineered scrap necessary to procure a blank. When the annual quantity for a particular part number is in the thousands or tens of thousands, custom coil sizes can sometimes be procured. If not, blank material will normally come from master coil sizes, like 36″, 48″, 60″ or 72″ wide that are cut to width and the “drop”, or material removed in the blank shearing process, still maintains more value. If quantities are very low, it is common to produce blanks from standard sheet sizes of 8, 10, or 12 foot in length from the various coil widths. Optimizing a blank diameter and square size to eliminate excessive amounts of engineered scrap or planned drops can dramatically impact final part cost. Blank size also includes adequate amounts of material for trimming and work holding to make the part shape.
2. Design to minimize the material needed for trimming & work holding.
The blank size for the finished part is normally different from the actual blank that is used. This is due to the method necessary to hold and process the part from start to finish. Aside from the dimensional requirements, the required surface finish and tolerance of dimensions may require additional material to accommodate secondary processes or to eliminate features that could be permitted, yet are not specified on the drawing.
3. Plan for thin out in the design phase.
The material formed in the drawing or deep drawing processes experience a lot of surface tension and stretching throughout the cycle of the forming process. This means that typically, a section of the material will thin out in one or more locations, normally towards the closed end of the shape or the first contact surface on the plug. Other sections will normally thicken towards the open end of the shape, or the flange. Allowing for this in the part design will help scrap remain low and the design to work well in the application.
4. Allow for a taper.
Inherent to the process, due to the punch and die needing adequate clearance, and to accommodate mill tolerance on metal thickness there is a taper in straight walls of parts. The taper depends on the metal thickness, the total depth of the part, the grade of material, and the clearance between the punch and die. Typical taper is between 0.005 to 0.010 of an inch per inch of depth. In order to minimize taper; minimize part depth, use tooling designed specifically for the application, select materials with better formability that thin less, and accommodate material flow with larger draw radius. If tapers are not acceptable, secondary forming processes can reduce and sometimes eliminate the taper, however it tends to drive cost.
5. Select material that has better ability to form.
Selecting the most formable material and/or temper for the draw process may minimize or even eliminate scrap generated during the drawing process. This sometimes may be difficult if the application requires a certain amount of stiffness and or strength. Some materials like stainless strain harden when formed and others like aluminum can be tempered to improve mechanical properties. Sometimes selecting a superior material for the design that well exceeds the properties required by the design may be more cost effective in the long run because the processing costs may be significantly lower, such as drawing 304 stainless steel compared to 410 stainless steel.
6. Look to use existing tooling.
Many press and drawing companies such as TMS, may have a lot of tooling available for customer use. Like TMS, a company that invests heavily in its own tooling can produce shapes that are very close to the designed dimensions. Sometimes, the design can be altered slightly to avoid an engineering charge. Alternatively, a re-cut charge can be offered when the tool is no longer active and can be repurposed.
7. Hydro-mechanical drawing (hydroforming) requires less tooling costs.
Hydro-mechanical deep drawing, or hydroforming uses hydraulic fluid as either a punch that pushes metal into a cavity or a die to push metal over a punch. In hydroforming, a rubber bladder acts as a die with 1,000’s of PSI behind it. Compared to conventional draw forming, the rubber bladder PUSHES the blank around the plug, instead of pinching and STRETCHING the material thus, putting less stress on the metal and allowing for greater reduction ratios and more elaborate part geometries.
8. Uniform metal thickness is achieved by hydro-mechanical deep drawing (hydroforming).
Due to the lower forces applied onto the metal during the hydro-mechanical drawing process, the material is not stretched as much, allowing for a more uniform metal thickness to be maintained. This is especially helpful on difficult to draw shapes that are irregular and asymmetrical, where a metal die would not permit simple metal flow or dynamically change to be forgiving of the metal’s needs.
9. Optimize for a minimum number of draws.
Each time a part is drawn, it is reduced in size with respect to the diameter of the part or the length and width. Depending on the percent elongation, some metals can be drawn more than others. To achieve the maximum amount of reduction a metal is able to be reduced, it is often necessary to go through a series of steps or reductions. 14 gauge stainless steel 304 for example, normally can be reduced 45% the first reduction, and then up to 30% the second. To further reduce it, SS 304 typically requires an annealing operation and then can be reduced another 15%. So, if the original blank is 10 inches, the final diameter would be (1-.45)(1-.30)(1-.15) x 10 inches = 3.27 inch diameter of the part.
10. Add features that leverage the benefit of in-house secondary operations.
Whenever there is forming, usually there is cutting, finishing, secondary forming, and sometimes joining processes that are needed to complete the part so it is useful. A deep drawing house usually offers a variety of processes that can improve the usability of your part and with minimal cost depending on part design. Once an order is placed during the prototyping phase of a project or product life cycle, a reputable manufacturing firm will normally provide a design for manufacturing and assembly (DFMA) review to help identify cost saving opportunities and features that can assist in overcoming design, and or cost barriers.