Have you ever been ‘no quoted’ by a component fabricator for a component you designed. Or the quote to make the component was way high? The likely reason for either was the fabricator saw that your component was going to be a hassle to fabricate. So, either they didn’t want to deal with the problems or they were going to charge you to deal with the problems.
Possible sources of fabrication hassles include:
Tolerances too tight.
Features cannot be easily produced.
Material not easy to use.
Material difficult to source.
Properties too difficult to obtain.
Similar problems occur for assemblies. The overarching problem – no considerations of design for manufacturing and assembly.
Video recording of Design for Manufacturing and Assembly webinar
Examples of component hassles
Here are some examples of designs that are a hassle to fabricate:
Through harden a steel shaft made of an alloy with low hardenability. Low hardenability will require using water quench, which risks distortion and cracking. If the hardenability is too low, it will not be possible to achieve the desired hardness at the center of the shaft.
High volume machining of a part using an alloy with poor or fair machinability. Using an alloy with poor or fair machinability will require slow machining speeds and other added attention. So, it won’t be possible to keep up with the required production volume.
Electroplate a component with small blind holes. The electroplating chemicals will not get into the holes, so the holes will not be properly coated.
Design for Manufacturing and Assembly
The focus of Design for Manufacturing and Assembly (DFMA) is to prioritize ease of manufacture of components and simplified assembly of components into final product. This must occur during the early design phases of product lifecycle. The goals are to reduce time-to-market and reduce total production costs. The focus in this article is on custom-made components.
Design for Manufacturing and Assembly principles
There are several Design for Manufacturing and Assembly principles, including these:
Select materials that are compatible with proposed fabrication and joining processes.
Design component features to be compatible with proposed fabrication and joining processes.
Consult with manufacturing experts early in design stage.
Minimize total number of parts in an assembly.
Standardize components across product lines.
Combine multiple components into one component.
Eliminate machining and finishing operations.
The remainder of this article will focus on the first three principles.
Select materials that are compatible with proposed fabrication processes
Form a sheet metal part out of stainless steel. 301 stainless is ok for simple parts or for a shallow draw. However, for deep draw or complicated shapes 304 has better cold forming properties because of the higher nickel content in 304.
Through harden a steel component. The part diameter, part features, required hardness, and required depth of hardening will dictate the alloy’s carbon content and hardenability. For complicated shapes, long parts, or thick parts the steel’s hardenability will influence the required quench rate and depth of hardening. Carbon steel, such as 1045, is low cost but risks distortion or cracking during the quench process. A low-alloy steel, such as 4140, is more expensive, but a slower quench can be used, reducing the risk of distortion or cracking.
Design component features that are compatible with proposed fabrication processes
This means designing component features that can be easily produced. For example:
Stamping holes in sheet metal. The allowable ratio of metal thickness to hole diameter (T/D) is inversely proportional to the metal shear strength. So, the minimum hole diameter that can be punched in increases with increasing metal strength and increasing metal thickness.
Die casting. Ease of casting is improved with uniform wall thickness, relatively thin walls, suitable draft to make parts easy to remove from the die, and adding fillets to sharp corners to prevent cracking.
Consult with manufacturing experts early in the design stage
Talk to suppliers when you’re starting to design components for a product. What do they think of materials, shape, and tolerances? Do they have material recommendations? But be careful with their material recommendations since suppliers are not design engineers and they don’t know or understand all the design requirements. A 15 minute discussion for critical components can have a huge impact on your ability to meet launch deadlines, keep costs low, and prevent quality and delivery problems once the product goes into production.
Component design decisions have a big impact on ease of component fabrication which influences component cost and the ability of meeting product launch schedules and product shipment targets.
Design for Manufacturing and Assembly may require working with not so low-cost suppliers, at least to get a product launched. But the benefits are huge. You can always cost reduce once you have a good design and have worked on the bugs. There are probably just a few of you who have tried to work with low-cost suppliers from the start and regretted it.
Check out these books to learn more about design for manufacturing and assembly