Design Considerations for Powder Metallurgy: 8 Tooling Do's & Don'ts.

Posted by Horizon Technology - May 30, 2019

The tools you use to create something are just as important as the “something” itself. That’s true in life, and it’s true with powder metal tooling.

The choices you make for tooling can send ripples through the entire manufacturing process.

Why? Tooling is like a mirror to your part. It is the “tool” that will compact the powder into its final shape.

Your tooling must:

  1. Form the desired shape
  2. Work within the limits of the press
  3. Survive hundreds of thousands of cycles of compacting powder

To keep your powder metal project from sinking, follow these eight basic design considerations for powder metallurgy.

Design Considerations for Powder Metallurgy: Tooling

When designing for powder metallurgy, take these factors into consideration in terms of tooling:

  1. Net metal shaping
  2. Compaction ratios
  3. Cost efficiency
  4. Powder metal part wall thickness
  5. All-in-1 manufacturing capabilities
  6. New & innovative metal powders
  7. Edging
  8. Tooling lifetime

Now let's examine them in greater depth!

DO Optimize for 'Net-Shape' Forming

The primary benefit of powdered metallurgy is that it’s a low-cost process. To maximize powdered metal’s benefit, consider using shapes that eliminate the need to add follow-up machining operations.

These include:

  • Undercuts
  • Tapers opposite of the pressing directions


DON’T
Ignore Compaction Ratios

There are limitations to the press that’s acting as the “driver” of your tools.

The use of powdered metal compaction tooling involves a stack of powder being placed into a cavity and compressed under high pressure to form a net shape part with a specific final length.

Horizontal composite compaction is what happens when two different materials are molded into one part. The outer layer is wear-resistant like you need it to be, while the inner material is cheaper. This thrifty thinking can cut your material costs by 80%.

So where does that final part length come into play? Powder metal compaction ratios. Typically your vendor uses a 2-to-1 ratio of “fill” to the final compact. So to have a part that is 1” long requires about 2” of “fill.”

If you have a 12” part, you need a 24” fill. Not a lot of high-tonnage presses will give you that kind of wiggle room. There’s a limit to what fits on a press.

In a straight-walled or single-level part, this 2:1 ratio is simple to visualize. But what if you add a second level to the part, perhaps in the form of a flange? The same principle still applies: You need a 2:1 fill ratio for each level throughout the compaction cycle or risk your part cracking. Each level requires a unique tool member to form that level, and each tool member must be uniquely “driven” by the press.

Most presses can only form two levels, while more complex presses can form many more.

DO Let a PM Vendor Show You the Key to Long Life

There’s a misconception around that powder metal tooling is expensive.

The key to managing the life of your tooling? Using the right combination to unlock efficiency.

A versatile tool set can have loads of combinations of:

  • Coatings
  • Platings
  • Materials
  • Heat treating

Your powdered metal parts vendor may have a huge number of tools at its disposal. Tool life is, more or less, trying to find the perfect recipe of coating, plating, material, and heat treatment to get you the most efficient process. An experienced supplier can help you get the most efficient combination.

DON’T Create a Brittle Risk

If you’re making, say, a ring-shaped component out of powder metal, you don’t want the thickness of its wall to be too thin.

Remember to allow for tool strength when you specify the wall thickness of your part. The thinner the wall you make, the thinner the tool you’ll need to produce it. This puts your tools at risk for breaking.

DO Take a Big-Picture Approach to Tooling

When it’s time to think tooling, the right powder metal vendor will connect it to the entire manufacturing process so every step is a success.

Decisions made on tooling can affect quality and cost in other steps of manufacturing. The right vendor will look at the whole application, assembly, etc. and use tooling to make your project as cost-effective as possible.

Your vendor should make sure its solution applies to both its own needs and your needs.

DON’T Be Afraid of New Materials

There are more materials tailor-made for powdered metal tooling than just the “Standard 35.” (Much of what we use is uncommon elsewhere in the industry or is entirely exclusive to us.)

Choice of tooling material is important. If you use a cheaper material on a certain application, your tools could break. Picking a material that doesn’t take the required part density into consideration can also throw a monkey wrench into your plan.

A qualified components supplier can help create a bridge between which tools you want to which materials you need. There are all sorts of new powder metal processing techniques out there, so don't be shy about exploring!

DO Consider Alternatives for Edging

Edging can be the enemy of tooling. Sometimes it’s simply impossible to put on an edge via tooling.

Wherever the edges meet, there has to be some sort of angle rather than a radius. Radii tend to turn out a razor-sharp edge, and it’s hard to mold that.

There are alternatives where you can mold an angle on and tumble finish it to a radius, but you’ve got to be careful. You can use secondary operations to achieve that.

Request options like brushing and tumbling after the fact to get your desired effect. In some cases a powder metal part vendor will handle this for you in-house, while in other cases it will outsource the work. Either way, they can make sure secondary operations literally finish the job for you.

DON’T Be Short-Sighted

The tool must be able to survive several hundred thousand cycles of compacting powder. To do this we must consider:

  • The force needed to compact the material
  • How the compaction process will stress the tool
  • Whether features will be prone to excessive wear
  • Whether features might fail
  • How the tool’s edge is designed to prevent excessive failures


Still Curious About Tooling?

Those are your top dos and don’ts of tooling for powdered metal. There are other smaller, more complex issues to consider, but stick to these six basics and work closely with a trusted vendor, and you’ll be fine.

Do you have additional questions about tooling, or about consolidating manufacturing costs as a whole? We’re happy to help -- feel free to get in touch via the button below:

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Topics: Tooling, Design


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