Best Practices for Prototyping PM or Sintered Metal Parts
Creating a prototype of a powdered metal (PM) component from a blank is often a cost-effective way to evaluate your design before creating an actual production tool for prototypes. While there are no hard and fast rules for when you want to create a prototype from a PM (also known as a sintered metal) blank before creating a high quality production tool, there may be instances in which it does make sense to go straight to a production tool. The decision depends on multiple factors, and there are a few specific issues you should consider to make the best choice for your situation.
A PM blank, also called a slug or puck, is a piece of sintered metal alloy fabricated to dimensions larger than the desired finished component, which can in turn be machined into a prototype of desired dimensions and function. The blank could be round, rectangular, a ring, or a variety of other shapes. The benefit of this method is that it’s made with the same material and process you want to use for the finished component. With a similar density and strength as a production component, you can evaluate whether the fit and function of the part will meet your needs.
At Atlas Pressed Metals, we customarily find out as much as possible about your application before making a recommendation to build prototypes from a production tool or create a prototype from a blank. We’ve had experience prototyping parts for a wide range of applications, including gears, cams, hinges, and more. In this article, we’ll review some of the key factors to consider when deciding how to create a prototype—and we’ll share a few best practices we’ve learned to optimize your PM prototyping experience.
Key Factors to Consider Before Making a PM Prototype
Quantity, Size, and Structural Considerations
The number of prototype pieces you need is one of the first things to consider. From a total cost standpoint, when the quantity of pieces you need is fairly low, choosing to prototype from a blank would be preferred since it’s priced on a per-piece basis with no tooling costs. Making 10 pieces is reasonable, but if you need to make hundreds of parts, the cost to build a set of production tools may be less than the eventual cost of those machined prototypes. Blank preparation is typically conducted in three phases: slug molding and sintering, machining to dimension, and possibly an additional secondary process such as sintering to relieve stresses that can be caused in the machining process. Considering those factors, you’re usually talking a couple hundred dollars per component to make a finished prototype, as opposed to a tool that might cost $5,000 or more. In some cases the long-term financial picture does justify making a finished production tool up front.
While scalability is one of the key benefits, other factors also influence this decision, including timing and the machining that needs to be done.
There are also several structural reasons why machining may not be as practical a solution to your application in comparison to production prototyping. In some cases, the machining operation may alter the prototype’s surface characteristics. Density and finishes may not be exactly the same as the result of a tooled prototype. If your application is sensitive to these concerns, you may want to build a tool instead of using a blank.
Your schedule is also a factor. It might take two or three weeks in some cases to get a slug into your hands, let alone the labor and timing to machine those blanks. At low volume, machining will only take a couple of days, however if you want to machine hundreds, the time to finish the prototypes obviously increases, and you would want to weigh that against the tooling lead time if you have a deadline to hit.
Best Practices for Creating a Prototype from a PM Blank
If you decide to make your prototype from a PM blank, there are some additional considerations you should be aware of during the process. Below are some of the best practices that we use and recommend to our customers.
- Try to make the blank as close as possible to the finished part length, because the length of the slug is related to density variation. However, you will need to consider that the machinist will need to hold the blank, and so the part may need to be larger or longer to accommodate for the machining operation. As an example, a blank may be a pressed plate from which the part will be wire cut, but the perimeter will be larger as needed for the machining center to hold the blank in place.
- Consider pre-sintering the component before machining. In some cases, we will pre-sinter a component in order to make it more readily machined. The material is heated to a temperature that allows the material to begin bonding but prior to the Carbon alloying into a hardened steel. Once the machining is completed, we will fully sinter the parts.
- Consider the impact the machining operation will have on the blank. Machining often introduces stresses and microcracks to the surface structure. Atlas can employ secondary processes, such as a second sinter, to relieve those stresses and aid in “healing” microcracks, ensuring a high quality and reliable prototype component.
- Machine the part in the same direction that it would be molded, so that the grains or density variants are mimicking how the part would be manufactured in the press. This will better represent how the prototype will perform in the application.
- Understand that porosity is natural in a PM component. During the machining process, a PM blank will absorb oil or other cutting fluids, so it may require additional steps to remove potential contaminants that can interfere with further processing. For example, if the blank is to be plated, the oils or cutting fluids used in the machining process can contaminate the plating bath and ultimately result in a poor plating finish. In this case, Atlas can first seal off the porosity with a plastic or grease impregnation process which fills the porosity in addition to improving machining characteristics.
Have More Questions About PM? Atlas Has Answers
We hope this article serves as a useful primer on issues with prototyping PM parts. At Atlas Pressed Metals, we believe that business is about serving customers. That’s why we strive to listen and deliver the best solution for your needs. Whether you need a prototype from a PM blank, a production tool, or just some advice on how to move forward with your project, we’re here to help.
So feel free to call, email, or otherwise get in contact with the PM professionals at Atlas. We’ll do what we can to help you succeed.