Waste-Conscious Design for Manufacturing

1. The Cost of Waste in Manufacturing

Every bit of material that doesn't end up in the final part represents a cost. This includes:

• The initial cost of the material itself.
• The cost of the machine time, energy, and tooling used to remove it (in subtractive processes).
• The cost associated with collecting, handling, and disposing of or recycling the scrap.

As a designer, your decisions directly influence all three of these factors. Let's explore several strategies to minimize waste, focusing on common manufacturing processes.

2. Designing for Material Efficiency in Subtractive Manufacturing (CNC Machining)

CNC machining is a subtractive process, meaning it starts with a block or bar of material (stock) and cuts away what's not needed. Therefore, a primary strategy for reducing waste is to minimize the amount of material that needs to be removed.

A great article from JLC-CNC, "5 cnc techniques to reduce waste in metal fabrication", outlines several practical methods. Let's start with one of the most impactful.

The key takeaway is to stop thinking of your starting point as a generic, oversized block. By specifying a starting stock that is a near-net-shape—such as an extrusion, a casting, or a forging—you offload the bulk material removal to a more efficient process and use the precise CNC machine only for finishing operations.

Another critical design consideration is ensuring your part fits efficiently within standard available stock sizes.

By designing to fit within standard stock dimensions, you avoid the waste (and cost) of having to machine a larger, more expensive piece of material down to size before you even begin making your part.

3. Material Efficiency in Other Processes

The strategies for minimizing waste are highly dependent on the manufacturing process. Let's look at two other common methods: sheet metal fabrication and die casting.

Sheet Metal: The Art of Nesting

For parts made from sheet metal, the design itself doesn't change as much as the layout of multiple parts on a single sheet of material. The goal is to arrange the flat patterns of the parts to maximize material utilization, a process called nesting.

To understand this better, let's return to the JLC-CNC article.

As a designer, your main contribution here is providing an accurate flat pattern. Onshape and other CAD tools generate this automatically, but being aware of how it will be used for nesting can inform your design choices, especially if you have control over a family of parts being cut from the same sheet.

Die Casting: Strength Through Geometry, Not Mass

In die casting, molten metal is injected into a mold. Here, using excess material is detrimental not only because of cost, but also because it can introduce manufacturing defects and increase cycle time. Thick sections are prone to shrinkage, porosity, and longer cooling times.

The solution is to use geometry to create strength and stiffness, rather than relying on solid mass.

This principle is a cornerstone of good mechanical design: use geometric features like ribs and gussets to achieve structural performance, not just brute-force material thickness.

4. Topology Optimization: Letting the Algorithm Find the Best Shape

So far, we've discussed manual design strategies. But what if you could tell the computer the loads and constraints, and it would figure out the most material-efficient shape for you? That's the purpose of topology optimization.

This process is a perfect application of your FEA knowledge. It's a computational method that starts with a design space (a block of material) and iteratively removes material from areas that don't carry significant stress, leaving behind an optimized, lightweight load-bearing structure.

The process is fascinating to watch. The following video demonstrates it using ANSYS, but the workflow is conceptually identical in other FEA-integrated tools, including Onshape's partners.

Topology optimization is an incredibly powerful tool for creating high-performance, lightweight components, making it invaluable in industries like aerospace, automotive, and medical devices where weight and material cost are critical.

Conclusion

In this lesson, you've learned to approach part design with material efficiency as a primary goal. This mindset is essential for creating cost-effective and sustainable products. By thinking about the manufacturing process early, you can make informed decisions that have a significant impact on the bottom line.

Key Takeaways:

• Minimizing material waste is a key driver of cost reduction in manufacturing.
• For CNC machining, use near-net-shape starting stock and design parts to fit within standard material sizes.
• For sheet metal, the focus is on efficient nesting of flat patterns to maximize material utilization.
• For casting, use ribs and coring to add strength and stiffness with geometry, avoiding thick, solid sections that waste material and can cause defects.
• Topology optimization is a powerful computational tool that automates the discovery of lightweight, material-efficient designs based on FEA principles.

Preview of the Next Lesson:

This lesson concludes our module on DFMA. You are now equipped with a solid foundation of principles for designing parts that are not only functional but also easy to manufacture, assemble, and economical to produce.

In our next lesson, we will begin a new module: Advanced Mechanical Components and Powertrains. We'll start by diving into a fundamental engineering decision: how to select between a gear train and a belt drive, and calculate required ratios and center distances. This will be our first step in designing the powertrain for our upcoming projects.