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  • Writer's pictureCharles McCarthy

Creating Cost-Effective Sheet Metal Parts: A Guide to Designing for Manufacturability

Updated: Feb 22


CNC laser machine cutting steel tabs




When Designing sheet metal and plate parts, it is crucial to be aware of the following design considerations. Designing parts that deviate from these rough guidelines may pose challenges, making fabrication either impossible or significantly more expensive due to to machinery and material constraints and limitations.

Cutting options for Sheet Metal


Waterjet


Waterjet cutting is a versatile and precise method in the world of metal fabrication. This process involves using a high-pressure stream of water mixed with abrasive particles to cut through various materials, including metals, stone, and composites. One major advantage is its ability to produce intricate designs with minimal material waste. Additionally, waterjet cutting doesn't generate heat, reducing the risk of material distortion. However, it has some drawbacks, such as slower cutting speeds compared to other methods and the need for periodic nozzle replacement due to wear. Despite its limitations, the waterjet process remains a valuable choice for projects demanding precision and versatility.

Laser


Laser cutting utilizes a concentrated laser beam for intricate cuts in various materials. Noteworthy for its high precision and minimal material waste, laser cutting is efficient and well-suited for diverse designs requiring tight tolerances. While it offers rapid cutting speeds, it's essential to consider the generated heat and potential thermal effects on materials. Additionally, the cost of laser machines is relatively high, especially in relation to the thickness of materials they can cut compared to a process like Oxyfuel and Plasma cutting. Despite this expense, many industries value laser cutting for its unmatched precision, speed, and adaptability across a broad spectrum of materials. As the price of laser machines continues to come down it is becoming more and more the go to cutting process for many shops.


Punch Press


Punch press work, a staple in metal fabrication, involves utilizing a machine equipped with punches and dies to shape, pierce, or cut materials. This method is known for its efficiency in mass production and speed, making it suitable for various industries. While punch presses excel in high-speed operations, they may result in more significant material waste compared to laser cutting. The initial setup costs are generally lower, making punch presses a cost-effective option for specific applications. However, their versatility can be limited compared to laser cutting. As with any fabrication process, careful consideration of material thickness, tooling, and production requirements is crucial in optimizing the benefits of punch press work.


CNC Plasma


Plasma cutting utilizes a high-velocity jet of ionized gas to precisely cut through metal. While not as precise as laser cutting, plasma cutting strikes a balance between speed and cost-effectiveness. It excels in handling thicker materials and offers an affordable alternative in terms of initial equipment costs. The adaptability and efficiency of plasma cutting make it a valuable choice for projects where speed and cost considerations are paramount.



Shear


Shearing sheet metal is a fundamental and efficient process in metal fabrication, involving the use of a shear to cut through flat metal sheets. This mechanical cutting method is known for its simplicity and speed, making it ideal for high-volume production. Shearing produces clean, straight cuts. While it may not be as suitable for intricate designs compared to laser cutting, shearing excels in swiftly processing large quantities of sheet metal with minimal material waste. Its straightforward operation and cost-effectiveness make shearing a go-to choice for projects where speed, simplicity, and precision in straight cuts are essential.

CNC Cutting Design Considerations



Kerf is important


During the cutting process, a small quantity of material is removed, known as the cutting kerf. Laser cutting typically yields the lowest kerf, averaging 0.3 mm. The exact amount depends on the material and cutting process used.


Cutting Method

Kerf Width

Application

Tolerances

Waterjet Cutting

0.020-0.040

Intricate and precise designs, various materials.

.008 in

Laser Cutting

0.004" - 0.020" 

High Precision, intricate designs, minimal material waste

.12-.4in

Plasma Cutting

0.060" - 0.250" 

Thicker Materials, Cost-effective.

.02-.7in



Pay attention to hole sizes


Having holes with a diameter less than the thickness can cause deformation or inaccuracies due to the kerf or cutting process distortion. When plasma cutting a standard rule of thumb is you can never cut a hole where the diameter is thinner than the thickness of the material. There are ways to push this boundary with certain technologies but generally speaking this is how you should design your parts if you know they are to be plasma cut. When laser cutting it is much easier to cut smaller-diameter holes than the material thickness, but even still playing it safe is wise—opt for a diameter equal to or greater than the sheet thickness.


If cutting holes smaller than the thickness of the material is required and drilling is not a viable option waterjet is the way to go. With waterjet a general rule of thumb to follow is that when cutting any metal plate under 3/16" the minimum hole diameter achievable is .060. When cutting over 3/16" plate the minimum diameter for a hole is 20% (Material Thickness x .20) You should also be sure to space holes at least 2 times the sheet thickness apart from each other and 1 sheets thickness from the edge. Designing parts this way reduces the risk of the holes tearing out when in use or when bending parts.


Design criteria for parts cost effective bending


A CNC press brake in a metal fabrication shop
CNC press brake

Standardize Bend Radii:

Standardizing bend radii across your designs can significantly contribute to cost reduction. Using common radii not only simplifies the bending process but also allows for better tool utilization, reducing setup time and tooling costs. Manufacturers often stock standard tooling sizes, so designing with these in mind can lead to substantial savings.

Optimize Bend Sequences:

Carefully planning the sequence of bends can enhance efficiency on the shop floor and reduce the need for complex tool setups. Designing parts that follow a logical bending sequence minimizes the number of tool changes, ultimately decreasing production time and costs.

Embrace Symmetry:

Symmetrical designs are not only visually appealing but also contribute to cost reduction in sheet metal bending. Symmetry simplifies the bending process by allowing for consistent tool setups and reducing the need for flipping or reorienting the part during fabrication. This results in less downtime and increased productivity.

Design for Material Efficiency:

Efficient material utilization is crucial in cost-effective sheet metal bending. Minimize scrap by optimizing the layout of your parts on a sheet of metal. Designing you parts so that they can be nested closely together can significantly reduce material waste, ultimately lowering material costs and therefore the final price.

Utilize Standard Materials:

Designing with readily available and standard sheet metal sizes can lead to cost savings. Standard materials are more affordable and readily accessible. Additionally, using standard sizes can reduce lead times, enabling quicker turnaround and potentially lowering production costs.

K-Factor

When sheet and plate metal are bent, the material actually stretches. Therefore, it is important to anticipate the stretch during the design process. This anticipation is referred to as "Bend Deduction," and the most common standard method is using what is known as the K-Factor.


The K-Factor is a formula that illustrates the ratio of the bending plate relative to the material thickness, and it is calculated as follows:


For more detailed information on K-Factor this article by Steve Benson of the Fabricator is a great resource




Reach out with any additional questions!


As always, if you have any questions feel free to reach out to any of our staff with any questions you may have. We will do our best to help you design your parts to be as cost effective as possible!


-Charles

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