How to Manufacture Parts with Manufacturing Variations

By Protolabs
quality inspection

As with any industry, no matter how meticulous a process is, it can still be subject to variations. In manufacturing, these variations can stem from various things, such as material properties, machine tolerances, and environmental conditions. While some variation is inevitable, the biggest challenge for product designers and engineers is to design parts that are forgiving of these variations. This, in turn, will help maintain consistent quality and reduce defects.


What are the main sources of manufacturing defects?

When it comes to manufacturing defects, the sources can be many and variable. The most common sources include material defects, process issues, human error, tooling problems, supplier issues and design flaws. Some of these sources are easier to control than others. Let’s look at a couple of those points in more detail.

  • Design Flaws—This could include poorly designed parts that may be more prone to defect, insufficient consideration of the manufacturing process and constraints, and inadequate allowance for tolerances or material selection.
  • Process Issues—This could include incorrect process parameters such as temperature, pressure, time, lack of process controls, tool wear, and improper maintenance.


How can Design for Manufacturability (DFM) help?

Design for Manufacturability allows efficient, iterative design and redesign of your parts. When it comes to design flaws and factoring in manufacturing processes and materials, DFM can help you perfect a part that is better equipped for variation and any consequent defects.
For example, utilising DFM will tell you beforehand whether the tolerances you are utilising can be produced using the manufacturing method you have selected. It will also highlight whether the selected tolerance will affect the functionality of the final product.
Using DFM will also show whether the material you have selected and the build you have chosen will be able to maintain their structural stability and integrity during the manufacturing process.
The feedback loop offered using DFM creates close collaboration between design engineers and manufacturing experts, allowing them to continuously improve designs based on the feedback provided.


Why do you need to be mindful when selecting tolerances?

There are many considerations to consider when selecting tolerances for your part, including manufacturability, functionality, cost, material selection, quality controls, assembly considerations, and even environmental factors. Tolerances can cause issues if they are not precise enough, but they can also cause problems if they are too tight. Tighter tolerances increase the complexity and cost of the manufacturing process. However, tight tolerances may be vital for certain functions and assemblies. Before you run away with the notion that a tighter tolerance is best, remember that sometimes it isn’t always a good thing; push it too far, and assembly of your part may become difficult, or functionality issues may occur. It is a fine line, and DFM can be a key tool in ironing out what tolerance works for your part before it is manufactured.
Let’s look at a scenario where this may be the case. Imagine a shaft and bearing assembled in a car gearbox. The shaft must fit snugly within the bearing to ensure proper alignment and smooth rotation; hence, a tight tolerance is required. However, if the tolerance is too tight, it can lead to several issues, such as increased difficulty assembling, increased friction, increased stress and issues with dimensional variation throughout the part.


How can process controls help improve end-use product quality?

Most controls to secure product quality as much as possible are general practices for manufacturing providers. These include,

  • Material inspection: Confirm that all materials meet the required standards and that no material degradation occurs (which can happen when materials are stored for a long time).
  • Process monitoring: ensuring that temperatures, pressures, flow rates, cycle time, etc., are consistent and maintained as required.
  • Tooling and Equipment Maintenance – making sure tools are regularly maintained or replaced if necessary.
  • Quality Assurance and Inspection: Verify that quality measures are in place to inspect parts post-production to ensure the required quality standard is met.
  • Training – checking all staff have the required training to maintain processes and machines at the optimum level.


What should you be considering during the product verification and validation phase?

Product verification and validation ensure the product meets its intended requirements and its functionality performs as expected.
This includes verifying and validating safety and regulatory compliance, reliability, durability, UX testing, compatibility, interoperability, scalability, adaptability and functionality.
Validating these is important to ensure that final product risk is mitigated and that your part/ product is optimised to deliver high-quality products that meet customer expectations and regulatory requirements.